Enzymes

Question 1

What are enzymes

Answer 1

they are biological catalysts because they speed up metabolic reactions in living organisms, there actions effect structure and functions in cells

Question 2

What is the turnover number

Answer 2

the number of reactions that an enzymes molecule can catalyse per second

Question 3

How do enzymes work

Answer 3

• they are catalysts so speed up the rate of reaction without themselves being used up in the first place so they can be used again
• a small amount of catalyst can be used to catalyse teh conversion of a large number of substrate molecules into product molecules

Question 4

why are enzymes better than normal chemical catalysts

Answer 4

• they are more specific than chemical catalysts
• do not produce unwanted products and do not make mistakes
• cells in which they are made in regulate their production and activity to fit the needs of the cell or organism at that time

Question 5

for some enzymes to catalyse reactions they may need help from….

Answer 5

cofactors

Question 6

what would prevent the enzyme from working

Answer 6

• if the instruction which code for the gene has a mutation this could alter the sequence of amino acids in the protein which will alter the enzymes tertiary structure and prevent it from functioning

Question 7

What happens when an enzyme that catalyses a metabolic reaction is deficient

Answer 7

• a metabolic disorder results

Question 8

What do enzymes also catalyse the reaction off

Answer 8

• the formation of the organisms structural components such as collagen in bone, cartilage, joints, connective tissue, if the enzyme does not function while this happens then it can be harmful and cause diseases such as stone man syndrome

Question 9

What is the active site

Answer 9

The indented area on the surface of an enzyme molecule with a shape that is complementary to the shape of the substrate molecule

Question 10

Describe the active site

Answer 10

• made from the tertiary structure
• the shape is complementary to the shape of the substrate molecule therefore its shape is very important
• therefore each type of enzyme is specific in its function as it can only catalyse reactions of substrate molecules which fit into the active site and produce product molecules

Question 11

What changes the active site of an enzyme

Answer 11

• temperature
• pH
  These both effects the bonds that hold proteins in there tertiary structure

Question 12

What is an intracellular enzyme

Answer 12

inside the cell

Question 13

What is an extracellular enzyme

Answer 13

outside the cell

Question 14

Describe a metabolic pathway (Intracellular enzymes)

Answer 14

• each metabolic pathway in a living cell is one of a series of consecutive reactions and every step is catalysed by an enzyme
• various reactants and intermediates act as substrates for the enzyme
• reactants, intermediates and products act as metabolites
• e.g. respiration and photosynthesis

Question 15

Describe anabolic and catabolic pathways (metabolic pathways for intracellular enzymes)

Answer 15

• in catabolic pathways - metabolites are broken down to smaller molecules and release energy
• in anabolic pathways - energy is used to synthesis larger molecules from smaller ones

Question 16

Describe the catalase example for intracellular enzymes

Answer 16

• catalase protects cells from damage by reactive oxygen by breaking down hydrogen peroxide to form water and oxygen
• catalase consists of four polypeptide chains and contains a haem group with iron, it is the fastest acting enzyme and has the largest turnover
• found in eukaryotic cells in vesicles called peroxisomes
• when white blood cells ingest pathogens catalase is used to help kill the invading microbe

Question 17

What type of enzyme is catalase

Answer 17

Intracellular

Question 18

What type of enzyme is amylase, trypsin, and mucor

Answer 18

Extracellular

Question 19

Describe the Mucor example for extracellular enzymes

Answer 19

• fungi such as the bread mucor release hydrolytic enzymes from their hyphae, the enzymes digest carbohydrates, proteins and lipids in the bread and the products of digestion - glucose, amino acids, glycerol and fatty acids are absorbed into the fungal hyphae for respiration and growth

Question 20

Describe the amylase example for extracellular enzymes

Answer 20

• amylase is produced in the salivary glands, it acts in the mouth and digests the polysaccharide starch to the disaccharide maltose, it is also made in the pancreas and acts to catalyse the same reaction in the lumen of the small intestine

