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Biology > Enzymes revision > Flashcards

Enzymes revision Flashcards

1
Q

Define an enzyme

A

An enzyme is a biological catalyst that speeds up the rate of a metabolic reaction

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2
Q

Describe what ‘complementary’ means in terms of enzymes

A

The substrate must react with the enzyme’s active site- (tertiary structure) must match that of the substrate (COMPLEMENTARY)

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3
Q

What does ‘specific’ mean in terms of enzymes

A

the shape of the enzyme’s active site must be SPECIFIC to the shape of the substrate
-specificity of enzymes lie in the TERTIARY STRUCTURE of the Protein molecule

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4
Q

Describe the structure of an enzyme

A

-Globular (soluble in water)
-not used up in the reaction they catalyse- can be used over
-substrate must react with the enzymes active site
-shape of the active site must be SPECIFIC to the shape of a particular substrate
-each enzyme will only catalyse one type of reaction

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5
Q

Define a Co-factor

A

A non- protein substance present to allow enzymes to function

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6
Q

How do cofactors work?

A

Cofactors work by influencing the shape of the enzyme or binding briefly with the enzyme to change the shape of the enzyme’s active site, in order to make the reaction more likely to happen

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7
Q

Describe the types of Cofactors

A

-Prosthetic Groups
a type of cofactor, eg haem is the prosthetic group in haemoglobin

-Coenzymes
non-protein organic molecules, that often contain a vitamin molecule as part of their structure
not permanently attached

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8
Q

How does activation energy impact on enzymes

A

-Enzymes are catalysts which operate by lowering the activation energy (energy needed to start a reaction)- means the reaction requires less energy and takes place more often- increased rate of reaction
-enzymes lower the activation energy by orientating the enzyme and substrate so they can react
-The activation energy is only lowered when the substrate molecule binds with the active site of an enzyme and an ENZYME SUBSTRATE COMPLEX IS FORMED

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9
Q

Explain the LOCK AND KEY hypothesis

A

-Explains why enzymes are specific and will only work on a particular substrate

-The active site of an enzyme has a complementary shape (lock) into which the substrate (key) molecule fits exactly- to form an ENZYME SUBSTRATE COMPLEX

-the reaction takes place at the enzymes active site, where the products are formed
-the products have a different shape to the substrate- therefore they no longer fit the active site and are repelled
-the active site is then free to react with more substrate

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10
Q

Describe the INDUCED FIT hypothesis

A

-This suggests that the active site of the enzyme may not exactly correspond to the shape of the substrate, but as the substrate begins to bind, the active site CHANGES SHAPE and ‘moulds’ itself around the substrate

-the products no longer fit the active site and are repelled.
enzyme reverts to its ‘relaxed’ state and can attach to more substrate
-this model considered more useful- better explains the way in which ACTIVATION ENERGY is reduced in catabolic (break down) reactions

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11
Q

How optimum temperature affects enzyme activity

A

-40 degrees is the temp at which enzymes work most rapidly
-MOST product is converted to product in the SHORTEST time

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12
Q

How above optimum affects enzyme activity

A

-enzyme is DENATURED (permanent and irreversible)
-INTERNAL bonds, (WEAK HYDROGEN BONDS) which maintain the shape of the active site are BROKEN
-rate of reaction DECREASES

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13
Q

How increasing pH affects enzyme activity

A

-each enzyme has an optimum pH in which rate of reaction is fastest
-as pH increases towards the OPTIMUM pH, the rate of reaction increases

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14
Q

How does above optimum affect enzyme activity

A

-as pH increases above the optimum, the enzyme becomes DENATURED, as bonds (IONIC), that determine the proteins 3D, tertiary structure are disrupted- substrate no longer fits into the enzymes active site
-rate of reaction FALLS TO ZERO
-substrate no longer fits into the active site
-DENATURATION

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15
Q

How does increasing SUBSTRATE concentration affect enzyme activity

A

-at low substrate concentrations, the reaction is slow, due to the lack of substrate
-as substrate concentrations INCREASE, the rate of reaction increases as:
1. greater chance of enzyme and substrate colliding
2. more enzyme substrate complex formed

