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Proteins 2
Structures of proteins 2.
| Question | Answer |
|---|---|
| What is the tertiary structure of proteins? | The 3D folding of secondary structure. |
| How does the tertiary structure relate to the aqueous environment? | Hydrophobic residues are buried and hydrophilic residues are exposed outwards to the aqueous environment. |
| What is a domain of a protein? | Many proteins are organised into multiple domains. Each domain contributes a specific function to the overall protein. Different proteins may share similar domain structures (e.g. kinase). |
| What are the three types of tertiary structures? | Alpha helical, beta sheets and a mixture of the two. |
| What are the bonds that stabilize the tertiary structure? | Disulphide bonds. H-bonds. Ionic interactions. Van der Waals interactions. Hydrophobic interactions. |
| How is a disulphide bond formed? | The SH groups of two neighbouring cysteine residues form a covalent -S-S- bond. |
| What is the quaternary structure? | The association of more than one polypeptide. |
| What is a single peptide chain called in the protein? | A subunit. |
| What is the function and other name of haemoglobin? | Carries oxygen in red blood cells (erythrocytes). |
| What is the structure of haemoglobin? | A symmetrical assembly of two different subunits (2 alpha globin and 2 beta globin chains). Each polypeptide chain contains a haem group. |
| What is an Haem? | Porphyrin ring with coordinated Fe atom- binds oxygen for transport to tissues. |
| What maintains the structure of the Haem? | Each haem molecule is held in place by hydrogen bonds from histidine F8 and the bound oxygen molecule stabilised by histidine E7. |
| What happens when oxygen binds to the haem? | O2 binding to the haem causes a change in the ring structure. This in turn influences the structure of haemoglobin and binding of further O2 molecules. |
| What happens to the affinity of oxygen after the first molecule binds? | The affinity of the first oxygen molecule is low but binding of subsequent oxygen molecules is then increased. |
| What causes the increase for oxygen in the Haem? | Upon oxygen binding, the histidine that H-bonds to the Haem molecule in helix F (F8) changes position. This causes major structural changes in the globin subunit. |
| Why is the change in affinity of oxygen biologically significant? | Relatively small changes in oxygen concentration result in large changes in the interaction of haemoglobin with oxygen. |
| What causes sickle cell anaemia? | Caused by a single amino acid change at position 6 in the beta chain of haemoglobin. |
| Which amino acid is changed in sickle cell anaemia? | Hydrophilic glutamic acid to hydrophobic valine. |
| What does the change in amino acid sequence in erythrocytes cause? | This causes sickling of erythrocytes due to aggregation of mutated haemoglobin that forms stiff fibres (change in surface chemistry of the protein). |
| What is the Bohr effect? | The pH of the blood influences oxygen binding to haemoglobin. |
| How does CO2 affect oxygen affinity? | CO2 (acidic) builds up during exercise, which lowers blood pH facilitating faster oxygen delivery. |
| How is foetal haemoglobin different to adult haemoglobin? | It has a different quaternary structure: composed of two alpha subunits and two gamma (not beta) subunits. |
| Why are foetal haemoglobin different to adult haemoglobin? | Low O2% by the time blood reaches placenta so needs to bind with greater affinity than maternal haemoglobin. |
| What is the structure of the protein? | Tropocollagen is the building block of the collagen fibre and consists of 3 polypeptide chains with a left handed twist wound together in a right handed supercoil. |
| What is the essential amino acid in tropocollagen formation? | Glycine is vital for the formation of the tropocollagen triple helix as it has a small side chain that allows tight turns. |
| How many amino acids are there per turn in tropocollagen? | There are 3 amino acid residues per turn. |
| What other amino acid is essential in tropocollagen structure? | Proline is also vital for the structure of tropocollagen as it imposes left hand twist in the helix that provides main stabilising force. |
| What happens to some of the prolines in tropocollagen? | Some prolines become hydroxylated to form hydroxyproline. |
| What is the function of hydroxyproline? | It forms strong hydrogen bonds that help to stabilise the triple helix. |
| How is a collagen fibre formed? | Lysine is deaminated by Lysyl oxidase to form an aldehyde derivative (allysine). This is then involved in a condensation reaction to form an Aldol condensation product. |
| What is the quarter stagger model? | Molecules are stitched together by covalent-crosslinks. The gaps provide access sites for lysyl oxidase. |
| What is the technical name for brittle bone disease? | Osteogenesis imperfecta. |
| What causes osteogenesis imperfecta? | A mutation in the gene coding for one of the collagen subunits leading to glycine being replaced by a cysteine residue at one point in the chain. |
| Why does osteogenesis imperfecta cause brittle bone disease? | The tropocollagen subunits cannot pack together properly and there is a knock-on effect on collagen fibre formation. |
| What are the symptoms of scurvy? | Dry skin and gum disorders. |
| What is the cause of scurvy? | Lack of proline hydroxylation (vitamin C). |
| What is a symptom of Ehler-Danloss Syndrome? | Loose skin and Hypermobile joints. |
| What is the cause of Ehler-Danloss Syndrome? | Lack of Procollagen peptidase or Lysyl oxidase. |
Created by:
robertspedding
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