monomers + polymers + carbohydrates

Question 1

Define monomer. Give some examples.

Answer 1

smaller units that join together to form larger molecules.
- monosaccharides (glucose, fructose, galactose)
- amino acids
- nucleotides

Question 2

Define polymer. Give some 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 and 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 the 3 hexose monosaccharides.

Answer 5

glucose.
fructose.
galactose.
all have the molecular formula C6H12O6.

Question 6

Name the 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 C12H22O11

Question 8

name the two isomers of glucose.

Answer 8

alpha and beta.

Question 9

what is an isomer?

Answer 9

same molecular formula different structure.

Question 10

what’s the difference in the structures of alpha and beta glucose.

Answer 10

hydroxyl group swaps position.

Question 11

Describe the structure and functions of starch.

Answer 11

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

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

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

Question 12

Describe the structure and functions of glycogen.

Answer 12

main storage polymer of alpha glucose in animal 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 13

Describe the structure and functions of cellulose.

Answer 13

polymer of beta glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up).
- 1,4 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 the Benedict’s test for reducing sugars.

Answer 14

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 minutes.
3. Positive result: colour change from blue to orange and brick-red precipitate forms.

Question 15

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

Answer 15

1. Negative result: Benedict’s reagent remains 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 minutes.
3. Neutralise the mixture using sodium carbonate solution.
4. Proceed with the Benedict’s test as usual.

Question 16

Describe the test for starch.

Answer 16

1. Add iodine solution.
2. Positive result: 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

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.