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Transcript
Lesson starter • What three elements are common to fats, carbohydrates and proteins? • What reaction unites single units of fats, carbohydrates and proteins? • What type of bond forms between: – Fats – Carbohydrates – proteins Title: The role of haemoglobin 23 May 2017 Learning question: Why is haemoglobin integral to our survival? Homework: Globular and fibrous proteins Fibrous proteins • Polypeptides join together to form long fibres or sheets. • Fibrous proteins are insoluble in water • Tend to be used for structural functions – Keratin (human hair) – Collagen (give skin elasticity amongst other things) Globular proteins • These proteins are roughly spherical, or globular in shape • Usually soluble in water and tend to have biochemical functions • Examples include – Enzymes – Haemoglobin • Folded in a particular way so that R groups are on the outside so that they are soluble in water based liquids e.g. cytoplasm and blood plasma. Summary • Write down the main differences between fibrous and globular proteins Denaturation • Tertiary structure of globular proteins is held together by fairly weak hydrogen bonds • High temperatures cause molecules to vibrate more. If protein molecules vibrate too much, weak hydrogen bonds will break. • This changes the conformation of the protein – the protein is denatured. • Most proteins denature at about 45oC Denaturation • Hydrogen bonds depend on weak attractions between H+ and O- in different parts of a protein molecule. • Ionic bonds also depend on small charges like this. • Because of the nature of these bonds, pH changes can break these bonds Denaturation • pH measures the concentration of hydrogen ions (positively charged, H+) • As the concentration of H+ ions surrounding the protein increases or decreases, this affects the charges holding the globular protein together. • If these bonds break, the protein can become denatured. Summary • What is denaturation? • What factors can cause denaturation in proteins? • Explain how these factors cause denaturation Carrying oxygen • Haemoglobin is made of 4 polypeptide chains. • Each has a haem group attached. • The haem group is a non-protein part of the protein structure and is called a prosthetic group. Carrying oxygen • The iron ion in the middle of the haem groups can associate or disassociate with oxygen. • This means that 4 oxygen molecules can combine with one RBC. • When the first haem group combines with oxygen, it changes the shape of haemoglobin, exposing the next haem group. • This makes it easier to pick up more oxygen. Summary • Describe the structure of haemoglobin • Describe what happens when more than one oxygen associates with haemoglobin When things go wrong • Beta thalassaemia – Common in Greek and Italian people – Haemoglobin beta chains are shorter than normal – This means that haemoglobin does not carry as much oxygen as normal haemoglobin When things go wrong • Diabetes – High blood glucose leads to glucose attaching to haemoglobin in red blood cells – This forms “glycosylated haemoglobin” which can pick up oxygen really well – Issues arise because glycosylated haemoglobin does not give up oxygen to respiring tissues very easily – Organs can be damaged by this, including blood vessels in the eyes, which can lead to blindness (diabetic retinopathy) When things go wrong • Sickle Cell Anaemia – Most common in people of African ancestry – Suffers of sickle cell anaemia have haemoglobin in which the alpha chains are normal, but the beta chains have the amino acid valine instead of glutamic acid (substitution mutation) – In the arteries and lungs, oxygen associates with this type of haemoglobin easily – In respiring tissues however, the molecules tend to stick together. When things go wrong • Sickle Cell Anaemia – Haemoglobin with the valine substituted for glutamic acid, changes the formation of the beta chains. – They become long and stiff, causing the red blood cells to change shape also – They become crescent or sickle shaped. Summary • Describe what issues arise for sufferers of: – betathalasemia – Sickle cell anaemia – Diabetes • In relation to oxygen and red blood cells. Questions • Complete questions 1-3 on page 15 • Correct your answers in a different coloured pen.