2.1.4 Enzymes Flashcards
(191 cards)
1
Q
What are enzymes?
A
Biological catalysts made up of globular proteins
2
Q
Define globular
A
have a roughly spherical tertiary structure
3
Q
Why can enzymes only attach to some substrates and not others?
A
-Active site of enzyme= specific + unique in shape
So substrates can only bind to the active site of enzymes that are complimentary in shape
4
Q
Why is the active site of an enzyme specific?
A
Because of the specific folding and bonding in the tertiary structure of the protein, so have a specific 3d shape
5
Q
Substrate molecules do what to what part of enzyme? What is the name given to this?
A
Substrate molecules bind to active site of enzyme to make an Enzyme Substrate complex
6
Q
How does the substrate binding into the enzyme help the reaction?
A
Makes the reaction occur more quickly
7
Q
What happens if the substrate doesn’t fit into the active site of the enzyme?
A
Reaction won’t be catalysed
8
Q
Enzymes catalyse what reactions?
A
Intracellular and extracellular
9
Q
Where do intracellular enzymes react
A
inside of cells
10
Q
Give me 3 examples of Intracellular enzymes.
A
Catalase
Hydrolases
ATPases
11
Q
Where is catalase found? Function?
A
Catalase- found inside liver cells, breaks down hydrogen peroxide into oxygen and water
12
Q
Where are hydrolases found? Function?
A
Hydrolases- found inside lysosomes, these enzymes break down substances that a cell has taken in by phagocytosis
13
Q
Where are ATPases found? Function?
A
ATPases= found inside mitochondria, these enzymes are involved in synthesis of ATP during aerobic respiration
14
Q
Where do extracellular enzymes act?
A
these enzymes act outside cells.
15
Q
Give me examples of 4 extracellular enzymes and where they are found
A
-Trypsin
-Amylase
-Lipase
- Proteases
16
Q
Where is Trypsin found? Function?
A
Trypsin- found in small intestine, hydrolyses proteins
17
Q
Where are the following extracellular enzymes found:
-Trypsin
-Amylase
-Lipase
- Proteases
A
The digestive enzymes in the alimentary canal (gastro-intestinal tract)
Trypsin= found in small intestine
18
Q
Where is Amylase found? Function?
A
Amylase = made in the salivary glands +pancreas; hydrolyses starch into maltose
19
Q
Where is Lipase found? Function?
A
Lipase = made in the pancreas; hydrolyses triglycerides into glycerol and fatty acids
20
Q
Where is Protease found? Function?
A
Protease= made in the pancreas, found in stomach, pancreas and small intestine, hydrolyses proteins into amino acids
21
Q
What is activation energy?
A
the minimum amount of energy required to initiate a reaction
22
Q
Why can we not add heat to increase the activation energy for reactions to occur in our cells?
A
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
23
Q
What is the role of enzymes
A
Enzymes attach to substrate to lower activation energy needed for reaction to occur by providing an alternative pathway and therefore speed up the reaction
24
Q
How does an enzyme lower activation energy
A
When the enzyme
is present, the energy
barrier is much lower,
Therefore the activation
energy needed for the
reaction to occur is much
lower.
25
What specifically lowers the activation energy
Formation of the enzyme substrate complex
26
What is a metabolic reaction?
a biochemical reaction that takes place in living organisms in order to keep them alive
27
What reactions are chemical reactions in cells with an enzyme, hapening in a living organism
Metabolic reactions
28
In an exothermic reaction energy is what?
Energy is released
29
What is an anabolic reaction?
- 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
30
Give an example of an anabolic reaction
Glucose+ Fructose------>Sucrose
31
How does an anabolic reaction allow a bond to be made more easily?
-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
32
What are 2 examples of anabolic reactions, one in animal and one in plant?
Photosynthesis and protein synthesis
33
What are catabolic reactions?
-larger molecules are broken down into smaller molecules
34
Give example of a catabolic reaction
Sucrose------> Glucose+ Fructose
-when sucrase is added
35
What is an anabolic reaction also known as?
Synthesis/ Building reaction
36
What is a catabolic reaction also known as?
Breakdown reaction
37
How does a catabolic reaction speed up the rate at which the substrate is broken into products?
- 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
38
What does the lock and key hypothesis suggest?
-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)
39
The lock and key model suggests Usually only one type of substrate will fit into active site of enzyme. Why is this?
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
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?
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
41
Suggest why most scientists accept the induced fit model rather than the lock and key model?
-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
42
What hypothesis is the current accepted hypothesis in enzymes
The induced fit hypothesis
43
What does the induced fit hypothesis suggest?
-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)
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?
These changes in shape are known as conformational changes
45
What do the conformational changes ensure?
The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved
46
The conformational changes ensure an ideal binding arrangement between the enzyme and substrate is achieved. How does this help the reaction?
