proteins Flashcards
what is the general structure of amino acids?
have a central carbon atom which four chemical groups are attached:
* amino group (NH2)
* carboxyl group (COOH)
* hydrogen amino (H)
* R group (range of chemical groups different for each amino acid)
how many amino acids are there that occur in all living organisms?
20
how is a peptide bond formed?
an OH from the carboxyl group of one amino acid combine with a H from another forming the water molecule that is released in a condensation reaction. a peptide bond then links the carbon atom of one and the hydrogen atom of another amino acid.
what do amino acid monomers form when they combine?
dipeptide
describe the primary structure of proteins.
a series of condensation reactions join together lots of amino acid monomers through polymerisation forming a polypeptide chain. the amino acids form in a repeating sequence that determines the structure and therefore its function.
how could a change of an amino acid in the primary structure affect it?
it can cause the shape of the overall protein to change so it may be unable to carry out its function.
describe the secondary structure of proteins.
the hydrogen of the NH group (which has a overall positive charge) and the oxygen of the carboxyl group (which has a overall negative charge) form weak hydrogen bonds together this causes the long polypeptide chain to twist forming a 3D coil.
describe the tertiary structure of proteins.
the a-helix coils created in the secondary structure twists and folds even more to form a shape specific to the protein.
what bonds are involved in the tertiary structure?
disulphide bridges –fairly strong
ionic bonds –weaker than disulphide bonds, formed between carboxyl group and amino group
hydrogen bonds –lots of these but they are easily broken
describe the quaternary structure of proteins.
a number of polypeptide chains are linked in various ways forming complex molecules. they may also have have non-protein groups associated.
what is the test for proteins?
Biuret test
describe the Biuret test for proteins.
- add equal volume of sodium hydroxide to the sample at room temp
- add drops of dilute copper sulphate solution.
- swirl to mix
a positive result shows a colour change from blue to purple there for indicating the presence of peptide bonds
what are the two basic types of molecular shape that determines the role of proteins? (+ example)
fibrous proteins e.g. collagen
globular proteins e.g. enzymes like haemoglobin
explain why the quaternary structure of collagen makes it a suitable molecule for a tendon.
the individual collagen polypeptide chains in the fibres are held together by bonds between amino acids of adjacent chains.
suggest how the cross-linkages between the amino acids of polypeptide chains increase the strength and stability of a collagen fibre.
the points where one collagen molecule ends and the next begins are spread through the fibre rather than all being in the same position along it.
