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OCR A-Level Biology > Chap 4 - Enzymes > Flashcards

Chap 4 - Enzymes Flashcards

1
Q

Define activation energy

A

energy required to initiate a reaction.

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2
Q

what is an enzyme?

A

a biological catalysts that interacts with substrate molecules to facilitate chemical reactions

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3
Q

what type of protein make up enzymes?

A

globular proteins

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4
Q

Define active site

A

area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind a substrate with specificity

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5
Q

Define anabolic reaction

A
  • metabolic reactions that construct molecules from smaller units
  • require energy
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6
Q

Define catabolic reaction

A
  • metabolic reactions that break molecules down into smaller units
  • release energy
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7
Q

Define apoenzyme

A

protein that forms an active enzyme by combination with a cofactor

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8
Q

Define cofactor

A

non-protein component necessary for effective functioning of an enzyme (can be ions or organic molecules)

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9
Q

Define coenzyme

A

organic cofactor not permanently attached to the protein

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10
Q

Define competitive inhibitor

A
  • inhibitor that competes with substrate to bind to active site on an enzyme
  • prevents enzyme activity by binding to active site
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11
Q

Define digestion

A

process by which large biomolecules such as carbohydrates, lipids and proteins get hydrolysed into smaller constituent molecules
- allows absorbtion across cell membranes.

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12
Q

Define end-product inhibition, and why it is useful

A
  • when product of a reaction inhibits the enzyme required for the reaction
  • useful bc it makes sure that no excess products are made and resources are not wasted - negative feedback
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13
Q

Define enzyme inhibitor

A
  • molecule prevents enzymes from carrying out their normal function of catalysis
  • reduce the enzyme’s rate of reaction
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14
Q

Define holoenzyme

A

active form of an enzyme

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15
Q

Define inactive precursor enzyme

A

an enzyme that requires a biochemical change for it to become active

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16
Q

explain why enzymes may be produced as inactive precursors

A
  • used to prevent some enzymes from causing damage within cells producing them/tissues when released
  • used when an enzyme’s action needs to be controlled and only activated under certain conditions
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17
Q

Give an example of an inactive precursor enzyme

A
  • trypsinogen and pepsinogen are inactive forms of trypsin and pepsin
  • used to prevent proteases from digesting membrane proteins in vesicles storing them - would result in vesicles breaking down, prevent proteases from digesting other enzyme
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18
Q

Define initial rate of reaction

A

the instantaneous rate at the start of the reaction
- gradient of tangent to curve at t=0

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19
Q

Describe the importance of initial rate of reaction

A
  • concentration of substrate is always changing - RoR constantly changes
  • so only true RoR is initial
  • (only moment where the two variables investigated are the only ones influencing rate)
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20
Q

Define irreversible inhibitor

A
  • inhibitor that cannot easily dissociate from the enzyme, permanently disabling the enzyme
  • effect cannot be reversed
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21
Q

what type of inhibitors are irreversible?

A

non-competitive

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22
Q

Define metabolism

A

sum of all of the different reactions and reaction pathways happening in a cell or an organism

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23
Q

Define non-competitive inhibitor

A

inhibitor that binds to an enzyme at an allosteric site

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24
Q

Define product

A

substances formed from a chemical reaction

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25
Q

Define substrate

A
  • substance used, or acted on by another process or substance
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26
Q

Explain why enzymes are necessary for life.

A
  • most important metabolic reactions are slow without catalysts - would need to happen at very high temp and pressures to be quick enough for important life processes
  • these conditions would damage cell components and impossible to reach in living cells
  • enzymes speed up metabolic reactions without need for harsh environmental conditions
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27
Q

define intracellular enzyme + example

A

enzymes that act within cells
- eg. catalase

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28
Q

define extracellular enzyme + example

A

enzymes that act outside of cells (released from cells to act outside them)
- eg. amylase, trypsin

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29
Q

State the substrates and products of enzymes catalase, amylase and trypsin.

