2.4* Flashcards
(234 cards)
1
Q
What is a active site?
A
Indented area on the surface of an enzyme molecule, with a shape that is complimentary tot he shape of a substrate molecule.
2
Q
What is catalyst?
A
Chemical that speeds up the rate of a reaction and remains unchanged and reusable at the end of the reaction.
3
Q
What is the meaning of extracellular?
A
Outside the cell.
4
Q
What is the meaning of intracellular?
A
Inside the cell.
enzymes catalyse a wide range of intracellular as well as extracellular reactions
5
Q
What is the meaning of metabolic/metabolism?
A
The chemical reactions that take place inside living cells or organisms.
6
Q
What is the meaning of product?
A
A molecule produced from substrate molecules, by an enzyme catalysed reaction.
7
Q
What is the meaning of substrate?
A
A molecule that is altered by an enzyme catalysed reaction?
8
Q
Why are enzymes called biological catalysts?
A
Enzymes are called biological catalysts because they speed up metabolic reactions in living organisms. Their actions affect both structure and function within cells, tissues and organs.
9
Q
Give examples of how enzymes effect both structure and function within cells?
A
Catalysts speed up chemical reactions and remain unchanged at the end of the reaction, able to be used again.
A small amount of catalysts can catalyse the conversion of a large number of substrate molecules into product molecules.
The number of reactions that an enzyme molecule can catalyse per second is known as its turnover number.
10
Q
Why are enzymes better than chemical catalysts, regarding energy usage?
A
Whereas chemical catalysts usually need very high temperatures increased pressures and extremes of PH, enzymes speed up metabolic reactions by up to 10 to the power of 12 times at lower temperatures, often at neutral PH and at normal pressures. Hence, as biological catalysts, they re able to function in conditions that sustain life.
11
Q
Why are enzymes better than chemical catalysts, concerning economy?
A
Enzymes are also more specific than chemicals catalysts. They do not produce unwanted by-products and rarely make mistakes. The cells in which they are made and/or act can also regulate their production and activity to fit the needs of the cell or organism at the time.
12
Q
What may prevent an enzyme from functioning apart from heat and PH?
A
For enzymes to catalyse some reactions, they may need help from co-factors.
The instruction fro making enzymes are encoded in genes. If the gene has a mutation that alters the sequence of amino acids in a protien, then this may alter the enzyme tertiary structure and prevent it from functioning.
13
Q
What causes a metabolic disorder?
A
If an enzyme that catalyses a metabolic reaction is deficient, then a metabolic disorder results.
14
Q
What do enzymes catalyse that may cause the ‘Stone man syndrome’
A
Enzymes also catalyse the formation of the organisms structural component, such as collagen in bone, cartilage, blood-vessel walls, joints and connective tissue. Some genetic disorders cause malformations of connective tissue and can be very harmful, such as ‘stone man syndrome’.
15
Q
Describe PKU.
A
Many metabolic disorders are caused by deficient or non-functioning enzymes, for example if the active site is misshapen. The genetic disorder phenylketonuria, PKU, results when the enzyme phenylalanine hydroxylase does not function and cannot convert the essential amino acid, phenylalanine, to another amino acid, tyrosine. As a result, sufferers cannot make melanin (which is made from tyrosine), and the accumulation of phenylaline in their blood impairs brain development leading to severe mental impairment.
16
Q
How do we treat PKU?
A
Because this enzyme deficiency is so severe, all new born babies are screened for PKU, so that if the result is positive their diet can be adjusted to include only very small amounts of phenylalanine, to prevent the irreversible brain damage.
17
Q
Describe the active site of an enzyme.
A
Enzymes are large molecules with a specific areas, an indentation or cleft on the surface of the molecule, called the active site. This consists of just a few - often about 6 to 10 - amino acids.
The active site is part of the enzyme molecule, not part of the substrate molecule.
18
Q
Why is each type of enzyme specific in its function?
A
So, each type of an enzyme is highly specific in its function, as it can only catalyse a reaction involving the particular type of substrate molecule that fits into its active site.
19
Q
What is crucial to make an enzymes shape complimentary to the shape of the substrate molecule?
A
The tertiary structure of the active site is crucial, as its shape is complimentary to the shape of the substrate molecule.
20
Q
What be altered by changes in temperature and PH?
A
The shape of the enzymes active site, and hence its ability to catalyse a reactions, can be altered by changes in temperature and PH, as these affect the bonds that hold proteins in their tertiary structure.
21
Q
Why might the same enzyme complex be known by different names?
A
Most enzymes catalyse a reaction in either direction depending on the cells needs. Hence ATPase can catalyse the formation of ATP or the hydrolysis of ATP. Sometimes an enzyme catalyses two reactions, because it is really a large enzyme complex and has more than one active site. So, the same enzyme complex may be known by different names.
22
Q
How many metabolic reactions go on inside your body?
A
In any cell, and within its organelles, there may be up to 1000 metabolic reactions going on at the same time, each being catalysed by a different enzyme. Some of these reactions are part of a metabolic pathways.
23
Q
What is each metabolic pathway in a living cell?
A
Each metabolic pathway in a living cell is one of a series of consecutive reactions, every step catalysed by a specific enzyme that produces a specific production.
24
Q
Metabolic pathways:
What acts as substrates?
A
The various reactants and intermediates act as substrates for specific enzymes.
25
Metabolic pathways:
| What are the reactants, intermediates and products known as?
The reactants, intermediates and products are known as metabolites.
26
Metabolic pathways:
| Where is energy released?
In some metabolic pathways, described as catabolic, metabolites are broken down to smaller molecules and release energy.
27
Metabolic pathways:
| When is energy used?
In other metabolic pathways, described as anabolic, energy is used to synthesise larger molecules from smaller ones.
28
Metabolic pathways:
| Give some examples of complex metabolic pathways.
Respiration and photosynthesis are examples of complex metabolic pathways, with many enzymes involved.
(diagram of enzyme at the top of page 101)
29
Where is catalase found?
In nearly all living organisms.
30
Why is catalase important?
It is a very important enzyme, as it protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide, a potentially harmful by-product of many metabolic reactions, to water and oxygen.
31
What does catalase consist of?
Four peptide chains and contains a haem group with iron.
32
What is unique about catalase?
It is the fastest-acting enzyme, having the highest turnover number known, of about 6 million per second.
33
Give two examples of where catalase is used.
In eukaryotic cells, catalase is found inside small vesicles called peroxisomes.
When white blood cells ingest pathogens they use catalase to help kill the invading microbe.
34
What the optimum conditions for catalase?
The optimum pH for human catalayse is around pH 7, but for other species it varies between pH 4 and 11. The optimum temperature also varies with species. For humans this is 45 degrees and for some thermophilic archaea it is 90 degrees.
