W1 - Amino acids Flashcards
How many aa are there?
20
What is special about the carbon centre of an aa?
It is chiral
At neutral pH, what are the amino acids called?
Zwitterions
When the pH is low, what happens to the aa?
Amine groups become protonated, creating a positive charge
When the pH is high, what happens to the aa?
The carboxyl group(s) become deprotonated, creating a negative charge
What is the most common form of aa found in proteins?
L-isomer
Which way does L/D isomers spin plane polarised light?
L - left (anticlockwise), D - right (clockwise)
What determines the properties of the aa?
The chemical nature of the R groups
What is the smallest aa and what does it’s side chain consist of?
Glycine, H only
What two things can D isomers not do?
Can’t be digested or interact with tRNA
How many amino acids are hydrophobic?
10
What is the relation between size and hydrophobicity in G, A, V, L, I and M
As size increases, hydrophobicity increases
What is the characteristic of GAVLIM hydrophobic aa side chains?
They are aliphatic
Where are the hydrophobic R groups typically found and what is the exception?
Inside proteins, exception = external surface of integral/transmembrane proteins (channel)
What can give an aa hydrophilic properties?
If it is charged/polar or both
What groups in side chains can give hydrophilicity?
-OH and -NH-
Which amino acid is an important buffer in blood?
Histidine
What other characteristics do acidic and basic aa have? (@ physiological pH)
Acidic are negatively charged and polar, basic are positively charged and polar
What are the uncharged derivatives of aspartate and glutamate?
Asparagine + Glutamine
What makes asparagine and glutamine uncharged compared to aspartate/glutamate?
The O- is replaced by a neutral NH2
Why is proline unique?
The R group is bound to both the chiral C centre and the NH2+
Where is proline usually found?
In bends in proteins
Are SH (thiol) and OH (hydroxyl) unreactive or reactive?
Reactive
Where is histidine often found and why?
Active sites of enzymes because it can bind and release protons
What are the three aromatic amino acids?
Phenylalanine, tryptophan, tyrosine
How many +vely/-vely charged aa are there?
3 +ve, 2-ve
How many uncharged hydrophilic aa are there?
5
How many hydrophobic aa are there?
10
