4. Enzymes Flashcards
1
Q
What is an enzyme?
A
Biological catalyst that speeds up the rate of chemical reaction without being used up
2
Q
Anabolic
A
forms 1 product
3
Q
Catabolic
A
1 substance broken into 2 products
4
Q
What do globular proteins have
A
Complex tertiary structures
5
Q
What is controlled by enzymes
A
Metabolic pathways
6
Q
How are enzymes produced
A
via protein synthesis inside cells
7
Q
Affect of high temperature on enzymes
A
- more kinetic energy = more successful collisions
- initial rate faster = more enzyme substrate complexes form
- enzymes eventually denature and less product formed
8
Q
How do non competitive inhibitors work
A
- inhibitor binds to allosteric site
- active site no longer complementary to substrate
9
Q
37
A
- non competitive inhibitor
- ROR doesn’t continue to rise as substrate conc rises
10
Q
Affect of low temperature on enzymes (29b)
A
- less kinetic energy = less successful collisions
- rate of reaction is slower = fewer enzyme substrate complexes form
- not all substrate reacted after x mins
11
Q
Affect of temperature on active site
A
- high temp affects bonds involved in tertiary structure
- change in shape of active site = prevents substrate binding to active site
- effects of high temp irreversible = results in denaturing
12
Q
Lock and key hypothesis
A
shape of substrate and
enzyme’s active site are complementary and so enzyme is specific
13
Q
Induced fit hypothesis
A
enzyme active site changes
shape to accommodate substrate once substrate binds
14
Q
Types of catalysts
A
Intracellular or Extracellular
15
Q
What are intracellular enzymes
A
produced and function inside the cell
16
Q
What are Extracellular enzymes
A
secreted by cells and catalyse reactions outside cells
17
Q
Examples of Extracellular protein
A
digestive enzymes in the gut
18
Q
Example of intracellular enzyme
A
Catalase
19
Q
Function of catalase
A
converts hydrogen peroxide into water and oxygen, preventing any damage to cells or tissues.
20
Q
Named example of Extracellular enzymes
A
Amylase and trypsin
21
Q
Function of amylase
A
Involved in the carb digestion
• hydrolyses starch into simple sugars
22
Q
Why is digestions usually carried our by extracellular proteins
A
Because macromolecules being digested are too large to enter cell
23
Q
Where is amylase secreted from
A
Salivary glands + pancreas
24
Q
If amylase is secreted from the salivary gland where is it digesting starch
A
Mouth
25
If amylase is secreted from the pancreas where is it digesting starch
Small intestine
26
Where is trypsin secreted from
Pancreas
27
Where does trypsin go
Small intestine
28
Function of trypsin
Breaks down proteins into peptides + amino acids
29
Which organisms only use extracellular digestion
Fungi / hyphae
30
How do some organisms only use extracellular digestion
secrete the necessary enzymes directly onto the food they are consuming (e.g. wood) so that the food is digested into smaller, simple molecules that the fungi can then absorb through the walls of the hyphae
31
Where do substrates bind on the enzyme
Active site
32
Main feature of active site
Specific shape
33
What does the active site having a specific shape mean
Can only bind to a specific substrate
34
How can the active site be denatured
pH / temp
35
How does an enzyme substrate complex form
substrates collide with enzyme active site
36
Metabolism
sum of all different reactions and reaction pathways happening in a cell or an organism
37
How is the shape of active site determined by DNA
shape of active site = determined by complex tertiary structure
o proteins = formed from chains of amino acids
o order of amino acids = determined by DNA
o change DNA / amino acids = change 3D shape
38
Enzyme substrate complex
forms when an enzyme and substrate join
39
Key point about enzyme substrate complex
only formed temporarily before enzyme catalyses reaction + products released
40
Enzyme product complex
Substrate(s) then react, and products) are formed = enzyme-product complex formed.
41
Active site
an area within the tertiary structure of the enzyme that has shape which is complementary to shape of a specific substrate molecule.
