Monomers, polymers and carbohydrates - Biological Molecules

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 & 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 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
all have molecular formula C12H22O11

Question 7

Name the type of bond formed when monosaccharides react.

Answer 7

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

Question 8

Describe the structure and functions of starch.

Answer 8

storage polymer of 𝛼-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 & 1,6 glycosidic bonds
● branched = many terminal
ends for hydrolysis into glucose

Question 8

Draw the structure of ⍺-glucose.

Answer 8

check google

Question 9

Draw the structure of 𝛽-glucose.

Answer 9

check google

Question 10

Describe the structure and functions of cellulose.

Answer 10

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

● 1,4glycosidicbonds

● straight-chain, unbranched molecule
●alternate glucose molecules are rotated 180°
● H-bond cross links between parallel strands form
microfibrils = high tensile strength

Question 11

Describe the structure and functions of glycogen.

Answer 11

main storage polymer of 𝛼-glucose in animal cells ( but also found in plant cells)
● 1,4&1,6 glycosidicbonds
●branched=many terminal ends for hydrolysis
●insoluble = no osmotic effect & does not diffuse out of cells
● compact

Question 12

Describe the Benedict’s test for reducing sugars.

Answer 12

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 change from blue to orange & brick-red precipitate forms.

Question 13

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

Answer 13

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 mins.
3. Neutralise the mixture using sodium carbonate solution.
4. Proceed with the Benedict’s test as usual.

Question 14

Describe the test for starch.

Answer 14

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

Question 15

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

Answer 15

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.