Enzymes part 2

Question 1

What does latic acid dissociate into

Answer 1

H+ and lactate

Question 2

What does pyruvic acid dissociate into

Answer 2

H+ and pyruvate

Question 3

What is a buffer

Answer 3

A buffer is something that resists change in pH so the pH of the blood remains at about 7.4

Question 4

How does a buffer work

Answer 4

• a buffer donates or accepts hydrogen ions

- some proteins such as haemoglobin can also donate or accept protons and act as buffers

Question 5

How does pH affect the bonds in molecules

Answer 5

• a hydrogen ion is attracted to the negative charged ions or molecules or parts of molecules,
• excess hydrogen ions interfere with the hydrogen bonds and ionic forces holding the tertiary structure of the enzyme together therefore the enzymes tertiary structure changes and the active site changes shape meaning that the substrate can no longer fit into the active site lowering the rate of reaction
• increasing the concentration of hydrogen ions will also alter the charges on the active site of enzyme molecules because more proteins cluster around the negatively charged group which interferes with the binding of the substrate molecules onto the active site

Question 6

why is pH so important to enzymes

Answer 6

enzymes work with a narrow change in pH

• small changes either side of the optimum pH slows the rate of reaction as the active site is disrupted
• if normal pH is restored then the enzyme can form hydrogen bonds again and the tertiary structure is formed again so the active site is restored
• at extremes of pH the active site is permanently changed and the enzyme is denatured and can no longer catalyse the reaction

Question 7

Draw the pH graph for enzymes

Answer 7

DRAW IT

Question 8

Draw the temperature graph for enzymes

Answer 8

DRAW IT

Question 9

What is the pH of intracellular enzymes

Answer 9

they have an optimum pH that is close to 7

Question 10

What is the pH of extracellular enzymes

Answer 10

they have optimum pH values which are different from pH 7,

For example amylase in the mouth works best at pH 6.8

Question 11

What is the pH of the stomach

Answer 11

between 1 and 2 as this is what pepsin works best in

Question 12

what is the pH in the small intestine

Answer 12

7.8 as this is the optimal for protein digesting enzymes such as trypsin and enterokinase so digest peptides into amino acids

Question 13

What is the effect of increasing substrate concentration on the rate of reaction

Answer 13

if you increase the concentration of substrate the rate of reaction increases
- more enzyme substrate complexes can form
- more product molecules are formed
- substrate concentration is limiting in the reaction because as it increases the rate of reaction increases therefore it is a limiting factor
The reaction will reach its maximum amount when the substrate is increased even further then this happens…..
- adding more substrate molecules to increase substrate concentration will not increase the reaction
- all the enzymes active sites are occupied by substrate molecules
- if more substrate molecules are added then they cannot successfully collide and fit into the enzymes active site

Question 14

Draw the effect of changing enzyme concentration graph

Answer 14

DRAW IT

Question 15

What is the effect of enzyme concentration on the rate of reaction

Answer 15

As the enzyme concentration increases the rate of reaction increases this is because

• more active sites of the enzyme become available
• more successful collisions between the enzyme and substrate occur
• more enzyme-substrate complexes can form per unit time so the rate of reaction increases
• enzyme concentration is the limiting factor as it increases and so does the rate of reaction

Question 16

What happens when the substrate concentration is fixed and you try to increase the rate of reaction by increasing the enzyme concentration

Answer 16

• the reaction would have reached the maximum rate
• so if the enzyme concentration has increased further then there will be no increase in the rate of reaction because the active site of the extra enzyme molecules will not be occupied by substrate molecules
• the enzyme concentration is no longer the limiting factor as enzyme concentration increases the rate of reaction increases
• substrate concentration is now the limiting factor as lack of substrate molecules is preventing the rate of reaction from increasing

Question 17

What is enzyme synthesis

Answer 17

this is when depending on the cells needs, genes for synthesising particular enzymes can be switched on o r off

