topic 1A: biological molecules

Question 1

monomers

Answer 1

smaller molecular units which can create larger molecules (e.g. monosaccharides, amino acids and nucleotides)

Question 2

polymers

Answer 2

large, complex molecules composed of long chains of monomers joined together (e.g. polysaccharide, polypeptide and polynucleotide)

Question 3

2 key chemical reactions

Answer 3

condensation reaction and hydrolysis reaction

Question 4

condensation reaction

Answer 4

joins two molecules together, with the formation of a chemical bond and involves the elimination of a molecule of water.

Question 5

hydrolysis reaction

Answer 5

separates two molecules by breaking a chemical bond and involves the addition of a water molecule.

Question 6

monsachharides + examples

Answer 6

the monomers which form larger carbohydrates e.g. glucose, fructose and galactose

Question 7

carbohydrates contain the elements…

Answer 7

-C (carbon)
-H (hydrogen)
-O (oxygen)

Question 8

hexose sugar

Answer 8

a monosaccharide with six carbon atoms in each molecule e.g glucose

Question 9

2 types of glucose

Answer 9

alpha and beta

Question 10

insomers

Answer 10

same molecular formula but different structure with atoms arranged in a different ways

Question 11

draw alpha glucose molecule

Answer 11

H
OH

Question 12

draw beta glucose molecule

Answer 12

OH
H

Question 13

disaccharides

Answer 13

a disaccharide is formed when two monosaccharides join together by a condensation reaction, forming a glycosidic bond (e.g. maltose, lactose and sucrose)

Question 14

disaccharides formulas

Answer 14

-(2 alpha) glucose + glucose ->maltose + water (glycosidic bond)
-glucose + galactose -> lactose + water
-glucose + fructose -> sucrose + water

Question 15

glycosidic bond

Answer 15

forms between two monosaccharides by a condensation reaction and releases a molecule of water

Question 16

polysaccharides + examples

Answer 16

polysaccharides are formed when more than 2 monosaccharides join together by a condensation reaction, releasing a water molecule for each glycosidic bond
e.g. starch, glycogen and cellulose

Question 17

starch function

Answer 17

-a main energy storage molecule in plants for excess glucose as starch (when a plant needs more glucose for energy, it breaks down starch to release the glucose)

Question 18

starch structure + formation

Answer 18

-made up of two polysaccharides of alpha glucose by a condensation reaction
-amylose and amylopectin

Question 19

amylose

Answer 19

-a long, unbranched chain of alpha glucose, the angles of the glycosidic bonds creates a coiled and compact structure

Question 20

amylopectin

Answer 20

-a long, branched chain of alpha glucose, its side branches allows starch to hydrolyse and release glucose rapidly

Question 21

starch structure related to function

Answer 21

-coiled structure - because the angle of the glycosidic bond, therefore this makes it compact to store more glucose in a small space
-branched chains: can be hydrolysed (broke down) quickly so that glucose can be released quickly
-insoluble in water: no osmotic effect so this doesnt affect the water potential (good for storage as water cant enter the cell by osmosis)

Question 22

glycogen function

Answer 22

-main energy storage molecule in animals for excess glucose as glycogen
-mainly stored in muscle and liver cells

Question 23

glycogen structure

Answer 23

-made up of two polysaccharides of alpha glucose by a condensation reaction
-loads more side branches coming of it
-very compact molecule

Question 24

glycogen structure related to function

Answer 24

-branched: rapid hydrolysis (break down) so that stored glucose can be released quickly which is important for energy release in animals
-compact: good for storage, so it can store more glycogen in a smaller space
-insoluble: no osmotic effect so it doesnt affect water potential

Question 25

cellulose function

Answer 25

-provides structural strength in cell walls of plants due to the microfibrils (strong fibres) formed by the hydrogen bonds

Question 26

cellulose structure

Answer 26

-polysaccharide of beta glucose monosaccharides bonded by a condensation reaction, they form straight cellulose chains
-the long, unbranched cellulose chains are linked together by many hydrogen bonds to form microfibrils (strong fibres) which provide structural support and strength for plant cells

Question 27

cellulose structure related to function

Answer 27

-hydrogen bonds form between chains: forms microfibrils (strong fibres) which create collective strength to the cell wall making it rigid
-straight and unbranched

Question 28

2 types of lipids

Answer 28

triglycerides and phospholipids

Question 29

structure of triglycecides

Answer 29

-contains one molecule of glycerol with three fatty acids attached to it

Question 30

explain how glycerol is bonded with the three fatty acids

Answer 30

• the glycerol bonds with the three fatty acids by three separate condensation reactions, which forms three water molecules and three ester bonds
  1. molecule of glycerol and a fatty acid bond by a condensation reaction which releases a water molecule and removed (this reaction repeats 3 times)
  2. therefore three ester bonds and three molecules of water are released and removed

