enzymes

Question 1

what are enzymes

Answer 1

• biological catalysts
• globular proteins
• interact with substrate molecules
• causing them to react at much faster rates

Question 2

what are anabolic reactions

Answer 2

• ‘building up’
• needed for growth
• catalysed by enzymes

Question 3

what are catabolic reactions

Answer 3

• ‘breaking down’
• in metabolic pathways which release energy
• catalysed by enzymes

Question 4

what is metabolism

Answer 4

• the sum of all different reactions and reaction pathways happening in a cell/organism
• can only happen with enzymes

Question 5

what is the Vmax

Answer 5

• enzymes can only increase the rates of reaction up to a certain point called the Vmax
• Vmax is the maximum rate of an enzyme-catalysed reaction

Question 6

what is the specificity of an enzyme

Answer 6

each enzyme catalyses one biochemical reaction, of which there are thousands in any given cell

Question 7

what is activation energy

Answer 7

• the energy needed to be supplied in order for a reaction to start
• enzymes can reduce the activation energy because they help molecules collide successfully

Question 8

Lock and key hypothesis

Answer 8

• only a specific substrate will fit in the active site of an enzyme
• an enzyme-substrate complex is formed when the substrate binds to the active site
• the R groups in the active site will interact with the substrate, forming temporary bonds
• these put a strain on the bonds within the substrate
• the substrates react and products are formed in an enzyme-product complex
• the products are released
• the enzyme is unchanged and able to be reused

Question 9

what is the active site of an enzyme

Answer 9

an area within the tertiary structure which has a shape that is complementary to the shape of a specific substrate molecule

Question 10

the induced fit hypothesis

Answer 10

• the active site of the enzyme changes slightly as the substrate enters
• the initial interaction between the enzyme and the substrate is relatively weak
• these interactions rapidly induce changes in the enzyme’s tertiary structure that strengthen binding
• this puts a strain on the substrate molecule
• this weakens bonds in the substrate. lowering the activation energy

Question 11

what are intracellular enzymes- give an example

Answer 11

• enzymes that act within cells
• catalase breaks down hydrogen peroxide (toxic byproduct of metabolic pathways) to oxygen and water

Question 12

what are extracellular enzymes

Answer 12

• enzymes that are released from cells to break down large nutrient molecules into smaller molecules (digestion)
• these smaller molecules can now be absorbed by the cell
• e.g. amylase, trypsin

Question 13

digestion of starch

Answer 13

• starch polymers are partially broken down into maltose (disaccharide) by amylase
• amylse is produced in the salivary glands and pancreas
• maltose is broken down into glucose(monosaccharide) by maltase
• maltase is present in the small intestine
• glucose is small enough to be absorbed by cells and the bloodstream

Question 14

digestion of proteins

Answer 14

• trypsin is a protease
• proteases are a type of enzymes that catalyse digestion of proteins into smaller peptides
• peptides are broken down further into amino acids by other proteases
• trypsin is produced in the pancreas and released with pancreatic juice to the small intestine where it acts on proteins
• amino acids produced are absorbed by cells and bloodstream

Question 15

what factors affect enzymes

Answer 15

• temperature
• pH

Question 16

what is the temperature coefficient Q10

Answer 16

• a measure of how much the rate of reaction increases with a 10C rise in temperature
• for enzyme controlled reactions it usually doubles with a 10C temperature increase

Question 17

why does increasing temperature increase rate of reaction of enzyme-controlled reactions

Answer 17

• increased K.E. of particles
• particles move faster
• more frequent successful collisions between substrate and enzyme

Question 18

why do enzymes denature

Answer 18

• at higher temperatures, the bonds holding the protein together vibrate more
• vibrations increase until the bonds strain and then break
• change in tertiary structure of the protein
• enzyme has changed shape
• the active site has changed shape and is no longer complementary to the substrate
• substrate can no longer fit into the active site so enzyme will no longer function as a catalyst
• enzyme is denatured

Question 19

what is the optimum temperature

Answer 19

• the temperature at which the enzyme has the highest rate of activity
• most enzymes in the human body have optimums of around 40C

Question 20

where are thermophilic bacteria found

Answer 20

hot springs

Question 21

where are psychrophilic orgnisms found

Answer 21

cold areas such as antarctic and arctic regions

Question 22

what are enzymes adapted to the cold like

Answer 22

• more flexible structures, particularly the active site
• making them less stable
• smaller temperature changes will denature them

Question 23

what are thermophiles

Answer 23

• organisms adapted to living in very hot environments like hot springs
• enzymes are more stable due to increased number of bonds (hydrogen, disulfide in tertiary s.)
• shape of these enzymes and active sites are more resistant to change as temperature increases

