CHAPTER 4 - ENZYMES Flashcards
1
Q
What are enzymes?
A
Biological catalysts (made from proteins)
2
Q
What type of proteins are Enzymes?
A
Globular
3
Q
What do Enzymes do?
A
Interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions
4
Q
What do anabolic enzymes catalyse?
A
Build up reactions
5
Q
What to catabolic enzymes catalyse?
A
Break down reactions
6
Q
What is Vmax?
A
Maximum initial velocity or rate of the enzyme catalysed reaction, Position where enzymes cannot speed up reaction rates any further
7
Q
What is the specificity of an enzyme?
A
Each enzyme catalyses only one type of biochemical reaction
(Means there are thousands of enzymes in a given cell)
8
Q
What is activation energy
A
Amount of energy required to start a reaction - cause a successful collision
9
Q
What are the two hypothesis on how enzymes react?
A
Lock and Key Hypothesis
Induced-fit hypothesis
10
Q
What is the Lock and Key Hypothesis?
A
Only a specific substrate will fit into the active site of the enzyme
11
Q
What is the area in on enzyme where Enzymes react?
A
Active site
12
Q
How do enzymes react
A
Substrate(s) successfully randomly collides with active site
Substrate(s) binds to enzyme and forms Enzyme-Substrate Complex
Substrate held so that atom-groups are close enough to react
Forms temporary bonds with R-groups of substrate to strain the bonds in substrate,
Substrate(s) react, forms Enzyme-product complex
Products are released, Enzyme is unchanged
13
Q
What is the induced-fit hypothesis?
A
Enzyme changes shape as the substrate enters
Initial interaction between enzyme and substrate is weak, but these induce changes in enzymes tertiary structure
Which strengthens binding, putting strain on molecule
Can weaken particular bonds, therefore lowering activation energy
14
Q
What are Intracellular enzymes?
A
Enzymes that remain within the cell
(eg breakdown of Hydrogen Peroxide, making polysaccharides from glucose)
15
Q
What are extracellular enzymes?
A
Enzymes that operate outside of the cell
(eg breakdown of large molecules into smaller ones in digestion, which then gets absorbed by cells)
16
Q
Examples of Extracellular enzymes
A
Amylase
Trypsin
17
Q
Describe the digestion of starch
A
Starch polymers are partially broken down into maltose (Disaccharide) by Amylase
Maltose is broken down into glucose (monosaccharide) by maltase
18
Q
Where is Amylase produced and released
A
produced by salivary glands and pancreas
Released into mouth and small intestine
19
Q
Where is maltase released?
A
Small intestine
20
Q
Why is glucose a desired product of the digestion of starch?
A
Small enough to be absorbed by cells lining digestive system and absorbed into blood stream
21
Q
What are protease enzymes?
A
Enzymes that catalyses digestion proteins
Eg Trypsin
22
Q
What does Trypsin do?
A
Digests proteins into smaller peptides, then subsequently broken down into amino acids by other proteases
Amino acids can then be absorbed by cells lining digestive system and then absorbed by the bloodstream
23
Q
Where is trypsin produced and released?
A
Produced in pancreas
Released by pancreatic juices in small intestine
24
Q
State the type of biological molecule used to form enzymes
A
Protein
25
Name the monomers that form the biological molecule that makes enzymes
Amino Acids
26
Describe how the structure(s)of this biological molecule determines enzyme activity
Specific, 3D shape / tertiary structure
(formation of) active site
binds to substrate(s)
catalyses reaction
27
Explain how catabolism and anabolism are related to metabolism
Catabolism is breaking down of molecules
anabolism is building of molecules
reactions involve breaking down and building of molecules
Metabolism is sum of all reactions
28
There are two theories explaining enzyme substrate interaction. The Lock and key model and induced fit model of enzyme action
A) explain what is meant by the term model in the sentence above
B) Explain how the Following terms are relevant to each of the models. Complementary, flexibility, R group Interactions, Bond strain
A) simple / easy to understand
representation
B) Lock and key substrate is complementary to active site (of enzyme)
Induced fit active site is flexible
Both models substrate interacts with R groups in active site (binds)
(leading to) bond strain in substrate molecule
29
What factors affect enzyme activity?
