2.1.4 Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts made up of globular proteins

Question 2

Define globular

Answer 2

have a roughly spherical tertiary structure

Question 3

Why can enzymes only attach to some substrates and not others?

Answer 3

-Active site of enzyme= specific + unique in shape
So substrates can only bind to the active site of enzymes that are complimentary in shape

Question 4

Why is the active site of an enzyme specific?

Answer 4

Because of the specific folding and bonding in the tertiary structure of the protein, so have a specific 3d shape

Question 5

Substrate molecules do what to what part of enzyme? What is the name given to this?

Answer 5

Substrate molecules bind to active site of enzyme to make an Enzyme Substrate complex

Question 6

How does the substrate binding into the enzyme help the reaction?

Answer 6

Makes the reaction occur more quickly

Question 7

What happens if the substrate doesn’t fit into the active site of the enzyme?

Answer 7

Reaction won’t be catalysed

Question 8

Enzymes catalyse what reactions?

Answer 8

Intracellular and extracellular

Question 9

Where do intracellular enzymes react

Answer 9

inside of cells

Question 10

Give me 3 examples of Intracellular enzymes.

Answer 10

Catalase
Hydrolases
ATPases

Question 11

Where is catalase found? Function?

Answer 11

Catalase- found inside liver cells, breaks down hydrogen peroxide into oxygen and water

Question 12

Where are hydrolases found? Function?

Answer 12

Hydrolases- found inside lysosomes, these enzymes break down substances that a cell has taken in by phagocytosis

Question 13

Where are ATPases found? Function?

Answer 13

ATPases= found inside mitochondria, these enzymes are involved in synthesis of ATP during aerobic respiration

Question 14

Where do extracellular enzymes act?

Answer 14

these enzymes act outside cells.

Question 15

Give me examples of 4 extracellular enzymes and where they are found

Answer 15

-Trypsin
-Amylase
-Lipase
- Proteases

Question 16

Where is Trypsin found? Function?

Answer 16

Trypsin- found in small intestine, hydrolyses proteins

Question 17

Where are the following extracellular enzymes found:

-Trypsin
-Amylase
-Lipase
- Proteases

Answer 17

The digestive enzymes in the alimentary canal (gastro-intestinal tract)

Trypsin= found in small intestine

Question 18

Where is Amylase found? Function?

Answer 18

Amylase = made in the salivary glands +pancreas; hydrolyses starch into maltose

Question 19

Where is Lipase found? Function?

Answer 19

Lipase = made in the pancreas; hydrolyses triglycerides into glycerol and fatty acids

Question 20

Where is Protease found? Function?

Answer 20

Protease= made in the pancreas, found in stomach, pancreas and small intestine, hydrolyses proteins into amino acids

Question 21

What is activation energy?

Answer 21

the minimum amount of energy required to initiate a reaction

Question 22

Why can we not add heat to increase the activation energy for reactions to occur in our cells?

Answer 22

Because our human body operates at 37*c = that is the optimum temperature at which reactions take place, increasing temperature will result in enzymes denaturing

Question 23

What is the role of enzymes

Answer 23

Enzymes attach to substrate to lower activation energy needed for reaction to occur by providing an alternative pathway and therefore speed up the reaction

Question 24

How does an enzyme lower activation energy

Answer 24

When the enzyme
is present, the energy
barrier is much lower,
Therefore the activation
energy needed for the
reaction to occur is much
lower.

Question 25

What specifically lowers the activation energy

Answer 25

Formation of the enzyme substrate complex

Question 26

What is a metabolic reaction?

Answer 26

a biochemical reaction that takes place in living organisms in order to keep them alive

Question 27

What reactions are chemical reactions in cells with an enzyme, hapening in a living organism

Answer 27

Metabolic reactions

Question 28

In an exothermic reaction energy is what?

Answer 28

Energy is released

Question 29

What is an anabolic reaction?

Answer 29

• involve building of more complex molecules from smaller molecules by drawing two or more substrates into the active site, forming bonds between them and releasing a single product

Question 30

Give an example of an anabolic reaction

Answer 30

Glucose+ Fructose——>Sucrose

Question 31

How does an anabolic reaction allow a bond to be made more easily?

Answer 31

-formation of ESC lowers activation enegry as
-it holds 2 moleules of substrates close together
-any repulsion forces caused by electrons in outer shells of the atoms are overcome
- allows bond to be made more easily

Question 32

What are 2 examples of anabolic reactions, one in animal and one in plant?

Answer 32

Photosynthesis and protein synthesis

Question 33

What are catabolic reactions?

Answer 33

-larger molecules are broken down into smaller molecules

Question 34

Give example of a catabolic reaction

Answer 34

Sucrose——> Glucose+ Fructose
-when sucrase is added

Question 35

What is an anabolic reaction also known as?

Answer 35

Synthesis/ Building reaction

Question 36

What is a catabolic reaction also known as?

Answer 36

Breakdown reaction

Question 37

How does a catabolic reaction speed up the rate at which the substrate is broken into products?

Answer 37

• formation of ESC lowers activation energy because when
  substrate fits into active site the bond in the substrate is put under strain
  -The strain means that the bond is broken and substrate molecule breaks up more easily into products

Question 38

What does the lock and key hypothesis suggest?

