Monomers & Polymers + Carbohydrates

Question 1

Define monomer (give examples)

Answer 1

Smaller units that join together to form larger molecules
- Monosaccharides (glucose, fructose, galactose)
- amino acids
- nucleotides

Question 2

Define polymer (give examples)

Answer 2

Molecules formed when many monomers join together
- polysaccharides
- proteins
- DNA/ RNA

Question 3

What happens in a condensation reaction?

Answer 3

A chemical bond forms between 2 molecules & a molecule of water is produced

Question 4

What happens in a hydrolysis reaction?

Answer 4

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

Question 5

Name 3 hexose monosaccharides

Answer 5

• glucose
• fructose
• galactose

all have the molecular formula C(6)H(12)O(6)

Question 6

Name type of bond formed when monosaccharides react

Answer 6

(1,4 or 1,6) glycosidic bond
2 monomers = 1 chemical bond = disaccharide
multiple monomers = many chemical bonds = polysaccharide

Question 7

Name 3 disaccharides (describe how they form)

Answer 7

condensation reaction forms glycosidic bond between 2 monosaccharides
- maltose: glucose + glucose
- sucrose: glucose + fructose
- lactose: glucose + galactose

all have molecular formula C(12)H(22)O(11)

Question 8

Describe structure and functions of starch

Answer 8

storage polymer of a-glucose in plant cells
- insoluble = no osmotic effect on cells
- large = does not diffuse out of cells

amylose:
- 1,4 glycosidic bonds
- helix with intermolecular H-bonds = compact

amylopectin:
- 1,4 & 1,6 glycosidic bonds
- branched = many terminal ends for hydrolysis into glucose

Question 9

Describe structure and functions of glycogen

Answer 9

main storage polymer of a-glucose in animal cells (but also found in plant cells)

• 1,4 & 1,6 glycosidic bonds
• branched = many terminal ends for hydrolysis
• insoluble = no osmotic effect & does not diffuse out of cells
• compact

Question 10

Describe structure and functions of cellulose

Answer 10

polymer of B-glucose gives rigidity to plant cell walls (prevent bursting under turgor pressure, holds stem up)

• 1,4 glycosidic bonds
• straight-chain, unbranched molecule
• alternate glucose molecules are rotated 180 degrees
• H-bonds crosslinks between parallel strands form microfibrils = high tensile strength

Question 11

Describe Benedict’s test for reducing sugars

Answer 11

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

Question 12

Describe Benedict’s test for non-reducing sugars

Answer 12

1. Negative result: Benedict’s reagent reminds blue
2. Hydrolyse non-reducing sugars e.g. sucrose 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
4. Proceed with the Benedict’s test as usual.

Question 13

Outline how colorimetry could be used to give qualitative results for presence of sugars & 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 absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration