Polymers

The term polymer comes from greek words meaning "many parts". A polymer is a substance with a high molecular mass that is composed of a large number of repeating units. These units, called monomers, are connected by covalent chemical bonds.

Some polymers are composed of a single type of monomer, while others may consist of two, three or more different monomers. Many biological macromolecules are examples of natural polymers. These include the carbohydrates, starch, cellulose and glycogen (branched chains of glucose monomers), and chitin (chains of N-acetyl-glucosamine). Examples of polymers consisting of mixtures of monomers are the nucleic acids, DNA and RNA, made from units of 4 different nucleotides, and proteins, which consist of a mixture of the 20 standard amino acids. Natural rubber, or latex, is a natural hydrocarbon polymer found in the sap of some plants. Natural, biological polymers have both structural roles and physiological functions, and are involved in the control of cellular operations such as growth, replication and metabolism.

Synthetic polymers can be produced commercially, and are traditionally derived from petroleum products. They have a wide variety of properties and uses. The most common synthetic polymers are plastics such as polyethylene and nylon. Synthetic polymers made out of glycolic and lactic acids, and other biodegradable materials, have become increasingly popular for use in biomedical applications. Man-made polymers that react to their surroundings are known as smart polymers, or stimulus-responsive polymers, and can be used for a variety of purposes in technology and biomedicine.

Examples: Starch is a natural polymer composed of chains of repeating units of glucose.

Macromolecules and Molecular Diversity

Without water and small organic molecules, life as we know it would not be possible. The structure of these molecules is intimately related to their function. A continuing theme throughout much of the biological world is this relationship between form and function. When these small organic molecules are joined together, "giant" molecules are produced. These giant molecules are known as macromolecules.

Polymers

Macromolecules are polymers. Polymers are large molecules of many similar "units" linked together. These individual units are called monomers.

DNA polymer formed from nucleic acid monomers. Protein polymer formed from amino acid monomers. Image credit: DOE Human Genome Program.

Form and Function

The variation in the form of macromolecules is largely responsible for molecular diversity. Much of the variation that occurs both within an organism and among organisms can ultimately be traced to differences in macromolecules. Macromolecules can vary from cell to cell in the same organism as well as from one species to the next.

Generally speaking, all macromolecules are produced from a small set of about 50 monomers. Different macromolecules vary because of the arrangement of these monomers. By varying the sequence, an incredibly large variety of macromolecules can be produced.

While polymers are responsible for the molecular "uniqueness" of an organism, the common monomers mentioned above are nearly universal.

Assembling and Disassembling Polymers

While there is variation among the types of polymers found in different organisms, the chemical mechanisms for assembling and disassembling them are largely the same across organisms. Monomers are generally linked together through a process called dehydration synthesis while polymers are disassembled through a process called hydrolysis.

Monomers and Polymers

Monomers are the building blocks of more complex molecules, called polymers. Polymers consist of repeating molecular units which usually are joined by covalent bonds. Here is a closer look at the chemistry of monomers and polymers.

Monomers

Monomers are small molecules which may be joined together in a repeating fashion to form more complex molecules called polymers.

Polymers

A polymer may be a natural or synthetic macromolecule comprised of repeating units of a smaller molecule (monomers). While many people use the term 'polymer' and 'plastic' interchangeably, polymers are a much larger class of molecules which includes plastics, plus many other materials, such as as cellulose, amber, and natural rubber.

Examples of Polymers

Examples of polymers include plastics such as polyethylene, silicones such as silly putty, biopolymers such as cellulose and DNA, natural polymers such as rubber and shellac, and many other important macromolecules.

How Polymers Form

Polymerization is the process of covalently bonding the smaller monomers into the polymer. During polymerization, chemical groups are lost from the monomers so that they may join together. In the case of biopolymers, this is a dehydration reaction in which water is formed.

7 Facts to Know about Carbohydrates

We've been spending time in this series of articles exploring carbohydrates -- what they are, what they do in our bodies, and the good, the bad, and the ugly carbs. Here are seven things for you to remember about carbohydrates.

1) Carbs = Sugar

Except for the carbohydrates like fiber that aren't broken down into glucose before they get to the colon, all carbs end up as sugar. Starches, or complex carbohydrates, are just longer strings of sugar. The only question is how quickly the sugar makes it into our bodies. Does it cause a rapid, high rise in blood glucose, or does it break down over a longer period of time? Unfortunately, most of the carbohydrate we eat is in the first category.

2) Misconception: Starches (complex carbohydrates) are broken down slowly in our bodies.

Not true. The vast majority of the carbs in the grocery store are rapidly digested. This is because the food manufacturers have kindly begun the process for us, by grinding grains into flour, refining grains and sugar, puffing rice and making it into rice cakes, etc. Whole wheat flour is almost as glycemic is white flour (though it is much more nutritious). (Read more about whole wheat bread on low-carb diets)

3) Best bets: Non-starchy vegetables, low sugar fruits, and legumes

We've always known that our best and most nutritious sources of carbohydrates are non-starchy vegetables and low-sugar fruits. These foods include most of the best sources of phytonutrients, as well as having loads of vitamins, minerals, and fiber. Now we know that legumes can be a good addition to the reduced-carb diet, because they contribute slowly digested carbohydrate and resistant starch to our diet. Each person will have to experiment with amounts when it comes to legumes.

4) When choosing grains, eat whole intact grains

For those who can tolerate more sugar, add whole grains such as rice, barley, quinoa, bulgar, etc. Whole intact grains are broken down more slowly than if they were ground into flour. There is also a small amount of resistant starch in grains eaten this way.

5) Misconception: By the time our food reaches our colons, the story is over.

Not true. There is a whole other digestive system taking place with fermentable carbohydrates that reach the colon. The friendly bacteria there make substances which contribute greatly to our health. Read more about the colon.