This maximises the ability of the enzyme to catalyse the reaction
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?
Electrostatic force of attraction between the substrate and active site
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
1) ESCs
2) Active site
3) negative
49
Why can humans digest starch but not cellulose?
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
50
In the exam, you might be asked why our bodies cannot digest certain chemicals.
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.
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
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
52
Name 2 of the bonds that are important in holding the enzyme in its tertiary structure
Disulphide bridges and Hydrogen bonds
53
Give one difference between the induced fit and the lock and key theory
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
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.
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.
55
What is enzyme specificity?
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
56
Suggest how the substrate changing shape slightly will assist enzyme action
-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
57
What's a difference between the induced fit model and the lock and key hypothesis?
The substrate is thought to cause a change in the enzymes active site shape, which enables a better fit
58
Explain why trypsin and chymotrypsin break peptide bonds between different amino acids
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
59
Name a reaction in which enzyme activity can be monitored
when the enzyme
catalase breaks down hydrogen peroxide to produce water and oxygen.
Hydrogen peroxide---->water + oxygen
(catalase goes above the arrow)
60
Formula for reaction between hydrogen peroxide and catalase
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
61
Catalase is an enzyme which is found in the tissues of most living things, why?
because hydrogen peroxide is a very toxic product of several different metabolic reactions.
62
Where is catalase found the most in the human body as well in plants?
-liver
-potatoes
-celery
-often used as source of enzymes in biological catalysts
63
What experiment can we use to measure the rate of reaction between the catalase and the hydrogen peroxide?
We can use the water displacement method of collecting gas
64
How can we use the water displacement method of collecting gas to work out the rate of reaction
the volume of
oxygen produced in a unit of time can be
measured.
65
What is a most accurate method of measuring the rate of reaction between catalase and hydrogen peroxide?
Method of gas collection using a gas syringe system
66
What is an advantage of using a gas syringe over the water displacement method?
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.
67
The curve is steepest at the beginning of the reaction – why? What is this called?
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.
68
What is the turnover rate?
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 –
69
How can you calculate the initial rate of reaction?
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.
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)
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.
71
The rate of reaction is lower after 5 minutes than it was at the start. Explain why?
Less substrate is available, it is used up and has become a limiting factor, fewer collisions between enzyme and substrate, so fewer ESC formed
72
Factors affecting enzyme activity.
-temperature
-pH
-concentration of substrate
-concentration of enzyme
-enzyme inhibition
-enzyme cofactors
73
Like any chemical reaction the rate of an enzyme-controlled reaction increases
when the temperature is increased.
* 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).
74
How does increasing temp affect rate of reaction
Like any chemical reaction the rate of an enzyme-controlled reaction increases
when the temperature is increased.
75
What happens when you increase the temperature a lot
* 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.
76
What is the optimum temp for enzymes in humans
Every enzyme has an optimum temperature.
For most human enzymes the optimum temperature is around 37°C.
77
State the difference between bacterial amylase and amylase found in humans
Enzymes have different optimum temperatures;
human amylase has optimum temp of 37*C, bacterial of 100*C;
human amylase denatures at a lower temperature
78
What happens the temperature is too low?
There is insufficient energy for successful collisions
79
What is Q10?
temperature coefficient= measure of the rate of change of an enzyme controlled reaction as a result of increasing the temperatures by 10*C
80
Formula of Q10?
Q10= R2/R1
81
What is R1
rate of a reaction at a temperature of X*C
82
What is R2?
Rate of reaction at a temperature (X+10)*C
83
What is the value of Q10 for most enzymes?
Most Enzyme controlled reactions have a Q10 value of around 2 which means an enzyme is used
84
What does pH measure?
-measures the concentration of Hydrogen ions, H in a solution
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
pH 5 has 10 times less H+
than pH 4, 100 times less than pH 3 and
1000 times less than pH 2.
86
What is the correlation between concentration and pH value
the higher the concentration of
H+ ions, the lower the pH value
87
Acids contain what?
high concentration of H+ ions
88
What does a small change in pH value represent?
small change in pH value represents a large change in H+
concentration
89
All enzymes have an optimum pH value, what does this mean?
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
90
Above and below the optimum pH the change in H+ concentration in the solution
surrounding the enzyme can do what?
disrupt the hydrogen bonds and ionic bonds that
hold the enzyme’s tertiary structure in place.
91
Why does the pH graph of enzyme have such a steep bell curve shape?
a small change in pH represents a large change to the concentration of
hydrogen ions, resulting in such a steep curve shape
92
Why do minor changes in pH not denature enzymes?
-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
93
What enzyme works best at pH 7
Salivary amylase
94
What exceptions are there to the optimum pH of an enzyme being 7?
Pepsin
This works best at pH 2 – very acidic - this
enzyme breaks down proteins in the stomach
where there is hydrochloric acid present.
