lecture 5

Question 1

how are energetically unfavourable rxns driven?

Answer 1

rxn Y–>X is favoured,
we can still drive this rxn forward
(X–>Y) by siphoning off Y in another favourable rxn (Y–>Z)

Question 2

energetically unfavourable rxns: what is the equilibrium?

Answer 2

Y is constantly being taken to make the product Z

you are left with a little X, a little Y and a lot of Z as the equilibrium

Question 3

example: K= [Y]/[X]= 1/5
for the rx X–> Y

what happens to [Y] when you siphon off Y in the rxn Y–>Z

Answer 3

siphoning off Y cases the [Y] to be very low such that the ratio of Y/X is low

[Y]/[X]= 0.5/5

this causes the conversion of X–> Y to be favoured so that levels of X and Y can be brought back to levels at the equilibrium

Question 4

molecules wander randomly into the cytosol in a process called

Answer 4

diffusion

Question 5

what size of molecules diffuse slower?

Answer 5

larger molecules

Question 6

what is important for diffusion in terms of the media

Answer 6

the viscosity of the media plays a role in diffusion speed

Question 7

highly viscous media:

Answer 7

enzyme will never function at 100%
(less efficient)

Question 8

How do we determine Vmax?

Answer 8

1/v= Km/Vmax??

Question 9

Enzyme inhibition

Answer 9

competitive inhibitors compete for the activation site

competitive inhibitors have the same or v similar structure to the enzyme

Question 10

enzyme inhibition: affinity

Answer 10

depending on the affinity of the substrate to the binding site

lower affinity= need more substrate to do the same thing

higher affinity= need less substrate to do the same thing

Question 11

Enzyme inhibition is a major method that cells use to

Answer 11

regulate gene expression

Question 12

enzyme inhibitors are important

Answer 12

pharmaceutical agents

Question 13

competitive inhibitors: Km and Vmax?

Answer 13

Competitive inhibitors increase the Km but Vmax remains the same

Question 14

why does Vmax remain the same with competitive inhibition?

Answer 14

Km will be different because you need a different amount of substrate to reach the same level

Vmax remains the same because you can add more substrate until it out competes the inhibitor

Question 15

Examples of activated carriers

Answer 15

ATP
NADH
NADPH

Question 16

Why are activated carriers reactive?

Answer 16

dipoles

phosphate-hydrogen bond is relatively unstable= able to give off energy easily

Question 17

How is energy captured using coupled reactions?

Answer 17

an energetically favourable rxn is used to drive an energetically favourable rxn

-cells have elaborate systems to capture energy from food

Question 18

NADH and NADPH general function

Answer 18

both are carriers of two high energy electrons and a proton (H+) that forms a hydride ion H-

Question 19

Why is it important that NADH and NADPH have different phosphate groups?

Answer 19

gives them a distinct shape and allows the binding of different sets of enzymes!!!!

but diff phosphate group does not affect the electron-transfer properties of NADH vs NADPH

Question 20

do NADH and NADPH have the same function?

Answer 20

NO! v similar molecule but diff functions

Question 21

NADH function

Answer 21

-catabolic rxns that generate ATP
-ratio of NAD+ to NADPH is HIGH

Question 22

NADPH function

Answer 22

-anabolic rxns
-ratio of NADP+ to NADPH is LOW

Question 23

Examples of NADH function

Answer 23

-NAD+ is reduced to NADH in the citric acid cycle
-Electrons from NADH are passed down the ETC to generate ATP

Question 24

Example of NADPH function

Answer 24

-biosynthesis of fatty acid
-biosynthesis of cholesterol

Question 25

How are activated carriers usually generated?

Answer 25

they are generated in rxns coupled to ATP hydrolysis

Question 26

Synthesis of biological polymers

Answer 26

synthesis usually needs energy input!

hydrolysis rxns are energetically favourable!