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Proteins 2

Structures of proteins 2.

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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