BIOLOGICAL MOLECULES -Proteins Flashcards
what is the general structure of an amino acid?
-COOH group
-R variable/side group which consists of carbon chain and may contain other functional groups . eg benzene ring or -OH
- NH2 amine/amino group
describe how to test for proteins in a sample.
Biuret test for proteins
1. add equal volume of sodium hydroxide to sample at room temperature
2. Add drops of dilute copper (II) sulfate solution. Swirl to mix.
3. Steps 1 and 2 make the biuret reagent
POSITIVE RESULT - COLOUR TURNS FROM BLUE TO PURPLE
NEGATIVE RESULT - SOLUTION REMAINS BLUE
How many amino acids are there and how do they differ from one another?
20
differ by the side ‘R’ group
How do dipeptides and polypeptides form?
- condensation reaction forms peptide bond (-CONH-) & eliminates molecule of water
- dipeptide - 2 amino acids
- polypeptide - 3 or more amino acids
How many levels of protein structure are there?
4
define ‘primary structure’ of a protein?
- sequence of amino acids in a polypeptide
- determined by sequence of codons on mRNA
define ‘secondary structure’ of a protein?
Hydrogen bonds form between O (partially negative) on the -C=O group and the H ( partially positive) on the -NH group.
This causes the long polypeptide chain to be twisted into a 3D shape such as a coil known as the alpha helix.
describe the two types of secondary strucutres.
a-helix:
- all N-H bonds are on the same side of protein chain
- spiral shape
- H bond are parallel to the helical axis
B-pleated sheet:
- N-H and C=O alternate from one side to the other
define the ‘tertiary structure’ of proteins. Name the bonds present
3D structure formed by further folding of polypeptide.
- disulfide bridges - strong and not easily broken. Strong S-S bonds between molecules of amino acid cysteine
-ionic bonds - formed between carboxyl and amino groups that are not involved in forming peptide bonds. Ph changes causes the bond to break
- hydrogen bonds - there are numerous and can be easily broken
the final 3D shape of the polypeptide, as it folds due to`;
covalent di-sulphide bonds
ionic bonds (weaker than disulphide bonds and easily broken by changes in pH)
hydrogen bonds
define ‘quaternary structure’ of protein
the structure of the protein when multiple polypeptide chains are linked (in various ways)
can include a prosthetic group (non-protein component) e.g. iron in haemoglobin
Describe the structure and function of globular proteins.
They have a spherical shape and are compact
Hydrophilic R groups face outwards and hydrophobic R groups face inwards
Involved in metabolic processes such as enzymes and haemoglobin
Describe the structure and function of fibrous proteins.
Can form long chains or fibres that run parallel to one another. They are linked by cross bridges so form very stable molecules
Insoluble in water
Useful for structure and support, eg collagen in skin or muscles
Outline how chromatography could be used to identify the amino acids in a mixture.
