Biological molecules

Question 1

Roles of lipids

Answer 1

Cell membrane
Insulation
Water proofing
Energy source
organ protection

Question 2

Characteristics of lipids

Answer 2

C, H, O
Insoluble in water
Soluble in organic solvents e.g alcohol, acetone

Question 3

Types of lipids

Answer 3

Phospholipids
Triglycerides

Question 4

Structure of Phospholipid

Answer 4

CH2COO - Fa
I
CHCOO - Fa
I
Phosphate–CH2

Question 5

Structure of triglyceride

Answer 5

CH2O-OC - FA
I
CHO-OC - FA. + 3H2O
I
CH2O-OC - FA

Question 6

What are the bonds between lipids

Answer 6

Ester bonds

Question 7

What are the bonds between proteins

Answer 7

Peptide bonds

Question 8

What are the 2 types of protein

Answer 8

Fibrous - structure
Globular - Metabolic

Question 9

What determines the shape and function of a protein

Answer 9

The primary structure

Question 10

What are the 3 bonds in the tertiary structure of a protein

Answer 10

Disulphide bridges
Ionic bonds
Hydrogen bonds

Question 11

Test for protein

Answer 11

Add sample in tube with equal volume of sodium hydroxide at room temp
Few drops of copper(II) sulfate solution
Purple colour positive test for peptide bonds
Negative remains blue

Question 12

Test for lipids

Answer 12

2cm cubed of sample, 5cm cubed of ethanol
Shake solution
Add 5cm3 of water
Cloudy white emulsion colour means lipid present

Question 13

Difference between a glucose and b glucose

Answer 13

b glucose only found in plants
B glucose has OH at top, a has H at top

Question 14

Test for reducing sugars

Answer 14

2cm^3 of sample in tube, grind in water if not in liquid form
Add benedict’s reagent
Heat for 5 minutes

green - very low
yellow - low
orange - medium
Red - high

Question 15

What are the reactants for the disaccharides

Answer 15

Glucose + Glucose —> maltose
Glucose + fructose —> sucrose
Glucose + galactose —> lactose

Question 16

Test for non reducing sugars

Answer 16

Carry out benedict’s test
If no colour change, add 2cm^3 of dilute hydrochloric acid and place in gently boiling water bath for 5 minutes
Add Sodium hydrogen carbonate to neutralise HCl
Repeat benedict’s test

Lower pH and higher temp should have hydrolysed the glycosidic bonds

Question 17

Test for starch

Answer 17

2cm^3 of sample
Add 2 drops of potassium iodide solution
Positive test - blue/black solution

Question 18

Characteristics of starch

Answer 18

Insoluble, doesn’t affect water potential
Does not diffuse out of cells
Compact so stored in small place
Forms a-glucose when hydrolysed, ready use in respiration
Branched in many ends, rapid simultaneous enzyme action for hydrolysis

Question 19

Glycogen characteristics

Answer 19

Insoluble, doesn’t draw water via osmosis or diffuse out of cells
Compact so stored in small space
More highly branched than starch, rapid hydrolysis for respiration, important in animals with high metabolic rate

Question 20

Cellulose characteristics

Answer 20

Made of b-glucose
unbranched straight chains
Chains run parallel to form collective strength
group to form microfibril to form fibres
Prevents cell bursting

Question 21

How are b-glucose arranged in cellulose

Answer 21

B-glucose rotates 180 degree each molecule to form glycosidic bond
Can form H bonds to parallel polysaccharides