A. Polymers
1. Most macromolecules are polymers.
a. Three of the four classes of macromolecules form chainlike molecules called polymers.
b. Polymers consist of many similar or identical building blocks linked by covalent bonds.
c. The repeated units are small molecules called monomers.
d. Monomers are connected by covalent bonds via a dehydration reaction. (Fig. 5.2)
1. One monomer provides a hydroxyl group and the other provides a hydrogen and together these form water.
e. The covalent bonds connecting monomers in a polymer are disassembled by hydrolysis.
1. In hydrolysis the covalent bond is broken. A hydrogen atom and hydroxyl group from a split water molecule attach where the covalent bond used to be. (Activity 5A)
2. Each cell has thousands of different macromolecules.
B. Carbohydrates-fuel and building material
1. Carbohydrates include both sugars and their polymers.
a. The simplest carbohydrates are monosaccharides or simple sugars.
b. Disaccharides, double sugars, consist of two monosaccharides joined by a dehydration reaction.
c. Polysaccharides are polymers of monosaccharides.
2. Sugars, the smallest carbohydrates, serve as a source of fuel and carbon.
a. Monosaccharides
1. Example: glucose has the formula C6H12O6
2. Monosaccharides, particularly glucose, are a major fuel for cellular work. (Fig. 5.3) (Fig. 5.4)
b. Two monosaccharides can join to form a disaccharide via dehydration. (Fig. 5.5)
1. Maltose is formed by joining two glucose molecules.
2. Sucrose, table sugar, is formed by joining glucose and fructose. (Activity 5C Part 4)
3. Polysaccharides, the polymers of sugars, have storage and structural roles.
a. Energy storage polysaccharides
1. Starch is a storage polysaccharide composed entirely of glucose monomers. (Fig. 5.6)
a. One unbranched form of starch, amylose, forms a helix.
b. Branched forms, like amylopectin, are more complex.
c. Plants store starch within plastids, including chloroplasts.
d. Plants can store surplus glucose in starch and withdraw it when needed for energy.
e. Animals that feed on plants, especially parts rich in starch, can also access this starch to support their own metabolism.
2. Animals store glucose in a polysaccharide called glycogen.
a. Glycogen is highly branched.
b. Humans and other vertebrates store glycogen in the liver and muscles.
b. There are two different ring structures of glucose that result in molecules with completely different functions.
1. While polysaccharides can be built from a variety of monosaccharides, glucose is the primary monomer used in polysaccharides.
2. One key difference among polysaccharides develops from 2 possible ring structures of glucose. (Fig. 5.7)
3. These two ring forms differ in whether the hydroxyl group attached to the number 1 carbon is fixed above (beta glucose) or below (alpha glucose) the ring plane.
4. Starch is a polysaccharide of alpha glucose monomers.
c. Structural polysaccharides form strong building materials.
1. Cellulose is a major component of the tough wall of plant cells.
a. Cellulose is also a polymer of glucose monomers, but using beta rings. (Fig. 5.7)
b. While polymers built with alpha glucose form helical structures, polymers built with beta glucose form straight structures.
1. This allows H atoms on one strand to form hydrogen bonds with OH groups on other strands. (Fig. 5.8)
c. The enzymes that digest starch cannot hydrolyze the beta linkages in cellulose.
d. Some microbes can digest cellulose to its glucose monomers through the use of enzymes.
2. Another important structural polysaccharide is chitin, used in the exoskeletons of arthropods (including insects, spiders, and crustaceans).
a. Chitin is similar to cellulose, except that it contains a nitrogen-containing appendage on each glucose.
b. Chitin also forms the structural support for the cell walls of many fungi.
C. Lipids include fats, phospholipids and steroids.
1. Fats store large amounts of energy.
a. Although fats are not strictly polymers, they are large molecules assembled from smaller molecules by dehydration reactions.
b. A fat is constructed from two kinds of smaller molecules, glycerol and fatty acids. (Fig. 5.10)
1. Glycerol consists of a three carbon skeleton with a hydroxyl group attached to each.
2. A fatty acid consists of a carboxyl group attached to a long carbon skeleton, often 16 to 18 carbons long.
c. The many nonpolar C-H bonds in the long hydrocarbon skeleton make fats hydrophobic.
d. In a fat, three fatty acids are joined to glycerol creating a triacylglycerol.
1. The three fatty acids in a fat can be the same or different.
e. Fatty acids may vary in length (number of carbons) and in the number and locations of double bonds.
