Structure of Proteins Flashcards
What do proteins do?
Provide structure - collagen found in bone, skin and tendons
Transport molecules - haemoglobin (02carrier) and LDL (transports cholesterol) with LDL receptors regulating its uptake into cells
Defence - Antibodies (defence against infection)
Biological Catalyst - Lysozyme (catalyses the cutting of polysaccharides)
Regulation of genes - Lac repressor - helps control gene expression
Describe the features of glycine, proline, cysteine, histidine and aspartate
Glycine - Smallest amino acid
Proline - side chain bends to form covalent bond with amino group, so creates kinks in the protein chains.
Cysteine - Forms disulphide bonds with other cysteine residues
Histidine - Has a basic side chain
Aspartate - Has an acidic side chain.
What is the pKa?
The pH at which half of the molecules are dissociated
What is the biological significance of pKa?
pH values close to the pKa can heavily influence the charge carried
What is secondary structure stabilised by? and what is their function?
Hydrogen bonds. They stabilise secondary structure
How many amino acids are requires to form a loop and what amino acid is commonly found in loops?
4 amino acids in a loop. Proline is commonly found.
Define tertiary structure
When loops/bends connect regions of alpha-helix and beta-sheets
What bonds stabilise tertiary structure?
Disulphide bonds Hydrogen bonds Ionic interactions van der Waals interactions Hydrophobic interactions
Define Quaternary structure and the bonds that stabilise it
- Association of more than one polypeptide. Stabilised by disulphide bonds
Give an example of Quaternary structure
Insulin
What is the importance of protein folding in haemoglobin?
The binding of an oxygen to a haem group causes a change in protein folding that increases its affinity for oxygen. This is called cooperative binding.
What is the biological significance of cooperative binding in haemoglobin?
Relatively small changes in oxygen concentration results in large changes in the interaction of haemoglobin with oxygen.
Describe the mutation that causes sickle cell anaemia
It is caused by the replacement of hydrophilic glutamic acid to hydrophobic valine at position 6 in the beta chain of haemoglobin.
Describe the differences between foetal and adult haemoglobin
Adult - two beta chains and two alpha
Foetal - Two gamma and two alpha, meaning foetus is not affect by sickle cell anaemia
What amino acids are vital for the formation of tropocollagen?
Glycine as it has a small side chain so allows for tight turns.
Proline as it imposes the left hand twist in the helix that provides the main stabilising force. Proline can become hydroxyproline which forms hydrogen bonds to help stabilise the structure.
