Enzymes

Question 1

What are enzymes

Answer 1

• catalysts (speed up chemical reactions without themselves being altered)
• do not alter equilibrium, only increases the rate of reaction/ time it takes to reach equilibrium

Question 2

Why are enzymes important

Answer 2

• catalyse chemical reactions in our metabolic system
• many roles in living organisms

Question 3

Two types of enzyme mechanisms

Answer 3

Lock and key
Induced fit

Question 4

Key words when describing how enzymes function

Answer 4

• enzyme
• enzyme substrate complex
• substrate
• product
• active site

Question 5

Enzyme are what type of biological molecules

Answer 5

• proteins
• special ones include riboenzymes ( catalytic rna molecule)

Question 6

What affects enzymes 3D structure

Answer 6

Ph
Temp
Inhibitors (non-competitive can bind at allosteric site)

Question 7

What is standard free energy change (delta g)

Answer 7

Standard free energy change is the energy difference between reactants (enzyme and substrate) and products

Question 8

Describe the mechanism of action of lysozyme

Answer 8

• cleaves the bacterial cell walls between carbon 1 of NAM and carbon 4 of NAG in the peptidoglycan cell wall of bacteria (beta 1-4 glycoside bond)

Question 9

What affects the rate of reaction?

Answer 9

Ph
Temp
Inhibitor presence
Enzyme conc
Substrate conc
Covalent modifications

Question 10

What is optimum temp of human enzymes

Answer 10

37

Question 11

Optimum temp of heat tolerant bacterial enzymes ?

Answer 11

77

Question 12

Optimum ph of trypsin?

Answer 12

8

Question 13

Optimum ph of pepsin?

Answer 13

2

Question 14

What is thermodynamic activation or inactivation?

Answer 14

Thermodynamic activation is when there is an increase in free energy
Thermodynamic inactivation is when the temp is too high and protein starts to denature

Question 15

Describe the effect of enzyme conc on reaction rate?

Answer 15

Enzyme conc increase, rate of reaction increases until equilibrium is reached

Question 16

What is the Michaelis constant?

Answer 16

Km = Vmax / 2

Question 17

What is Vmax

Answer 17

Vmax is the maximum rate of reaction
(Enzymes are fully saturated)

Question 18

What is Km

Answer 18

Michaelis constant
High affinity Low Km
Low affintiy high Km

Question 19

Describe the affinities linked with Km

Answer 19

When Km is high, affinity of enzyme FOR its substrate is Low

Question 20

Draw the graph of high and Low Km

Answer 20

Labels on each axis
Refer to slides for answers

Question 21

Rate of reaction At Low Km

Answer 21

The enzyme is usually saturated so the rate of reaction is fairly constant

Question 22

Rate of rxn at high Km

Answer 22

Low affinity so enzyme is usually not saturated with substrate, activity will vary as substrate conc varies. Rate of product formation depends on substrate availability

Question 23

Explain what is the Michaelis- Menten equation and give the equation

Answer 23

V = Vmax . [S] / (Km + [S])

Michaelis menten equation is a representation of the graph of V against [S]

Question 24

The Km of dextran surcease is 4nm. When is this enzyme saturated?

Answer 24

8nm because Vmax is when an enzyme is saturated and Km= Vmax over 2 so the enzyme is saturated when 4x2=8nm

Question 25

Draw the Lineweaver-Burk plot and describe when is it used

Answer 25

Graph of 1/V against 1/[S]. Used to see a linear graph The y intercept is 1/Vmax The x intercept is NEGATIVE 1/Km Gradient is Km/Vmax

Question 26

Allosteric site def

Answer 26

Site away from the active site

Question 27

Describe how the non competitive inhibitor works

Answer 27

Binds at the allosteric site, causes a conformational change, active site is no longer functional

Question 28

Feedback inhibiton

Answer 28

Control metabolic pathways Basically, when a lot of the product has formed, it can act as an inhibitor and bind to the enzyme in the earlier step of the metabolic pathway, stopping the pathway from continuing

Question 29

What inhibitor is this? Km changes Vmax stays same Km increases or decreases? Explain why and also draw the graph

Answer 29

1. Competitive inhibitor 2. Vmax stays same because increasing the substrate concentration can outcompete the inhibitors 3. Km increases because affinity decreases 4. Y intercept same x intercept shifts to the RIGHT

Question 30

What inhibitor is this? Km stays the same Vmax changes. Vmax increases or decreases? Explain why and also draw the graph

Answer 30

Non competitive inhibitor Km stays the same because binding of substrates can still occur Vmax decreases because a proportion of enzymes are inactive due to it binding to inhibitor The x intercept stays the same and y intercepts increases ( remember that even though the Vmax decreases, the y axis Is 1/Vmax so the intercept goes up)

Question 31

What are Allosteric enzymes NOT allosteric binding sites

Answer 31

Allosteric enzymes possesses multiple subunits Allosteric enzymes are enzymes which have an additional site for an effector to bind to, as well as the active site Efforts regulate the activity of the enzyme – they can either activate or inhibit Allosteric enzymes are larger and more complex than normal enzymes They are regulated through homotropic regulation or heterotropic regulation

Question 32

Graph of allosteric enzymes

Answer 32

CANNOT use Michaelis menten equation! CANNOT use Lineweaver-Burk plot!! Graph is sigmoidal shape

Question 33

Covalent modification of enzymes

Answer 33

Adding example phosphate group can activate or inactive an enzyme

Question 34

How does an allosteric enzyme function?

Answer 34

Binding of substrate, inhibitor or modulator/ activator to one subunit of the allosteric enzyme causes a conformational change in all subunits of the allosteric enzyme

Question 35

What are the two types of modulators and what do they do?

Answer 35

Positive - increases affinity for substrate Negative - decreases affinity for substrate