Lecture 8

Question 1

Structure: myoglobin vs hemoglobin

Answer 1

Myoglobin
1 subunit

Hemoglobin
4 subunits (a2B2)
-strong interaction between "unlike" subunits

Heme’s Fe 2+ binds porphyrin with two coord bonds. Remaining two spots: His and O2 (His shields Fe from oxidizing by reacting with other Hemes)

Question 2

oxygen binding curves: myoglobin vs hemoglobin

Answer 2

myoglobin: nH = 1 always (similar to T state)

hemoglobiin:
nH=1 (T) =>
nH=3 (R) =>
nH=1 (saturation?)

Question 3

T and R states of hemoglobin.

What determines state?

Answer 3

T
-Heme puckered
low affinity (great in tissues)
nh = 1

R
Heme flat
high affinity (great in lungs)
nh = 3

cooperative binding

O2 binding triggers change
sigmoidal (s shaped) instead of hyperbolic binding curve

Question 4

functions and properties of hemoglobin

Answer 4

regulation of R and T states

1. Bohr Effect
   - –H+ binding to some AA residues
   - –stabilizes T (promoting O2 dissociation)
2. CO2 binds to N-terminus of subunits
   - –also stabilizes T
3. BPG binding stabilizes T
   - binding site for BPG absent in R state

Question 5

hperbolic, sigmoid binding curve

Answer 5

Hill plot. Works for O2 binding with hemoglobin.

Question 6

interpreting a Hill plot

Answer 6

n is number of subunits.

Question 7

cooperativity

Answer 7

characteristic of an enzyme or other protein in which binding the first molecule of a ligand changes the affinity for the second molecule.

Positive cooperativity: affinity for second ligand increases

Negative cooperativity:
affinity decreases

Question 8

ligand

Answer 8

small molecule that binds specifically to a larger one

-example, a hormone is the ligand for its specific protein receptor

Question 9

binding site

Answer 9

the crevice or pocket on a protein in which a ligand binds

Question 10

induced fit

Answer 10

when ligand gets close protein’s shape conformation change and ligand now fits
- - - - - - - - - -
from glossary: change in conformation of an enzyme in response to substrate binding that renders enzyme catalytically active.

also denotes changes in conformation of any macromolecule in response to ligand binding, such that the binding site better conforms to the shape of the ligand

Question 11

substrate

Answer 11

specific compound acted on by enzyme

Question 12

active site

Answer 12

region of an enzyme surface that binds the substrate molecule and catalytically transforms it

also called catalytic site

Question 13

heme

Answer 13

iron-porphyrin prosthetic group of heme proteins

Question 14

allosteric protein

Answer 14

protein (usu with mult subunits) with mult ligand-binding sites, such that ligand binding at one site affects ligand binding at another

Question 15

homotropic

Answer 15

describes allosteric modulator that is identical to the normal ligand

homotropic enzyme uses substrate as modulator

Question 16

heterotropic

Answer 16

describes allosteric modulator that is distinct from normal ligand

heterotropic enzyme requires modulator other than its substrate

Question 17

Hill coefficient

Answer 17

called nh (should be sub h)

measure of cooperative interaction between protein subunits

slope of Hill plot

less than or equal to actual number of subunits binding oxygen

Question 18

hypoxia

Answer 18

metabolic condition in which supply of oxygen is severely limited

Question 19

conformation change

Answer 19

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