3 — biological molecules

Question 1

Definition & composition of carbohydrates

Answer 1

Carbon:Hydrogen:Oxygen
(CnH2mOm)
H:O -> 2:1

Monosaccharides:
glucose, fructose, galactose

Disaccharides:
maltose, sucrose, lactose

Polysaccharides:
starch, glycogen, cellulose

Definition: Carbohydrates r organic molecules made up of the elements carbon, hydrogen & oxygen. Hydrogen & oxygen atoms r present in 2:1.

Question 1

Define nutrients in food

Answer 1

• chemical substances in food that release energy and raw materials (to make protoplasm) needed by body

Question 2

Definition & composition of Fats

Answer 2

Carbon, hydrogen, oxygen
- Contains much less oxygen in proportion to hydrogen
- Proportions unfixed
Made up of
- 1 glycerol molecule
- 3 fatty acid molecules

Fats r organic molecules made up of elements carbon, hydrogen n oxygen & contains much less oxygen in proportion to hydrogen.

Tristearin -(lipase)-> glycerol + 3 stearin acid molecules

Question 3

Definition & composition of Proteins

Answer 3

Proteins are organic molecules made up of one or more polypeptide chains folded together in a three-dimensional structure held by hydrogen bonds and consists of elements carbon, hydrogen, oxygen & nitrogen, Sulfur may be present.

Carbon, hydrogen, oxygen, nitrogen, Sulfur (may (not) be present)

Made up of amino acids (building blocks of protein) consisting of
- Amino grp
- Acid grp
- Side chain
Peptide bonds link up amino acids -> polypeptide chain (2 or more) -> (hydrogen bond to hold) 3 dimensional molecule: protein

Question 4

Functions of carbs (carbohydrates)

Answer 4

• Substrate for respiration to provide energy for cell activities (source of energy)
• Form supporting structures (cell wall)
• Converted into other organic compounds (amino acids & fats)
• Form part of nucleic acids (DNA)
• Used to synthesise lubricants & nectar in flowers

Question 5

Test for carbs

Answer 5

Benedict’s Test:Reducing sugars
1. Add equivalent amt of 2cm3 Benedict’s solution to 2cm3 of food sample in test tube
2. Shake the mixture
3. Heat the contents in boiling water-bath for 2-3mins
4. Record colour of solution
- Absent -> blue precipitate
- Present in trace/moderate/large amts -> green - red

Iodine test: Starch
1. Add 2cm3 of food sample to clean test tube
2. Add 2-3 drops of iodine solution to test tube
- Brown: absent
- Blue-black: present

Question 6

Function of fats

Answer 6

• Source & store of energy (contain 2x as much energy as carbs)
• Insulating material to prevent excessive heat loss
• Solvent for fat soluble vitamins & some hormones
• Forms main part of cell membranes
• Helps reduce water loss from skin surface

Question 7

Test for fats

Answer 7

Ethanol-emulsion test
1. If solid: (Crush solid sample into small pieces with mortar & pestle)
2. Add 2cm3 of ethanol to sample (liquid/solid) in test tube
3. Shake thoroughly
4. (Allow solid particles to settle)Decant ethanol into another test tube with 2cm3 of water & shake well
- Present: cloudy white emulsion observed
- Absent solution remains colourless & clear

Question 8

Function of proteins

Answer 8

• Synthesis of new protoplasm for growth & repair of worn-out cells
• Synthesis of enzymes & some hormones
• Synthesis of antibodies

Question 9

Test for proteins

Answer 9

Biuret test
1. + 2cm3 of NaOH solution to 2cm3 of food sample into a test tube
2. Shake mixture thoroughly
3. + 1% CuSO4 solution drop by drop, shaking mixture aft each drop

1. OR + 2cm3 of Biuret Reagent & shake the mixture thoroughly.

• Present: violet colouration observed
• Absent: solution remains blue

Question 10

Monosaccharides examples

Answer 10

Basic unit of carbohydrates that cannot be further digested into smaller molecules.

• Can pass thru cell membranes + absorbed into cells
  (Single/reducing sugars)

Glucose
- Found in plants & animals
Fructose
- Common in plants, rare in animals
Galactose

Question 11

Disaccharides

Answer 11

Made up of 2 molecules of monosaccharides or single sugars bonded together.

• Can be split into 2 single sugar molecules via enzyme

Maltose
- G+G -> M
- M -(maltase)-> G+G
Sucrose
- G+F -> S
Lactose
- G+ galactose

Question 12

Polysaccharides

Answer 12

(Complex carbs)
Made up of many monosaccharide molecules bonded together to form a large molecule

• starch, cellulose, glycogen

Question 13

Complex carbohydrate: starch’s structure, role and occurrence

Answer 13

S: Several thousand glucose molecules joined together, linear molecule

R:
Storage form of carbohydrates in plants
Can be digested to glucose to provide energy for cell activities

O: Storage organs of plants
- potato tubers, tapioca

Question 14

Complex carbohydrate: cellulose’s structure, role and occurrence

Answer 14

S: Many glucose molecules joined tgt; bonds r diff from starch, linear molecule

R:
- Cellulose cell wall protects plant cells from bursting and from mechanical damage
- Cannot be digested
- Serves as dietary fibre -> prevents constipation

O: Cell walls of plants

Question 15

Complex carbohydrate: glycogen’s structure, role and occurrence

Answer 15

S: Many glucose molecules joined tgt; branched molecule

R:
- Storage form of carbohydrates in liver and muscle cells of mammals
- Digested to glucose to provide energy for cell activities

O: Liver & muscles of mammals

Question 16

Why starch and glycogen r storage materials in cells

Answer 16

• Insoluble in water, does not change water potential (WP) in cells
• Large molecules that cannot diffuse thru cell membranes, won’t be lost from cell
• Easily broken down to glucose when needed (tissue respiration)
• Molecules hv compact shapes -> occupy less space than individual glucose molecules that make up a glycogen/starch molecule

Question 17

Process of breakdown of fats

Answer 17

Hydrolysis
- Fats can be digested/broken down into simpler substances via hydrolysis
- Produces fatty acids & glycerol

Fat molecule + 3 water molecules -(lipase enzyme)-> glycerol + 3 fatty acid molecules

Question 18

Types of fats

Answer 18

Saturated fats
Structure: Fatty acid chain is straight
Characteristic: Most r solid at room tempt (eg butter)

Unsaturated fats
Structure: Fatty acid chain has kinks
Characteristics: Liquid at room tempt (Eg olive oil)

Question 19

Compare and contrast between fats and carbohydrates. [4]

Answer 19

Similarities:
The first similarity is both are made up of the carbon, hydrogen and oxygen
elements.
The second similarity is both can serve as a source of energy / energy
storage.
Differences:
The first difference is fats do not have a fixed ratio between the hydrogen and
oxygen elements, but for carbohydrates, there is a fixed ratio between the
hydrogen and oxygen elements of 2:1.
The second difference is fats contain twice as much energy as carbohydrates.