Temperature
pH
Substrate and Enzyme Concentration
30
What affect do extremes in pH and Temperature do to most enzymes?
Causes Denaturing and a change in shape of their active site
31
What is the Temperature Coefficient or Q10
A measure of how much the rate of reaction increases with a 10 degree rise in temperature
32
What happens during the denaturing of an enzyme due to high temperature
Bonds holding proteins together vibrate more
As the temperature increases, vibrations increase
Causes bonds to strain then break
Changes Tertiary Structure, Active sit has changed, no longer acts as a catalyst as its active site cannot accept substrate
33
What is Optimum temperature of an enzyme?
The temperature at which the enzyme has the highest rate of activity
34
Are all enzymes optimum temperatures the same?
No, most in human body are around 40 degrees
Thermophilic bacteria (found in hot springs) is around 70 degrees
Psychrophilic organisms (live in areas of cold) can be below 5 degrees
35
Why are enzymes that are adapted to the cold more likely to denature after a small temperature change?
More flexible structures, making them less stable than enzymes that work at higher temperatures
36
Why are enzymes that are adapted to the heat more stable than other enzymes?
Increased number of bonds (especially Hydrogen and disulphide bridges) and are more resistant to change
37
What does tyrosinase catalyse?
The production of melanin (pigment responsible for dark coloured fur)
38
Why are Siamese cats extremities (tail, ears, limbs) dark when their fur is Cream/white?
Tyrosinase is at too low a temperature and is too low to denature the mutant tyrosinase, so black fur pigment is still catalysed
39
What is the optimum pH of an enzyme?
Where the active site will only be in the right shape at that certain hydrogen ion concentration
40
Why will enzymes denature under changes in pH?
Differing H+ ion concentration affects interactions between the polar and charged R-groups present in the amino acids
41
What happens to an enzyme when the pH changes slightly
The Active site will change shape, but not denature
Will return to shape once pH returns to optimum
42
What happens if the pH changes Drastically?
The structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate .
43
Examples of Enzymes and their Optimum pHs and where they operate
Amylase
Pepsin
Maltase
Amylase - pH 7-8 - Mouth
Pepsin - pH 1-2 - Stomach
Maltase - pH 8 - Small Intestine
44
Suggest why Siamese Kittens are born completely white
Extremities are at, same temperature as rest of the body in womb
Tyrosinase, not denatured
pigment is broken down
45
Why does an increasing substrate concentration increase rate of reaction?
higher collision rate with active site of enzymes
More Enzyme-substrate complexes are formed
increases up until Vmax
46
Why does an increasing enzyme concentration increase rate of reaction?
Increase number of available active sites in a particular volume,
more Enzyme-substrate complexes are formed
Increases up until Vmax
47
Once Vmax is reached, how would you increase Rate of Reaction?
Increase Temperature
Add more enzyme
48
Suggest an experiment into how different factors would effect enzyme activity
Placing Liver tissue (containing catalase) into a conical flask of Hydrogen peroxide with a gas syringe (or water trough technique)
Repeat experiment for Boiled and un-boiled liver
49
Explain why a student would use liver tissue to investigate the effects of different factors on enzyme activity
Easy to obtain
contains catalase
50
Show the chemical reaction that occurs resulting in the release of oxygen from the decomposition of Hydrogen Peroxide by Catalase
2H2O2 ➝ 2H2O + O2
51
Explain the shape of the graph (page 91) for the gas production from Un-Boiled liver
volume of oxygen released increased
figures quoted
Catalase, catalysed reaction
52
Describe and explain what has happened in the second experiment - involving boiled liver in the decomposition of H2O2 into oxygen and water
Enzymes are proteins
(boiling) denatures protein
Tertiary structure (of protein) changed
Active site no longer complementary to substrate
Fewer enzyme-substrate complexes formed
Decreased reaction rate
53
What is a serial dilution?
A repeated stepwise dilution of a stock solution of known concentration (usually done by a factor of 10)
54
How would a serial dilution be set up?
Add 1ml of stock solution with 9ml distilled water (1/10)
Take 1ml of this and add 9ml of distilled water (1/100)
Take another 1ml of this and add 9ml of distilled water (1/1000)
Etc......
