Describe the differences between mRNA and tRNA Lesson starter Describe the differences between mRNA and tRNA

Oxygen transport in the body describe and explain the oxygen dissociation curve for haemoglobin; describe and explain the significance of the oxygen dissociation curves of adult oxyhaemoglobin at different levels of carbon dioxide (Bohr effect); describe and explain the difference in affinity for oxygen between haemoglobin and myoglobin; describe and explain the build up of an oxygen deficit and oxygen debt/EPOC (Excess Post-exercise Oxygen Consumption);

Haemoglobin and myoglobin

Haemoglobin Majority of blood’s oxygen is combined with haemoglobin as oxyhaemoglobin 4 molecules of oxygen can be carried by one haemoglobin Oxygen is tightly bound to the haem groups When all haem groups are occupied, the molecule is said to be saturated. One of 4 prosthetic haem groups where oxygen combines

Myoglobin Only has one haem group and only one polypeptide chain Acts as an oxygen reserve in the muscles Only gives up oxygen when concentration is very low e.g. intense exercise Much higher affinity for oxygen than haemoglobin

Question Compare the structure of haemoglobin and myoglobin. Write you answer out in full sentences

Oxygen association/dissociation Where would you get lots of oxygen combining with haemoglobin? Disassociation Where would you get lots of oxygen leaving haemoglobin?

Oxygen association/dissociation pO2 refers to the partial pressure of oxygen At low pO2 oxygen finds it difficult to join up with haemoglobin  this means there is not a lot of percentage saturation of haemoglobin As the pO2 builds up, it gets easier for oxygen to combine with haemoglobin  If the pO2 gets too high however, haemoglobin cannot get fully saturated, so the curve starts to level off (plateau). This gives an S-shaped, or sigmoid curve. 3 2 1

Dissociation curves for haemoglobin The S-shaped dissociation curve is of physiological importance to the body Haemoglobin becomes saturated in the lungs where the pO2 is high. The opposite is true for respiring tissues such as muscle. This means that when RBCs in capillaries get to muscle tissue, oxygen quickly unloads from haemoglobin. This is seen in the steep part of the curve % saturation of haemoglobin Partial pressure of oxygen (Kpa)

Questions Why do you think haemoglobin is used to transport oxygen around the body? Why is the dissociation curve for oxygen described as S-shaped? Remember to write your answers in sentences

The Bohr shift and effect of CO2 on the oxygen dissociation curve Carbon dioxide can be dissolved in blood plasma to form carbonic acid When this acid dissociates, it forms H+ ions and bicarbonate ions. The H+ ions are picked up by haemoglobin to form haemoglobinic acid Haemoglobin acts as a buffer to prevent a drop in blood pH levels The effect this causes is to lower the affinity of haemoglobin for oxygen. This means that oxygen is given up to the surrounding tissues easier, even when the pO2 is high

The Bohr shift and effect of CO2 on the oxygen dissociation curve The effect of increasing CO2 levels on % saturation of haemoglobin is called the Bohr effect. The effect of shifting along the S-shaped curve to the right is known as the Bohr shift. It is significant to the human body because it leads to greater unloading of oxygen from haemoglobin when the concentration of CO2 is high i.e. during exercise

The oxygen debt and excessive post-exercise oxygen consumption (EPOC) After exercise, oxyhaemoglobin and oxymyoglobin stores need to be replenished. This occurs during the recovery period.

The graph eventually levels out when the oxygen usage is equal to oxygen delivery and uptake by cells. At this point, the Bohr effect is shifting the S-shaped curve to the right, allowing oxygen to leave haemoglobin easily. O2 uptake rises over the first few minutes of exercise. Eventually, ATP demand cannot be met therefore anaerobic respiration takes place Creatine phosphate (energy store in muscles) can be used when ATP is in short supply. Myoglobin unloads oxygen to release energy, but some lactate will be produced as ATP is made anaerobically

The oxygen debt and excessive post-exercise oxygen consumption (EPOC) As exercise stops, O2 uptake in cells decreases, but is still higher than at rest. This phase is known as the oxygen debt. The purpose of this is to: Reload stocks of oxyhaemoglobin and oxymyoglobin Replace stocks of ATP, creatine phosphate and glycogen Convert lactate, made during aerobic respiration, to glucose or glycogen Meet the demands of increased metabolic rate, heart and respiratory functions as a result of the temperature rise during exercise EPOC = total oxygen consumed after exercise – pre-exercise level of oxygen consumption

Question Explain why most exercise will result in an oxygen debt being formed even if the person does not push themselves so hard that they go above their aerobic threshold.