Question 21

Describe the typsin example for extracellular enzymes

Answer 21

• made in the pancreas, and acts in the lumen of the small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds
• Optimum pH between 7.5 - 8.5

Question 22

What are cofactors

Answer 22

these are substances that have to be present to ensure that an enzyme catalysed reaction takes place at the appropriate rate

• prosthetic groups are part of the enzyme structure
• mineral ion co-factors and organic coenzymes form temporary associations with the enzyme

Question 23

What type of enzymes-catalysed reactions especially need help from cofactors

Answer 23

• oxidation-reduction reactions

Question 24

What is a prosthetic group

Answer 24

• a cofactor that is permanently bound by covalent bonds to an enzyme molecule

Question 25

Give an example of an prosthetic group catalysed reaction

Answer 25

- carbonic anhydrase which contains a zinc ion permanently bound to its active site - found in the erythrocytes and catalyses the intercoversion of carbon dioxide to water and carbonic acid, this then breaks down to a hydrogen ion and hydrogencarbonate ions - important as it enables carbon dioxide to be carried from the respiring tissues to the lungs

Question 26

During an enzyme-catalysed reaction the enzyme and substrate molecules temporarily bind together to form

Answer 26

an enzyme-substrate complex

Question 27

What happens when certain ions that temporarily bind to the substrate or enzyme molecule

Answer 27

- this may ease the formation of enzyme-substrate complexes and increase the rate of the enzyme catalysed reaction

Question 28

What do cofactors do when they bind to an enzyme

Answer 28

- some act as co-substrates, they and the substrate together form the correct shape to bind to the active site of the enzyme - some change the shape of distribution on the surface of the substrate molecule or on the surface of the enzymes active site to make the temporary bonds in the enzyme-substrate complex easier to form

Question 29

What are coenzymes

Answer 29

these are small organic non-protein molecules that bind temporarily to the active site of enzyme molecules either before or at the same time that the substrate binds - they are chemically changed during the reaction and need to be recycled to there original state sometimes by a different enzyme

