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Biology > 2:1:4 Enzymes > Flashcards

2:1:4 Enzymes Flashcards

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1
Q

What are enzymes

A

Biological catalysts (speed up the rate of chemical reactions without being used up)

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2
Q

What is the structure of enzymes

A

Globular proteins with complex tertiary structures, or sometimes quaternary structures, produced via protein synthesis

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3
Q

Why are enzymes important

A

Control metabolic pathways, where almost every metabolic reaction is catalysed by an enzyme, so they are essential for life

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4
Q

What is an intracellular enzyme

A

An enzyme that is produced and function (is active) inside the cell

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5
Q

What is an extracellular enzyme

A

An enzyme that is secreted by cells and function (is active) outside the cell

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6
Q

What is an example of an intracellular enzyme and its function

A
  • Catalase
  • Hydrogen peroxide produced as a byproduct of metabolic reactions and is harmful to cells
  • Catalase converts hydrogen peroxide into water and oxygen to prevent harm to cells
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7
Q

What is an example of an extracellular enzyme

A
  • Amylase
  • Secreted by the salivary glands and pancreas
  • Digestion carried out by extracellular enzymes as macromolecules digested need to be broken down to enter the cell
  • Amylase hydrolyses starch into maltose
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8
Q

What is trypsin

A

An extracellular digestive enzyme that is secreted by the pancreas, which breaks proteins into peptides and amino acids

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9
Q

How do fungi feed

A

Through extracellular digestion, where hyphae of fungi secrete enzymes directly onto their food so that it can be broken down and be absorbed through the hyphae walls

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10
Q

What is an active site

A

The specifically shaped site on an enzyme where specific substrates bind forming an enzyme-substrate complex

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11
Q

What is denaturation

A

When extreme heat or pH changes the shape of the active site, which prevents the substrate from binding and denatures the enzyme

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12
Q

What is the enzyme substrate complex and how is it formed

A
  • Formed when the substrate collides with the enzyme at the correct orientation and speed
  • Formed temporarily before enzyme catalyses the reaction and products are released
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13
Q

What is enzyme specificity

A

The complementary nature between the shape of the active site (determined by the complex tertiary structure of the protein) and its substrate

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14
Q

What is the lock and key hypothesis

A

Emil Fischer’s (1890’s) first model of enzyme activity suggested that both enzymes and substrates were rigid structures that locked into each other precisely

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15
Q

What is the induced fit hypothesis

A

The modified understanding of lock and key enzyme activity, where the enzyme and substrate interact so the enzymes active site can change shape slightly as the substrate enters the enzyme (conformational change) which ensures ideal binding arrangement, maximising the ability of the enzyme to catalyse the reaction

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16
Q

What is activation energy

A

The amount of energy needed by the substrate to become just unstable enough for a reaction to occur and its products to be formed

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17
Q

How do enzymes speed up chemical reactions

A

Reducing the stability of bonds in the reactants (substrate) making it more reactive

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18
Q

How do enzymes speed up a reaction

A

They provide an alternative energy pathway with a lower activation energy, so that high temperatures and pressures (which would kill cells) aren’t needed for the reactants to gain the required energy

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19
Q

How is enzyme activity affected by pH

A
  • Enzymes have an optimum pH
  • In extreme pH’s (excess H+ or OH-) the hydrogen and ionic bonds in the tertiary structure of the protein are broken
  • The active site shape is changed causing the enzyme substrate complex to stop forming
  • The enzyme denatures
20
Q

Describe the process to test the effect of pH on enzymes

A
  • Place single drops of iodine solution on a spotting tile
  • Add 2cm^3 of amylase (enzyme) to a test tube with the pH to be tested
  • Add 1cm^3 buffer solution to the test tube
  • Add 2cm^3 of starch solution to the test tube and start a stopwatch and mix
  • In 10 second increments add a drop of the solution to the iodine spots
  • Iodine solution is orange/brown, but turns blue/black in starch, which is broken down by amylase, so when the iodine solution remains orange/brown, all the starch has been broken down
  • Serial dilution and colorimeter can be used to test amount of amylase present
21
Q

How is enzyme activity effected by low temperature

A
  • Enzymes have specific optimum temperatures
  • Low temperatures slow down reactions as molecules move slowly due to less kinetic energy
  • There are less frequent and successful collisions between the substrate and enzyme, so less substrate enzyme complexes form
  • Also substrates and enzymes collide with less energy, so it’s less likely for bonds in the substrate to be broke/formed
22
Q

How is enzyme activity effected by high temperatures

A
  • Enzymes have optimum temperatures
  • High temperatures cause enzymes to speed up as molecules move more quickly due to more kinetic energy
  • There are a higher frequency of successful collisions between the substrate and enzyme so the enzyme substrate complex forms more
  • Also substrates and enzymes collide with more energy, so it’s more likely for bonds in the substrate to be formed/broken
23
Q

How does temperature denature enzymes

A
  • If temperatures increase past a certain point, enzyme molecules have too much kinetic energy and vibration, putting a strain on them causing the hydrogen and ionic bonds to break
  • This causes the tertiary structure to change
  • The active site becomes permanently damaged and is no longer complementary to the substrate so the enzyme substrate complex can’t form
  • The enzyme denatures
24
Q