35
Give an example of impacts of low catalase levels.
Some people lose hair pigment and go grey earlier in life than others. One reason may be that these people have lowered levels of catalase, and so more hydrogen peroxide bleaches their hair shafts from the inside.
36
Apart from animals digestive system give an example and explain an example of extracellular enzymes.
Some enzymes are secreted from the cells where they are made and act on heir substrates, extracellularly. Fungi, such as the bread mould Mucor, release hydrolytic enzymes from their thread-like hyphae. The enzymes digest carbohydrates proteins and lipids in the bread, and the products of digestion - glucose, amino acids, glycerol and fatty acids, are absorbed into the fungal hypahe for use in respiration and growth.
37
Describe an example of how extracellular enzymes are used in our bodies.
In our digestive system many enzymes are secreted, from cells lining the alimentary canal, into the gut lumen. There they extracellularly digest the large molecules, such as proteins, lipids, carbohydrates and nucleic acids, found in food. The products of digestion are then absorbed, via epithelial cells of the gut wall, into the bloodstream in order to be used for respiration, growth and tissue repair.
38
Where is amylase produced and what is its purpose?
Amylase is produced in the salivary glands, and acts in the mouth to digest the polysaccharide starch to the disaccharide maltose. It is also made in the pancreas, and acts to catalyse the same reaction in the lumen of the small intestine.
39
Where is trypsin produced and what is its purpose?
Trypsin is made in the pancreas, and acts in the lumen of the small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds. Its optimum pH is between 7.5 and 8.5.
40
Why are enzymes needed in the digestive system, what would happen without them?
If you had to wait for a meal to digest without any enzymes, it would take several years. Hence, without enzymes, the speed of chemical reactions inside living organisms could not sustain life . Humans produce about six times as much amylase as chimpanzees do. Chimpanzees eat some meat and a lot of fruit, but very few starchy vegetables.
41
What is a cofactor?
A substance that has to be present to ensure to ensure that an enzyme-catalysed reaction takes place at the appropriate rate. Some cofactors (prosthetic groups) are part of the enzymes structure, and others (mineral ion co-factors and organic co-enzymes)form temporary associations with the enzyme.
42
What is a enzyme-substrate complex?
Complex formed by temporary binding of enzyme and substrate molecules during an enzyme-catalysed reaction.
43
What do some enzymes need to have attached to them?
Some enzymes, particularly those involved in catalysing oxidation-reduction reaction, can only work if another small non-protien molecule is attached to them. These small molecules are called cofactors.
44
What is a cofactor permanently bound, by covalent bonds, to an enzyme molecule called?
A prosthetic group.
45
How does which enzyme catalyse the interconversion of carbon dioxide and water yo carbonic acid?
The enzyme carbonic anhydrase contains a zinc ion permanently bound, as a prosthetic group, to its active site. This enzyme is found in erythrocytes (red blood cells) and catalyses the interconversion of carbon dioxide and water to carbonic acid, which then breaks down to protons and hydrocarbonate ions.
46
Describe the enzyme controlled reaction of carbon dioxide and water to carbonic acid.
CO2 + H2O H2CO3 H+ + HCO3-
As with most enzyme-catalysed reactions, this reaction may proceed in either direction, depending on the concentration of substrate or product molecules.
47
When is the enzyme controlled reaction of carbon dioxide and water to carbonic acid important?
The reaction is vitally important, as it enables carbon dioxide to be carried in the blood from respiring tissues to the lungs.
48
Give examples of molecules with a haem group or a prosthetic group.
The enzyme catalyse contains a haem group with iron. Other proteins, besides enzymes, have prosthetic groups. For example haemoglobin also has a haem group.
49
Why is zinc important to humans?
Zinc is important to humans. As well as being needed to make carbonic anhydrase, Zinc is necessary for the polypeptide hormone, insulin, to function correctly. People whose diets do not contain much meat may be deficient in zinc.
50
How are scientists tackling zinc deficiency?
Some genetically modified crop plants such as plantain (a type of banana), use a lot in East Africa, are nutritionally enhanced to contain more zinc. This is useful, as meat is still too expensive for many people in these countries to obtain enough of it, but plantain is their staple diet.
51
How may cofactors work with enzymes without permanently binding to them?
Whereas the zinc associated with carbonic anhydrase is present in compound that is permanently bound to the enzymes active sit, some enzymes work better in the presence of ions that are not permanently bound to them. These ions are also called cofactors.
52
How may the presence of certain ions increase the rate of the enzyme catalysed reaction.
During an enzyme-catalysed reaction, the enzyme and substrate molecules temporarily bind together to form an enzyme-substrate complex. The presence of certain ions that may temporarily bind to either the substrate or the enzyme molecule may ease the formation of such enzyme-substrate complexes and therefore increase the rate of the enzyme-catalysed reaction.
53
What can cofactors act as apart from to ensure that the reaction happens at the appropriate rate?
Some co-factors act as co-substrates - they and the substrate together form the correct shape to bind to the active site of the enzyme.
Some of the co-factors change the charge distribution on the surface of the substrate molecule or on the surface of the enzyme's active site, and make the temporary bonds in the enzyme-substrate complex easier to form.
54
Give an example of enzyme that needs the presence of chloride ions.
The enzyme amylase digests starch to maltose, and will only function if chloride ions are present.
55
Describe what cofactors can be made up of and how each type bond to the enzyme.
Coenzymes are a type of cofactor. they are organic but not made of protien. They bind temporarily to the enzymes active site.
Metallic ions may also be cofactors of certain enzymes. Some stay bound to the enzyme permanently, forming prosthetic groups.
Some metallic ions temporarily attach to the enzyme or to the substrate in order to aid the formation of enzyme-substrate complexes.
56
Describe the role of the co-enzyme in the reaction, and how it is affected by the reaction.
Coenzymes are small organic non-protien molecules that bind temporarily to the active site of enzyme molecules, either just before or at the same time that the substrate binds. The coenzymes are chemically changed during this reaction, and they need to be recycled to their original state, sometimes by a different enzyme.
57
Where are many coenzymes derived from?
Many co-enzymes are derived from water-soluble vitamins. If these vitamins are deficient in the diet of humans, then certain diseases may result.
58
What coenzyme is derived from, and which human deficiency disease is caused from a lack of B12.
```
Cobalamin coenzymes.
Pernicious anaemia (progressive and fatal anaemia)
```
59
What coenzyme is derived from, and which human deficiency disease is caused from a lack of Folic acid?
```
Tetrahydrofolate .
