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CHEM 471 > Ch. 7 and 8 > Flashcards

Ch. 7 and 8 Flashcards

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1
Q

What is the significance of P50 for Hb?

A

P50 is the concentration of O2 required to saturate 50% of the binding sites

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2
Q

What is the site of O2 binding for Mb and Hb?

A

the Heme group

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3
Q

What does a lower value of P50 indicate?

A

a binding site with a high O2 binding affinity

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4
Q

What does a higher value of P50 indicate?

A

a binding site with a low O2 binding affinity

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5
Q

What are the 4 subunits of Hb?

A

2 identical alpha-globins and 2 identical beta-globins

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6
Q

What are some characteristics of the T state of Hb?

A

Low O2 binding affinity
High P50
more stabilizing non-covalent interactions

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7
Q

What are some characteristics of the R state of Hb?

A

High O2 binding affinity
Low P50
less stabilizing non-covalent interactions compared to the T state

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8
Q

What is the idea of cooperativity of Hb?

A

each binding of an O2 molecule lowers the P50 for that specific Hb

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9
Q

Does the R state have more or fewer Fe2+-O2 (iron-oxygen) bonds than the T state?

A

More

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10
Q

Does the T state have more or fewer Fe2+-O2 (iron-oxygen) bonds than the R state?

A

Fewer

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11
Q

What are the 3 negative effectors of Hb that stabilize the T state?

A

CO2, H+, and 2,3-BPG

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12
Q

What is the positive effector that stabilizes the R state of Hb?

A

O2

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13
Q

Which state (R or T) is favored in the lungs?

A

R state favored, binding of O2 and release of CO2, H+, and BPG

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14
Q

Which state (R or T) is favored in the capillaries?

A

T state favored, binding of CO2, H+ and BPG, release of O2

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15
Q

Is the T state stabilized or destabilized when going from a higher to lower pH?

A

stabilized

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16
Q

Explain the Perutz mechanism

A

O2 binds, Fe2+ ion is pulled into the plane of the heme, this pulls the F-helix down, causes steric strain, which is relieved in the T-state

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17
Q

Explain the molecular basis for HbS (Sickle cell anemia)

A

A Glu –> Val mutation at Beta 6
Hb forms long rod-like structures that distort and can rupture the membrane of the RBCs

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18
Q

How do you recognize a general acid catalyst?

A

transfers a H+ to an atom

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19
Q

How do you recognize a general base catalyst?

A

removes a H+ from an atom

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20
Q

How do you recognize a covalent catalyst?

A

formation of a covalent E-S adduct that alters the rxn pathway

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21
Q

How do you recognize an electrostatic catalyst?

A

occurs when the enzyme active site stabilizes the transition state of the reaction by forming electrostatic interactions with the substrate

22
Q

which is faster: intramolecular interactions or intermolecular interactions?

A

always intramolecular

23
Q

define Km

A

the substrate concentration at which the Vo is 1/2 of Vmax

24
Q

What is Km analogous to?

A

P50

25
Q

define Kcat

A

measures the rate of the catalytic process (how rapidly S –> P)

26
Q

what is the significance of kcat/Km?

A

a measure of enzyme efficiency and substrate specificity

27
Q

What structural features of an enzyme are most likely to affect Km?

A

the binding of S (selectivity of “target”)

28
Q

What structural features of an enzyme are most likely to affect kcat?

A

Stabilization of the transition state

29
Q

What does the slope of the Lineweaver-Burk plot represent?

A

Km/Vmax

30
Q

What does the y-intercept of the Lineweaver-Burk plot represent?

A

1/Vmax

31
Q

How do you recognize competitive inhibition?

A

slope changes, no change in y-intercept

32
Q

How do you recognize uncompetitive inhibition?

A

y-intercept changes, no change in slope

33
Q

How do you recognize mixed inhibition?

A

changes in both y-intercept and slope

34
Q

define a competitive inhibitor - where does it bind?

A

inhibitor competes with the substrate - binds and blocks the active site

35
Q

how can you overcome competitive inhibition?

A

very high levels of substrate concentration

36
Q

define an uncompetitive inhibitor - where does it bind?

A

binds at a site on the enzyme different from the substrate and diminishes the enzyme’s catalytic activity

37
Q

define a mixed inhibitor - where does it bind?

A

binds to both the active site or a site other than the active site

38
Q

How do Km and Vmax change with a competitive inhibitor?

A

Km increases, Vmax unchanged

39
Q

How do Km and Vmax change with an uncompetitive inhibitor?

A

Km and Vmax both reduce

40
Q

How do Km and Vmax change with a mixed inhibitor?

A

Vmax decreases
Km typically increases

41
Q

What type of modification do irreversible inhibitors make?

A

a covalent modification

42
Q

How do you increase flux? (movement of material through a pathway)

A
  1. increase substrate concentration
  2. remove products as they are generated
43
Q

What are the features of the “committed step” in a pathway

A

usually early in the pathway, delta G &laquo_space;0 which allows for regulation of “off” and “on”

44
Q

What are the features of the R state of an enzyme?

A

higher binding affinity for substrate
lower Km
higher kcat
activators (+ effectors) stabilize

45
Q

What are the features of the T state of an enzyme?

A

lower binding affinity for substrate
higher Km
lower kcat
inhibitors (- effectors) stabilize

46
Q

What are the 2 things an enzyme must do to be an effective catalyst?

A

Bind to Substrate
Stabilize the transition state

47
Q

What amino acids can be phosphorylated?

A

Thr, Ser, Tyr

48
Q

What enzyme does phosphorylation?

A

Kinase

49
Q

What enzyme removes a phosphate group?

A

Phosphatase

50
Q

What type of modification is phosphorylation?

A

reversible covalent modification

51
Q

explain an irreversible covalent modification

A

usually the result of proteolytic cleavage
enzymes produced in the inactive form, they mature and become fully active as a result of proteolysis

CHEM 471 (4 decks)

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