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16
Q

how does higher concentrations of SUBSTRATE affect enzyme concentration

A

-rate of reaction becomes constant and increasing concentration has NO FURTHER EFFECT- no more ESC can form
-enzymes are fully employed
-enzyme concentration is now the LIMITING FACTOR
-

17
Q

how increasing ENZYME concentration affects enzyme concentration

A

-enzymes active site can be used again and again so only a small number of enzyme is needed to CATALYSE a lot of substrate, after the reaction has taken place at the enzymes active site, the products are REPELLED and the enzyme is free to accept more substrate
-at low enzyme concentrations, the rate of reaction is low as there are only a few enzymes to react with the substrate
as enzyme concentration increases, the rate of reaction increases LINEARLY- more enzyme molecules available to catalyse the reaction

18
Q

how does higher ENZYME concentrations affect enzyme activity

A

-as enzyme concentrations increase, the rate of reaction increases- greater chance of enzyme and substrate colliding
-at a certain point, the rate of reaction LEVELS OFF, as the SUBSTRATE is a limiting factor.
-provided conditions, eg temperature and pH are suitable, and there is an excess of substrate, rate of reaction will be DIRECTLY PROPORTIONAL to enzyme concentration

19
Q

What is an enzyme inhibitor

A

-Enzyme Inhibitors are molecules that bind to enzymes, stopping it from attaching to the substrate.-This decreases enzyme activity, slowing down or stopping a reaction

20
Q

Describe a COMPETITIVE inhibitor

A

-Inhibitor has a SIMILAR shape to the normal substrate and is able to bind to the ACTIVE SITE

-they DON’T react with the aftive site, but leave after a time WITHOUT product forming
-enzymic reaction is reduced- while the inhibitor is in the active site, NO substrate can enter
-Substrate molecules COMPETE for the active site- rate of reaction DECREASES
-the higher the proportion of competitive inhibitor, the SLOWER the rate of reaction

21
Q

What is the effect of a competitive inhibitor

A

-the degree of inhibation depends on concentration of inhibitor and substrate present as EACH ARE COMPETING FOR THE ACTIVE SITE
-if substrate concentration increases, the effect of the inhibitor DECREASES

22
Q

What are NON-COMPETITIVE inhibitors

A

Molecules that bind to some part of the enzyme other than the active site

23
Q

Describe NON- COMPETITIVE inhibitors

A

-different shape to the normal substrate
-change the shape of the active site- no longer allow binding of the substrate
-some substrate may reach the active site BEFORE the inhibitor- rate of reaction is REDUCED
-they leave their binding sites, but substrate molecules do not compete for these- GREATER INHIBITORY EFFECT

24
Q

What is the effect of the NON COMPETITIVE inhibitor

A

-substrate and inhibitor are NOT COMPETING for the same site- therefore an increase in substrate concentration does not decrease the effect of the inhibitor

25
Q

Explain the importance of enzymes with 2 active sites

A

ALLOSTERIC ENZYMES
-important in regulation of enzyme activity through negative feedback, eg when an enough product has been produced by a cell during a reaction, the molecule will attach to the second active site, act as a NON COMPETITIVE inhibitor- Cease enzyme activity

26
Q

how can inhibitors be irreverible

A

-can be REVERSIBLE- when they are removed, the enzyme can work as normal
-can be IRREVERSIBLE- their effects can’t be reversed- enzyme is permanently damaged
-this occurs through weakening bonds that hold TERTIARY structure of the enzyme (active site),
eg cyanide is a non-reversible inhibitor of the respiratory enzyme, cytochrome oxidase

27
Q

What is a biomarker

A

-biomarker is an enzyme present in the blood which may indicate health or disease- used in monitoring or diagnosing a disease

28
Q

How can enzymes be used in in lung infections

A

-if someone has a lung infection, ELASTASE is released into the WBC- destroy bacterial pathogens as part of the natural immune system
-elastase also breaks down ELASTIN
-elastin- protein component in LUNG TISSUE- elasticity of alveoli, helps lung tissue STRETCH and RECOIL
-elastin isn’t normally broken down- ELASTASE INHIBITOR (A1AT) prevents elastase activity after a lung infection
-Cigarettes cause excess elastase released in lungs- without enough A1AT- can break down ELASTIN in alveoli- CAUSE ELASTASE-INDUCED emphysema (BREATHING ISSUES)