Answer 38

-model suggests enzyme is like a lock and substrate is the key complimentary to that lock;

substrate fits into active site of enzyme exactly;

due to enzyme’s specific tertiary structure resulting in a complementary shape

-Enzyme active site is in a fixed, inflexible shape and that due to random collision the substrate can collide and attach to the enzyme, forming an ESC
-the charged group within active site are thought to distort the substrate and therefore lower the activation energy (1) which therefore results in substrate being broken/joined together

(1)= for understanding:

(bond in substrate is put under strain, breaking bond in substrate molecule more easily)

Question 39

The lock and key model suggests Usually only one type of substrate will fit into active site of enzyme. Why is this?

Answer 39

Due to enzyme specificity

-Active site of enzyme= specific + unique in shape
So substrates can only bind to the active site of enzymes that are complimentary in shape. In the same way that a key has a specific shape that will into one particular lock

Question 40

The lock and key model suggests that the active site of the enzyme is the same as the substrate so that it will fit in perfectly for the reaction to be catalyzed. True or false? Why?

Answer 40

False

Explanation:
-shapes are not the same as one another, they are co0mplementary to one another, that’s why they fit together like jigsaw pieces

Question 41

Suggest why most scientists accept the induced fit model rather than the lock and key model?

Answer 41

-induced fit model= supported by evidence

-lock and key model= unable to explain extent to which Activation energy is lowered, particularly in catabolic reactions

• we have improved knowledge on molecular structure of proteins and understanding they are slightly flexible+ can move, that hypothesis was updated, induced fit hypothesis is the current accepted model

Question 42

What hypothesis is the current accepted hypothesis in enzymes

Answer 42

The induced fit hypothesis

Question 43

What does the induced fit hypothesis suggest?

Answer 43

-enzyme is like a glove and substrate is like your hand

-induced fit is when, enzyme active site is flexible and is induced, or slightly changes shape to mold around the substrate until active site of enzyme fits shape of substrate exactly

-when enzyme substrate complex occurs it puts a strain on the bonds and therefore lowers the activation energy

(1)= for understanding:

(bond in substrate is put under strain, breaking bond in substrate molecule more easily)

Question 44

In the induced fit model the changes in the shape of active site of the enzyme to fit the substrate molecule is known as what?

Answer 44

These changes in shape are known as conformational changes

Question 45

What do the conformational changes ensure?

Answer 45

The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved

Question 46

The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved. How does this help the reaction?

Answer 46

This maximises the ability of the enzyme to catalyse the reaction

Question 47

Complementary charges can also play a role in the formation of ESCs. For example
if the substrate molecule carries a positive charge then the active site will have
amino acids with R groups with a negative charge. What is this opposing of charges known as?

Answer 47

Electrostatic force of attraction between the substrate and active site

Question 48

Complementary charges can also play a role in the formation of ———-. For example
if the substrate molecule carries a positive charge then the —— —- will have
amino acids with R groups with a ——–charge. Fill in blanks

Answer 48

1) ESCs
2) Active site
3) negative

Question 49

Why can humans digest starch but not cellulose?

Answer 49

Starch and cellulose are both polysaccharides – polymers of glucose molecules.
* Starch is made up of αlpha glucose and contains some branching.
* Cellulose is made up of beta glucose and is not branched.
These differences are enough to mean that they need their own specific enzyme

Starch is digested by amylase= The glycosidic bonds of starch fit
into the active site of amylase

Cellulose is digested by cellulase. The glycosidic bonds of cellulose do not fit into the active site of amylase

Amylase cannot bind with cellulose.
Cellulase cannot bind with starch.

Because cellulose does not fit into the active site of amylase and because we do not produce cellulase, we are
unable to digest cellulose

Question 50

In the exam, you might be asked why our bodies cannot digest certain chemicals.

Answer 50

Whatever the chemical is, the answer will always be the same – we cannot digest
something if we do not produce an enzyme with an active site which is
complementary to fit the chemical.

Question 51

Use the lock and key theory of enzyme action to explain why:
a) an enzyme is highly specific to one substrate
b) enzyme lowers the activation energy needed for a chemical reaction to occur

Answer 51

a) only the correct substrate has the right shape to fit into the active site of the enzyme

b) When the substrate(s) fit into the active site of the enzyme, it makes the reaction much more likely to occur. This lowers the activation energy needed

Question 52

Name 2 of the bonds that are important in holding the enzyme in its tertiary structure

Answer 52

Disulphide bridges and Hydrogen bonds

Question 53

Give one difference between the induced fit and the lock and key theory

Answer 53

Induced fit theory suggests enzymes active site changes when the substrate is present, , but the lock and key theory suggest that the active site of the enzyme is always the same shape

Question 54

Starch and cellulose are both polysaccharides made from glucose. However the bonds in the cellulose are a different shape to that in starch. Enzyme in the human gut can digest starch into sugars which are absorbed in the human body but they cannot hydrolyze cellulose. It is therefore known as ‘dietary fiber’ Use your knowledge of enzymes to explain why the enzyme that digests starch cannot digest cellulose.