Megablastic anaemia (large, irregularly shaped erythrocytes)
```
60
What coenzyme is derived from, and which human deficiency disease is caused from a lack of Nicotinamide B3?
NAD, NADP.
| Pellagra (diarrhoea, dermatits and dementia)
61
What coenzyme is derived from, and which human deficiency disease is caused from a lack of Pantothenate, B6?
Coenzyme A
| Elevated blood-plasma triglyceride levels.
62
What coenzyme is derived from, and which human deficiency disease is caused from a lack of Thaimine, B1?
Thaimine pyrophosphate
| Beriberi (mental confusion, irregular heartbeat, muscular weakness, paralysis and heart failure)
63
What are NAD and NADP both?
Hydrogen acceptors, they are both derivatives of nucleotides.
64
What is a enzyme-product complex?
Enzyme molecule with product molecule(s) in its active site. The two are joined temporarily by non-covalent forces.
65
What is a enzyme-substrate complex?
Enzyme molecule with substrate molecule(s) in its active site. The two are joined temporarily by non-covalent forces.
66
Why does the substrate molecule fit in the specific indented area on the surface of the enzyme?
The tertiary structure of the enzymes active site gives it a shape that is complimentary to that of the substrate molecule - rather like the way in which only one specific key will fit into a lock.
67
In the lock and key hypothesis explain how smaller product ,molecules are formed.
Substrate molecules fits into the enzyme's active site. Temporary hydrogen bonds hold the two together forming an enzyme-substrate complex (ES complex). The substrate molecule is broken into smaller product molecules that leave the active site.
68
In the lock and Key hypothesis describe how a larger product molecule is formed.
Substrate molecules fit into the active site, forming an enzyme-substrate complex (ES complex). Bonds form between substrate molecules forming an enzyme-product complex.
69
The lock and key hypothesis;
| What do enzymes forming a larger and smaller molecule have in common?
In each case at the end of the reaction, the enzyme is able to form an ES complex with another substrate molecule and catalyse another reaction.
70
How is a ES complex formed?
If a substrate molecule successfully collides with an enzyme, them an enzyme-substrate complex (ES complex) forms as the substrate molecule fits onto the complementary-shaped active site on the enzyme molecule.
71
Why do the substrate and enzyme molecules collide?
The substrate and enzyme molecules have kinetic energy and are constantly moving randomly.
72
When is the enzyme-product complex formed?
The substrate molecules are either broken down or built up into the product molecule(s) and these form an enzyme-product complex whilst still in the active site.
73
What happens when the product is formed?
The product molecules leave the active site.
The enzyme molecule is now able to form another enzyme-substrate complex.
A small number of enzyme molecules can therefore convert a large number of substrate molecules into product molecules.
74
What did the scientist Emil Fischer discover?
A scientist, Emil Fischer, discovered in 1894 that glycolytic (sugar-splitting) enzymes could distinguish between sugar molecules that have the same molecular formula but slight differences in he geometry of how the atoms are arranged within the molecules (think of a left hand and a right hand glove). This led him to form his lock-and-key hypothesis, which explains enzyme specificity.
75
What have scientists inly known about since the 1930's?
Although scientists have known about enzymes since the late 19th century, it was only in the 1930's that it was established that enzymes are proteins.
76
What was the first enzyme to have its amino acid sequence worked out?
The first enzyme to have its amino acid sequence worked out was bovine pancreatic ribonuclease, in 1963.
77
What has been discovered about enzymes since 1965?
In 1965 , the first 3D structure of an enzyme, hen egg-white lysozyme, was worked out using X-ray diffraction. Since then, the structures of many enzymes have been elucidated. In the 1990s, scientists discovered that some types of RNA have catalytic properties in cells.
78
What does the lock and key hypothesis not explain?
Although the lock and key hypothesis explains enzyme specificity, it does not explain how the transition state - namely the ES complex - is stabilised.
79
Who modified the lock and key hypothesis and when?
In 1958 Daniel Koshland modified the lock and key hypothesis by suggesting that the active site of the enzyme is not a rigid fixed structure, but that the presence of the substrate molecule in it induces a shape change giving it a good fit.
80
What did Daniel Koshland suggest?
When the substrate molecules fit into the enzyme's active site, the active site changes shape slightly to mould itself around the substrate molecule. Think of putting on a glove - it will only accept a hand shaped object, but when you insert your hand the glove moulds around and fits your hand perfectly.
81
In the induced fit hypothesis what changes to induce the fit of the substrate?
The active site still has a shape complimentary to the shape of the substrate molecule. But, on binding, the subtle changes of shape of the side chains (R-groups) of the amino acids that make up the active site give a more precise conformation that exactly fits the substrate molecule. This moulding enables the substrate to bind more effectively to the active site.
82
What binds the substrate molecule to the enzyme and what does this form?
An enzyme-substrate complex is formed, and non-covalent forces such as hydrogen bonds, ionic attractions, van der Waals forces and hydrophobic interactions, bind the substrate molecule to the enzyme's active site.
83
When is an enzyme-product complex formed?
When substrate molecules have been converted to the product molecules and these are still in the active site, they form an enzyme-product complex.
84
Why does the product detach from the active site of an enzyme?
AS the product ,molecules have a slightly different shape from the substrate molecule, they detach form the active site.
85
What happens the the product molecule has detached from the active site of an enzyme?
The enzyme molecule is now free to catalyse another reaction with another substrate molecule of the same type.
86
What equation outlines how an enzyme catalyses a reaction?
Enzyme + substrate -> Enzyme - substrate complex -> Enzyme product complex -> Enzyme + product.
E + S -> ESC -> EPC -> E + P
87
Chemical reactions need energy to activate or begin them. How can this activation energy be provided outside of the body?
Many chemicals can be heated to provide this activation energy and make them react together. This increases the kinetic of the molecules so that they move about more, in a random fashion, and are more likely to successfully collide and then react together.
88
Chemical reactions need energy to activate or begin them. How can this activation energy be provided inside of the body?
In a living cell, the temperature cannot be raised too much or the proteins within it would denature and lipids would melt. Because enzymes have an active site specific to only the substrate molecules, they bring the substrate molecules close enough together to react, without the need for excessive heat. Therefore they lower the activation energy and hence speed up metabolic reactions.
89
How does the enzyme maltase change the activation energy required to hydrolyse maltose to glucose?
Adding the enzyme maltase reduces the amount of activation energy required for the reaction to take place. (graph on page 107)
90
What does the word digestion mean and what word should it be used with in an explanation?
Digestion means to break down. Large molecules in food, such as proteins and starch, are digested by being broken down by hydrolysis to smaller molecules, such as amino acids and glucose, Therefore the words 'digestion' and 'hydrolysis' may be used synonymously.
