GLYCOLYSIS

• Occurs in the cytosol
• Anaerobic
• Inputs: 1 Glucose
• Outputs: 2 Pyruvates, 2 ATP, 2 NADH

PYRUVATE DECARBOXYLATION

• Occurs in the matrix
• Aerobic
• Input: 2 Pyruvates
• Outputs: 2 Acetyl CoA, 2 CO2, 2NADH

CITRIC ACID CYCLE

Kreb’s Cycle of Tricarboxylic Acid Cycle

• Occurs in the mitochondrial matrix
• Aerobic
• Input: 2 Acetyl CoA
• Output: 4CO2, 2ATP, 6NADH, 2FADH2

OXIDATIVE PHOSPHORYLATION

• Electron transport
• Chemiosmosis
• Aerobic
• Inputs: 10 NADH, 2FADH2
• Outputs: 30-34 ATP

Total ATP Output: 30-38 ATP

• Intertextual variation exists: exact calculations beyond the scope of this tutorial.
• Approximates yield for both eukaryotes & prokaryotes.

ENZYME NOMENCLATURE

• Derived from substrate or chemical reaction the enzyme catalyzes
• Most enzyme names have suffix “–ase”

Isozymes (isoenzymes)

• Enzymes that catalyze same reaction but have different amino acid sequences (different proteins)

ENZYMES REQUIRING COFACTORS

Apoenzyme

• Enzyme without the cofactor.

Holoenzyme

• Enzyme and cofactor together

6 CLASSES OF ENZYMES

Oxidoreductases

• Catalyze electron transfer reactions (oxidation/reduction reactions)
• A- + B → A + B-

Transferases

• Catalyze transfer of functional groups to a molecule
• A-B + PO4 → A-B-PO4

Hydrolases

• Catalyze breakage of bonds by hydrolysis (addition of water)
• A-B-C + H2O → A-B + C

Lyases

• Catalyze bond cleavage reactions that are not oxidation or hydrolysis reactions
• A-B-C → A-B + C

Isomerases

• Catalyze rearrangement reactions
• A-B-C → A-C-B

Ligases

• Catalyze reactions in which covalent bonds join two molecules
• A-D + B-C→ A-D-B-C

ENZYME ACTIVE SITE

• 3-dimensional cleft where substrate can bind
• Substrate specificity: depends on atom arrangement in cleft

Lock and key

• Enzyme’s substrate fits perfectly into active site

Induced fit

• Active site conforms to substrate’s 3D shape upon binding
• Lock-and-key and the induced-fit are 2 models of substrate binding to active site

ENZYME REGULATION

Allostery

• Effector molecules bind to enzyme and change substrate binding affinity

Transcription

• Enzyme synthesis turned on or off to regulate production

Reversible covalent modification

• Enzymes can be phosphorylated (activation or deactivation)

Isozymes

• Different forms of enzymes can be used to affect reaction rates

Proteolytic activation

• Some enzymes have part of their sequence cleaved to become active

ALLOSTERIC REGULATION

• Effector molecule (inhibitor or activator) binds to effector site
• Effector site: distinct from active site