Answer 54

the bonds in cellulose are a different shape from those in starch so they will not fit into the active site of the starch digesting enzyme.

Question 55

What is enzyme specificity?

Answer 55

shape of active site;
complementary;
to substrate which will fit in exactly;
forming an ESC;
other substrate molecules will not fit into this specific active site as they won’t be complimentary to its shape

Question 56

Suggest how the substrate changing shape slightly will assist enzyme action

Answer 56

-not only does the substrate have to be the correct shape to fit into the active site, it has to make the active site change shape too
-when the substrate changes shape, it puts strain on the bonds within the substrate molecule, so bonds break more easily, this lowers activation energy

Question 57

What’s a difference between the induced fit model and the lock and key hypothesis?

Answer 57

The substrate is thought to cause a change in the enzymes active site shape, which enables a better fit

Question 58

Explain why trypsin and chymotrypsin break peptide bonds between different amino acids

Answer 58

Enzymes are specific;
only substrate with complimentary shape will fit into the enzymes active site;
different amino acids will have different shapes;
will only be broken down by a specific enzyme

Question 59

Name a reaction in which enzyme activity can be monitored

Answer 59

when the enzyme
catalase breaks down hydrogen peroxide to produce water and oxygen.

Hydrogen peroxide—->water + oxygen

(catalase goes above the arrow)

Question 60

Formula for reaction between hydrogen peroxide and catalase

Answer 60

2H2O2 ——>2H2O + O2

catalase goes above the arrow as it is not involved in the reaction itself, doesn’t react, only speeds up the rate of reaction

Question 61

Catalase is an enzyme which is found in the tissues of most living things, why?

Answer 61

because hydrogen peroxide is a very toxic product of several different metabolic reactions.

Question 62

Where is catalase found the most in the human body as well in plants?

Answer 62

-liver
-potatoes
-celery
-often used as source of enzymes in biological catalysts

Question 63

What experiment can we use to measure the rate of reaction between the catalase and the hydrogen peroxide?

Answer 63

We can use the water displacement method of collecting gas

Question 64

How can we use the water displacement method of collecting gas to work out the rate of reaction

Answer 64

the volume of
oxygen produced in a unit of time can be
measured.

Question 65

What is a most accurate method of measuring the rate of reaction between catalase and hydrogen peroxide?

Answer 65

Method of gas collection using a gas syringe system

Question 66

What is an advantage of using a gas syringe over the water displacement method?

Answer 66

A gas syringe is a direct
method of measuring the volume of oxygen produced.
One advantage is that less of the oxygen will dissolve in the water.

Question 67

The curve is steepest at the beginning of the reaction – why? What is this called?

Answer 67

the rate of an enzyme controlled reaction is always fastest at the beginning, when enzyme and substrate molecules are first mixed there are plenty of each, so virtually at any one moment every enzyme molecule has a substrate molecule in its active site, meaning the reaction occurs very fast, explains the steepness at the start on the graph

This is called the initial rate of reaction.

Question 68

What is the turnover rate?

Answer 68

The rate at which the reaction occurs will depend only on how many enzyme
molecules there are and the speed at which each enzyme molecule can bind with
another substrate molecule –

Question 69

How can you calculate the initial rate of reaction?

Answer 69

You can measure the initial rate of the reaction by calculating the slope of a
tangent to the curve, as close to time 0 as possible.

Question 70

Why is it better to calculate the initial rate of reaction from a curve on a graph
rather than simply measure how much oxygen is given off in the first 30 seconds?
(Think about the difficulty of making this single measurement of oxygen given off
in the first 30 seconds, unless you have a datalogger)

Answer 70

There is a risk of inaccuracy in a single measurement at 30 seconds. The shape of
the curve is more likely to give an accurate value because it is based on many
readings taken over a period of time rather than just one.

Question 71

The rate of reaction is lower after 5 minutes than it was at the start. Explain why?

Answer 71

Less substrate is available, it is used up and has become a limiting factor, fewer collisions between enzyme and substrate, so fewer ESC formed

Question 72

Factors affecting enzyme activity.

Answer 72

-temperature
-pH
-concentration of substrate
-concentration of enzyme
-enzyme inhibition
-enzyme cofactors

Question 73

Like any chemical reaction the rate of an enzyme-controlled reaction increases
when the temperature is increased.

Answer 73

• More heat means more kinetic energy so molecules move faster.
• This makes the enzymes more likely to collide with the substrate molecules.
• The energy of these collisions also increases which means that each collision
  is more likely to result in a reaction (an ESC being formed).

Question 74

How does increasing temp affect rate of reaction

Answer 74

Like any chemical reaction the rate of an enzyme-controlled reaction increases
when the temperature is increased.

Question 75

What happens when you increase the temperature a lot

Answer 75

• The rise in temperature makes the enzyme’s molecules vibrate more.
• If the temperature goes above a certain level this vibration breaks some of
  the bonds in the tertiary structure that hold the enzyme in shape.

*When tertiary structure alters, The active site changes shape and the enzyme and substrate no longer fit
together.

