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Biology > B4 - enzymes > Flashcards

B4 - enzymes Flashcards

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1
Q

Why are enzymes so important? (2)

A
  • Many biological processes need to happen very fast, requiring very high temperature and pressure. Wouldn’t be possible w/o enzymes.
  • They are biological catalysts which allow reactions to occur in normal/less extreme conditions.
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2
Q

What is an anabolic reaction?

A
  • Required for growth/ build up molecules
  • 2 substrate molecules drawn to 1 active site, chemical bonds cause them to join as one product, which is then released so enzyme can work again.
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3
Q

What is a catabolic reaction?

A
  • 1 substrate drawn to active site, forms to products (bonds broken)
  • breaks down molecules
  • exergonic: net release of energy (required for living processes)
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4
Q

Give an example of an intracellular enzyme.

A

catalase:
- breaks down hydrogen peroxide (product of metabolic processes & toxic/harmful to cells) into oxygen and water to prevent cell damage.

DNA polymerase

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5
Q

What are extracellular enzymes?

A
  • secreted & work outside cell
  • released from cell to breakdown larger nutrients (often polymers) that need to be broken down to enter cell & supply the materials needed for growth.
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6
Q

Give 2 examples of extracellular enzymes. (2)

A

Amylase:
- digestive enzyme produced in salivary glands & pancreas.
- Acts in mouth & small intestine (hydrolyse starch to simple sugars)

Trypsin:
- Protein-digesting enzyme
- hydrolyses peptide bonds
- Produced inactive (won’t react) & secreted in small intestine by pancreas.
- Reactivated in small intestine.

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7
Q

What is activation energy and how is it affected by enzymes?

A
  • energy required for a reaction to occur.
  • needed to form transition state
  • enzymes lower the Ea by stabilising the transition state. (change active site conditions)
  • Gives more substrates sufficient energy to overcome Ea barrier.
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8
Q

Describe the enzyme-substrate reaction mechanism. (4)

A

1) substrate binds to enzyme’s complimentary active site
- molecules must collide w/ sufficient speed & correct orientation for reaction to happen.
2) enzyme-substrate complex forms
3) substrate converted to product whilst attached to enzyme.
4) Product released.

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9
Q

What is the lock and key hypothesis? (5)

A

Active site = within TERTIARY structure of enzyme & has complimentary shape to specific substrate molecule.

1) substrate drawn to active site. Active site DOESN’T CHANGE shape.
- enzyme’s R-groups form temporary bond with substrate
- strains bonds within substrate, helping the rxn
2) ES complex forms
3) EP complex foms
4) P released

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10
Q

What is the induced fit hypothesis? (4)

A
  • Enzyme’s active site CHANGES SHAPE as substate binds, making it more likely to change to a product.
  • substrate and enzyme have weak bonds, straining bonds in the substrate & allowing reaction to proceed more regularly
  • EP forms IMMEDIATELY after ES
  • End product released & active site reverts back to inactive state
  • ENZYMES = FLEXIBLE
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11
Q

What is the turnover number?

A

Number of substrate molecules transformed per minute by 1 enzyme molecule.

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12
Q

Explain the process of the digestion of starch. (3)

A

Begins in mouth, continues in small intestine.
Amylase produced by salivary glands & pancreas, released in saliva & in pancreatic juice to the small intestine.
1) Amylase breaks starch polymers into maltose
2) Maltose broken into glucose by maltase in the small intestine
3) Glucose is small enough to be absorbed into the bloodstream.

