Biological molecules

Question 1

Compare and contrast between fats and carbohydrates [4]

Answer 1

Similarity:
Made up of elements C,H,O (write out in full words)
energy storage
Differences:
Not fixed ratio of H : O for fats, but for carbohydrates it’s fixed ratio of 2:1 Fats contain twice as much energy as carbohydrates

Question 2

Define condensation and hydrolysis reaction [4]

Answer 2

Condensation – synthesis of larger, more complex substance from chemical bonding of two smaller, simpler substances with the removal of one molecule of water
Hydrolysis – chemical breakdown of lager, complex substance into two smaller, simpler substances with the addition of one molecule of water

Question 3

describe the various food tests required to test for the nutritional value of peanuts

Answer 3

Iodine – [2]
Crushed sample of peanut, add iodine soln drop by drop
Observation: blue-black (positive)

Benedict’s- [3]
Crushed sample of peanut, decant using water to dissolve out nutrients
Add 2cm3 of decant soln to 2cm3 of benedict’s soln, put in boiling water bath for 2- 3min
Observation: remain blue (negative)

Biuret’s- [2]
Crushed sample of peanut, decant using water to dissolve out nutrients Add 2cm3 of decant soln to 1cm3 of NAOH, add CuSO4 soln drop by drop Observation: violet colour (positive),

Ethanol emulsion – [3]
Crushed sample of peanut, decant using ethanol to dissolve out nutrients Add 2cm3 of decant soln to 2cm3 of water
Observation: cloudy, white emulsion (positive)

Question 4

compare and contrast between polypeptides and proteins. [4]

Answer 4

Similarities : both made up of a.a [1] both involve condensation to form peptide bonds [1]
Differences: polypeptide does not have three dimensional shape but protein has [1], protein can be made by more than one polypeptide [1] OR polypeptide involve peptide bonds whereas proteins involve peptide bonds and hydrogen bonds [1]