• At this point the enzyme is denatured – it no longer functions as a catalyst.

Question 76

What is the optimum temp for enzymes in humans

Answer 76

Every enzyme has an optimum temperature.
For most human enzymes the optimum temperature is around 37°C.

Question 77

State the difference between bacterial amylase and amylase found in humans

Answer 77

Enzymes have different optimum temperatures;
human amylase has optimum temp of 37C, bacterial of 100C;
human amylase denatures at a lower temperature

Question 78

What happens the temperature is too low?

Answer 78

There is insufficient energy for successful collisions

Question 79

What is Q10?

Answer 79

temperature coefficient= measure of the rate of change of an enzyme controlled reaction as a result of increasing the temperatures by 10*C

Question 80

Formula of Q10?

Answer 80

Q10= R2/R1

Question 81

What is R1

Answer 81

rate of a reaction at a temperature of X*C

Question 82

What is R2?

Answer 82

Rate of reaction at a temperature (X+10)*C

Question 83

What is the value of Q10 for most enzymes?

Answer 83

Most Enzyme controlled reactions have a Q10 value of around 2 which means an enzyme is used

Question 84

What does pH measure?

Answer 84

-measures the concentration of Hydrogen ions, H in a solution

Question 85

According to the logarithmic scale, pH 5 has how many times less H+ ions than pH 4 and then pH 3 and then pH 2

Answer 85

pH 5 has 10 times less H+
than pH 4, 100 times less than pH 3 and
1000 times less than pH 2.

Question 86

What is the correlation between concentration and pH value

Answer 86

the higher the concentration of
H+ ions, the lower the pH value

Question 87

Acids contain what?

Answer 87

high concentration of H+ ions

Question 88

What does a small change in pH value represent?

Answer 88

small change in pH value represents a large change in H+
concentration

Question 89

All enzymes have an optimum pH value, what does this mean?

Answer 89

When hydrogen ion concentration of the surrounding solution maintains all
the hydrogen and ionic bonds within the tertiary structure of the globular protein

As the tertiary structure is maintained there is no change in shape of the active
site so there are the maximum numbers of successful collisions to form ESCs.

This is optimum conditions in terms of enzymes pH

Question 90

Above and below the optimum pH the change in H+ concentration in the solution
surrounding the enzyme can do what?

Answer 90

disrupt the hydrogen bonds and ionic bonds that
hold the enzyme’s tertiary structure in place.

Question 91

Why does the pH graph of enzyme have such a steep bell curve shape?

Answer 91

a small change in pH represents a large change to the concentration of
hydrogen ions, resulting in such a steep curve shape

Question 92

Why do minor changes in pH not denature enzymes?

Answer 92

-only happens with extreme changes in pH

-With minor changes in pH the hydrogen and ionic bonds are disrupted temporarily but can re-form if the pH returns to optimum

Question 93

What enzyme works best at pH 7

Answer 93

Salivary amylase

Question 94

What exceptions are there to the optimum pH of an enzyme being 7?

Answer 94

Pepsin
This works best at pH 2 – very acidic - this
enzyme breaks down proteins in the stomach
where there is hydrochloric acid present.

Question 95

How can pH disrupt the hydrogen bonds and ionic bonds that
hold the enzyme’s tertiary structure in place?

Answer 95

Hydrogen bond + ionic bonds (but not the Disulphide bonds) can be disrupted by change in conc. of H+ ions in the surrounding
solution

If the hydrogen bonds or ionic bonds are broken then the protein’s tertiary structure begins to unfold or uncoil – the enzyme becomes denatured

Question 96

How specifically does the change in H+ ions affect the protein structure

Answer 96

Increasing conc. of H+ ions will alter the
charges around the active site – the positively charged hydrogen ions are attracted to any negatively charged R groups in the active site and therefore effectively cancel/ replace hydrogen bonds, in the alpha helix . This will make the formation of ESCs less likely.

Question 97

How can we maintain a constant pH when investigating the effect of factors on enzyme action

Answer 97

Use of buffers

Question 98

If pH is IV how can we use buffers to produce a range of required pH environments

Answer 98

You can use different pH buffers e.g. pH 4, pH5 and pH6 with the pH buffer being changed to investigate the
effect of changing pH on the rate of enzyme-driven reaction rates

Question 99

Explain why both increasing and decreasing pH away from the optimum
results in a reduction in the reaction rate.

Answer 99

Changing pH means changes to the hydrogen ion concentration

Since the tertiary structure of a protein is held by intramolecular bonds derived from charge differences, (hydrogen bonds and ionic bonds) then changes to the hydrogen ion concentration will affect tertiary structure and so active site shape.

Question 100

Individual hydrogen bonds are fairly weak. Explain how such weak bonds can
be responsible for holding the tertiary structure of an enzyme in place.

Answer 100

There are many hydrogen bonds; each one is weak but lots of them
together are very stabilising.

Question 101

Explain why the optimum pH for pepsin is different from the optimum pH
for trypsin, even though both enzymes are proteases.

Answer 101

tertiary structure of each enzyme is held in place by a number of
charge-based bonds

-optimum tertiary structure is
achieved when H+ ion conc. does not cause interference of hydrogen or ionic bonding and
the shape of the active site is best maintained.

