CHEM 120 EXAM 4

What is a zwitterion?

An amino acid with both positive (NH₃⁺) and negative (COO⁻) charges and an overall net charge of zero at physiological pH

How are amino acids classified?

By their R groups: nonpolar, polar (uncharged), polar acidic, and polar basic

What makes an amino acid nonpolar?

R groups that are hydrogen, alkyl, or aromatic and hydrophobic

What functional groups are found in polar amino acids?

Hydroxyl (-OH), thiol (-SH), or amide (-CONH₂)

How is a peptide drawn?

N-terminus (H₃N⁺) on the left and C-terminus (COO⁻) on the right

How are peptides named?

From N-terminus to C-terminus using 3-letter or 1-letter abbreviations

What defines a protein?

A peptide of 50 or more amino acids with biological activity

What is primary protein structure?

The specific sequence of amino acids joined by peptide bonds

What determines protein function?

Its primary structure

What stabilizes secondary protein structure?

Hydrogen bonding between backbone atoms

What are the two main secondary structures?

Alpha helix and beta-pleated sheet

What characterizes an alpha helix?

A coiled structure stabilized by hydrogen bonds within the chain

beta-pleated sheet characteristics

Side-by-side strands stabilized by hydrogen bonds with R groups above and below

What is a triple helix?

Three alpha helices woven together, typical of collagen

What is tertiary protein structure?

The overall three-dimensional shape formed by R-group interactions

What interactions stabilize tertiary structure?

Hydrophobic interactions, hydrogen bonds, salt bridges, and disulfide bonds

What is quaternary protein structure?

A protein composed of two or more polypeptide chains

What is protein hydrolysis?

Breaking peptide bonds by adding water to form smaller peptides or amino acids

What is denaturation?

Disruption of secondary, tertiary, and quaternary structure without affecting primary structure

What is an enzyme?

A protein that acts as a biological catalyst

How do enzymes affect activation energy?

They lower activation energy

What is an enzyme active site?

The region where the substrate binds and the reaction occurs

What interactions bind substrate to enzyme?

Hydrogen bonds, hydrophobic interactions, and salt bridges

What is the lock-and-key model?

A rigid active site that fits only a specific substrate

What is the induced-fit model?

A flexible enzyme active site that changes shape to fit the substrate

What do oxidoreductases do?

Catalyze oxidation-reduction reactions

What do transferases do?

Catalyze the transfer of a functional group between 2 compounds

What do hydrolases do?

Catalyze hydrolysis reactions

What do lyases do?

Add or remove groups without hydrolysis

What do isomerases do?

Catalyze the rearrangement of atoms within a molecule

What do ligases do?

catalyze the joining of two molecules using ATP

What is the optimum temperature for human enzymes?

Approximately 37°C

Why do extreme pH levels reduce enzyme activity?

They disrupt tertiary structure and R-group charges

What happens when enzyme concentration increases?

The reaction rate increases if substrate is available

What happens when substrate concentration is very high?

Enzymes become saturated and reach maximum activity

What is an allosteric enzyme?

An enzyme regulated by binding at a site other than the active site

What is feedback inhibition?

The final product inhibits an earlier enzyme in a pathway

What are zymogens?

Inactive enzyme precursors

What is a competitive inhibitor?

An inhibitor that competes with substrate for the active site

How is competitive inhibition reversed?

By increasing substrate concentration

What is a noncompetitive inhibitor?

An inhibitor that binds outside the active site and changes enzyme shape

What is an irreversible inhibitor?

A substance that permanently inactivates an enzyme

What is a cofactor?

A non-protein component required for enzyme activity

What is a metal ion cofactor example?

Iron (Fe²⁺) in hemoglobin

What is a coenzyme?

A small organic molecule, often a vitamin, required for enzyme activity

What are the components of a nucleotide?

Nitrogenous base, pentose sugar, phosphate group

What sugar is found in DNA?

Deoxyribose

What sugar is found in RNA?

Ribose

What are DNA base pairs?

A-T and G-C

What are RNA base pairs?

A-U and G-C

What bond joins nucleotides together?

Phosphodiester bond

What enzyme unwinds DNA during replication?

Helicase

What enzyme synthesizes DNA?

DNA polymerase

In what direction does DNA polymerase work?

5′ to 3′

What are Okazaki fragments?

Short DNA segments formed on the lagging strand

What is transcription?

The process of making mRNA from DNA

What is translation?

The process of making protein from mRNA

What is the function of tRNA?

Brings specific amino acids to the ribosome

What is a point mutation?

A substitution of one nucleotide base

What is a silent mutation?

A mutation that does not change the amino acid

What do insertion and deletion mutations cause?

Frameshift mutations

What is metabolism?

The sum of all chemical reactions in the body

What are catabolic reactions?

Reactions that break down molecules and release energy

What are anabolic reactions?

Reactions that build molecules using energy

What is the net ATP yield of glycolysis?

2 ATP

Where does glycolysis occur?

The cytosol

What is the aerobic fate of pyruvate?

Converted to acetyl-CoA in the mitochondria

What is the anaerobic fate of pyruvate in muscle?

Converted to lactate

What is the Cori cycle?

The conversion of lactate to glucose in the liver

Where does the citric acid cycle occur?

The mitochondria

What is produced per acetyl-CoA in the citric acid cycle?

3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂

What drives ATP synthesis in the electron transport chain?

The proton gradient across the inner mitochondrial membrane

How many ATP are produced per NADH?

Approximately 2.5 ATP

How many ATP are produced per FADH₂?

Approximately 1.5 ATP

What is the total ATP yield per glucose?

Approximately 32 ATP