1. If there are no carbon-carbon double bonds, then the molecule is a saturated fatty acid - a hydrogen at every possible position. (Fig. 5.11)
2. If there are one or more carbon-carbon double bonds, then the molecule is an unsaturated fatty acid - formed by the removal of hydrogen atoms from the carbon skeleton.
3. Saturated fatty acids are straight chains, but unsaturated fatty acids have a kink wherever there is a double bond.
4. Fats with saturated fatty acids are saturated fats-most animal fats.
a. Saturated fats are solid at room temperature.
5. Fats with unsaturated fatty acids are unsaturated fats.
a. Plant and fish fats, known as oils, are liquid are room temperature.
b. The kinks provided by the double bonds prevent the molecules from packing tightly together.
f. The major function of fats is energy storage.
1. A gram of fat stores more than twice as much energy as a gram of a polysaccharide.
2. Plants and animals store fats as long-term energy reserves.
3. Fat also functions to cushion vital organs.
4. A layer of fats can also function as insulation.
2. Phospholipids are major components of cell membranes.
a. Phospholipids have two fatty acids attached to glycerol and a phosphate group at the third position.
1. The phosphate group carries a negative charge.
2. Additional smaller groups may be attached to the phosphate group.
b. The interaction of phospholipids with water is complex. (Fig. 5.12)
1. The fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head.
2. When phospholipids are added to water, they self-assemble into aggregates with the hydrophobic tails pointing toward the center and the hydrophilic heads on the outside. (Fig. 5.13)
3. This type of structure is called a micelle.
c. At the surface of a cell phospholipids are arranged as a bilayer.
1. The hydrophilic heads are on the outside in contact with the aqueous solution and the hydrophobic tails form the core.
2. The phospholipid bilayer forms a barrier between the cell and the external environment.
3. Steroids include cholesterol and certain hormones. (Fig. 5.14)
a. Steroids are lipids with a carbon skeleton consisting of four fused carbon rings.
1. Different steroids are created by varying functional groups attached to the rings.
b. Cholesterol, an important steroid, is a component in animal cell membranes.
1. Cholesterol is also the precursor from which all other steroids are synthesized.
2. Many of these other steroids are hormones, including the vertebrate sex hormones.
D. Proteins
1. Introduction
a. Proteins are instrumental in about everything that an organism does.
1. These functions include structural support, storage, transport of other substances, intercellular signaling, movement, and defense against foreign substances. (Table 5.1) (Activity 5E)
2. Enzymes in a cell are proteins and regulate metabolism by selectively accelerating chemical reactions. (Activity 5E)
3. Humans have tens of thousands of different proteins, each with its own structure and function.
b. Proteins are the most structurally complex molecules known.
1. Each type of protein has a complex three-dimensional shape or conformation.
2. All protein polymers are constructed from 20 different amino acids.
3. Polymers of amino acids are called polypeptides.
4. A protein consists of one or more polypeptides folded and coiled into a specific conformation.
2. A polypeptide is a polymer of amino acids connected in a specific sequence.
a. Amino acids consist of four components attached to a central carbon.
1. These components include a hydrogen atom, a carboxyl group, an amino group, and a variable R group (or side chain).
2. Differences in R groups produce the 20 different amino acids.
b. The twenty different R groups may be as simple as a hydrogen atom to a carbon skeleton with various functional groups attached.
1. The physical and chemical characteristics of the R group determine the unique characteristics of a particular amino acid.
2. One group of amino acids has hydrophobic R groups. (Fig. 5.15)
3. Another group of amino acids has polar R groups, making them hydrophilic.
4. The last group of amino acids includes those with functional groups that are charged (ionized) at cellular pH.
a. Some R groups are bases, others are acids.
c. Amino acids are joined together when a dehydration reaction removes a hydroxyl group from the carboxyl end of one amino acid and a hydrogen from the amino group of another. (Fig. 5.16)
1. The resulting covalent bond is called a peptide bond.
2. Repeating the process over and over creates a long polypeptide chain.
3. Polypeptides range in size from a few monomers to thousands.
3. A protein�s function depends on its specific conformation.
a. A functional protein consists of one or more polypeptides that have been precisely twisted, folded, and coiled into a unique shape. (Fig. 5.17)
1. It is the order of amino acids that determines what the three-dimensional conformation will be.
2. A protein�s specific conformation determines its function.
3. In almost every case, the function depends on its ability to recognize and bind to some other molecule.
a. For example, antibodies bind to particular foreign substances that fit their binding sites.
b. Enzymes recognize and bind to specific substrates, facilitating a chemical reaction.
c. Neurotransmitters pass signals from one cell to another by binding to receptor sites on proteins in the membrane of the receiving cell.
b. 4 levels of protein structure
1. The folding of a protein from a chain of amino acids occurs spontaneously.
a. Three levels of structure: primary, secondary, and tertiary structure, are used to organize the folding within a single polypeptide.
b. Quaternary structure arises when two or more polypeptides join to form a protein.