A
  • amylase ( starch ⟶ maltose)
  • trypsin (proteins ⟶ peptides)
  • catalase (hydrogen peroxide ⟶ water + oxygen)
30
Q

Explain the role of extracellular enzymes in general.

A
  • reactions in cells require constant supply of raw materials to make products required by organisms
  • nutrients present in diet/environment are supply for raw materials
  • nutrients often in form of polymers (proteins and polysaccharides) - can’t enter cells directly
  • extracellular enzymes used to digest nutrients into smaller molecules so can be absorbed and used by cells
31
Q

Summarise the digestion of starch as an example of the role of extracellular enzymes.

A
  • starch polymers partially broken down into maltose (disaccharide) using amylase (released in saliva, produced by salivary glands and pancreas)
  • maltose is broken into glucose (monosaccharide that can be absorbed by cells) using maltase (present in small intestine)
32
Q

Summarise the digestion of proteins as an example of the role of extracellular enzymes.

A
  • proteins are digested into smaller peptides using trypsin (produced in pancreas and released into small intestine)
  • peptides are broken down further into amino acids by other proteases
  • amino acids are absorbed by cell lining of digestive system and then absorbed into bloodstream
33
Q

Define specificity

A

term that describes how each enzyme catalyses one biochemical reaction

34
Q

Explain why an enzyme only catalyses one type of reaction.

A
  • different enzymes have differently shaped active sites
  • each specific active site shape complementary to a specific substrate
  • each enzyme will only be able to catalyse a specific substrate and therefore only one type of reaction
35
Q

State the sequence of events in an enzyme-controlled reaction.

A
  • molecules in solution move & collide randomly
  • when specific substrate collides with specific enzyme and it fits the active site, substrate binds to active site = enzyme-substrate complex
  • substrate(s) react and product(s) are formed = enzyme-product complex
  • product(s) released, leaving enzyme unchanged and able to catalyse more reactions
36
Q

Describe the lock and key hypothesis of enzyme action.

A
  • enzymatic action works the same way a specific key will fit into a specific lock
  • the shape of the active site is exactly complementary to the shape of the substrate
  • enzyme does not change shape
37
Q

Describe the induced-fit hypothesis.

A
  • enzyme changes shape slightly as substrate enters
  • weak interactions between substrate and enzyme induce changes in enzyme’s tertiary structure - strengthen binding putting strain on substrate molecule
  • weakens bonds in the substrate, lowering activation energy
38
Q

Suggest how R-groups of amino acids are involved in catalysing reactions.

A
  • R-groups interact with substrate, forming temporary bonds
  • bonds put strain on bonds within substrate - helps lower the activation energy
39
Q

Define rate of reaction

A

speed at which reactants are being turned into products

40
Q

State what the presence of an enzyme does to the activation energy for a reaction and explain why this increases the rate of reaction.

A
  • enzymes lower the activation energy
  • lowers the minimum amount of energy required in particles in order for them to react
  • higher proportion of particles are able to react - more reactions happen during a given time interval - higher rate
41
Q

State 4 factors that affect the rate of an enzyme-controlled reaction.

A
  • temperature
  • pH
  • substrate concentration
  • enzyme concentration
42
Q

Explain why increasing temp from below the optimum towards the optimum increases the rate of reaction.

A
  • increasing temp increases kinetic energy of particles
  • causes particles to move faster and collide more frequently
  • results in more frequent successful collisions between substrate and enzyme –> increase in rate of reaction
43
Q

Define temperature coefficient (Q10)

A

measure of how much the rate of a reaction increases with a 10˚C rise in temperature

44
Q

State the usual Q10 value for enzyme controlled reactions.

A

for enzyme-controlled rxns = 2 (rate doubles with 10˚C increase)

rate of reaction at (t +10)˚C / rate of reaction at t˚C

45
Q

Explain why increasing the temperature up from the optimum decreases the rate of reaction abruptly.