95
How can pH disrupt the hydrogen bonds and ionic bonds that
hold the enzyme’s tertiary structure in place?
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
96
How specifically does the change in H+ ions affect the protein structure
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.
97
How can we maintain a constant pH when investigating the effect of factors on enzyme action
Use of buffers
98
If pH is IV how can we use buffers to produce a range of required pH environments
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
99
Explain why both increasing and decreasing pH away from the optimum
results in a reduction in the reaction rate.
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.
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.
There are many hydrogen bonds; each one is weak but lots of them
together are very stabilising.
101
Explain why the optimum pH for pepsin is different from the optimum pH
for trypsin, even though both enzymes are proteases.
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.
102
Why do enzymes usually work only within a very narrow pH ranges?
-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.
103
Explain why an enzyme might not be active at pH 7
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
104
Explain how raising temperature to 35* C affects carbohydrase activity?
-increase in temp, increases kinetic energy
-this increases no. of successful collisions/formation of enzyme substrate complexes, which increases rate of breakdown of starch
105
Explain how decreasing pH affects carbohydrase activity
-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
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
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.
107
What would happen around a control well? ( In an agar assay which shows the effect of pH on amylase action)
There would not be a clear zone around the control well because there is no enzyme
present to digest the starch.
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)
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.
109
What happens if there is a low conc of substrate?
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
110
Increase substrate conc will have what effect?
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
111
Describe a graph where it shows the effect of addition of substrate molecules
linear increase in reaction rate as substrate is added, which then plateaus when all active sites become occupied
112
What is Vmax
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'
113
what happens when we increase the enzyme conc?
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
114
Describe the graph where we increase the enzyme conc
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
115
What affect would limited substrate have on increasing the enzyme conc?
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
116
What happens at low enzyme conc?
Reaction rate will decrease per unit time
117
Without increasing substrate conc, how else can we speed up the rate of ESC formation?
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.
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
-slows down enzyme activity, as molecules have less kinetic energy
-t/f fewer collisions between enzyme and substrate molecules
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
Heating denatures enzymes so they cannot form ESC and t/f cannot break down substrate molecules
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
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
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?
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
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)
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
123
When doing an experiment with enzymes, explain why it is necessary to
control the temperature and pH of the solutions involved.
(8 marks)
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
124
What is a reversible inhibitor?
An enzyme's activity can be reduced or stopped, temporarily, by a reversible inhibitor
125
How many types of reversible inhibitors are there?
2
126
What are competitive inhibitors
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
127
What are 2 types of reversible inhibitors?
Competitive inhibitors
Non-competitive inhibitors
128
Most competitive inhibitors are what
Reversible
129
What does the following statement mean:
Most competitive inhibitors are reversible
binding of the inhibitor to the active site is usually only temporary – most inhibitors are reversible
130
How is the rate of reaction per unit time affected by a competitive, reversible inhibitor?
the enzyme turnover rate is decreased as each time
an enzyme-inhibitor complex is made (rather than an ESC) there is no product
131
What is an enzyme inhibitor?
A substance/molecule that reduces the reaction rate in an enzyme controlled reaction because they affect the enzyme molecule
132
In competitive inhibitors what can we do to counter the increase in inhibitor concentration?
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)
133
What does the level of inhibition depend on?
Concentration of inhibitor and substrate
134
How does the concentration of inhibitor and substrate affect the level of inhibition?
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
135
In high concentration of substrate the effect of the competitive inhibitor is what?
reversed
136
Difference between reversible and irreversible inhibitor?
Reversible can be removed from the enzyme, irreversible cannot be removed from the enzyme
137
What effect do reversible inhibitors have on reaction rates
reversible inhibitors slow down or stop enzyme activity, decreasing the rate of reaction
138
What effect does increasing the conc of inhibitor have on the rate of reaction?
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
139
How does a non-competitive inhibitor affect the rate of reaction
-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
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 ----
inhibitor molecules
enzyme molecules
stop
141
For non-competitive inhibitors, increasing the substrate concentration cannot increase the rate of reaction. Why?
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.
142
Non competitive inhibitor binds to what site of the enzyme molecule
Allosteric site
143
Suggest a method of determining whether the inhibition of an enzyme controlled reaction is competitive or non-competitive
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.
144
Competitive inhibitor molecules can be much larger than the substrate molecule
they “compete” with. Suggest how this is possible.
The competitive inhibitor may be a large molecule with a small part the same
shape as the substrate.
145
Why is inhibition not always a bad thing
The regulation of a number of metabolic pathways involves the inhibition of enzymes to
control the reaction rates.
146
Explain why inhibition of enzyme activity is important in controlling metabolic
processes.
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.
147
The products of some reactions are what?
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
148
What is end product inhibition?
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
149
How do poisonous substances affect enzymes?
because they inhibit or over-activate
enzymes.