42
How are substrates held in enzymes
Temporary Hydrogen and ionic bonds between active site and substrate
43
Activation energy
Minimum amount of energy required to start a reaction
44
How do enzymes speed up chemicals reactions
reduce the stability of bonds in the reactants
o The destabilisation of bonds in the substrate makes it more reactive
45
How do enzymes work
providing an alternative energy pathway with a lower activation energy
46
How do enzymes help organisms
Without enzymes, extremely high temperatures or pressures would be needed to reach the activation energy for many biological reactions
o Enzymes avoid the need for these extreme conditions(that would otherwise kill cells)
47
How does changing pH denature an enzyme
o Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together
o Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause these bonds to break
o The breaking of bonds alters the shape of the active site, which means enzyme-substrate complexes form less easily
48
What holds the tertiary structure together in enzyme
Ionic bonds between positively and negatively charged r groups
Disulphide bonds (cysteine only)
Hydrogen bonds
Hydrophobic/ hydrophilic interactions
49
Where’s pepsin located
Stomach
50
What does pepsin being found in the stomach indicate
Suited to an acidic environment at pH 2
51
Why does the stomach have a pH of 2
Presence of hydrochloric acid
52
What are buffer solutions
Solution = Have a specific pH
53
Purpose of buffer solutions
maintain pH through reaction
54
When we are investigating the effect of pH on enzymes - what should we test it kn
Use the enzyme amylase to breakdown starch at a range of pH values,
55
What does amylase don
digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose)
56
What would we use to test for presence / lack of starch
Iodine
57
Cokour change of iodine in pH practical + what that means to breaking down
starch
58
Method - Investigating the effect of pH on enzyme reaction rates for starch
Place single drops of iodine solution in rows on the tile
• Label a test tube with the oH to be tested
• Use the syringe to place 2cm3 of amylase in the test tube
• Add 1cm3 of buffer solution to the test tube using a syringe
• Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
• After 10 seconds, use a pipette to place one drop of the mixture on the first drop of iodine, which should turn blue-black o This test indicates whether starch is still present
• Wait another 10 seconds and place another drop of the mixture on the second drop of iodine
• Repeat every 10 seconds until iodine solution remains orange-brown
• Repeat experiment at different pH values
59
Iodine solution colour
Orange-brown
60
How do we control variables
Equal volume and concentration of enzyme should be used in each test tube
o Equal volume and concentration of the substrate (starch) should be used
61
What does it mean when the solution remains orange brown
amylase has broken down all of the starch so nothing is left to react with the iodine
62
How to interpret results from - Investigating the effect of pH on enzyme reaction
rates
less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
63
Limitations of starch + iodine = pH = practical
Colour = difficult to distinguish = use a colorimeter
64
How can this practical be adapted to control temperature
using a water bath at 35°C
65
How does increased temp denature enzymes
• increased kinetic energy of = puts a strain on enzymes = causing the weaker hydrogen and ionic bonds to break
• breaking of bonds causes the tertiary structure of the protein (i.e. the enzyme)
to change
• The active site is permanently damaged and its shape is no longer complementary
Denaturation has occurred if the substrate can no longer bind
66
What temp do enzymes denature at in humans
Most denature at temps over 60
67
Temp coefficient formula
Temperature coefficient = (rate of reaction at (X + 10) °C) / (rate of reaction at x
°C)
68
Effect of increasing enzyme concentration
- higher enzyme concentration
- greater amount of active sites
- more successful collisions per second
- greater the likelihood of enzyme-substrate complex formation
69
How does the initial rate of reaction increase =
enzyme conc
As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration
70
Why would the rate of reaction be limited at some point
amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor
71
Enzyme concentration x rate of reaction
As enzyme concentration increases, so does rate of reaction AS
• LONG AS
SUFFICIENT
SUBSTRATE IS
AVAILABLE
72
State how substrate concentration effect rate of
reaction
• The greater the substrate concentration, the higher the rate of reaction
73
Explain why substrate concentration effects rate of reaction
As the number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases
74
Why does the graph eventually plateau off substrate concentration
If the enzyme concentration 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
75
Reversible inhibitor
Temporarily stops / reduces enzyme activity
76
Two types of reversible inhibitor
Competitive + non competitive
77
Competitive inhibitor
similar shape to that of the substrate molecules and therefore compete with the substrate for the active site
78
How do reversible inhibitors effect reaction rate
Reduce ROR
79
What happens if you increase concentration if inhibitor
reduces rate further = eventually stop the reaction
80