55
You are provided with a stock solution of enzyme X with a concentration of 20mmol/dm-3. Explain how you would prepare a range of five solutions with a different concentrations of enzyme X using the stock solution. Show your working and state concentrations produced
Serial dilution (1);
described e.g., 1 ml of stock solution and 9 ml of distilled water, 2 mmol dm−3 solution
repeat with diluted solution (s) 0.2 mmol dm−3 and 0.02 mmol dm−3 and 0.002 m mol dm−3 (1)
56
Explain the term 'denatured' with reference to enzymes
R-group interactions are disrupted
Change in tertiary structure
change in 3D shape of active site preventing binding with substrate
57
Bacteria that colonise hydrothermal vents, where temperatures are very high, have enzymes with high optimum temperatures. Suggest why these bacteria are unlikely to cause infections in humans
Bacterial enzymes have high optimum temperatures,
human body temperature is lower
Enzymes will have low activity
Bacteria will not thrive
58
Enzymes with very low optimum temperatures tend to have quite flexible. Using your knowledge of collision theory, explain why this flexibility is necessary
(at low temperatures) Kinetic energy is low
substrates / enzymes, move slowly
Fewer collisions
Collisions have less energy
Increased flexibility of active site
increases chances of successful collision
59
Why is it important that sometimes reactions do not happen too fast?
Could lead to the build up of (harmful) excess products
60
How can enzymes be inactivated
Inhibitors
61
What are the types of Inhibitors
Competitive
Non-competitive
62
What do inhibitors do
Prevents enzymes carrying out their normal function of catalysis
63
How does Competitive inhibition work
A molecule with a similar shape to active site blocks substrate from entering
Stops enzyme catalysing reaction
Enzyme cannot carry out function (inhibited)
Most bind reversibly to active site, exception aspirin
64
How do competitive inhibitors affect rate of reaction?
Reduces rate of reaction, doesn't change Vmax
If substrate concentration is increased, Original Vmax can still be reached
65
Example of competitive inhibition
Statins inhibit enzyme used in synthesis of cholesterol
Prescribed to help people reduce blood cholesterol concentration and reduce risk of heart disease
Aspirin irreversibly inhibits COX enzymes, preventing synthesis of Prostaglandins and thromboxane, chemicals responsible for pain and fever
66
How does Non-competitive inhibition work?
Inhibitor binds to location other than active site (Allosteric site)
Binding causes change in tertiary structure of enzyme, changes active site
Active site no-longer complementary, substrate cannot bind to enzyme
Cannot carry out function - said to be inhibited
67
How do non-Competitive inhibitors affect rate of reaction?
Affects Vmax and reduces Rate of Reaction
Increasing concentration of inhibitor will decrease rate of reaction as more active sites become unavailable
68
Examples of Irreversible non-competitive inhibitors
(often toxic)
Organophosphates used as insecticides and herbicides will inhibit enzyme acetyl cholinesterase, necessary for nerve impulse transmission
Leads to muscle cramps, paralysis and death if accidentally ingested
69
What is End-product inhibition?
Enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
70
What type of feedback is End-product Inhibition and why is it beneficial?
Negative feedback
Acts as control mechanism so excess products are not made and resources aren't wasted
71
Explain why a non-competitive inhibitor does not need to have a similar shape to a substrate molecule
A non-competitive inhibitor binds to an enzyme away from the active site
at an allosteric site
Which has a different shape than the active sit
72
Explain why increasing the concentration of substrate will never produce the Vmax of a reaction after the addition of a non-competitive inhibitor
Inhibitor will always be present
Some enzymes always inhibited
73
End-product inhibition is likely to be competitive rather than non-competitive. Suggest reasons for this, and give an example of end-product inhibition
End-product inhibition regulates rate of reaction
concentrations of substrate and product determine reaction rate
(so must be) competitive
substrate concentration has no effect in non- competitive inhibition
e.g. ATP and PFK in respiration
74
What is an example of an End-product inhibition
ATP and PFK in respiration
Addition of two phosphates to glucose
Addition of second phosphate group results in the initial breakdown of glucose, catalysed by Phosphofructokinase (PFK)
This enzyme is competitively inhibited by ATP, Therefore ATP regulates its own production
When levels of ATP are high, ATP binds to allosteric site on PFK, preventing addition of second phosphate on glucose, so ATP is not produced at the same rate
As ATP is used up, less binds to PFK, so enzyme is able to add Second phosphate group to glucose, respiration resumes leading to production of more ATP
75
Ethylene Glycol present in antifreeze is poisonous when ingested. Ethylene glycol is oxidised using the same enzymes used to oxidise ethanol. The product made during the breakdown of ethylene glycol, rather than ethylene glycol itself, are responsible for the toxic effects. Ethylene glycol is able to leave the body unchanged in urine. Suggest why ethanol is often used in emergency departments as an antidote to antifreeze poisoning.
