F212 Enzymes

Question 0

What are enzymes?

Answer 0

Globular proteins with a specific tertiary structure

Catalyse metabolic reactions in living organisms

Question 1

What do organisms use enzymes for?

Answer 1

To catalyse metabolic reactions

Question 2

Endothermic animals

Answer 2

Animals that are able to maintain their internal body temperature independent of the environment
This allows enzymes to function at near optimum temperature inside the organism

Question 3

Heterotrophs

Answer 3

Organisms that obtain nutrients by consuming other organisms

They break down the bodies of these organisms to extract the nutrient molecules they need for growth and energy

Question 4

Digestion

Answer 4

The breaking down of larger molecules into their subunits

This requires the breaking of bonds e.g. glycosidic, peptide and ester bonds

Question 5

Digestion

Enzyme Secretion

Answer 5

Some organisms secrete enzymes outside of themselves in to the food source
The enzymes digest the molecules into their monomers which the organism can take in and use

Question 6

Digestion

Internal Digestive System

Answer 6

As food taken in by the organism passes through the digestive system various enzymes are mixed with it to digest the nutrients it contains
Many enzymes is digestive systems are extra cellular

Question 7

Extracellular Enzymes

Answer 7

Enzymes that are released from the cells that make them

Question 8

Intracellular Enzymes

Answer 8

Enzymes whose actions take place inside of cells

Question 9

Enzymes and Protection

Answer 9

Enzymes that catalyse reactions to break down molecules are useful tools in protecting an organism
Many organisms use enzymes as a defence mechanism e.g. phagocytes take in and digest bacteria using lysosomal enzymes

Question 10

Covalently Bonded Molecules…

Answer 10

…are too stable to just assemble or break down

Question 11

Maltose

Answer 11

Two glucose molecules joined together by a glycosidic bond

Question 12

Splitting Maltose

Answer 12

To split maltose in a hydrolysis reaction in to two glucose molecules the glycosidic bond has to be broken and a water molecules needs to be split

To make this reaction happen in a test tube maltose can be boiled in acid providing the right conditions for molecules of maltose and water to collide with enough energy to achieve hydrolysis

Question 13

Activation Energy

Answer 13

The energy required for a reaction to take place

Question 14

How do Enzymes Reduce the Activation Energy?

Answer 14

By holding the substrate molecule in a certain way that allows the reaction to proceed more easily

Question 16

Catalysts and Metabolic Reactions

Answer 16

Boiling in acid gives molecules a great deal of extra energy
However cells would not survive boiling in acid so need catalysts to drive the metabolic reactions
Without catalysts metabolic reactions could not occur fats enough to sustain life

Question 17

Active Sites

Answer 17

An enzyme has a specifically shaped active site

The active site of the enzyme is the complementary shape substrate molecule(s) involved in the reaction

Question 18

Lock and Key Model

Answer 18

The substrate, key, fits in to the active site, lock, of the enzyme
The substrate is then held in place so that the reaction can take place

Question 19

The Induced Fit Hypothesis

Answer 19

As the substrate molecule collides with the active site, the enzyme changes shape slightly
This makes the actives site fit more closely around the substrate
The substrate is also held in place by the oppositely charged groups that make up the substrate and the active site
The change in enzyme shape also puts strain on the substrate molecule, destabilising it allowing the reaction to occur more easily
This produces a product which is a different shape from the substrate
The product(s) no longer fits into the active site so move away
The enzyme is now able to catalyse the same reaction with another substrate molecule

Question 20

Enzyme-Substrate Complex

Answer 20

The intermediate structure formed when a substrate molecule binds to an enzyme molecule

Question 21

Enzyme-Product Complex

Answer 21

The intermediate structure in which product molecules are bound to the enzyme molecule

Question 22

Heat and Kinetic Energy

Answer 22

The molecules in a gas or liquid move around continually
If a gas or liquid is heated the kinetic of the molecules is increased meaning they collide more frequently and with more force

Question 23

Enzymes and Collisions

Answer 23

An enzyme can only catalase a reaction if the substrate collides with the active site
Random movements lead to these collisions
Heating the enzyme and substrate increases the kinetic energy therefore increasing the number of collisions and therefore the rate of reaction

Question 24

Heat and Vibration

Answer 24

Applying heat to molecules not only makes them move faster but also causes them to vibrate
These vibrations out strain on the bonds holding the molecule together
In large molecules like enzymes these vibrations can break weaker bonds e.g. hydrogen and ionic bonds
These bonds hold together the tertiary structure of the enzyme (protein) and maintain the shape of the active site

Question 25

Heat, Vibration and Denaturation

Answer 25

As heat is increased more bonds are broken The tertiary structure is held less and less in the shape of the working active site This causes the rate of reaction to decrease If enough bonds are vp broken the whole tertiary structure will unravel and the enzyme will stop working This process, denaturation, is irreversible

Question 26

Effect of Increasing Temperature

Answer 26

At first increasing temperature will increase the reaction rate at first But as the temperature increases further the rate of reaction decreases

Question 27

What bonds would you expect to find holding together the tertiary structure of a heat resistant enzyme?

Answer 27

Disulphide binds because they aren't broken down by Heat, only reducing agents

Question 28

Optimum Temperature

Answer 28

The temperature that gives the maximum rate of reaction is the enzymes optimum temperature It is a ball prance between energy and vibrations Optimum temperature varies between enzymes depending on the environment that they have to function in

Question 30

What is pH?

