ORGANIC COMPOUNDS OF BIOLOGICAL IMPORTANCE

Carbohydrates

Contain C (carbon), H (hydrogen), O (oxygen) usually in the ratio of 2 hydrogens for each carbon or oxygen
CH20

Monosaccharides - Simplest type. Consists of a one-ring structure. Examples: glucose (given in hospitals intravenously) and fructose. Both glucose and fructose are found in honey.

Disaccharides - Two Monosaccharides are bonded together (linked together), to do this a water molecule is removed. Two-ring structure. Examples:

Sucrose - consisting of one glucose joined to a fructose.

Sucrose is table sugar; it is also the form in which carbohydrate is transported in plants (usually from the leaves to the roots). (The sugar of transport in man is glucose).

Sucrose is obtained from sugar beets or sugar cane, which store large quantities of sucrose - most plants do not.

Maltose - composed of two glucoses.

Lactose - composed of glucose and galactose. It is found in milk. Many people lack the enzyme to digest it = lactose intolerance.

Polysaccharides - chain of monosaccharides. Examples:

Cellulose - chain of glucoses. Component of plant cell walls. Function support

Starch - chain of glucoses. Form in which energy is stored in plants. Found in leucoplasts and chloroplasts.

Glycogen - chain of glucoses. A form in which energy is stored in animals. Found in the liver, skeletal muscles. In humans most energy storage is in the form of fat.

LIPIDS

Lipids are large molecules that do not dissolve in water. They contain carbon, hydrogen and oxygen. Functions include energy storage, insulation, component of cellular membranes.

Fats - lipid composed of 3 fatty acid molecules combined with one glycerol molecule. Glycerol (glycerine) is found in handcream and lubricants.

saturated fat - fatty acids contain all hydrogens possible. There are no double bonds in the fatty acid portion of the molecule. Solids at room temperature.

unsaturated fat - more hydrogens can be added to the (a) fatty acid molecules). There is at least one double bond in the fatty acid portion of the molecule. Liquids at room temperature.

Phospholipids - phosphorus - and nitrogen - containing compound replaces a fatty acid. Component of cellular membranes.

Steroids - differ greatly from fats and phospholipids in structure; they are complex ring compounds (5 fused rings). Like fats and phospholipids they do not dissolve in water. Examples of steroids - cholesterol, vitamin D, cortisone, estrogen.

PROTEINS

Gigantic molecules which contain carbon, hydrogen, oxygen, nitrogen and sulfur. Proteins are made up of chains of amino acids. A protein may consist of one or more chains.

The sequence of amino acids - which amino acid is where- is the primary structure of a protein. The chain of amino acids is then folded to form a helix, (imagine a wire wrapped around a cylinder) or a pleated sheet, these are secondary structures. How the chain is folded in 3-dimensions to result in a compact globular shape is the tertiary structure. In some proteins there is more than one chain. How 2 or more chains are arranged is the quaternary structure. Not all proteins have tertiary and quaternary structures.

Functions of Protein
Structural - hair, nails, skin, feathers, collagen in cartilage.

Enzymes - catalysts, increase rate of chemical reactions.

Hormones - chemical messengers, some are proteins.

NUCLEIC ACIDS

Nucleic acids contain carbon, hydrogen, oxygen, nitrogen and phosphorus. They are composed of nucleotides. A nucleotide consists of a nitrogen-containing base, a sugar and a phosphate group. There are two kinds of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

In DNA, the bases are adenine A, thymine T, guanine G and cytosine C. The sugar is deoxyribose. In RNA the bases are the same except thymine is replaced by uracil. The sugar in RNA is ribose.

In DNA, there are two chains of nucleotides held together by hydrogen bonds. The chains are coiled into a helix. An adenine in one chain is always across from a thymine in the other and vice versa. Guanine is always across from cytosine. RNA molecules are single- stranded. Genes are segments of DNA.

RNA functions in synthesis of proteins. There are three types. Messenger RNA (m-RNA) carries the genetic message from the nucleus to the ribosomes in the cytoplasm. Transfer RNA (t-RNA) brings amino acids to the ribosomes and serves as an adapter. Ribosomal RNA (r-RNA) is part of the structure of ribosomes.

7/12/07