3.3.4.1 Mass Transport in animals

Question 1

The haemoglobins

Answer 1

A group of chemically similar molecules found in a variety of organisms

Question 2

What type of protein are haemoglobins?

Answer 2

Quaternary structure proteins - evolved to make it efficient at loading oxygen under one set of conditions and unloading oxygen under a different set of conditions

Question 3

Haemoglobin: primary structure

Answer 3

Sequence of amino acids in the 4 polypeptide chains

Question 4

Haemoglobin: secondary structure

Answer 4

Each polypeptide chain is coiled into a helix

Question 5

Haemoglobin: Tertiary structure

Answer 5

Each polypeptide is folded into a precise shape (important for its ability to carry oxygen)

Question 6

Haemoglobin: Quaternary structure

Answer 6

• All 4 polypeptides are linked together to form an almost spherical molecule.
• Each polypeptide is associated with a haem group

Question 7

Structure of a haem group and how it works

Answer 7

Contains a ferrous ion (Fe2+) which can combine with a single oxygen molecule (O2)

So together it makes 4 x )2 molecules that can be carried by a single haemoglobin molecule in humans

Question 8

Loading or associating oxygen

Answer 8

The process by which haemoglobin binds with oxygen

Question 9

Unloading or dissociating oxygen

Answer 9

The process by which haemoglobin releases its oxygen

Question 10

Where does loading/associating oxygen occur in humans?

Answer 10

Lungs

Question 11

Where does unloading/dissociating oxygen occur in humans?

Answer 11

Tissues

Question 12

Affinity of haemoglobin

Answer 12

Haemoglobin with high affinity for oxygen takes up O2 more easily, and releases it less easily

Question 13

Role of haemoglobin

Answer 13

• Readily associate with O2 at the surface where gas exchange takes place
• Readily dissociate from O2 at those tissues requiring it

These 2 requirements contradict eachother!!

Question 14

How are the contradicting requirements of haemoglobin achieved?

Answer 14

Haemoglobin can change its affinity for O2 under different conditions (its shape changes under the presence of CO2 or O2)

Question 15

Affinity

Answer 15

Chemical attraction

Question 16

Why do different species have different haemoglobins?

Answer 16

Each species has a different shape haemoglobin (due to slightly different amino acid sequence -> leads to slightly different tertiary and quaternary structure -> different O2 binding properties)

Question 17

Oxygen dissociation curves

Answer 17

Graph that shows the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen

Question 18

Shape of oxygen dissociation curve: 1

Answer 18

• The haemoglobin molecule’s shape makes it difficult for the 1st O2 molecule to bind to one of the sites on its 4 polypeptide subunits -> due to them being closely united.
• Therefore at low O2 concentrations, little O2 binds to haemoglobin -> shallow gradient

Question 19

Shape of oxygen dissociation curve: 2

Answer 19

• The binding of the 1st O2 molecule changes the quaternary structure of the haemoglobin molecule -> causing it to change shape
• The change in shape makes it easier for the other subunits to bind to the O2 -> **the binding of the 1st O2 molecule induces the other subunits to bind to an O2 molecule

Question 20

Shape of oxygen dissociation curve: 3

Answer 20

• It only takes smaller increase in the partial pressure of O2 to bind the 2nd O2 molecule than it did to bind to the 1st one = positive cooperativity -> gradient steepens

Question 21

Positive cooperativity

Answer 21

Binding of the 1st molecule makes binding of the 2nd easier and so on.

Question 22

Shape of oxygen dissociation curve: 4

Answer 22

After the binding of the 3rd molecule, although theoretically it should be easer for the 4th molecule to bind, it is not practically due to probability -> gradient of the curve reduces and the graph flattens off

Question 23

Movement of the oxygen dissociation curve

Answer 23

• Shift to the left
• Shift to the right

Question 24

Shift to the left of the oxygen dissociation curve

Answer 24

The further to the left the curve, the greater the affinity of haemoglobin for oxygen (so it loads oxygen readily but unloads it less easily)