91
How can you investigate enzyme specificity?
Yeast, Saccharomyces Cerevisiae, is a single celled fungus. It is a facultative anaerobe, which means it can respire with or without oxygen. If oxygen is absent then it can respire anaerobically.
When yeast respires anaerobically it produces ethanol and carbon dioxide. The carbon dioxide produced during a unit time, such as 10 minutes, can be collected and its volume measured.
Yeast may respire different sugars. Enzymes are specific and each type will catalyse a specific sugar. You can investigate whether yeast can metabolise the monosaccharide sugars glucose, fructose and galactose.
92
What is Q10?
Temperature coefficient, calculated by divided the rate of reaction at (T + 10) degrees, by the rate of reaction at T degrees.
93
What makes molecules collide with one another?
All molecules have kinetic energy and can continuously move around randomly. In doing so, molecules will collide with none another.
94
What happens to the particles when a substance is heated.
The extra energy, in the form of heat, causes the molecules to move faster.
This increases the rate of collisions between molecules.
It also increases the force with which they collider, as they are moving faster.
95
If the reactant mixture containing enzyme and substrate molecules is heated what will happen?
Both types of molecule will gain kinetic energy and move faster.
This will increase the rate (number per second) of successful collisions.
At a particular temperature, called the enzymes optimum temperature, the rate of reaction is at its maximum.
96
What does an increased rate of successful collisions of an enzyme and substrate caused by increased heat change?
The rate of formation of ES complexes increases, and the rate of reaction increases, increasing the number of enzyme-product complexes per second, up to a point.
97
As well as making molecules move faster what else does heat change about molecules?
Increasing the temperature also make molecules vibrate.
98
What does molecules vibrating due to heat change in an enzyme catalysed reaction?
The vibrations may break some of the weak bonds, such such as hydrogen and ionic bonds, that hold the tertiary of the enzymes active site.
99
Describe the denaturing of enzymes.
As the active site shape begins to change, the substrate molecules will not fit in so well and the rate of reaction begins to decrease.
As more heat is applied, the shape of the enzyme's active site completely and irreversibly changes so that it is no longer complementary to the shape of the substrate molecule.
The reaction cannot proceed at all.
The enzyme is denatured.
100
What does not change when an enzyme denatures?
Heat does not break the peptide bonds between amino acids, so the enzymes primary structure is not altered.
101
Describe an enzyme's structure.
The protien would have been folded into a correct 3D shape, part of which, in an enzyme molecule, is an active site.
The hydrophobic core would have contained non polar side chains, and hydrogen bonds can form to the polar side chains of the molecule.
(diagram of page 108)
102
Describe a denatured enzyme.
Heat has broken hydrogen bonds so that the protien has unfolded. It no longer has its 3D shape and the active site is of complimentary to the shape of the substrate molecule.
103
What is the optimum temperature?
This is the temperature at which the enzyme works best. It is the temperature at which the enzyme has its maximum rate of reaction.
104
Why might some enzymes work better in cold conditions, give an example.
Because some organisms are adapted to living in cold places. For example there are psychrophilic bacteria which live in very cold conditions. There enzymes can work at really low temperatures.
105
How do some enzymes adapt to a hot climate, give an example.
Some organisms, such as thermophilic bacteria in hot springs, live at very high temperatures. There enzymes (as well as their proteins) are heat stable. They more disulfide bonds that do not break with the heat and keep the shape of their protien molecules stable. Their enzymes will have high optimum temperatures.
106
Name an enzyme obtained from a thermophilic bacterium.
Thermophilus aquaticus, called Taq polymerase, that is used at high temperatures in the polymerase chain reaction (PCR) to amplify fragments of DNA for forensic gene-screening analysis or cloning.
107
How would a graph look for an enzyme catalysed reaction, such as the hydrolysis of cooked egg white (the protien albumen) by the protease enzyme pepsin.
As the temperature increases the rate of reaction increases due to the increases kinetic energy.
Increasing temperature beyond the optimum temperature will reduce the rate of reaction due to the breaking of bonds holding the enzymes tertiary structure in place.
108
What equation calculates Q10?
Rate of reaction at (T+10) degrees/rate of reaction at T degrees
The temperature coefficient here refers to the increase in the rate of a process when the temperature is increased by 10 degrees.
109
What is Q10 for chemical reactions in a test tube?
Q10 is approximately 2, which means that for every 10 degrees rise in temperature the rate of reaction is doubled.
110
For metabolic reactions catalysed by enzymes between the temperatures of 0 degrees and approximately 40 degrees how does a change of temperature of about 10 degrees change the rate of reaction?
The rate of reactions is roughly doubled. This is because the increase in temperature provides more kinetic energy, so enzyme and substrate move faster an collide more often.
111
How is the value of the temperature coefficient affected when the enzyme is above its optimum temperature?
For enzymes at temperatures above their optimum temperature, the value of the temperature coefficient Q 10 drops. This is because the higher temperatures alter the structure of the active sites of the enzyme molecules so that they are no longer complementary to the shape of the substrate molecule.
112
What enzymes can you to investigate the effect of temperature change?
There are many, one is phosphatase enzyme. This enzyme breaks down organic phosphates in cells in order to maintain the pool of phosphate ions for use by cells to make chemicals such as ATP, ribulose bisphosphate and NADP.
113
In an investigation on the effect of temperature on phosphatase enzymes what chemical substrate would be used?
Phenolphthalein phosphate, (PPP)
114
In an investigation on the effect of temperature on phosphatase enzymes what enzyme breaks down phenolphthalein phosphate?
Phosphatase enzyme breaks this down, liberating free phenolphthalein.
115
In an investigation on the effect of temperature on phosphatase enzymes how do you measure the effect of the enzyme?
When sodium carbonate, which is alkaline, is added in excess, the free phenolphthalein proceeds a deep pink colour. The intensity of the colour is proportional to the concentration of free phenolphthalein. The intensity can be measured using a colorimeter with a green filter. If each reaction tube has been given the same length of time, the intensity of the colour gives an indication of the rate of reaction - the darker the pink, the more molecules of PPP were hydrolysed by the enzyme in the set period of time.
116
What does pH indicate?
The pH indicates whether a substrate is acidic, alkaline or neutral.
117
What pH values indicate which levels of acidity?
pH values of 0-6 are acidic, pH 7 indicated neutral, and pH 8-14 indicates that the solution is alkaline.
118
What makes a substance acidic?
Acids such as hydrochloric acid and sulphuric acid dissociate into protons and a negatively charged ion.
HCL -> H+ +Cl-
H2SO4 -> H+ +HSO4-
119
What does pyruvic acid dissociate into and what is this an example of; give another example.
