2.2 - Protein Structure Flashcards
amino acid group at acid pH
protonated
carboxyl group at basic pH
ionised
amino acid group and carboxyl group at neutral pH (2)
- amino acid group = protonated
- carboxyl group = ionised
(total charge = 0)
amino acid ion state at physiological pH
zwitterions
zwitterions
molecules that contain both positively and negatively charged functional groups with an overall charge of 0
amino acid shape
chiral
chiral
asymmetric in such a way that the structure and its mirror image are not superimposable
amino acid form in biological systems
L form
peptide bonds
linkage of carboxyl group of one amino acid to amine group of another, with elimination of a water molecule
why are peptide bonds planar?
due to sharing of electrons
Trans-peptide group
R groups at opposite ends
Cis-peptide group
R groups next to each other
why is the core amino acid chiral in 19/20 amino acids?
because it has 4 different groups
stereoisomers
same molecular formula and atomic connectivity, but their atomic arrangement in space is different
which amino acid cant exist as a stereoisomer?
glycine-R=hydrogen atom
Enantiomers (2)
amino acids can be:
1. L (left)
2. D (right)
amino acid enantiomers found in proteins in living organisms
L amino acids
enantiomers
two stereoisomers related to each other by a reflection (mirror images of each other, which are non-superimposable)
number of amino acid combinations for a 100 residue protein
20^100
amino acid classes (5)
- non-polar
- polar
- acidic
- basic
- generic
how are amino acids abbreviated?
three letter and one letter abbreviations
e.g. Alanine, Ala, A
unique properties of glycine (
- side chain is - H
- glycines occur in tightly packed protein regions
unique properties of proline (3)
- introduces “kink” in chain
- can form ‘cis’ backbone
- difficult to fit into category, shares many properties with aliphatic amino acids
what increases the hydrophobicity of amino acids?
more CH
amino acids with aromatic R groups (3)
- Phe
- Tyr
- Trp
feature of aromatic amino acids
absorb UV light
wavelength of light absorbed by Trp and Tyr at neutral Ph
280nm
wavelength of light absorbed by Phe at neutral pH
260nm
how are disulfide bonds formed? (2)
- side chains d cysteine contain highly reactive thiol group
- two thiol groups form disulfide bond
effect of oxidising/reducing environments on disulfide bonds (2)
- formed in oxidising environments
- broken in reducing environments
purpose of disulfide bridge
link distant amino acids
cytochrome c
protein found in all aerobic organisms and protein sequences from distantly related species such as mammals and bacteria (similar enough to conclude proteins are homologous)
what does the globin gene encode for?
haemoglobin
haemoglobin in adults
iron containing heme molecule surrounded by 4 globin proteins (2 a-globins and 2 B-globins)
how does sickle cell anaemia result from defective haemoglobin? (2)
- haemoglobins stick together
- RBCs damaged
what causes sickle cell anaemia?
single mutation (significant change to protein structure and RBC structure as a result)