Question 31

protein

Answer 31

a protein is a polymer made up of the monomer, amino acids

Question 32

4 groups from the structure of an amino acid

Answer 32

-carboxyl group (COOH)
-amine group (NH2)
-R (variable group- 20 different amino acids)
-hydrogen atom

Question 33

peptide bond

Answer 33

formed by a condensation reaction between two amino acids

Question 34

dipeptide

Answer 34

formed by the condensation of two amino acids

Question 35

polypeptide

Answer 35

formed by the condensation of many amino acids
-1 or more polypeptide chains is a protein

Question 36

peptide bond formation

Answer 36

a condensation reaction between the OH on carboxyl group and the H on amine group, which releases a water molecule and forms a peptide bond

Question 37

proteins structural levels

Answer 37

1. primary structure
2. secondary structure
3. tertiary structure
4. quaternary structure

Question 38

primary structure

Answer 38

a specific sequence of amino acids in a polypeptide chain, this determines the shape and function of the protein

Question 39

secondary structure

Answer 39

-hydrogen bonds form between the amino acids in the chain this causes the polypeptide chain to be coiled (alpha helix) or folded (beta sheet)

Question 40

tertiary structure and additional bonds

Answer 40

-the tertiary structure is the secondary structure which is coiled and folded further, to form a unique 3D shape, which leads to additional bonds forming between different parts of the polypeptide chain

-hydrogen bonds, ionic bonds and disulphide bridges

-hydrogen bonds: between R groups
-disulphide bridges: only occur between cysteine amino acids (if there is a sulfur in R group)
-ionic bonds: between charged R groups

-tertiary structure creates the final 3D structure for proteins of only one polypeptide chain

Question 41

Quaternary structure

Answer 41

-a Quaternary structure is a protein made up of more than one polypeptide chain (which are bounded together)
-the Quaternary structure is the proteins final 3D structure
-examples: haemoglobin, insulin collagen

Question 42

relationship between protein structures and function

Answer 42

-the sequence of amino acids is determined by the genetic code, this effects the primary structure
-the primary structure determines how the polypeptide is coiled or folded in the secondary structure
-the secondary structure determines where bonds form, this affects the whole shape of the protein
-the shape of a protein determines its function
-altering the primary structure affects the tertiary structure shape, which affects its function

Question 43

protein types

Answer 43

-globular- soluble, R group folded creates 3D shape (e.g. enzymes)
-fibrous- insoluble, structural, 3D shape (e.g. collagen + keratin - structural protein)

Question 44

enzymes

Answer 44

enzymes are biological catalysts which speeds up the rate of a chemical reaction without getting used up (a tertiary structure with a specific 3D shape)

Question 45

how do enzymes speed up a reaction?

Answer 45

lower the activation energy by:

-providing an alternative pathway for the reaction with lower energy

-binding reactants at active site and positioning them correctly

-bringing reactants together so less kinetic energy is used by moving round and trying to collide

Question 46

two types of enzyme action models

Answer 46

-lock and key theory
-induced fit model

Question 47

lock and key theory

Answer 47

-old and outdated model

-every enzyme has an active site which has a fixed shape and has a specific and unique shape due to the specific folding and bonding in the tertiary structure of proteins

-the substrate is complementary to the enzymes active site, so the substrate binds to it - this forms an enzyme-substrate complex

• the enzyme catalyses a reaction to release products - enzyme is unchanged and can be reused

Question 48

induced fit model

Answer 48

-active site of enzyme is not completely complementary to substrate

-the induced fit is when the enzymes active site changes shape, to mould itself around the substrate in order to complete the fit - the enzyme is flexible and disorts the hydrogen bonds holding the enzyme in shape (changes)

-the enzyme-substrate complex is formed, the enzyme catalyses a reaction and releases products

• the enzyme’s active site returns to its original shape

Question 49

enzymes properties relate to their tertiary structure - enzyme specificity

Answer 49

-enzymes are very specific - they only catalyse on reaction as only one substrate is complementary to the active site

-the shape of the active site is determined by the tertiary structure which is determined by the primary structure (sequence of amino acids in a polypeptide chain)

-if there is a mutation which affects the gene, the primary structure is affected, this changes the way the polypeptide is bonded and folded, and therefore affects the shape of the protein in its tertiary structure which alters the shape of the active site, this means that the substrate will not fit and the reaction wont be catalysed

