Download Biochemistry and Nutrition

Biochemistry and Nutrition
(You need to know this for lecture test)
Macromolecule: large organic molecules found in living things
All living things, including humans, are formed from four basic types of macromolecules:
proteins, carbohydrates, lipids, and nucleic acids.
Proteins may be enzymes, hormones, regulatory factors, or structural. They may be
found in the cell or outside the cell. Fibrous proteins like collagen and elastin form
much of your connective tissue. Proteins are made up of amino acids connected end-toend in unbranching chains. Very small proteins are called peptides. There are twenty
different amino acids found in proteins.
Carbohydrates or saccharides are made up of different types of sugar molecules.
Carbohydrate macromolecules may be branched or unbranched. Starch and glycogen are
examples of carbohydrates that are used to store glucose for later use as a fuel source.
They are made entirely of glucose subunits. Cellulose, another glucose polymer, is
inedible by human beings because the linkage between glucose subunits is different from
that used in starch. Cellulose makes up most of the mass of the plant life on earth.
Carbohydrates make up the cell walls of plant cells as well as of some bacteria.
Monosaccharide: a simple sugar. Examples are glucose, galactose, ribose, deoxyribose.
Disaccharides: two linked sugars. For instance, sucrose (table sugar) is composed of
glucose linked to fructose. Maltose is two glucose molecules linked together.
Oligosaccharides have many sugar units. Simple sugars and oligosaccharides are
sometimes found linked to proteins, particularly on the outer cell membranes.
Lipids are the molecules contained in fat. Examples are fatty acids, triglycerides,
cholesterol and lecithin. Triglycerides are composed of three fatty acids linked by a
glycerol molecule. Phospholipids, which form the cellular membranes, are composed of
two fatty acids linked to a phosphate group. Prostaglandins are formed from certain fatty
acids.
Nucleic acids include ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
DNA and RNA are unbranched polymers of nucleotides. Both contain four different
types of nucleotides. It is the sequence of nucleotides that gives DNA and RNA their
informational content. Your genes are composed of DNA. RNA is used in many ways
by the cell (take General Bio for further info). ATP is a nucleotide and is similar to one
of the units of RNA except that it contains three phosphates rather than one. The high
energy phosphate of ATP is the major energy currency of the cell, and is used to drive
many chemical reactions. GTP and cyclic AMP are nucleotides that serve as intracellular
messengers to regulate cellular functions.
Besides proteins, carbohydrates, lipids and nucleic acids, humans and other living things
are composed mainly of water. However, other inorganic minerals are important for the
functioning of the human body, including sodium, potassium, chloride, calcium,
phosphate, sulfur, iron, and magnesium. Trace amounts of other elements like copper
and selenium are important for certain enzymatic functions. Gases like carbon dioxide,
oxygen, and nitric oxide are also necessary for metabolic functions.
Catabolism
Catabolism is the process by which large molecules are broken down into small
molecules with the release of energy. This can also be called chemical digestion. In
general, it involves the use of specific enzymes which serve as catalysts in the digestive
process (a catalyst is something that speeds up a chemical reaction, but is not itself
changed in the process). Most enzymes are proteins (but not all proteins are enzymes).
Some RNA molecules also have catalytic activity.
Proteins are digested by enzymes called proteases to yield amino acids. Examples of
protease enzymes are trypsin, chymotrypsin, carboxypeptidase, and elastase.
Because individual proteases cut the protein chain only at specific amino acids, it usually
takes many different proteases to completely digest a protein.
Carbohydrates are cleaved by amylase and other enzymes to yield oligosaccharides and
simple sugars. Many enzymes are specific for certain disaccharides. For instance,
lactase cleaves lactose into galactose and glucose. An insufficiency of lactase leads to
lactose intolerance. Maltase cleaves maltose into two glucose monomers. Sucrase
cleaves sucrose into glucose and fructose.
Glucose is the primary fuel source for the body, particularly the muscles and the brain.
Completely catabolysed to carbon dioxide and water, one molecule of glucose can yield
up to 38 ATPs.
Lipases break down triglycerides into fatty acids and glycerol, which are absorbed in the
small intestine. Triglycerides are reformed to be stored as fat. These are converted into
fatty acids again, when they are used as fuel in skeletal muscle and the heart. The brain
cannot use fatty acids as fuel.
RNA and DNA are broken down by specific nucleases into their constituent nucleotides.
Nutrition
Carbohydrates are the main source of energy for most human populations. Large
complex carbohydrates are digested more slowly that simple sugars, which are absorbed
immediately. Ingestion of large quantities of sugar can cause a spike in blood glucose
levels.
There are no “essential” carbohydrates. The body is capable of building all the various
types of carbohydrates that it needs.
Fat can serve as an energy source. However, certain fatty acids are absolutely required
by the human body because we cannot make our own. These are linoleic acid and alpha
linoleic acid. These are found widely in plant oils. The essential fatty acids are
necessary to make prostaglandins, which have hormone-like properties.
The body can convert alpha linoleic acid to omega 3 fatty acids; however the omega 3
fatty acids found in fish oils can make that conversion unnecessary. Fish oil
(surprisingly) also has the property of reducing triglyceride levels in the bloodstream,
which helps prevent atherosclerosis. Many other health benefits are claimed for omega 3
and omega 6 fatty acids (also found in fish oil).
Trans fatty acids and saturated fatty acids created by processing of vegetable oils (and to
a lesser extent by bacterial metabolism) may contribute to atherosclerosis, heart disease,
and promote inflammation.
Of the twenty amino acids of which proteins are made, eight cannot be made by the
human body, and therefore must be obtained through the diet. These are the essential
amino acids. An additional three are required by infants and rapidly growing children. In
general, Americans have no trouble getting all the amino acids they need through diet
that includes animal protein and dairy products. In some countries where dietary options
are limited by poverty, people may not get all the amino acids they need. The result may
be stunted growth and mental deficiency.
Vitamins are organic compounds required in small amounts by the human body, and
include vitamins A, C, D, E, K and the B vitamins (thiamine, riboflavin, niacin,
pantothenic acid, biotin, vitamin B-6, vitamin B-12 and folate). Vitamin A is converted
into pigments used by the photoreceptors for your eyes, and lack of vitamin A can lead to
blindness. Various metabolic diseases have been associated with the lack of the other
vitamins, most of which are used as coenzymes in metabolic processes. Vitamin D is
involved in calcium metabolism and can be made by the skin. It is difficult to obtain
enough vitamin B12 through an all vegetarian diet.
Diets—Dr. Edwards’ opinion
A recent long term study tried to replicate the use of various popular diets, Dr. Atkins,
South Beach diet, the Mediterranean diet, low carb, low fat, etc. The results were fairly
unequivocal; in terms of weight loss, it didn’t matter so much WHAT you eat, it is HOW
MUCH you eat that determines whether you lose weight. Calories are calories no matter
what their source. Carbohydrates can easily be converted to fat in the human body.
Likewise, excess amino acids from a high protein diet can also be converted to fat.
If you want to lose weight, you have to eat less food or burn more calories through
exercise. Unfortunately exercise tends to stimulate the appetite, so the easier option is to
eat less food.
Various diet pills are effective at suppressing appetite and can lead to weight loss.
Unfortunately, experience suggests that such weight loss is ephemeral, since it is usually
regained after one stops taking the pills.