Ethanol has similar shape to ethylene glycol
(ethanol) binds to active site of enzyme which breaks down ethylene glycol
competitive inhibition
less ethylene glycol broken down
more (ethylene glycol) leaves body unchanged
fewer toxic effects
76
What is a cofactor?
A non-protein helper component that is needed to carry out enzyme function.
Transfer atoms or groups from one reaction or may form active site of an enzyme
77
What is a Coenzyme?
If a cofactor is an organic molecule
78
How are inorganic cofactors obtained?
Via Diet as minerals eg. iron, calcium, chloride and Zinc
79
What ion acts as a cofactor to Amylase?
Chloride ion - forms part of active site
80
How are coenzymes obtained?
Derived from vitamins in diet
81
What Vitamin is a coenzyme of NAD?
Vitamin B3 - Transfers hydrogen atoms between molecules in respiration
82
What does a Prosthetic group act as, a cofactor or coenzyme?
Permanent Cofactor (eg Zinc in carbonic anhydrase)
83
What is inactive precursor enzymes?
When enzymes are produced in an inactive form, usually those that can cause damage within cells (needs to be controlled)
84
How do Inactive precursor enzymes become active?
Change in Tertiary (structural) shape, particularly to active site, usually by addition of a cofactor
85
What is an inactive precursor protein called before a cofactor is added?
Apoenzyme (inactive enzyme)
86
What is a precursor inactive enzyme called after a cofactor is added
Holoenzyme (active enzyme now)
87
How else can tertiary structure be changed to activate an enzyme?
Actions of another enzyme (eg protease) which cleaves certain bonds in the molecule
pH and temperature can also result in a change in structure (these are called zymogens or proenzymes)
88
What is an example of enzyme activation by pH?
Inactive pepsinogen released into stomach to digest proteins, pH transforms enzyme into active pepsin
This adaption protects the body tissues against digestive action of pepsin
89
Describe enzyme activation in blood-clotting mechanism
Blood clotting is when platelets aggregate at site of tissue damage, releasing clotting factors, such as Factor X
Factor X is an enzyme that is dependant on cofactor vitamin K for activation, and catalyses the conversion of prothrombin into the enzyme thrombin by cleaving specific bonds in the molecule (tertiary structure)
Thrombin is a protease and catalyses conversion of soluble fibrinogen into insoluble fibrin fibres - which together with platelets, form a blood clot
This series of successive enzyme activations in blood clotting is called the coagulation cascade
90
Explain the importance of enzyme activation in controlling blood clotting
Enzymes responsible for blood clotting are present as precursors e.g., Factor X,
prothrombin
prevents clotting unless required
91
Describe two ways in which cofactors are necessary for the catalytic role of some enzymes
Transfer, atoms / groups, between reactions
form part of active site
92
Explain using an appropriate example of each, how prosthetic groups are different from coenzymes
Coenzymes bind loosely to enzymes e.g. NAD
prosthetic groups are a permanent feature of and bind tightly to, proteins / enzymes e.g. iron ion in haemoglobin
93
Using blood clotting as your example, explain the different ways in which enzymes can be activated
Presence of cofactor
e.g., vitamin K and Factor X
change in tertiary structure / described
e.g. (activated) factor X catalyses the breaking of bonds in prothrombin
forming thrombin
thrombin catalyses the conversion of fibrinogen to fibrin
94
