Tutorial 2 myoglobin & hemoglobin

Question 1

what is the function of myoglobin?

Answer 1

oxygen store

takes oxygen off of hemoglobin and releases oxygen at very low O2 partial pressure

binds hemoglobin + stores oxygen

Question 2

describe the structure myoglobin (Mb). include a description of both the protein and non protein parts

Answer 2

a-helices

1 heme group that contains an iron atom
heme group made from 4 pyrrole rings that form protoporphyrin ring
forms compact 3D structure

Question 3

what is the function of hemoglobin?

Answer 3

transports oxygen

binds oxygen in high pO2 and releases oxygen at medium pO2

Question 4

describe the structure hemoglobin (Hb). Include a description of both the protein and non protein parts

Answer 4

very similar to myoglobin - 4 subunits

tertiary structure that allows for cooperativity between subunits

Question 5

how is the heme held in place?

Answer 5

histamine bond to iron

histamine interrupts (weakens) oxygen binding

hydrophobic pocket

Question 6

how would you determine if there was oxygen bound to hemoglobin?

Answer 6

shape change
Spectroscopy - spectrophotometre - accurate
by colour
adding dithionate and see if solution changed colour

Question 7

draw an oxygen binding curve for hemoglobin and myoglobin. what is the shape of the curves?

Answer 7

Mb - hyperbolic

Hb - linear

Question 8

describe the R and T state of hemoglobin

Answer 8

R state
- relaxed, Hb bind oxygen well, heme flat, high affinity for oxygen

T state
- tense, low affinity for oxygen, heme dished

transition between helices F and C, move 1 turn past one another

Question 9

name one allosteric effector of myoglobin

Answer 9

lactate

Question 10

name one allosteric effector of hemoglobin

Answer 10

CO2
2,3-BPG
Protons (H+)

Question 11

describe how 2,3-BPG acts as an allosteric effector of hemoglobin

Answer 11

middle

-‘ve charges of BPG interact with +’ve charge of histidine in the allosteric location in the centre of hemoglobin. this locks Hb into the T state reducing the affinity for oxygen.

Question 12

why is cooperativity important in hemoglobin?

Answer 12

without hemoglobin wouldn’t bind and release oxygen of the needed partial pressures

Question 13

what does a hill plot show and how?

Answer 13

shows whether or not there’s cooperativity

Hb steep point = 3.
curved = have cooperativity

straight = no cooperativity

Question 14

describe and contrast the concerted model and sequential model for Hb cooperativity

Answer 14

sequential
- change 1 at a time. influence by pair, act independently

concerted

• all change or none changes at all.
• won’t act until they all act together
• T and R
• all subunits act and transition all together
• more accurate

Question 15

how is the foetal Hb different from adult Hb? what effect does this have on its function?

Answer 15

foetal

• different subunit that can’t bind BPG that well
• R state preferred
• can take oxygen of mum Hb

Question 16

describe methemoglobin

Answer 16

Hb with Fe3+ or ferric state

Question 17

describe boston hemoglobin

Answer 17

HisE7 changes to TyrE7, causing Fe2+ ⟶ Fe3+

HbM remains in T state with low affinity for oxygen

Question 18

describe sickle cell hemoglobin

Answer 18

Hb b6 Glu to Val mutation enable an abnormal hydrophobic interaction between Hb molecules, particularly when in the deoxy form, causing polymerisation of Hb into chains that distort the RBC.