03. Amino acids Flashcards
What are the 3 different ways to classify / identify amino acids?
- Based on side chain (polar, ionisable, hydrophilic / non-polar, hydrophobic) etc
- Based on chemical structure – aromatic / straight chain etc
- Essential / non-essential
How many standard amino acids are there, and how many are essential?
20, only 9 are essential
What is meant by essential / non-essential amino acids?
Essential : cannot be manufactured by the body, must be obtained by diet (meat/dairy or combination of cereals and legumes)
Non-essential : can be manufactured by the body
In mammalian proteins, amino acids are only in which configurationand amino group is on which side?
L-configuration
Which means amino group (N-terminus) is on left;
D-configuration : amino group is on right
Where do non-essential amino acids come from?
The carbon backbone of these amino acids are intermediate products from glucose undergoing glycolysis / TCA cycle
Glycolytic and TCA cycle intermediates generate the nonessential and conditionally essential amino acids.
What is the general formula of an amino acid?
NH3+ – C(H)R – COO- (zwitterion at neutral pH)
NH2 – C(H)R – COOH
Will the acidic or basic form of amino acids exist if:
(a) pH = pKa
(b) pH < pKa
(c) pH > pKa
Ka : dissociation constant of acid
(a) 50% acidic form, 50% basic form
(b) acidic form dominates
(c) basic form dominates
What are non-standard amino acids?
Amino acids which are not naturally found in proteins, and are usually modified after they are incorporated into the protein.
What are 2 ways in which an amino acid can be modified into a non-standard amino acid?
Hint : not the TYPES OF MODIFICATION
- After translation in the cell –> protein formed (amino acids are modified by golgi apparatus after being incoporated into protein)
- chemical modification(in labs etc)
What is the importance of non-standard amino acids in biological systems?[2]
- Some are metabolic precursors
- some have specific biological functions in the body.
what is the main purpose of modification of amino acids?
To increase functionality of proteins
Modification 1: Hydroxylation
What is hydroxylation?
Proline is an amino acid found in collagen. What is the purpose of hydroxylation of proline?
Replacing a hydrogen atom with –OH group
Proline has an additional OH group for hydrogen bonding, can strengthen structure of collagen and hence, tendon and tissues.
What is acetylation? Why is it important?
It is to form an amide bond at the amino group (-NH2 –> -NH=O-CH3)
It reduces positive charge of amino acids and reduces degradation of amino acids (since most amino acids need NH2 group to react)
What is phosphorylation? What is it significance in biological systems?
Replacing of -OH group to H2PO4 on serine, threonine, and tyrosine residues.
- Phosphorylation affects protein function by activating or inactivating them. Thus, when an amino acids are phosphorylated, certain cellular processes can be turned on / off.
What is disulfide bond? What is the significance?
It occurs between 2 cysteine residues to form (-S-S-) bonds.
Disulfide bonds can link 2 or more polypeptide chains together covalently, which affects primary structure and thus subsequently affecting other structures (secondary, tertiary…)
