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OCR Biology A Level > 2.1.4 Enzymes > Flashcards

2.1.4 Enzymes Flashcards

1
Q

What is meant by a biological catalyst?

A
  • catalsyst = speed up reactions
  • biological - reactions happen inside living organisms
    enzymes are proteins that speed up metabolic reactions
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2
Q

Bords and mammals are entotherms. What does this mean and how does it enmsure enzymes function corrrectly?

A
  • they maintain an optimum body temperature o, even if the external enviornmental temperature changes
  • ensures enzymes work at maxinum rate + don’t denature
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3
Q

Where can enzymes be found in household products?

A

biological washing powders
- remove biological molcules e.g. egg yolk
- can work at low temps
- save energy - good for environment

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4
Q

What type of protein are enymes?

A
  • globular
  • have a specific 3d shape
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5
Q

Give key features of globular proteins

A
  • soluble in water
  • have a specific shape
  • have a tertiary structure
  • have hydrophobic r groups on their surface
  • have metabolic roles
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6
Q

Give key features of enzymes

A
  • globular proteins
  • specific 3d shape
  • soluble in water
  • biological catalysts
  • have an active site specific to one substrate
  • their activity is effected by temperature, ph and concentration of substrate enzyme
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7
Q

What is the difference between extracellular and intracellular enzymes?

A

extracellular = reactions occur outside the cell
ontracellular = reactions occur inside the cell

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8
Q

Give examples of when extracellular proteins are used

A
  • nutrients in polymer form are too large to enter cells via cell surface membrane - must be hydrolysed by enzymes into smaller components
  • fungi break down molecules outside cell so they can be absorbed and used for growth
  • enzymes in saliva + stomach which break down food
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9
Q

Give examples of when intracellular proteins are used

A

Inside lysosomes to hydrolyse bacteria

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10
Q

What factors affect rate of enzyme reactions?

A
  • temperature
  • concentration of reactants ( substrate + enzyme)
  • ph
  • presence of cofactors
  • presence of inhibitors
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11
Q

What is activation energy and how do enzymes affect this?

A
  • the minimum energy required to start a chemical reaction
    -enzymes form enzyme-substrate complexes
  • these speed up metabolic reactions witout the need for higher temperatures
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12
Q

Name the two models of enzyme action

A
  • lock and key
  • induced fit
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13
Q

What is a model?

A
  • a simple representation of a process
  • to help understand how the process works
  • offen a visual representation
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14
Q

Explain the key aspects of the lock and key model

A
  • suggests the shape of the active site of the enzyme is complementory to shape of the substrate
  • like a key is complimentary to its lock
  • shape of active site doesn’t change
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15
Q

Explain the key aspects of the induced fit model

A
  • suggests the shape of the active site of the enzyme is not fully complementory to shape of the substrate
  • as substrate collides with active site, active site changes shaoe
  • causing active site to fit more closely with substrate
  • puts strain on bonds, so they break more easily - lowering activation energy
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16
Q

Why is the induced fit model more widely accepted by scientists?

A
  • new technology + research from x ray crystallography
  • more evidence that enzyme shape changed during reaction
  • new evidence fits more closely with this model
  • explains how enzymes lower activation energy
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17
Q

How do higher and lower temperatures affect enzyme action?

A

Temperature Below Optimum
- low temperatures = less kinetic energy
- decreasing random collisions of substrate + active site per second
- less enzyme substrate complexes formed per second
- slower rate of reaction as less successful collisions
- enzyme not denatured

Temperature Higher But Still Below Optimum
- high temperatures = more kinetic energy
- increasing random collisions of substrate + active site per second
- more enzyme substrate complexes formed per second
- faster rate of reaction as more successful collisions
- enzyme not denatured

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18
Q

What is temperature coefficient Q10 and how is it calculated?

A

A measure of how much the rate of reaction increases within a 10°C rise in temperature
Q10 = Rate at +10°C / Rate before

19
Q

What is an enzymes optimum temperature?

A
  • the temperature at which the enzyme has the highest rate of activity
  • 37°C in humans
  • when enzyme denatures above its optimum temperature, Q10 no longer applies
  • enzymes don’t denature under optimum temperature
20
Q

How do enzymes denature?

A
  • as temperature increases enzymes have increase kinetic energy
  • enyme vibrates more
  • too much kinetic energy breaks hydrogen + ionic bonds
  • causes 3D shape to change
  • active site altered
  • active site no longer complementary to shape of substrate
  • substrate no longer binds
  • enzyme-substrate complexes can no longer form
21
Q

Explain the basics of pH and how ions affect it

A

pH below 7 = acid = higher concentration of H+ ions
pH above 7 = alkali = higher concentration of OH+ ions

22
Q

How does pH affect enzyme action?

A
  • charged ions attract to or repel from charges in protein structure
  • charged ions interact with polar and charged R groups - changing ion concentration cahnges this interaction
  • these could change the charge of the R-groups of the active site (could affect binding of substrate)
  • tertiary structre (3D shape) of active site changes
  • substrate binds less efficiently - less enzyme-substrate complexes form - enzyme denatured
  • eventually, active site no longer complimentory to substrate, so can no longer bind
23
Q

What is renaturation?

A

Small changes in pH away from optimum pH, followed by return to optimum pH causes active site to return to complimentory shape

24
Q

What is initial reaction rate and why is it also the highest reaction rate?

