lecture 5 Flashcards
how are energetically unfavourable rxns driven?
rxn Y–>X is favoured,
we can still drive this rxn forward
(X–>Y) by siphoning off Y in another favourable rxn (Y–>Z)
energetically unfavourable rxns: what is the equilibrium?
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
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
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
molecules wander randomly into the cytosol in a process called
diffusion
what size of molecules diffuse slower?
larger molecules
what is important for diffusion in terms of the media
the viscosity of the media plays a role in diffusion speed
highly viscous media:
enzyme will never function at 100%
(less efficient)
How do we determine Vmax?
1/v= Km/Vmax??
Enzyme inhibition
competitive inhibitors compete for the activation site
competitive inhibitors have the same or v similar structure to the enzyme
enzyme inhibition: affinity
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
Enzyme inhibition is a major method that cells use to
regulate gene expression
enzyme inhibitors are important
pharmaceutical agents
competitive inhibitors: Km and Vmax?
Competitive inhibitors increase the Km but Vmax remains the same
why does Vmax remain the same with competitive inhibition?
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
Examples of activated carriers
ATP
NADH
NADPH
Why are activated carriers reactive?
dipoles
phosphate-hydrogen bond is relatively unstable= able to give off energy easily
How is energy captured using coupled reactions?
an energetically favourable rxn is used to drive an energetically favourable rxn
-cells have elaborate systems to capture energy from food
NADH and NADPH general function
both are carriers of two high energy electrons and a proton (H+) that forms a hydride ion H-
Why is it important that NADH and NADPH have different phosphate groups?
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
do NADH and NADPH have the same function?
NO! v similar molecule but diff functions
NADH function
-catabolic rxns that generate ATP
-ratio of NAD+ to NADPH is HIGH
NADPH function
-anabolic rxns
-ratio of NADP+ to NADPH is LOW
Examples of NADH function
-NAD+ is reduced to NADH in the citric acid cycle
-Electrons from NADH are passed down the ETC to generate ATP
Example of NADPH function
-biosynthesis of fatty acid
-biosynthesis of cholesterol
How are activated carriers usually generated?
they are generated in rxns coupled to ATP hydrolysis
Synthesis of biological polymers
synthesis usually needs energy input!
hydrolysis rxns are energetically favourable!