What are anabolic reactions

A

Chemical reactions required for growth, catalysed by enzymes

25
Q

What are catabolic reactions

A

Chemical reactions that break down molecules to release energy, catalysed by enzymes

26
Q

Graph to show the effect of pH on enzyme activity

A
27
Q

Graph to show the effect of temperature on enzyme activity

A
28
Q

How is the optimum/denaturation temperature of an enzyme decided

A
  • Varies due to the habitat in which an organism has adapted
  • Most enzymes in organisms denature at 60 degrees
  • Few human enzymes function above 50 degrees
  • Thermostable enzymes can withstand high temperatures
29
Q

What is the temperature coefficient

A

The ratio between the rates of a biological reaction at two different temperatures: Q= (rate of reaction of x) / (rate of reaction of x + 10 degrees)
Q10=2

30
Q

How does enzyme concentration affect enzyme activity

A
  • The higher the concentration, the greater the number of active sites, the more likely for enzyme substrate complex to form
  • With sufficient substrate availability the rate of reaction increases linearly
  • Rate of reaction will plateau eventually due to lack of substrate (limiting factor)
31
Q

How does substrate concentration effect enzyme activity

A
  • The higher the substrate concentration, the higher the rate of reaction
  • More substrates mean it’s more likely for enzyme substrate complexes to form, and if there is a sufficient amount of enzymes, the rate of reaction with increases linearly
  • The rate of reaction eventually plateaued as the active sites become saturated and the substrates have nowhere to bind and form the enzyme substrate complex
32
Q

What are reversible inhibitors

A

Inhibitors that can temporarily reduce or stop an enzymes activity

33
Q

What are competitive inhibitors

A

Inhibitors with similar shapes to the substrate molecules, so compete with the substrate for the active site

34
Q

What are non-competitive inhibitors

A

Inhibitors that bind to the enzyme at an alternative site, which alters the shape of the active site and prevents the substrate from binding to it

35
Q

How to increase the rate of reaction with inhibitors

A
  • Increasing the substrate concentration can increase the rate of reaction with competitive inhibitors by countering the increase in inhibitor concentration
  • As non-competitive inhibitors change the active site, increasing the substrate concentration doesn’t increase the rate of reaction
36
Q

What are irreversible inhibitors

A

Inhibitors that form covalent bonds with enzymes and inhibit them permanently, resulting in the complete inactivation of the enzyme (metabolic poisons)

37
Q

Why are some irreversible inhibitors dangerous and how can they be avoided

A
  • They can cause the biological reaction the enzyme is catalysing to completely stop
  • E.g. Cyanide stops a metabolic reaction by acting as an irreversible inhibitor to cytochrome oxidase, an enzyme that is key in reactions of aerobic respiration
  • Can be avoided by the organism producing more of the enzyme being inhibited by protein synthesis
38
Q

What is an example of a beneficial irreversible inhibitor

A

Penicillin is an irreversible inhibitor of the enzymes that form the cross links in bacterial cell walls, but has a medical benefit as it results in the destruction of bacteria by breaking down the cell walls

39
Q

What is end product inhibition

A
  • Where an enzyme converts the substrate into a product, which then binds to an alternative site on the enzyme, changing its active site and preventing the enzyme substrate complex from forming
  • The end product can detach and be used elsewhere, allowing the active site to reform and the enzyme to become active
  • As product levels fall, the enzyme can catalyse again so its a continuous feedback loop
40
Q

How do reversible inhibitors act as regulators in metabolic pathways

A

Metabolic reactions are tightly controlled and balanced, and the end product of a sequence of metabolic reactions can be used as a non-competitive reversible inhibitor to control the metabolic reactions

41
Q

What are cofactors

A

Inorganic ions that help to stabilise the structure of the enzyme, or take part in the reaction at the active site to help the enzyme to function (e.g. chloride ions are cofactors for amylase)

42
Q

What are coenzymes

A

Large non-protein organic cofactors sourced from vitamins which can be permanently bonded or temporarily bonded in or near the active site, which are involved in carrying electrons or chemical groups between enzymes to help them function

43
Q

How do coenzymes work

A
  • Link enzyme catalysed reactions into a sequence during metabolic processes
  • E.g. ATP is responsible for the transfer of phosphate groups between respiration and energy consuming processes in cells
  • Coenzyme A is responsible for the transfer of acetyl groups from fatty acids and glucose in respiration
44
Q

What are prosthetic groups

A

Cofactors which are permanent parts of the enzyme structure, which help the function of the enzyme by forming its final 3D

45
Q

Describe a practical to measure catalase activity

A
  • Potato cubes (source of catalase) are placed in a conical flask with hydrogen peroxide
  • A bung with a delivery tube that links to a water bath and gas collecting tube is placed on the conical flask
  • The catalase breaks down the hydrogen peroxide into oxygen and water, and the volume of oxygen generated is measured in a set time
  • Rate of reaction is calculated

Biology (25 decks)

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