A
  • the maximum possible reaction rate for an enzyme under a particular experimental solution
  • when first mixed together reaction rate is highest
  • as reation proceeds, product moleciules are formed + substrate molecules are used up and decrease in concentration
  • frequency of collisions decreases as reaction proceeds
25
Q

What is a limiting factor?

A

The factpr that will determine the rate of reaction when at sub-optimal level. Prevents the rate from increasing and causes a plateau.

26
Q

Give examples of limiting factors and how cells use them

A
  • temperature (if too cold)
  • concentration of substrate
  • concentration of enzyme
  • cells regulate concentration of enzyme + substrate to control metabolism
27
Q

How will an increasing substrate concentration affect the rate of an enzyme-controlled reaction?

A
  • to begin, substrate is limiting factor, so rate will increase
  • after all active sites are occupied of enzyme, substrate concentration wil not afect rate as enzyme is limiting factor
28
Q

What is an inhibitor and what are the two types?

A

A substance that slows down the rate of an enzyme catalysed reaction by affecting the enzyme in some way
- competitive + non-competitive

29
Q

How do competitive inhibitors work?

A
  • have a similar shape to substrate
  • fit into active site to block substrate from binding
  • fewer active sites + fewer enzyme-substrate complexes made
  • reduces rate of reaction
  • most can leave active site (non permanent)
30
Q

How do non-competitive inhibitors work?

A
  • bind to allosteric site (away from active site)
  • changes shape of tertiary structure + 3D shape of enzyme
  • active site shape altered - substrate can no longer fit
  • fewer active sites + fewer enzyme-substrate complexes made
  • reduces rate of reaction
  • can be permanent
31
Q

How can the effect of inhibition by competitive inhibitors be increased?

A

Increase in concentration compared to substrate molecules - greater chance of inhibitors colliding with active site = greater chance of inhibition

32
Q

How could you find out if a competitve or non-competitive inhjibitor was used on a graph showing initial rate of reaction compared to substrate concentration?

A

Competitive Inhibitor
- increasing the concentration of the substrate will reduce the inhibition effec
- if as the increasing substrate concentration increases, the rate of reaction increases and eventually reaches a maximum plateau, it suggests competitive inhibition
- reason for plateau = at higher substrate concentrations, most enzyme active sites are occupied by the substrate, reducing the impact of the inhibitor

Non-competitive Inhibitor
-increasing the concentration of the substrate will not fully overcome the inhibition effect
- visible decrease in the maximum rate of reaction, but substrate concentration remains unchanged
- inhibitor binds to a different site on the enzyme, affecting its activity without competing with substrate

33
Q

What is a metabolic pathway?

A

Sequences of chemical reactions each controlled by a specific enzyme

34
Q

What is a cofactor and name two types, as well as another molecule that enzymes sometimes need to function

A

Any substance that must be present for an enzyme-controlled reaction to take place at the appropriate rate
- coenzymes
- inorganic ions

  • prosthetic groups (not classed as a cofactor, as permanently bound to enzyme)
35
Q

Give key aspects of coenzymes

A
  • often made from vitamins
  • smalll, organic, non-protein
  • bind loosley with the active site before or after the substrate does
  • can be recycled to take part in the reaction again
  • can take chemical groups from one enzyme to another, forming a link between them
36
Q

Give key aspects of inorganic ions

A
  • can bind with the enzyme or substrate
  • binding of ions to the enzyme can make enzyme-substrate complexes form easier
  • can affect charge disttribution + change shape of active site
37
Q

Give key aspects of prosthetic groups

A
  • permanent part of enzyme
  • contribute to the final 3D shape
  • bound tightly to enzyme
38
Q

What is a precursor activation?

A
  • many enzymes made in an inactive form (inactive precursor enzymes)
  • important for enzymes that could damage cells
  • often need to undergo changes in shape to become activated
  • changes in shape can occur via addition of cofactor or action of another enzyme
  • can also activate due to pH or temperature changes
39
Q

Explain how blood clotting occurs using enzyme activation

A
  • platelets move towards site of tissue damage, releasing clotting factors (thromboplastin)
  • thromboplastin is an enzyme dependant on cofactor Ca2+ ions
  • once activated, catalyses conversion of prothrombin into enzyme thrombin (cleaves bonds to alter tertiary structure)
  • thrombin (protease) catalyses conversion of solube fibrinogen into insolule fibrin fibres - clots blood
40
Q

What is an independent, dependent and control variable?

A

Independant = variable that is changed - x axis
Dependant = variable that is measured - y axis
Control = variable that is kept the same otherwse results are invalid

41
Q

What is an control, negative control , and positive control group

A

Control group = a standard comparison for checking the results of an experiment
Negative control group = a control group that is not exposed to the experimental treatment or any other treatment expected to have an effect
Positive control group = a control group that is not exposed to the experimental treatment, but is exposed to another treatment known to have the expected effect

42
Q

What is meant by accuracy?

A

A measure of closeness of agreement between an individual test result and the true value

43
Q

Why are experiments repeated?

A
  • to identift and remove anomalous results - to reduce the impact of anomalies
  • to measure and increase repeatability
  • to calculate a mean, standard deviation and a statistical test
  • improves confidence in the results
44
Q
A

OCR Biology A Level (13 decks)

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