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biology - core concepts > enzymes > Flashcards

enzymes Flashcards

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1
Q

what type of proteins are enzymes?

A

globular

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2
Q

what are the three types of bonds present in the structure of enzymes?

A

hydrogen
ionic
disulphide bridge

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3
Q

what does it mean by biological catalysts?

A

things that speed up the rate of reaction (by lowering activation energy) without being used up

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4
Q

aerobic respiration involves a series of reactions that break bonds to produce smaller molecules from larger molecules - what sort of reaction is this?

A

catabolic

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5
Q

what are the two models of enzyme activity?

A

induced fit
lock and key

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6
Q

what is the key difference between the two models?

A

in lock and key, the substrate is complementary to the active site
in induced fit, the substrate is not complementary to the active site so the active site must change shape

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7
Q

if increasing temperature increases the rate of reaction, what is the limiting factor?

A

temperature

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8
Q

why does a small increase in pH reduce the rate of a reaction?

A

cause reversible changes in the shape of an active site so fewer enzymes substrate complexes form

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9
Q

Using the induced fit model, explain how an enzyme is able to increase the rate of a reaction

A
  • enzyme binds/collides with the substrate
  • active site changes shape to fit the substrate
  • enzyme lowers the activation energy
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10
Q

define activation energy

A

energy required for a reaction to begin

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11
Q

define anabolic

A

a metabolic reaction involving formation of bonds
e.g photosynthesis

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12
Q

define catabolic

A

a metabolic reaction involving breaking of bonds
e.g respiration

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13
Q

define active site

A

the functional part of an enzyme

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14
Q

define enzyme inhibition

A

the reduction in the rate of an enzyme controlled reaction by another molecule

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15
Q

what are the two types of enzyme inhibitors?

A
  • competitive inhibitor
  • non competitive inhibitor
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16
Q

define competitive inhibitor

A

an inhibitor that is similar in shape to a substrate

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17
Q

define non competitive inhibitor

A

an inhibitor that is dissimilar in shape to the substrate

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18
Q

define allosteric site

A

a point on the enzyme where the non competitive inhibitor binds to, that is not the active site

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19
Q

define immobilised enzymes

A

enzymes that are fixed, trapped or bound on an inert matrix

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20
Q

define lock and key

A

a model in which active site and substrate and exactly complementary to one another

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21
Q

define induced fit

A

a model in which active site and substrate are not exactly complementary to one another

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22
Q

what are enzymes?

A
  • globular proteins with a specific tertiary structure
  • held by hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions
  • act as biological catalysts
23
Q

what are the two metabolic reactions?

A

anabolic
catabolic

24
Q

describe the lock and key model

A
  • the substrate molecule fits into the active site of the enzyme molecules like a key fitting into a lock as they are complementary shapes this forms the enzyme substrate complex
  • the product is then formed and as it no longer fits into the active site it is released
  • this model explains why enzymes are very specific
25
Q

describe the induced fit model

A
  • the substrate and the active site of the enzyme are not complementary shapes
  • when a substrate molecule binds to the active site, the active site changes shape and fits itself around the substrate
  • this places a strain on the substrate molecule and distorts a particular bond, lowering the activation energy required to break the bond
  • the products are formed and leave the active site which then returns to its original shape
26
Q

what is an example of the induced fit model?

A

lysozymes

27
Q

describe the enzyme, lysozyme

A
  • helps to kill bacteria by catalysing the hydrolysis of sugars in the peptidoglycan cell walls
  • cell walls are weakened, the bacteria absorbs water by osmosis and they burst=
  • it is present in many secretions such as tears, saliva, human milk
28
Q

name 3 properties of enzymes and describe them

A
  1. SPECIFIC - due to sequence of amino acids that make up their active site
  2. HIGH TURNOVER NUMBER (FAST ACTING) - convert many molecules of substrate per unit time
  3. SOLUBLE - hydrophilic R groups are found on the outside of the molecule
29
Q

what are the factors that can affect the rate of an enzyme-controlled reaction?

A
  • temperature
  • pH
  • substrate concentration
  • enzyme concentration
  • inhibitors
30
Q

describe the effect of temperature on an enzyme controlled reaction at LOW TEMPERATURES

A

the rate of reaction is low
the enzyme and substrate molecules have little to no kinetic energy

31
Q

describe the effect of temperature on an enzyme controlled reaction at INCREASING TEMPERATURE

A

increases rate of reaction
the kinetic energy of the enzyme and substrate molecules increases, increasing the chance of successful collisions, more enzyme-substrate complexes are formed

32
Q

describe the effect of temperature on an enzyme controlled reaction at OPTIMUM TEMPERATURE

