2.1.4 enzymes

Question 1

What are enzymes

Answer 1

proteins that act as biological catalysts for intra and extracellular reactions to determine structure and function. Therefore they affect metabolism of cells and whole organisms

specific tertiary structure determines shape of active site, complimentary to a specific substrate

Formation of enzyme substrate complex is lower activation energy of metabolic reactions

Question 2

What are the differences between catabolic and anabolic Reactions

Answer 2

catabolic: bonds are broken, breaks molecules apart, exergonic (releases energy), E.g. hydrolysis and cellular respiration
anabolic: bonds are made, molecules are joined, endergonic (take in energy) E.g. protein synthesis and photosynthesis

Question 3

What is the activation energy

Answer 3

Activation energy is the minimum energy required before a reaction can occur.

a reaction will not occur unless the particles involved collide with a certain minimum energy called the activation energy of the reaction

Activation energy is often provided as heat,

an enzyme catalysed reaction lowers the amount of activation energy required to allow a reaction to proceed.

It allows stable molecules to be broken down at a fast enough rate for life processes

and substrate and product level stay the same even after an enzyme catalysing

Question 4

Give an example of an enzyme that catalyse intracellular reactions

Answer 4

Catalase: catalyses decomposition of hydrogen peroxide into water and oxygen

Question 5

Give two examples of enzymes that catalyse extracellular reactions

Answer 5

amylase: carbohydrates catalyses digestion of starch to maltose and saliva
trypsin: pancreatic endopeptidase Catalyses hydrolysis of peptide bonds in small intestine lumen

Question 6

Explain the induced fit model of enzyme action

Answer 6

shape of active site is not directly complimentary to substrate and is flexible

conformational changes enable ES complexes to form when substrate adsorbs

This put strain on substrate bonds, lowering activation energy. Bonds in enzyme-product complexes our week, so products desorbs

Question 7

Explain the lock and key model of enzyme action

Answer 7

Suggests that active site has a rigid shape determined by tertiary structure so it’s only complimentary to 1 substrate. Formation of enzyme substrate complex lower activation energy. Bonds in enzyme product complex a week so product desorbs

Question 8

Name five factors that affect the rate of enzyme controlled reactions

Answer 8

enzyme concentration

substrate concentration

concentration of inhibitors

PH

Temperature

Question 9

How does substrate concentration affect rate of reaction

Answer 9

Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration. The rate levels off when maximum number of enzyme substrate complexes form at any given time

Question 10

effects of temperature: What happens when you increase the temperature

Answer 10

More random collisions between enzyme and substrate occur, at a greater force. More enzyme substrate complexes are formed and more products are formed

Question 11

effects of temperature: What happens during the optimum temperature

Answer 11

Maximum rate of successful collisions between enzyme and substrate occurs, maximum rate of enzyme substrate complex formation and the maximum rate of reaction occurs

Question 12

effects of temperature: What happens if you increase the temperature above the optimum

Answer 12

molecule starts to vibrate, a strain is put on bonds in the molecules, weaker hydrogen and ionic bonds are broken, tertiary structure changes, active site is affected, enzyme denatured and the enzyme substrate complexes Can no longer be formed and this is irreversible

Question 13

How does enzyme concentration affect rate of reaction

Answer 13

Given that substrate is in excess, rate increases proportionally to enzyme concentration. rate levels off when maximum number of enzyme substrate complex is formed at any given time

Question 14

How does temperature affect the rate of enzyme controlled reactions

Answer 14

rate increases as kinetic energy increases and peaks at optimum temperature. Above optimum, ionic and hydrogen bonds break and active site no longer is complimentary to substrate (denature)

Question 15

ph: What are buffers

Answer 15

To resist changes to PH, buffers are used. Buffers are certain chemicals that can donate or except protons and they are therefore able to maintain a pH within fairly narrow limits. Hydrogen carbonate ions act as an important buffer in biological systems

Question 16

What is the temperature, coefficient

Answer 16

Q10 measures the change in rate of reaction per 10°C temperature increases

Q10 = R2 divided by R1 ( where r represents rate)

Question 17

How does PH affect rate of reaction

Answer 17

enzymes have a narrow optimum pH range. Outside range, hydrogen ions interact with hydrogen bonds and ionic bonds in 3 degree structure = denature

Question 18

How do competitive inhibitors work

Answer 18

bind to active site since they have similar shape to substrate. Temporarily prevent enzyme substrate complexes from forming until released. Increasing substrate concentration decreases their affect

Question 19

How do non-competitive inhibitors work

Answer 19

bind at allosteric binding site. Trigger confirmational change of active site. Increasing substrate concentration has no impact on their affect

Question 20

What is endproduct inhibition

Answer 20

One of the products of a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathway. Prevents further formation of products

Question 21

What are irreversible inhibitors

Answer 21

permanently prevent formation of enzyme substrate complexes

Heavy metal ions e.g. mercury, silver cause disulphide bonds in tertiary structure to break.

