10. The Variety Of Life

Question 0

Describe the secondary structure of a haemoglobin molecule.

Answer 0

Secondary structure: in which each of these polypeptide chains is coiled into a helix.

Question 1

Describe the primary structure of a haemoglobin molecule:

Answer 1

Primary structure: four polypeptide chains.

Question 2

Describe the tertiary structure of a haemoglobin molecule.

Answer 2

Tertiary structure: in which each polypeptide chain is folded into a precise shape - an important factor in its ability to carry oxygen.

Question 3

Describe the quaternary structure of a haemoglobin molecule.

Answer 3

Quaternary structure: in which all polypeptides are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group- which contains a ferrous (Fe2+) ion. Each Fe2+ ion can combine with a single oxygen molecule (O2) making a total of four O2 molecules that can be carried by a single haemoglobin molecule in humans.

Question 4

What is the role of haemoglobin?

Answer 4

To transport oxygen.

Question 5

To be efficient at transporting oxygen haemoglobin must:

Answer 5

Readily associate with oxygen at the surface where gas exchange takes place.
Readily dissociate from oxygen at those tissues requiring it.

Question 6

As a result of which property are the requirements of haemoglobin achieved?

Answer 6

It changes it’s affinity for oxygen under different conditions. It’s shape changes in the presence of certain substances, for example, carbon dioxide.

Question 7

At the gas exchange surface where the oxygen concentration is high and carbon dioxide concentration low what is the affinity of haemoglobin and what is the result of this?

Answer 7

High haemoglobin affinity for oxygen - oxygen is attached.

Question 8

At respiring tissues where oxygen levels are low and carbon dioxide levels are high what is the affinity of haemoglobin for oxygen and what is the result?

Answer 8

Low haemoglobin affinity for oxygen and so oxygen is released.

Question 9

Describe haemoglobins with a high oxygen affinity.

Answer 9

These take up oxygen more easily but release it less readily.

Question 10

Describe haemoglobins with a low oxygen affinity.

Answer 10

These take up oxygen less easily but release it more readily.

Question 11

There is a correlation between…

Answer 11

The type of haemoglobin in an organism and factors such as the environment in which it lives or it’s metabolic rate.

Question 12

An organism living in an environment with little oxygen requires…

Answer 12

A haemoglobin that readily combines with oxygen if it is to absorb enough of it.

(Provided that the organism’s metabolic rate is not very high, the fact that this form of haemoglobin does not release it’s oxygen as readily into the tissues will not be a problem.)

Question 13

An organism with a high metabolic rate needs…

Answer 13

Haemoglobins with a low oxygen affinity. Oxygen must be readily released into its tissues. As long as there is plenty of oxygen in the organism’s environment, it is more important that the haemoglobin releases oxygen readily rather than taking it up readily.

Question 14

Why do different haemoglobins have different affinities for oxygen.

Answer 14

Different haemoglobin molecules have slightly different sequences of amino acids and therefore slightly different shapes.

Question 15

What is loading/associating?

Answer 15

The process by which haemoglobin combines with oxygen.

Question 16

What is unloading/dissociating?

Answer 16

The process in which haemoglobin releases it’s oxygen.

Question 17

When haemoglobin is exposed to different partial pressures of oxygen…

Answer 17

It does not absorb the oxygen evenly.

Question 18

How does haemoglobin absorb the first oxygen molecule at very low concentrations of oxygen?

Answer 18

The four peptides of the haemoglobin molecule are closely united and so it is difficult to absorb the first oxygen molecule.

Question 19

What happens after the first oxygen molecule is loaded?

Answer 19

The initial oxygen molecule causes the polypeptides to load the remaining three oxygen molecule very easily.

Question 20

What is the loading/unloading graph of oxygen to/from haemoglobin named?

Answer 20

The oxygen dissociation curve.

Question 21

In the oxygen dissociation curve why does it level off at the top?

Answer 21

The haemoglobin is almost saturated with oxygen.

Question 22

What occurs in the middle of the oxygen dissociation curve?

Answer 22

A very small decrease in the partial pressure of oxygen leads to a lot of oxygen becoming dissociated from haemoglobin.

Question 23

There are a number of different types of haemoglobin molecules…

Answer 23

Each with a different shape and hence, different affinity for oxygen.
The shape of any one type of haemoglobin can change under different conditions.

Question 24

What are there a large number of because of the variability of haemoglobin molecules?

Answer 24

There are a large number of different oxygen dissociation curves. They all have a roughly similar shape but differ in their position on the axes.

Question 25

If an oxygen dissociation curve is far to the left what is the oxygen affinity?

Answer 25

The further to the left, the greater the oxygen affinity.

Question 26

If an oxygen dissociation curve is far to the right what is the oxygen affinity?

Answer 26

The further to the right, the lower the oxygen affinity.

Question 27

Haemoglobin has a ............ Affinity for oxygen in the presence of carbon dioxide.

Answer 27

Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.

Question 28

E greater the concentration of carbon dioxide...

Answer 28

The more readily the haemoglobin releases its oxygen.

Question 29

At the gas exchange surface (lungs) how high are carbon dioxide levels? What effect does this have on the oxygen affinity of the haemoglobin?

Answer 29

The level of carbon dioxide is low because it diffuses across the exchange surface and is expelled from the organism. Therefore the oxygen affinity is increased, which, coupled with the high concentration of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin. The curve is to the left.

Question 30

In rapidly respiring tissues the level of carbon dioxide is high. What is the oxygen affinity of haemoglobin near these tissues?

Answer 30

The affinity for oxygen is low, the coupled with the low oxygen concentration in the muscles means oxygen is readily unloaded from the haemoglobin into the muscle cells. The curve is to the right.

Question 31

Explain this statement: the greater the concentration of carbon dioxide, the more readily haemoglobin releases it's oxygen.

Answer 31

Dissolved carbon dioxide is acidic and the low pH causes haemoglobin to change shape.

Question 32

If carbon dioxide concentration is high, where does the oxygen dissociation curve shift to?

Answer 32

The right, the lower pH changes the shape of haemoglobin to one with a lower affinity for oxygen. Oxygen is released to highly respiring tissues readily.

Question 33

Tell me the carbon dioxide/affinity for oxygen in haemoglobin cycle/progression.

Answer 33

The higher the rate of respiration --> the more carbon dioxide the tissues produce --> the lower the pH --> the greater the haemoglobin shape change --> the more readily oxygen is unloaded --> the more oxygen is available for respiration.

Question 34

How many oxygen molecules are released form one haemoglobin molecule in i) low respiratory rate ii) high respiratory rate

Answer 34

i) 1 | ii) 3