2.4-Enzymes

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  • Created by: McTighe
  • Created on: 01-02-18 18:07
Why are enzymes Biological catalysts?
Because they speed up chemical reactions, and remain unchanged, so can be used again
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What is a metabolic reaction?
A reaction that takes place inside living cells or organisms
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What is the turnover number?
The number of reactions an enzyme can catalyse per second
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If enzymes are not present, how can a reaction be sped up?
By energy, usually heat energy
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What type of protein are enzymes?
Globular proteins
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Why are enzymes specific?
They can only catalyse one type of reaction as the tertiary structure makes the active site a specific shape.
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Why is the active site specific?
It has a specific shape which is complementary in shape to one kind of substrate molecule
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Why type of enzyme can usually be complementary in shape to more than one type of substrate molecule?
Digestive enzymes
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How are enzymes different to chemical cataylsts?
They do not produce unwanted by-products
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If the genes, encoded for making the enzyme, has a mutation what happens?
It will affect the order of amino acids made, so will affect the tertiary structure and therefore the active site.
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What happens if an enzyme catalyses a deficient metabolic reaction?
A metabolic disorder occurs
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What is the active site?
An indentation of the enzyme, 6-10 amino acids long
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Name two ways the shape of the enzyme can be altered?
pH, temperature
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Name the two types of enzymes
Extracellular and Intracellular
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What happens in catabolic reactions?
Metabolites are broken down into smaller pieces (energy released)
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What happens in anabolic reactions?
Metabolites are synthesised into large molecules from smaller one (energy taken in)
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Give two examples of complex metabolic pathways
Respiration and Photosynthesis
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Give an example of an intracellular enzyme
Catalase
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What is catalase used for?
To protect cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide to water and oxygen
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What conditions do catalase work in?
pH 7 45*C
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Describe the quartnerary structure of catalase
4 polypeptides with a haem group
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How do Fungi use extracellular enzyme?
They release hydrolytic enzymes from thread-like hyphae which digest carbohdrates, lipids, proteins in bread. Products are absorbed into fungi hyphae for respiration and growth
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Give an example of an extracellular enzyme
Amylase
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Where is amylase produced and used
Produced in salivary glands and act in mouth to digest starch into maltose. Can also be made in pancreas, to catalyse reaction in small intestine
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Give another example of an extracellular enzyme
Trypsin
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Where is Trypsin made and acts?
Made in Pancreas and acts in lumen of small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds
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What is a cofactor
Any substance that must be present to ensure an enzyme-catalysed reaction takes place at an appropriate rate and allows function to take place
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Name the two groups of cofactors
Organic and Inorganic
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What are prosthetic groups?
Inorganic cofactors, permanently bound to enzyme
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Give an example of an enzyme that needs a prosthetic group
Enzyme carbonic anhydrase which has a zinc ion as a prosthetic group
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What is the function of carbonic anhydrase
Vital in red blood cells as it cataylses conversion of carbon dioxide and water into carbonic acid. Allows CO2 to be carried in blood
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What are co-substrates?
Non-organic co factors which bind to substrates which form the correct shape to bind to the active site of the enzyme
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Why do some cofactors change charge distribution on a substrate or enzyme surface?
To make temporary bonds in an enzyme-substrate complex so its easier to form
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Give an example of another cofactor
amylase catalyses breakdown of starch to maltose with a chloride ion present
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What is a coenzyme?
A non-protein organic cofactor that interacts with an enzyme and allows it to work
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How is a coenzyme different to the substrate?
It recycles back to its original state by a different enzyme
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What is a main function of coenzymes?
They carry chemical groups between enzymes so that enzyme-controlled reactions can occur in sequence
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Give an example of a Vitamin used as a coenzyme?
Vitamin B3
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What is the function of Vitamin B3?
Used to breakdown fats and carbohydrates to release energy. It is used to make the coenzyme pyruvate dehydrogenase to function properly
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What happens if there is a lack of Vitamin B3?
Pellagra disease forms
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What is the name of the simple model that shows how enzymes work?
The lock and Key model
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What does the lock and key model show?
How large molecules are split into smaller molecules, or smaller molecules join to form a large molecule. It shows the active site is complementary in shape to the substrate
