Lecture 5

Question 1

molecular motions are very _______

Answer 1

fast

Question 2

What is diffusion

Answer 2

• molecules wandering randomly in cytosol
• large molecules diffuse slower than small ones

Question 3

In terms of enzyme kinetics, what is velocity, Vmax, and Michaelis constant (Km)?

Answer 3

• velocity: rate of reaction
• Vmax: the maximum rate of reaction for an enzyme. How quickly it can catalyze a reaction when fully saturated with substrate
• Km: concentration of substrate at which enzyme is at 1/2Vmax

Question 4

Why is a double-reciprocal plot made?

Answer 4

• because we can calculate Vmax more precisely

Question 5

Give 2 reasons why enzyme inhibitors are important

Answer 5

• important for pharmaceutical agents
• major method used by cells to regulate gene expression (ex. feedback inhibition)

Question 6

What is competitive inhibition? and what effect does it have on Km and Vmax? Why?

Answer 6

• competitive inhibitors compete with the substrate to bind to the active site
• This increase Km, but not Vmax because we can add more substrate until it outcompetes the inhibitor

Question 7

What are activated carriers? Give some examples.

Answer 7

• small organic molecules that store energy or chemical groups in an easily exchangeable form
• ATP, NADH, NADPH

Question 8

How is energy captured?

Answer 8

• energy is captured by using coupled reactions:
• energetically favoured reactions are used to drive energetically unfavoured reactions
• cells have an elaborate system to capture energy from food (glycolysis, beta oxidation of fatty acids)

Question 9

ATP

Answer 9

• stands for adenosine 5’ triphosphate
• most widely used activated carrier
• is the energy currency of the cell

Question 10

How is ATP synthesized?

Answer 10

• synthesized in a phosphorylation reaction when a phosphate group is added to ADP

Question 11

How is ATP used to do work?

Answer 11

• ATP is used to generate a high energy intermediate by phosphorylating a reactant

Question 12

Compare and contrast NADH and NADPH.

Answer 12

• Both are carriers of 2 high energy electrons and proton H+ (forming a hydride ions, H-)
• the differing phosphate group does no affect on the electron transfer properties of NADH vs. NADPH

Question 13

Why is the distinction of differing phosphate group of NADH vs NADPH important

Answer 13

• because it gives each a distinct shape and allows the binding of different sets of enzymes

Question 14

What types of reactions are NADH and NADPH involved in?

Answer 14

NADH: primarily involved in catabolic reaction that generate ATP, ratio of NAD+ to NADH is high

NADPH: primarily involved in anabolic reaction, ratio of NAD+ to NADPH is low

Question 15

Why do we divide the functions between NADH and NADPH

Answer 15

• because anabolic and catabolic reactions need to be regulated independently

Question 16

Give some examples of NADH function.

Answer 16

• NAD+ is reduced to NADH during the citric acid cycle
• electrons from NADH are passed down the electron transport chain to generate ATP

Question 17

Give some examples of NADPH function.

Answer 17

• biosynthesis of fatty acids
• biosynthesis of cholesterol

Question 18

When are activated carriers usually generated?

Answer 18

• they are usually generated in reactions coupled to ATP hydrolysis

Question 19

What is required to syntheses biological polymer

Answer 19

• an input of energy

Question 20

Describe an alternative route for ATP hydrolysis

Answer 20

• in some reaction when ATP is hydrolyzed, AMP and pyrophosphate (PPi) is released
• PPi is further hydrolyzed into two molecules of phosphate
• this results in larger change in free energy