AAs and Proteins Flashcards
Functional Group
Amino
carboxyl
R
R group
determines
the biochemical
properties of the
amino acids.
* Charge
* Polarity
* Size
POLAR, and
POLAR, and
and uncharged
Chiral Carbon
4
different groups/atoms
attached to it
amino acid
DOES NOT
have a chiral centre?
GLYCINE
naturally occurring amino acids
classified as left-handed or L-amino
acids.
D Amino Acids
found in bacterial cell
walls and in some secondary
metabolites.
Properties of Core Region
At the pH levels
typically found in
cells (usually pH
7.0–7.4 - neutral
pH), both the
carboxyl and amino
groups of amino
acids are ionized
What happens at the carboxyl end?
the carboxyl group loses a hydrogen ion -COOH -COO- + H+ ACID
What happens at the amino end?
the amino group
gains a hydrogen ion
-NH2 + H+ -NH3+ BASE
What happens at the overall core region?
Amino Acids exist as ZWITTERIONS.
They show the properties of acids and bases at the same time!
At neutral pH, the core of an amino
acid has no net charge.
Non Polar AAs (10)
Glycine (Gly,G)
Cysteine ( Cys, C)
Alanine (Ala, A)
Proline ( Pro, P)
Isoleucine (Ile, I)
Leucine (Leu, L)
Methionine (Met, M)
Tryptophan (Trp, W)
Valine (Val, V)
Phenylalanine (Phe, F
Polar Uncharged AAs (5)
Serine (Ser, S)
Threonine (Thr, T)
Asparagine (Asn, N)
Glutamine (Gln, Q)
Tyrosine (Tyr, Y)
Positively Charged Polar AAs
Histidine (His, H)
Lysine (Lys, K)
Arginine (Arg, R)
Negatively Charged Polar AAs
Aspartic acid (Asp, D)
Glutamic acid (Glu, E)
Non-polar amino acids - hydrophobic
They have hydrocarbon
chains and/or rings.
Non-polar amino acids – special amino acid
Cysteine contains a thiol group
(SH)
Glycine is the smallest amino acid
and is not chiral
Proline forms a ring – which is
NOT a benzene ring
Polar – uncharged amino acids
They all have a C-O or C=O bonds
Primary protein structure
Specified by the genetic code of the organism.
The sequence in which amino acids are linked by
peptide bonds in a protein.
Peptide bonds
Two amino acids are joined by condensation reaction
forming a peptide bond
Oligopeptide
2 -25 amino acids
polypeptide
More than 25 amino acids
Short oligopeptides have specific names
2 amino acids – dipeptide
3 amino acids – tripeptide
4 amino acids - tetrapeptide
Linear arrays of amino acids can make a huge number of different molecules
Consider a peptide with
two amino acids (AAs) AA1 AA2 20 × 20 = 400 different molecules
Consider a peptide with
three amino acids AA1 AA2 AA3 20 × 20 × 20 = 8000 different molecules
For any protein that is made of 100 amino acids, the number of possibilities is:
20100 = 1.267 × 10130
Secondary protein structure
Secondary structure refers to 3D form of local segments
of proteins, stabilised by intramolecular and sometimes
intermolecular hydrogen bonding.
Hydrogen bonds form between the R groups of amino acids.
This bonding causes coiling or folding of the polypeptide.