Question 24

what does a change in PH refer to

Answer 24

• a change in the hydrogen ion concentration
• low pH- more hydrogen ions
• high pH- less hydrogen ions

Question 25

what is the optimum pH

Answer 25

the certain hydrogen ion concentration at which the active site will be in the right shape

Question 26

what is renaturation

Answer 26

when the pH returns to the optimum pH, the protein will resume its normal shape and catalyse the reaction again

Question 27

why does the shape of the enzyme change as the pH changes

Answer 27

- the more H+ ions, the less the R-groups are able to interact with each other - this leads to bonds breaking and enzyme shape changing - this is because H+ ions interact with polar/charged R-groups - the degree of this interaction is changed when pH changes

Question 28

what can enzymes be activated by

Answer 28

cofactors

Question 29

what can enzymes be inactivated by

Answer 29

inhibitors

Question 30

what are inhibitors

Answer 30

molecules that prevent enzymes from carrying out their normal function of catalysis

Question 31

what is competitive inhibition

Answer 31

- molecule with similar shape to substrate can fit into the active site - substrate is blocked from the active site - enzyme is prevented from catalysis - enzyme cannot carry out its function so it is inhibited - reduced number of enzyme-substrate complexes so reduced rate of reaction

Question 32

do competitive inhibitors bind temporarily?

Answer 32

- they only bind temporarily to the active site - their effect is reversible - with the exception of aspirin

Question 33

effect of competitive inhibitors on rate of reaction

Answer 33

- reduced rate of reaction for a given concentration of a substrate - does not change the Vmax of the enzyme it inhibits - if substrate concentration is increased enough, the Vmax can still be reached

Question 34

example of competitive inhibition

Answer 34

- statins are competitive inhibitors of an enzyme used in the synthesis of cholesterol - aspirin irreversibly inhibits the active site of COX enzymes, preventing synthesis of chemicals which produce pain

Question 35

non-competitive inhibition

Answer 35

- inhibitor binds to enzyme at allosteric site - causes change in the tertiary structure of the enzyme so active site changes shape - active site no longer complementary to substrate and unable to bind to it - enzyme cannot carry out its function so it is inhibited

Question 36

effect of non-competitive inhibition on rate of reaction

Answer 36

- increasing concentration of enzyme or substrate will not overcome inhibitor - increasing concentration of inhibitor will decrease rate of reaction as more active sites become unavailable

Question 37

what is end-product inhibition

Answer 37

- enzyme inhibition that occurs when the product of a reaction acts as an inhibitor for the enzyme that produces it - negative feedback - non-competitive reversible inhibition

Question 38

what is a cofactor

Answer 38

- non-protein component needed by the enzyme to carry out its function as a biological catalyst - inorganic - obtained via the diet as minerals

Question 39

what is a coenzyme

Answer 39

- non-protein component needed by the enzyme to carry out its function as a biological catalyst - organic - obtained from the diet as vitamins

Question 40

what cofactor does amylase contain

Answer 40

chloride ion necessary for formation of a correctly shaped active site

Question 41

what does vitamin B3 synthesise

Answer 41

- NAD- a coenzyme responsible for transfer of hydrogen atoms between molecules in respiration - NADP- photosynthesis

Question 42

what does vitamin B5 make

Answer 42

- coenzyme A which is essential for breakdown of fatty acids and carbohydrates in respiration

Question 43

what are prosthetic groups

Answer 43

- required by enzymes to carry out their catalytic function - they are tightly bound to form a permanent feature of the protein - e.g. carbonic anhydrase contains Zn2+ ions . It is an enzyme for metabolism of CO2

Question 44

what are inactive precursor enzymes

Answer 44

- enzymes that are produced in an inactive form - particularly those that cause damage within the cells producing them or to tissues when they are released, or enzymes that need to be controlled and only activated in certain conditions

Question 45

how can precursor enzymes be activated

Answer 45

- they need to undergo a change in shape (tertiary) to be activated - can be achieved by the addition of a cofactor

Question 46

what is an apoenzyme

Answer 46

a precursor enzyme before its cofactor is added

Question 47

what is a holoenzyme

Answer 47

a precursor enzyme after its cofactor is added and the enzyme is activated

Question 48

what are zymogens or proenzymes

Answer 48

when a change in conditions (pH or temp) results in a change of tertiary structure and activates a precursor enzyme

Question 49

what happens when pepsinogen is released into the stomach

Answer 49

- pepsinogen is inactive - it digests proteins - the acid pH transforms it into the active enzyme pepsin - this protects body tissues against the digestive action of pepsin