Biological molecules (mon pol and carbs so far)

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 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

Draw the structure of ⍺-glucose.

Answer 8

(hydrogen hydrogen on top, HO Oh on bottom)

Question 9

Draw the structure of 𝛽-glucose.

Answer 9

(H OH on top. H OH ob bottom)

Question 10

Describe the structure and functions of starch.

Answer 10

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

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

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

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 glycosidic bonds
● branched = many terminal ends for hydrolysis
● insoluble = no osmotic effect & does not diffuse
out of cells
● compact

Question 12

Describe the structure and functions of cellulose.

Answer 12

polymer of 𝛽-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°
● H-bond crosslinks between parallel strands form
microfibrils = high tensile strength

Question 13

Describe the Benedict’s test for reducing sugars

Answer 13

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

Question 14

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

Answer 14

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 15

Describe the test for starch.

Answer 15

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

Question 16

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

Answer 16

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.