Topic 3.2 Carbohydrates, Lipids and Proteins

Question 1

3.2.1 Distinguish between organic and inorganic compounds.

Answer 1

Organic: molecules containing element carbon

• exceptions: some carbon-containing elements such as CO₂, carbonates, hydrogen garbonates

Inorganic: molecules NOT containing carbon

Question 2

3.2.2 Identify amino acids, glucose, ribose and fatty acids from diagrams showing their structure.

Answer 2

• amino acids: amine group (NH₂) + carboxylic acid group (COOH)
• glucose: 6 carbon ring
• ribose: 5 carbon ring
• fatty acid: carboxylic acid group (COOH)

Question 3

3.2.3 List three examples each of monosaccharides, disaccharides and polysaccharides.

Answer 3

-saccharide = carbohydrate molecules linked in condensation reactions (produces water)

• Monosaccharides: glucose, galactose, fructose
• Disaccharides: maltose, lactose, sucrose
• Polysaccharides: glycogen, cellulose, starch

Question 4

3.2.4 State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants.

Answer 4

Animals:

• Glucose: chemical fuel for cell respiration
• Lactose: makes up some of the solutes in milk; provides energy to young mammals until they’re weaned
• Glycogen: stores glucose in liver & muscles

Plants:

• Fructose: makes fruits sweet
• Sucrose: carried by phloem to often transport energy from leaves to other cells in plants
• Cellulose: one of the primary components of plant cell walls (makes strong fibres)

Question 5

3.2.5 Outline the role of condensation and hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol and triglycerides; and between amino acids and polypeptides.

Answer 5

Condensation: forms larger biochemically important molecules; H₂O is a product; requires catalyzing reactions in which covalent bonds are created

Hydrolysis: reverse of condensation; digestion of foods to gain building block molecules which make up larger molecules. H₂O (reactant) is split in hydrolysis reactions.

• Carbohydrates:
  
  • monosaccharides = single monomers joined to form disaccharides; sugars containing multimple subunits (>10) called polysaccharides
  • glycosidic linkage
• Fatty acids:
  
  • fatty acid + glycerol = glyceride. Max 3 fatty acids added, to form triglyceride.
  • ester linkage
• Amino acids:
  
  • condensation rxn with 2 amino acids = dipeptide; multiple amino acids = polypeptide
  • peptide linkage

Question 6

3.2.6 State three functions of lipids.

Answer 6

1. energy storage in the form of fat in humans and oil in plants.
2. heat insulation as fat under the skin to reduce heat loss.
3. buoyancy as they are less dense than water (so animals can float in water).
4. form a tissue layer around many key internal organs –> provide protection against physical injury.
5. (phospholipids) make up double layer of all cell membranes.
6. (steroids) involved in hormonal signalling (e.g. estrogen, progesterone, testosterone).

Question 7

3.2.7 Compare the use of carbohydrates and lipids in energy storage.

Answer 7

• Carbohydrates
  
  • short-term storage
  • water-soluble
  • more readily & rapidly digested
  • contain less energy per gram than lipids
  • stored as glycogen in animals, cellulose in plants
  • more effect on osmotic pressure
• Lipids
  
  • long-term storage
  • non-water-soluble
  • less readily & rapidly digested
  • contain more energy per gram than carbs (approx. 2X more)
  • stored as fat in animals, oil in plants
  • less effect on osmotic pressure