BIOC 2161: Regulation of Enzyme Activity and Primary Metabolism

Vocabulary flashcards generated from lecture notes covering key mechanisms of enzyme regulation, allosteric modulators, genetic induction/repression, covalent modifications, and constitutive versus inducible enzymes.

BIOC 2161

A theoretical course covering how animals source both endogenously and exogenously the major energy metabolites (carbohydrate, protein, fats), and how these materials are used, stored, recycled, and excreted.

Regulation of change in activity of existing enzyme

A mechanism of enzyme regulation that adjusts the catalytic speed of enzyme molecules already present in the cell, without altering total enzyme concentration or synthesizing new proteins.

Regulation of change in enzyme concentration

A long-term regulatory mechanism that modifies enzyme activity at the genetic level by changing the total quantity of enzyme produced or maintained in the cell via induction, repression, or degradation.

Allosteric site

A regulatory site on an allosteric enzyme that is distinct from the active site.

Tense state (T state)

The inactive state of an allosteric enzyme.

Relaxed state (R state)

The active state of an allosteric enzyme.

Positive modulator (Allosteric activator)

An allosteric regulator that binds to an enzyme in its relaxed state, increases enzyme activity and substrate affinity, shifts the saturation curve to the left, and decreases $K_m$.

Negative modulator (Allosteric inhibitor / Negative effector)

An allosteric regulator that favors the tense state of an enzyme, decreases enzyme activity and substrate affinity, shifts the saturation curve to the right, and increases $K_m$.

Cooperativity (Co-operative binding)

The phenomenon occurring when an allosteric modulator binds to an allosteric site and changes the shape of the active site, altering substrate binding and product formation.

$$K_m$$

The substrate concentration required for an enzyme to reach $\frac{1}{2} V_{\frac{\text{max}}{}}$.

Acetyl CoA Carboxylase regulation

An enzyme regulation example where citrate serves as the allosteric activator and palmitoyl CoA serves as the allosteric inhibitor to decrease fatty acid synthesis.

Aspartate (Asp) Transcarbamylase regulation

An allosteric enzyme system where ATP acts as the allosteric activator and CTP acts as the allosteric inhibitor.

PhosphoFructoKinase (PFK) regulation

An enzyme system where AMP functions as the allosteric activator and citrate functions as the allosteric inhibitor.

Covalent modification

A regulatory process where enzyme activity is altered through structural covalent changes, predominantly phosphorylation and dephosphorylation.

Phosphorylation

The addition of a phosphate group to a protein using ATP as the donor molecule, catalyzed by protein kinases.

Glycogen phosphorylase

An enzyme that stimulates glycogenolysis to turn glycogen into glucose-1-phosphate, which is active in its phosphorylated state.

Glycogen synthase

An enzyme involved in glycogen metabolism that is active in its dephosphorylated state.

Proteolysis (Limited proteolysis)

The activation of inactive enzyme precursors (zymogens) by the cleavage of specific peptide bonds.

Zymogen

An inactive precursor form of a protein or enzyme produced in the body that requires proteolytic cleavage to become active (e.g., pepsinogen, trypsinogen, proelastase, procarboxypeptidase).

Pepsinogen

An inactive zymogen converted into active pepsin in the stomach via autocatalysis with the help of $HCl$ or pepsin.

Cascade mechanism

A pathway in which a small initial signal is amplified into a larger physiological response through a series of sequential enzyme activations.

Compartmentalisation

A method of enzyme regulation that involves translocating an enzyme to a specific subcellular compartment.

Aminolevulinic acid (ALA) synthase

The regulatory enzyme in haem synthesis whose synthesis occurs in the cytosol before it is transported into the mitochondria.

Calmodulin

A small universal messenger protein in cells that binds calcium ions and acts as an intermediate calcium sensor to undergo conformational changes and enhance the activity of calmodulin-dependent kinases.

Induction

A genetic-level mechanism that increases enzyme activity and synthesis by enhancing gene transcription into mRNA and subsequent translation into protein.

Repression

A genetic-level mechanism that decreases enzyme synthesis by reducing gene transcription, leading to lower mRNA levels and decreased protein synthesis.

Degradation (of enzymes)

The breakdown of enzymes back into amino acids via ubiquitin ATP-dependent or ATP-independent proteolysis.

Constitutive enzymes

Enzymes that are constantly synthesized at a steady baseline rate regardless of physiological state because they are required for basic ongoing cell functions (e.g., hexokinase, pyruvate kinase).

Inducible enzymes

Enzymes whose synthesis is normally off or low but can be upregulated (induced) in response to a specific substrate, hormone, or environmental trigger (e.g., $\beta\text{-galactosidase}$ in Escherichia coli).