PHSC1212 Biochemistry - Lecture 9: Enzyme Regulation pt 2

Maintain order, conserve energy, respond rapidly to environmental changes

reasons for enzyme regulation

Normal cell structure and function

Why is it important to maintain order in the cell through enzyme regulation?

Prevent wasting energy on unnecessary reactions

Why is it important to conserve energy in the cell through enzyme regulation?

Genetic control, covalent modification, allosteric regulation, compartmentation

four levels of enzyme regulation

Genetic control

induction/repression of genes that code for enzymes as a regulation method

Covalent modification

enzyme regulation method that can involve phosphorylation and dephosphorylation to activate or deactivate enzymes

Phosphorylation and dephosphorylation

can activate or deactivate enzymes

Proenzymes

enzymes that are inactive until they have certain residues cleaved off

Allosteric regulation

enzyme regulation where binding of regulators increases or decreases enzyme activity

Compartmentation

enzyme regulation where there is physical segregation of enzymes

Enzyme induction

genetic control of enzymes by increasing synthesis due to metabolic needs

Increase synthesis

What does an enzyme inducer do to enzymes in response to changing metabolic needs?

Enzyme inducers

bind DNA or RNA to increase expression

Enzyme repression

genetic control of enzymes by decreasing synthesis due to metabolic needs

Decrease synthesis

What does an enzyme repressor do to enzymes in response to changing metabolic needs?

Enzyme repressors

bind DNA or RNA to decrease expression

Drugs

often inducers of cytochrome P450 enzymes

Cleavage of peptide bonds, phosphorylation and dephosphorylation

two types of covalent modification to regulate enzyme activity

Zymogens

another name for proenzymes

Cleavage of specific peptide bonds

How are proenzymes or zymogens converted into active form?

Chymotrypsin

converted to its active form when trypsin cleaves certain peptide bonds

Serine, threonine, or tyrosine

amino acid residues that can be phosphorylated or dephosphorylated to activate/deactivate enzymes

Irreversible

Is proenzyme conversion to active form reversible or irreversible?

Allosteric regulators

molecules that bind to enzymes and regulate their activity

Separate from active site

Where is the binding site in allosteric regulation?

Activate or inhibit

What can allosteric regulators do to enzyme activity?

Homotropic

an allosteric regulator that is the same as the substrate

Heterotropic

an allosteric regulator that is different than a molecule

Allosteric

means "other site" or "different place"

Decreases

What happens to enzyme activity with an inhibitor as substrate concentration increases?

Increases

What happens to enzyme activity with an activator as substrate concentration increases?

Feedback inhibition

an enzyme is inhibited by a downstream product in the pathway

Divide and control, diffusion barriers, specialized reaction conditions, and damage control

four mechanisms of compartmentation inhibition

Divide and control

compartmentation method that separates competing reactions and prevents waste of resources

Separation of kinases and phosphatases

divide and control regulation example

Diffusion barriers

compartmentation method that uses concentration of enzymes and substrates in a microenvironment

Lipid rafts

diffusion barrier regulation example

Specialized reaction conditions

compartmentation method that could use pH

pH

What is an example of a specialized reaction condition?

Damage control

compartmentation method that help with protection against toxic reaction products/intermediates

Peroxisomes isolating and degrading

damage control regulation method example