2. The primary structure of a protein is its unique sequence of amino acids.
a. Lysozyme, an enzyme that attacks bacteria, consists of a polypeptide chain of 129 amino acids. (Fig. 5.18)
b. Even a slight change in primary structure can affect a protein�s conformation and ability to function.
1. In individuals with sickle cell disease, abnormal hemoglobins, oxygen-carrying proteins, develop because of a single amino acid substitution. (Fig. 5.19)
2. These abnormal hemoglobins crystallize, deforming the red blood cells and leading to clogs in tiny blood vessels.
3. The secondary structure of a protein results from hydrogen bonds between an amino group of one amino acid and a carboxyl group of another. (Fig. 5.20)
a. Typical shapes that develop from secondary structure are coils (an alpha helix) or folds (beta pleated sheets).
4. Tertiary structure is determined by a variety of interactions among R groups and between R groups and the polypeptide backbone. (Fig. 5.22)
a. These interactions include hydrogen bonds among polar and/or charged areas, ionic bonds between charged R groups, disulfide bridges and interactions among hydrophobic R groups.
5. Quaternary structure results from the aggregation of two or more polypeptide subunits. (Fig. 5.23)
a. Collagen is a fibrous protein of three polypeptides that are supercoiled like a rope.
b. Hemoglobin is a globular protein with two copies of two kinds of polypeptides. (Activity 5F)
6. Structure summary (Fig. 5.24)
c. Protein conformation also depends on physical and chemical conditions in its environment.
1. Alterations in pH, salt concentration, temperature, or other factors can unravel or denature a protein.
2. These forces disrupt the hydrogen bonds, ionic bonds, and disulfide bridges that maintain the protein�s shape.
3. Some proteins can return to their functional shape after denaturation, but others cannot, especially in the crowded environment of the cell. (Fig. 5.25)
E. Nucleic acids-informational polymers
1. Introduction
a. The amino acid sequence of a polypeptide is programmed by a gene.
b. A gene consists of regions of DNA, a polymer of nucleic acids.
2. Nucleic acids store and transmit hereditary information
a. There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
1. DNA stores the code for making all the polypeptides in the body.
2. RNA translates the code into a polypeptide.
b. Organisms inherit DNA from their parents.
1. Each DNA molecule is very long and usually consists of hundreds to thousands of genes.
2. When a cell reproduces itself by dividing, its DNA is copied and passed to the next generation of cells.
3. A nucleic acid strand is a polymer of nucleotides.
a. Nucleic acids are polymers of nucleotides.
b. Each nucleotide consists of three parts: a nitrogen base, a pentose sugar, and a phosphate group. (Fig. 5.29)
c. The nitrogen bases, rings of carbon and nitrogen, come in two types: purines and pyrimidines.
1. Pyrimidines have a single six-membered ring.
2. The three different pyrimidines, cytosine (C), thymine (T), and uracil (U) differ in atoms attached to the ring.
3. Purines have a six-membered ring joined to a five-membered ring.
4. The two purines are adenine (A) and guanine (G).
d. The sugar joined to the nitrogen base is ribose in RNA and deoxyribose in DNA.
1. The only difference between the sugars is the lack of an oxygen atom on carbon two in deoxyribose.
e. Polynucleotides are synthesized by connecting the sugars of one nucleotide to the phosphate of the next with a phosphodiester link.
1. This creates a repeating backbone of sugar-phosphate units with the nitrogen bases as appendages.
f. An RNA molecule is single polynucleotide chain.
g. DNA molecules have 2 strands that form a double helix.
1. The sugar-phosphate backbones of the two polynucleotides are on the outside of the helix.
2. Pairs of nitrogenous bases, one from each strand, connect the polynucleotide chains with hydrogen bonds. (Fig. 16.5)
3. Most DNA molecules have thousands to millions of base pairs.
4. Because of their shapes, only some bases are compatible with each other.
a. Adenine (A) always pairs with thymine (T) and guanine (G) with cytosine (C).
b. The two strands are complementary.
5. The sequence of nitrogen bases in DNA is unique for each gene.
a. Genes are normally hundreds to thousands of nucleotides long.
b. The order of nucleotides in a gene specifies the order of amino acids - the primary structure of a protein.