A
  • at higher temp, bonds holding enzyme protein structure together vibrate more and eventually strain and break
  • breaking of bonds result in change in the precise tertiary structure of the protein
  • enzyme has changed shape - denatured
  • active site has changed shape and is no longer complementary to substrate - substrate cant fit - enzyme is no longer a functional catalyst
46
Q

Explain why a pH change away from optimum decreases the rate of reaction.

A
  • hydrogen bonds and ionic bonds between amino R-groups hold protein in its precise 3D shape
  • change in pH changes H+ concentration (more H+ - acidic - low pH) (less H+ - alkaline - high pH)
  • active site is only in right shape at optimum pH so when it changes, structure and therefore active site is altered - reduces RoR
  • f change is not too significant = enzyme can renature if pH is back to optimum
  • if change is too significant = enzyme is irreversibly altered, active site no longer complementary - denatured
  • happens because H+ intreact with polar and charged R-groups if more H+ less R-groups can interact with each other leading to ionic and hydrogen bonds breaking
47
Q

Define Vmax

A

maximum initial rate of an enzyme-catalysed reaction

48
Q

Explain how increasing the substrate concentration affects the initial rate of an enzyme-controlled reaction.

A
  • as substrate concentration increases, rate of successful colisions between substrate and enzyme increases
  • this increases the rate of formation of ES complexes = RoR increases
  • rate stops increasing when all of the active sites are occupied
  • at this point substrate is no longer limiting and increasing conc will not affect rate (Vmax)
49
Q

Explain how increasing enzyme conc. affects the initial rate of an enzyme-controlled reaction.

A
  • as enzyme concentration increases, more active sites are available and reaction rate increases
  • leads to more frequent successful collisions between substrate and enzyme
  • increases the rate of formation of ES complexes = rate increases
  • rate stops increasing when substrate starts to run out and enzymes collide more often with each other than with substrate
  • enzyme is no longer limiting and increasing conc will not affect rate (Vmax) because there will be nothing for enzymes to bind to
50
Q

Describe and explain how to investigate any of the factors that affect the rate of enzyme-controlled reactions.

A
  • use catalase from any living tissue and add it to hydrogen peroxide, measure gas produced (oxygen):

changing the ind. variables:
- substrate conc - increase hydrogen peroxide conc
- enzyme conc - eg crush up potatoes in solution and perform serial dilution of the solution
- temperature - heat the tissue/perform experiment in water bath where everything is at same temp
pH - add buffer solution to the reaction mixture

51
Q

Explain how to calculate the rate of change from a graph showing a linear relationship.

A
  1. pick two points on the line, calculate ∆y/∆x (gradient)
  2. suitable units will be units of dependent variable per unit independent
52
Q

Explain how to estimate a rate of change at a particular point on a graph showing a non-linear relationship.

A
  1. draw a tangent to the point at which you are trying to find the gradient
  2. find ∆y/∆x of that straight line which will be the estimated gradient at the chosen point
53
Q

Define cofactor and coenzyme.

A
  • cofactor - non-protein component necessary for effective functioning of an enzyme (can be ions or organic molecules)
  • coenzyme - organic cofactor not permanently attached to the protein
54
Q

Describe the similarities and differences between cofactors, coenzymes and prosthetic groups.

A
  • coenzymes and prosthetic groups are both cofactors
  • coenzymes are organic cofactors that are not permanently attached to the protein
  • prosthetic groups are cofactors that are permanently attached to the enzyme
  • cofactors and prosthetic groups can be organic or inorganic (org molecules or ions)
55
Q

Explain why the chloride ion necessary for the correct formation of the active site in amylase is a cofactor, not a coenzyme or prosthetic group.

A
  • it is inorganic, coenzymes are organic
  • it is not permanently attached, prosthetic groups are
56
Q

Explain why zinc ion that forms an important part of the structure of carbonic anhydrase is a prosthetic group, not a cofactor or coenzyme.

