Enzymes, Part 2

Question 1

enzyme kinetics

Answer 1

• study of chemical reactions that are catalyzed by enzymes
  
  • enzyme’s catalytic mechanism
  • control of enzyme activity
  • role in metabolism
  • possible inhibition by drugs or agonists

Question 2

michaelis-menten equation

Answer 2

• describes how reaction velocity varies with substrate concentration
• enzyme reversibly combines with its substrate to form an ES complex that yields a product P, releasing the enzyme

Question 3

michaelis-menten constant Km

Answer 3

• characteristic of an enzyme and its particular substrate and reflects the affinity of the enzyme for that substrate
• Km is equal to the substrate concentration at which the reaction velocity is 1/2Vmax
• Km does not vary with enzyme concentration

Question 4

hyperbolic

Answer 4

• michaelis-menten kinetics

- myoglobin oxygen binding

Question 5

allosteric

Answer 5

• sigmoidal curve

- hemoglobin binding to O2

Question 6

factors that affect reaction velocity: SUBSTRATE CONCENTRATION

Answer 6

• maximal velocity -> number of substrate molecules converted to product per unit time (umol/min)
• rate of enzyme/catalyzed reaction increases with substrate concentration until a max velocity is reached -> saturation (substrate are bound to all available binding sites in enzyme)

Question 7

factors that affect reaction velocity: TEMPERATURE

Answer 7

• reaction velocity increases with temp until peak is reached
• increase is result of increased number of molecules having sufficient energy to pass over the energy barrier
• further elevation of temp results in decrease in reaction velocity (denaturation)
• optimal temp for most mammalian enzymes is 35-40C

Question 8

factors that affect reaction velocity: PH

Answer 8

• extreme pH (concentration of H+) conditions can affect reaction velocity
• pH can affect ionization state of active site
• extreme pH conditions can also denature enzymes
• pH optimum of enzymes may vary

Question 9

inhibitor

Answer 9

• any substance that can diminish velocity of an enzyme-catalyzed reaction

Question 10

inhibition of enzyme activity

Answer 10

• can be irreversible (covalent bonds)

Question 11

reversible inhibitors

Answer 11

• bind to enzyme through non-covalent bonds
• ex: dilution of enzyme-inhibitor complex leads to separation of reversibly bound inhibitor -> enzyme activity can be restored

Question 12

2 most common types of reversible inhibition

Answer 12

• competitive inhibition

- noncompetitive inhibition

Question 13

competitive inhibitor

Answer 13

• binds reversibly to the same site that the substrate would normally attach to thus competes with substrate for that site
• reduce affinity
• increase Km
• LB plot Km moves closer to zero, Vmax unchanged

Question 14

noncompetitive inhibitor

Answer 14

• inhibitor binds at a site different from substrate
• can also bind free enzyme (not only ES complex) -> preventing reaction from occurring
• decrease the Vmax
• Km remains unchanged

Question 15

enzyme inhibitors as drugs

Answer 15

• B-lactam antibiotics (penicillin, amoxicillin): act by inhibiting enzymes that are important for bacterial cell wall synthesis
• Angiotensin-converting enzyme (ACE) inhibitors: block enzyme that cleaves angiotensin I to the potent vasoconstrictor angiotensin II -> cause vasodilation -> lower blood pressure
• aspirin: irreversibly inhibits prostaglandin and thromboxane synthesis