Chapter 3 Nucleic Acids, Proteins and Enzymes

Nucleic Acids Informational polymers Made of C,H,O,N and P No general formula Examples: DNA and RNA

Nucleic Acids Polymers of nucleotides Nucleotides have three parts: nitrogenous base pentose sugar phosphate

Nitrogenous Bases Rings of C and N The N atoms tend to take up H + Make it basic Two types: Pyrimidines (single ring) Purines (double rings)

Pentose Sugar 5-C sugar Ribose - RNA Deoxyribose – DNA RNA and DNA differ in a –OH group on the 2 nd carbon.

Nucleosides and Nucleotides Nucleoside = base + sugar Nucleotide = base + sugar + Pi

DNA Deoxyribonucleic Acid. Makes up genes. Genetic information for life.

RNA Ribonucleic Acid. Structure and protein synthesis. Genetic information for a few viruses only.

Proteins The molecular tools of the cell. Polypeptide chains of Amino Acids monomer linked by peptide bonds. Made of C,H,O,N, and sometimes S. No general formula. Has Amino group NH 3

Uses Of Proteins Structure Enzymes Antibodies Transport Movement Receptors Hormones

Amino Acids All have a Carbon with four attachments: -COOH (acid) -NH 2 (amine) -H -R (some other side group)

R groups The properties of the R groups determine the properties of the protein. 20 different kinds: Nonpolar - 9 AA Polar - 6 AA Electrically Charged Acidic - 2 AA Basic - 3 AA

Amino Acids

Polypeptide Chains Formed by dehydration synthesis between the carboxyl group of one AA and the amino group of the second AA. Produce an backbone of: (N-C-C) X

Levels Of Protein Structure Organizing the polypeptide into its 3-D functional shape. Primary Secondary Tertiary Quaternary

Primary Sequence of amino acids in the polypeptide chain. Many different sequences are possible with 20 AAs.

Secondary 3-D structure formed by hydrogen bonding between parts of the peptide backbone. Two main secondary structures:  helix pleated sheets

Tertiary Bonding between the R groups. Examples: hydrophobic interactions ionic bonding Disulfide bridges (covalent bond)

Quaternary When two or more polypeptides unite to form a functional protein. Example: hemoglobin

Is Protein Structure Important?

Denaturing Of A Protein Events that cause a protein to lose structure (and function). Example: pH shifts salt concentrations heat

Enzymes Activation Energy Energy needed to reach the transition state Needed to start reaction Activation Energy Potential Energy

Enzymes Biological catalysts made of protein. Cause the rate of a chemical reaction to increase. Usually specific to one substrate. Each chemical reaction in a cell requires its own enzyme.

Reactions Enzymes lower the activation energy for a chemical reaction to take place. Makes it faster/easier to reach transition state

Active Site The area of an enzyme that binds to the substrate. Structure is designed to fit the molecular shape of the substrate. Therefore, each enzyme is substrate specific.

Example Lactose A disaccharide Enzyme breaks into 2 monosacharides Lactase Is added to milk to break the sugar so the body doesn’t have to This makes lactose-free milk Many people of African/Asian descent are lactose intolerant. Only areas where cattle were raised developed the ability to digest lactose

Factors that affect Enzymes Environment pH, temp, salt Cofactors Non-organic helpers to enzymes. Ex. Fe, Zn, Cu Coenzymes Organic helpers to enzymes. Ex. vitamins Inhibitors Competitive - mimic the substrate and bind to the active site. Noncompetitive - bind to some other part of the enzyme. Allosteric Sites

Metabolic Control Feedback Inhibition When a metabolic pathway is switched off by its end-product. End-product usually inhibits an enzyme earlier in the pathway. Structural Order Separation of enzymes and metabolic pathways in time or space by the cell's organization. Example: enzymes of respiration