biological molecules

Question 1

describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers with examples

Answer 1

1. condensation joins monomers and forms a chemical bond and releases water
2. hydrolysis breaks a chemical bond between monomers and uses water
3. amino acid and polypeptide (peptide bonds)
4. cellulose and beta glucose (glycosidic bonds)

Question 2

what is a monomer?

Answer 2

smaller unit from which larger molecules are made

Question 3

describe the chemical test for a non reducing sugar

Answer 3

1. heat with HCl and neutralise
2. heat with benedict’s solution
3. positive tests produces red precipitate

Question 4

describe two differences between the structure of a cellulose molecule and a glycogen molecule

Answer 4

1. cellulose is made of beta glucose and glycogen is made up of alpha glucose
2. cellulose is a straight chained molecule and glycogen is branched

Question 5

describe features of starch that make is a good storage molecule

Answer 5

1. insoluble in water so doesn’t effect water potential
2. coiled so it makes it compact
3. branched so more ends for a fast breakdown
4. polymer of alpha glucose so provides glucose for respiration

Question 6

which test identifies the presence of starch?

Answer 6

iodine test will turn blue-black if present

Question 7

describe the structure of glycogen

Answer 7

1.polymer of alpha glucose joined by glycosidic bonds
2.branched structure

Question 8

how does glycogen act as a source of energy?

Answer 8

1. hydrolysed to glucose
2. glucose is used in respiration

Question 9

explain the difference in structure of cellulose and starch

Answer 9

1. starch is formed from alpha glucose but cellulose is formed from beta glucose
2. position of hydrogen and hydroxyl groups on carbon atom 1 are inverted

Question 10

explain how is starch adapted for its function in plant cells

Answer 10

1. insoluble so doesn’t effect water potential
2. helical so it’s compact

Question 11

explain how cellulose is adapted for its function in plant cells

Answer 11

1. long straight chains
2. become linked by many hydrogen bonds to form fibrils
3. provides strength because of the strong hydrogen bonds

Question 12

what’s the general formula for a monosaccharide?

Answer 12

(CH2 O) n

Question 13

what are monosaccharides used for?

Answer 13

1. energy for respiration
2. building blocks for other molecules

Question 14

what is maltose made of?
lactose?
sucrose?

Answer 14

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

Question 15

describe the test for reducing sugars

Answer 15

1. add sample to test tube
2. add equal benedict’s reagent
   3.heat mixture
   red precipitate formed means positive result

Question 16

describe the difference between amylose and amylopectin

Answer 16

amylose is straight chained where as amylopectin is branched so can be broken down more quickly

Question 17

fatty acid general structure is RCOOH, name the group represented by COOH

Answer 17

carboxyl

Question 18

describe the test for lipids

Answer 18

add ethanol and shake vigorously then add water and shake gently
milky emulsion= positive result

Question 19

describe how a triglyceride molecule is formed

Answer 19

1. one glycerol and three fatty acids
2. condensation reactions and removal of three molecules of water
3. ester bonds formed

Question 20

describe how an ester bond is formed in a phospholipid molecule

Answer 20

1. condensation reaction and loss of water
2. between glycerol and fatty acid

Question 21

describe a triglyceride

Answer 21

glycerol with three fatty acids attached to it via ester bonds

Question 22

what is this?
CH2-CH-CH2
| |
O O

Answer 22

glycerol

Question 23

what makes something unsaturated?

Answer 23

if it has double carbon bonds

Question 24

describe the induced fit model of enzyme action and how an enzyme acts as a catalyst

Answer 24

1. substrate binds to the active site and enzyme substrate complex forms
2. active site changes shape slightly so it is complementary to substrate
3. reduces activation energy

Question 25

describe amino acid structure

Answer 25

an amine group (NH2) a carboxyl group (COOH) hydrogen atom variable R group

Question 26

how could an enzyme be stopped ?

Answer 26

boil or add strong acid or alkali to denature the enzyme

Question 27

explain how a competitive inhibitor decreases the rate of an enzyme controlled reaction

Answer 27

1. inhibitor similar shape to substrate 2. binds to active site 3. prevents enzyme substrate complexes forming

Question 28

describe how the structure of a protein depends on the amino acid it contains

Answer 28

1. structure is determined by position of amino acid hydrogen bonds 2. primary structure is sequence of amino acids 3. secondary structure formed by hydrogen bonding between amino acids 4. tertiary structure formed by hydrogen bonds between R groups 5. creates specific shapes in proteins 6. quaternary structure formed by hydrogen bonds between polypeptides

Question 29

describe how amino acids join so there is always NH2 at one end and COOH at the other end

Answer 29

1. one amine group joins to a carboxyl group for form a peptide bond 2. each amino acid is oriented in the same direction in the chain

Question 30

explain how the active site of an enzyme causes a high rate of reaction

Answer 30

1. lowers activation energy 2. induced fit causes active site to change shape 3. so enzyme substrate complex causes bonds to form and break

Question 31

describe a biochemical test for proteins

Answer 31

add sodium hydroxide and copper sulphate purple=positive result blue=negative

Question 32

describe how all dipeptides are similar and one way they differ

Answer 32

1. all contain CHNO and have two R groups 2. variable R group

Question 33

describe how a non competitive inhibitor can reduce the rate of an enzyme controlled reaction

Answer 33

1. attached to enzyme at a site other than the active site 2. changes tertiary structure of the enzyme 3. so active site and substrate are no longer complementary so less substrate can bind

Question 34

describe how a peptide bond is formed between two amino acids to form a dipeptide

Answer 34

1. condensation reaction and loss of water 2. between amine and carboxyl groups

Question 35

describe how the secondary structure of a polypeptide is produced by bonds between amino acids

Answer 35

1. hydrogen bonds 2. between NH group of one amino acid and C=O group

Question 36

explain why two proteins with the same number and type of amino acids have different tertiary structures

Answer 36

1.different sequence of amino acids 2. forms disulfide bridges in different places

Question 37

explain how formation of an enzyme substrate complex increases the rate of a reaction

Answer 37

1. reduces activation energy 2. due to bending bonds

Question 38

what is meant by degenerate genetic code

Answer 38

1. more than one codon codes for a single amino acid

Question 39

what is a globular protein?

Answer 39

1.eg enzymes usually ball shaped and soluble

Question 40

what is a fibrous protein?

Answer 40

1. eg collagen long chains that run parallel to

Question 41

why are enzymes important?

Answer 41

1.they allow reactions to take place a lower temperatures 2. they control metabolic pathways

Question 42

what factors effect enzyme action?

Answer 42

temp, pH, substrate concentration, competitive and non competitive inhibitors

Question 43

what is end- product inhibition?

Answer 43

when the product inhibits one of the enzymes at the beginning of the pathways