Question 102

Why do enzymes usually work only within a very narrow pH ranges?

Answer 102

-mall change in pH results in a significant change in H+ ion
conc.

• pH range is a logarithmic rather
  then a linear scale

-The significant change in H+ ion conc. has an
effect on the enzyme tertiary structure and so on the shape of the
active site.

Question 103

Explain why an enzyme might not be active at pH 7

Answer 103

Due to loss of tertiary structure- enzyme has denatured

-changes in pH (conc of H+ ions) alters charge distribution on enzyme molecule, meaning Hydrogen + Ionic bonds are affected, changing the shape of the active site
-ESC cannot be formed and substrate cannot bind to active site and reaction wont be catalyzed

Question 104

Explain how raising temperature to 35* C affects carbohydrase activity?

Answer 104

-increase in temp, increases kinetic energy
-this increases no. of successful collisions/formation of enzyme substrate complexes, which increases rate of breakdown of starch

Question 105

Explain how decreasing pH affects carbohydrase activity

Answer 105

-increased no. of H+ ions are attracted to the amino acids
-this breaks Hydrogen+ ionic bonds
-which denatures enzyme by changing its tertiary structure as shape of active site is changed
-so active site of enzyme cannot bind with starch or form ESC
-decreases rate of breakdown of starch, t/f rate of reaction

Question 106

State the pH value which is closest to the optimum for salivary amylase. How would you go about working the above question, if presented with an Agar assay which shows the effect of pH on amylase action

Answer 106

You would first state the pH e.g. pH 7

And then state why:

It has the largest diameter clear zone because the enzyme has digested the
most starch because it was most active at pH7.

Question 107

What would happen around a control well? ( In an agar assay which shows the effect of pH on amylase action)

Answer 107

There would not be a clear zone around the control well because there is no enzyme
present to digest the starch.

Question 108

Why might at pH 11 well there not be a clear zone? ( In an agar assay which shows the effect of pH on amylase action)

Answer 108

At pH 11 the amylase enzyme would have been denatured – so there would be no
enzyme activity and the starch would not be broken down.

Question 109

What happens if there is a low conc of substrate?

Answer 109

Reaction will decrease as there will be fewer collisions between enzyme and substrate, so fewer ESC formed per unit time because there will be some enzymes with empty active sites, won’t be enough substrate molecules present for enzymes to work at their fastest rate

Question 110

Increase substrate conc will have what effect?

Answer 110

Increase rate of reaction and then plateau

As no. of substrate molecules increases, the likelihood of ESC formation increases per unit time

If enzyme conc remains fixed but the amount of substrate is increased past a certain point however, all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate, rate of reaction will plateau

When active sites of enzymes are all full, any substrate molecules that are added have nowhere to bind in order to form an ESC

Question 111

Describe a graph where it shows the effect of addition of substrate molecules

Answer 111

linear increase in reaction rate as substrate is added, which then plateaus when all active sites become occupied

Question 112

What is Vmax

Answer 112

the enzyme is working at its maximum possible rate, known as Vmax (V stands for velocity), at this point all active sites of all enzymes are occupied and the substrate molecules are essentially ‘queuing up’

Question 113

what happens when we increase the enzyme conc?

Answer 113

The higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation per unit time

As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration

Question 114

Describe the graph where we increase the enzyme conc

Answer 114

As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration, however if substrate becomes a limiting factor then rate of reaction plateaus as there will be insufficient substrate to bind with the large no. of enzymes which will be unused

Question 115

What affect would limited substrate have on increasing the enzyme conc?

Answer 115

If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate per unit time as the amount of substrate becomes a limiting factor

Question 116

What happens at low enzyme conc?

Answer 116

Reaction rate will decrease per unit time

Question 117

Without increasing substrate conc, how else can we speed up the rate of ESC formation?

Answer 117

An increase in temperature would also cause a rise towards a new Vmax because
with more kinetic energy less time would pass between product leaving and new
substrate entering the active site.

Question 118

Enzyme can cause the spoilage of stored foods. Use your knowledge of enzymes to explain why:

a) food can be stored for longer if you keep it in a refrigerator

Answer 118

-slows down enzyme activity, as molecules have less kinetic energy
-t/f fewer collisions between enzyme and substrate molecules

Question 119

Enzyme can cause the spoilage of stored foods. Use your knowledge of enzymes to explain why:

b) food is heated before sealing it in tins or bottles

Answer 119

Heating denatures enzymes so they cannot form ESC and t/f cannot break down substrate molecules

Question 120

Enzyme can cause the spoilage of stored foods. Use your knowledge of enzymes to explain why:

c) some foods are preserved by putting them into vinegar

Answer 120

Vinegar has low pH, so it denatures enzyme by changing the tertiary structure of the protein, this means enzyme cannot form ESC and therefore cannot breakdown substrate molecules

Question 121

Solutions called buffer solutions prevent changes in ph. A student carried out a lab investigation to find the optimum temperature of an enzyme. She measured the rate of reaction of an enzyme at several different temperatures. At each temp, the same amount of enzyme and substrate were used, together with a buffer solution. Why was it important to include a buffer solution?

