Cells contain very large molecules called macromolecules. A macromolecule forms when smaller molecules join together. Each of these smaller molecules is called a monomer. When monomers form a chain, the macromolecule is a polymer. The polymers (macromolecules) of cells and their monomers are:

Protein - amino acids

Carbohydrates - monosaccaride

Lipid - glycerol + fatty acid

Nucleic acid - nucleotide

When monomers join to form a macromolecule (below), a bond forms between adjacent monomers. This bond forms when a hydrogen (H) from one monomer is caused to link with a hydroxyl group (OH) from another monomer. As a water molecule forms, dehydration synthesis occurs. (see figure 2.26 Page 38)

Conversely, a macromolecule is broken down by the addition of water molecules. During this process, called hydrolysis, one monomer takes on a hydrogen and the adjacent monomer takes on a hydroxyl group. This leads to a disruption of the bonds linking the monomers.

The two major functions: Structure and Metabolism. Protein macromolecules sometimes have a structural function. For example, in humans, the protein keratin makes up hair and nails, while collagen is found in all types of connective tissue, including ligaments, cartilage, bones, and tendons. The muscles contain proteins, which account for their ability to contract. Some proteins are enzymes, necessary contributors to the chemical workings of the body. Enzymes speed up chemical reactions; they work so quickly that a reaction that normally takes several hours or days without an enzyme takes only a fraction of a second with an enzyme. Specific enzymes in the body assist synthetic reactions, which build up macromolecules; others carry out hydrolytic reactions, which break down macromolecules.

Most amino acids have the structural formula shown to the left. Proteins are polymers, or chains, of amino acids. A protein is characterized by the sequence of amino acids it contains. The term amino acid is appropriate because this type of molecule has 2 functional groups: an amino group (NH2) and an acid (carboxyl) group (COOH). Amino acids differ from one another by their R group, the Remainder of the molecule. In amino acids, the R group varies from a single hydrogen (H) to complicated rings. There are 20 different amino acids, and therefore, about 20 different types of R groups that are commonly found in proteins. Although many other amino acids are known, these 20 amino acids are joined in all proteins in all species of living organisms, from bacteria to humans. (see Figure 2.25 Page 37)

The bond that joins 2 amino acids is called a peptide bond. As you can see in figure on the first page, when dehydration synthesis occurs, the acid group of one amino acid reacts with the amino group of another amino acid, and water is given off. A dipeptide results when 2 amino acids join; a polypeptide (below) is a string of amino acids joined by peptide bonds. A polypeptide can contain hundreds, even thousands, of amino acids and a protein consists of one or more polypeptides.

The atoms associated with a peptide bond, oxygen (O), carbon (C), nitrogen (N), and hydrogen (H), share electrons in such a way that the oxygen carries a partial negative charge and the hydrogen carries a partial positive charge: Therefore, the peptide bond is polar, and hydrogen bonding, occurs frequently between the peptide bonds in polypeptides and proteins.

Proteins commonly have 3 levels of organization in their structure (see fig. 2.27 Page 39), although some have a fourth level as well

The first level, called the primary structure, is the linear sequence of the amino acids joined by peptide bonds and is shown in the above polypeptide. Any number of the 20 different amino acids can be joined in any sequence. Any given protein has a characteristic sequence of amino acids.

The secondary structure (shown to the left) of a protein comes about when the polypeptide chain takes a particular orientation in space. One common arrangement of the chain is the alpha helix, or a right-handed coil, with 3.6 amino acids per turn. Hydrogen bonding between amino acids, in particular, stabilizes the helix. Hydrogem bonds are drawn with a dotted line to indicate that they are weak bonds.

The atoms associated with a peptide bond–oxygen (O), carbon (C), nitrogen (N), and hydrogen (H)–share electrons in such a way that the oxygen carries a partial negative charge and the hydrogen carries a partial positive charge: Therefore, the peptide bond is polar, and hydrogen bonding, occurs frequently in polypeptides and proteins.

The tertiary structure of a protein is its final threedimensional shape (left). In muscles, the helical chains of myosin form a rod shape that ends in globular heads. Enzymes are globular proteins in which the helix bends and twists in different ways. The tertiary shape of a protein is maintained by various types of bonding between the R groups. Covalent, ionic, and hydrogen bonding are all seen.

Some proteins have more than one type of polypeptide chain, each with its own primary, secondary, and tertiary structures. These separate chains are arranged to give a fourth level of structure, termed the quaternary structure (right). Ex. Hemoglobin

The final shape of a protein is very important to its function. When proteins are exposed to extremes in heat and pH, they undergo an irreversible change in shape called denaturation. For example, we are all aware that the addition of acid to milk causes curdling and that heating causes egg white, a protein called albumin, to coagulate. Denaturation occurs because the normal bonding between the R groups has been disturbed. Once a protein loses its normal shape, it is no longer able to perform its usual function.

Carbohydrate molecules are characterized by the presence of the atomic grouping CH2O, in which the ratio of hydrogen atoms (H) to oxygen atoms (O) is approximately 2:1. [Because water has this same ratio of hydrogen to oxygen, the term carbohydrate, which means hydrates of carbon, was originally thought to be appropriate].

If the number of carbon atoms in a molecule is low (from 3 to 7), then the carbohydrate is a simple sugar, or monosaccharide. Thereafter, larger carbohydrates are created by joining monosaccharides. [ in the same manner described for the synthesis of proteins]

Monosaccharides: - As their name implies, monosaccharides are simple sugars of one molecule each (fig. 2.17 Page 32). These molecules are often designated by the number of carbon atoms they contain; for example, pentose sugars, such as ribose, have 5 carbon atoms in a ring with attach groups, and hexose sugars, such as glucose, have 6 carbon atoms in a ring with attached groups. Glucose is the primary energy source of the body, and most carbohydrate polymers can be broken down into monosaccharides that either are or can be converted to glucose. Other common monosaccharides are fructose, found in fruits, and galactose, a constituent of milk. These 3 monosaccharides have a ring structure with the molecular formula C6H12O6, but they differ in the shape of the ring and/or in the arrangement of the hydrogen (-H) and the hydroxyl groups (-OH) attached to the ring.