150
Name a poisonous substance that can have effect on enzyme activity
Potassium cyanide
151
How does potassium cyanide affect enzyme activity?
It inhibits cell respiration, by being a non-competitive inhibitor for a vital respiratory enzyme called cytochrome oxidase
152
Why is potassium cyanide harmful to the human body?
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
153
What quantity of potassium cyanide will have what affect on the human body?
-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
154
How do metabolic poisons have an effect on the human body?
Metabolic poisons interfere with metabolic reactions (the reactions that occur in cells)
-causing:
-damage
-illness
-death
- they're often enzyme inhibitors
155
Metabolic poisons are often enzyme what?
Inhibitors
156
List 3 substances that are metabolic poisons and what enzymes in our human body they affect (1~)
1. Cyanide is an irreversible inhibitor of the enzyme cytochrome c oxidase, an enzyme that catalyzes respiration reactions, cells that can't respire die
157
List 3 substances that are metabolic poisons and what enzymes in our human body they affect (2~)
2. Malonate inhibits enzyme succinate dehydrogenase ( also catalyzes respiration reactions)
158
List 3 substances that are metabolic poisons and what enzymes in our human body they affect (3~)
3. Arsenic inhibits the action of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions
159
Give an example of enzymes in medicine used as treatment
Anti-viral treatment
160
Cyanide is an example of what?
Irreversible inhibitor
161
Cyanide, can be thought of as a non-competitive inhibitor and an irreversible inhibitor, why is this?
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
161
Irreversible inhibitors bind to the active site of the enzyme through what?
Strong covalent bonds, so inhibitor cannot be removed easily and the inhibition is irreversible
162
Reversible inhibitors bind to the active site of the enzyme through what?
hydrogen bonds and weak ionic interactions, therefore do not bind permanently
163
How are enzymes used in anti-viral treatment
-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
164
How are infection by viruses e.g. HIV treated?
Using chemicals that act as competitive
inhibitors to viral proteases
165
The virus’s ------contains genes to produce ---------
genome
proteases
166
Explain how infection by viruses including HIV are spread and how this is treated.
- 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
167
Suggest why protease inhibitors can inhibit viral proteases but do not affect the human
protease enzymes in the cell.
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.
168
What is PERT
Pancreatic Enzyme Replacement Therapy
169
What defect do people with cystic fibrosis suffer with and how does this affect the digestive system?
People with cystic fibrosis have extra thick mucus in their digestive system, makes it difficult to absorb food digested
170
85% of people with cystic fibrosis have what?
85% of people with cystic fibrosis have mucus blocking the pancreatic duct
171
What is the function of the pancreatic duct?
- 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.
172
Function of protease is what
To breakdown proteins into amino acids
173
Function of Amylase?
Breakdown starch into Maltose
174
Function of Lipase?
Breakdown Triglycerides into fatty acids and a glycerol molecule
175
What effect does the blockage of the pancreatic duct have on the digestion of the food?
-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.
176
People with cystic fibrosis are prescribed what to replicate the idea of the pancreatic juices?
- capsules containing artificial enzymes which
are taken before or with a meal or snack
-replaces digestive enzymes usually released by pancreas
177
How does giving people with cystic fibrosis capsule containing artificial enzymes help?
-are able to digest and absorb proteins, carbohydrates and fats and eat a greater range of foods without experiencing
digestive discomfort
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?
enzymes are packaged in an acid-resistant coat so that they
are not destroyed by the acid and protein-digesting enzymes in the stomach.
179
Why would the enzymes in tablets given to individuals with cystic fibrosis be destroyed
in the stomach if they were not packaged properly?
Enzymes are proteins, and the stomach contains potent protease enzymes. The enzymes
would be broken down, and so, useless.
180
How does penicillin affect bacterial function?
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
181
True or false:
Antibiotics can kill or inhibit the growth of microorganisms
True
182
Antibiotics are used in treating what
diseases caused by bacterial infections
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 --- ----- ------- --- ---- --- ---- -----.
similar
substrate
penicillin
walls formed are
weak and fall apart.
184
What is a problem in treating bacterial infections?
Resistance to antibiotics
185
how do different Forms of bacterial resistance occur?
among populations of
bacteria, there may be an individual with a mutation and altered enzymes, that may be capable of inactivating antibiotics
186
why do different Forms of bacterial resistance occur?
bacterium is naturally
selected when bacterial population is exposed to antibiotics It will survive and then reproduce
187
Bacteria are resistant o penicillin because what?
they
produce an enzyme (beta-lactamase) that breaks down the penicillin molecule
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?
The fungus releases antibiotics to destroy other organisms so that the other organisms
cannot take up its food supply
189
What do some enzymes require to catalyze a reaction
-require an additional non-protein molecule e.g. coenzyme, cofactor, or a prosthetic group to catalyse a reaction
190