6) Eat plenty of fiber

Fiber is a very good thing. Seek out sources of insoluble fiber (e.g., vegetables) and fermentable fiber (soluble fiber, resistant starch, and oligosaccharides).

7) You may have put extra effort into getting sources of resistant starch

People who are able to eat high-carb diets, and focus on whole, unprocessed foods, get small amounts of resistant starch in most of the carbs they eat. This becomes an issue for low-carb eaters -- for example, even though potato salad has some resistant starch, it is too "expensive" in terms of rapidly-available sugar for us to indulge in often. This is why including legumes in our diets is a good idea, and possibly experimenting with cooking with resistant starch, such as this flax meal bread with added resistant starch.

All About Fiber

In this series about understanding carbohydrates, we have been focusing on what happens in our digestive systems as we eat various types of carbohydrates. We will continue this theme when it comes to fiber. Most fiber is, like other carbohydrates, made up of many glucose molecules. However, fiber does not break down into glucose before it gets to the colon, and often not even there. Even so, fiber does have effects on our digestion all along the way.

Need to review the basics about fiber? Check it out here.

The stomach: In the stomach, fiber is bulky, so it tends to make us feel full. However, insoluble fiber moves out of the stomach fast unless there is fat, protein, or soluble fiber to slow it down. Soluble fiber, especially the viscous types that hold onto water, will slow down stomach emptying, especially when eaten with lots of fluid and some fat. This is at least partly why soluble fiber tends to decrease the glycemic effect of a meal - the contents of the stomach more gradually enter the small intestine, and from there, the blood.

The small intestine: In the small intestine, it's a similar situation - the presence of insoluble fiber tends to speed "transit time" up, and the gel-like soluble fiber slows things down.

The colon: As we have seen in the other parts of this series, in the colon there is a whole other digestive world happening with the (mostly friendly) bacteria in the colon.

Life in the Colon

It's common to think of the colon as a place where water is removed from whatever is left from digesting the food, and the rest is moved along towards the toilet. But there is actually a whole world in our guts, occupied by ten times the bacteria as the numbers of all of our human cells (this includes all bacteria from the mouth to the anus). We literally could not stay alive if it wasn't for the wonderful friendly bacteria in our digestive systems, where battles are fought, helpful substances are manufactured, and the immune system is bolstered. Did you know that in "Colon World":

• Vitamins are constructed (particularly Vitamin K and some B vitamins)
• More minerals are absorbed into the bloodstream
• Friendly bacteria crowd out the ones that cause disease, such as Salmonella
• Friendly bacteria lower the levels of some toxins, such as ammonia
• Special fats, called short-chain fatty acids, are manufactured, most of which are absorbed into the bloodstream, but some are used to feed the cells of the colon.
• The health of colon cells, which turn over rapidly, is for the most part dependent upon the bacteria of "Colon World", which in turn is dependent upon the food we give these bacteria.

It is the short-chain fatty acids which are getting the most attention recently. It is difficult to get these in our food, so the body relies on the process going on in "Colon World" to make these fats for us. Evidence is building that they are important in keeping the cells of the colon healthy and preventing such conditions as ulcerative colitis, colon cancer, and diverticular disease. They may also help regulate cholesterol and even, to some extent, insulin responses.

What Types of Fiber Feed the Colon?

The fiber types that are most amenable to fermentation are the soluble ones - gums, pectins, etc, found in such foods as berries, beans, flax seeds, plums, apples, and oats, and in some fiber supplements, such as those using psyllium and guar gum. Oligosaccharides and resistant starch also provide fodder for the bacteria. Different "bacteria food" produces different kinds of SCFAs and other products, so it's important to get a variety of fibers in our foods.

Insoluble fiber (found in such foods as vegetables, the bran of grains e.g. wheat bran, nuts, and seeds) isn't available for much fermentation, but it is still important in the colon. Not only does it provide bulk in the stool, its tendency to "speed things along" means that the fermentation will take place all along the length of the colon, including the near the end, where the majority of colon cancer occurs. Without insoluble fiber, most of the fermentation would take place in the top part of the colon, so the colon cells there would get most of the benefit.

New Recipe: Flax Bread with Resistant Starch has lots of soluble and insoluble fiber plus resistant starch.

What are the other benefits of dietary fiber?

Besides reducing the glycemic effect of meals and contributing to colon health, there is evidence that fiber may benefit us in other ways. It seems to help lower cholesterol and triglycerides, and also may help to prevent:

• Ulcers, particularly in the beginning of the small intestine (duodenal ulcers)
• Diabetes
• Heart Disease
• Cancer

Don't Resist this Starch!

What is resistant starch?

As we have already learned, starch that we eat is digested at different rates. The starch in potatoes, cereals, and baked goods digests very rapidly. Other starchy foods, such as beans, barley, or long grained brown rice, are digested more slowly, and cause a much slower and lower blood sugar rise. Resistant starch actually goes all the way through the small intestine without being digested at all. In this way, it is more like fiber, and in some cases is classified and labeled as fiber.

What makes some starch resistant?

There are four types of resistant starch:

1. Starch that is difficult for the digestive process to reach, often due to a fibrous "shell". Grains and legumes which are cooked intact are an example. Also, some altered starches, such as Hi-Maize corn starch, are in both this category and the next.
   
   
2. Some foods, such as unripe bananas, raw potatoes, and plantains, have a type of starch which our digestive enzymes can't break down.
   
   
3. Small amounts of resistant starch (about 5% of the total) are produced when some starchy cooked foods, such as potatoes and rice, are allowed to cool before eating.
   
   
4. Manufactured resistant starch, made by various chemical processes. It is not known whether these starches have the same benefits as those in the other three groups.

Most starchy foods have at least a small amount of resistant starch in them.

Does resistant starch have calories?

Yes, but not in the way you would think, and less than regular starch. When resistant starch reaches the colon, it is used for fuel by the bacteria there. This process, called fermentation, produces a certain type of fat called short-chain fatty acids (SCFAs). It is these fatty acids which produce most of the calories from resistant starch, and many of the benefits. SCFAs are also produced by soluble fiber and oligosaccharides - this is the reason why on some food labels, some fiber is shown as having calories associated with it, but these calories do not raise blood glucose.