A

rate of reaction is at the highest
maximum turnover number

33
Q

describe the effect of temperature on an enzyme controlled reaction at TEMPERATURE ABOVE OPTIMUM

A

rate of reaction decreases

the molecules have more kinetic energy. the increasing vibrations begins to break hydrogen bonds, changing the tertiary structure of the enzyme. This alters the shape of the active site so it is no longer complementary to the substrate. This lowers the rate of reaction as enzyme-substrate complexes cannot form

34
Q

describe the effect of temperature on an enzyme controlled reaction at HIGH TEMPERATURES

A

rate of reaction falls to zero

the enzymes are denatured. this is why the active site is permanently distorted by irreversible breaking of hydrogen bond, this prevents the substrate from binding as it is no longer complementary to the active site

35
Q

describe pH and enzymes

A
  • enzymes only work within a narrow range of pH values
  • extremes of pH can permanently denature an enzyme
36
Q

why does a extreme increase in pH reduce the rate of a reaction?

A

alters the electrostatic charge on the side chains of the amino acid
if the active site has too many H+ ions (acidic) or OH- ions (alkali) the active site and substrate may both have the same charge and the enzyme will repel the substrate

37
Q

how do you maintain a constant pH?

A

buffer solution

38
Q

describe the effect of substrate concentration on an enzyme controlled reaction at FIXED ENZYME CONCENTRATION

A

the rate of reaction will increases as substrate concentration increases

39
Q

describe the effect of substrate concentration on an enzyme controlled reaction at LOW SUBSTRATE CONCENTRATION

A

the substrate concentration is the limiting factor
the enzyme molecules only have a few substrate molecule to collide with

40
Q

describe the effect of substrate concentration on an enzyme controlled reaction at HIGH SUBSTRATE CONCENTRATION

A

there are more successful collisions and more eznyme active sites become occupied, until the rate of reaction reaches a maximum and substrate molecules are in excess
the enzyme concentration becomes the limiting factor

41
Q

describe competitive inhibitors

A
  • similar in shape to the substrate
  • complementary to the enzyme active site and bind to it. this blocks the actual substrate from entering the active site and so less enzyme-substrate complexes can form
  • the rate of reaction decreases so therefore less product is produced
  • if the concentration of substrate increases, the effect of the inhibitor is reduced
42
Q

what is an example of a competitive inhibitor

A

malonic acid

43
Q

how does malonic acid work?

A

in the mitochondrial matrix, a reaction involved in aerobic respiration is catalysed by the enzyme succinic dehydrogenase. this competitive inhibitor maloic acid has a similar shape to the substrate, succinic acid

44
Q

describe non-competitive inhibitors

A
  • not a similar shape to the substrate : it binds to the enzyme at a point other than the active site known as the allosteric site
  • this changes the shape of the enzyme so therefore the shape of the active site so it is no longer complementary to the substrate. the enzyme is permanently damaged.
45
Q

what is an example of a non-competitive inhibitor

A

cyanide

46
Q

enzymes immobilised in beads have a lower rate of reaction that those immobilised on a membrane. WHY?

A
  • some active sites are inside the beads and the substrate will take time to diffuse into them
  • enzymes on a surface have active sites that are more available to the substrate so there is a higher reaction rate
47
Q

what are the advantages of immobilised enzymes?

A
  • enzymes are easily recovered for re-use
  • product is not contaminated with the enzyme
  • increased stability over a wider range of pH values
  • increased stability over a range of temperatures, and enzymes denature at higher temperatures
  • several enzymes with differing temperatures or pH optima can be used in the process
  • enzymes can be easily added or removed giving greater control over the rate of reaction
48
Q

what are some uses of immobilised enzymes?

A
  1. lactose free milk
  2. biosensors
  3. high-fructose corn syrup
49
Q

describe how lactose free milk is produced from immobilised enzymes.

A

produced using immobilised enzymes trapped in an aliginate bead in a column to hydrolyse the lactose to its monosaccharides glucose and galactose

50
Q

describe how biosensors in terms of immobilised enzymes

A
  • these devices convert a chemical signal into an electrical signal
  • they quickly detect and measure very low concentrations of a specific substrate in a complex mixture
51
Q

give an example of biosensors and describe it

A
  • measurement of glucose concentration in blood samples
  • the enzyme glucose oxidase is immobilised on a selectively permeable membrane, when placed in the sample the enzyme binds to glucose
  • a small electric current is produced and detected by an electrode
  • the concentration of glucose can then be read on the screen
52
Q

name a medical condition that could be detected using a glucose biosensors

A

diabetes

53
Q

describe how high-fructose corn syrup is produced from immobilised enzymes.

A
  • a sweetener manufactured in a multi-step process from starch
  • involves several immobilised enzymes which require different conditions

biology - core concepts (6 decks)

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