The Structure and Function of Macromolecules

AP Biology Chapter 5

Macromolecules

Macromolecules are giant molecules .Four main classes of macromolecules are:

1. Carbohydrates2. Lipids3. Proteins4. Nucleic Acids

Polymers

A polymer is a long molecule made of many similar or identical monomers (small molecules).Polymers are linked by covalent bonds.The covalent bonds occur through

condensation reactions called dehydration.The polymers are disassembled by a

hydrolysis reaction.

Dehydration Reactions

Condensation involves a dehydration synthesis because a water is removed (dehydration) and a bond is made (synthesis). When two monomers join, a hydroxyl (OH)

group is removed from one monomer and a hydrogen (H) is removed from the other. This produces the water given off during a

condensation reaction.

Carbohydrates

in short-term energy storage as intermediate-term energy storage

(starch for plants and glycogen for animals); as structural components in cells (cellulose

in the cell walls of plants and many protists), and chitin in the exoskeleton of insects and other arthropods.

Carbohydrates function:

Monosaccharides

Monosaccharides are single (mono=one) sugars. Sugars are structurally the simplest

carbohydrates. They are the structural unit which makes

up the other types of carbohydrates. Important monosaccharides include

ribose, glucose, and fructose.

Disaccharides

Disaccharides are formed when two monosaccharides are chemically bonded together. Sucrose, a common plant disaccharide is

composed of the monosaccharides glucose and fructose. Lactose, milk sugar, is a disaccharide

composed of glucose and the monosaccharide galactose.

Polysaccharides

Polysaccharides are large molecules composed of individual monosaccharide units. A common plant polysaccharide is starch,

which is made up of many glucoses.Glycogen is an animal storage product

that accumulates in the vertebrate liver. Cellulose is a polysaccharide found in

plant cell walls. Cellulose forms the fibrous part of the plant cell wall.

Amylopectin

Lipids

Lipids are involved mainly with long-term energy storage. They are generally insoluble in polar

substances such as water. Secondary functions of lipids are as structural

components and as hormones that play roles in communications within and between cells. Lipids are composed of three fatty acids

(usually) covalently bonded to a 3-carbon glycerol.

Fatty Acids

Fatty acids can be 1. saturated (meaning they have as

many hydrogens bonded to their carbons as possible) or

2. unsaturated (with one or more double bonds connecting their carbons, hence fewer hydrogens).

Fats

A fat is solid at room temperature, while an oil is a liquid under the same conditions. The fatty acids in oils are mostly unsaturated, while those in fats are mostly saturated.

Fats and Oils

Fats and oils function in energy storage. Animals convert excess sugars into fats. Most plants store excess sugars as starch, although some seeds and fruits have energy stored as oils

Fats

Another use of fats is as insulators and cushions. The human body naturally accumulates some fats in the "posterior" area. Subdermal ("under the skin") fat plays a role in insulation.

Phospholipids

Phospholipids and glycolipids are important structural components of cell membranes.

Waxes

Waxes are an important structural component for many organisms, such as the cuticle, a waxy layer covering the leaves and stems of many land plants; and protective coverings on skin and fur of animals.

Cholesterol and Steroids

Cholesterol and steroids: Most mention of these two in the news is usually negative. Cholesterol has many biological uses, such as its occurrence in the cell membranes, and its role in forming the sheath of some neurons.

Proteins

Proteins are very important as control and structural elements. Control functions of proteins are carried out by enzymes and proteinaceous hormones.

Enzymes

Enzymes are chemicals that act as organic catalysts (a catalyst is a chemical that promotes but is not changed by a chemical reaction).

Structural Proteins

Structural proteins function in the cell membrane, muscle tissue, etc.

Proteins

The building block of any protein is the amino acid, which has an amino end (NH2) and a carboxyl end (COOH). The R indicates the variable component of each amino acid.

Basic Amino Acid

Amino Acids

Evolutionary Significance

All living things use various combinations of the same twenty amino acids. A very powerful bit of evidence for the phylogenetic connection of all living things.

Peptide Bond

Amino acids are linked together by joining the amino end of one molecule to the carboxyl end of another. Removal of water allows formation of a type of covalent bond known as a peptide bond.

Primary Structure

Amino acids are linked together into a polypeptide, the primary structure is the sequence of amino acids in a polypeptide.

Secondary Structure

The secondary structure is the tendency of the polypeptide to coil or pleat due to H-bonding between R-groups.

Tertiary Structure

The tertiary structure is controlled by bonding (or in some cases repulsion) between R-groups.The protein tends to fold upon itself.

Quaternary Structure

Many proteins, such as hemoglobin, are formed from one or more polypeptides. Such structure is termed quaternary structure.

Nucleic Acids

Nucleic acids are polymers composed of units known as nucleotides. The main functions of nucleotides are information storage (DNA), protein synthesis (RNA), and energy transfers (ATP and NAD).

Nucleic Acids Cont’d

Nucleotides consist of a sugar, a nitrogenous base, and a phosphate. The sugars are either ribose or deoxyribose. There are five nitrogenous bases. Purines

(Adenine and Guanine) are double-ring structures, while pyrimidines (Cytosine, Thymine and Uracil) are single-ringed.

DNA

Deoxyribonucleic acid (better known as DNA) is the physical carrier of inheritance for 99% of living organisms. The bases in DNA are C, G, A and T.

RNA

RNA functions in protein synthesis. There are three types of RNA, each is involved in

protein synthesis. Messenger RNA (mRNA) is the blueprint for

construction of a protein. Ribosomal RNA (rRNA) is the construction site

where the protein is made. Transfer RNA (tRNA) is the truck delivering the

proper amino acid to the site at the right time.