What are the benefits of resistant starch?

It seems that the more it is studied, the more positive effects are being found. Many of these are common to oligosaccharides and fermentable fiber. We will discuss fermentable fiber more in Part 5 of this series. Here are some of the benefits of resistant starch:

• Resistant starch is especially associted with one type of SCFA, called butyrate, which is protective of colon cells and associated with less genetic damage (which can lead to cancer). Butyrate also protects the cells in other ways. This is one of the real strengths of resistant starch over oligosaccharides and soluble fiber. Their fermentation does produce butyrate, but not at the levels of resistant starch.
• As with other fermentable fiber, resistant starch is associated with more mineral absorption, especially calcium and magnesium.
• Perhaps most exciting for people with sugar issues, resistant starch seems to improve insulin sensitivity. In the so-called "second meal effect", fermentable fiber and resistant starch are associated with improved glucose tolerance the next day. There is evidence that this is caused by the presense of the short chain fatty acids, and by a peptide produced in the fermentation process.
• Resistant starch produces more satiety, possibly partly through the release of a different peptide (PYY).
• Resistant starch consumption is associated with lower cholesterol and triglyceride levels.
• Promotes "good" bacteria, and supresses "bad" bacteria and their toxic products.
• Promotes bowel regularity.
• Resistant starch in a meal is associated with less fat storage after that meal.

What foods have resistant starch?

Beans are the very best food source. Although the types of beans and preparation methods cause varying amounts of resistant starch (canned beans are more glycemic), in general, the starch in beans is about evenly dividied between slowly-digested starch and resistant starch. Note, though, that products such as Bean-o, which increase the digestibility of beans, will also decrease the amount of resistant starch. List of Legumes

Whole, intact grains are decent sources of resistant starch. The starch in pearl barley is about 12% resistant and 43% slowly-digesting. Bulgar wheat and long grain brown rice are similar.

The starch in shirataki noodles is classified as soluble fiber, but it seems fairly close to resistant starch in composition, from what I can tell.

Hi-Maize corn starch is also a possibility. It can be used to substitute for part of the flour in baked goods. I've been experimenting with it. I've developed a recipe that is a variation on my flax meal bread. It produces a slightly lighter texture. I will report on my ongoing experiments. Hi-Maize can also be added to shakes. One source is available at King Arthur Flour. There is also resistant wheat starch, and other related products. I have not read as much research on their effects.

Starch Can Be As Bad as Sugar for Your Health

On a low carb diet, the main goal is to avoid raising blood glucose too much. This is why we avoid foods which are high in sugars and starches. But it turns out that not all starches are created equal. Some starches are digested very quickly, and cause a rapid and large rise in blood sugar. Others are digested more slowly, causing blood glucose to rise less and over a longer period of time. And some starch, called resistant starch, is not digested in the small intestine at all, and so causes little or no blood sugar rise. The larger the percentage of rapidly-digested starch in a starchy food, the higher the glycemic index of that food.

What is starch?

Starches are long complex chains of simple sugars. This is why they are often called “complex carbohydrates”. It was once thought that complex carbohydrates do not raise blood sugar as quickly or as much as sugars, but now we know that some starches are actually more glycemic than some sugars. In this sense, they are not “complex” for very long at all. People who are sensitive to sugar should avoid most starchy foods as well, since most starchy foods are rapidly broken down into sugar.

Which foods have a lot of starch?

Grains (wheat, rice, barley, oats), potatoes, corn, and beans are all very starchy foods. Grains are made into bread, cereal and pasta, as well as crackers, biscuits, cookies, cakes, pie crust, and anything else made with flour.

What determines whether starches are digested rapidly or slowly?

There are several factors at work:

What is done to the starch before we eat it. Particularly when it comes to grains (and especially wheat), we have a tendency to grind it, puff it, flake it, roll it, and generally beat it into submission so we can form it into any number of processed foods. This has the effect of doing some of the work of our digestive systems before the food even goes into our mouths. It’s really no wonder that these foods are turned into sugar so efficiently within minutes of being in our bodies. The starches that are most rapidly digested are those made from flour (including whole grain flour) and most breakfast cereals.

On the other hand, if grains or legumes remain whole, such as beans, brown rice or whole barley, the starch is broken down into sugars much more slowly, and some never is turned into sugar at all, but reaches the large intestine intact – this is called resistant starch.

Starch Structure. Different kinds of starch have different arrangements of molecules, and some are easier for our digestive enzymes to get at than others. One kind of starch, called amylose, is broken down quite slowly. The higher the amount of amylose in a starch, the more slowly it is digested. Different types of rice have differing percentages of amylose. Long grain rices, which tend to stay more separate, are higher in amylose. Shorter grain rices, which tend to produce creamier and stickier rice are low in amylose and are more glycemic. New potatoes (sometimes described as “waxy”) have a starch that is closer to amylose in structure than more mature potatoes, and they are somewhat less glycemic.

Most of the starch in beans has a structure which is only slowly broken down into sugars.

Surprises: One processed food that seems to be digested more slowly than would be guessed is pasta. Apparently the starch molecules are so tightly packed that only about half is rapidly digested when the pasta is cooked “al dente” (slightly firm). Cooking time and thickness of the pasta greatly affects how the glycemic it is.

Additionally, when some cooked starches, such as potatoes and rice, are cooked and cooled, a small percentage of the starch takes longer to digest.

How can we tell how quickly a starch is digested?

It is difficult to know how quickly any one person will digest any individual food. Relatively few foods have been tested for exactly where they are digested, and there are various means of testing that are not standardized. Also, “slowly digested” is a range, and some foods are logically on the faster end of it. Additionally, each person’s digestive system is a little different, and factors such as how thoroughly the food is chewed and what other foods are eaten with it also have an effect.

