Lecture 3

Question 1

What type of protein domains are myoglobin and haemoglobin?

Answer 1

α-domain proteins.

Question 2

What is the purpose of myoglobin?

Answer 2

Intracellular oxygen transport.

Question 3

What is the purpose of haemoglobin?

Answer 3

Oxygen transport in the blood.

Question 4

What is hypoxia?

Answer 4

A deficiency of oxygen at the tissues.

Question 5

What can hypoxia cause, and how long does it take?

Answer 5

Unconsciousness - 15 sec,
Irreversible brain damage - 2 min,
Cell death - 4-5 min.

Question 6

How much oxygen by volume is contained within the earth’s atmosphere? (2d.p.)

Answer 6

20.95%

Question 7

At 20ºC and 50% humidity, what is the water vapour pressure?

Answer 7

17.5mmHg.

Question 8

What is pO2 at 20ºC and 50% humidity?

Answer 8

155.5mmHg.

Question 9

Does the amount of time oxygen is in the alveoli influence the pO2 of oxygen?

Answer 9

Yes, it lowers it.

Question 10

What does myoglobin facilitate in humans?

Answer 10

The diffusion of oxygen.

Question 11

What was myoglobin first purified from, by whom, and when?

Answer 11

Whale blood.

Max Perutz, 1958.

Question 12

How much of the main chain is folded into RH α-helices?

Answer 12

75%.

Question 13

How many amino acids does myoglobin consist of, and how much does it weigh?

Answer 13

155 amino acids, 17kDa.

Question 14

What terminates helical sequences in myoglobin?

How may the structure of this terminator link to its purpose?

Answer 14

Proline residues.

It’s cyclic, forming a locked conformational angle.

Question 15

What type of residues form the majority of the interior of myoglobin?

Answer 15

Hydrophobic, non-polar.

Question 16

Where is a haem group located, and what is it surrounded by?

Answer 16

In a crevice, surrounded by non-polar residues except for 2 histidines.

Question 17

O2 binding to a haem group is irreversible. How is this prevented?

Answer 17

By enclosing haem in a protein - allows reversible binding.

Question 18

What is O2’s solubility in water?

Answer 18

1X10^-4M.

Question 19

How is the solubility limitation of O2 overcome?

Answer 19

Binds to proteins.

Question 20

What effects does O2 altering the heme electronic structure have?

Answer 20

It causes changes in the heme electronic spectrum, creating bright scarlet colour of blood in arteries, and dark purple colour of blood in veins.

Question 21

What effects does O2 altering the heme electronic structure have?

Answer 21

It causes changes in the heme electronic spectrum, creating bright scarlet colour of blood in arteries, and dark purple colour of blood in veins.

Question 22

What metal ion of note does the haem group contain?

Answer 22

Fe++

Question 23

Is haem a polypeptide?

Answer 23

No.

Question 24

What organic part features in the haem?

Answer 24

protoporphyrin IX.

Question 25

What does the FeII in heme bind to, and in what shape?

Answer 25

4 N molecules in a plane.

Question 26

How many free coordination positions does the FeII have when bonded to 4 Ns? Where are they?

Answer 26

2 (positions 5 and 6). Either side of the haem plane.

Question 27

What is the only thing that can bind to O2 in the haem group?

Answer 27

The FeII state.

Question 28

How are the only two histidines in helices E and F referred to?

Answer 28

``` Distal His (E7) Proximal His (F8). ```

Question 29

Which histidine is the iron of the haem bonded to?

Answer 29

F8 - occupies 5th coordination position.

Question 30

How far out of the plane of the porphyrin is the iron atom?

Answer 30

0.3Å.

Question 31

What can iron in the haem group bind with (given its 6 coordination positions)?

Answer 31

Positions 1-4, 4N of haem group. Position 5, 1N from proximal His. Position 6, H2O or O2. Can also bind CO.

Question 32

What is the 6th coordination position occupied by? | What 2 roles does this have?

Answer 32

Distal histidine at E7. Reduces affinity of binding CO (still higher than O2), sterically blocks formation of myoglobin associates where haem-O2-haem sandwiches could form.

Question 33

What shape does CO form when bound to Fe(II), and why?

Answer 33

Linear, bound tightly.

Question 34

What shape does O2 form when bound to Fe(II), and why?

Answer 34

Bent, bound less tightly.

Question 35

What is p50?

Answer 35

The partial pressure at which 50% of myoglobin molecules have released their O2.

Question 36

What equilibrium can be used to express Myoglobin binding to O2? Therefore, how do you represent the dissociation constant?

Answer 36

Mb + O2 MbO2. Kd = [Mb][O2]/[MbO2].

Question 37

Are kd and p50 the same in the case of myoglobin and O2?

Answer 37

Yes.