8585215
Description
Flashcards by Katie Flaherty, updated more than 1 year ago
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Created by Katie Flaherty
over 7 years ago
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| Question | Answer |
| Naturally occuring form of amino acids? |
L-form with central alpha carbon
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Picture1 (image/png)
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| Rotation in the bonds in amino acids? | -no rotation about the C-N bond due to resonance (delocalisation of electrons out of the double C=O bond causing C-N to be partially double -two rotatable bonds are Phi and Psi bonds but their rotation is limited by Steric Hindrance (rotation is blocked because atoms in the R-group collide) |
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Phi and Psi bonds?
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Phi = C^a --N Psi = C--C^a |
| Orientation fo polypeptide chains? | TRANS - the chain compromises of alternating alternating C--C^a and C^a --N bonds |
| Significance of Ramachandran Plot? | Theoretically, the areas circled with orange are the only regions where bonds can be in rotation, but in practice the other white regions can also happen When Phi and Psi plots are on different areas of the graph, it means that the structure of the protein isn't alpha helix or beta pleated sheet (because all bond angles are the same in those structures) |
| Essential features of Alpha helix? | - Hydrogen bonds formed between C=O group of one AA and the N-H of another AA four residues along the polypeptide chain - All carbonyl groups point up and all amide down - All alpha helices form in a 'right-handed' spin because all naturally occurring AA's are in L-orientation - H-bond = 2.8 Angstroms long (0.28 nm) -3.5 residues/turn - Myoglobin = one alpha helix - Alpha-keratin = fibrous structure made up of alpha-helices |
| Essential features of ß-sheets ? | - Form from the interaction of two adjacent polypeptide chains, which are held in close association by hydrogen bonds between C=O and N-H on the two strand -The two strands run in opposite directions (anti-parallel ß-sheets) – this is because if they ran in the same direction, the bonds wouldn’t align properly and structure wouldn’t be stable -Very strong and flexible (spider silk is made only of this structure) |
| Essential features of ß-turn/reverse turn? | -One of the simplest secondary structures in polypeptides, which causes the chain to double back on itself –comprises of just 3 or 4 amino acid residues and is stabilised by hydrogen bonds occurring between the carbonyl oxygen of one amino acid residues and the amide N-H of the residue 3 places further along. |
| How does ß-turn form ß-sheet? | By doubling back on itself in a ß-turn, the polypeptide chain now has two adjacent strands – these can be stabilised by hydrogen bonds = ß-sheet |
| Collagen structure? | -made up of 3 alpha helices wound around one another in a rope like superhelix (but superhelix has left handed rotation, not right -3 residues per turn - has Glycine every 3 AA's |
| Difference bewteen Alpha-helix and Collagen triple helix? |
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| Two super-secondary motifs? | - a ß-barrel - Alpha-helix bundle proteins/coiled coil |
| Alpha-helix bundle proteins/coiled coil? | When two or more alpha-helix strands come together in close proximity |
| ß-barrel? | - With 8 strands, polypeptide chains can form a ß-barrel - it is stabilised by hydrogen bonds, which operate between the first and last ß-stands to maintain the shape. |
| Folding in Proteins? | - there are a limited number of protein folds - many proteins are made up of several commonly occurring domains/modules |
| Two structural motifs used by proteins to span membranes? | The two kinds of transmembrane proteins are alpha-helical and beta-barrels. |
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