The only real way for a person to know how glycemic a food is to them is to monitor their blood glucose. But there are some guidelines that everyone can use.

What Starches Should We Eat?

1. The best starchy foods are whole beans or lentils. The starch is mostly either slowly-digested starch or resistant starch (though canned beans are more fully digested than ones cooked from the dried state).
2. When choosing grains, eat ones which are whole and intact when cooked, such as brown rice, barley, amaranth, or quinoa.
3. Avoid most baked goods or anything made with flour. Best choices are specially-made low carb breads which have less starch and more fiber.
4. Avoid processed cereals with little fiber. Best choices are cold cereals, such as All-Bran with Extra Fiber, are which are mostly fiber.

Oligosaccharides and Prebiotics

Sandwiched in between the simple sugars (monosaccharides) and the starches (polysaccharides) are a group of carbohydrates that we never heard much about until recently, and most people still probably have no idea what they are. But if you read labels you might see ingredients like inulin and oligofructose on food packages – and probably will more and more. You also may have seen the word “prebiotic” creeping into the nutritional vocabulary.

What is an Oligosaccharide?

As we discussed in Part One, oligosaccharides are carbohydrates which have 3-10 simple sugars linked together. They are found naturally, at least in small amounts, in many plants. Plants with large amounts of oligosaccharides include chicory root, from which most commercial inulin is extracted, and so-called Jerusalem artichokes (the root of a member of the sunflower family). They are also found in onions (and the rest of the "onion family", including leeks and garlic), legumes, wheat, asparagus, jicama, and other plant foods. It is estimated that North Americans get about 1-3 grams naturally in their diets each day, while Europeans get 3-10 grams.

Most oligosaccarides have a mildly sweet taste, and have certain other characteristics, such as the mouthfeel they lend to food, that has drawn the interest of the food industry as a partial substitute for fats and sugars in some foods as well as improved texture. Because of this, more and more of the oligosaccharides in food are synthetically produced.

Recent interest has also been drawn to oligosaccarides from the nutritional community because of an important characteristic: the human digestive system has a hard time breaking down many of these carbohydrates. Almost 90% escapes digestion in the small intestine and reaches the colon where it performs a different function: that of a prebiotic.

What is a Prebiotic?

Prebiotic is a kind of an odd term, fairly recently coined to refer to food components that support the growth of certain kinds of bacteria in the colon (large intestine). At first it was thought that oligosaccharides were the main prebiotics, but it turns out that resistant starch and fermentable fiber also feeds these bacteria. We’re learning now that a whole other digestive system is happening in the colon, with important influences on the rest of the body.

What Are The Health Benefits of Prebiotics?

The bacteria that feed on fermentable carbohydrate produce many beneficial substances, including short-chain fatty acids (SCFAs) and certain B-vitamins. Additionally, there is some evidence that they may promote further absorption of some minerals that have escaped the small intestine, including calcium and magnesium.

The SCFAs probably provide many benefits, both locally in the colon, and in the rest of the body, although the research in this area is quite new. In particular, butyrate has received attention as possibly being protective of colon tissues from damage, including colon cancer and ulcerative colitis. Other possible benefits include:

• lower cholesterol
• lower triglycerides
• improved insulin sensitivity and glucose metabolism
• improved immune system function

Interestingly, different oligosaccharides tend to produce different SCFAs – more reinforcement for eating a variety of foods.

Are Oligosaccharides Fiber?

Although oligosaccharides are fiber in most senses of the word (in particular, they would fall under the categories of both soluble fiber and fermentable fiber), they are mostly not labeled as fiber on food labels in the US at this time. Inulin from chicory root may be the only exception.

Where Can I Get More Oligosaccharides in my Diet?

In addition to beans and the vegetables listed above, food additives are also a source – inulin and oligofructose are the most common. However, if you don’t eat many of these foods, you can also get the prebiotic benefits of oligosaccharides by getting more fermentable fiber in your diet, including resistant starch. I will be discussing these carbohydrates in the next two sections of this series.

Understanding Carbohydrates

You may think you know all you need to know about carbohydrates. There are the simple ones, which are digested quickly, and the complex ones, which are digested more slowly. Carbs give us energy, and sometimes raise our blood sugar too much. End of story. Right? Wrong! It turns out that there is much more to carbs than we’ve known until recently. In fact, one of the hottest areas of nutritional research has to do with the hows and wheres of carbohydrate digestion. For example, did you know:

• Many starches (“complex” carbohydrates) are digested more rapidly than some sugars (“simple” carbohydrates). In fact, the very term “complex carbohydrates” may be rapidly becoming obsolete, at least as it has been traditionally defined.
• Some starches aren’t digested in the small intestine, but go on to be broken down in the colon, where they may play a vital role in the health of the colon as well as the rest of the body.
• Some of the fibers and starches which ferment in the colon and produce an important type of fat which is difficult for the body to obtain in any other way.

In this six-part series, we will explore what is known about carbohydrates and what it means to you and your health. I’ll tell you what is being discovered in the emerging areas of fermentable fiber and resistant starch, and how the type of starch in a food is linked to its glycemic index.

The New Basics About Carbohydrates

Carbohydrates, along with fats and protein, are one of the three main classes of food. Carbohydrates are organic compounds consisting mainly of sugars, starches and fiber.

Plants make carbohydrates during photosynthesis and store them as any of the saccharides (sugars) described below. They are used primarily for energy in the body. If carbohydrate isn't used in short order, it is stored. A certain amount can be stored in the liver and muscles as glycogen, and the rest is stored as fat. Unlike protein and essential fats, our bodies can get along without dietary carbohydrate if needed.