29
Q

Examples of enzymes only present for diagnosis of disease

A

Heart Enzymes
-can enter blood after a heart attack- heart damaged- test can determine if these are present

Liver enzymes
-elevated liver enzymes- due to inflammation/ damaged liver cells

30
Q

Describe examples of how enzymes can be used as Therapeutic Drugs

A

-enzyme inhibitor can be used to slow down/ stop the progression of a disease
have to be:
-specific and only target enzyme involved
-work well in low doses- prevent a build up of inhibitor- can be TOXIC

-Penicillin/ antibiotics- inhibit enzymes involved in making cell walls in bacteria
-Antiviral Drugs- INHIBIT DNA/ RNA polymerases required for replications
-A1AT- prevents elastase activity after infection has cleared
Angiotensin Converting Enzyme- treat high blood pressure. They inhibit the enzyme that causes high blood pressure (constriction of blood vessels). Reducing constriction, reduces blood pressure, which reduces CVD

31
Q

What is Enzyme Immobilisation

A

A technique where the enzymes are attracted to, or retained within an insoluble support materials, eg fibres, gels or plastic beads
-Ensures the enzyme doesn’t contaminate the product

32
Q

Describe a Batch Reactor

A

The enzyme and substrate are dissolved and hence allowed to mix together in a solution
-Isolated enzymes as industrial catalysts need to be removed from the product which is expensive and they cannot be used over again
-The use of enzymes in industry is expensive and the increasing demand for pure enzymes and products led to ENZYME IMMOBILISATION

33
Q

Describe the Column Reactor

A

-Substrate molecules are dissolved in solution flow past enzymes which have been physically attacked or enclosed within some type of INERT support material that doesn’t dissolve in the solvent used
-This allows the continuous flow of substrate across the material holding the enzyme and hence called a CONTINUOUS FLOW COLUMN REACTOR

34
Q

How to speed up the rate of reaction in a column Reactor

A
  1. Smaller beads- enzyme is closer to the surface- more is readily available
  2. Increase Concentration of immobilised enzyme/ substrate- increased chance of reaction
  3. Reduce trickle speed- increase chance of collisions with enzyme
  4. Warm column- increased kinetic energy of substrate- increased chance of collisions between enzyme and substrate
35
Q

What are properties of materials used for enzyme immobilisation

A
  1. must be inert (chemically inactive)
  2. permeable to allow substrate and product to pass through
  3. Impermeable to enzyme
  4. Insoluble in nature- enzyme can be recovered
36
Q

What are the methods of Enzyme Immobilisation

A
  1. Adsorption- enzymes are attached by weak forces to an INERT substance- glass or matrix
  2. Entrapment- enzymes trapped within POLYMERS- alginate beads
  3. Encapsulation (enmeshment)
    Enzymes trapped inside a selectively permeable membrane- nylon
  4. Covalent cross- linking
    Enzymes covalently bonded to a matrix- cellulose, as the result of a chemical reaction
37
Q

What are advantages of immobilised enzymes

A
  1. Enzymes can be reused if confined within a reactor- COST EFFECTIVE
  2. Final product not contaminated with enzymes- no time consuming purification needed- no risk of allergic reactions
  3. Bonding between enzyme and insoluble material helps prevent disruption of tertiary structure of enzyme- shape of active site isn’t easily disrupted by Temperature/ pH
  4. Enzymes are thermostable- remain stable and more effective over a wide range of temperatures
38
Q

Explain Disadvantages

A
  1. associated with slow reactions due to:
  2. diffusion into supporting material is slower/ mixing is less efficient as the continuous flow may reduce opportunity for substrate molecules to bind with enzyme- slower rate of reaction- forming ESC
  3. Not all enzyme available as some active sites are orientated to the supporting material- access to the active site is limited

Biology (22 decks)

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