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Biochemistry is the chemistry of living organisms. It encompasses all living things and how they synthesize energy and use it for their specific purposes. This includes plants as well as animals including mammals. Humans unlike plants are unable to use solar energy in a process called synthesis, therefore, they depend on plant photosynthesis to provide their bodies with the necessary nutrients needed to thrive and survive. All living organisms whether single cells or multi-celled are very organized and produce complex functions necessary for life. There are many types of complex chemical reactions taking place at any given time in the body of a living organism. In order to accomplish this highly organized environment, there is an increase in energy demands which in turn necessitates an increase in consumption, whether it is animal or plant. In large living organisms there are many different types of molecules such as proteins, polysaccharides and nucleic acids, as well as lipids.
Proteins are very large molecules, macromolecular, that make up about half of an organisms body weight.
"Proteins serve as the major structural components in animal tissues; they are a key part of skin, nails, cartilage, and muscles. Other proteins catalyze reactions, transport oxygen, serve as hormones to regulate specific body processes, and perform other tasks. "(Brown, 2009, p. p. 1080)
All proteins are comprised of the same basic makeup, amino acids. Proteins use amino acids as their building blocks. Amino acids are:
"substances in which the amino group is located on the carbon atom immediately adjacent to the carboxylic acid group. There is always one carbon atom between the amino group and the carboxylic acid group. The doubly ionized form, zwitterions, usually predominated at near neutral values of pH. This form is a result of the transfer of a proton from the carboxylic acid group to the basic amine group." (Brown, 2009, pp. 1080-1081)
There have been 22 amino acids found in nature. Our bodies use 20 of these amino acids, although our bodies can synthesize only 10 of these amino acids, and we must ingest the other 10. They are essential amino acids because they are a requirement for our diet or optimal functioning. They are joined together by amide groups. This link is called a peptide bond. It is formed by a reaction between the carboxyl group and amino group. When multiple amino acids are linked together by peptide bonds it forms polypeptides. A primary structure, or arrangement of amino acids in a protein chain, is unique to each type of protein. The function and biochemical composition of each protein can be altered by just one amino acid out of place. There is a secondary structure which refers to how the protein chain is oriented. The most common secondary structure is the helix.
"The helix is held in position by hydrogen bond interactions between N-H bonds and the oxygen's of nearby carbonyl groups in the amide backbone of the protein; the R groups are not involved. The pitch of the helix and the diameter of the cylinder must be such that (1) no bond angles are strained and (2) N-H and C=O functional groups on adjacent turns are in proper position for hydrogen bonding." (Brown, 2009, p. 1084)
Another structural format is the beta sheet, which contains two strands of peptides that are held together by hydrogen bonds along their back resembling a zipper. There is also a tertiary structure, which is the overall shape of the protein in its folded form. This form is maintained by many different types of interactions, mainly the folding pattern contributes to the stability of the protein, and some are more effective than others. Enzymes are one of the most important types of proteins because they are catalysts for other specific reactions.
Carbohydrates are found in both plant and animal material. They are polyhydroxy aldehydes and ketones, not hydrates of carbon. There are several carbohydrates including glucose and fructose. Glucose can react with itself, mainly due to the functional groups alcohol and aldehyde and the structure of a long flexible back. Fructose can "cyclize" to form either five or six member rings. Both fructose and glucose are monosaccharides, or simple sugars incapable of being broken down into smaller forms. There are also disaccharides, two monosaccharide's bonded together. The most common are sucrose or table sugar, and lactose or milk sugar. These forms react with water while an acid catalyst is present to form monosaccharides. The resulting form of sugar when this happens is actually sweeter than normal table sugar. Polysaccharides are many monosaccharides joined together such as starch, glycogen, and cellulose. Starch refers to a group of polysaccharides that are found in plant matter. It is the major form of food storage in plants such as potatoes, corn, wheat and rice. In turn, humans use these foods as a major source of energy fulfillment. The starch can either have branched or unbranched chains. Glycogen, another polysaccharide, is synthesized in the body. It acts as the primary energy bank in the body and is concentrated in organs of the body. Muscles and the liver use glycogen, in the muscles it is immediately used, although in the liver it is used to help keep the blood sugar levels under control. Cellulose is a major structure element in plant material. Cellulose resembles starch, but is not easily digested by the body, whereas starch is. A person could consume the same amount of starch and cellulose, but would only consume a fraction of the caloric intake from the cellulose. Human bodies do not contain the enzyme necessary for the hydrolyzing effect for the cellulose, although grazing animals such as cows do break it down and use it as energy.
Another molecule that is essential to biological life is lipids. Lipids are used to store fats and oils that the biological entities for a long period of time. Plants tend to store their energy in a liquid oil form, while animals store energy as fats. Both are basically glyercol and 3 fatty acids, which are made up of carboxylic acids. Alkanes are present in saturated fats which are usually solids at room temperature such as shortening used for cooking. In plant fats that are liquid not solid such as olive oil or vegetable oil there are alkenes. The essential difference as far as structural form is the presence of either alkenes or alkanes. Fats are broken down even further into monounsaturated and polyunsaturated. The mono- and poly- refer to the number of carbon-carbon double bonds. Monounsaturated fats have one carbon-carbon double bond; while polyunsaturated have multiple carbon-carbon double bonds. There is also another form of fats, trans-fats, which are unsaturated fats that have been converted into saturated fats by a process called hydrogenation. Although these fats are abundantly available, the only essential fats we must have are omega-3 and omega-6 fats. One type of fat that is necessary to cell structure is a phospholipid. They are responsible for the bilayer that is needed in cells.
Another component necessary for biological function are nucleic acids. Nucleic acids are carriers of an organism's genetic makeup. There are a few of these that most people are familiar with: deoxyribonucleic acid or DNA and ribonucleic acids or RNA. DNA is a very large molecule, while RNA is much smaller in size and molecular weight. DNA is found in the nucleus and RNA is found in the cytoplasm of the cell. The RNA assists the cell in moving the genetic information from the nucleus of the cell into the cytoplasm where a process of protein synthesis occurs. There substances called monomers of nucleic acids, nucleotides formed from a phosphoric acid molecule, a nitrogen base and a five carbon sugar. The base of one of these monomers attach to a ribose or deoxyribose molecule with a nitrogen atom. DNA is actually two strands that are hooked together in the form of a double helix. There are four bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). The two strands are connected by bonds between the four bases, A with T and G with C, which are called complementary bases. During replication the double helix separates and new complementary bases are created on a new strand, resulting in two DNA strands. This process takes place with the replication of any type of cell, whether it is plant, animal, or viral.