Chapter 4 - Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that interact with substrate molecules to facilitate chemical reactions, without being used up

Question 2

What are anabolic reactions?

Answer 2

Chemical reactions required for growth (building up) -catalysed by enzymes - energy is required

Question 3

What are catabolic reactions?

Answer 3

Chemical reactions that involve the breaking down of large organic molecules - this process releases energy

Question 4

Metabolism

Answer 4

The sum of all the different reactions and reaction pathways happening in a cell or an organism

Question 5

What is Vmax?

Answer 5

Is the maximum initial velocity or rate at which the enzyme catalysed a reaction

Happens when all active sites are saturated by substrates

Question 6

What is the specificity of an enzyme ?

Answer 6

The ability of an enzyme to bind with a specific substrate or catalyse a specific set of chemical reactions

Question 7

Activation energy

Answer 7

The minimum amount of energy required to start a reaction

Question 8

The two enzyme hypothesis :

Answer 8

The lock and key hypothesis

Induced fit hypothesis

Question 9

Lock and key hypothesis

Answer 9

• an area within the tertiary structure of the enzyme has a complementary shape to the substrate which is called the active site
• the enzyme and substrate bind to form an enzyme-substrate complex
• the substrate is held so that the right atom groups are close enough to react
• r groups in the active site interact with the substrate forming temporary bonds
• these put strain on the bonds within the substrate - helps réaction along
• enzyme-product complex is formed
• products released

Question 10

Induced fit hypothesis

Answer 10

• active site slightly changes shape as substrate enters it
• initial reaction between the enzyme and substrate is weak, however these interactions cause changes in the enzymes tertiary structure that strengthen binding , putting strain on the substrates molecule
• this can weaken bonds in the substrate - lowering the activation energy
• forms enzyme-product complex
• products leave the active site

Question 11

What are intracellulaire enzymes?

Answer 11

Enzymes that act within cells

E.g catalase - breaks down hydrogen peroxide which is a toxic product of many metabolic pathways

Question 12

What are extracellular enzymes ?

Answer 12

Enzymes that work outside the cell that made them

• enzymes are released to break down polymer nutrients into smaller molecules in the process of digestion, so they can become able to pass through the cell surface membrane (can be absorbed in bloodstream) to provide cells with components necessary for survival and growth

Amylase , trypsin

Question 13

Why is amylase and maltase needed to digest starch

Answer 13

• Amylase partially breaks down starch polymers into maltose
  Amylase is produced by salivary glands and pancreas - released as salivai and pancreatic juice (in small intestine)
• maltase is then used to break down maltose into glucose
• maltase is present in the small intestine

Question 14

What is protease

Answer 14

Type of enzyme that catalysés the digestion of proteins into smaller peptides, further broken down into amino acids

Question 15

The digestion of protein

Answer 15

• trypsin is produces in the pancreas and released with pancreatic into small intestine juice
• it acts on proteins , breaking it down
• amino acids are absorbed by cells lining the digestive system
• then absorbed into bloodstream

Question 16

Temperature affecting the enzyme rate of reaction

Answer 16

- increase temperature 
= more kinetic energy 
= more frequent collisions 
= more successful collisions 
- increase in rate of reaction

Question 17

Température coefficient q10

Answer 17

Measure of how much the ror increases with a 10C rise in temperature

Is usually 2

Question 18

Dénaturation from temperature

Answer 18

• bonds holding the protein together vibrate
• vibrations increase until the bonds strain and then break
• results in a change in the tertiary structure
• changes shape of active site - no longer function as a catalyst
• no longer complementary
• denatured

Question 19

Optimum temperature

Answer 19

Temperature at which enzymes has the highest rate of activity

40c in human body

Question 20

Temperature extremes

Cold environments
Thermophiles

Answer 20

Cold

• enzymes have more flexible structures
• less stable
• smaller temperature changes will denature

Thermophiles
- more stable
because of hydrogen bonds and sulphur bridges in tertiary structure
- more resistance to change as the temperature rises

Question 21

How does ph affect enzymes

Answer 21

• hydrogen ions interact with polar and charged rgroups, changing ph changes this interaction.
• affects hydrogen and ionic bonds causing bonds to break and the shape of the enzyme to change
• alters active site
• RENATURATION = ph returns to optimum and resumes its normal shape
• DENATURED = ph changes significantly

Question 22

Substrate and enzyme concentration

Answer 22

When substrate / enzyme concentration is increased

• higher collision rate with active site
• formation of more enzyme-substrate complexes
• reaction increases until Vmax
• at this point all of the active sites are occupied by substrate particles
• no more enzyme-substrate particles can be formed until products are release from active site

The concentration of … becomes the limiting factor

Question 23

Denatured

Answer 23

R group interactions are interrupted

Change in tertiary structure

Change in 3D shape of active site

No longer complementary

Question 24

What are inhibitors

Answer 24

Molecules that prevent enzymes from carrying out their function of catalysis - slow them down