Answer 121

This keeps the pH constant, so there is only one variable i.e. temperature

-this means any change in the rate of reaction must be the result of the change in temp and not any other factor

Question 122

“Sug-stitute” is an artificial sweetener. It is used in food and drink as a
low-calorie alternative to sugar. The sweetener contains a chemical that
is not digested by our bodies.
Suggest why the chemical cannot be digested.

(2 marks)

Answer 122

The sweetener molecules will be a different shape to natural sugars so won’t fit into the active site of any of our digestive enzymes

Question 123

When doing an experiment with enzymes, explain why it is necessary to
control the temperature and pH of the solutions involved.

(8 marks)

Answer 123

1. If solution is too cold, enzyme will work very slowly—> because at low temperatures, molecules have very little kinetic energy so move more slowly, making the collisions between enzyme + substrate molecule less likely. Also fewer of the collisions will have enough energy to result in a reaction.
2. if the temperature gets too high the reaction will stop—-> as the enzyme is denatured (the active site changes shape and this will no longer fit the substrate). Denaturation is caused by increasing vibration, breaking bonds in the enzyme.
3. Enzymes have an optimum pH, pH values too far from the optimum causes denaturation. Denaturation by pH is cause by disruption of ionic and hydrogen bonds, which alters the enzymes tertiary structure

Question 124

What is a reversible inhibitor?

Answer 124

An enzyme’s activity can be reduced or stopped, temporarily, by a reversible inhibitor

Question 125

How many types of reversible inhibitors are there?

Answer 125

2

Question 126

What are competitive inhibitors

Answer 126

Competitive inhibitors have a similar shape to that of the substrate molecules and complementary in shape to the active site and therefore bind to the active site

they compete with the substrate for the active sit, prevents substrate from binding to active site of enzyme so Enzyme-inhibitor complexes are formed instead of enzyme substrate complexes, decreasing rate of reaction

Question 127

What are 2 types of reversible inhibitors?

Answer 127

Competitive inhibitors
Non-competitive inhibitors

Question 128

Most competitive inhibitors are what

Answer 128

Reversible

Question 129

What does the following statement mean:

Most competitive inhibitors are reversible

Answer 129

binding of the inhibitor to the active site is usually only temporary – most inhibitors are reversible

Question 130

How is the rate of reaction per unit time affected by a competitive, reversible inhibitor?

Answer 130

the enzyme turnover rate is decreased as each time
an enzyme-inhibitor complex is made (rather than an ESC) there is no product

Question 131

What is an enzyme inhibitor?

Answer 131

A substance/molecule that reduces the reaction rate in an enzyme controlled reaction because they affect the enzyme molecule

Question 132

In competitive inhibitors what can we do to counter the increase in inhibitor concentration?

Answer 132

For competitive inhibitors, countering the increase in inhibitor concentration by increasing the substrate concentration can increase the rate of reaction once more (more substrate molecules mean they are more likely to collide with enzymes and form enzyme-substrate complexes)

Question 133

What does the level of inhibition depend on?

Answer 133

Concentration of inhibitor and substrate

Question 134

How does the concentration of inhibitor and substrate affect the level of inhibition?

Answer 134

Where the numbers of substrate molecules are increased the level of inhibition
decreases because a substrate molecule is more likely than an inhibitor molecule to successfully
collide with an active site

-t/f more likely to create an ESC instead of Enzyme inhibitor complex

-which then increases the rate of reaction

Question 135

In high concentration of substrate the effect of the competitive inhibitor is what?

Answer 135

reversed

Question 136

Difference between reversible and irreversible inhibitor?

Answer 136

Reversible can be removed from the enzyme, irreversible cannot be removed from the enzyme

Question 137

What effect do reversible inhibitors have on reaction rates

Answer 137

reversible inhibitors slow down or stop enzyme activity, decreasing the rate of reaction

Question 138

What effect does increasing the conc of inhibitor have on the rate of reaction?

Answer 138

Reversible inhibitors slow down or stop enzyme activity, decreasing rate of reaction
Increasing the concentration of an inhibitor, therefore, reduces the rate of reaction and eventually, if inhibitor concentration continues to be increased, the reaction will stop completely

Question 139

How does a non-competitive inhibitor affect the rate of reaction

Answer 139

-The attachment of a non-competitive inhibitor molecule to an enzyme distorts the tertiary structure (3D shape) of the enzyme

• This leads to a
  change in shape of the active site
• This means that the substrate no longer fits into the active site, so ESCs cannot form

-the reaction rate decrease

Question 140

The level of inhibition depends on the number of ——— ——– present. If there are enough inhibitor molecules to bind all the —— ——— present, then the
enzyme-controlled reaction will —-

Answer 140

inhibitor molecules
enzyme molecules
stop

Question 141

For non-competitive inhibitors, increasing the substrate concentration cannot increase the rate of reaction. Why?

Answer 141

Many non-competitive inhibitors bind permanently to the enzyme (irreversible binding), changing its tertiary structure, t/f active site, which prevents substrate molecules from binding/ forming ESC so reaction rate decreases
Changing the substrate concentration will have no effect on this form of inhibition.

