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enzymes Flashcards

1
Q

What is the Vmax?

A

Maximum initial velocity or rate of an enzyme-catalysed reaction

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2
Q

What kind of proteins are enzymes?

A

Globular

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3
Q

What is an enzyme?

A

A protein that acts as a catalyst in biological reactions

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4
Q

What is the relationship between the shape of the active site and the shape of the substrate?

A

They have complementary shapes

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5
Q

Give an example of an intracellular enzyme

A

Catalase

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6
Q

Give an example of an extracellular enzyme

A

Amylase

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7
Q

Define metabolic reactions

A

The reactions occurring inside the body at any given time

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8
Q

Where are enzymes produced?

A

On the ribosomes of a cell

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9
Q

How do enzymes speed up the rate of reaction?

A

They reduce the activation energy of a reaction

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10
Q

What are the two models for enzyme action?

A

The lock and key
and

The induced fit

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11
Q

Lock and key hypothesis

A

Shape of active site caused by sequence of amino acids (specific tertiary structure - 3D)

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12
Q

Induced fit hypothesis

A

Explains how activation energy is reduced
Active site is not perfectly complementary but when substrate moves into active site, interferes with the bonds holding active site together
Induces changes in 3’ structure to strengthen binding and weaken bonds in substrate
Active site alters to give perfect fit. Changed shape of active site —> bonds in substrate easier to make or break (reduces activation energy)

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13
Q

What does the lock and key model of enzyme action suggest about the active site?

A

The active site is ridgid

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14
Q

What does the induced fit model suggest about the active site?

A

The active site has a degree of flexibility

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15
Q

Outline how an enzyme causes a reaction to occur

A
  • the substrate and active site collide, forming an enzyme-substrate complex
  • the active site puts pressure on the bonds of the substrate
  • this causes them to break, forming an enzyme-product complex
  • the products are released and the enzyme reused
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16
Q

How do enzymes reduce the activation energy of a reaction?

A
  • They put pressure on the bonds in a substrate

- They bring atom groups close enough to react

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17
Q

Define metabolic pathway

A

A series of enzyme reactions whereby the product becomes the substrate of the next

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18
Q

What are anabolic reactions?

A

Reactions that build molecules

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19
Q

What are catabolic reactions?

A

Reactions that break bonds/break up molecules

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20
Q

How do R-groups of the enzyme help to break apart substrates?

A

The R-groups interact with the substrate, forming temporary bonds with the substrate which puts pressure on the bonds in the substrate bonds

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21
Q

Outline how starch is broken down in the body

A
  • starch polymers are partially broken down into maltose by amylase
  • amylase is released into the mouth via the salivary glands
  • amylase is released into the small intestine via the pancreas
  • maltose is then broken down into glucose by maltase in the small intestine
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22
Q

Outline how protein is broken down in the body

A
  • trypsin is produced by the pancreas
  • trypsin breaks proteins into smaller peptides in the small intestine

-other proteases then break the small peptides into amino acids

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23
Q

What is the active site?

A

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

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24
Q

Why are enzymes important to life?