How do you counter an increase in competitive inhibitors
can counter increase in inhibitor concentration by increasing substrate
concentration = more substrate molecules mean they are more likely to collide
with enzymes and form enzyme-substrate complexes
81
Does the way to counter competitive work for non competitive
No
82
Why does the way to counter competitive not work for non competitive
as the shape of the active site of the enzyme remains changed and enzyme-substrate complexes are still unable to form
83
Does the amount of product change with competitive
no
84
Why does the amount of product not change with competitive
lower the initial rate of reaction (by occupying some of the available active sites)
= eventually same amount of product will be produced as would have been produced without the competitive inhibitor (the maximal rate is not affected)
85
Do non competitive inhibitors lower the amount of product formed
YES
86
Draw a graph - rate of reaction against substrate concentration - do normal enzyme / competitive inhibitor and non - competitive
87
Describe end product inhibition
when the last product of the last enzyme can go back to the first enzyme of the cycle and act as an inhibitor to it therefore the cycle stops. Non competitor inhibitor but it is reversible
88
How is the end product inhibitor a negative feedback
Loop
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
o This means that as product levels fall, the enzyme begins catalysing the reaction once again, in a continuous feedback loop
89
What are non reversible inhibitors
Some inhibitors can form covalent bonds with enzymes, inhibiting them
permanently = non-reversible
90
What do non reversible inhibitors result in
complete inactivation of the enzyme
91
Why is non reversible inhibition dangerous
the biological reaction the enzyme is catalysing to be completely stopped
92
How does the cell avoid this danger of non reversible inhibition
the cell or organism to produce more of the enzyme being inhibited
93
Why is producing more of the enzyme not as easy as it sounds
only be achieved by transcribing and translating the gene(s) for that enzyme = relatively slow process
94
What can irreversible inhibitors also be known as
metabolic poisons
95
Example of metabolic poison
Cyanide
96
What is a temperature coefficient
shows how much the rate of reaction changes when the temperature increases by 10 degrees Celsius.
97
Cyanide
inhibits an enzyme used in respiration so it stops which leads to death
98
Snake venom
inhibits an enzyme called acetylcholinesterase which causes organisms to be paralysed
99
Aspirin
prevents the formation of prostaglandins which means it acts as a painkiller.
100
Cofactors
- inorganic ions
- non proteins
101
.what are cofactors needed for
enzymes require them to function properly
102
Cofactors function
help stabilise the structure of an enzyme or take part in a reaction at active site
103
Example of cofactors
chloride ions act as a cofactor for amylase
104
How do cofactors actually work
may accept hydrogen ions, electrons or other small molecules that enable the main reaction to occur
105
What are coenzymes
• larger organic cofactors = coenzymes
• non-protein
106
Are co enzymes permanent or temporary
some = permanently bound to the enzyme = in / near active site
some = bind temporarily
107
Are cofactors permenatly or temporarily blind
Typically permanently
108
How do coenzymes work
often changes the shape of the active site to allow the binding of a substrate
109
Cofactors are from inorganic ions. Where are co enzymes from
often vitamins / derived from vitamins = especially vitamin B
110
What are co enzymes involved in
Electron transfer reactions
111
Prosthetic group
cofactors are actually a permanent part of the structure of the enzyme they assist = prosthetic group
112
Why are prosthetic groups important
essential to the enzyme functioning properly, as they help to form the final 3D shape of the enzyme
113
How to investigate enzyme activity using water
The rate of product formation is used to measure the rate of enzyme controlled reactions
114
How to investigate enzyme activity using water
Hydrogen peroxide is a common but toxic by-product of metabolism o This means it must be broken down quickly
o Catalase is an enzyme found in the cells of most organisms that breaks down hydrogen peroxide into water and oxygen
o Hydrogen peroxide and catalase are combined and the volume of oxygen generated is measured in a set time o The rate of reaction can then be calculated
115
Cofactor for amylase
Cl-
116
Prosthetic group for carbonic anhydrase
Zn 2+ = carbonic anhydrase transports co2 around the body
117
Name 3 cofactors
Prosthetic group, coenzymes, ions
118
Serial dilutions
- start with a stock solution and take 1 cm^3 and add 9 cm^3 of water which makes it 1/10 diluted
- Then take 1cm^3 this solution and add 9cm^3 water to this which makes it 1/100 diluted and repeat
119
120
C
121
B
122
C
123
124
125
A
126
ii
127
128
129
130
ii
131
132
133
134
135
136
137
138
What can be concluded from the results in Table 4.1 about the optimum temperature for lipase activity?
(the optimum temperature) is between 30°C and 35°C J
139
The normal maximum rate of malate dehydrogenase activity is 100 mmol dm-3 s-1.
The data in Table 19.1, on the Insert, were obtained in the presence of latrotoxin.
What can be deduced from these results about latrotoxin's mode of action as a poison? Justify your answer.
