2.1.4

Question 1

Why are enzymes needed?

Answer 1

For chemical reactions to occur at a fast rate without the need for high temperatures and pressured which living cells cannot cope with

Question 2

What are enzymes?

Answer 2

Biological catalysts - globular proteins that interact with substrate molecules (catalyse) without being used up

Question 3

What are anabolic enzymes?

Answer 3

Enzymes that catalyse “building up” reactions - such as synthesis of cellulose or assembly of cells, tissues, organs and then the whole organism

Question 4

What are catabolic enzymes?

Answer 4

Enzymes that help catalyse the “breaking down” reactions

Question 5

What is metabolism?

Answer 5

Sum of all the different reactions and reaction pathways happening in an organism - can only happen as a result of the control and order imposed by enzymes

Question 6

What factors have an effect on the rate of a chemical reaction?

Answer 6

Temperature, pressure, ph

Question 7

What is Vmax?

Answer 7

Maximum rate of an enzyme catalysed reaction

Question 8

Positive collision theory?

Answer 8

Molecules in a solution will move and collide randomly - for a reaction to occur, they must collide with the activation energy and in the right orientation ; with higher temperature (more KE) and higher pressure (less space) there are more frequent collisions and therefore more frequent successful collisions - increase rate of reaction

Question 9

Specificity of an enzyme?

Answer 9

Each enzyme catalysed one specific biochemical reaction of which there are thousands in any cell

Question 10

Activation energy?

Answer 10

Minimum amount of energy required to catalyse a reaction - sometimes energy needed is so large it prevents the reaction from happening under normal conditions ; enzymes help molecules collide successfully by providing alternative reaction pathway with a lower activation energy

Question 11

Lock and Key Hypothesis

Answer 11

Area within tertiary structure of enzyme has shape complementary to a specific substrate molecule (active site) - only a specific substrate will fit into the active site (this is lock and key hypothesis). When substrate is bound it forms an enzyme-substrate complex which reacts to form an enzyme-produce complex ; products are released, leaving the enzyme unchanged and able to take part in more reactions. R groups in active site of enzyme (protein) interact with substrate forming temporary bonds ; these put strain on the bonds within substrate which helps reaction along too

Question 12

Induced fit hypothesis

Answer 12

Active site of enzyme changes shape slightly as substrate enters ; initial interaction between enzyme and substrate is weak but these rapidly induce changes to enzyme’s tertiary structure that strengthens the binding and puts strain on the substrate molecule (weakening bonds in substrate and thus lowering activation energy) ; changes shape TO BECOME COMPLEMENTARY ; allows for substrate to bind

Question 13

What are intracellular enzymes?

Answer 13

Enzymes that act within cells - synthesis of polymers from monomers requires enzymes

Question 14

How is hydrogen peroxide removed?

Answer 14

It is toxic and can damage DNA - many metabolic pathways find it toxic and therefore the intracellular enzyme catalase breaks down H2O2 into oxygen and water - preventing accumulation of hydrogen peroxide (found in animals and plants7

Question 15

Extracellular enzymes

Answer 15

Intracellular reactions all need raw materials as substrates - these are supplied by nutrients in our diet and environment ; these polymers (proteins for example) need to be broken down and cannot directly enter cells through the membrane. In digestion enzymes are released from cells to break down the large nutrients into smaller molecules - these are extracellular and work outside cells that made them (in fungi outside the body)

Question 16

How do single celled organisms use extracellular enzymes?

Answer 16

Bacteria and yeast release enzymes which break down larger molecules such as proteins and the smaller molecules produced are absorbed into the cell

Question 17

How do multicellular organisms use extracellular enzymes?

Answer 17

Nutrients are digested so they can be absorbed into bloodstream and they are transported around body to be used as substrates in cellular reactions (amylase and trypsin - milk in humans)

Question 18

Why are two different enzymes needed for digestion of starch?

Answer 18

Each enzyme only catalysed one specific reaction - 2 steps needed

Question 19

How is starch broken down?

Answer 19

1) Amylase breaks down starch into disaccharide maltose - released in the saliva and by the pancreas
2) Maltose then broken down into glucose which is a monosaccharide - enzyme here is maltase (small intestine)
GLUCOSE SMALL ENOUGH TO BE ABSORBED BY LINING OF DIGESTIVE SYSTEM AND THEN BLOODSTREAM

Question 20

How are proteins digested?

