BIOCHEM 4 - AMINO ACIDS Flashcards
Essential Amino acids
L, I, V, H, K, M, F, T, W
Non-essential amino acids
A, R, N, D, C, E, Q, G, P, S, Y
aa (obtained from nutrition)
Essential Amino acids
aa (synthesized by the body)
Non-essential amino acids
properties of AA (4)
Amphoteric
dipolar
optically active
tetrahedral structure
– reference to determine if the
amino acid has L- or D-configuration
α-amino group
All amino acids in naturally occurring proteins are
L-isomers
◦ derived from glutamate; neurotransmitters (has something to do with the brain)
GABA
GABA is derived from
glutamate
◦ derived from tryptophan; important in sleep
Serotonine
serotonine derived from
derived from tryptophan
- Thyroxine
derived from tyrosine
indole acetic acid
- Dopamine –
– side chain is a primary alcohol; looks like Ala with -OH
Serine
side chain is a secondary alcohol;
◦ Threonine
has two chirality centers
threonine and isoleucine
contains a thiol group; important in disulfide linkages; weak acid; can form H-bonds
◦ Cysteine
- ionized cysteine is —–, while the protonated form is much ——–than serine.
polar
less polar
also has the ability to form covalent bonds called disulfide bonds between cysteine side chains.
Cysteine
– side chain is phenolic –OH; borderline case
Tyrosine
not very soluble in water, but contains a polar hydroxyl group in the para position of the phenyl ring
Tyrosine
amide groups do not become charged at biologically relevant pH values (i.e. pH 2-12), true or false
TRUE
simplest amino acid
GLYCINE
does not really have a polar or non-polar character
GLYCINE
- has much less steric hindrance than the other AAs;
GLYCINE
No chiral center/achiral
GLYCINE
no asymmetric carbon
GLYCINE
– side chain is isopropyl
Valine
side chain is isobutyl
Leucine
side chain is sec-butyl; has 2 chiral carbons
Isoleucine –
more hydrophobic than cysteine (S-containing amino acids)
Methionine
start amino acid
Methionine
having thioether
Methionine
– cyclic but not aromatic; 2ndary α-amino group or α-imino acid
- has a conformationally restricted structure
Proline
behaves more like a polar amino acid since —– has a fairly high tendency to appear on the solvent-exposed surface of proteins
proline
– has an indole ring; borderline hydrophobic/polar
Tryptophan
what AA has the proton attached to the indole nitrogen can act as a hydrogen bond donor to water or other hydrogen bond acceptors
Tryptophan
majority of the large tryptophan side-chain is polar or not?.
non-polar
acidic form of asparagines; β-carboxyl group
Aspartate-
acidic form of glutamine; γ-carboxyl group
Glutamate–
– has a primary amino group
protonated at pH 7.0
◦ Lysine
contains ε-amino group
◦ Lysine
diamino acid
◦ Lysine
– most basic amino acid
Arginine
contains guanido group
Arginine
guanidinium ion always protonated
Arginine
heterocyclic ring side chain; not aromatic
Histidine
contains imidazole
Histidine
only amino acid that functions as buffer in physiological range
Histidine
all are very hydrophobic
absorbs UV at 280 nm
aromatic amino acids
Tyrosine, Tyr (Y)
Tryptophan, Trp (W)
Phenylalanine, Phe (F)
contain carboxyl groups (weaker than α-carboxyl group)
negatively charged at physiological pH;
Aspartate, Asp (D)
Glutamate, Glu (E)
present as conjugate bases
carboxyl groups function as nucleophiles in some enzymatic reactions
Aspartate, Asp (D)
Glutamate, Glu (E)
classified as β-branched
have greater steric hindrance
exhibit more restricted conformational flexibility
Valine, Val (V)
Isoleucine, Ile (I)
Threonine, Thr (T)
18 of the 19 L-amino acids have — configuration
S
cysteine has – configuration
R
is neither very
hydrophobic nor very hydrophilic.
Proline
As the pH increases, the charge on the molecule becomes
more negative,
as the pH decreases,
the charge on the molecule becomes
more positive.
zero net charge state is known as the
zwitterionic state
is capable of both accepting
and donating protons
zwitterion
characteristic of free amino acids with non-ionizable side chains near pH
7.0
zwitterion
At pH»_space; pKa, the ionizable group will be .
-
deprotonated
At pH»_space; pKa, For carboxylic acids, the group will be ____ charged;
negatively
At pH»_space; pKa, amines will be ____
neutral
At pH «_space;pKa, the ionizable group will be _______
protonated.
At pH «_space;pKa, For carboxylic acids, the group will be __
neutral
At pH «_space;pKa, amines will be _____
positively charged
has a chemically basic side chain but acidic pKa
histidine
pKa values of amino groups of common AA
occur in a range from pH 9 to pH 11
pKa values of carboxyl groups of common AA
ph 2