Question 18

What is enzyme degradation

Answer 18

cells are continuously degrading old enzyme molecules to their component amino acids and synthesising new enzyme molecules from amino acids

Question 19

What are the advantages for enzyme degradation

Answer 19

• elimination of abnormally shaped proteins that might otherwise accumulate and harm the cell
• the regulation of metabolism in the cell by eliminating any superfluous enzymes
  it is important in order for a cell to regulate its metabolism properly

Question 20

DRAW graph for enzyme concentration on the rate of reaction

Answer 20

DRAW IT

Question 21

Describe how the rate of reaction catalysed by an enzyme progresses over time

Answer 21

• At the beginning of the reaction, enzyme and substrate molecules are in high concentration and are moving randomly this means that there is a greater chance of a substrate molecule colliding with an enzymes active site
• as the reaction goes on the substrate molecules are used up as they are converted to products therefore the concentration of the substrate drops
• therefore the frequency of the collisions between enzymes and substrate molecules decreases because enzymes may collide with product molecules therefore the rate of the reaction decreases
• the initial rate is the maximum rate

Question 22

what are inhibitors

Answer 22

they are substance that reduces or stops a reaction by reducing the activity of an enzyme

Question 23

How do inhibitors work

Answer 23

they collide with an enzyme molecule in a way which effects how the substrate binds to the enzymes r effects the enzymes turnover number
- some block the active site while others change the shape of the active site

Question 24

what are competitive inhibitors

Answer 24

this is where the enzyme has a similar shape to that of the substrate molecule and competes with the substrate molecules for the enzymes active site, it blocks the active site and prevents the formation from enzyme-substrate complex

Question 25

How do competitive inhibitors work

Answer 25

• the competitive inhibitors fit into the active site so a substrate cannot enter
• the amount of inhibition depends on the relative concentration of substrate and inhibitor molecules, more inhibitor molecules collide with active sites so the effect of inhibition is greater
• increasing the substrate concentration would reduce the effect of the inhibitor, if enough substrate is added the inhibitor will not collide with the enzyme

Question 26

How do substrate and competitive inhibitors compete with each other

Answer 26

• inhibitors compete directly with the substrate molecule for the enzymes active site they form an enzyme-inhibitor complex which inactivates the enzyme
• the inhibitor is not changed by the active site of the molecule
• the presence of the inhibitor effects the substrate molecule from joining to the active site which reduces the rate of formation of the ES complex and the product molecule formation
• inhibitor reduces the number of free enzyme active sites available for the substrate molecule
• mostly reversible as collisions between enzyme and substrate and enzyme and inhibitor are random therefore by increasing the concentration of the substrate you increase the chance that the substrate will collide with the enzyme and form an ES complex rather than the inhibitor
• when binding irreversibly to the active site it is called an inactivator

Question 27

What is a non-competitive inhibition

Answer 27

this is where the competitor molecule that attaches to a part of the enzyme molecule that is not the active site - it binds to the allosteric site, this changes shape of the active site which prevents the ES complex from forming this is because the enzymes active site is no longer complementary in shape to the substrate molecule

Question 28

Draw graph with the competitive inhibitor

Answer 28

DRAW IT

Question 29

Draw graph with non-competitive inhibitor

Answer 29

DRAW IT

Question 30

How do non-competitive inhibitors work

Answer 30

• they bind to the allosteric site this changes the tertiary\ry structure of the enzyme which changes its active site this means that the substrate molecule can no longer bind to the enzyme and a ES complex cannot form as the active site is no longer complementary
• this reduces the maximum rate of reaction, by adding more substrate” the reaction will be able to carry on at this lower rate but adding the concentration of substrate will not allow it to return to its maximum rate
• the more inhibitor molecules present the greater the inhibition as more enzyme molecules are distorted and cannot either form ES complexes or cannot complete catalytic reaction involving ES complexes
• can be reversible but mostly irreversible

