What do you already know about haemoglobin? Clue: it’s a protein

What are proteins? Proteins are made up of C, H, O, N and some S and P Transport proteins such as haemoglobin carry oxygen. The monomer molecules making up proteins are called amino acids. There are 20 different naturally occurring amino acids. All amino acids have the same general structure: A carboxyl group (-COOH) An amino group (-NH2) attached to a C atom A variable group called R

Joining amino acids together When amino acids join together, they do so by a condensation reaction. This means one water molecule is removed, using the OH group from the carboxyl group of one amino acid, and one H from the amino group of another. The resulting bond is called a peptide bond.

Proteins have 4 structural levels. Proteins are big, complicated, 3-dimensional molecules. The structure is described in four ‘levels’: Primary Secondary Tertiary Quaternary

Primary structure The primary structure of a protein is the sequence of amino acids in the chain. The primary structure determines the eventual shape of the protein, hence its function.

Secondary structure The amino acids in the primary structure of a protein do not lie flat and straight. Hydrogen bonds form between the amino acids in the chain. This makes the protein coil into an a helix or fold into a b pleated sheet. This is the secondary structure.

Tertiary structure The coiled or folded chains often coil or fold further. More bonds form due to interactions between the R-groups of the polypeptide chain. This is called the tertiary structure. For proteins formed from a single polypeptide chain this is the final 3D structure of the protein.

Protein bonds The four structural levels in proteins are held together by different bonds: Peptide bonds (primary) Hydrogen bonds (secondary and tertiary) Ionic bonds (tertiary) Disulphide bonds (tertiary) Hydrophobic and hydrophilic interactions (tertiary) Quaternary structure depends on the tertiary structure of the individual polypeptides, and so is influenced by all these bond types.

Quaternary structure Some proteins are made up of several polypeptide chains held together by bonds. The quaternary structure is how these chains are put together. The best known example is haemoglobin, which is made of four polypeptide chains bonded together. For proteins such as haemoglobin, the quaternary structure determines the final 3D structure.

Haemoglobin

Types of protein Globular proteins – these are round, compact and easily soluble so they can be transported in fluids. Examples are haemoglobin and enzymes.

Haemoglobin Haemoglobin is a globular protein. It’s structure is curled up so that hydrophilic side chains face outwards and hydrophobic side chains face inwards. This makes haemoglobin soluble and therefore good for transport in the blood.

What is this? One blood cell contains about 280 million molecules of haemoglobin

WHAT? HOW? WHERE? WHEN? WHY?

Specification The haemoglobins are a group of chemically similar molecules found in many different organisms. Haemoglobin is a protein with a quaternary structure. The role of haemoglobin in the transport of oxygen. The loading, transport and unloading of oxygen in relation to the oxygen dissociation curve. The effects of carbon dioxide concentration. Candidates should be aware that different organisms possess different types of haemoglobin with different oxygen transporting properties. They should be able to relate these to the environment and way of life of the organism concerned. There is an attached file with specification points for AQA for pupils to self assess how they feel about this topic. This is better used for a revision lesson.

Learning Outcomes: We will revise haemoglobin, looking at the structure and function. We will look at why there is a need for different types of haemoglobin, and what animals these may be associated with and why.

crabs, lobsters, snails, octopus have blue blood. Haemoglobin Haemocyanin β - polypeptide α - polypeptide Copper unit Haem unit crabs, lobsters, snails, octopus have blue blood.

Task: Haemoglobin – true/false piles regarding structure, role, different types, affinity, load and unload. Attached.

This can be summarised as: Hb + 4O2 Hb(O2)4 Oxygen Transport Haemoglobin is globular protein which is made up of 4 peptide chains, each chain contains one haem (iron) group. Each haem group can combine with one oxygen molecule (O2). This can be summarised as: Hb + 4O2 Hb(O2)4 Note – this is a reversible reaction

Haemoglobin in different species 2+ Haemoglobin in different species The structure of haem is the same in all haemoglobin, but the globin chains vary between species. What causes this change?

Haemoglobin reversibly binds with oxygen so is a good transporter of oxygen: At the gas exchange surface e.g. lungs: Haemoglobin has a high affinity for O2 so O2 binds At the respiring tissues: Haemoglobin has a low affinity for oxygen. The high conc. of CO2 causes haemoglobin to change shape, releasing oxygen.

Terms Affinity Saturation Partial pressure Loading Unloading

Partial Pressure of O2: The partial pressure of oxygen (pO2) is a measure of oxygen concentration. pO2 will be high in the lungs, and lower in body tissues such as muscle. Haemoglobin's affinity for oxygen depends on the pO2. Oxygen combines with haemoglobin to form oxyhaemoglobin where there's a high pO2, and oxyhaemoglobin breaks down to haemoglobin and oxygen where there's a lower pO2.

Lungs Tissues Partial pressure of O2 Hb affinity for O2 Hb saturation

Lungs Tissues Partial pressure of O2 High Low Hb affinity for O2 Hb satuartion

3 10 4 25 7 75 95 15 97 Partial pressure of O2 (kPa) Saturation of haemoglobin with oxygen (%) 3 10 4 25 7 75 95 15 97

Draw a line up and across where haemoglobin loads oxygen in the lungs. What is the likely percentage saturation of haemoglobin in the lungs? Draw a line up and across where haemoglobin loads oxygen in the lungs.

Lungs 10 95

Is the percentage saturation of haemoglobin with oxygen high or low when the partial pressure of oxygen is low? Draw a line up and across where haemoglobin unloads oxygen in the tissues.

25 4 Active Tissues

Oxygen will move from high to low partial pressure of oxygen. Blood arriving at the lungs has a lower pO2 than that in the lungs. There is therefore a diffusion gradient and oxygen will move from the alveoli into the blood. The O2 is then loaded onto the Hb until the blood is about 96% saturated with oxygen. The Hb is now called oxyhaemoglobin (HbO2). The blood is then taken to tissues where the cells are respiring all the time, using oxygen. The pO2 will be low. As the red blood cell enters this region, the Hb will start to unload the O2, which will diffuse into the tissues and be used for further respiration. Since much of the Hb will have unloaded the O2, a much lower percentage of the blood will be saturated with O2. Oxygen will move from high to low partial pressure of oxygen. Oxygen Carbon dioxide

Why is the curve S shaped? At higher partial pressures there isn’t a great deal of change in the saturation of the Hb A small change in the pO2 can result in a large change in the percentage saturation of the blood At lower partial pressures there isn’t a great deal of change in the saturation of the Hb

Why is the curve S shaped? It flattens off at the top because joining the fourth O2 is more difficult. After the Hb has changed shape a little, it becomes easier and easier for the second and third O2 to join. The first molecule of O2 combines with an Hb and slightly distorts it. The joining of the first is quite slow.

What is the rate of oxygen loading: 0 – 1 kPa 2 – 3 kPa 8 – 10 kPa

Haemoglobin Saturation at High Values Lungs at sea level: PO2 of 100mmHg haemoglobin is 98% SATURATED Lungs at high elevations: PO2 of 80mmHg, haemoglobin 95 % saturated When the PO2 in the lungs declines below typical sea level values, haemoglobin still has a high affinity for O2 and remains almost fully saturated. Even though PO2 differs by 20 mmHg there is almost no difference in haemoglobin saturation.

The blood system carries the red cells through the pulmonary vein, to the heart and out through arteries and arterioles to the tissues where oxygen is finally unloaded. Explain why the haemoglobin does not unload its oxygen until it reaches the capillaries in the tissues.

Changes in the Partial Pressures of Oxygen and Carbon Dioxide http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter44/animations.html

Haemoglobin Saturation at Low Values

Describe how haemoglobin loads and unloads oxygen in the blood. (4) Oxygen loads onto haemoglobin at high partial pressure. In the lungs haemoglobin has a high affinity for oxygen. Tissues have a low partial pressure of oxygen as it has been used in respiration. In tissues haemoglobin has a lower affinity for oxygen. Haemoglobin unloads oxygen at low partial pressure.

Explain how oxygen is loaded, transported and unloaded in the blood

Haemoglobin carries oxygen (or has a high affinity for oxygen, or oxyhaemoglobin; In red blood cells; Loading of oxygen takes place in the lungs; At high p.O2; Unloads oxygen to respiring cells or tissues; At low p.O2; Unloading linked to higher carbon dioxide (concentration);

Factors that effect the oxygen dissociation curve.

Conformational change CO2 + H2OH2CO3H+ + HCO3- Carbonic anhydrase Conformational change Decreased affinity for O2

The Effect of Carbon Dioxide: To complicate matters the CO2 concentration also affects how haemoglobin functions! Haemoglobin gives up its oxygen more readily at high partial pressure of CO2 (pCO2). This enables more oxygen to get to cells that are respiring at a high rate. When cells respire they produce CO2, therefore increasing pCO2

What would the graph look like if there were high CO2 levels? Sketch the curve. Remember an increase in CO2 reduces Hb affinity for oxygen.

Plot the O2 dissociation curve for high PCO2 PO2 %SaO2 1 2 10 3 20 4 30 5 40 6 54 7 68 8 80 9 86 90 11 92 12 94 13 97 Plot the O2 dissociation curve for high PCO2 What sort of line should be drawn?

PO2 %SaO2 1 2 10 3 20 4 30 5 40 6 54 7 68 8 80 9 86 90 11 92 12 94 13 97 Because there are no assumptions about the ‘inbetween’ points we use a curve of best fit.