A
  • it is permanently attached - stating it is a cofactor is ambiguous - cofactors include both permanently and not permanently attached components
  • it is inorganic, coenzymes are organic only
57
Q

Give two examples of coenzymes synthesised from vitamins in our diet.

A

NAD (vitamin B3)
NADP (vitamin B3)

58
Q

Describe 4 ways in which multi-step reaction pathways can be regulated by cells.

A
  • competetive inhibition
  • non-competetive inhibition
  • end-product inhibition
  • cofactors?
59
Q

Explain how a competitive inhibitor affects the rate of an enzyme-controlled reaction.

A
  • molecule/part of molecule with similar shape to substrate fits into the active site of the enzyme
  • this blocks substrate from entering active site, preventing enzyme from catalysing
  • enzyme cant carry out its function - inhibited
    Substrate and inhibitor molecules will compete to bind to active sites
  • # of molecules binding to active site in given time reduced, rate of reaction slowed
60
Q

State two examples of competetive inhibitors and describe their actions.

A
  • statins are inhibitors of enzyme used in synthesis of cholesterol, reducing its production and blood conc
  • aspirin irreversibly inhibits COX enzymes preventing synthesis of chemicals responsible for producing pain and fever
61
Q

Explain how a non-competetive inhibitor affects the rate of an enzyme-controlled reaction.

A
  • inhibitor binds to enzyme at allosteric site
  • binding of inhibitor causes tertiary structure of enzyme to change, active site changes shape
  • active site no longer has complementary shape to substrate so substrate is unable to bind to enzyme
  • enzyme cannot carry out function - inhibited
  • the inhibitor does not compete with the substrate for the active site
  • # of available active sites is reduced permanently, less molecules bind to them in given time, rate of reaction reduced
62
Q

State two examples of non-competetive inhibitors and describe their action.

A
  • organophosphates (herbicides and insecticides) inhibit enzyme acetyl cholinesterase (responsible for nerve impulse transmission) - leads to muscle cramps, paralysis or death
  • proton pump inhibitors (treat long-term indigestion) block enzyme system responsible for secreting H+ ions into stomach, reduces production of excess acid, preventing ulcers
63
Q

Describe the effects of competitive inhibitors on an enzymes Vmax

A
  • does not lower the Vmax of a reaction
  • adding more substrate will result in more substrate than inhibitor
  • original Vmax will be reached
64
Q

Describe the effects of competitive inhibitors on an enzymes Vmax

A
  • permanently lower the Vmax of a reaction
  • adding more substrate will not overcome effect of them
65
Q

Define end-product inhibition

A

when final product of a reaction inhibits the enzyme required for the next reaction

66
Q

Describe end-product inhibition’s usefulness in controlling metabolic pathways.

A

makes sure that no excess products are made and resources are not wasted - negative feedback loop

67
Q

Define inactive precursor enzyme

A

enzyme that requires biochemical change for it to become active

68
Q

Explain why enzymes may be produced as inactive precursor enzymes

A
  • used to prevent some enzymes from causing damage within cells producing them/tissues where released
  • used when an enzyme’s action needs to be controlled and only activated under certain conditions
  • used to prevent proteases from digesting membrane proteins in vesicles storing them which would result in vesicles breaking down, prevent proteases from digesting other enzymes
69
Q

Describe 3 ways in which inactive precursor may be activated.

A
  • adding a cofactor
  • action of another enzyme
  • change in conditions
70
Q

Define zymogens and proenzymes

A

inactive enzymes that require a biochemical change (change in conditions/acted on by another enzyme) to become an active enzyme.

71
Q

Give 2 examples of inactive precursor enzymes and describe how they are activated.

A
  • pepsinogen becomes pepsin when exposed to stomach acid bc the low pH brings about the transformation
  • trypsinogen becomes trypsin when cleaved into active form by enteropeptidase

OCR A-Level Biology (16 decks)

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