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13
Q

Use collision theory to explain why increasing temperature increases the rate of reaction. (2)

A
  • particles have more Ek, so move faster & collide more frequently
  • more enzyme-substrate complexes form, hence more products form
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14
Q

What is Q10? (3)

A
  • The temperature coefficient
  • Measures how much the rate of reaction will increase with a temperature rise of 10 degrees

= rate of rxn at (x+10) degrees / rate of rxn at x degrees

  • Q10 is usually 2, meaning the rate doubles.
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15
Q

What happens in a reaction when temperature is raised by too much? (3)

A
  • enzymes denature = active site & substrate no longer complimentary, don’t fit together so doesn’t function as catalyst.
  • bonds holding the enzyme’s tertiary structure vibrate & break from straining.
  • changes tertiary structure and shape of enzyme
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16
Q

Explain the significance of optimum temperature. (3)

A
  • where enzyme has highest activity rate
  • rate rapidly drops after optimum temperature.
  • abrupt and happens to all enzymes
  • enzymes less active just before optimum temp but don’t denature, just slower rxn rate.
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17
Q

How are extremophiles adapted to their extreme conditions? (2)

A

V. cold:
- more flexible active site = adapted to cold
- less stable when temp inc, so small temp change = denature.

V hot:
- more stable (more bonds in tertiary structure)
- more resistant to temp changes

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18
Q

Explain the significance of optimum pH. (3)

A
  • Active site only correct shape at optimum pH
  • If pH changes, structure changes
  • H+ reacts with polar R-groups, changing the degree of interactions
  • more H+ = less R-group interactions = bonds break and change shape.
19
Q

Why is the pH graph symmetrical?

A

Reversible reduction in enzyme activity as pH moves away from optimum.

20
Q

Explain the change in reaction rate as substrate concentration increases.

A
  • low substrate conc = low product formation
  • enzyme/active sites in excess so more collisions
  • rate increases, more ES complexes
  • Reaches Vmax, more substrates than enzyme active sites available/ all active sites occupied
  • enzyme concentration = limiting factor.
20
Q

How would you set up a PAG to determine the H2O2 concentration on catalase? (5)

A

H2O2 acts as substrate, catalase is the enzyme.
1) Use source of catalase (e.g. potato)
2) even slices placed into boiling tube of hydrogen peroxide serial dilution(2,4,6,8 vol)
3) Put measuring cylinder full of water upside down in a trough of water.
4) Place bung on top of boiling tube with delivery tube attached & start timer. Oxygen volume collected determines rate of reaction.
5) Repeat for each serial dilution.

21
Q

Why are inhibitors so important?

A
  • Reduce reaction rate & slow enzymes
  • Control metabolic activity = regulate product formation (reaction too fast = excess products)
  • Living processes have multi reaction pathways & must be regulated to meet needs w/o wasting resources.
22
Q

How do competitive inhibitors work?

A
  • Compete w/ substrate for active site & form EI complex (prevent product formation)
  • Similar complementary shape to substrate = blocks active site, so no ES complex.
23
Q

Why is Vmax still reached at high concentrations of substrate when competitive inhibitors are present?

A
  • Substrate outcompetes for active site
  • more substrate = more likely collide than the competitive inhibitors = Vmax reached.
24
Q

Give an example of a competitive inhibitor.

A

Cyanide:
- competitive inhibitor for cytochrome c. oxidase
- prevents ATP production by inhibiting respiration

Aspirin:
- Inhibits COX, preventing chemicals responsible for pain & fever.

25
Q

How do non-competitive inhibitors work?

A
  • Don’t compete for active site.
  • compete for allosteric site & distorts enzyme’s tertiary structure, changing the shape of the active site.
  • Active site and substrate no longer complimentary = no ES complex = REDUCE rate.
26
Q

Non-competitive inhibitors never reach the enzyme’s Vmax. Instead, a new Vmax is formed. Explain why.

A
  • Not competing for active site
  • Even with substrates in excess and active sites filled, the non comp binds to the allosteric site, preventing product formation nonetheless.
27
Q

Give an example of a non-competitive inhibitor.

A

proton pump inhibitors:
- Block enzyme that secretes H+ into stomach = reduced production of excess acid.

Penicillin:
- Bind to bacterial enzyme that forms cross-
links in cell wall.
- Cause holes in cell wall = shed most of cell wall

28
Q

What are the dangers of irreversible non-competitive inhibitors?

