Unit 1

Question 1

Name 3 monosaccharides

Answer 1

Glucose
Galactose
Fructose

Question 2

Name 3 disaccharides and the monosaccharides that form them

Answer 2

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

Question 3

What Bond is formed between monosaccharides?

How is this bond formed?

How is this bond broken?

Answer 3

Glycosidic bond

Condensation reaction in which water is released

Hydrolyses reaction where an enzyme brings H20

Question 4

Define polysaccharide

Name 3 polysaccharides

Answer 4

Polymers which are formed when more than 2 monosaccharides join together

Cellulose, starch, glycogen

Question 5

What is the use of starch?

Answer 5

Excess glucose if stored as starch in plants - when energy is needed starch is broken down

Question 6

What is starch made of?

What are the properties of these chains?

Answer 6

Mixture of two polysaccharides of alpha glucose called amylose and amylopectin

Amylose: long unbranched chain of alpha glucose. Coiled structure which is good for storage because it can fit a lot in a small space

Amylopectin: long branched chain of alpha glucose. Side branches allow enzymes to break bonds easily so glucose can be released easily

Question 7

Why is starch good for storage

Answer 7

It is insoluble in water and doesn’t affect water potential so water cannot enter in via osmosis preventing turgidity so it is good for storage

Question 8

What is glycogen used for?

What are the properties of glycogen?

Answer 8

Excess glucose stored as glycogen in animals

Polysaccharide of alpha glucose
Similar structure to amylopectin + more side branches so glucose can be released quickly
Very compact - good for storage

Question 9

What is cellulose used for?

What are the properties of cellulose?

Answer 9

Structural support in plant cell walls

Long unbranched chains of beta glucose bonded together to form straight cellulose chains
Cellulose chains are linked together by H bonds which form strong microfibrils

Question 10

Test for reducing sugars

Answer 10

Sample + benedicts reagent
Heat
Brick red precipitate

Remains blue if not present

Question 11

Test for starch

Answer 11

Sample + iodine

Dark blue

Question 12

Test for non reducing sugar

Answer 12

Sample + HCl
Heat
Sodium bicarbonate
Benedicts reagent 
Reheat
Green, orange to brick red

Remains blue if not present

Question 13

What is the name of the lipid structure?

Describe this structure

What is the name of the bond

Answer 13

Triglyceride

Glycerol head bonded to 3 fatty acid hydrocarbon chain tails via condensation reactions

Ester bond

Question 14

What are the properties of the glycerol head and fatty acid tail

Answer 14

Glycerol is polar - charged and attracted to water

Fatty acid tail is non polar

Question 15

Define saturated fatty acid

Define unsaturated fatty acid

Why would a fatty acid be unsaturated?

Answer 15

Single bonds between carbon atoms

Double bonds between carbon atoms causing chains to kink

There is less number of hydrogens

Question 16

Why is a triglyceride not considered a polysaccharide?

Answer 16

It is not made of repeating units

Question 17

Emulsion test

Answer 17

Sample + ethanol
Shake
Add water + shake
Cloudy if lipid present

Question 18

Structure of amino acid

Answer 18

H
                 |
                 |
NH2 ---- C ---- COOH
                 |
                 |
                R
Amino group 
Carboxyl group
R group - range of chemical groups different in each amino acid

Question 19

What is the bond between 2 amino acids?

What is it caused by?

What is the resulting molecule called when more than two amino acids are bonded together

Answer 19

Peptide bond

Condensation reactions

Polypeptide

Question 20

Describe the formation of protein - primary structure

Answer 20

Polymerization occurs between amino acids to form polypeptide
Triplet sequence in base sequence in DNA codes for each amino acid - determines structure of polypeptide

Question 21

Describe the formation of protein - secondary structure

Answer 21

Hydrogen bonds form due to attraction via slight negative charge in primary structure
Causes structure to coil into alpha helix or pleat in beta pleated sheet

Question 22

Describe the formation of protein - tertiary structure

Answer 22

Chain is coiled or folded further

Hydrogen, ionic and disulfide bonds form

Question 23

Biuret test

Answer 23

Sample + sodium hydroxide
Copper sulphate solution
Purple layer forms

Remains blue if not present

Question 24

Explain is a change in the primary structure may result in a different 3D structure

Answer 24

Sequence of amino acid changes
Bonds form in different places
The structure will cool of fold into a different 3D tertiary structure

Question 25

Describe and explain how an enzyme forms a product

Answer 25

The substrate has a complimentary shape to the active site

The substrate binds to active site, forming an enzyme substrate complex

Question 26

Why does the enzyme lower the activation energy of the reaction it catalyses?

Answer 26

Reduces repulsion between molecules so they can be bonded easily
If catalysing, fitting into the active site puts a strain on the bonds in the substrate m, thus it breaks down more easily

Question 27

Describe the lock and key model of the enzyme

Why is it discredited?

Answer 27

Substrate fits exactly to active site supported by observations that enzymes are specific in reactions

Because bonds in tertiary structure of the protein are not strong enough to hold a rigid structure

Question 28

Describe the induced fit model of the enzyme

Answer 28

Initially the substrate is not complimentary to the active site
The active site changes shape and moulds itself around the substrate and thus becomes complimentary
After product is produced, enzyme returns to original shape

Question 29

What type of sugar is glucose?

What are the two types of glucose ?

Answer 29

Hexose sugar

Alpha and beta