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12 Cards in this Set
- Front
- Back
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Describe the general structure of an amino acid |
1 hydrogen, 1 carboxylic group, 1 amino group and an R hydrocarbon chain all connected to a carbon |
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What is a chiral carbon |
A carbon which has 4 different groups/Molecules attached to it. Also known as an asymmetric carbon For each chial carbon there are two optical isomers. |
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What are the directions in which amino acids are read in. |
N to C terminus |
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What are optical isomers? Why is this important for proteins? |
Molecules with a chiral carbon that have the sane structure and are mirror images of each other but don't superimpose them perfectly. Like left and right hand - physically different in space So two different Molecules so can have chemical properties can be different Can form different proteins with different functionz when added to a polypeptide as side chains may be pointing at wrong angles |
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What optical isomers are found in nature? |
L isomers are incorporated into proteins - cells and viruses. Because preiten synthesis is an Enzyme driven reaction, if amino acid doesn't natch Enzyme, it will be ignored or not work. D-isomers can occur in nature tbo in things like venoms. |
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How do you distinguish between L and D isomers |
CORN rule - centre of amino acid, should find COOH,R NH2 |
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What is the only amino acid with no optical isomers? |
GLYCINE as it has H as its R group |
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At physiological pH what happens in amino acid |
The amino and carboxylic groups are ionised |
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Define zwitterions |
This means they carry a positive and negative charge as amino group picked up extra H tp become positive and COOH donated a hydrogen to become negative. Gone from neutral molecule to zwitterion - if ignoring R group, then main spine of the amino acid has a positive and negative at pH7 - those charges cancel each other out, so technically neutral but polar. Gives its interesting chemical properties for an amino acid |
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What is pka |
The pH at which an ionisation group is one-half charged and one-half neutral. |
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Why is Histidine a special amino acid? |
Because its side chain has a pKa around physiological pH. The ability of histidine to change its charge status at physiological pH is important in the folding of many proteins and in the activity of many enzymes. |
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Histidine's side chain has a pKa of 6.8, what happens at pH: 5.8 6.8 7.8 |
5.8 - 90% NH+ and 10% neutral 6.8 - 50% NH+ and 50% neutral 7.8 - 10% NH+ and 90% neutral So not like spine of amino acid - not just positive NH3+ and negative COO- |