Organic acids are also proton donors:
Lactic acid dissociates into H+ and lactate
pyruvic acid disassociates into H+ and pyruvate
120
In biology what is a buffer?
Something that resists changes in pH.
121
What acts as a buffer in your blood?
There are certain chemicals in your blood that help resist changes in pH so the blood pH remains in a fairly narrow limit close to pH 7.4.
122
How do the buffers in your blood work?
These chemicals can donate or accept hydrogen ions. Some protiens such as haemoglobin, can also donate or accept protons and so act as buffers.
123
In laboratory conditions how will you use buffers?
In laboratory investigations, you will use buffer solutions to maintain the desired pH for investigating enzyme action at different pH constant whilst you investigate another factor.
124
How is the pH worked out?
The formula log 1/[H+] so a large concentration of hydrogen ions gives a small value of pH. If the acidity increases, then the pH decreases.
125
What are hydrogen ions?
Protons
126
How does the pH the rate of reaction of an enzyme?
Excess hydrogen ions will interfere with these hydrogen bonds and ionic forces, and so the active site of the enzyme molecule will change shape. If the substrate molecule does not fit well into the active site, then the rate of reaction that the enzyme catalyses will be lowered.
127
What is a hydrogen ion attracted to?
A hydrogen ion, which is a proton, has a positive charge, molecules or parts of molecules.
128
How will changing the pH alter the binding of a substrate molecule to the active site?
Increasing the concentration of hydrogen ions will also alter the charges on the active site of enzyme molecules, as more protons will cluster around negatively charged groups (for example amino acid R-groups) in the active site. This interferes with the binding of the substrate molecule to the active site.
129
Hydrogen bonds hold structures like an alpha helix in place in protien molecule, what happens as H+ is increased in concentration?
As H+ is increased in concentration, the positive charges are attracted to the negative charges on the alpha helix and so 'replace' the hydrogen bonds.
130
What range of pH do enzymes work in?
Small changes of pH, either side of the optimum pH, slow the rate of reaction, because the shape of the active site is disrupted.
131
What happens if the normal optimum pH is restored after an enzyme has been in the wrong pH?
If the normal optimum pH is restored, the hydrogen bonds can re-form and the active site's shape is restored.
At extremes of pH, the enzymes active site may be permanently changed. when the enzyme is thus denatured, it cannot catalyse the reaction.
132
What does increasing or reducing the pH away from the optimum change?
It reduces the rate of reaction because the concentration of H+ in a solution affects the tertiary structure of the enzyme molecule.
133
What would the optimum pH of enzymes that work intracellularly be?
Close to pH 7
134
What would the optimum pH of enzymes that work extracellularly be, give n example from the first stage of digestion.
Enzymes that work extracellularly may have optimum pH values different from pH 7. During digestion, for example, food is first taken into your mouth, and the amylase enzymes that digest starch to maltose there work best at a pH of 6.8.
135
Give an example of the optimum pH of extracellular enzymes in the stomach.
As food passes through your stomach, hydrochloric acid is secreted, giving a very low pH. One of the acids functions is to kill bacteria and other pathogens in food. The protease enzyme, pepsin, in the stomach works best at very low pH values, of between 1 and 2. It digests large protien molecules into smaller peptide molecules.
136
Give an example of the optimum pH of extracellular enzymes in the small intestine.
As the partially digested food moves into the small intestine, salts in bile made in the liver neutralise it and raise the pH to around 7.8. This is optimal for the protein-digesting enzymes, trypsin and enterokinase, that the catalyst further digestion of the peptides to amino acids in the small intestine.
137
What limits does blood pH need to be kept in.
It is important that your blood is maintained within quite narrow limits, between 7.35 and 7.45.
138
Why does the blood pH need to be kept within limits?
There are plasma proteins within the blood. Changes in pH can absolutely cause vasoconstriction and vasodilation.
139
In the blood plasma there are buffers that resist changes in pH, what are these buffers?
Potassium dihydrogenphosphate can donate hydrogen ions. Some proteins act as buffers, as they can donate or accept protons. Hydrogencarbonate ions also act as buffers.
140
Give an example of enzymes you can use to carry out an investigation on the effect of pH changes on the rate of an enzyme-catalysed reaction.
You can design an investigation to find the effect of the changing pH on the activity of the enzyme phosphatase. You can carry out similar experiments with the enzymes pepsin and trypsin.
141
What would you need to include in an investigation plan?
Write a plan for your investigation. Include a clearly stated testable hypothesis; a list of apparatus needed; the independent and dependant variables; control variables with details of how and why you need to control them; and how you will deal with your data.
142
What is concentration?
The number of molecules per unit volume.
143
If there is no substrate why can an enzyme catalysed reaction not proceed?
Because there are no substrate molecules to fit into the enzymes molecules' active sites, and so no enzyme-substrate complexes can be formed.
144
As substrate is added to an enzyme catalysed reaction what else changes?
Its concentration increases and the rate of reaction increases.
145
Why does the rate of reaction increase as more substrate is added to an enzyme catalysed reaction?
Because more enzyme substrate (ES) complexes can form.
As a result, more product molecules are formed.
Substrate concentration is limiting the reaction, because, as it increases, the rate of reaction increases.
Substrate concentration is the limiting factor.
146
What will happen if the concentration of the substrate keeps increasing in an enzyme catalysed reaction?
The reaction will reach its maximum rate.
Adding more substrate to increase the substrate concentration will not increase the rate of reaction.
This is because all the enzymes' active sites are occupied with substrate molecules.
If more substrate molecules are added, then they cannot successfully collide with and fit into the enzymes active site.
147
Describe what is happening to the initial rate of reaction as the substrate concentration increases before it reached its maximum rate.
Substrate concentration is the limiting factor.
| Increased concentration leads to increased reaction rate .
148
Describe what is happening to the initial rate of reaction as the substrate concentration increases after it reaches its maximum rate.
All enzymes present are working at maximum rate.
| Substrate concentration is no longer limiting the reaction. Another factor is limiting the reaction.
149
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction;
What is urease and what does it break own?
Uraese is a hydrolytic enzyme found in some bacteria, fungi and plants. It breaks the C-N bonds in amides, such as urea.
(NH2)2 + H20 -> 2NH3 + CO2.
This releases ammonia, which can be used by the organisms as a scource of nitrogen.
150
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; How do you test the amount of ammonia released form the enzyme urease?
As ammonia is released, the pH of the solution is increased. The indicator phenol red changes from yellow to pink when alkaline. Universal Indicator solution may also be used to detect the change of pH due to the evolution of ammonia. The solution will change from green to blue.
151
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; When using urease as the enzyme how can colorimetry be use?
