proteins Flashcards
what are the roles of proteins?
- Structural – cytoskeleton
- Catalysts – enzymes
- Carrier/storage – haemoglobin
- Protective – antibodies
- Signalling – receptors, intracellular signalling
- Channels – transport through membranes
- Transporters – transport through membranes and barriers
- Cell adhesion – ECM
what are the levels of structure of a protein?
primary - amino acid sequence
secondary - 2D folding
tertiary - 3D folding
quaternary - interaction of subunits
what are the ends of a protein?
N terminus - comes out the ribosome first
C terminus - comes out the ribosome last
which end of the amino acid is the amine end?
N terminus
which end of the amino acid is the carboxylic acid end?
C terminus
what chemical implications does the peptide bond have?
planar molecule
H bonding
what determines secondary structure?
hydrogen bonding between peptide bonds
which amino acid isnt found in an alpha helix?
proline
describe an alpha helix
- Peptide chain spiralling and the peptide bonds are essentially running vertically
- R groups facing outwards
what kind of bonding can you have in a tertiary structure?
hydrogen bonding, ionic bonding, disulphide bridges and hydrophobic and hydrophilic interactions
what are the types of tertiary structure?
o Globular = water soluble e.g haemoglobin MAJORITY
o Fibrous= insoluble e.g collagen, keratin
what is quaternary subunits?
when multiple subunits come together
what type of protein is collagen?
fibrous protein
where can you find large scale quaternary protein complexes?
viral capsid
describe the amino acid sequence of collagen?
proline-proline-glycine
how much of collagen is glycine?
35%
describe the structure of collagen
collagen triple helix - helps with strength bc of H bonding
post-translational modifications which enable covalent modifications e.g. di-sulphide bridges between cystines and lysines
what is the most common type of protein?
globular
when is a protein at its lowest energy level?
when its fully folded
what is the hydrophobic effect?
when proteins fold so you can get a hydrophobic centre
what can unfold proteins?
heat
ph
detergent
what are molecular chaperones?
help fold proteins
when do levels of chaperones increase?
when the cell is subjected to stress
what can cause protein disease and by what mechanism?
cause; environmental stress or inherited mutation
mechanism; loss of function, toxic gain of function, dominant negative
what diseases can misfolding of proteins cause?
neurodegeneration (alzheimers or parkinsons)
metabolic disorders (monogenic obesity)
cancer
what do post-translational modifications involve?
adding other functional groups, adding other proteins, changing the chemical nature of amino acids and structural changes
what is phosphorylation?
addition of a phosphate group
what is a disulphide?
covalent bond between cysteines which can stabilise a 3D structure
