3.4.1.5: Dissociation curves

Question 1

what is the structure of haemoglobin

Answer 1

4 subunits - 2 alpha and 2 beta, each subunit has a polypeptide chain and a haem group, each haem group associates with one oxygen molecule.

Question 2

how many molecules of oxygen can one molecule of haemoglobin and why

Answer 2

4 molecules of oxygen as one molecule of Hb has 4 polypeptide chains, one chain associates with one oxygen molecule

Question 3

what is partial pressure

Answer 3

the pressure exerted by an individual gas in a mixture

Question 4

what in the haem group does the oxygen molecule bind to

Answer 4

in each haem group there is Fe 2+, oxygen molecule binds to this Fe 2+

Question 5

what is the equation for haemoglobin

Answer 5

Hb + 4O2 <-> HbO8

Question 6

describe and explain the process of co-operative binding in oxygen

Answer 6

At low pO2, it is difficult for oxygen to bind as there is low access to oxygen. When first oxygen molecule associates, the other haem groups open up more making it easier for the second oxygen molecule to associate, for the third - even easier, but for the fourth oxygen molecule to bind, although it is even easier it is less likely to happen as you need large pO2 for it to occur as you need enough oxygen for all 4 haem groups to be saturated

Question 7

what is the shape of a dissociation curve for pO2 and Hb

Answer 7

s shaped curve

Question 8

what does affinity mean

Answer 8

the degree to which a substance tends to combine with another

Question 9

describe the 3 parts (low pO2, middle part of the curve, and high pO2) of a dissociation curve

Answer 9

1- At low pO2, Hb has low % saturation of O2 and so low affinity for oxygen
2- In the middle part of the curve, a small change in pO2 results in a large change in % saturation
3- At high pO2, Hb has high % saturation of O2 and so high affinity for oxygen

Question 10

What happens to the dissociation curve of pO2 and Hb when there is a small increase in respiration rate

Answer 10

small increase in respiration rate, leads to a small decrease in pO2 of blood, and so a large decrease in % sat of Hb of oxygen, therefore more O2 is supplied to tissues and increased respiration rate is maintined

Question 11

Describe the process of Hb being associated with oxygen
and write the equation

Answer 11

Oxygen diffuses into blood plasma, increased pO2 of blood plasma, increased Hb affinity of oxygen, and so association of oxygen with Hb occurs
Hb + 4O2 -> HbO8

Question 12

Describe the process of Hb being dissociated with oxygen
and write the equation

Answer 12

Oxygen diffuses into respiring tissue (muscle cells), decrease in pO2 of blood plasma, decreased Hb affinity for oxygen, and so dissociation of oxygen occurs
Hb + 4O2 <- HbO8

Question 13

Does oxygen load or unload in the alveoli

Answer 13

load

Question 14

does oxygen load or unload in muscle tissues

Answer 14

unload

Question 15

What does a left shift mean on a dissociation curve

Answer 15

Hb has increased affinity for oxygen which means that there is more oxygen availability in the environment of the organism

Question 16

What does a right shift mean on a dissociation curve and name the effect

Answer 16

Bohr effect:
increase in pCO2 in blood (as there is an increase in activity and so increase in aerobic respiration)
decrease in pH of blood
decreased affinity of Hb for O2
more O2 unloaded at the same pO2
so more O2 released to tissues overall
so tissues can maintain increased rate of aerobic respiration

Question 17

What are the advantages of a left shift on a dissociation curve and which organisms do this?

Answer 17

llama and foetus
advantages: in low pO2 conditions, Llamal Hb can still associate with a lot of O2 and therefore can still achieve high % saturations levels at low pO2, so O2 can be unloaded to tissues at low pO2 to maintain aerobic respiration even in low O2 environments