Enzyme Catalysis

Question 1

Chemical bonds & energy

Answer 1

Break bonds: require energy

BUT

Energy released by formation of new bonds > energy required to break

Question 2

Oxidation-Reduction rxn (OIL-RIG)

Answer 2

Oxydation: molecule loses electron
Reduction: gains electron

Question 3

Laws or thermodynamics (flow of E)

Answer 3

1) Energy not created or destroyed, simply transformed

• energy transfer imperfect, Lost as heat
• cells can’t use heat for processes
• so, use energy in chemical bonds

2) Disorder (entropy) in universe continuously increasing

-rxn ordered (less stable) to disordered (more stable)
—Takes more energy to maintain order

Electrons in chemical bonds: ordered state (electrons in predictable spots)

Heat: break bond, increase entropy
Bonds: decrease entropy, maintain order

Question 4

Energy rxn (G)

Answer 4

Net energy from breaking and formation of bonds available for work: free energy: G=H-TS

Exergonic rxn: release G (E in products bonds < E in reactants bonds)
-spontaneous (happens on its own-Ea), cuz increases disorder
-Ea: required to destabilize bonds reactants for rxn
Graph

Endergonic rxn: require G (E in products bonds > E in reactants bonds)
Increase order
Graph

Speed up spontaneous rxn:

1) add energy to system (ex: stirring)
2) lower Ea (catalyst)

Question 5

Catalyst (speed up rxn)

Answer 5

1) Lowers Ea (energy needed to start rxn)
2) stabilizes intermediate products (transition state)

NOT CHANGE NATURE OF RXN

Question 6

Hydrolysis of ATP (photos)

Answer 6

1) Energy currency of cell

2) exergonic, E released used in endergonic processes

Question 7

Enzymes (biological catalysts)

Answer 7

Proteins or RNA: catalyze biological rxn in cell

1) Orient substrates - proper fashion
2) Bring reactants close together
3) Stress certain bonds in mol.

Substrate: molecule undergoes rxn in enzyme

Enzymes unchanged, reused

Photo

Question 8

Induced Fit (photos)

Answer 8

1) substrate binds to active site
2) enzyme adjusts shape to bind to substrate
3) enzyme-substrate complex (induced fit)
4) after rxn: product dissociates from enzyme
5) enzyme unchanged, reused

Question 9

Multienzyme complex

Answer 9

Groups of related enzymes- speed up sequential step (multi step rxn)

1) efficient delivery of product to next enzyme
2) prevent unwanted side reactions
3) rxn controlled as one unit

Question 10

Affects of enviro. on enzymes

Answer 10

1) Temperature
Slight increase=increase rxn rate (more collisions b/w substrate & enzyme)
Too high increase =denaturation (breaking of H-bonds)

2) pH
Acidic or basic conditions: cations & anions interact w/ charged, polar amino acids in proteins, denature

3a) Competitive inhibition
Inhibitor binds to active site (substrate cannot bind)

3b) Allosteric/noncompetitive inhibition
Allosteric Inhibitor binds to allosteric site (not active site), changes shape of enzyme
Substrate cannot bind (shape doesn’t match)
Activators exist

4a) Substrate concentration (Binding affinity)
-Km= C of substrate required to reach 1/2 Vmax
-Strength of non-covalent bond
-High Km, high affinity, less substrate needed for rxn, more efficient
-Feedback inhibition (photo)
Graph

5) Cofactors & Coenzymes
- Increase function of enzymes

Cofactors:Metal ions, divalent cations (Mg2+, Fe2+, Mn2+)
Coenzymes: non-protein organic molecules (vitamins)

6) Ribozymes (segments RNA, active catalysts)
- Ribosomes catalyze Dehydration synthesis (peptide bonds)
- Cleave RNA