Enzymes (Spencer)

Question 1

Enzymes

Answer 1

size: 10 kDa - 1,000 kDa
speed up biological rxns that otherwise would occur too slowly to meet our metabolic needs

Question 2

Carbonic anhydrase

Answer 2

• one of the FASTEST enzymes
• enzyme speeds rxn to hydrating 1 mill molecules of CO2 per second

Question 2

Cofactors

Answer 2

small, NONPROTEIN molecules, that when bound to enzyme enhances enzyme’s catalytic power

Question 3

Holoenzyme

Answer 3

enzyme WITH its cofactor
= ACTIVE enzyme

Question 4

Apoenzyme

Answer 4

enzyme WITHOUT its cofactor
= INACTIVE enzyme

Question 5

Inorganic cofactors

Answer 5

metal ions that activate an enzyme’s activity

Question 6

Coenzymes

Answer 6

ORGANIC cofactors and are derived from vitamins

Question 7

Co-substrate

Answer 7

coenzyme that is LOOSELY bound to the enzyme and is CHANGED by the reaction
- is released once the reaction occurs
- circulates around the cell to be used by another enzyme

Question 8

Prosthetic group

Answer 8

coenzyme that is TIGHTLY bound to the enzyme and is NOT CHANGED by the reaction
- CAN change DURING, but will NOT change from start to finish
- ex: biotin, coenzyme A, Monoamine oxidase: FAD (from riboflavin)

Question 9

Enzyme specificity

Answer 9

enzymes catalyze only ONE reaction or ONE SET of closely related reactions
- they recognize a particular bond pattern/structure
- ex: proteases ONLY cleave peptide bonds via hydrolysis but will cleave esters bc related reactions

Question 10

Enzyme specificity

Answer 10

nonspecific:
- ex: papain protease does not care what residues are on other side of peptide, just hydrolyzes
specific:
- ex: trypsin protease requires lysine or arginine to recognize and cleave residues
very specific:
- ex: thrombin protease requires arginine AND glycine on either side of the peptide bond and THEN cleaves
- specificity relies on the precise interaction of substrate with the 3D
structure of enzyme!!!

Question 11

Free-energy change ΔG

Answer 11

ΔG = Gproducts – Greactants
- ΔG <0 = spontaneous
- ΔG>0= non-spontaneous
- ΔG=0 rxn is at EQUILIBRIUM and the FLUXES of the forward and reverse rxns CANCEL OUT (does not mean ZERO flux of products)

Question 12

Coupling of enzymatic rxns

Answer 12

want each step of a coupling rxn to have a negative ΔG to proceed
- if positive, the cell has to do something to encourage progression of the rxn to yield a negative ΔG

Question 13

Active site

Answer 13

region of catalytic activity (2-3 residues that make/break bonds) of an enzyme that binds substrate and any cofactors
- responsible for lowering delta G
- enzyme-substrate complex at the active site is what promotes the formation of the transition state

Question 14

Active site structure

Answer 14

• 6 residues create microenvironment for the active site (~5% of enzyme) and 2 residues have catalytic activity (~2% of enzyme)
• rest of the enzyme for scaffolding/structural support of the enzyme

Question 15

Lock and Key Model of Enzymes

Answer 15

enzyme and substrate are rigid structures destined to fit
- explains enzyme specificity for substrate but NOT stabilization of the transition state

Question 16

Induced Fit Model of Enzymes

Answer 16

enzyme changes conformation based off interaction w substrate
- explains enzyme specificity AND stabilization of transition state
–> acknowledges the weak interactions’ role in binding of substrate and enzyme

Question 17

Maximum binding energy

Answer 17

many weak interactions occur at the ES binding-complex requiring close contact b/n enzyme and substrate
–> as the weak interactions form, they release free energy (binding energy)
- used by enzyme use for stabilization of transition state

Question 18

Free energy (binding energy)

Answer 18

energy released by the weak interactions formed by the INDUCED FIT of the enzyme substrate complex
- the right substrate= MORE interactions= HIGHEST binding energy

Question 19

Transition state

Answer 19

point in the reaction where the MAX weak interactions occur

Question 20

covalent catalysis

Answer 20

covalent bond forms between substrate
and enzyme (usually involves a nucleophilic attack)
- ex: