Lesson 9 - Transport of Oxygen and Carbon dioxide in the blood

Question 1

Erthyroctyes

Answer 1

Red blood cells

Question 2

Adaptations of Erythrocytes:

Answer 2

• Biconcave shape
• No nuclei

Question 3

Effects of biconcave structure

Answer 3

• Large surface area for diffusion of gases
• Helps pass through narrow capillaries

Question 4

Where are RBCs formed?

Answer 4

Red bone marrow

Question 5

Effects of no nuclei of RBCs?

Answer 5

• Limits lifetime
• More haemoglobin fits into cells

Question 6

Haemoglobin:

Answer 6

Red pigment that carries oxygen and gives RBCs colour

Question 7

Structure of haemoglobin?

Answer 7

• Large globular conjugated protein
• Quaternary structure
• 4 polypeptide chains. Each has an iron containing haem prosthetic group

Question 8

Reaction between oxygen + haemoglobin and oxyhaemoglobin

Answer 8

Reversible reaction
Hb + 4O2 –> Hb(O2)4

Question 9

Name for process:
- Oxygen binds to haem group
- Molecule changes shape
- Easier for the next oxygen to bind

Answer 9

Positive cooperativity

Question 10

Definition of haemoglobin

Answer 10

A group of chemically similar molecules found in a wide variety of organisms. Protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions but unloading it under a different set of conditions. It has four polypeptide chains which are linked together – each polypeptide is associated with a haem group which contains a ferrous (Fe2+) ion which can combine with an oxygen molecule (O2).

Question 11

Loading oxygen

Answer 11

The process by which haemoglobin binds with oxygen. Associating.
In humans this takes place in the lungs.

Question 12

Oxygen unloading:

Answer 12

Process by which haemoglobin releases oxygen. Dissociation.
Occurs in humans in tissues

Question 13

High affinity:

Answer 13

Haemoglobins with this for oxygen take up oxygen more easily but release it less easily.

Question 14

Low affinity:

Answer 14

Haemoglobin with this for oxygen takes up oxygen less easily but releases it more easily.

Question 15

Oxygen dissociation curve:

Answer 15

The graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen. Shows how at low oxygen concentrations little oxygen binds to haemoglobin (shallow gradient initially). After the first oxygen molecule binding the quaternary structure of the haemoglobin molecule changes, making it easier for the other subunits to bind an oxygen molecule, therefore it takes a smaller increase in the partial pressure of oxygen to bind the second molecule and third molecule so the gradient steepens. After the binding of the third molecule, it is less likely that a single oxygen molecule will find an empty site to bind to so the gradient of the curve reduces and the graph flattens off.

Question 16

Positive cooperativity

Answer 16

Binding of the first molecule makes binding of the second easier and so on, so the gradient of the curve steepens.

Question 17

Partial pressure

Answer 17

A measure of the concentration of a gas in a mixture of gases by calculating the pressure it contributes to the overall pressure.

Question 18

Bohr shift

Answer 18

The greater the concentration of carbon dioxide the more readily the haemoglobin releases its oxygen because the more carbon dioxide there is, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded, the more oxygen is available for respiration.

Question 19

How many oxygen molecules can bind to one haemoglobin molecule?

Answer 19

4

One oxygen molecule (O2) binds to one Fe2+ molecule.

Question 20

Conditions that effect haemoglobin’s affinity for oxygen?

Answer 20

• Partial pressure of oxygen (pO2)
• Haemoglobin saturation
• Partial pressure of carbon dioxide (pCO2)

Question 21

High affinity –>

Answer 21

high pO2
low pCO2

Question 22

How does pCO2 effect haemoglobin’s affinity for oxygen?

Answer 22

CO2 leads to reduction in pH of blood. Water and CO2 react to form carbonic acid.

Low pH causes the tertiary structure of haemoglobin to be altered, decreasing affinity for oxygen. This is known as the bohr effect.

Question 23

Bohr shift

Answer 23

Left -> pH increases
Right -> pH decreases

Question 24

Haemoglobin of foetus in the womb?

Answer 24

Higher affinity.

Low oxygen –> shift to the left

Question 25

Why does foetus haemoglobin have a high affinity to oxygen?

Answer 25

A different structure gives foetal haemoglobin a greater affinity to oxygen than adult haemoglobin. Oxygen binds to foetal haemoglobin more easily and is more reluctant to dissociate. This is important, as foetal haemoglobin needs to “steal” oxygen away from the mother’s haemoglobin when they pass in the placenta. If the foetal and maternal haemoglobin had the same affinity for oxygen, there would be no incentive for the oxygen to switch from the maternal blood to foetal blood.

Question 26

Low oxygen environments examples:

Answer 26

• High altitude
• Live in sand or sea bed

Question 27

Animals living in low oxygen environment haemoglobin?

Answer 27

High affinity
Low oxygen –> left

Question 28

Smaller organisms with high SA:V

Answer 28

lower affinity
High respiration –> right

Question 29

Organisms with high metabolic rate

Answer 29

lower affinity
High respirations –> shift to right

Question 30

Higher metabolic rate explanation

Answer 30

Higher metabolic rate = more respiration = greater oxygen demand. This means the organisms need haemoglobin with a lower affinity for oxygen as they need it to easily unload oxygen to meet their high oxygen demand and allow a faster respiration rate.

Question 31

Larger SA:V explanation

Answer 31

Small mammals that have a higher SA:V than larger mammals will lose heat more quickly so they have a higher metabolic rate to help maintain their body temperature. Other high activity organisms will also have a higher metabolic rate.

Question 32

Means of transporting carbon dioxide:

Answer 32

• 5% dissolved in plasma
• Carbaminohaemoglobin
• Hydrogen carbonate ions in cytoplasm of red blood cells

Question 33

Carbaminohaemoglobin:

Answer 33

CO2 is combined with amino groups in the polypeptide chains of haemoglobin to form a compound.

Question 34

Hydrogen carbonate ions

Answer 34

HCO3^-

Question 35

Reaction of CO2 and water to carbonic acid to hydrogen and hydrogen carbonate ions

Answer 35

CO2 + H2O <–> H2CO3 <–> H+ + HCO3-

Question 36

How does reaction of carbon dioxide and water occur in blood plasma?

Answer 36

Slowly

Question 37

How does reaction of carbon dioxide and water occur in the red blood cells?

Answer 37

High levels of enzyme carbonic anhydrase.

Question 38

Chloride shift

Answer 38

Negatively charged hydrogen carbonate ions move out of erythrocytes into the plasma by diffusion down a concentration gradient. Negatively charged chloride ions move into the erythrocytes, which maintains the electrical balance of the cell.

Question 39

Why is CO2 converted into HCO3- ions.

Answer 39

Maintain steep concentration gradient of CO2 to diffuse from the respiring tissue into the erythrocytes.

Question 40

When there is a relatively low CO2 concentration?

Answer 40

Hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form carbonic acid.
Chloride ions diffuse out of the RBCs back into the plasma down the electrochemical gradient.

Question 41

Haemoglobins role in the chloride shift

Answer 41

• Acts as a buffer
• Prevents change in pH by accepting free hydrogen ions in a reversable reaction to form haemoglobinic acid

Question 42

Haemoglobinic acid

Answer 42

Hydrogen ions + haemoglobin