L5-7: Enzymes and inhibitors

Question 1

What are enzymes?

Answer 1

Proteins
Catalysts
Have specific structures (stereo specific)

Question 2

What are the most common type of drugs and poisons?

Answer 2

Enzyme inhibitors

Question 3

What does Haemagglutinin do?

Answer 3

Facilitates entry of virus into host cells

Question 4

How does Haemagglutinin enter the host cell?

Answer 4

Binds to sugars on the cell surface, changes conformation in host cell to fuse membranes and release virus in hosts

Question 5

What is the enzyme that facilitates exit of the virus from the host cell?

Answer 5

Neuraminidase

Question 6

How is the exit of the virus facilitated?

Answer 6

Binds to sugars on host cell surface and cleaves sialic acid sugars from cell glycoproteins, preventing virus sticking to cells

Question 7

What are 2 anti-flu drugs?

Answer 7

Tamiflu and Relenza

Question 8

How do the anti-flu drugs work?

Answer 8

They target the neuraminidase enzyme of influenza, drug has a similar shape so blocks active site

Question 9

How does drug resistance arise?

Answer 9

From mutations (change in AAs in neuraminidase which allows infection of influenza)

Question 10

How does Penicillin work?

Answer 10

Acts as a substrate which stops the crosslinking of peptides in glycan cell wall in bacteria (causes them to weaken and lyse)

Question 11

How did bacteria become resistant to Penicillin?

Answer 11

Altered binding to beta-lactams so Penicillin is broken down with a beta lactamase enzyme

Question 12

What is the key class of anti-viral drugs?

Answer 12

Nucleoside analogue drugs

Question 13

What are examples of anti-viral drugs?

Answer 13

AZT- Azidothymidine (HIV)
Acyclovir (Herpes)
Remdesivir (COVID)

Question 14

How do anti-viral drugs work?

Answer 14

Interact with RNA/DNA polymerases and reverse transcription enzymes (block active site and prevent further extension of DNA/RNA)

Question 15

How do enzymes work?

Answer 15

Catalyse making and breaking of covalent bonds
Allow higher rate of reaction
Reactions can occur under milder conditions
Have high specificity
Regulate biochemical reactions

Question 16

What is the equilibrium constant in a reaction, Keq, correlated to?

Answer 16

The energy release by the reaction (change in Gibbs)

Question 17

What is the effect of catalysts on activation energy?

Answer 17

Lowers activation energy

Question 18

What does free energy in a reaction determine?

Answer 18

Keq

Question 19

How do enzymes impact equilibrium?

Answer 19

Speed up equilibrium but don’t change concentration

Question 20

What is first formed before a product can form?

Answer 20

An enzyme-substrate complex

Question 21

What are the properties of the mechanism of enzyme catalysis?

Answer 21

Proximity - close together
Orientation - correct relative rotation
Strain/distortion - binding puts strain on bond so easier for rection to occur

Question 22

What is covalent catalysis?

Answer 22

Temporary covalent bond between enzyme and substrate

Question 23

How do enzymes show specificity?

Answer 23

By having interactions between specific structural regions on the substrate and enzyme

Question 24

What are the 2 different ways of an enzyme binding?

Answer 24

Lock and key- active site complementary to substrate
Induced fit- contact between active site and substrate changes shape allowing binding

Question 25

What are the 7 different classes of enzymes?

Answer 25

Oxidorectuctases, transferases, hydrolases, lysases, isomerases, ligands, translocases

Question 26

What is Kcat?

Answer 26

The number of substrate molecules converted to product by 1 enzyme in 1 second

Question 27

When is an enzyme fastest in a reactions?

Answer 27

At the start

Question 28

What does enzyme activity depend on?

Answer 28

Substrate concentration

Question 29

What are the different effects of varying substrate concentration?

Answer 29

Low conc- number of substrate molecules determines how fast reaction takes place Increased conc- more chance colliding (for catalysis to occur) & higher proportion of enzyme molecules will have bound to substrate

Question 30

What happens when an enzyme is saturated?

Answer 30

The rate slows down as the increase of [S] does not make the reaction go faster

Question 31

What happens in a first order reaction? (enzyme kinetics)

Answer 31

Rate of reaction increases proportionally with increased [S]

Question 32

What is the equation derived from the relationship between velocity and substrate concentration?

Answer 32

𝑣= Vmax[S]/Km+[S] Where 𝑣 is rate at a specified [S]

Question 33

What is the Km constant?

Answer 33

[S] at half Vmax

Question 34

What does Km mean?

Answer 34

It indicated the affinity of the enzyme for the substrate which is the stability of the ES complex

Question 35

What do low and high Km mean in terms of affinity?

Answer 35

High Km= low affinity Low Km= high affinity

Question 36

What is the equation for Michaelis-Menten kinetics for a first order reaction?

Answer 36

V0=Vmax[S]/Km

Question 37

What are the unis of Km?

Answer 37

Units of concentration (M)

Question 38

What is Vmax and when does it occur?

Answer 38

It is the fastest rate at which an enzyme can work and only occurs at infinite [S]

Question 39

How can Vmax be found?

Answer 39

Using Lineweaver-Burk plot (slope = Km/Vmax)

Question 40

What are the classes of enzyme inhibitors?

Answer 40

Irreversible (covalent complexes) Reversable (useful + have an affinity) -comp -non-comp -uncomp

Question 41

Where do irreversible inhibitors usually bind?

Answer 41

To amino acid side chain or near active site

Question 42

How do irreversible inhibitors work?

Answer 42

They bind permanently which inactivates the enzyme and prevents the substrate from binding

Question 43

Name examples of irreversible inhibitors

Answer 43

Aspirin Penicillin Sulbactam Allopurinol AZT Eflornithine Sarin 5-fluorouracil Exemestane

Question 44

How does the irreversible inhibitor Sarin work?

Answer 44

It prevents the breakdown of NT acetylcholine as it binds to serine residue in acetylcholinesterase

Question 45

How does Penicillin work?

Answer 45

Binds to Serine in penicillin binding proteins which irreversibly blocks the active site

Question 46

What are the characteristics of a competitive inhibitor?

Answer 46

Competes with substrate for active site Has similar structure to substrate When bound blocks active site

Question 47

How does competitive inhibition effect kinetics?

Answer 47

Increases Km Vmax stays the same

Question 48

What are examples of competitive inhibitors?

Answer 48

Tamiflu Acarbose - type II diabetes (prevents digestion of natural carbs) Statins- target hepatocytes and inhibit HMG-CoA reductase

Question 49

What are the characteristics of non-competitive inhibition?

Answer 49

Binds away from active site Modifies reaction rate Binds substrate with same affinity

Question 50

How does non-competitive inhibition effect kinetics?

Answer 50

Km unaltered Vmax decreased

Question 51

What is uncompetitive inhibition?

Answer 51

Occurs with multi-substrates Binds only to ES complex

Question 52

How does uncompetitive inhibition effect kinetics?

Answer 52

Km decreases Vmax decreases (ratio stays the same)

Question 53

What reaction conditions influence enzyme activity?

Answer 53

Temperature pH Salts Other chemicals Molecular crowding

Question 54

How does pH change enzyme activity?

Answer 54

3D structure changes Groups involving in binding substrate or catalysis change charge

Question 55

How does temperature change enzyme activity?

Answer 55

Change diffusion rate Flexibility of active site Stability of enzyme (denaturation)

Question 56

What is molecular crowding and how does it impact enzyme activity?

Answer 56

Large proteins diffuse slower than small substrates/products Cells can increase amounts of slower enzyme Pathways with volatile intermediates cell can trap them

Question 57

What is the carboxysome?

Answer 57

Carbon concentration mechanism Balances activity of carbonic anhydrase and rubisco Protein shell to localise CA next to rubisco Traps CO2