Answer 20

Trypsin is a protease (enzyme that catalysed digestion of protein into smaller peptides - then into amino acids) ; trypsin produced by pancreas and released in small intestine and then amino acids which are ultimately produced are absorbed by the cell lining into bloodstream

Question 21

What must be measured to investigate factors affecting enzyme action?

Answer 21

Rate of reaction (affected by temperature and ph which causes changes to tertiary structure/active site)

Question 22

How does temperature affect rate of reaction?

Answer 22

Increase KE - move faster - collide more frequently - more frequent successful collisions between substrate and enzyme - increase in rate of reaction

Question 23

What is the temperature coefficient?

Answer 23

Q10 - measure of how much rate of reaction increases with a 10^ rise in temperature (for enzyme controlled reactions this is usually taken as 2 - which means rate of reaction DOUBLES)

Question 24

Denaturation from temperature?

Answer 24

Enzymes are proteins - higher temperatures means the bonds vibrate more until bonds strain and break ; causes change in tertiary structure and enzyme has changed shape (denatured) - active site is no longer complementary to substrate and it can no longer fit into the active site

Question 25

What is optimum temperature?

Answer 25

Temperature at which there his highest rate of activity (human temperature about 40 degrees) meanwhile thermophilic bacteria have it at about 70 degrees and psychrophilic < 5 degrees

Question 26

Why is decrease in rate of reaction so rapid after optimum?

Answer 26

Slight change in shape causes denaturation - happens to all enzyme molecules at same temperature therefore loss of activity is abrupt and now Q10 no longer apples as enzymes have denatured
Below optimum temperature decrease is less rapid because they have not denatured - just less KE

Question 27

Adaptations to extreme cold (enzymes)

Answer 27

Deep oceans/polar regions ; enzymes need to be adapted to the cold therefore they have more flexible structures (particularly at the active site) ; making them less stable than enzymes at higher temperatures with small temperature changes denature glucose them

Question 28

Adaptations to heat

Answer 28

Very hot environments - enzymes are more stable due to increased number of hydrogen bonds in tertiary structure ; shape and structure of active site are more resistant to change as temperature rises

Question 29

What holds the protein in its tertiary structure?

Answer 29

Hydrogen bonds and disulfide bridges/ interactions between R groups hold them in a precise 3D shape (due to polarity and charge on amino acid R groups in primary structure)

Question 30

What does change in ph mean?

Answer 30

More H+ ions in low acidic ph

Less H+ ions in high alkaline ph

Question 31

What is the optimum ph?

Answer 31

Active site will only be in the right shape at a certain H+ ion concentration - structure of enzyme and active site changes with change in pH BUT THIS IS REVERSIBLE AS IF PH RETURNS TO OPTIMUM THEN PROTEIN RETURNS TO NORMAL SHAPE AND CATALYSES REACTIONS - CALLED RENATURATION

Question 32

What if PH changes more significantly?

Answer 32

Change to the structure of the enzyme is irreversibly altered and active site is no longer complementary to substrate (now denatured)

Question 33

How do H+ ions affect enzyme?

Answer 33

They attract polar and charged R-groups : changing concentration of H+ ions changes degree of this interaction ; interaction of r groups with H+ ions also affects interaction of R groups with each other
MORE H+ = less R groups interacting with each other ; bonds break and shape of enzyme changes
Few H+ ions = more R group interaction which means enzyme will only function within narrow ph range

Question 34

Increased substrate concentration?

Answer 34

More substrate molecules in a particular area which means higher collision rate with active sites of enzymes and the formation of more enzyme substrate complexes (rate of reaction increases)

Question 35

Increase concentration of enzyme?

Answer 35

Increase number of available active sites - more enzyme substrate complexes at a faster rate

Question 36

Where does rate of reaction increase up to?

Answer 36

V max - at this point all active sites are occupied by substrate particles and no more complexes formed until products are released from active sites ; only way to increase would be to add more enzyme or increase temperature (limiting factors)

Question 37

How would more enzymes affect V max?

Answer 37

Concentration of enzyme increased more active sites available therefore reaction rate can rise towards higher Vmax - concentration of substrate becomes limiting factor and if this is increased it will allow reaction rate to rise to a new Vmax

Question 38

Why is it important that reactions do not happen too fast?

Answer 38

To prevent the build up of excess products - multi step metabolic pathways need to be closely regulated

Question 39

Enzymes can be activated with

Answer 39

Cofactors

Question 40

Enzymes can be inactived with

Answer 40

Inhibitors

Question 41

What are inhibitors?