Colorimetry can be used to measure absorbance and hence the depth of colour, and therefore the amount of ammonia produced in a set time. This gives an indication of the rate of reaction.
152
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; When using urease as the enzyme what is the independent and dependant variables?
The independent variable is the concentration of urea. The dependant variable is rate of reaction as measured by absorbance.
153
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; When using urease as the enzyme what is the controll variables?
concentration of enzyme solution
volume of enzyme and substrate solutions
temperature (use of thermostatically controlled water-bath at a specified temperature within the range 30-40 degrees)
time for reaction, e.g. 20 minutes
stirring/shaking of reactants
wavelength of light/filter in the colorimeter.
154
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; Give an example of the concentrations of urea you my use.
0.10, 0.19, 0.18, 0.17, 0.06, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.00
(for 0.06 use 0.06 cm3 of urea and 0.04 cm3 of water)
155
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; what concentration of urease should be used?
Use a 0.05% solution of urease, which has to be kept in the water bath at a specified temperature withn the range 30-40 degrees.
156
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction;
To begin the procedure you must label 11 test tubes with your initials and the numbers 1 - 10, what should yo add to the test tubes?
Place 5 cm3 of urea solution of differing concentrations into the test tubes.
add 1 cm3 of phenol red to each tube.
Place these tubes in the water bath for 10 minutes.
157
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; What are the next two steps after placing the tubes inn a water bath for 10 minutes?
Add 1cm3 of urase solution to each of your 11 tubes, in the water-bath. Shake each tube.
leave the tubes for 20 minutes.
158
The effect of increasing substrate concentration on the rate of an enzyme-catalysed reaction; What are the next two steps after placing the tubes inn a water bath for 10 minutes?
Just before the 20 minutes is up, fill a corvette with solution from tube 0. Use this for calibration and set the absorbance at 0, using a blue or green filter in the colorimeter.
After 20 minutes, read the absorbance of the contents of each tube, 1-10. Make sure that you give each one a final shake before filling the curvette.
(I haven't included all the information from this investigation on page 114)
159
Give an interesting example of where the protease enzyme can be used in the production of something.
Tanning animal skins to make leather is an ancient craft. After the were soaked urine and water, scraped to remove fat and treated with lime to remove the hairs, they were placed in a vat of water and dung to make them softer. Children were often employed to gather dog and pigeon dung from the streets. We now know that there are protease enzymes in the dung that partially digest the collagen protien in hides and make them soft and supple. This process is called bating. the hides were de-limed before dung was added, to make the pH less alkaline.
160
How should you indicate the amount of substances in a solution?
We refer to concentration of substances in solution, not just 'the amount'. Concentration indicates how many moles are present in a unit volume. Hence it will affect the rate of reaction.
161
In living cells what does the enzyme availability depend on?
In living cells, the enzyme concentration or availability depends on the rate of synthesis of the enzyme and its rate of degradation.
162
What is enzyme synthesis?
Depending on the cell's needs, genes for synthesising particular enzymes can be switched on or off.
163
What is enzyme degradation?
The protien component of living cells is constantly being turned over. Cells are continuously degrading old enzyme molecules to their component amino acids and synthesising new enzyme molecules from amino acids.
164
What are the advantages of enzyme degradation?
The elimination of abnormally shaped proteins that might otherwise accumulate and harm the cell.
The regulation of metabolism in the cell by eliminating any superfluous (surplus to requirement) enzymes.
165
To regulate the cells metabolism properly how does the importance of enzyme degradation compare to enzyme synthesis.
They are equally important.
166
Name one of the longest lived proteins in humans.
One of the longest-lived proteins in humans is haemoglobin, found inside erythrocytes. Each haemoglobin molecule lasts for about 120 days.
167
As enzyme concentration increases what happens in an enzyme controlled reaction?
More active sites on the enzyme become available.
More successful collisions between the enzyme and substrate occur.
More enzyme substrate (ES) complexes can form per unit of time, so the rate of reaction increases.
Enzyme concentration becomes the limiting factor - as it increases, so does the rate of reaction.
168
When will an enzyme controlled reaction reach its maximum rate for a fixed substrate concentration.
If substrate concentration is fixed or limited and all the substrate molecules are occupying an active site, or have occupied an active site an been released as product molecules.
169
What will happen if the enzyme concentration is increased is increased past the maximum rate?
The there will be no increase in the rate of reaction because the active sites of the extra enzyme molecules will not be occupied by substrate molecules.
The enzyme concentration is no longer the limiting factor; as enzyme concentration increases, the rate of reaction does not increase.
Substrate concentration is ow the limiting factor. Lack of substrate molecules is preventing the rate of reaction from increasing.
170
What do you describe when studying a graph?
Describe what is happening in each region and explain why these changes are occurring. Refer to both axes and quote data figures if you can.
there is a graph on page 115 which I have not included.
171
What is the initial rate of reaction?
In any reaction, the initial rate of reaction between the reactants is fastest. The same is true of an enzyme catalysed reaction.
172
Describe the rate of reaction at the beginning of a reaction.
When the enzyme and substrate molecules are first mixed and are then moving randomly, there is a great chance of a substrate molecule successfully colliding with an enzymes active site.
173
Describe the rate of reaction as the reaction proceeds from the beginning rate.
As the reaction proceeds, substrate molecules are used up as they are converted to product molecules, so the concentration of the substrate drops.
174
What is a result of a reaction proceeding that affects the rate of reaction?
The frequency of successful collisions between enzyme and substrate molecules decreases because some enzymes may collide with product molecules, and so the rate of reaction slows down.
175
What stage of the reaction gives the maximum reaction rate for an enzyme under a particular experimental situation.
The initial rate.
176
How is the initial rate of reaction calculated from a graph?
The initial rate of reaction is calculated by drawing a tangent to the steepest part of each curve. The gradient of the tangent gives a reading of the initial reaction rate in whatever unit is used.
(Apparatus for the investigation of hydrogen peroxide and an example of finding the rate of reaction on page 116)
177
How would you carry out an investigation on the effect of enzyme concentration on an enzyme catalysed reaction?
Instead of changing the substrate (urea) concentration, affecting the activity (rate of reaction) of the enzyme urease, change the enzyme (urease) concentration as this will affect the rate of the same reaction - the breakdown of urea catalysed by urease.
(a full investigation check-list is on page 16)
178
What is competitive inhibition?
Inhibition of an enzyme, where the inhibitor molecule has a similar shape to that of the substrate molecule and competes with he substrate for the enzymes active site. It blocks the active site and prevents formation of enzyme-substrate (ES) complexes.
179
What is a inhibitor?
A substance that reduces or stops a reaction.
180
What is a non-competitive inhibitor?
