3.1.4 Proteins

Question 1

What is the general structure of an amino acids

Answer 1

-NH2 amino group
R group
Carboxyl group (COOH)

Question 2

Describe how to test for proteins in a sample

Answer 2

Add biuret
Blue to lilac

Question 3

How many amino acids are there and how do they differ from one another

Answer 3

20
Differ only by R group

Question 4

How do dipeptides and polypeptides form

Answer 4

Condensation reaction forms peptide bond and removes molecule of water
Dipeptide: 2 amino acids
Polypeptide: 3 or more amino acids

Question 5

How many levels of protein structure are there

Answer 5

4

Question 6

Define primary structure of a protein

Answer 6

Sequence, number and type of amino acids in the polypeptide
Determined by sequence codons of mRNA

Question 7

Define secondary structure of a protein

Answer 7

Hydrogen bonds form between O delta negative attatched to -C=O and H slightly positive attatched to -NH

Question 8

Describe the 2 types of secondary structure

Answer 8

a helix
All N-H bonds on same side of protein chain
Spiral shape
H-bonds parallel to helical axis

b pleated sheet
N-H and C=O groups alternate from one side to the other

Question 9

Define tertiary structure and name the bonds present

Answer 9

3D structure formed by further folding of polypeptide
Disulfide bridges
Ionic bonds
Hydrogen bonds

Question 10

Describe each type of bond in the tertiary structure of proteins

Answer 10

Disulfide bridges - strong covalent S-S bonds between molecules of the amino acid cysteine
Ionic bonds - relatively strong bonds between charged R groups (broken by pH change)
Hydrogen bonds - numerous and easily broken

Question 11

Define quaternary structure of a protein

Answer 11

Functional proteins may consist of more than one polypeptide
Precise 3D structure held together by the same types of bon as tertiary structure
May involve addition of prosthetic groups eg metal ions or phosphate groups

Question 12

Outline how chromatography could be used to identify the amino acids in a mixture

Answer 12

Use capillary tube to spot mixture onto pencil origin line and place chromatography paper in solvent
Allow solvent to run until it almost touches either end of paper. Amino acids mover different distance based on relative attraction to paper and solubility in solvent
Use revealing agent or UV light to see spots
Calculate Rf values and match to database