These are the types of carbohydrates:

Monosaccharides and Disaccharides (Sugars or Simple Carbohydrates)

Monosaccharides are the simplest types of sugars, and are building blocks for the larger carbohydrate molecules. The most common is glucose, but fructose, galactose, and others are also in this group. All the carbohydrate in our food must be broken down into monosaccharides if it is to be absorbed by the small intestine, and these sugars are very readily absorbed as soon as they hit the intestines.

Disaccharides are combinations of two monosaccharide molecules. For example, a molecule of sucrose (table sugar) is made up of one molecule of glucose and one of fructose. Lactose, the sugar in milk, is made up of glucose and galactose. Disaccharide molecules must be split up to be absorbed. Lactose intolerance occurs when people lack the enzyme needed to break lactose into the monosaccharide molecules that make it up. Sucrose is quickly broken down and absorbed.

Oligosaccharides

“Oligo” is a prefix from Greek meaning “few”, so oligosaccharides are a few monosaccharides together. There is no hard cutoff, but usually carbohydrates with 3 to 10 monosaccharides fall into this category. Oligosaccarides are found in certain plant foods -- legumes, onions, asparagus, and others. Many oligosaccharides are poorly absorbed in the small intestine and have drawn recent attention as “prebiotics” – food for certain beneficial bacteria in the colon.

More about oligosaccharides in Part Two of this series.

Polysaccharides (Starches or Complex Carbohydrates)

Longer chains of glucose molecules, often with many branches, are called polysaccharides. The configuration of the molecules has a lot to do with how quickly they are digested. One recent categorization of starches is to label them according to how the human body digests them.

Rapidly Digested Starch (RDS): As the label implies, rapidly digested starch breaks down quickly into simple sugars. Carbohydrates with a lot of RDS tend to have a high glycemic index -- that is, they cause blood glucose to rise quickly and stay high longer. Some starch digestion actually begins in the mouth, with an enzyme in the saliva. There are many starchy foods, such as potatoes, which have higher glycemic index numbers than table sugar. Beans, on the other hand, have very little rapidly-digested starch, and have a low glycemic index. Most of the starch in beans is split between the next two categories.

Slowly Digested Starch (SDS): Slowly digested starch breaks down over a period of time in the small intestine -- up to two hours. Often this is because it is physically difficult to break it into small bits. For example, the starch in whole barley, which is difficult to chew and otherwise mechanically break down, is almost half of the SDS type. Therefore, barley has a low glycemic index. In some foods the slow digestion has to do with enzymes needed to digest the food.

Resistant Starch: Resistant starch actually reaches the large intestine (colon) without being broken down into sugars at all. In the colon, it is fermented by the bacteria there. The products of this fermentation, primarily short-chain fatty acids, contribute to colon health and may have other positive effects, including lowering insulin resistance and a lessened glycemic response to carbohydrates eaten later (the so-called “second meal effect”).

More about starch in Parts Three and Four of this series.

Fiber

Recent research, including that into resistant starch, has brought the definition of fiber up for a certain amount of debate. Traditionally, fiber has been thought of as carbohydrate that reaches the colon undigested. Now, however, we know that along with resistant starch certain kinds of fiber are fermented in the colon -- in other words, digested further by the bacteria there, producing products useful for the body. Should it still be called fiber? What about undigested oligosacchardides which also feed bacteria in the colon? Fiber is turning out to be much more complex than we realized, and new interesting questions are being investigated about it.

Carbohydrates

What are carbohydrates? Carbohydrates are the main source of energy for the body. Those carbohydrates come from the plant-based foods that you eat. You can either use carbohydrates right away for your energy needs or your body can convert them into fat to use later. There are three types of carbohydrates -- sugars, starches and fiber.

First, a Little Chemistry

No matter how big they are, all carbohydrates are made of carbon, hydrogen and oxygen with the general formula of C_m(H₂O)_n. For example, a simple little sugar molecule like glucose is made up of six carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. It is shaped like a hexagon and has the formula C₆(H₂O)₆. A large starch molecule can be made of many little sugar molecules attached together, which forms a long chain. The little m and n in our general formula, C_m(H₂O)_n, can run into the hundreds.

Simple Sugars

Simple sugars are little molecules made up of one or two sugar units. In nutrition, the most basic simple sugar is glucose, C₆(H₂O)₆, and it is the type of sugar our bodies and brains use for energy every day. Glucose is called a monosaccharide, which means "single sugar." Other monosaccharides include fructose, galactose, and ribose. Fructose is found in fruits and in vegetables, galactose is found in milk and ribose is best known as a component in ribonucleic acid, which is a part of genetic transcription and is found in the cells in our bodies.

I don't want to get much deeper into the chemistry of simple sugars, but it is important to know that the single sugars glucose, fructose and galactose can form different combinations to become disaccharides, a term that means "two sugars.” These sugars include:

• Lactose (milk sugar) is made up of glucose and galactose molecules. People who are "lactose intolerant" can't digest this sugar properly.
• Sucrose (table sugar) is comprised of glucose and fructose molecules. This is the white powdery or granular substance we typically refer to as "sugar" when we are cooking or baking.
• Maltose (malt sugar) is produced during the malting of cereals such as barley.

Simple sugars are water-soluble and sucrose, or table sugar, is easy to digest. The individual glucose and fructose molecules are quickly absorbed into the bloodstream via the small intestine. This can be a problem for people with diabetes or metabolic syndrome who have to watch their blood sugar, or blood glucose levels.

Complex Carbohydrates

Complex carbohydrates are long chains of the single sugar units. For example, the complex carbohydrate we know as starch is made up of many glucose units. These complex carbohydrates can be in the shape of long chains, or the chains can form branches. The complex carbohydrates include:

• Starch, the energy storage form of carbohydrates found in plants, especially in the seeds and roots. Starch is made up of many glucose units linked together. Starchy food examples include rice, wheat, corn, carrots and potatoes. Starches are not water-soluble and require digestive enzymes called amylases to break them apart.
• Glycogen, the energy storage form of glucose found in the muscles and livers of animals. You don't consume any carbohydrates when you eat meats; however, the amount of glycogen in animal tissue at the time of slaughter does affect the pH of meat.
• Cellulose, the structural component of plants. Cellulose helps plants keep their shape; so in a way, cellulose acts like a plant skeleton. We are unable to digest cellulose; however cellulose is one of the important components of fiber, along with lignin, chitin, pectin, beta-glucan, inulin and oligosaccharides.