Inhibition of an enzyme, where the competitor molecule attaches to a part of the enzymes molecule but not the active site. his changes the shape of the active site, which prevents ES complexes forming, as the enzyme active site is no longer complimentary in shape to the substrate molecule.
181
What are inhibitors.
Inhibitors are substances that reduce the activity of an enzyme. They do this by combining with the enzyme molecule in a way that influences how the substrate binds to the enzyme or affects the enzymes turnover number. Some may block the active site and some change he shape of the active site. Both of these actions will inhibit the formation of ES complexes and therefore of product formation.
182
How do inhibitors work?
They combine with the enzyme molecule in a way that influences how the substrate binds to the enzyme or affects the enzymes turnover number. Some may block the active site and some change he shape of the active site. Both of these actions will inhibit the formation of ES complexes and therefore of product formation.
183
What are competitive inhibitors?
Substances whose molecules have a similar shape to an enzymes substrate molecules.
184
How do competitive inhibitors work?
The competitive inhibitor fits into the active site and so a substrate molecule cannot enter.
185
What does the amount of inhibition form a competitive inhibitor depend on?
The amount of inhibition depends on the relative concentration of substrate and inhibitor molecules. More inhibitor molecules means more inhibitors collide with active sites and so the effect of inhibition is greater.
186
What does increasing the substrate concentration do to a competitive inhibitor?
Increasing substrate concentration effectively 'dilutes' the effect of the inhibitor. if enough substrate is added, the inhibitor is unlikely to collide with the enzyme.
187
On a graph how would the rate of reaction compare with and without a competitive inhibitor as the substrate concentration increases.
Without a inhibitor the rate of reaction increases with a steeper gradient and reaches the maximum rate quicker than with a inhibitor. With an inhibitor the rate of reaction increases with a shallow gradient but still reaches the same maximum rate when the substrate concentration is high enough. (graph on page 117)
188
Why does increasing the amount of substrate reduce the effect of a competitive inhibitor.
They compete directly with substrate molecules for a position on the enzymes active site, forming an enzyme-inhibitor complex that is catalytically inactive.
189
How is the competitive inhibitor affected by the enzyme.
Once on the active site, the inhibitor is not changed by the enzyme, as the normal substrate would be.
190
The presence of the inhibitor prevents the substrate molecule form joining the active site. What does this reduce?
This reduces the rate of formation of ES complexes and of product molecule formation. A competitive inhibitor reduces the number of free enzyme active sites available for the substrate molecules to bind to and form ES complexes.
191
Are competitive inhibitors permanent why?
Most enzyme inhibition by competitive inhibitors is reversible. As collisions between enzyme and substrate or inhibitor molecules are random, increasing the concentration of the substrate would reduce the effect of reversibly competitive inhibition, as there would be more chance of an enzyme molecule colliding with a substrate molecule than with an inhibitor molecule.
192
What is a competitive that binds permanently called?
If the competitive inhibitor binds irreversibly to the enzymes's active site it is called an inactivator.
193
What type of molecule is called an non-competitive inhibition?
If the inhibitor, molecule binds to the enzyme somewhere other than at the active site it is called non-competitive inhibition.
194
How do competitive inhibitors bind to the enzyme?
Non-competitive inhibitor do not compete with substrate molecules for a place on the active site. They attach to the enzyme molecule in a region (known as an allosteric site) away from the active site and, in so doing, they disrupt the enzymes tertiary structure and change its shape.
195
What stops ES complexes forming with non-competitive inhibitors?
This distortion changes the shape of the active site so that it is no longer complimentary to the shape of the substrate molecule, and the substrate molecule can no longer bind to the enzymes active site. ES complexes cannot form.
196
With a non-competitive inhibitor can an enzyme reach its maximum rate of reaction?
The maximum rate of reaction is reduced by the presence of non-competitive inhibitors. Adding more substrate might allow the reaction to attain this new, lower rate, but even very high concentrations of substrate will not allow the rate of reaction to return to its uninhibited maximum.
(there is a diagram for how non-competitive inhibitors work and the rate of an enzyme-catalysed reaction with and without a non-competitive inhibitor on page 118)
197
With non-competitive inhibitors what increases the inhibition?
The more inhibitor molecules are present, the greater the degree of inhibition, because more enzyme molecules are distorted and either cannot form ES complexes or cannot complete the catalytic reaction involving ES complexes.
198
Are non-competitive inhibitors permanent?
Some non-competitive inhibitors bind irreversibly to the allosteric site. Other non-competitive inhibitors bind irreversibly to the allosteric site.
199
What is end product inhibition?
One way in which enzyme-catalysed reactions may be regulated is by end product inhibition. After the catalysed reaction has reached has reached completion, product molecules may stay tightly bound to the enzyme. In this way, the enzyme cannot form more of the product than the cell needs. Such regulation is an example of negative feedback.
200
How do enzymes that are produced in an inactive precursor form work?
Some enzymes are synthesised and produced in an inactive precursor form. Before they can carry out their function some of their amino acids have to be removed so that their active sites assume th correct shape or are exposed.
201
Why would enzymes be produced in an inactive precursor form?
Many digestive enzymes are produced in this way so that while in cells they do not digest any of the cells molecules.
202
Give two examples of enzyme's produced in an inactive precursor form.
The proteolytic enzyme, trypsin, is produced in the small intestine in the inactive form trypsinogen and, after a portion of its molecule is removed by another enzyme, it becomes active as trypsin.
The proteolytic enzyme pepsin is secreted as inactive pepsinogen and this is converted to active pepsin, by the action of hydrochloric acid, in the stomach.
203
What happens to the product of an enzyme-catalysed reaction in a metabolic sequence?
Many metabolic processes, such as photosynthesis and respiration, involve a series of enzyme-catalysed reactions.
The product of one enzyme-catalysed reaction becomes the substrate for the next enzyme-catalysed reaction in the metabolic pathway.
204
In a metabolic sequence how may cells stop the accumulation of too much product molecule?
Cells do not need to accumulate too much of the end product, so the product of the last enzyme-catalysed in the metabolic pathway may attach to a part of the first enzyme in the pathway, but not at its active site.
This binding changes the shape of enzyme 1s active site, preventing the pathway from running.
205
How may a metabolic sequence stopped by negative feedback start again?
When the product molecule attaches to the first enzyme the process is non-competitive inhibition but it is reversible.
When the concentration of this product within the cell falls, those molecules will detach from enzyme 1 and allow its active site to resume its normal shape: the metabolic pathway can run again.
206
If you were describing a metabolic pathway with different enzymes being represented by increasing numbers and the products being represented by increasing letters how would you describe the process?
The substrate A is converted into product B by the action of the first enzyme (enzyme 1). Product B is the substrate for enzyme 2, converted to product C, and so on.