Disaccharides: Two Sugars - The term disaccharide tells us that the molecule contains 2 monosaccharides. When 2 glucose molecules join, maltose (see Fig. 2.18 Page 32) results. When glucose and fructose join, the dissacharide sucrose forms. Sucrose derived from sugarcane and sugar beets is commonly known as table sugar. Lactose, milk sugar, is a disaccharide composed of glucose and the monosaccharide galactose.

Polysaccharides: Many Sugars - A polysaccharide is a polymer of monosaccharides. Three polysaccharides are common in organisms: starch, glycogen and cellulose.

Even though all three polysaccharides contain only glucose they are distinguishable from one another.

Starch ( see Fig 2.19 Page 33 ) has few side branches, or chains of glucose that branch off from the main chain. Starch is the storage form of glucose in plants. [Just as we store orange juice as a concentrate, plants store starch as a concentrate of glucose. This analogy appropriate because water is removed when glucose molecules join to form starch.] The following equation could represent the synthesis of starch:

Glucose + Glucose + Glucose + Glucose + Glucose --------> starch + 4 water molecules

Cellulose is found in plant cell walls and accounts in part for the strong nature of these walls. In cellulose (see figure 2.21 Page 33), the glucose units are joined by a slightly different type of linkage than that in starch or glycogen. Oberve the alternating position of the oxygen atoms linking with the glucose units. While this might seem to be a technicality, actually it is important because we are unable to digest foods ,containing this type of linkage; therefore, cellulose passes through our digestive tract as fiber, or roughage. Recently, it has been suggested that fiber in the diet is necessary to good health and may even help to prevent colon cancer.

Glycogen - (see Fig. 2.20 Page 33) Another polysaccharide, glycogen, is characterized by the presence of many side chains of glucose.

Glycogen is the storage form of glucose in animals. After an animal eats, the liver stores glucose as glycogen; in between eating, the liver releases glucose so that the concentration of glucose in blood is always about 0.1%.

Carbohydrates are first and foremost a source of short term energy for all organisms, including humans. Sometimes, they also join with other molecules to play a structural role. Glucose is the primary energy source of the body. Starch is the storage form of glucose in plants. Glycogen is the storage form of glucose in animals. After an animal eats the liver stores glucose as glycogen; in between eating, the liver releases glucose so that the concentration of glucose in blood always about 0.1%. The polysaccharide cellulose is found in plant cell walls and accounts in part for the strong nature of these walls. Cellulose passes through our digestive tract as fiber, or roughage, because we are unable to digest it. Recently, it has been suggested that fiber in the diet is necessary to good health and may even help to prevent colon cancer

Fats (see figures 2.22, 2.25,page 34) are nonpolar because they have no parts that can become ionized. During fat dehydration synthesis glycerol (which has three OH groups) reacts with 3 fatty acids to form one fat molecule and 3 water molecules. The reverse of the above reaction is hydrolysis of a fat molecule. A fatty acid has a hydrocarbon chain ( a string of carbons surrounded by hydrogens) and ends with a -COOH acid group. [Most are 16 - 18 C's long but there are shorter.]

There are two types of fatty acids: Saturated or Unsaturated

Familiar lipids are neutral fats and oils. - What is the main difference between the two? Fats are solid at room temperature, oils are liquid at room temperature. Fxns of fats in the body: Long term energy storage, Insulation, Protective cushion

Phospholipids (see fig. 2.23 Page 35)- Contain a phosphate group in place of the third fatty acid. The phosphate group can ionize forming a polar head while the two fatty acids form a nonpolar tail. The cell membrane is a phospholipid bilayer in which the heads face outward and the tails face inward because they are hydrophobic (water repelling).

Steroids - [structure is different from that of fats] (see fig. 2.24 Page 36) Backbone of 4 fused carbon rings with functional groups attached. Each type of steroid differs primarily by the arrangement of atoms in the rings and the functional groups attached to them. Cholesterol is the precursor to several other steroids. Aldosterone is a hormone that helps to regulate the sodium level of blood. Estrogen and Testosterone are sex hormones which help to maintain the female and male secondary sex characteristics.

(see figure 2.28 Page 41) Important for the growth and reproduction of cells and organisms. Human genes are composed of a nucleic acid called DNA.The nucleic acid RNA works in conjunction with DNA to synthesise proteins. DNA and RNA are formed through dehydration synthesis by joining nucleotides to form a polymer (far left).

A single nucleotide (see figure 2.28 Page 40) contains a pentose sugar, a phosphate, and a nitrogen base. In DNA the sugar is deoxyribose, in RNA the sugar is ribose. In RNA (far left) nucleotides join to form a strand of sugar - phospate - sugar - phosphate

molecules with the nitrogen bases projecting to one side. In DNA a second sugar - phosphate strand lines up next to the first and is held there by hydrogen bonds between the nitrogen bases.

( see fig. 2.29 Page 41) ATP is a nucleotide that functions as the energy carrier in cells. The base adenine is joined to a ribose sugar (adenosine) and 3 phosphate groups. The energy is stored in the two high energy bonds between the phosphate groups. Wavy line = high energy in diagram.

Make sure that you can recognize carbohydrates, lipids, proteins and nucleic acids (monomers and polymers) given a diagram (or description) of their chemical structure.