Ch. 7 and 8

Question 1

What is the significance of P50 for Hb?

Answer 1

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

Question 2

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

Answer 2

the Heme group

Question 3

What does a lower value of P50 indicate?

Answer 3

a binding site with a high O2 binding affinity

Question 4

What does a higher value of P50 indicate?

Answer 4

a binding site with a low O2 binding affinity

Question 5

What are the 4 subunits of Hb?

Answer 5

2 identical alpha-globins and 2 identical beta-globins

Question 6

What are some characteristics of the T state of Hb?

Answer 6

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

Question 7

What are some characteristics of the R state of Hb?

Answer 7

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

Question 8

What is the idea of cooperativity of Hb?

Answer 8

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

Question 9

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

Answer 9

More

Question 10

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

Answer 10

Fewer

Question 11

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

Answer 11

CO2, H+, and 2,3-BPG

Question 12

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

Answer 12

O2

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

stabilized

Question 16

Explain the Perutz mechanism

Answer 16

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

Question 17

Explain the molecular basis for HbS (Sickle cell anemia)

Answer 17

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

Question 18

How do you recognize a general acid catalyst?

Answer 18

transfers a H+ to an atom

Question 19

How do you recognize a general base catalyst?

Answer 19

removes a H+ from an atom

Question 20

How do you recognize a covalent catalyst?

Answer 20

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

Question 21

How do you recognize an electrostatic catalyst?

Answer 21

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

Question 22

which is faster: intramolecular interactions or intermolecular interactions?

Answer 22

always intramolecular

Question 23

define Km

Answer 23

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

Question 24

What is Km analogous to?

Answer 24

P50

Question 25

define Kcat

Answer 25

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

Question 26

what is the significance of kcat/Km?

Answer 26

a measure of enzyme efficiency and substrate specificity

Question 27

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

Answer 27

the binding of S (selectivity of "target")

Question 28

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

Answer 28

Stabilization of the transition state

Question 29

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

Answer 29

Km/Vmax

Question 30

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

Answer 30

1/Vmax

Question 31

How do you recognize competitive inhibition?

Answer 31

slope changes, no change in y-intercept

Question 32

How do you recognize uncompetitive inhibition?

Answer 32

y-intercept changes, no change in slope

Question 33

How do you recognize mixed inhibition?

Answer 33

changes in both y-intercept and slope

Question 34

define a competitive inhibitor - where does it bind?

Answer 34

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

Question 35

how can you overcome competitive inhibition?

Answer 35

very high levels of substrate concentration

Question 36

define an uncompetitive inhibitor - where does it bind?

Answer 36

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

Question 37

define a mixed inhibitor - where does it bind?

Answer 37

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

Question 38

How do Km and Vmax change with a competitive inhibitor?

Answer 38

Km increases, Vmax unchanged

Question 39

How do Km and Vmax change with an uncompetitive inhibitor?

Answer 39

Km and Vmax both reduce

Question 40

How do Km and Vmax change with a mixed inhibitor?

Answer 40

Vmax decreases Km typically increases

Question 41

What type of modification do irreversible inhibitors make?

Answer 41

a covalent modification

Question 42

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

Answer 42

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

Question 43

What are the features of the "committed step" in a pathway

Answer 43

usually early in the pathway, delta G << 0 which allows for regulation of "off" and "on"

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

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

Answer 46

Bind to Substrate Stabilize the transition state

Question 47

What amino acids can be phosphorylated?

Answer 47

Thr, Ser, Tyr

Question 48

What enzyme does phosphorylation?

Answer 48

Kinase

Question 49

What enzyme removes a phosphate group?

Answer 49

Phosphatase

Question 50

What type of modification is phosphorylation?

Answer 50

reversible covalent modification

Question 51

explain an irreversible covalent modification

Answer 51

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