The end product can bind to enzyme 1, and acts as a non-competitive inhibitor. This means that the end product will not build up in the cell because the product is made so it slows the formation of itself by inhibiting the first enzyme in the sequence.
207
Name two benefits of metabolic reactions?
Multi-enzyme complexes increase the efficiency of metabolic reactions without increasing substrate molecules in the same vicinity and reduce diffusion time.
Many metabolic reactions are carried out in particular regions or organelles in cells, and this also increases the efficiency of metabolism. Some of the enzymes within organelles are bound to the organelle membranes.
208
Give an example of how many enzyme-catalysed metabolic pathways are driven in one direction by being coupled to hydrolysis of ATP?
DNA helicase is one such enzyme, and will only move in one direction along a molecule of DNA, causing the DNA to unwind.
209
On a graph how do you know if a enzyme inhibitor is a non-competitive inhibitor?
If the rate of enzyme controlled reaction stays low, even if the substrate concentration is increased, then it is non-competitive inhibition.
210
On a graph how do you know if a enzyme inhibitor is a competitive inhibitor?
If the rate of the enzyme-controlled reaction increases when the substrate concentration is increased, then it is competitive inhibition.
211
How do metabolic poisons act as enzyme inhibitors?
Many toxins (poisons) exert their effect because they inhibit or inactivate enzymes.
212
What metabolic poison inhibits aerobic respiration?
Potassium cyanide (KCN) is highly toxic because because it inhibits aerobic respiration.
213
How does potassium cyanide inhibit aerobic respiration?
When ingested, KCN is hydrolysed to produce hydrogen cyanide, a very toxic gas that can readily dissociate into H+ and CN- ions.
The CN- ions binds irreversibly to an enzyme found in mitochondria and inhibit the final stage of aerobic respiration. Because the final stage is inhibited, earlier stage cannot run and aerobic respiration stops.
214
Where has a metabolic poison been used?
During the second world war British secret agents were issued with cyanide pills so thy could commit suicide and avoid torture if captured.
In 1954, the mathematician, computer scientist and Enigma code-breaker Alan Turing died after eating an apple poisoned with cyanide.
215
Who survived a cyanide poisoning?
The monk Grigori Rasputin, who seemed to exert quite an influence over the Tsarina Alexandra, grand-daughter of Queen Victoria and wife of Tsar Nichols II of Russia, was given cyanide but survived. This may be because his stomach acid was unusually low, reducing the formation of hydrogen cyanide from potassium cyanide.
216
How do you know if yo ingest the metabolic poison cyanide?
To many people, potassium cyanide tastes of bitter almonds, but some people, due to a genetic mutation, cannot taste it.
217
What enzyme does venom from the green mamba snake inhibit?
The enzyme acetylcholinesterase. (AChE)
218
Why is the enzyme acetylcholinesterase, (AChE) important?
(inhibited by green mamba snake venom) The enzyme is important at neuromuscular synapses (gaps between neurones and muscles) to break down the neurotransmitter, acetylcholine. (ACh)
219
What happens if the enzyme acetylcholinesterase, (AChE) is inhibited?
If this enzyme is inhibited (by green mamba snake venom) The neurotransmitter ACh stays attached to receptors on the muscle membrane and keeps the muscle contracted.
This causes paralysis, as movement depends on muscles being able to contract and relax alternatively. If the muscles involved in breathing are paralysed, then victims die from suffocation.
220
Describe the green mamba snake.
Dendroapsis angusticeps, is a solitary, tree dwelling snake from East Africa. Its venom is highly toxic and can be fatal to humans.
221
What enzymes may snake venom contain?
Snake venom may also contain hydrolytic enzymes, such as hyaluronidase, to break down the connective tissues of the prey and allow the toxin to spread more rapidly through the body.
222
State a medicinal drug that acts by enzyme inhibition.
Aspirin has been used for over 3000 years, and marketed as aspirin since the late 19th century.
223
How was Aspirin discovered?
In 1971, Professor John Vane and his team discovered that salicylic acid binds to enzymes that catalyse the formation of prostaglandins. Thus it prevents the formation of prostaglandins that are cell-signalling molecules produced by cells when tissues are infected or damaged. prostaglandins make nerve cells more sensitive to pain and increase swelling during inflammation.
224
What affects does Aspirin have apart from decreasing swelling and pain?
Aspirin can also reduce the risk of blood clots forming in blood vessels, and many people take a low dose to reduce the risk of strokes. However children under the age of 12 should not take it, as aspirin can damage the stomach lining.
225
Give an example of an ATPase inhibitor.
Extracts from purple foxglove leaves have been used for centuries to treat heart failure and atrial arrhythmia (abnormal beat rate of the atria).
226
What are chemicals that are present in the purple foxglove leaves (ATPase inhibitior)?
The chemicals are now identified as cardiac glycosides, also known as digitalis, digitoxin or digoxin.
227
What do the chemicals in purple foxglove leaves inhibit?
They inhibit the sodium potassium pump in the cell membrane of heart-muscle cells, and allow more calcium ions to enter the cells. Calcium ions increase muscle contraction, and this strengthens the heartbeat.
228
What are ACE inhibitors?
These are medical drugs that inibit the angiotensin converting enzyme (ACE), which normally operates in a metabolic pathway that ultimately increases your blood pressure.
229
What are ACE inibitors used for?
To lower blood pressure in patients with hypertension who cannot take beta-blockers.
To treat heart failure - a low dose is given first, and the patients blood pressure is checked incase it falls too low.
To minimise risk of a second heart attack or a stroke in patients who sufferd a myocardial infarction.
230
Give two examples of protease inihbitors.
Protease inibitors such as amprenavir and ritonavir are used to treat some viral infections.
231
What do protease inhibitors inhibit?
They prevent the replication of the virus particles within the host cells, by inhibiting protease enzymes so that the viral coats cannot be made. These inibitors often inhibit viral protease enzymes by competitive inhibition.
232
What is the use of nucleoside reverse transcriptase inhibitors?
Many of the antiviral drugs, such as zidovudine and abacavir, used to treat patients who are HIV-positive are nucleodside reverse transcriptase inhibitors. They inhibit enzymes involved in making DNA using the viral RNA as a template.
233
There is a difference between venom and poison, what is venom?
Venom is intoduced into the victims body by injection - e.g. by a snake's fangs during a bite. An adder is another venomous snake.
234
There is a difference between venom and poiso, what is poison?
Poisons are toxins that are ingested. The fungus Amantia phalloides, the death cap, is poisonous or toxic. The toxin in a puffer fish that has not been properly prepared (to make the Japenese dish fugu) is a poison.