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Describe the process of an anabolic reaction in the lock and key model
1.Substrate molecules bind to active site 2.Temporary hydrogen bonds hold the substrate and enzyme together to form an enzyme-substrate complex 3.Enzymes catalyse condensation reaction, causing products to join to form an enzyme-product complex.
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What happens after the enzyme-product complex is formed?
It leaves the active site
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Describe the process of a catabolic reaction in the lock and key model
1.Substrate molecule bind to active site 2.Temporary hydrogen bonds hold substrates and enzyme together to form enzyme-substrate complex 3.Enzyme catalyses hydrolysis reaction, causing product to split, forming enzyme-product complex.
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What is the more recent hypothesis?
Induced-fit hypothesis
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What does this hypothesis state?
That active sites are not exactly complementary but change shape in the presence of a specific substrate to become more complementary
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How does this work?
When a substrate fits into the enzyme's active site, the active site changes shape slightly to mold itself around the substate molecules. The R-groups give a more precise conformation to exactly fit the substrate molecules
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Which forces allow the substrate molecule to bind to the active site?
Hydrogen, Ionic, London dispersion etc
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Why do products detach from the active site?
As the products have a different shape to the substrates
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What is the energy called needed to kickstart a reaction?
The activation energy
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What do enzymes do to the activation energy of a reaction?
Lowers it by providing an alternative pathway. They bring the substrate molecules closer together, so are less likely to react without heat.
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What happens to the reactants when the temperature increases?
Molecules have more kinetic energy so they move around faster, increasing number of collisions between molecules, so more enzyme-substrate complexes form This causes the rate of reactions to increase
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What is the optimum?
Where the rate of reaction is at its maximum
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What happens if the temperature increases above the optimum?
Vibrational energy increases to molecules vibrate putting strain on bonds in tertiary structure. The weaker bonds break causing it to denature. The enzyme is less complementary so fewer enzyme-substrate complexes so a lower rate of reaction.
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What happends if the temperature is lower than the optimum temperature?
Enzymes and substrate molecules have less kinetic energy so move around slower. Causes a reduced chance of collisions between enzymes and substrate so less enzyme-substrate complexes, so reduced rate of reaction
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Does a lower temperature affect the shape of the active site?
NO
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Name the bacteria which has an low optimum temperature
Psychrophilic bacteria
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Name the bacteria that has a high optimum temperature
Thermophilic bacteria
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What is the temperature coefficent Q10
Increases the rate of a process when the temperature increases by 10*C
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How do you work out Q10?
Rate of reaction at (T + 10*C)/Rate of reaction at T*C
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What is pH the measure of?
Acidity and basicity of a solution
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What is a buffer?
Certain chemicals which donate/accept hydrogen ions to resist changes in pH. (e.g. some proteins or chemicals in blood)
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How does an acidic pH affect the shape of an enzyme?
H+ ion attracted to negative R groups. It interferes with weak bonds that hold active site shape, causing it to change shape. It also alters charges in active site. This interefers with binding as it does not fit in shape, so less enzyme-complexes
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How does an alkaline pH affect the shape of an enzyme?
OH- ions attracted to positive R groups. Interferes with weak bond causing active site to change. It alters charges as well. Causes the substrate molecule to be unable to bind so less enzyme-substrate complexes
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What happens if the pH changes slightly?
Causes a lower rate of reaction as active site is disrupted temporarily. If pH is restored, hydrogen bonds can reform so active site shape is restored
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What happens if pH changes dramatically?
pH causes active site to be permanently damaged, it is denatured and loses function
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What is the pH of Amylase?
pH 7
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What is the function of Amylase?
Digests starch into Maltose
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What is the pH of Pepsin?
pH 2
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What is Pepsin used for?
When food passes to stomach, hydrochloric acid is secreted. Kills bacteria in food and digests large protein molecules into smaller peptide molecules
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What is the pH of Trypsin?
pH 8
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What is Trypsin used for?
Digested food moves into small intestine, salts made in liver neutralises it. Enzymes catalyse further digestion of peptides into amino acids
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When will the substrate concentration affect the rate of reaction?
When it is a limiting factor. As the substrate concentration increases, the rate of reaction will increase
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What happens when the substrate concentration increases?
The rate of reaction increases as more substrate molecules will collide with enzyme molecules, so more enzyme-substrate complexes are formed. This means more enzyme-product complexes are formed.
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When will the reaction meet a maximum rate of reaction?
