Lecture 7 - proteins in action

Question 1

explain the structure of myoglobin at all levels

Answer 1

• primary structure = 150 amino acids
• secondary structure = 8 a-helices A-H and connecting loops (AB, BC etc)
• tertiary structure = globin fold with a hydrophobic pocket
• quaternary structure = monomeric (a single polypeptide chain)

Question 2

where does haem bind to in myoglobin

Answer 2

haem binds to His F8 (the 8th amino acid in helix F, which is histadine) in a globin protein

Question 3

what does haem include

Answer 3

four pyrrole rings linked together in a plane

Question 4

how many coordinate bonds does iron have and what do they bind to

Answer 4

6
- 4 to nitrogen atoms of the haem
- one to a nitrogen atom of histidine F8
- one to O2

Question 5

what gives haem the red colour

Answer 5

the electronic orbitals

Question 6

is the binding of oxygen to the Fe2+ a reversible interaction

Answer 6

yes

Question 7

what does lactate do to myoglobins affinity for oxygen

Answer 7

decreases myoglobins affinity for oxygen, but does not bind where oxygen does

Question 8

what does lactate build up in muscles do

Answer 8

promotes the release of myoglobin, increasing O2 availability for respiration

Question 9

what does the concept of “allosteric” build on

Answer 9

builds on ‘steric hinderance’, the impossibility of two atoms occupying the same space

Question 10

what has haemoglobin evolved to be

Answer 10

a tetramer

Question 11

what is a tetramer

Answer 11

four globin proteins associate together non covalently (4 structural sub-units)

Question 12

how many O2 can bind to one haemoglobin tetramer

Answer 12

maximum of four
- because each globin protein contains one haem that can bind to one oxygen

Question 13

is myoglobin saturated or unsaturated at low pO2

Answer 13

saturated

Question 14

when will myoglobin release O2 to muscle cells

Answer 14

only when the cellular pO2 is very low

Question 15

what is the partial pressure of oxygen in the lungs

Answer 15

pO2 is ~100 Torr

Question 16

what is the partial pressure of oxygen in resting muscle

Answer 16

pO2 is ~20 Torr

Question 17

does haemoglobin have a stronger or weaker binding affinity for oxygen and why is it important

Answer 17

much weaker than myoglobin, this is important as its function is to transport oxygen

Question 18

what is the function of myoglobin

Answer 18

back up store of O2 in muscle cells

Question 19

what is the function of haemoglobin

Answer 19

O2 transporter

Question 20

what is the structure of haemoglobin

Answer 20

tetramer

Question 21

what is the structure of myoglobin

Answer 21

monomer

Question 22

in both myoglobin and haemoglobin the affinity for oxygen is altered by …

Answer 22

by molecules (e.g lactate to myoglobin) binding elsewhere (allosteric control)

Question 23

what type of curve does myoglobin show on the degree of saturation vs O2 pressure graph

Answer 23

tighter, hyperbolic

Question 24

what type of curve does haemoglobin show on the degree of saturation vs O2 pressure graph

Answer 24

weaker, sigmoidal binding curve

Question 25

what is cooperative interaction in terms of haemoglobin

Answer 25

• when an oxygen atom binds to one of hemoglobin’s four binding sites, the affinity to oxygen of the three remaining available binding sites increases
• this gives the sigmoidal binding curve

Question 26

what does the MWC model say about subunits states

Answer 26

all subunits will be in the same state
- either low affinity, tense (T) or high affinity, relaxed (R) confirmation

Question 27

what does the binding of each successive substate shift the equilibrium in favour of

Answer 27

the R form

Question 28

what form do inhibitors stabilise

Answer 28

the T form

Question 29

what form do activators stabilse

Answer 29

the R form