1.1-Monomers and Polymers + 1.2-Carbohydrates

Question 1

Define Polymer. Give some examples.

Answer 1

Molecules formed when many monomers join together.
- Polysaccharides
- Proteins
- DNA/RNA

Question 1

Define Monomer. Give some examples

Answer 1

Smaller units that join together to form larger molecules.
- Monoscaccharides (glucose, fructose,galactose)
- Amino acids
- Nucleotides

Question 2

What happens in a condensation reaction?

Answer 2

• A chemical bond forms between 2 molecules
• A molecule of water is formed

Question 3

What happens in a hydrolysis reaction?

Answer 3

A water molecule is used to break a chemical bond between 2 molecules.

Question 4

Name the 3 hexose monosaccharides.

Answer 4

• Glucose
• Fructose
• Galactose

Question 5

Name the type of bond formed when monosaccharides react.

Answer 5

Glycosidic Bonds (1-4, 1-6)

2 monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharides

Question 6

Name 3 disaccharides. Describe how they form.

Answer 6

Condensation reaction forms glycosidic bond between 2 monosaccharides
- Maltose: glucose + glucose
- Sucrose: glucose + fructose
- Lactose: glucose + galactose

Question 7

Describe the structure and functions of starch.

Answer 7

Storage Polymer of a-glucose in plant cells
- Insoluble = no osmotic effect on cells
- Large = does not diffuse out cells

Made from amylose:
- 1,4 glycosidic bonds
- Helix with intermolecular H-bonds = compact

Amylopectin:
- 1,4 and 1,6 glycosidic bonds
- Branched = many terminal ends for hydrolysis into glucose.

Question 8

Describe the structure and functions of glycogen.

Answer 8

Main storage polymer of a-glucose in animal cells but can also be found in plant cells.
- 1,4 and 1,6 glycosidic bonds
- Branched = many terminal ends for hydrolysis
- Insoluble = no osmotic effect and does not diffuse out of cells
- Compact

Question 9

Describe the structure and functions of cellulose.

Answer 9

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

Question 10

Describe the Benedict’s test for reducing sugars.

Answer 10

1. Add an equal volume of Benedict’s reagent to a sample.
2. Heat the mixture in an electric water bath at 100*C for 5 mins.
3. Positive result: colour will change from blue to orange & brick-red precipitate forms.

Question 11

Describe the Benedict’s test for non-reducing sugars.

Answer 11

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

Question 12

Describe the test for starch.

Answer 12

1. Add iodine solution.
2. Positive result: colour change from orange to blue-black.

Question 13

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

Answer 13

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