The haemoglobin loses its oxygen more readily The haemoglobin loses its oxygen more readily. This is good – the cells are respiring faster - they need more oxygen.

This increases the rate of oxygen dissociation and the dissociation curves 'shift' to the right. This means the saturation of blood with O2 at a given pO2 is lower because more oxygen is being released. We call this the Bohr effect.

Lungs 10 95 25 4 Active Tissues

Remember levels of carbon dioxide go up when rates of respiration increase. Carbon dioxide dissolves in the blood to form carbonic acid. This change in blood pH affects the haemoglobin in the red blood cells causing them to lose their oxygen more readily. This is known as the Bohr effect.

Factors affecting Disassociation Respiratory Response to Exercise This means that more oxygen is being uploaded from the haemoglobin at tissue level. Factors affecting Disassociation BLOOD TEMPERATURE increased blood temperature reduces haemoglobin affinity for O2 hence more O2 is delivered to warmed-up tissue BLOOD Ph lowering of blood pH (making blood more acidic) caused by presence of H+ ions from lactic acid or carbonic acid reduces affinity of Hb for O2 and more O2 is delivered to acidic sites which are working harder Factors Affecting Haemoglobin Saturation – Blood Acidity If the blood becomes more acidic the dissociation curve shifts right. This means that more oxygen is being uploaded from the haemoglobin at tissue level. See overhead. Factors Affecting Haemoglobin Saturation – Blood Acidity The rightward shift of the curve is due to a decline in pH. This is referred to as the BOHR effect. The pH in the lungs is generally high. So haemoglobin passing through the lungs has a strong affinity for oxygen, encouraging high saturation. At the tissue level, however the pH is lower, causing oxygen to dissociate from haemoglobin, thereby supplying oxygen to the tissues. With exercise, the ability to upload oxygen to the muscles increases as the muscle ph decreases. Factors Affecting Haemoglobin Saturation – Blood Temperature Increased blood temperature shifts the dissociation curve to the right, indicating that oxygen is uploaded more efficiently. Factors Affecting Haemoglobin Saturation – Blood Temperature Because of this, the haemoglobin will upload more oxygen when blood circulates through the metabolically heated active muscles. In the lungs, where the blood might be a bit cooler, haemoglobin’s affinity for oxygen is increased. This encourages oxygen binding. CARBON DIOXIDE CONCENTRATION the higher CO2 concentration in tissue the less the affinity of Hb for O2 so the harder the tissue is working, the more O2 is released

Different types of haemoglobin.

Why have different haemoglobins? Different types of haemoglobins have different affinities for oxygen. Some have a high affinity for oxygen (take up oxygen very easily - but do not release it as readily) Some have a low affinity for oxygen (do not take up oxygen easily - but release it more readily) Organisms with less O2 in their environment (e.g. fish) need haemoglobin with a high affinity for O2 Animals with a high metabolic rate need haemoglobin with a low affinity for O2 so that O2 released more easily at the respiring tissues

Different Haemoglobins Different organism have different haemoglobins, this depends upon the organisms metabolism and environment. Haemoglobins with a high affinity for oxygen. These take up oxygen more easily but release it less readily Haemoglobins with a low affinity for oxygen. These take up oxygen less readily but release it more readily

Foetal haemoglobin. Foetal haemoglobin has a higher affinity for oxygen than maternal haemoglobin

Foetal Haemoglobin: This means maternal haemoglobin will dissociate itself in the placenta and the foetal haemoglobin will load with oxygen. Explain why it is essential for the survival of the foetus that the foetal curve is to the left of the maternal curve.

Higher affinity for oxygen Foetal Heamoglobin Loading tension 50 4 Unloading tension

Higher affinity haemoglobins Myoglobin – red pigment in mammalian muscles. Has a higher affinity for O2 than Hb – only releasing it a very low pp. Myoglobin ‘STORES’ O2.

Llamas. Live at high altitudes where there is less oxygen.

Llamas – high altitude, little O2. Need higher affinity Hb – picks up O2 more readily, but releases it less readily. Curve also shifted to left for other organisms inhabiting low O2 environments – only releasing O2 when pp very low.

Altitude sickness Caused by acute exposure to low partial pressure of oxygen at high altitude Compensated by altitude acclimatisation – body combats it by producing more red blood cells.

Smaller animals – have a high metabolic rate.

Smaller animals (shrews/mice) and birds have curves shifted to the right. Have high metabolism so need O2 to be released readily.

Organisms that live in low oxygen environments have haemoglobin with a higher affinity for O2 than human haemoglobin. The dissociation curve is to the left of ours. Organisms that are very active (high respiration rate) have a high oxygen demand and haemoglobin with a lower affinity for oxygen than human haemoglobin. Their curve lies to the right of ours.