Dietary starch and cellulose are the complex carbohydrates that are important in nutrition. Potatoes, dry beans, grains, rice, corn, squash and peas contain a large amounts of starch. Vegetables like broccoli, cauliflower, asparagus, lettuces and other greens are not starchy. That is because the stems and leafy parts of plants do not contain much starch, but they do contain more cellulose. Since we can't digest cellulose, that means that the green and leafy vegetables contain fewer calories than the starchy vegetables.

Carbohydrates and Metabolism

The body begins the process of breaking carbohydrates down into their individual monosaccharides almost before we start to eat them. When you smell the delicious aroma of fresh-baked bread or think about that tasty chocolate that you're about to consume, your mouth begins to water. Since table sugar is water-soluble, it begins to dissolve in the saliva in your mouth. Your saliva also contains a small amount of amylase, which is an enzyme that starts to break starch down into glucose while you are chewing.

Carbohydrate digestion is continued in the small intestine where pancreatic amylase is secreted, which breaks down the rest of the carbohydrates. The individual monosaccharides are then absorbed into the blood stream. Once in the blood, the monosaccharides are either used for energy, stored in the liver and muscles as glycogen, or if there is more energy available than you can use, they are converted and stored as fat.

The storage of glucose is triggered by insulin, which forces your body to store any extra blood sugar as glycogen. People with diabetes or metabolic syndrome either can't produce enough insulin or they are not sensitive enough to the insulin they produce and need to regulate their blood sugar with medications, insulin or dietary changes.

Your body prefers to use glucose as the main source of fuel for daily activity. Your muscles need glucose to move and your organs need glucose to function, including your brain. While the body can make glucose from extra dietary protein and fats you may eat, it is suggested that half of your daily calories come from carbohydrates. Try to get your carbohydrates from healthy sources such as whole grains, fruits and vegetables. Cookies, sodas, candy and other sweets are not so healthy.

An average healthy diet should have half of your daily calories coming from carbohydrates. One gram of carbohydrate, whether is it is sugar or starch, contains four calories. One slice of bread has about 12 grams of carbohydrates. One typical chocolate bar may have about 50 grams of carbohydrates. A medium potato has about 35 grams of carbohydrates.

Although all carbohydrates have four calories per gram, some sources of carbohydrates are better for your diet than others. Fruits, vegetables, legumes, nuts, seeds and grains are healthier than candy, sodas and pastries. Why? The healthy carbohydrate sources have great amounts of vitamins, minerals, phytochemicals and fiber, all of which are vital to good health. Candy, sodas, pastries and other junk foods usually are poor sources of nutrients and sometimes we refer to these foods as having "empty calories." This means the foods have lots of calories with little or no nutrition.

Since you need half of your calories from carbohydrates, you can calculate how many you need per day. For example, let's say a person needs 2,000 calories per day. That means that 1,000 calories should come from carbohydrates (2,000 X 0.5). Since each gram of carbohydrate has four calories, then you divide 1,000 by four (1,000/4) to get 250. A person who needs 2,000 calories each day needs about 250 grams of carbohydrates per day. Of those 250 grams, about 10 percent can come from added table sugar and sweeteners. That would be about 25 grams for a 2,000 calorie per day diet. That would equal about half of a candy bar, or less than one can of sugary soda. Unfortunately many people exceed that amount every day.

In order to meet your carbohydrate requirement each day, you need to know how many carbohydrates are in all of the foods you eat. It really is impossible to list every carbohydrate containing food here, however, here are some approximate amounts from common examples:

• One slice of bread - 12.5 grams total, of which 10 grams are starch and less than one gram is fiber
• One cup of pasta - 43 grams total, of which 36 grams are starch and 2.5 grams are fiber
• One medium apple - 19 grams total, of which eight grams are starch and three grams are fiber
• One Snickers candy bar - 63.5 total grams, of which 53 grams are sugar, two grams are fiber
• One cup of raisin bran cereal - 43 grams total, of which seven grams are fiber, 17 grams are starch and 16 grams are sugar
• One cup of sugar frosted corn flake cereal - 28 grams total, of which 15 grams are starch, one gram is fiber, 12 grams are sugar
• One four ounce glass of red wine - three grams total, of which, less than one gram is sugar
• One eight ounce serving of low fat milk - 12 grams total, of which 12 grams are lactose
• One cup broccoli - six grams total, of which 2.5 grams are fiber and 1.5 grams are sugar
• One cup green beans - eight grams total, of which four grams are fiber
• One cup sweet corn - 31 grams total, of which 21 grams are starch, three grams are fiber
• Two cups lettuce - two grams total, of which one gram is fiber
• One cup asparagus - four grams total, of which two grams are fiber
• One medium orange - 15 grams total, of which three grams are fiber
• One half medium grapefruit - nine grams total, of which 1.5 grams are fiber
• One medium chocolate chip cookie - 16 grams total, of which seven grams are sugar
• One cup strawberries - 12 grams total, of which three grams are fiber
• One cup blueberries - 21 grams total, of which four grams are fiber and 15 grams are sugar
• One half cup marinara sauce - 14 grams total, of which less than one gram is fiber
• One medium tomato - five grams total, of which 1.5 grams are fiber
• One medium potato with skin - 29 grams total, of which three grams are fiber, 25 grams are starch
• One cup carrots - 12 grams total, of which 3.5 grams are fiber and two grams are starch
• One slice of an apple pie - 40 grams total, of which 18 grams are sugar
• One eight ounce cup of orange juice - 26 grams total, of which 21 grams are from fruit sugars
• One cup of dry beans like pinto beans or navy beans - 47 grams total, of which 19 grams are fiber, 28 grams are starch
  Source: USDA National Nutrient Database for Standard Reference

You can search for more carbohydrate information online for all of your favorite foods at Calorie Count Plus.

