introduction to protein structure Flashcards
Primary structure
linear sequence of AA
joined by peptide bind
in ribosome - rRNA and protein
amino terminus bind to carboxyl terminus
nomenclature - amino to carboxyl
no freedom to rotate around peptide bond
in the same plane
secondary structure
local structural motifs
B pleated sheet - antiparallel/parallel
a helix
hydrogen bonds
Tertiary structure
specific 3D structure
arrangement of secondary structure motifs into compact globular structures - domains
quaternary structure
3D structure of multimeric protein composed of several subunits
eg oxyhaemoglobin
post translation - novel AA
summarise the reaction by which amino acids are joined together
condensation COOH and NH2
loss of H2O
need energy input
stable bond in aq env
side chain
side chain
The bonds that stabalise them
hydrogen - sidechain/water - 2 partially -ve share +ve H - between C=O and N-H 4 AA along sequence stabilises helix structure - between 2 or more B stands holds B pleated sheet together
covalent - share electrons - strongest - primary structure - disulphide bridge when cysteine side chain oxidised
salt bonds - electrostatic attraction - charged side chain (glu, asp, lys, arg) - protein interior excluded from H2O
van der walls - transient - weak electrostatic attraction - sheer number - induce/repel depending on distance which depends on atom and size of electron cloud [van der walls radius]
hydrophilic/phobic - proteins juxtapose hydrophobic side chains by packing into interior of protein - phobic core - philic surface
The a helix
side chains project out
right/left handed but L AA mean R handed is favoured
proline - NH group lost - prevent H bonding - kink
B pleated sheet
almost 2D
NH and CO groups point out at right angles to backbone
parallel - alternate strands same direction
anti-parallel - strands run in opposite directions
electrophoresis
protein move to anode when current given
lighter/smaller protein travel further
based on charge
single mutation - react differently with buffer/paper
post translational modification of proteins
N-linked glycosylation - addition of sugar groups to asparagine ensures it adopts correct conformation in cell membrane
mutation of 2 asparagines to glutamine picked up on electrophoresis - weight of LHR
AAs with hydrophilic side chain and their properties
readily dissociate serine threonine tyrosine asparagine cysteine
what is special about histidine
Active site of enzymes
what does it mean if an AA ends in ate
it is an acid
AA with non-polar sidechains - hydrophobic
glycine
proline
