Myoglobin & Haemoglobin

Question 1

Shape of globular proteins

Answer 1

Round and compact - made up of multiple polypeptide chains

Question 2

Solubility of globular proteins and why?

Answer 2

Soluble; chains coiled up so hydrophilic residues on outside and hydrophobic residues on inside

Question 3

What is advantage of this solubility?

Answer 3

Easily transported in fluids (e.g blood)

Question 4

Shape of fibrous proteins

Answer 4

Elongated - long polypeptide chains, often with repeating amino acid sequences

Question 5

Solubility of fibrous proteins?

Answer 5

Insoluble

Question 6

Why does oxygen need transport system?

Answer 6

Is only sparingly soluble in blood so needs transport and storage system

Question 7

Difference in jobs of myoglobin and haemoglobin?

Answer 7

Mb is for oxygen storage and Hb is for oxygen transportation

Question 8

Structure of Mb?

Answer 8

Globular protein, highly folded and compact, consist of single polypeptide unit. Contains haem group

Question 9

What feature of Mb makes it suitable as storage for oxygen?

Answer 9

Has a very high affinity for oxygen so only releases in tissue thats hypoxic

Question 10

Structure of Hb?

Answer 10

4 polypeptide chains (subunits) held together by non-covalent interactions to give overall 4ary structure. Each subunit contains a haem group and a globular protein

Question 11

Hb is an allosteric protein. What does this mean?

Answer 11

Binding of oxygen to one of the subunits affects binding of other subunits

Question 12

Binding of oxygen to Hb is said to be cooperative. What does this mean?

Answer 12

Binding of oxygen to one subunit raises other subunits affinity for oxygen

Question 13

What is the ‘T-state’ for Hb?

Answer 13

Tense state

Question 14

How does t-state affect oxygen binding?

Answer 14

More salt bridges between subunits. Oxygen struggles to get to its binding site and Hb has a low affinity for oxygen

Question 15

What is the ‘R-state’?

Answer 15

Relaxed state

Question 16

How does r-state affect oxygen binding?

Answer 16

Fewer salt bridges between subunits. The binding sites are more accessible so Hb has a high affinity for oxygen

Question 17

What is the shape of the binding curve for Mb?

Answer 17

Hyperbolic

Question 18

What is the shape of the binding curve for Hb?

Answer 18

Sigmoidal

Question 19

What is the difference between the binding of oxygen for Mb and Hb?

Answer 19

For any oxygen pressure, the degree of saturation of Mb is higher than that of Hb. Mb has a greater affinity for oxygen

Question 20

What does the Bohr effect describe?

Answer 20

Describes how the affinity of Hb for oxygen changes depending on C02 concentration. These changes ensure efficient oxygen delivery.

Question 21

What causes areas of low pH?

Answer 21

Active tissues are respiring, producing CO2 which dissolves in the blood to form carbonic acid. Lactic acid is also produced during anaerobic respiration

Question 22

What happens in areas of low pH?

Answer 22

Low pH causes greater dissociation of oxygen from Hb which allows efficient delivery of O2 to areas of respiring tissues, and takes away CO2

Question 23

How does low pH cause Hb to release O2?

Answer 23

pH affects protonation state of amino acid residues. When [H]+ is high, additional residues are protonated which can form more salt bridges. These bridges stabilise the T-state, decreasing Hb’s affinity for O2

Question 24

What causes curve to shift to the left?

Answer 24

High affinity of Hb for O2, caused by higher pH and lower conc of CO2

Question 25

What causes curve to shift to the right?

Answer 25

Low affinity of Hb for O2, caused by lower pH and higher conc of CO2

Question 26

What is danger of CO?

Answer 26

CO binds to Hb with greater affinity that O2 so prevents O2 binding

Question 27

Where is BPG found?

Answer 27

Is found at high concentrations in erythrocytes (red blood cells)

Question 28

What is purpose of BPG?

Answer 28

Regulates affinity for O2 of Hb

Question 29

When would levels of BPG increase and what is effect of this?

Answer 29

Levels increase at high altitude and in hypoxia. BPG decreases affinity of Hb for O2, causing more O2 to be released

Question 30

How does BPG cause more O2 to be released?

Answer 30

Negative charges on BPG interact with positive amino acid residues, causing an increase in salt bridges between subunits. This pushes Hb further towards T-state, causing Hb to release O2 as it lowers the affinity

Question 31

How is foetal Hb different from adult Hb

Answer 31

HbF binds more strongly to O2 than HbA

Question 32

What causes HbF to have a greater affinity for O2 than HbA?

Answer 32

HbF binds BPG less effectively

Question 33

What is advantage of HbF binding O2 more strongly?

Answer 33

Allows efficient transfer of O2 across the placenta and protects foetus in cases of mild female hypoxia

Question 34

Define haemoglobinopathies

Answer 34

A range of inherited disorders affecting Hb synthesis, structure and function, many of which are caused by single gene mutations

Question 35

What happens to Hb molecules during sickle cell anaemia?

Answer 35

1. Small hydrophobic patch on Hb molecules appears, causing Hb molecules to stick together
2. Creates long chains of Hb molecules which slowly compress the erythrocytes until they form sickle shape

Question 36

What is result of sickle shaped erythrocytes?

Answer 36

They are misshapen and rigid, so get stuck in capillaries. This prevents blood blow as erythrocytes build up, so areas of tissue become deoxygenated