LECTURE 3: Amino Acids & Proteins Flashcards
How many substituents does the alpha-carbon atom have and what does that make it?
4 & Chiral
What determines the identity and properties of the amino acid?
The R group
All amino acids have mirror images, except which one? EXPLAIN WHY
Glycine - it is the only one that does not have a chiral centre, and therefore, it lacks stereoisomers or mirror images.
What form are the amino acids in proteins in? (chirality)
L (laevus) form
What form are the amino acids in bacterial cell walls in? (chirality)
D (dexter) form
Best unit for expressing acid strength
pKa
Higher pKa means
smaller Ka and weaker acid
Lower pKa means
higher Ka
Carboxyl group in zwitterion
Carboxyl group is deprotonated, COO-
pKa= 3.1
Amino group in zwitterion
Amino group is deprotonated, NH3+
pKa=8.0
What is a zwitterion
amino acids in solution at a neutral pH (7.0) exist predominantly as dipolar ions called zwitterions.
Glycine, Gly, G
- R-group is -H
- shows no chirality
-provides flexibility to proteins where other side chains would be too bulky
Alanine, Ala, A
- R group is -CH3
- aliphatic side chain
- small size, no reactivity
- non-polar
- hydrophobic
Proline, Pro, P
- pyrrolidine ring
- imposes tight restraints on the conformation of the protein
- found in proteins that need to be rigid e.g. collagen, and in turns of globular proteins.
Serine, Ser, S
- R group is -CH2-OH
- hydroxyl functional group
- polar due to electronegativity values between O and H
- hydrophilic
- often found in active sites of enzymes
Histidine, His, H
- R group imidazole ring
- pKa 6.7, can be neutral or positively charged
- found in active site of enzymes
What is an imidazole ring?
A five-membered aromatic ring
Cysteine, Cys, C
- R group is -CH2-SH
- thiol functional group
- hydrophobic amino acid
- pKa of 8.4
Positively charged R group amino acids
Arginine
Lysine
Histidine
Hydrophobic amino acids with non-polar R groups
Glycine
Alanine
Valine
Cysteine
Proline
Leucine
Isoleucine
Methionine
Tryptophan
Phenylalanine
Polar amino acids with neutral R groups
Serine
Threonine
Tyrosine
Asparagine
Glutamine
Negatively charged R groups
Aspartate
Glutamate
Residue
Each amino acid unit within a polypeptide
N-terminal
Amino acid sequences are written starting with the amino acid terminal residue
C-terminal
End of amino acid sequence
Purines
Adenine and guanine
- bigger looking structure
Pyrimidines
Cytosine, thymine and uracil
- singular looking structure
What type of inhibitor is PALA
competitive inhibitor
