Proteins 2 Flashcards
(24 cards)
Essential amino acids
(9) cannot be produced naturally, must be consumed through our diet
Non-essential amino acids
(11) synthesised from products or intermediates of crucial metabolic pathways
What is alanine synthesised from?
pyruvate, a product of glycolysis
What is aspartate synthesised from?
oxaloacetate, an intermediate of the citric acid cycle
How can amino acids be classfied?
Based on their metabolic fate:
- glucogenic
- ketogenic
- both
Based on their R-group which determines the amino acids properties/characteristics such as solubility in water
What proteinogenic amino acids?
‘protein creating’ –> there are 22 genetically encoded amino acids in known life:
- 20 standard amino acids
- 2 additional which are incorporated by special transformational mechanisms
define non standard amino acids
refers to amino acids that have been chemically modified after they have been incorporated into a protein
have biologically important roles
define standard amino acids
non-proteinogenic, not naturally encoded amino acids
example = pyrrolysine- has broad potential in biotech
classification of amino acids on the basis of their R-groups
non-polar - hydrophobic polar, hydrophilic - but uncharged basic - +ve charged acidic - -ve charged aromatic - relatively non-polar, participates in hydrophobic interactions
how can amino acids be visualised?
ball and stick model
space filling model
amino acids with non polar R-groups
glycine alanine valine leucine methionine isoleucine proline phenylalanine tryptophan
amino acids with polar R groups
serine threonine asparagine glutamine cysteine tyrosine aspartic acid glutamic acid histidine lysine arginine
basic amino acids
lysine
arginine
histidine
acidic amino acids
asparagine/aspartic acid
glutamine/glutamic acid
aromatic amino acids
phenylalanine
tyrosine
tryphophan
features of globular proteins
compact, soluble, spherical
features of fibrous proteins
elongated and insoluble
Most living systems are based on which enantiomer of alpha amino acids
L form- only L amino acids are constituent of proteins.
S absolute configuration (with the exception of cysteine)
define pK
the logarithmic value of the dissociation constant, Ka, of a hydrogen atom present on a molecule
Zwitterionic form
At neutral pH, the carboxyl group of an amino acid is deprotonated and the amino group is protonated –> the net charge is zero
The amino acid can act as an acid or a base and is said to be amphoteric
Types of amino acid configuration
- Operational classification
- Fischer convention
- Cahn Ingold Prelog
Operational Classification
Amino acids classified depending on whether they rotate the plane of polarise light clockwise ot counter clockwise from the point of view of the observer
Fischer convention
Configuration based on glyceraldehyde.
Have to look down the alpha carbon- hydrogen bond with the hydrogen hid behind the plane of view
CORN anticlockwise = L
CORN clockwise = D
The amino acid must be orientated so that the carbon chain is vertical and the carboxyl group is on the top.
The amino acid is projected onto a flat screen:
L isomer - if the amino group is on the left of the chiral carbon
D isomer - if the amino group is on the right of the chiral carbon
Cahn Ingold Prelog System
The 4 groups surrounding a chiral centre are ranked according to a priority scheme.
CORN anticlockwise, lowest –> highest Ar = S isomer
CORN clockwise, lowest –> highest Ar = R isomer