Question 30

What coenzymes are derived from what vitamins

Answer 30

``` B12 - cobalamin coenzymes Folic acid - tetrahydrofolate Nicotinamide B3 - NAD, NADP Pantothenate B6 - Coenzyme A Thiamine B1 - Thiamine Pyrophosphate ```

Question 31

What deficiency disease is caused by lack of B12

Answer 31

- lack of B12 means there is lack of coenzyme cobalamin coenzymes - pernicious anaemia this is progressive and fatal anaemia

Question 32

What deficiency disease is caused by lack of Folic acid

Answer 32

- lack of folic acid means there is a lack of tetrahydrofolate - megablastic anaemia - these are larger irregularly shaped erythrocytes

Question 33

What deficiency disease is caused by lack of Nicotinamide B3

Answer 33

- Lack of B3 means lack of NAD and NADP | - pellagra - diarrhoea, dermatitis and dementia

Question 34

What deficiency disease is caused by lack of Pantothenate B6

Answer 34

- Lack of B6 means lack of coenzyme A | - elevated blood-plasma triglyceride levels

Question 35

What deficiency disease is caused by lack of Thiamine B1

Answer 35

- Lack of B1, this means lack of thiamine pyrophosphate | - Beriberi - mental confusion, irregular heart beat, muscular weakness, paralysis and heart failure

Question 36

What is an enzyme-product complex

Answer 36

enzyme molecules with product molecules in its active site, the two are joined temporarily by non-covalent forces

Question 37

What is an enzyme-substrate complex

Answer 37

- enzyme molecules with substrate molecules in its active site, the two are joined temporarily by non-covalent forces

Question 38

Describe the lock and key hypothesis

Answer 38

1. the enzymes tertiary structure of the enzymes active site gives it a shape that is complementary to that of the substrate molecule that it needs to catalyse the reaction for 2. the substrate molecule fits into the enzymes active site and temporary hydrogen bonds hold the two together forming an enzyme-substrate complex (ES complex) 3. the substrate molecule is broken into smaller product molecules that leave the active site or. .. 1. the substrate molecules fit into the active site forming a enzyme - substrate complex 2. bond forms between the substrate molecules 3. the larger product molecule leaves the active site

Question 39

Describe in depth the lock and key hypothesis

Answer 39

1. the substrate molecules and enzyme molecules both have kinetic energy and are constantly moving randomly 2. if a substrate molecule successfully collides with an enzyme molecule then an enzyme substrate complex forms this is because the substrate molecule fits into the complementary shaped active site on the enzyme molecule 3. the substrate molecules are either broken down or built up into the product molecule and form an enzyme -product complex while still in the active site 4. product molecules now leave the active site 5. the enzyme is now able to form another enzyme-substrate complex 6. a small number of enzyme molecules can therefore convert a large number of substrate molecules into product molecules

Question 40

Describe the induced fit hypothesis

Answer 40

1. when the substrate molecules fit into the enzymes active site the active site changes shape to mould around the substrate molecule 2. the active site still has a shape which is complementary to the substrate molecule but while binding the changes of the side chains of the amino acid give a more precise conformation that fits the substrate molecule exactly 3. binds more effectively 4. enzyme substrate complex is formed and non-covalent forces such as hydrogen bonds, ionic attractions, hydrophobic interactions bund the substrate to the enzymes active site 5. substrate molecules have been converted to the product molecules and these are still in the active site they form an enzyme-product complex 6. the product molecules have a slightly different shape from the substrate molecule so they detach from the active site 7. the enzyme is now free to catalyse another reaction with another substrate molecule of the same type

Question 41

How do the enzymes lower the activation energy

Answer 41

- enzymes have an active site specific to only the substrate molecules they bring the substrate molecules close enough together to react without the need for excessive heat therefore they lower the activation energy as the molecules do not need to overcome the activation energy as they need less energy to do so

Question 42

What happens when a substance is heated

Answer 42

- the extra energy in the form of heat causes the molecules to move faster - this increases the rate of collisions between molecules - it increases the force with which they collide as they are moving faster

Question 43

What happens when the reactant mixture is heated

Answer 43

both types of molecules gain kinetic energy and move faster, this increases the rate and number per seconds of successful collisions, therefore the rate of formation of ES complexes increases and the rate of reaction increases this increases the number of enzyme-product complexes per second up to a point at a particular temperature called the enzymes optimum temperature the rate of reaction is at its maximum

Question 44

What happens when the temperature increases above the optimum

Answer 44

as the temperature increases this may break some of the weak bonds such as the hydrogen and ionic bonds that hold the tertiary structure of the enzymes together as the molecules active site changes the substrate molecules do not fit into it therefore the reaction cannot be catalysed and the rate of reaction decreases - when more heat is applied the enzymes active site is completely changed and can not be reversed this is when the reaction has been denatured

Question 45

What is the optimum temperature

Answer 45

this is the temperature the enzyme works best at and at which the enzyme has reached its maximum rate of reaction - this can be hot or cold

Question 46

describe the thermophilic bacteria hot spring high temperatures example

Answer 46

- can survive in hot temperatures - the enzymes are heat stable this means that they have more disulphide bonds that do not break with heat and keep the shape of the protein molecules stable therefore there enzymes have high optimum temperatures

Question 47

How do you work out the rate of reaction

Answer 47

1/ time taken to reach end point

Question 48

What is the temperature coefficient

Answer 48

this refers to the increase in the rate of a process when the temperature is increased by 10degrees

Question 49

what is the equation of temperature coefficient

Answer 49

Q10= rate of reaction at (T+10) degrees/ rate of reaction at T degrees

Question 50

what happens to the temperature coefficient when temperatures are above the optimum

Answer 50

the temperature coefficient value drops, because higher temperatures alter the structure of the active sites of the enzyme molecule so that they are no longer complementary to the shape of substrate molecules