Proteins Flashcards
(22 cards)
Define genome.
Full set of genes
Define proteome.
Full set of proteins encoded by the genome
Amino acids differ from one another because of the different chemical properties of their R groups. Identify 5 ways in which these R groups can differ.
Size Shape (aliphatic/aromatic) Hydophobicity Charge (acid/base) Sulphur Imino (proline is not an AA)
Are all amino acids optically active?
All except glycine
Identify 8 different protein functions.
- Enzymes - catalyse metabolic reactions
- Transport/storage - e.g. Hb
- Motion - muscle proteins
- Communication - receptors
- Structure - keratin, collagen
- Channels/transporters
- Regulation - cell division, protein synthesis, hormones
- Immunity - antibodies, self-recognition
Why are peptide bonds quite rigid?
They have partial double bond characteristics, resonating between single & double bonds.
Rotation around the bond is also very limited.
What is the primary structure of a protein?
Sequence of amino acids
What is the secondary structure of a protein?
The local spatial arrangements of amino acids in the chain
What is the tertiary structure of a protein?
3D shape of the folded protein chain
What is the quaternary structure of a protein?
The spatial arrangement of different folded chains in relation to each other
Polypeptide chains have direction because amino acids have different ends.
When writing a sequence down, it is convention to start with which end?
N-terminus (the amino)
written on the left
How is the a-helix structure formed?
Side chains stick outwards.
H bonds between N-H and C=O 4 residues ahead.
These are intrachain H-bonds.
Helix has some elasticity.
How is the B-pleated sheet structure formed?
Fully extended polypeptide chains run alongside one another.
Can be parallel or antiparallel.
H-bonding between adjacent strands.
May be intrachain or interchain.
Side chains lie above & below the plane of the sheet.
What is the function of molecular chaperones?
They bind to short segments of a protein to facilitate correct folding of that area.
What is the function of chaperonins?
They form protein chambers which provide a stable space where the protein can fold correctly.
What is thought to be the biochemical basis for Alzheimer’s Disease? (how it occurs)
Fragments from a normal membrane protein amyloid precursor protein (APP) accumulate and aggregate to form insoluble fibrils of amyloid B.
This forms plaques which destroy neurones.
What is the biochemical basis for Creutzfeldt Jacob Disease (CJD)? (how it occurs)
The normal membrane protein PrPc has an identical primary sequence to the abnormal PrPSc which has more B-pleated sheets.
Contact with this abnormal form (usually through ingestion) causes the PrP*c protein to acquire the abnormal structure.
Thus forming insoluble aggregates.
The exterior of soluble proteins is mostly hydrophobic.
True or False?
FALSE
Interior of soluble proteins is hydrophobic.
Exterior is hydrophilic.
Give 2 examples of the advantages of multi-subunit proteins.
- Structural proteins - multiple chains provide strength and rigidity e.g. collagen.
- Multi-enzyme complexes - multiple sites catalysing the same reaction or several different active sites close together to maximise efficiency.
What is the strongest type of interaction which stabilises protein structures? and how does this occur?
Disulphide bonds.
Oxidation occurs between 2 Cys residues which come close together to form a disulphide bond.
How does a salt bridge interaction occur in proteins?
Electrostatic attraction between oppositely charged amino acids, called an ‘ion pair’.
What is the Hydrophobic effect?
In order to minimise contact with water, non-polar amino acids are buried in the core of proteins.
Polar amino acids are found on the surfaces of proteins.