A
  • life processes require chemical reactions
  • the reactions need to happen quickly
  • enzymes allow these reactions to occur quickly without high pressure/temperature
  • allow organisms to get the nutrients needed to function i.e through digestion
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25
What is the substrate of catalase?
Hydrogen peroxide
26
What are the products of the reaction of catalase?
2H2O and O2
27
What is the substrate of amylase
Starch
28
What are the products of the reaction of amylase?
Maltose
29
What is the substrate of trypsin?
Protein
30
What are the products of the reaction of trypsin?
polypeptides
31
How are metabolic pathways controlled?
- By allosteric enzymes whereby the end product of the pathway binds to the allosteric site - once the end product levels fall, the inhibition is lifted
32
Give an example of control of a metabolic pathway
In respiration the enzyme PFK is inhibited by ATP and activated by ADP
33
What is the approximate optimum temperature for most enzymes in the human body?
40 degrees
34
What happens to the rate of reaction during the exponential phase?
-rate of reaction doubles every time temperature increases by 10 degrees
35
Why does the rate of reaction increase up to 60 degrees, as temperature increases?
- as temperature increases, kinetic energy of particles increases - this means particles move faster and collide more frequently -increasing rate of reaction
36
Why does the rate of reaction decrease beyond 60 degrees?
- hydrogen bonds and ionic bonds break - loss of tertiary structure - change in shape of the active site - substrate no longer fits - decreasing rate of reaction
37
Across how many pH units do enzymes work across?
4
38
Describe the rate of reaction graph for pH
symmetrical curve -optimum pH - range of pH, 2 pH units either side of optimum - rate of reaction falls to 0 beyond pH range
39
What is lost in denaturation?
tertiary structure/ shape of active site
40
What occurs in denaturation?
- active site changes shapes - shape no longer complementary to the substrate - substrate can no longer fit into the active site - enzyme no longer acts as a catalyst
41
How does an increase in substrate concentration increase rate of reaction?
- higher chance of collisions - limited by enzyme concentration - higher chance of successful collisions - more substrate-enzyme complexes can be formed
42
Is the change in shape of active site due to pH reversible?
yes
43
Which 5 factors affect rate of enzyme controlled reaction?
temperature -pH - substrate concentration - enzyme concentration - enzyme inhibitors
44
What are the two main types of inhibitors?
- competitive | - non-competitive
45
What is the effect of an increase in enzyme concentration on the rate of reaction?
- it increases the rate of reaction | - up to a point where rate of reaction is limited by substrate concentration
46
Why does an increase in enzyme concentration increase rate of reaction?
- there are more active sites - higher chance of a successful collision -to form an enzyme-substrate complex
47
How do competitive inhibitors reduce rate of reaction?
- compete with the substrate for the active site | - sit in the active site and block the substrate from entering the active site
48
What is the relationship between the shape of the inhibitor for a particular reaction and it's substrate?
They have SIMILAR shapes
49
Are competitive inhibitors reversible
yes
50
Why are competitive inhibitors reversible
They do not cause the enzyme to lose its shape
51
What is the effect of a greater concentration of a competitive inhibitor on the rate of reaction?
It decreases the rate of reaction
52
Why does a greater concentration of a competitive inhibitor decrease the rate of reaction?
a greater concentration of inhibitor relative to substrate means: -the probability of a collision between an enzyme and an inhibitor is greater than the probability of a collision between an enzyme and a substrate
53
Give a difference between competitive and non-competitive inhibitors
-non-competitive do not compete with the substrate for the active site whilst competitive do or -non-competitive inhibitors bind to allosteric site whilst competitive do not
54
What are the two types of non-competitive inhibitor?
reversible | -irreversible
55
Give an example of a reversible non-competitive inhibitor
Metabolic poisons, such as cynanide
56
How does cyanide act as a poison
- acts on cytochromeoxidase (an enzyme involved in respiration) - inhibits respiration -no ATP therefore is produced so death occurs
57
What reaction is cytochromeoxidase involved in?
Aerobic respiration
58
How do non-competitive inhibitors inhibit the action of enzymes?
-they bind to the allosteric site | causing the active site to change shape so the substrate no longer fits
59
Give an example of an irreversible non-competitive inhibitor
Heavy metals, such as mercury
60
How does mercury act as an irreversible non-competitive inhibitor?
breaks covalent bonds in the enzyme -loss of tertiary and quaternary structures - loss of shape of active site - substrate can no longer fit so the enzyme loses its function
61
Define cofactors
non-protein components required for the effective functioning of an enzyme
62
What are the 3 types of cofactors?
inorganic ion cofactors -coenzymes -prosthetic groups
63
What are coenzymes?
Organic molecules, mostly derived from B vitamins, which bind temporarily to an enzyme
64
Give an example of a coenzyme
NAD
65
What is NAD synthesised from?
Vitamin B3
66
What process is NAD used in?
Aerobic respiration
67
What is coenzyme A used for?
Breakdown of fatty acids and carbohydrates (in respiration)
68
Do cofactors bind temporarily or permanently to an enzyme?
temporarily
69
Define inorganic ion cofactor
Inorganic ions obtained from the diet which bind temporarily to the enzyme
70
Give an example of an inorganic cofactor
Cl- ion for amylase
71
How does Cl- act as a cofactor for amylase?
Temporarily binds with amylase active site Modifies the active site shape Allowing the starch (substrate) to fit into the active site and the enzyme to work
72
Which enzyme requires a zinc ion as a prosthetic group?
Carbonic anhydrase
73
Define prosthetic group
Organic or metal ions which bind permanently to the enzyme
74
What is the function of carbonic anhydrase?
Enables CO2 to be quickly dissolved in the blood for transporation
75
Which enzyme is a chloride ion an essential cofactor for?
amylase
76
What is the difference between a coenzyme and an ion cofactor?
A coenzyme is an organic molecule whereas ion cofactors are inorganic ions
77
Give 2 examples of competitive inhibitors
Aspirin and statins

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