Nutrition Facts labels on packaged foods will also list the amount of carbohydrates per serving. It takes a little extra time and effort to look up the carbohydrate counts for all of the foods you eat, but with experience you will begin to have a good idea of approximate calorie counts and carbohydrate counts.

This Week's Assignment

Well, you made it through lesson one and I have an easy assignment for you. You have learned about carbohydrates and why your body needs them. I want you to focus on eating healthful carbohydrates by increasing the amount of fruits and vegetables you eat. This week I want you to choose three new fruits or vegetables that you have never eaten before. You may eat them as snacks or as part of your regular meals. You may wish to continue to try new foods once each week or once a month after that.

Amino Acids

Amino acids contain both a carboxyl group (COOH) and an amino group (NH₂). The general formula for an amino acid is given below. Although the neutrally-charged structure is commonly written, it is inaccurate because the acidic COOH and basic NH₂ groups react with one another to form an internal salt called a zwitterion. The zwitterion has no net charge; there is one positive (COO^-) and one negative (NH₃⁺) charge.

There are 20 amino acids derived from proteins. While there are several methods of categorizing them, one of the most common is to group them according to the nature of their side chains.

Amino Acid Chirality

Amino acids (except for glycine) have a chiral carbon atom adjacent to the carboxyl group (CO₂^-). This chiral center allows for stereoisomerism. For example, take a look at the stereorepresentations and Fischer projection formulas of the enantiomers of serine.

All amino acids found in proteins occur in the L-configuration about the chiral carbon atom. D-amino acids are not naturally found in proteins and are not involved in the metabolic pathways of eukaryotic organisms, although they are important in the structure and metabolism of bacteria. For example, D-glutamic acid and D-alanine are structural components of certain bacterial cell walls.

Protein and Polypeptide Structure

There are four levels of structure found in polypeptides and proteins. The primary structure of a polypeptide of protein determines its secondary, tertiary, and quaternary structures.

Primary Structure

The primary structure of polypeptides and proteins is the sequence of amino acids in the polypeptide chain with reference to the locations of any disulfide bonds. The primary structure may be thought of as a complete description of all of the covalent bonding in a polypeptide chain or protein.

The most common way to denote a primary structure is to write the amino acid sequence using the standard three-letter abbreviations for the amino acids. For example:

gly-gly-ser-ala

is the primary structure for a polypeptide composed of glycine, glycine, serine, and alanine, in that order, from the N-terminal amino acid (glycine) to the C-terminal amino acid (alanine).

Secondary Structure

Secondary structure is the ordered arrangement or conformation of amino acids in localized regions of a polypeptide or protein molecule. Hydrogen bonding plays an important role in stabilizing these folding patterns. The two main secondary structures are the alpha helix and the anti-parallel beta-pleated sheet. There are other periodic conformations, but the α-helix and β-pleated sheet are the most stable. A single polypeptide or protein may contain multiple secondary structures.

An α-helix is a right-handed or clockwise spiral in which each peptide bond is in the trans conformation and is planar. The amine group of each peptide bond runs generally upward and parallel to the axis of the helix; the carbonyl group points generally downward.

The β-pleated sheet consists of extended polypeptide chains with neighboring chains extending anti-parallel to each other. As with the α-helix, each peptide bond is trans and planar. The amine and carbonyl groups of peptide bonds point toward each other and in the same plane, so hydrogen bonding can occur between adjacent polypeptide chains.

The helix is stabilized by hydrogen bonding between amine and carbonyl groups of the same polypeptide chain. The pleated sheet is stabilized by hydrogen bonds between the amine groups of one chain and the carbonyl groups of an adjacent chain.

Tertiary Structure

The tertiary structure of a polypeptide or protein is the three-dimensional arrangement of the atoms within a single polypeptide chain. For a polypeptide consisting of a single conformational folding pattern (e.g., an alpha helix only), the secondary and tertiary structure may be one and the same. Also, for a protein composed of a single polypeptide molecule, tertiary structure is the highest level of structure that is attained.

Tertiary structure is largely maintained by disulfide bonds. Disulfide bonds are formed between the side chains of cysteine by oxidation of two thiol groups (SH) to form a disulfide bond (S-S), also sometimes called a disulfide bridge.

Quaternary Structure

Quaternary structure is used to describe proteins composed of multiple subunits (multiple polypeptide molecules, each called a 'monomer'). Most proteins with a molecular weight greater than 50,000 consist of two or more noncovalently-linked monomers. The arrangement of the monomers in the three-dimensional protein is the quaternary structure. The most common example used to illustrate quaternary structure is the hemoglobin protein. Hemoglobin's quaternary structure is the package of its monomeric subunits. Hemoglobin is composed of four monomers. There are two α-chains, each with 141 amino acids, and two β-chains, each with 146 amino acids. Because there are two different subunits, hemoglobin exhibits heteroquaternary structure. If all of the monomers in a protein are identical, there is homoquaternary structure.

Hydrophobic interaction is the main stabilizing force for subunits in quaternary structure. When a single monomer folds into a three-dimensional shape to expose its polar side chains to an aqueous environment and to shield its nonpolar side chains, there are still some hydrophobic sections on the exposed surface. Two or more monomers will assemble so that their exposed hydrophobic sections are in contact.

More Information

Do you want more information on amino acids and proteins? Here are some additional online resources. In addition to general chemistry texts, information about protein structure can be found in texts for biochemistry, organic chemistry, general biology, genetics, and molecular biology. The biology texts usually include information about the processes of transcription and translation, through which the genetic code of an organism is used to produce proteins.

