1.1 Monomers and Polymers, 1.2 Carbohydrates

Question 1

Define a monomer

Answer 1

Smaller units that join together to form larger molecules

Question 2

Examples of monomers

Answer 2

• Monosaccharides (glucose, fructose, galactose)
• Amino acids
• Nucleotides

Question 3

Define a polymer

Answer 3

Molecules formed when many monomers join together

Question 4

Examples of polymers

Answer 4

• Polysaccharides
• Proteins
• DNA/RNA

Question 5

What happens in a condensation reaction?

Answer 5

A chemical bond forms between two molecules and a molecule of water is produced

Question 6

What happens in a hydrolysis reaction?

Answer 6

A water molecule is used to break a chemical bond between two molecules

Question 7

Name three hexose monosaccharides

Answer 7

• Glucose
• Fructose
• Galactose
  All have the molecular formula C6 H12 O6

Question 8

Name the type of bond formed when monosaccharides react

Answer 8

• 1,4 or 1,6 glycosidic bond
• 2 monomers = 1 chemical bond = disaccharide
• Multiple monomers = many chemical bonds = polysaccharide

Question 9

Name three disaccharides

Answer 9

• Maltose: glucose+glucose
• Sucrose: glucose+fructose
• Lactose: glucose+galactose
  All have molecular formula C12 H22 O11

Question 10

How are disaccharides formed?

Answer 10

Condensation reaction forms glycosidic bond between 2 monosaccharides

Question 11

Describe the structure and function of starch

Answer 11

• Storage polymer of alpha glucose in plant cells
• Insoluble = osmotically inactive
• Larger = does not diffuse out of cells
• Amylose starch: 1,4 glycosidic bonds
• Amylose starch: helix with intermolecular H-bonds = compact
• Amylopectin starch: 1,4 and 1,6 glycosidic bonds
• Amylopectin starch: branched = many terminal ends for hydrolysis into glucose

Question 12

Describe structure and function of glycogen

Answer 12

• Main storage polymer of alpha glucose in animal cells (found in plant cells also)
• 1,4 and 1,6 glycosidic bonds
• Branched = many terminal ends for hydrolysis
• Insoluble = osmotically inactive
• Alpha helix = compact
• Large = doesn’t diffuse out of cells

Question 13

Describe structure and function of cellulose

Answer 13

• Polymer of beta glucose
• Gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)
• 1,4 beta glycosidic bonds
• Straight chain, unbranched molecule
• Alternate glucose molecules are rotated 180 degrees
• H-bond crosslinks between parallel strands form microfibrils = high tensile strength

Question 14

Describe Benedict’s test for reducing sugars

Answer 14

1) Add 2cm3 food sample
2) Add equal volume of Benedict’s reagent to a sample
3) Heat the mixture in a electric water bath at 100 degrees Celsius for 5 mins
4) Positive result: colour change from blue to orange and brick-red precipitate forms

Question 15

Describe Benedict’s test for non-reducing sugars

Answer 15

1) Negative result: Benedict’s reagent remains blue
2) Hydrolyse non-reducing sugars into their monomers by adding 1cm3 of HCl. Heat in a boiling water bath for 5 mins
3) Neutralise the mixture using sodium carbonate solution
- Proceed with the Benedict’s test as usual

Question 16

Describe test for starch

Answer 16

1) Add 2cm3 food sample
2) Add iodine solution to food sample
3) Positive test: colour change from orange to blue-black

Question 17

Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

Answer 17

• Make standard solutions with known concentrations. Record absorbance or % transmission values
• Plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis)
• Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration