Module 2 - Enzymes

Question 1

How do you speed up a chemical reaction in a lab setting?

Why can’t this be done in the human body?

Answer 1

Raising temperature
Increasing pressure
The thermal energy transferred to the particles causes them to move rapidly (kinetic energy) which means they bump into one another more frequently, allowing chemical reactions to occur more frequently.

In the human body cells and their structures would denature.

Question 2

What are enzymes?

Answer 2

Biological catalysts that speed up the metabolic reactions in living organisms.
A small amount of catalyst can catalyse the conversion of a large number of substrate molecules into product molecules.
They remain unchanged at the end of the reaction and can be used again.

Question 3

What is the number of reactions that an enzyme molecule can catalyse per second called?

Answer 3

Turnover number.

Question 4

Why are enzymes so important?

Answer 4

Without them, chemical reactions wouldn’t occur fast enough and many processes needed to sustain life wouldn’t be possible.

Question 5

What type of protein is an enzyme?

Answer 5

A globular protein that is soluble in water because of the hydrophilic nature of it’s side groups on amino acids.

Question 6

What are anabolic reactions? Examples.

Answer 6

These reactions build up or synthesise large molecules.

Examples include cellulose for the walls of plants and long protein molecules that form muscle contractile filaments.

Question 7

What are catabolic reactions? Examples

Answer 7

These break down large organic molecules.

Examples include the digestion of the large organic molecule starch into it’s monomer glucose, and the release of energy from glucose during respiration.

Question 8

Where do enzymes function?

Answer 8

Both intracellularly and extracellularly.
DNA replication is an intracellular process that involves many enzymes including DNA polymerase and DNA ligase.
Some intracellular reactions perform their actions in membranes, an example is within the mitochondria’s inner membrane respiration takes place where ATPase synthesises ATP.
Digestion is extracellular.

Question 9

What is amylase?

Answer 9

It is an enzyme produced in the salivary glands and pancreas and digests starch into maltose.

Question 10

What type of enzyme is catalase?

Answer 10

Intracellular.
Protects cells from damage by breaking down hydrogen peroxide to water and oxygen.
Consists of 4 polypeptide chains (subunits) and a haem group.
Has the highest turnover number of 6 million per second.

Question 11

What is a metabolic pathway?

Answer 11

A series of consecutive reactions with each step being catalysed by a different enzyme, specific for the substrate produced.
If one enzyme can’t function, the pathway cannot run.

Question 12

What are metabolites?

Answer 12

The reactants, intermediaries and and products are known as metabolites.

Question 13

Are metabolic pathways anabolic, catabolic or both?

Answer 13

Both

Question 14

What are the main two examples of metabolic pathways?

Answer 14

Respiration and photosythesis.

Question 15

What are oxidoreductases?

Answer 15

Enzymes that catalyse the transfer of electrons during oxidation and reduction reactions.

Question 16

What are transferases?

Answer 16

Enzymes that help with the transfer of a functional group from one molecule to the other.

Question 17

What are hydrolases?

Answer 17

They catalyse the hydrolysis of bonds by the addition of water.

Question 18

What are lyases?

Answer 18

The splitting of bonds other than oxidation and hydrolysis.

Question 19

What are isomerases?

Answer 19

The rearranging of a molecule (same type and number of atoms but different arrangement).

Question 20

What are ligases?

Answer 20

The joining of two molecules by formation of covalent bonds.

Question 21

Where does the substrate fit in the enzyme?

Answer 21

The active site.

Question 22

How specific are enzymes?

Answer 22

Highly specific.

Question 23

What is the general word equation for an enzyme controlled reaction?

Answer 23

Enzyme + substrate —> enzyme substrate complex —> enzyme product complex —> enzyme + product

Question 24

What is the energy needed for a reaction to start?

Answer 24

Activation energy.

Question 25

What do enzymes do to activation energy?

Answer 25

They lower it by creating a transition state between the enzyme and the substrate that is more stable (it holds less energy than in the uncatalysed reaction)

Question 26

Why does forming an enzyme-substrate complex lower the activation energy?

Answer 26

If two substrate molecules need to be joined, attaching to the enzyme holds them close together so they can bond more easily.

It the enzyme is catalysing a breakdown reaction then fitting into the active site puts a strain on the bonds in the substrate allowing the molecule to break more easily.

Question 27

What does an enzyme’s effect on activation energy look like on a graph?

Answer 27

It lowers the peak of activation energy.

Question 28

What are enzymes made up of?

Answer 28

The sequence of amino acids and their folding make up and maintain the precise shape of the active site.

Question 29

What would a mutation do to the sequence of amino acids?

Answer 29

It will change their shape - tertiary structure - will be changed which may prevent it from functioning.

Question 30

What is the active site of the enzyme?

Answer 30

It is usually a cleft or indentation on the surface of the enzyme.
Often made up of 6 - 10 amino acids.
Tertiary structure of the active site is crucial as it’s shape is complementary to the shape of the substrate molecule. This means the enzyme is highly specific.

Question 31

What can change the structure and shape of the active site?

Answer 31

Changes in the shape and structure can be due to changes in temp and pH, this is bc the bonds that hold the structure in the tertiary structure will be affected.

Question 32

What is the lock and key hypothesis?

Answer 32

The shape of the active site is very specific and is maintained by the tertiary structure of the rest of the enzyme.
Molecules that don’t have the complementary shape to the active site won’t fit and bind to the enzyme.
The substrate fits exactly like a key in the lock of the active site and is held here by various bonds, now it is the enzyme-substrate complex.

Question 33

What is the induced fit theory of enzyme action?

Answer 33

It suggests the active site is not exactly the perfect shape for the substrate.
It argues that as the substrate moves into the active site, forces between the two molecules distort the enzyme and it’s active site so that it tightly envelops the substrate, fitting like a hand in a glove.
The forming of the enzyme-substrate complex allows the lowering of activation energy required to form the products.

Question 34

What is the overall process of enzyme action?

Answer 34

Enzyme-substrate complex is formed.
Enzyme-product substrate formed
Products leave the active site
-Lock and key model
-Induced fit model

Question 35

What are cofactors?

Answer 35

They are small non-protein molecules that attach to enzymes to allow them to work.

Question 36

What are the two main types of co-factors?

Answer 36

Activators - inorganic groups that are permanently bound to the enzyme and are therefore a prosthetic group, common examples are iron, zinc, copper.

Coenzymes - large organic molecules that bind temporarily to the enzyme, transferring a chemical group that is necessary for the reaction to occur. Examples, NAD (respiration), vitamin B3 (niacin), vitamin C and ATP. Many coenzymes are derived from water soluble vitamins.

Question 37

What is precursor activation?

Answer 37

Many enzymes are in an inactive form, known as inactive precursor enzymes.
This is important bc some enzymes cause damage in an activated form.
Precursor enzymes often undergo a change in their shape (tertiary structure) to be activated.
Can be achieved by addition of a cofactor.
Before the cofactor is the precursor protein is called an apoenzyme. When it’s added it’s called a holoenzyme.

Question 38

What factors affect enzymes?

Answer 38

Temperature
pH
Concentration of enzyme
Concentration of substrate

Question 39

What happens when temperature is increased in a reactant of both substrates and enzymes?

Answer 39

Both gain kinetic energy and move faster. This increases rate (number per second) of collisions.
The rate of formation of enzyme-substrate complexes will therefore increase and the rate of reaction will increase which increases the number of enzyme-product complexes formed.

Question 40

Why is reaction rate always the highest initially?

Answer 40

At the beginning of the reaction, the enzyme and substrate molecules have a greater chance of successfully colliding.
As the reaction continues, substrate molecules are used up so the rate of successful collisions decreases.

Question 41

What is the effect of low temperatures on enzymes?

Answer 41

At lower temps the enzyme and substrate have reduced kinetic energy and so fewer enzyme-substrate complexes form.

Question 42

What is the change in rate of reaction for every 10oC called?

Answer 42

The temperature coefficient, (Q10), at sub optimum temps this is about 2.

Question 43

What is the optimum temperature for enzymes in the human body?

Answer 43

Around 37oC.

Question 44

What happens to enzymes when temperature is too high?

Answer 44

Enzyme vibrates, some of the bonds (H and ionic) that hold the tertiary structure of the enzyme break.
As the active site changes, the substrate won’t fit as well and the rate of reaction will decrease.
More heat causes the active site to change so much that is no longer complementary to the substrate, it is denatured.

Question 45

What is pH?

Answer 45

It stands for power of hydrogen.
It is a measure of the concentration of hydrogen ions present.
Hydrogen ions are protons and have a positive charge.

Question 46

How does pH affect enzymes?

Answer 46

H+ are attracted to negative charges. Excess H+ will interfere with hydrogen and ionic bonds that hold the tertiary structure of an enzyme.
If the shape of the active site changes, the substrate won’t fit well and the rate of reaction will decrease.
At extremes, the enzyme’s active site may be permanently changed/denatured.

Question 47

What is a buffer?

Answer 47

It is something that resists a change in pH.
Blood pH must remain close to 7.4.
A buffer can accept or donate hydrogen ions to control the amount of them in the blood.

Question 48

What will happen to the rate of reaction if the concentration of substrate increases?

Answer 48

The rate increases bc more ES complexes form.
More EP complexes form.
More product molecules form.
Substrate concentration is the limiting factor because as it increases, the rate of reaction increases.

Question 49

What is it called when all active sites are in use?

Answer 49

Active site saturation.

Question 50

What will happen to the rate of reaction as enzyme concentration increases?

Answer 50

Rate increases bc more active sites become available.
More ES complexes form.
More EP complexes form.
More product molecules are formed.
Enzyme factor is the limiting factor because as concentration increases, so does rate.

Question 51

Why doe enzyme inhibitors exist?

Answer 51

To prevent build up of excess product.
Inefficient in terms of energy usage.

Question 52

What are enzyme inhibitors?

Answer 52

Molecules that prevent enzymes from carrying out normal function or slow them down.

Question 53

What are the two types of inhibitors?

Answer 53

Competitive and non-competitive.

Question 54

How do competitive inhibitors work?

Answer 54

They compete with the substrate for binding at the enzyme’s active site.
They form an enzyme-inhibitor complex and physically block entry for the substrate.
They bind to the active site with weak bonds like hydrogen bonds.

Question 55

How do non-competitive inhibitors work?

Answer 55

Don’t compete with the substrate for the active site.
Bind to the allosteric site.
Causes a change in conformation of the active site so the substrate cannot bind.
If it is reversible it can dissociate with the allosteric site and the active site returns to normal.

Question 56

What determines if the inhibitor is reversible or irreversible?

Answer 56

Hydrogen and ionic bonds are weak and break easily and are reversible.
Strong bonds like covalent mean the inhibitor cannot be removed and it is often irreversible.

Question 57

What are the 4 main examples of medical inhibitors?

Answer 57

Statins
Aspirins
Protein pump inhibitors
Reversible transcriptase inhibitor (HIV)

Question 58

What drugs use inhibitors and how?

Answer 58

Penicillin inhibits enzymes involved in production of bacterial cell walls.
Extracts from purple foxglove leaves are used to treat heart failure.

Question 59

What is the effect of a competitive inhibitor on rate of reaction?

Answer 59

R of R will occur more slowly because the inhibitor and enzyme compete for the active site.
Eventually the substrate overwhelms the inhibitor.

Question 60

What is the effect of a non-competitive inhibitor on rate of reaction?

Answer 60

The max rate of reaction is much lower.

Question 61

What are the roles of inhibitors in metabolic poisons?

Answer 61

Inhibitors in toxins/venoms can irreversibly block enzymes causing paralysis and death.
Heavy metals like mercury and cadmium are are reversible non-competitive inhibitors that block a range of metabolic reactions.

Question 62

What is end product inhibition?

Answer 62

Often the end-product of a metabolic pathway acts as a regulator of the pathway.
If the end product is high, it binds non-competitively to the enzyme and reduces it’s production of itself.
When end product falls other way around.