Alkanes

The simplest organic compounds are hydrocarbons. Hydrocarbons contain only two elements, hydrogen and carbon. A saturated hydrocarbon or alkane is a hydrocarbon in which all of the carbon-carbon bonds are single bonds. Each carbon atom forms four bonds and each hydrogen forms a single bond to a carbon. The bonding around each carbon atom is tetrahedral, so all bond angles are 109.5&deg. As a result, the carbon atoms in higher alkanes are arranged in zig-zag rather than linear patterns.

Straight Chain Alkanes

Here is a table that gives the names of the straight chain alkanes. It's a good idea to commit this table to memory. The general formula for an alkane is C_nH_2n+2 where n is the number of carbon atoms in the molecule. There are two ways of writing a condensed structural formula. For example, butane may be written as CH₃CH₂CH₂CH₃ or CH₃(CH₂)₂CH₃.

# Carbon	Name	Molecular Formula	Structural Formula
1	Methane	CH4	CH4
2	Ethane	C2H6	CH3CH3
3	Propane	C3H8	CH3CH2CH3
4	Butane	C4H10	CH3CH2CH2CH3
5	Pentane	C5H12	CH3CH2CH2CH2CH3
6	Hexane	C6H14	CH3(CH2)4CH3
7	Heptane	C7H16	CH3(CH2)5CH3
8	Octane	C8H18	CH3(CH2)6CH3
9	Nonane	C9H20	CH3(CH2)7CH3
10	Decane	C10H22	CH3(CH2)8CH3

Rules for Naming Alkanes

• The parent name of the molecule is determined by the number of carbons in the longest chain.
• In the case where two chains have the same number of carbons, the parent is the chain with the most substituents.
• The carbons in the chain are numbered starting from the end nearest the first substituent.
• In the case where there are substituents having the same number of carbons from both ends, numbering starts from the end nearest the next substituent.
• When more than one of a given substituent is present, a prefix is applied to indicate the number of substituents. Use di- for two, tri- for three, tetra- for four, etc. and use the number assigned to the carbon to indicate the position of each substituent.

Branched Alkanes

• Branched substituents are numbered starting from the carbon of the substituent attached to the parent chain. From this carbon, count the number of carbons in the longest chain of the substituent. The substituent is named as an alkyl group based on the number of carbons in this chain.
• Numbering of the substituent chain starts from the carbon attached to the parent chain.
• The entire name of the branched substituent is placed in parentheses, preceded by a number indicating which parent-chain carbon it joins.
• Substituents are listed in alphabetical order. To alphabetize, ignore numerical (di-, tri-, tetra-) prefixes (e.g., ethyl would come before dimethyl), but don't ignore don't ignore positional prefixes such as iso and tert (e.g.,. triethyl comes before tertbutyl).

Cyclic Alkanes

• The parent name is determined by the number of carbons in the largest ring (e.g., cycloalkane such as cyclohexane).
• In the case where the ring is attached to a chain containing additional carbons, the ring is considered to be a substituent on the chain. A substituted ring that is a substituent on something else is named using the rules for branched alkanes.
• When two rings are attached to each other, the larger ring is the parent and the smaller is a cycloalkyl substituent.
• The carbons of the ring are numbered such that the substituents are given the lowest possible numbers.

What Is a Carbohydrate

Carbohydrates or saccharides are the most abundant class of biomolecules. Carbohydrates are used to store energy, though they serve other important functions as well. This is an overview of carbohydrate chemistry, including a look at the types of carbohydrates, their functions, and carbohydrate classification.

What Is a Carbohydrate?

Carbohydrates are a common class of simple organic compouds. A carbohydrate is an aldehyde or a ketone that has additional hydroxyl groups. The simplest carbohydrates are called monosaccharides, which has the basic structure (C·H₂O)_n, where n is three or greater. Monosaccharides link together to form oligosaccharides and polysaccharides. Two monosaccharides link together to form a disaccharide.

Functions of Carbohydrates

Carbohydrates serve several biochemical functions:

• Monosaccharides are a fuel for celular metabolism.

• Monosaccharides are used in several biosynthesis reactions.

• Monosaccharides may be converted into space-saving polysaccharides, such as glyocogen and starch. These molecules provide stored energy for plant and animal cells.

• Carbohydrates are used to form structural elements, such as chitin in animals and cellulose in plants.

• Carbohydrates and modified carbohydrates are important for an organism's fertilization, development, blood clotting and immune system function.

Examples of Carbohydrates

Monosaccharides: glucose, fructose, galactose

Disaccharides: sucrose, lactose

Polysaccharides: chitin, cellulose

Carbohydrate Classification

Three characteristics are used to classify monosaccharides:

• number of carbon atoms in the molecule
• location of the carbonyl group
• the chirality of the carbohydrate

aldose - monosaccharide in which the carbonyl group is an aldehyde

ketone - monosaccharide in which the carbonyl group is a ketone

triose - monosaccharide with 3 carbon atoms

tetrose - monosaccharide with 4 carbon atoms

pentose - monosaccharide with 5 carbon atoms

hexose - monosaccharide with 6 carbon atoms

aldohexose - 6-carbon aldehyde (e.g., glucose)

aldopentose - 5-carbon aldehyde (e.g., ribose)

ketohexose - 6-carbon hexose (e.g., fructose)

A monosaccharide is D or L depending on the orientation of the asymmetric carbon located furthest from the carbonyl group. In a D sugar, the hydroxyl group is on the right the molecule when written as a Fischer projection. If the hydroxyl group is on the left of the molecule, then it is an L sugar.

Elements in the Human Body

99% of the mass of the human body is made up of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Every organic molecule contains carbon. Since 65-90% of each body cell consists of water (by weight), it isn't surprising that oxygen and hydrogen are major components of the body.

Here's is a look at the major elements in the body and what these elements do.

1. Oksigen

2. Carbon
3. Hydrogen
4. Nitrogen
5. Calcium






6. phosporus
7. potassium
8. Sodium
9. Chlorine
10. Magnesium