Answer 30

A measure of hydrogen ion H+ concentration between pH1 and pH14 pH7 = neutral pH7 < alkaline - high H+ concentration pH7 > acid (proton donor) - low H+ concentration

Question 31

pH and Bonds

Answer 31

A hydrogen ion carries a positive charge so will be attracted to negatively charged molecules and parts of molecules and will repel positively charged molecules

Question 32

Pepsin

Answer 32

Protein digesting enzyme Optimum pH - pH 2 Ideal for working in the stomach which contains hydrochloric acid

Question 33

Trypsin

Answer 33

Protein digesting enzyme Optimum pH - pH 7 Ideal for working in the small intestine

Question 34

Effect of pH

Answer 34

Because of their charge hydrogen ions can interfere with hydrogen bonds and ionic bonds that hold the tertiary structure of the enzyme in place Changes in pH cause changes in the shape of the active site and therefore effect the rate of the reaction

Question 35

Optimum pH

Answer 35

Enzymes only function in a fairly narrow pH range Outside of this range the concentration of the hydrogen ions disrupts the shape of the active site denaturing the enzyme Optimum pH varies depending on the location that the enzyme has adapted to work best in

Question 38

Increasing Substrate Concentration

Answer 38

As the concentration of the substrate increases collisions between enzyme and substrate occur more often increasing the rate of reaction As the concentration is increased the rate of reaction will reach a maximum where all of the active sites are full and further increasing the substrate concentration will have no effect

Question 39

Increasing Enzyme Concentration

Answer 39

As the enzyme concentration increases more active sites become available More enzyme-substrate complexes form and therefore kore products p ,increasing the rate of reaction As enzyme concentration increases further a maximum rate is reached where all substrate molecules are in an active site and further increasing the enzyme concentration will have no effect

Question 40

Initial Reaction Rate

Answer 40

In an experimental situation where enzyme and substrate are mixed together the rate of the enzyme controlled reaction will be at its highest when they are first mixed As the reaction proceeds product molecules are formed an increase in number At the same time substrate molecules are used up and decrease in number So frequency of collisions decreases The highest reaction rate or initial reaction rate gives the maximum possible rate of reaction for an enzyme under a particular experimental situation

Question 41

Enzyme and Substrate Concentration in Cells

Answer 41

Enzyme concentrations in cells are usually fairly low | Partly because enzymes, being catalysts, work over and over again

Question 42

Advantages of an Internal Digestive System Compared With Secreting Enzymes

Answer 42

The enzymes produced are not lost to the outside environment | The internal environment can be regulated to provide optimum conditions for the enzyme

Question 43

Competitive Inhibitors

Answer 43

Molecules of a similar shape to the substrate Occupy the active site forming an enzyme-inhibitor complex This slows down the rate of reaction because less enzyme-substrate complexes are formed Most competitive inhibitors do not bind permanently, the removal of the inhibitor leaves the enzyme unaffected

Question 44

Non-Competitive Inhibitors

Answer 44

Molecules do not compete with substrate molecules for the active site they instead attach elsewhere on the enzyme This attachment distorts the tertiary structure of the enzyme leading to a change in shape of the active site The denaturing of the enzymes reduces the rate of the reaction

Question 45

Cofactor | Definition

Answer 45

Any substance that must be present to ensure an enzyme controlled reaction can take place at the appropriate rate Can be an inorganic ion or a coenzyme

Question 46

Coenzyme | Definition

Answer 46

Small organic non-protein molecules that bind briefly to the active site just before or at the same time as the substrate They are essential for enzyme activity Often take part in the reaction in that they are changed in some way by the enzyme but are recycled to take part again Often used to carry chemical groups between enzymes to link reactions together in sequence

Question 47

Prosthetic Group | Definition

Answer 47

A coenzyme that is a permanent part of an enzyme | They contribute to the final 3D shape of the enzyme and other properties including charge

Question 48

Cofactors - Inorganic | Definition

Answer 48

In some reactions the presence of certain ions can increase reaction rate The ions may combine with either the substrate or the enzyme to affect charge distribution making it easier for the enzyme-substrate complex to form

Question 49

Poisons | How they work

Answer 49

Many poisonous substances have an effect by inhibiting or over activating enzymes

Question 50

Poisons | Potassium Cyanide

Answer 50

Non competitive inhibitor Effects vital respiratory enzymes in the mitochondria meaning that ATP cannot be made This causes the organism to respire anaerobically Build up of lactic acid in the blood Death

Question 51

Poisons | Ethylene Glycol

Answer 51

Found in antifreeze Broken down in the liver by an enzyme called alcohol dehydrogenase The break down product oxalic acid is very toxic Treated with the drug, fomepizole, which is a strong inhibitor of alcohol dehydrogenase Ethanol can also inhibit break down, as a competitive inhibitor it is metabolised in preference to ethylene glycol

Question 52

Medicines | Viruses

Answer 52

Infections caused by viruses are treated using chemicals that act as competitive inhibitors for protease enzymes They prevent the virus from replicating by inhibiting the activity of protease enzymes which viruses need to build new virus coats

Question 53

Medicines | Antibiotics

Answer 53

Can kill or inhibit the growth of microorganisms Penicillin is an inhibitor of a bacterial enzyme that forms cross links in bacterial cell walls to stop the bacteria from reproducing

Question 54

Medicines | Cystic Fibrosis

Answer 54

Doctors prescribe digestive enzymes as the normal passage of produced digestive enzymes in the pancreas to the gut is blocked