A
  • can’t be removed from the enzyme they’re attached to = often very toxic.
  • Form covalent bonds w/ enzymes & permanently inhibit
  • Dangerous: Can stop biological processes catalysed by enzymes.
29
Q

Give an example of an irreversible non-competitive inhibitor.

A

Insecticides:
- inhibit acetyl cholinesterase (enzyme for nerve impulse transmission). Leads to muscle cramps, paralysis, death.

30
Q

What is end-product inhibition?

A
  • When the end product of a reaction acts as an inhibitor for the enzyme that produced it.
  • Negative feedback, no excess or waste products
31
Q

ATP is an example of end product inhibition. Explain what and how it inhibits.

A

ATP regulates it’s own production.
- enzyme PFK (phosphofructokinase) adds the second phosphate group to glucose in respiration which initiates its breakdown.
- ATP inhibits PFK
- High ATP: ATP binds to allosteric site on PFK, preventing addition of a 2nd phosphate to glucose, therefore glucose isn’t broken down & ATP produced less
-Low ATP: less binds to PFK, so it adds 2nd phosphate to glucose, respiration resumes, and more ATP produced.

32
Q

What are cofactors?

A
  • INORGANIC IONS e.g. (Cl-, Fe2+)
  • temporary
  • help stabilise enzyme structure (bind to ENZYME OR SUBSTRATE) and affects charge distribution.
  • ES more easily formed.
33
Q

Why are cofactors, coenzymes and prosthetic groups so important?

A
  • some enzymes only function if a non-protein substance is present.
  • Changes tertiary structure for active site to bind with substrate
34
Q

Give an example of a cofactor.

A
  • Cl- is the cofactor the amylase
  • Cl- needed to digest starch into maltose.
35
Q

What is a coenzyme? (4)

A
  • Binds loosely to ACTIVE SITE, before or same time as substrate.
  • ORGANIC (many derived from vitamins)
  • temporary
  • carry chemical groups between enzymes
  • Link enzyme-catalysed reactions into a sequence during metabolic processes e.g. photosynthesis.
  • Coenzymes themselves take part in reaction and are changed in some way
  • recycled and reused
36
Q

Give an example of a coenzyme.

A

NAD:
- Transfers H+ between molecules in respiration
- obtained from vitamin B3

Coenzyme A (CoA):
- Breakdown of fatty acids & carbohydrates in respiration
- obtained from vitamin B5

ATP:
- transfers phosphate groups between respiration & energy-consuming cell processes.

37
Q

What are the main differences between a coenzyme and a cofactor?

A

cofactor:
- inorganic
- binds to enzyme or substrate to affect charge distribution

coenzyme:
- organic
- binds to the active site itself and takes part in the reaction

38
Q

What are prosthetic groups?

A
  • TIGHTLY bound to enzyme
    -PERMANENT
  • Help form final tertiary structure of enzyme to function properly
39
Q

Give an example of a prosthetic group.

A

Haemoglobin:
- prosthetic group has Fe2+
- Transports O2 ( allows binding and releasing of O2 to and from cells)

Carbonic anhydrase:
- Prosthetic group has Zn2+
- allows enzyme CO2 + H20 to produce carbonic acid in RBCs.

40
Q

What is precursor enzyme?

A
  • Inactive
  • Controlled & activated in certain conditions otherwise would damage tissues when released.
  • Add cofactor to undergo shape change (tertiary/active site) & to be activated.
41
Q

What are zymogens/proenzymes?

A

Precursor enzymes which require another enzyme to change their tertiary structure and be activated.

Could also be activated by conditions e.g. pH or temp changes.

42
Q

Give an example of a zymogen/proenzyme

A

pepsinogen:
- Inactive pepsinogen released into stomach.
- Acid pH of stomach causes transformation into active pepsin to digest proteins.
- This helps protects the body against the digestive action of pepsin (by having an inactive form)

43
Q

protein(inactive) + non-protein(activator) = whole enzyme (active)

What are the specific names given to these?

A

inactive = apoenzyme
activator = cofactor
active = holoenzyme

Biology (20 decks)

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