3.2 - Protein structure and function Flashcards
what does a proteins sequence always start with and what is it coded by?
Met, coded for by AUG
N-terminus (2)
- start of polypeptide chain
- amino group (NH2)
C-terminus (2)
- end of protein chain
- carboxyl group (COOH)
what does the 5’-3’ of the mRNA sequence correspond to
the N-terminal to C-terminal of the polypeptide q
what do all amino acids contain (apart from proline) (3)
- acidic carboxyl group
- basic amino group
- hydrogen
what are the 2 ionisable protons in amino acids? (2)
- carboxylic acid
- amino group
what does ionisation of amino acids depend on?
pH (usually have 0 charge at physiological pH)
structure of amino acids
chiral (L isomer)
what has a different chemical property in amino acids?
each ‘R’ group
which amino acids are hydrophobic?
non-polar
where are hydrophobic amino acids found?
inside of cytosolic globular proteins
which amino acids are hydrophillic?
polar (able to form H-bonds)
which amino acids can form electrostatic interactions and are basic (+ve charge) or acidic (-ve charge)?
polar amino acids with charged side groups
which amino acid can form disulfide bonds?
cysteine
describe peptide bond formation
carboxyl group of one amino acid bonds to amino group of another amino acid, with elimination of a molecule of water (condensation reaction)
what is the structure of a protein dictated by? (2)
- properties of amino acid side chains
- partly by properties of the peptide bond
where are hydrophilic/hydrophobic amino acid residues found? (2)
- hydrophilic - predominantly on surface of protein
- hydrophobic - predominantly found in interior of protein (cystolic)
primary structure
linear sequence of amino acids linked by peptide bonds
secondary structure (2)
- 3D structure formed by H-bonds between peptide NH and CO groups
- folding of polypeptide chain into a-helices or B-sheets
tertiary structure (2)
- adopt specific 3D conformation, able to fulfil specific biological function
- achieved by numerous weak interactions between amino acid side chains
quaternary structure
some functional proteins composed of more than one polypeptide (association through non-covalent interactions)