quiz 3

Question 1

describe myoglobin

Answer 1

a monomer
small and compact

Question 2

where is myoglobin found? why?

Answer 2

muscle tissue for oxygen storage

Question 3

what does myoglobin contain

Answer 3

8 alpha helices
prosthetic heme groups

Question 4

what does myoglobin do

Answer 4

reversibly binds O2

Question 5

describe hemoglobin

Answer 5

a porphyrin ring system in a hydrophobic pocket with an iron at the center for covalent bonds

Question 6

how can the iron be formed

Answer 6

can be ferrous (Fe2+) or ferric (Fe3+)

Question 7

what are the 6 coordination sites of ferrous iron

Answer 7

4 pyrrole N
1 proximal histidine
1 O2
1 histidine to O2

Question 8

what function does histidine play

Answer 8

keeps heme coordinated in protein
keeps other hemes from binding

Question 9

define binding affinity

Answer 9

ligand (L) binding to protein (P)

Question 10

BA equations:

Answer 10

P+L=PL
Keq=PL/[P][L]
Ka= PL/[P][L]
dissociation: Kd=[P][L]/[PL]

Question 11

what does an increased Ka cause?

Answer 11

stronger binding

Question 12

what does an increased Kd cause?

Answer 12

weaker binding

Question 13

what is the equation for fractional saturation

Answer 13

occupied binding sites/total binding sites
OR
[PL]/[PL]+[P]

Question 14

describe a stronger binding

Answer 14

left curve
lower Kd
less [L] needed

Question 15

describe a weaker binding

Answer 15

right curve
higher Kd
more [L] needed

Question 16

define hyperbolic

Answer 16

one binding site

Question 17

define KD

Answer 17

concentration of O2 when half of mb binds to O2

Question 18

where is hemoglobin found

Answer 18

in red blood cells

Question 19

define heterotetramer

Answer 19

4 subunits

Question 20

define cooperative binding

Answer 20

binding of ligand to one site increases binding affinity for another ligand at another site

Question 21

describe deoxygenated

Answer 21

heme is domed and nonpolar

Question 22

describe oxygenated

Answer 22

heme is planar and polar

Question 23

describe deoxyhemoglobin

Answer 23

no bound O2
heme ring is not planar

Question 24

describe oxyhemoglobin

Answer 24

O2 is bound
heme ring is planar
relaxed (R) conformation

Question 25

describe conformational switch

Answer 25

O2 binding pulls iron into plane of heme
histidine is pulled up with iron
entire F helix moves

Question 26

define allostery

Answer 26

conformational switches underlie cooperatively
transmits change in one subunit across the interface of the next subunit
15° rotation

Question 27

describe concerted heme bonding

Answer 27

protein found at T or R
binds to single subunit
stabilizes R state
more complex

Question 28

describe sequential heme bonding

Answer 28

protein found at T and R
does not convert only to R state
alters affinity of adjacent subunits
shifts equilibrium to R state

Question 29

describe positive effectors

Answer 29

increase Hb affinity for O2
shifts equilibrium to R state

Question 30

describe negative effectors

Answer 30

decreases Hb affinity for O2
shift equilibrium to T state