1.1 biological molecules proteins and chemical tests

Question 1

Describe the primary structure of a protein:

Answer 1

Sequence of amino acids in a polypeptide chain. The sequence of amino acids is determined by DNA; one gene codes for one polypeptide. The bond between each amino acid is a peptide bond.

Question 2

Describe the secondary structure of a protein:

Answer 2

the shape that the polypeptide chain forms due to hydrogen bonding. Hydrogen bonds twist and fold the polypeptide forming an alpha helix or a less common beta pleated sheet.

Question 3

Describe the tertiary structure of a protein:

Answer 3

Formed by the bending and twisting of the polypeptide helix into a compact structure giving the molecule its three - dimensional shape. ionic, hydrogen, disulphide bonds and hydrophobic/hyrophylic interactions

Question 4

Describe the quaternary structure of a protein:

Answer 4

arises from a combination of two or more polypeptide chains in tertiary form. These are associated with non-protein groups and form large complex molecules such as haemoglobin. which is made of two α chains and two β chains.

Question 5

haemoglobin

Answer 5

a water soluble globular protein​ ​which consists of ​two​ ​beta polypeptide chains and a haem group​. It ​carries oxygen​ ​in the blood as oxygen can bind to the haem (Fe2+) group and oxygen is then released when required.

Question 6

test for protein method:

Answer 6

1. Mix 2 cm3 of the test solution with 2 cm3 of Biuret reagent in a test tube.2. Cover the top of the boiling tube and invert it once.3. Record vour observations

Question 7

test for starch method:

Answer 7

Mix 2cm3 of the test solution with 2 drops of iodine in potassium-iodide solution then record the colour changeResult if positive: Sample turns blue/black

Question 8

reducing sugars method:

Answer 8

Mix 2cm3 of test solution with equal vol of Benedict reagent, boil in water bath between 70-90º for 5 mins Result if positive: Sample turns blue to yellow/green/orange brick-red

Question 9

non reducing sugars method:

Answer 9

boil sample in dilute hydrochloric acid (hydrolyse disaccharide) Neutralise by adding 2 drops sodium hydroxide Add 2cm3 Benedict’s reagent Boil solution 70-90º Result if positive: Sample turns from blue to brick red

Question 10

What is the test for a lipid?

Answer 10

The Emulsion Test
1. Add ethanol and shake thoroughly 2. Add distilled waterIf test is positive: emulsion is cloudy white and indicates that lipids are present.