Question 50

factors affecting enzyme activity

Answer 50

-pH
-temperature
-enzyme concentration
-substrate concentration
-competitive inhibitor
-non competitive inhibitor

Question 51

temperature affecting enzyme activity

Answer 51

-as the temperature increases, the rate of an enzyme controlled reaction increases
-as temperature increases there is more kinetic energy so the molecules vibrate more and move faster
-this makes the enzyme more likely to collide with the substrate molecule - the energy of collisions also increase
-the rate of reaction increases up to the optimum temperature

-if the temperature goes above the optimum temperature, the vibration cause some of the hydrogen bonds to break, which are holding the enzymes tertiary structure shape
-the enzyme is denatured, as the active site changes shape - no longer functions as a catalyst

Question 52

pH affecting enzyme activity

Answer 52

-all enzymes have an optimum pH (usually pH 7 (neutral), but pH 2 for pepsin since it’s found in the acidic stomach)

-if the pH is above and below the optimum pH, the enzyme denatures (active site changes shape) due to the H+ and OH- ions altering the ionic and hydrogen bonds that are holding the enzymes in its tertiary structure

Question 53

substrate concentration affecting enzyme activity

Answer 53

-increasing the substrate concentration, increase rate of reaction
-more substrate molecules means a collision between substrate and enzyme is more likely - enzyme-substrate complexes are more likely
-increases up to a ‘SATURATION’ POINT where all the enzymes active sites are in use
-increasing substrate concentration after this point has NO FURTHER EFFECT
-over the reaction time, substrate concentration reduces as the product is formed, meaning rate of reaction decreases over time - this makes the initial rate of reaction, the highest rate of reaction

Question 54

enzyme concentration affecting the rate of reaction

Answer 54

-increasing enzyme concentration, increases the rate of reaction
-the more enzyme molecules there are in a solution, the more likely collisions with substrate molecules and form enzyme-substrate complexes
-if substrate concentration is limiting, increasing concentration of enzyme has no further effect

Question 55

enzyme inhibitors

Answer 55

molecules that bind to the enzyme that they inhibit - prevents enzyme activity

Question 56

competitive inhibitors affecting enzyme activity

Answer 56

-competitive inhibitors molecules have a similar shape to the substrate molecule, which means it competes with the substrate molecules to bind to the active site, but no reaction takes place, instead they block the active site so no substrate molecules can fit in it

-this reduces the amount of enzyme-substrate complexes that can form

-increasing competitive inhibitors, reduces the rate of reaction, as they take up nearly all the active sites (and hardly any of the substrate will get to the enzyme)

-increasing substrate concentration, increases the chances of the substrate getting to an active site before the inhibitor, so this increases the rate of reaction

Question 57

non competitive inhibitors affecting rate of reaction

Answer 57

-non competitive inhibitor molecules dont compete for the active site as they have a different shape, the inhibitors binds away from the enzyme’s active site and instead binds to an allosteric (alternative) site, this alter the tertiary structure of the enzyme causing a permanent conformational(shape) change in the active site and becomes a different shape so the substrate is no longer complementary to the enzyme and can no longer bind to it

-therefore substrates cannot bind and form enzyme-substrate complexes

-increasing the substrate concentration, has no effect to the rate of reaction, as the non competitive inhibitors doesn’t compete and alters the shape of the active sites - enzyme activity will still be inhibited

Question 58

Reducing sugar test

Answer 58

-glucose - also fructose, galactose and maltose

METHOD
(use an excess of benedict’s solution - this makes sure that all the sugar reacts)

-add benedict’s reagent (blue) to a sample and heat it in a boiling water bath for 5 minutes

Question 59

non reducing sugar method

Answer 59

-if the result of the reducing sugar is negative, there could still be a non reducing sugar present:

-sucrose

METHOD
-add dilute hydrochloric acid (to break them down into monosaccharides) and heat it in a boiling water bath for 5 minutes
-neautralise it with an alkali (sodium hydrogen carbonate)
-carry out the benedict’s test for a reducing sugar (adding benedict’s solution and heating it in a boiling water bath for 5 minutes)

Question 60

positive and negative result of non reducing sugars

Answer 60

-positive result: solution changes from blue to brick red

-negative result: the solution will stay blue which means it doesn’t contain any sugar (either reducing or non reducing)

Question 61

positive result of reducing sugar

Answer 61

POSITIVE RESULT
solution changes from blue, green, yellow, orange to brick red
-the further the colour change goes (the more red) the higher the concentration of reducing sugar - compare amounts of reducing sugar in different solution

Question 62

test for starch - iodine + positive result

Answer 62

METHOD
-add iodine in a potassium iodide solution to the test sample

POSITIVE RESULT
-the solution will change from orange to blue/black