Question 25

Competitive inhibition

Answer 25

- molecule with a similar shape to the substrate fits into the active site - this prevents the enzyme from binding to a substrate and forming an enzyme substrate complex - the enzyme can not carry out its function - molecule and substrate will compete to bind to the active site , and catalyse the reaction - reduces the number of enzyme substrate complexes at any given time, therefore slows down the rate of reaction

Question 26

Effects on rate of reaction - competitive inhibitors

Answer 26

Reduces the rate of reaction | Does not change the Vmax

Question 27

Examples of competitive inhibitors

Answer 27

Statins Used to help people reduce blood cholesterol concentration Aspirin Irreversibly inhibits the active site of COX, preventing the synthesis of chemicals responsible for pain and fever

Question 28

Non competitive inhibitors

Answer 28

- the inhibitor binds to the enzyme at the ALLOSTERIC site - the binding causes a change in the tertiary structure of the enzyme , causing active site to change - active site is no longer complementary - can’t carry out its function

Question 29

Effect of rates or reaction - non competitive

Answer 29

Increasing enzyme concentration will not overcome the effect Adding more inhibitor will further decreases the active sites

Question 30

WHAt is End product inhibition

Answer 30

final Product of the metabolic pathway acts as the inhibitor to an enzyme that acts previously in the pathway - negative feedback

Question 31

Example of end product inhibition

Answer 31

In the breakdown of glucose, ATP regulates its own production. This is because the two phosphate groups that results in initial breakdown of glucose is catalysed by the enzyme PFK, which is competitively inhibited by ATP - When ATP levels are high, more ATP binds to the PFK, preventing the addition of the second phosphate - Glucose is not broken down, and ATP is neither made -ATP is used, PFK catalyses the addition of the second phosphate leading to more production of ATP

Question 32

What are cofactors

Answer 32

Non protein components necessary for the effective functioning of an enzyme , help transfer atoms and molecules between the reaction pathway and can form part of the active site to help bind together enzyme and substrate

Question 33

What is the role of cofactors

Answer 33

They work by helping the enzyme and substrate bind together They don’t directly participate

Question 34

What is the role of coenzymes

Answer 34

They participate in the reaction and are changed by it Carriers that move chemical groups between different enzymes

Question 35

what is a Prosthetic group

Answer 35

Prosthetic groups are cofactors that are tightly bound to and enzyme to form a permanent feature of the protein

Question 36

What is precursor activation used for

Answer 36

Enzymes are synthesised as inactive precursors to prevent them from causing damage to cells / whose actions need to be controlled and only activated under certain conditions - protease To be activated they need to undergo a chemical change Achieved by an additions of a cofactors

Question 37

Adding a cofactors to a precursor protein

Answer 37

Apoenzyme inactive + cofactors activator —> haloenzyme active

Question 38

Other ways precursor enzymes can be activated

Answer 38

A change in the tertiary structure brought about by the action of another enzyme, which breaks bonds Change in conditions (ph and temperature) E.g Pepsinogen is released and activated in stomach by ph levels

Question 39

How do enzymes affect activation energy

Answer 39

Help molecules collide successfully And reduce activation energy

Question 40

What are serial dilutions And when are they useful

Answer 40

Repeated stepwise dilution of a solution Even when solution is unknown Gives relative concentrations

Question 41

How to make serial solutions

Answer 41

Add 1ml of stock solution to 9ml of distilled water Take 1ml of that made solution and add 9ml of water

Question 42

Why do enzymes at low temperatures have flexible structures

Answer 42

``` Low kinetic energy Enzymes move slower Less frequent collisions Collisions have less energy Flexible active sites needed to Increase the number of successful collisions ```

Question 43

How do drugs act as enzyme inhibitors Penicillin Drugs that stop hiv

Answer 43

Antibiotics Inhibits enzyme that catalyses formation of protein in cell wall - can’t regulate osmotic pressures - bacteria bursts and dies Antivirals Inhibits enzyme that catalyses replication of viral DNA - prevents virus from replicating

Question 44

How do metabolic poissons interfere with metabolic reactions Cyanide Arsenic Malonate

Answer 44

Inhibits enzyme that catalyses respiration | Cells die

Question 45

What is the bonding in inhibitors that makes them non reversible

Answer 45

Covalent bonds | Can’t be removed easily

Question 46

What is the bonding in inhibitors that makes them reversible

Answer 46

Weaker hydrogen bonds or ionic bonds | Inhibitor can be removed

Question 47

What does end product inhibition do

Answer 47

Regulates the pathway Controls the amount of product made

Question 48

What is a coenzyme

Answer 48

Organic cofactors

Question 49

Example of cofactor

Answer 49

Cl-

Question 50

Example of coenzyme

Answer 50

Vitamin

Question 51

Example of prosthetic group for carbonic anhydrase

Answer 51

Zn2+