Answer 41

Molecules that prevent enzymes from carrying out their normal function of catalysis

Question 42

Two types of inhibitors?

Answer 42

Competitive and non-competitive

Question 43

How does competitive inhibition work?

Answer 43

Molecule that has similar shape to substrate (complementary to enzyme) can fit into active site - blocks substrate from entering active site and thus stops the enzyme catalysing the reaction (inhibited) - substrate and inhibitor molecules will compete with each other to bind to the active sites which reduces the number of bound substrate molecules in a given time, slowing down the rate of reaction - therefore they are COMPETITIVE

Question 44

Reversible inhibitors?

Answer 44

Most competitive inhibitors only bind temporarily to their active site so they are reversible (no permanent effect) - ASPIRIN IS A COMPETITIVE INHIBITOR WHICH IS IRREVERSIBLE

Question 45

What does a competitive inhibitor do to rate of reaction?

Answer 45

Reduces rate of reaction for a given concentration of a substrate ; but it does not change the Vmax of the enzyme it inhibits ; if the substrate concentration is increased enough, there will be so much more substrate than inhibitor that the original Vmax can be reached

Question 46

Examples of competitive inhibitors?

Answer 46

Statins are competitive inhibitors of an enzyme used in the synthesis of cholesterol and aspiring irreversible binds to active site of COX enzymes

Question 47

Non-competitive inhibition?

Answer 47

Inhibitor binds to enzyme at a location other than active site (ALLOSTERIC SITE) ; binding causes tertiary structure changes shape of enzyme and active site which means it is no longer complementary and cannot bind to active site (now inhibited) - does not compete with substrate for active site

Question 48

Effect of non-competitive inhibitors on rate of reaction?

Answer 48

Increase concentration of enzyme/substrate will not overcome the effects of a non-competitive inhibitor (permanent) BUT increase the concentration of inhibitor will increase the number of unavailable active sites (reducing rate of reaction)

Question 49

Irreversible/reversible inhibitors

Answer 49

Irreversible inhibited cannot be removed from the part of the enzyme they are attached to (often toxic)

Question 50

What is end product inhibition?

Answer 50

Product of a reaction acts as an inhibitor to the enzyme that produces it - negative feedback control mechanism and excess products are not made/wasted IT IS NON-COMPETITIVE REVERSIBLE INHIBITION

Question 51

What is PFK?

Answer 51

Enzyme that catalyse the initial breakdown of glucose (to make ATP) - ATP non-competitively inhibits the enzyme to regulate its own production

Question 52

When ATP levels are high?

Answer 52

More atp binds to the allosteric site preventing addition of second phosphate to glucose (to break it down) - therefore it is not broken down and ATP produced at same rate

Question 53

If ATP is used up?

Answer 53

Less binds to PFK and enzyme is able to catalyse the addition of a second phosphate to glucose - respiration resumes meaning more ATP produced

Question 54

What are cofactors?

Answer 54

Non-protein molecules which help in activating the enzyme and carry out their function as a biological catalyst - COENZYME IS AN ORGANIC COFACTORS

Question 55

How are inorganic cofactors obtained?

Answer 55

Via diet as minerals - iron calcium chloride and zinc ; amylase for example needs a chloride ion for the shape of its active site

Question 56

Where do coenzymes come from?

Answer 56

Vitamins

Question 57

What are prosthetic groups?

Answer 57

They are cofactors - required by certain enzymes to carry out their catalytic functions ; prosthetic groups are tightly wound and form a permanent feature of the protein - Zn2+ ions form an important part of the structure of carbonic anhydrase (needed for metabolism of CO2).

Question 58

What is precursor activation?

Answer 58

Many enzymes are produced in an inactive form (inactive precursor enzymes) - particularly those enzymes that could cause damage to the cells they are acting upon

Question 59

How do precursor enzymes work?

Answer 59

Need to undergo a change in shape of tertiary structure - particularly to active site to be activated (ONLY ACHIEVED BY ADDITION OF A COFACTOR)

Question 60

Before the cofactors is added the precursor protein is called

Answer 60

Apoenzyme

Question 61

After the precursor protein has been activated (by cofactor) it is called

Answer 61

Haloenzyme

Question 62

What else can activate a precursor enzyme?

Answer 62

Other enzymes such as protease cleave certain bonds in the molecules - sometimes change in conditions like ph and temperature could cause change in tertiary structure (these are called ZYMOGENS or Proenzymes)