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Lecture 2.2
Element 2- Biochemistry
| Question | Answer |
|---|---|
| What forces are there stabilising Proteins? | Hydrogen Bonds Ionic Bonds (including disulphide bridges) Hydrophobic Interactions Hydrophilic Interactions |
| What is the Hydrophilic Effect? | Polar side chains prefer to interact with the aqueous solvent where it can make hydrogen- bonds and ionic bonds. Hydrophilic amino acids stick together and fold around protein, burying the hydrophobic amino acids in the interior of the protein. |
| What is the hydrophobic effect? | Water forms ordered 'cages' around non-polar molecules. Hydrophobic molecules stick together to minimise the ordering of water |
| Describe the shape of an alpha helix and the relative positions of the amino acid side chains | A rod-like, right handed helical structure. All side chains sticking out of the helix (because all L optical isomers). |
| What is an amino acid residue? | It's what's left of the amino acid after peptide bond formation and subsequent loss of the water molecule. So in alpha amino acid polypeptides its -NH-CHR-COO- |
| How is the alpha helix stabilised | Alpha helix is stabilised by backbone hydrogen bonds. Formed of hydrogen bonding between the C=O of one amino acid residue and the N-H of the amino acid residue four units along (denoted= residue i and residue i+4) |
| Describe the beta pleated sheet. | Antiparallel polypeptides |
| How is the beta pleated sheet stabilised? | Through hydrogen bonding between N-H and C=O of different polypeptide strands, often running in opposite directions, or between the same polypeptide chain after an abrupt beta-turn |
| What is a beta turn? | In a beta turn, a tight loop is formed when the carbonyl oxygen of one residue forms a hydrogen bond with the amide proton of an amino acid three residues down the chain. |
| Alpha- helix and beta-sheets are part of which type of amino acid structure | Secondary structure |
| What group is responsible for disulphide bridges and which amino acid has this group? | Thiol, Cysteine |
| What is tertiary Structure? | Involves side chain- side chain interactions which are packed tightly to leave very little free space. Secondary structure elements pack together to form the territory structure. |
| How do proteins span the membrane? | Using alpha helices |
| What is Quaternary Structure? Give an example | The arrangement of sub units (single polypetide chains) in proteins containing more than one subunit. e.g. Disulphide bonds |
| Whats the difference between alpha helices inside the cell membrane and those outside the cell? | Hydrophobic side chains are now on the outside of the helix |
Created by:
macdonkr
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