Haemoglobin Use the paper scissors and glue provided

Haemoglobin

Use the paper, scissors and glue provided to build a model of a protein. 10 minutes!

Protein structure 3 of 29 © Boardworks Ltd 2008

Bonds in proteins The 3 D shape of a protein is maintained by several types of bond, including: hydrogen bonds: involved in all levels of structure. hydrophobic interactions: between non-polar sections of the protein. disulfide bonds: one of the strongest and most important type of bond in proteins. Occur between two cysteine amino acids. 4 of 29 © Boardworks Ltd 2008

Fibrous proteins are formed from parallel polypeptide chains held together by cross-links. These form long, rope-like fibres, with high tensile strength and are generally insoluble in water. l collagen – the main component of connective tissue such as ligaments, tendons, cartilage. l keratin – the main component of hard structures such as hair, nails, claws and hooves. l silk – forms spiders’ webs and silkworms’ cocoons. 5 of 29 © Boardworks Ltd 2008

Globular proteins usually have a spherical shape caused by tightly folded polypeptide chains. The chains are usually folded so that hydrophobic groups are on the inside, while the hydrophilic groups are on the outside. This makes many globular proteins soluble in water. l transport proteins – such as haemoglobin, myoglobin and those embedded in membranes. l enzymes – such as lipase and DNA polymerase. l hormones – such as oestrogen and insulin. 6 of 29 © Boardworks Ltd 2008

Haemoglobin is a protein making up 95% of the dry mass of a red blood cell. It is the means of transport of oxygen around the body. Haemoglobin is made up of four polypeptide chains, each bound to one haem group. Each haem group can combine with one oxygen molecule, so that one molecule of haemoglobin can combine with a maximum of four oxygen molecules. This forms oxyhaemoglobin. polypeptide chain 7 of 28 © Boardworks Ltd 2008

Independent learning Try to complete tasks 1 -3 on the sheet. 15 minutes If you finish early, get a textbook and start reading about oxygen dissociation curves. 8 of 28 © Boardworks Ltd 2008

How is oxygen concentration measured? Oxygen binds to haemoglobin when oxygen is at a high concentration, and dissociates from haemoglobin when oxygen is at a low concentration. The concentration of a gas in a mixture of gases can be quantified in terms of its partial pressure. This is the amount of pressure exerted by the gas relative to the total pressure exerted by all the gases in the mixture. Partial pressure is measured in kilopascals (k. Pa) and is written as PO 2, PCO 2, etc. 9 of 28 © Boardworks Ltd 2008

The oxygen dissociation curve 10 of 28 © Boardworks Ltd 2008

Factors affecting oxygen dissociation 11 of 28 © Boardworks Ltd 2008

Foetal haemoglobin The red blood cells in the foetal bloodstream contain a special form of haemoglobin known as foetal haemoglobin. This helps maximize oxygen uptake from the mother’s blood stream, which has already lost some of its oxygen by the time it reaches the placenta. 12 of 28 100 90 80 70 60 50 40 30 20 10 0 foetal haemoglobin oxyhaemoglobin (% saturation) Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin 0 2 4 6 8 10 12 14 oxygen partial pressure (k. Pa) © Boardworks Ltd 2008

What is myoglobin? Myoglobin is a molecule with a similar structure to haemoglobin, but with only one haem group. This means oxymyoglobin will only dissociate when oxygen levels are low. It is found in muscle cells, where it acts as an oxygen reserve. 13 of 28 100 90 80 70 60 50 40 30 20 10 0 myoglobin oxyhaemoglobin (% saturation) Myoglobin has a very high affinity for oxygen, even at very low partial pressures. haemoglobin 0 2 4 6 8 10 12 14 oxygen partial pressure (k. Pa) © Boardworks Ltd 2008