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OCR Biology > 2.4 ENZYMES > Flashcards

2.4 ENZYMES Flashcards

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1
Q

What is an enzyme?

A
  • Biological catalysts made of globular proteins that speed up rate of metabolic reactions by lowering activation energy (via a different pathway)
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2
Q

Give an example an intracellular enzyme

A
  • Catalase in the liver breaking down hydrogen peroxide into oxygen and water
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3
Q

Give an example of an extracellular enzyme

A
  • Trypsin in the small intestines hydrolyses proteins
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4
Q

Describe the active site of enzyme

A
  • An indented area complementary to a substrate molecule as a result of folding and bonding in the proteins tertiary structure
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5
Q

What is a catabolic reaction?

A
  • A reaction that breaks down substrates
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6
Q

What is an enzyme-substrate complex?

A
  • An enzyme molecule with a substrate molecule temporarily joined to its active site by non-colavent forces (e.g van der waals/hydrogen bonding/ionic bonding/hydrophobic interaction)
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7
Q

what is an enzyme-product complex?

A
  • An enzyme molecule with a product molecule temporarily joined to its active site by non-colavent forces (e.g van der waals/hydrogen bonding/ionic bonding/hydrophobic interaction)
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8
Q

Describe the lock and key model

A
  • Complementary enzyme and substrate molecules have kinetic energy
  • When they collide, an enzyme-substrate complex forms
  • Substrate molecule is either broken down into product or built up into product
  • Enzyme-product complex forms
  • Product released from active site and enzyme catalyses another substrate
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9
Q

Describe the induced fit model

A
    • Complementary enzyme and substrate molecules have kinetic energy
  • When they collide the active site side chain/R-groups change shape slightly so substrate can bind for effectively to the enzymes active site
  • An enzyme-substrate complex forms
  • Substrate molecule is either broken down into product or built up into product
  • Enzyme-product complex forms
  • As the product has a slightly different shape from the substrate molecule, they detach from the active site
  • Enzyme catalyses another substrate
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10
Q

Draw an activation energy graph to show the action of enzymes

A

(EXOTHERMIC LAYOUT)

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11
Q

Define the optimum temperature for an enzyme

A
  • The temperature at which they catalyse a reaction at the maximum rate
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12
Q

Explain the effect of increased temperature on an a mixture containing enzymes and substrates

A
  • Enzyme and substrate molecules gain kinetic energy so move faster
  • Thus, more frequent successful collisions with sufficient energy to overcome activation energy
  • Rate of formation of enzyme-substrate complexes increases so rate of reaction also increases
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13
Q

Define activation energy

A
  • The minimum amount of energy required for reactants to start forming products
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14
Q

Explain how high temperatures result in enzyme denaturation in regards to 3D tertiary structure and the effect on rate of reaction

A
  • Heat = KE = molecues vibrate
  • This breaks the weak forces that hold the tertiary structure of the enzymes active site
  • Active site changes shape, substrate cannot fit in effectively
  • Rate of reaction decreases
  • More heat means the active site shape changes irreversibly, no longer complementary
  • The reaction cannot be catalysed as 3D shape is destroyed
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15
Q

Explain how high temperatures effect an enzymes primary structure

A
  • NO EFFECT on primary structure
  • Because heat does not break peptide bonds between amino acids
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16
Q

Draw a rate-temperature graph and label the optimum temperature/maximum rate of reaction

A
17
Q

State the equation to determine rate of reaction for an enzyme

A
18
Q

Explain what the temperature coefficient Q₁₀ tells us

A
  • The increase in the rate of reaction when the temperature is increased by 10°C
19
Q

State the formula for temperature coefficient Q₁₀

A
20
Q

State what the value of Q₁₀ is for most reactions and explain what this means

A
  • 2
  • This means for every 10°C increase in temperature, the rate of reaction is doubled (x2)
21
Q

Define acid

A
  • A proton donor when they dissociate in aqueous solution
22
Q

Define buffer

A
  • A substance that minimised changes in pH on small additions of acid or alkali
23
Q

Explain how pH effects the shape of an enzyme in terms of 3D tertiary structure and the effect on rate of reaction

A
  • When acid is added, protons are attracted to and cluster around negative areas (e.g R-groups) of the enzyme, which alters the charge
  • This interferes with the tertiary structure by interfering with the hydrogen bonds and ionic bonds of the active site
  • Shape of active site changes so substrate cannot fit in effectively so rate of reaction decreases
24
Q

State the effect of slight/extreme pH on the reversibilty of an enzymes active site

A
  • Slight pH changes alter the active site reversibly (can be restored if optimum pH is restored)
  • Extreme pH changes alter the active site perminantly (thus its denatured)
25
Q

Draw a rate-pH graph and label the optimum pH/maximum rate of reaction

A
26
Q

Explain the effect of substrate concentration on rate using a rate-substrate concentration graph

A
  • As concentration of substrates increase the rate of reaction also increases
  • Because, more enzyme-substrate complexes form
  • So more enzyme-product complexes form
  • So more product molecules are formed
  • Substrate concentration is the limiting factor because as it increases, rate increases
  • Once the maximum rate is reached, substrate concentration no longer is the limiting factor because adding more doesnt increase rate of reaction
  • This is because all enzymes active sites are occupied with substrate molecules
  • Another factor is the limiting factor now
27
Q

Explain the effect of enzyme concentration on rate using a rate-enzyme concentration graph

A
  • As enzyme concentration increases more active sites become available
  • More frequent successful collisions between the enzyme molecules and substrate molecules
  • More enzyme-substrate complexes form
  • So more product molecules are formed so rate of reaction increases
  • Enzyme concentration is the limiting factor because as it increases, rate increases
  • If the substrate concentration is fixed/limited all the substrates will be occupying an active site or have been released as products
  • Therefore, substrate concentration now becomes the limiting factor
28
Q

State how cells regulate their metabolism in terms of enzymes

A
  • Enzyme synthesis and enzyme degradation
29
Q

Explain why initial rate of reaction is the fastest

A
  • Initial rate gives maximum rate of reaction because:
  • At the start,

OCR Biology (27 decks)

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