proteins 1 Flashcards
What do proteins do?
provide structure (bone, skin, tendon)
Transport molecules (LDL-cholesterol, haemoglobin-oxygen)
Defence (antibodies)
Biological catalysts (enzymes, eg lysosomes)
Regulation of genes (lac repressor)
Hypercholesterolemia
mutation histadine residue in LDL receptor
What do the functions of protein really come down to?
Specific binding which depends on conformation
What changes the activity of a protein?
A change in conformation
What are proteins?
Linear polymers: amino acids joined by peptide bonds
What defines the structure and function of a protein?
The R group of it’s amino acids
Classification of hydrophilic amino acids
Basic
Acidic
Polar with uncharged R groups
Basic amino acids (hydrophillic)
Lysine
Arginine
Histidine
Acidic amino acids (hydrophillic)
Aspartate and Glutamate
Polar amino acids with uncharged R groups (hydrophillic)
Serine, Threonine, Asparagine, Glutamine
Hydrophobic amino acids
Alanine, Valine, Isoleucine, Leucine, Methionine, phenylalaline, Tyrosine, Tryptophan
Special amino acids
Cysteine (covanent S-S)
Glycine (smallest)
Proline (ring R, kink)
what do we mean by acid
a molecule that tends to release a hydrogen ion
what do we mean by base
ion that readily binds to H
How is the pH of a reaction calculated?
Henderson hasselbach equation
pH=pKa + log [A-]/[HA]
What is the pKa of an acid?
The pH at which half the molecules are disassociated.
Why is pH relevant?
Affect disassociation(mainly over 2 units of pH centred on pKa) Changes charge of overall aminoacid. Means local environment affect pKa.
Give an example where a reduction in pH affects proteins
histadine residues -on LDL acting as carriers (cholesterol)- change conformation with change in pH, release cholesterol in endosomes
Peptide bond
condensation reaction, carbon from carboxylate shares electron with N from amino
Why is there a limit to the number of 3D conformations possible for a peptide?
peptide bond does not permit rotation, bulky R groups positioned on either side of backbone
What is secondary structure of a protein? (Stabilised by H bonds)
periodic repeats, initial folding patter.
a helix, b sheet, bend/loop
What groups are capable of hydrogen bonding?
H and oxygen, nitrogen or fluorine
