Haemoglobin and Myoglobin Structure

Question 1

How does myoglobin deliver more O2 than blood?

Answer 1

By storing oxygen in muscles

Question 2

How much myoglobin do human miscles have?

Answer 2

0.5-0.7 mmol/L myoglobin which is enough for about 7 seconds of intense activity.

Question 3

The tissue, after it has exhausted its store of myoglobin - where does it depend on for oxygen delivery? (which organ)

Answer 3

The lungs

Question 4

This is known as muscle globin and has an ancient globin fold that provides a hydrophobic pocket to bind a haem group.

Answer 4

Myoglobin

Question 5

How many amino acids are there in the primary structure of myoglobin?

Answer 5

150 amino acids

Question 6

How many secondary structures are there in myoglobin? (include helices and loops)

Answer 6

8 alpha helices (A-H) and connecting loops in between

Question 7

What is the tertiary structure of myoglobin?

Answer 7

globin fold with hydrophobic pocket (the structure is in the name)

Question 8

Which amino acid does the haem group in a globin protein bind to?

Answer 8

Histidine F8 (8th amino acid)

Question 9

What is the quaternary structure of myoglobin?

Answer 9

Monomeric (one polypeptide chain)

Question 10

This includes four pyrrole rings linked together in a plane. This is a prosthetic group or a cofactor.

Answer 10

Haem/heme

Question 11

These are structures that bind to proteins or enzymes to enable them to do a certain function. (such as release oxygen)

Answer 11

Cofactors/prosthetic groups

Question 12

What is the difference between oxyhaemoglobin and deoxyhaemoglobin under spectroscopy?

Answer 12

Oxyhaemoglobin has a bright red colour
Deoxyghaemoglobin has a dull red colour

Question 13

This is the process by which concentration of dissolved molecules is quantified by wavelength of light and absorbance of light.

Answer 13

Spectroscopy

Question 14

What gives the haem its characteristic red colour?

Answer 14

Molecular electronic orbitals / Fe2+

Question 15

The binding of oxygen to the Fe2+ is a what kind of reaction?

Answer 15

Reversible reaction meaning oxygen can bind and unbind from the Fe2+

Question 16

How is Haem Fe2+ attached to the globin protein? Where does it link?

Answer 16

Histidine F8

Question 17

This builds on the concept of steric hindrance in that the impossibility of 2 atoms occupying the same space.

Answer 17

Allosteric control

Question 18

What is an example of allosteric control of oxygen affinity in myoglobin?

Answer 18

Lactate. Lactate reduces myoglobin’s affinity for oxygen but doesn’t bind where it binds

Question 19

Myoglobin is saturated with ______ at low ____. So it releases this when cellular _____ is very low.

Answer 19

O2, pO2, pO2

Question 20

The availability of O2 to cellular proteins depends on: (2 things)

Answer 20

pO2 in local environment
binding affinity of O2 to hemoglobin

Question 21

Hemoglobin in RBCs need to be able to do these: (2 things)

Answer 21

Bind to O2 in the lungs under 100 torr (pO2)
Bind to O2 in the peripheral tissues under 20 torr (pO2)

Question 22

What did hemoglobin evolved to in terms of binding?

Answer 22

It evolved to binding less tightly on oxygen in comparison to myoglobin because it needs to be able to dump oxygen pretty quickly

Question 23

This is a tetramer that has four globin proteins associated together non-covalently. It can bond to up to 4 oxygens.

Answer 23

Haemoglobin

Question 24

This acts as O2 store in the muscle.

Answer 24

Myoglobin

Question 25

What shape are the crystals (hemoglobic conformations) under aerobic conditions?

Answer 25

Needle shaped

Question 26

What shape are the crystals (hemoglobic conformations) under anaerobic conditions?

Answer 26

Hexagonal, plate shaped crystals

Question 27

This type of haemoglobin has a high affinity for oxygen

Answer 27

Oxyhaemoglobin

Question 28

This type of haemoglobin has a low affinity for oxygen

Answer 28

Deoxyghaemoglobin

Question 29

This model was proposed in 1965 by Monod, Wyman and Changeux. States that subunits an be in a low activity of high activity conformation. Especially that all subunits must be in the same state.

Answer 29

MWC concerted model

Question 30

In the MWC concerted model, what does it say about equilibrium?

Answer 30

That binding each substrate shifts equilibrium in favour of R.

Question 31

These stabilise the T form according to MWC model.

Answer 31

inhibitors

Question 32

These stabilise the R form according to MWC model.

Answer 32

Acceptors

Question 33

This model states that one substrate binding induces a T-R conformational change in only one subunit. This conformational change influences the neighbouring subunits and changes their affinity for one substrate; introduces the idea of cooperativity.

Answer 33

KNF sequential model (Koshland, Nemethy, and Filmer)

Question 34

Where does the oxygen bind to in myoglobin and haemoglobin?

Answer 34

To the haem group

Question 35

Affinity for oxygen in myoglobin and haemoglobin are altered by _______ binding elsewhere.

Answer 35

molecules (like lactate)

Question 36

This requires multiple interacting subunits and gives a sigmoidal binding curve.

Answer 36

Cooperativity

Question 37

This shifts the binding affinity to a physiologically relevant oxygen concentration.

Answer 37

Cooperativity

Question 38

Approximately how much myoglobin do human muscles have?

Answer 38

0.5-0.7 mmol/L of myoglobin (only enough for about 7 seconds of intense activity)

Question 39

True or false. The quaternary structure of myoglobin is multimeric and the quaternary structure of haemoglobin is monomeric.

Answer 39

False. Myoglobin is monomeric and haemoglobin is multimeric (tetramer)

Question 40

How many coordinate bonds does haem have? Where do they bond?

Answer 40

6 coordinate bonds. 4 to nitrogen, 1 to histidine F8 and 1 to O2.

Question 41

True or false. Haem includes four pyrimidine rings linked together in a plane.

Answer 41

False. Haem includes four pyrrole rings.

Question 42

This is located on the opposite side of the haem and distorts the binding of gas molecules to the 6th coordination position (of O2) on haem Fe2+.

Answer 42

Histidine E7

Question 43

What is the purpose of histidine E7?

Answer 43

To reduce the binding affinity of oxygen to myoglobin which will make it easier to release oxygen to the muscle cell.

Question 44

True or false. Allosteric means without overlapping.

Answer 44

That’s true. In terms of myoglobin, this means having another binding spot for another molecule (like lactate)

Question 45

What is the partial pressure of oxygen in the lungs and muscle respectively?

Answer 45

100 torr and 20 torr. So the partial pressure of the lungs is higher than that of the muscle.

Question 46

True or false. Haemoglobin can change shape when dumping oxygens more efficiently in peripheral tissues.

Answer 46

True

Question 47

True or false. The globin proteins in haemoglobin are associated together with covalent bonds.

Answer 47

False. They are linked to each other with non-covalent bonds.

Question 48

What’s the difference between the KNF and MWC concerted model?

Answer 48

KNF Sequential Model - states that haemoglobin states change gradually from Tense to Relaxed
> supports positive and negative cooperativity
> support sigmoidal binding curve

MWC Concerted Model - states that haemoglobin states change all at once from Tense to Relaxed. So the state of haemoglobin can only be one or the other.

Question 49

True or false. Allosteric control is only found in myoglobin.

Answer 49

False. Allosteric control is found in both haemoglobin and myoglobin.

Allosteric control is important for changing the affinity of oxygen via molecules binding elsewhere.

Question 50

What is the shape of myoglobin and haemoglobin curves? Respectively.

Answer 50

Hyperbolic curve; sigmoidal curve