Question 142

Non competitive inhibitor binds to what site of the enzyme molecule

Answer 142

Allosteric site

Question 143

Suggest a method of determining whether the inhibition of an enzyme controlled reaction is competitive or non-competitive

Answer 143

Carry out the reaction with a range of substrate concentrations. If the rate of
reaction increases up to the same as that given without the inhibitor present,
then the inhibitor is a competitive inhibitor.

Question 144

Competitive inhibitor molecules can be much larger than the substrate molecule
they “compete” with. Suggest how this is possible.

Answer 144

The competitive inhibitor may be a large molecule with a small part the same
shape as the substrate.

Question 145

Why is inhibition not always a bad thing

Answer 145

The regulation of a number of metabolic pathways involves the inhibition of enzymes to
control the reaction rates.

Question 146

Explain why inhibition of enzyme activity is important in controlling metabolic
processes.

Answer 146

Cells must be able to control the concentration of various molecules in the cell.
Where these are products of enzyme-controlled reactions it is important to
regulate enzyme activity so that the optimum level of product is achieved and
maintained.

Question 147

The products of some reactions are what?

Answer 147

Reversible inhibitors, for the enzyme involved in controlling the reaction

-enables reactions to be controlled
- if there is a lot of that reversible product present that the enzyme has produced, it will inhibit the enzyme from creating more of that reversible product and the reaction will slow or stop
- this prevents resources from being wasted

Question 148

What is end product inhibition?

Answer 148

Metabolic reactions can be controlled by using the end-product of a particular sequence of metabolic reactions as a non-competitive, reversible inhibitor:

-As the enzyme converts the substrate into product, the process is itself slowed down as the end-product of the reaction chain binds to an alternative site on the original enzyme, changing the shape of the active site and preventing the formation of further enzyme-substrate complexes

-The end-product can then detach from the enzyme and be used elsewhere, allowing the active site to reform and the enzyme to return to an active state

-This means that as product levels fall, the enzyme begins catalyzing the reaction once again, in a continuous feedback loop

-This process is known as end-product inhibition

Question 149

How do poisonous substances affect enzymes?

Answer 149

because they inhibit or over-activate
enzymes.

Question 150

Name a poisonous substance that can have effect on enzyme activity

Answer 150

Potassium cyanide

Question 151

How does potassium cyanide affect enzyme activity?

Answer 151

It inhibits cell respiration, by being a non-competitive inhibitor for a vital respiratory enzyme called cytochrome oxidase

Question 152

Why is potassium cyanide harmful to the human body?

Answer 152

It inhibits cell respiration as it is a non-competitive inhibitor
for a vital respiratory enzyme called cytochrome oxidase which is found in mitochondria

-Inhibition of this enzyme decreases the use of oxygen so ATP cannot be made

• The organism can only respire anaerobically which leads to a build-up of lactic acid

Question 153

What quantity of potassium cyanide will have what affect on the human body?

Answer 153

-Only 100 – 200 mg of cyanide must be absorbed in order to make an adult lose
consciousness

-This can occur in as little as 10 seconds

-If untreated the body goes into a coma in around 45 minutes and death results in around 2 hours

Question 154

How do metabolic poisons have an effect on the human body?

Answer 154

Metabolic poisons interfere with metabolic reactions (the reactions that occur in cells)

-causing:
-damage
-illness
-death

• they’re often enzyme inhibitors

Question 155

Metabolic poisons are often enzyme what?

Answer 155

Inhibitors

Question 156

List 3 substances that are metabolic poisons and what enzymes in our human body they affect (1~)

Answer 156

1. Cyanide is an irreversible inhibitor of the enzyme cytochrome c oxidase, an enzyme that catalyzes respiration reactions, cells that can’t respire die

Question 157

List 3 substances that are metabolic poisons and what enzymes in our human body they affect (2~)

Answer 157

2. Malonate inhibits enzyme succinate dehydrogenase ( also catalyzes respiration reactions)

Question 158

List 3 substances that are metabolic poisons and what enzymes in our human body they affect (3~)

Answer 158

3. Arsenic inhibits the action of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions

Question 159

Give an example of enzymes in medicine used as treatment

Answer 159

Anti-viral treatment

Question 160

Cyanide is an example of what?

Answer 160

Irreversible inhibitor

Question 161

Cyanide, can be thought of as a non-competitive inhibitor and an irreversible inhibitor, why is this?

Answer 161

Because it’s a nerve gas which covalently binds to the active site, it prevents the binding of the substrate, as the tertiary structure of the enzyme is broken and the active site of the enzyme is no longer complementary to that of the substrate so ESC cannot form

Question 161

Irreversible inhibitors bind to the active site of the enzyme through what?

Answer 161

Strong covalent bonds, so inhibitor cannot be removed easily and the inhibition is irreversible

Question 162

Reversible inhibitors bind to the active site of the enzyme through what?

