biological molecules

Question 1

define a monomer and give three examples

Answer 1

smaller units that join together to form larger molecules

• monosaccharides
• amino acids
• nucleotides

Question 2

define polymer and give three examples

Answer 2

molecules formed when many monomers join together

• DNA/RNA
• protein
• polysaccharides

Question 3

what happens during a condensation reaction?

Answer 3

a chemical bond forms between two molecules and a molecule of water is produced

Question 4

name the three hexose monosaccharides

Answer 4

glucose
fructose
galactose

Question 5

type of bond formed when monosaccharides react

Answer 5

glycosidic bond

Question 6

name three disaccharides and what they are made of

Answer 6

lactose = glucose + galactose 
sucrose = glucose + fructose 
maltose = glucose + glucose

Question 7

structure and function of starch

Answer 7

storage polymer of a-glucose in plant cells
insoluble so no osmotic effect on cells
large so doesn’t diffuse out of cells
compact

Question 8

structure and functions of glycogen

Answer 8

main storage polymer of a-glucose in animal cells (animal starch)

branched - many terminal ends for hydrolysis
insoluble - no osmotic effect + doesn’t diffuse out of cells
compact

Question 9

structure and function of cellulose

Answer 9

polymer of B-glucose
gives rigidity to cell walls (avoid bursting)

straight chain + unbranched
H bonds between parallel strands
form microfibrils — high strength

Question 10

Benedict’s test for reducing sugars

Answer 10

add equal vol benedict’s solution to sample

heat mixture gently for five mins

positive result - blue to orange/brick red ppt formed

Question 11

benedict’s test for non reducing sugars

Answer 11

negative result - remains blue
hydrolyse non reducing sugars by reacting with HCl
heat in boiling water bath for five mins
neutralise the mixture with sodium hydrogen carbonate solution
proceed with usual benedict’s twst

Question 12

test for starch

Answer 12

add iodine solution

positive result is orange to blue black

Question 13

general structure of an amino acid

Answer 13

COOH group
R side group
NH2 amino group

Question 14

how to test for proteins in a sample

Answer 14

BIURET TEST presence of PEPTIDE bond

add equal vol NaOH solution to sample

add drops of DILUTE COPPER II SULFATE solution

positive - blue to purple

Question 15

how many amino acids are there and how do they differ from one another?

Answer 15

20

differ by side R group