Question 31

What is end-product inhibition

Answer 31

after the enzyme catalyses reaction has reached completion product molecules may be tightly bound to the enzyme therefore the enzyme cannot form more of the product that the cell needs this is negative feedback

Question 32

How does the presence of organelles within a cell increase the efficiency of metabolic reactions

Answer 32

• many metabolic reactions are carried out in particular regions of the cell organelles this increases the efficiency of metabolism, some enzymes within organelles are bound into the organelle membrane

Question 33

What do multi-enzyme complexes do

Answer 33

they increase the efficiency of metabolic reactions without increasing substrate concentration as they keep the enzyme and substrate molecules in the same vicinity and reduce diffusion time

Question 34

How do metabolic sequences work

Answer 34

• the product of one enzyme catalysed reaction becomes the substrate of the next enzyme catalysed reaction in the metabolic pathway
• cells do not need to accumulate to much end product therefore the last enxyme catalyses reaction may also attach to part of the first enzyme in its pathway but not the active site
• this changes the active site of the first enzyme preventing the pathway from running it is non-competitive inhibition but it is reversible
• the concentration of this product within the cell falls and the molecules with detach from enzyme 1 and allow its active site to resume to its normal shape therefore the metabolic pathway can run again

Question 35

How does cyanide work

Answer 35

when ingested potassium cyanide is hydrolysed to produce hydrogen cyanide, this is a toxic gas that can dissociate into H+ and CN- ions
- the CN- ions bind irreversibly to an enzyme found in the mitochondria and inhibit the final stage of aerobic respiration, this is because the final stage in inhibited, earlier stages cannot run and aerobic respiration stops

Question 36

How does snake venom work

Answer 36

Venom of the green mamba snake contains a chemical that inhibits the enzyme AChE, this enzyme is important at neuromuscular synapse to break down the neurotransmitter ACh, if this enzyme is inhibited the ACh stays attached to the receptors on the muscle membrane and keeps the muscle contracted
- causes paralysis as movement depends on muscles being able to relax alternately, if muscles are involved in breathing are paralysed then victims die from suffocation

Question 37

How does aspirin work

Answer 37

Professeur John Vane discovered that salicylic acid binds to enzymes to catalyse the formation of prostaglandins, this prevents the formation of prostaglandins that are cell signalling molecules produced by cells when tissues are infected or damaged this makes nerve cells more sensitive to pain and increase swelling during inflammation

• reduces the risk of blood clots forming and reduces the risk of strokes
• can damage stomach lining

Question 38

How does ATPase inhibitors work

Answer 38

estracts from foxglove leaves are used to treat heart failure and atrial arrhythmia

• these chemicals are now known as cardiac glycosides
• these inhibit the sodium potassium pump in the cell membranes of heart muscle cells and allow more calcium ions to enter the cell, calcium ions increase muscle concentration and strengthen the heartbeat

Question 39

How does ACE inhibitors work

Answer 39

they are medical drugs which inhibit the angiotensin converting enzyme ACE which normally operates in a metabolic pathway which increases the blood pressure

• they reduce blood pressure in patients with hypertension who cannot take beta-blockers
• to treat heart failure - low dose at first and patients blood pressure is checked in case it falls to low
• to minimise risk of a second heart attack or stroke in patients who suffered myocardial infarction

Question 40

What do protease inhibitors do

Answer 40

protease inhibitors such as amprenavir and ritonavir and are used to treat viral infections in order to prevent the replication of virus particles within the host cells by inhibiting protease enzymes so viral coats cannot be made - this happens by competitive inhibition

Question 41

How does Nucleoside reverse and transcriptase inhibitors work

Answer 41

• many antiviral drugs such as zidovudine and abacavir are used to treat patients who are HIV positive are nucleoside reverse transcriptase inhibitors, these inhibit enzymes involved in making DNA using the viral RNA as a template