Find the enzymes by strong covalent bonds

Question 22

What are reversible inhibitors

Answer 22

Maybe competitive or non-competitive. bind to enzyme temporarily e.g. by hydrogen bonds and enzyme substrate complexes can form after the inhibitor is released

Question 23

Define metabolic poison

Answer 23

Substance that damages cells by interfering with metabolic reactions. Usually an inhibitor

Question 24

Give some examples of metabolic poisons

Answer 24

respiratory inhibitors include

cyanide: non-competitive, irreversible, inhibits cytochrome c oxidase
arsenic: competitive, inhibits pyruvate dehydrogenase

Question 25

How do some medicinal drugs act as inhibitors

Answer 25

penicillin: non-competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross links in bacterial cell wall

Question 26

Give examples of extracellular digestion

Answer 26

saprophyte digestion: saprophytes like fungi digest what they sit on, they secrete digestive enzymes onto the food source and the food source is broken down into its monomers e.g. amino acids.

Humans: food taken into organism, passes through digestive system, enzymes released out of cells to break food down to his monomers and passes into cells and is used

Question 27

Give examples of intracellular digestion

Answer 27

amoeba

Food taken into sell and digestion takes place within the cell

Question 28

What are in active pre-cursors in metabolic pathways

Answer 28

to prevent damage to cells, Some enzymes in metabolic pathways are synthesised as inactive precursors. One part of the precursor acts and inhibitor. Enzyme substrate complexes formed when it is removed

Question 29

What are cofactors

Answer 29

non-protein compounds required for enzyme activity e.g. coenzymes, inorganic cofactors, prosthetic groups

Question 30

What are coenzymes

Answer 30

Organic cofactors. Do not bind permanently. Often transport molecules or electrons between enzymes

Frequently derived from water-soluble vitamins

Question 31

What are inorganic cofactors

Answer 31

Facilitate temporary binding between substrate and enzyme. Often metal ions

Question 32

What are Prosthetic groups

Answer 32

Tightly bound cofactors act as a permanent part of enzymes binding site

Question 33

ppq: To calculate the rate of starch breakdown, the student measured the concentration of the breakdown product. Stay the other variable the student needed to know in order to calculate the rate of this reaction

Answer 33

time taken

Question 34

ppq: explain why it is important that pH is kept constant during an experiment

Answer 34

So charges in active site do not change, so hydrogen bonds are unaffected. So tertiary structure is on altered and so the enzymes do not denature

Question 35

ppq: Suggest why the lock and key and induced fit explanations are termed models

Answer 35

To make the process easier to understand and because it is a visual representation

Question 36

ppq: Suggest why most scientists now except the induced fit model rather than the lock and key model

Answer 36

Be induced fit model is supported by more evidence and the evidence links more closely to the induced fit model

Question 37

ppq: Certain parts of the enzyme molecule from the Antarctic fish are more flexible than the equivalent parts of the molecule from the non-Antarctic fish. Suggest how a more flexible structure might help this enzyme work faster at lower temperatures

Answer 37

It is easier for the substrate to enter the active site and more bonds can form between the active site and substrate.

Question 38

ppq: Enzymes are proteins. The enzymes in Antarctic fish have a different structure from those found in non-Antarctic fish. suggest how the structure of the enzymes may differ in Antarctic and non antarctic fish

Answer 38

They have different amino acids and different structures e.g. different tertiary structures

Question 39

ppq: If species of Antarctic fish were to become extinct, their unique enzymes would be lost. Suggest why the loss of these enzymes might be undesirable

Answer 39

The enzyme could have potential future application e.g. medical use

Question 40

ppq: Enzymes are biological catalysts, explain the term biological catalyst

Answer 40

Enzymes are used in metabolism and they speed up metabolic reactions

Question 41

ppq: Explain the effect of increasing the concentration of substrate on the rate of reaction without an inhibitor

Answer 41

More successful collisions between substrate and active site, at high concentration all active sites occupied and cannot work any quicker

Question 42

ppq: Explain the effect of increasing the concentration of substrate on the rate of reaction with and inhibitor

Answer 42

Inhibitor can bind to active site and occupies it for a short time. Substrate can’t access the active site and more substrate reduces chance of an inhibitor getting in

Question 43

ppq: Describe how an enzyme such as pepsin breaks down a substrate

Answer 43

The substrate is nearly complimentary to the active site. The substrate enters the active site on the enzyme and induced fit occurs. This forms the enzyme substrate complex which destabilising of bonds then forms the enzyme product complex. And the products leave active site

Question 44

ppq: Explain why different enzymes are involved in each stage of the digestion process

Answer 44

enzymes are specific and the substrate have different shapes. Active site and substrate are complimentary so that the substrate will fit and form enzyme substrate complexes = induced fit occurs

Question 45

ppq: Explain what might happen to an enzyme’s activity if the gene encoding its production was altered by mutation

Answer 45

The specific substrate might not be able to bind with the active site as they don’t have a complimentary shape anymore because the mutation could potentially damage the shape of the active site

Question 46

ppq: why is the enzyme amylase described as being extracellular

Answer 46

Works outside cells

Question 47

PPQ: Suggest how a student could produce a desired concentration of a solution from a stock solution

Answer 47

volume of stock solution = required concentration X final volume needed divided by concentration of stock solution

volume of distilled water = Final volume needed - Volume of stock solution