When the enzyme molecules become saturated. This means no more enzyme-sustrate complexes can form, so products are being produced at the same rate
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What two factors does enzyme concentration depend on?
-Synthesis of the enzyme and its degradation
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What is the advantage of these two factors?
-Elimination of abnormally shaped proteins -Regulation of metabolism in a cell by eliminating superfluous enzymes
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What happens when the enzyme concentration increases?
More active sites are available so more enzyme-substrate complexes are formed per unit of time, so an increases rate of reaction
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What is an Inhibitor?
A substance that reduces or stops a reaction
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Are competitive inhibitors temporary or permanent?
Temporary
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How do competitive inhibitors affect enzymes?
They have a similar shape as active site, so bind to active site to prevent the substrate from binding.
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How does adding more substrate molecules reduce the affect of competitive inhibitors?
It 'dilutes' the effect as there is a greater chance a substrate and enzyme will collide, rather than an inhibitor. This means the maximum rate of reaction is eventually reaches
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What is the complex called when the inhibitor binds to the enzyme?
An enzyme-inhibitor complex
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Are competitive inhibitors reversible or irreversible?
Reversible
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What is a competitive inhibitor which is irreverisble called?
An inactivator
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What is a non-competitive inhibitor?
An molecule which binds to the enzyme anywhere but the active site
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Are non-competitive inhibitors temporary or permanent?
Permanent
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What is the region called where the inhbitor will bind to?
The allosteric site
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How does this prevent enzyme-substrate complexes being formed?
By distrupting the tertiary structure, causing the active site to change shape, so no longer complementary
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Will adding high substrate concentrations increase the rate of reaction?
no because the enzymes are distorted, so cannot produce enzyme-substrate complexes
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Once a metabolic reaction finishes, what happens to the product of the last enzyme-catalysed reaction?
It can bind to the first enzyme (Allosteric site) to prevent any more of those reactions occuring
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How do multi-enzyme complexes increase the efficency of metabolic reactions without increasing the substrate concentration?
They keep the enzyme and substrate molecules in the same vicinity and reduce diffusion time.
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Give an example of a metabolic poison
Cyanide/ Snake Venom
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Why is Potassium Cyanide a metabolic poison?
It is toxic as it inhibits aerobic respiration and catalase
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What happens when Potassium Cyanide is digested?
It is hydrolysed to produce hydrogen cyanide (A toxic gas)
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What do CN- ions do in aerobic resipation?
Bind irreversiliby to an enzyme found in mitochondria and inhibits the final stage of aerobic respiration
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Give a example of snake venom
Venom of Green mamba
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Why is Venom from the green mamba toxic?
It contains a chemical that inhibits the enzyme acetylchlolinesterase. This is important at neuromuscular synaspses to break down the neurotransmitter
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Why is this bad?
It the enzyme is inhibited, ACH stays attached to receptors and muscles stay contracted. This causes paralysis, and victims die of suffocation
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Where are ATPase inhibitors found?
Extracts from purple foxglove leaves
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What are ATPase inhibitors used for?
To treat heart failure and atrial arrthmia
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How do ATPase inhibitors work?
They inhibit sodium-potassium pump in cell membranes of heart-muscle cells and allow more calcium ions to enter the cells. Calcium ions increase muscle contractions and this strengthens the heartbeat
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How do ACE inhibitors work?
Medical drugs that inhibit the angiotensin converting enzyme (ACE) which normally operates a metabolic pathway that increase blood pressure. Used to lower blood pressure
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What are ACE inhibitors used for?
To treat heart failure and to minimise the risk of a second heart attack or stroke in patients who have suffered a myocardial infarction
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How do protease inhibitors work?
They prevent the replication of the virus particles within host cells, by inhibiting protease enzymes so that the viral coats cannont be made. These inhibitors often inhibit viral protease enzymes by competitive inhibition
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What are Protease inhibitors used for?
Treat viral infections
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How do Nucleoside reverse transcriptase inhibitors work?
They inhibit enzymes involved in making DNA using the viral RNA as a template
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What are Nucleoside reverse transcriptase inhibitors used for?
Treat patients who are HIV-positive
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Card 2

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What is a metabolic reaction?

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A reaction that takes place inside living cells or organisms

Card 3

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What is the turnover number?

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Card 4

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If enzymes are not present, how can a reaction be sped up?

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Card 5

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What type of protein are enzymes?

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