Answer 162

hydrogen bonds and weak ionic interactions, therefore do not bind permanently

Question 163

How are enzymes used in anti-viral treatment

Answer 163

-some anti-viral drugs (drugs that stop viruses like HIV)

e.g. reverse transcriptase inhibitors, inhibit the enzyme transcriptase, which catalyses the reaction of viral DNA

• This prevents the virus from replicating

Question 164

How are infection by viruses e.g. HIV treated?

Answer 164

Using chemicals that act as competitive
inhibitors to viral proteases

Question 165

The virus’s ——contains genes to produce ———

Answer 165

genome
proteases

Question 166

Explain how infection by viruses including HIV are spread and how this is treated.

Answer 166

• virus’s genome contains genes to produce proteases

-When this is incorporated
into host cell genome proteases are made, and break down proteins to amino acids

-These amino acids are then used to build up the new virus coats (the capsid)

-The treatment with protease inhibitors specifically inhibits the viral protease

-This means that viruses cannot build new protein coats and therefore cannot replicate

Question 167

Suggest why protease inhibitors can inhibit viral proteases but do not affect the human
protease enzymes in the cell.

Answer 167

The protease enzymes from viruses differ in overall shape from the proteases found in
humans. Protease inhibitors can be specific to the parts of the molecule that differ.

Question 168

What is PERT

Answer 168

Pancreatic Enzyme Replacement Therapy

Question 169

What defect do people with cystic fibrosis suffer with and how does this affect the digestive system?

Answer 169

People with cystic fibrosis have extra thick mucus in their digestive system, makes it difficult to absorb food digested

Question 170

85% of people with cystic fibrosis have what?

Answer 170

85% of people with cystic fibrosis have mucus blocking the pancreatic duct

Question 171

What is the function of the pancreatic duct?

Answer 171

• allows pancreatic juice to be added to the food once it has passed
  through the pyloric sphincter and into the duodenum

-Pancreatic juice contains
proteases, amylase and lipase.

Question 172

Function of protease is what

Answer 172

To breakdown proteins into amino acids

Question 173

Function of Amylase?

Answer 173

Breakdown starch into Maltose

Question 174

Function of Lipase?

Answer 174

Breakdown Triglycerides into fatty acids and a glycerol molecule

Question 175

What effect does the blockage of the pancreatic duct have on the digestion of the food?

Answer 175

-digestive enzymes produced in the pancreas cannot enter gut

-So food is not digested properly, t/f less food would be absorbed

-can lead to digestive discomfort.

Question 176

People with cystic fibrosis are prescribed what to replicate the idea of the pancreatic juices?

Answer 176

• capsules containing artificial enzymes which
  are taken before or with a meal or snack

-replaces digestive enzymes usually released by pancreas

Question 177

How does giving people with cystic fibrosis capsule containing artificial enzymes help?

Answer 177

-are able to digest and absorb proteins, carbohydrates and fats and eat a greater range of foods without experiencing
digestive discomfort

Question 178

So that they
are not destroyed by the acid and protein-digesting enzymes in the stomach, what helps the artificial enzyme containing capsules survive to be able to break down the food in people with cystic fibrosis?

Answer 178

enzymes are packaged in an acid-resistant coat so that they
are not destroyed by the acid and protein-digesting enzymes in the stomach.

Question 179

Why would the enzymes in tablets given to individuals with cystic fibrosis be destroyed
in the stomach if they were not packaged properly?

Answer 179

Enzymes are proteins, and the stomach contains potent protease enzymes. The enzymes
would be broken down, and so, useless.

Question 180

How does penicillin affect bacterial function?

Answer 180

Penicillin is an inhibitor of a bacterial
enzyme that forms cross-links in the bacterial cell wall of some bacterial this means the walls of growing bacteria are not made, so bacterial reproduction is halted

Question 181

True or false:

Antibiotics can kill or inhibit the growth of microorganisms

Answer 181

True

Question 182

Antibiotics are used in treating what

Answer 182

diseases caused by bacterial infections

Question 183

Inhibition
of the enzymes responsible for building the wall
occurs because penicillin is structurally ——— to one of the ——— used in wall building

However, the ——–molecule is different
from the substrate so — —– ——- — —- — —- —–.

Answer 183

similar
substrate
penicillin
walls formed are
weak and fall apart.

Question 184

What is a problem in treating bacterial infections?

Answer 184

Resistance to antibiotics

Question 185

how do different Forms of bacterial resistance occur?

Answer 185

among populations of
bacteria, there may be an individual with a mutation and altered enzymes, that may be capable of inactivating antibiotics

Question 186

why do different Forms of bacterial resistance occur?

Answer 186

bacterium is naturally
selected when bacterial population is exposed to antibiotics It will survive and then reproduce

Question 187

Bacteria are resistant o penicillin because what?

Answer 187

they
produce an enzyme (beta-lactamase) that breaks down the penicillin molecule

Question 188

Many antibiotics are chemicals naturally produced by fungal organisms and released into
their environment. What is the advantage to a fungus of producing and releasing
antibiotics?

Answer 188

The fungus releases antibiotics to destroy other organisms so that the other organisms
cannot take up its food supply

Question 189

What do some enzymes require to catalyze a reaction

Answer 189

-require an additional non-protein molecule e.g. coenzyme, cofactor, or a prosthetic group to catalyse a reaction