Mitochondria + Chloroplasts Flashcards
What is the primary function of M + C?
ATP synthesis
via ATP synthase
How efficient is ATP synthase?
What does it require?
100 ATP/sec
3H+ for 1 ATP
Describe how ATP synthase functions
H+ pass through F0
-> stalk rotates
-> conformational change in F1
= facilitates ATP production
What are the 2 subunits of ATP synthase?
F0 - embedded in membrane
F1 - peripherally associated with membrane
Where is ATP synthase found?
M’s inner membrane
C’s thylakoid membrane
Eubacteria’s inner membrane
What are the 2 components of a proton gradient?
Difference in voltage across membrane
= membrane potential
Difference in H+ conc
= pH
How is a proton gradient generated?
High energy e- passed along ETC (via series of REDOX reactions)
- > release large amounts of energy
- > used to pump H+ across membrane
What is a proton gradient a form of?
Stored energy
Describe proton pumping in mitochondria
- Fats + carbs enter Kreb’s cycle
- NADH generated
- Passes 2e- onto ETC
(including cytochrome bc complex) - Passes 2e- onto O2
- Forms H2O
What does NADH stand for?
Nicotinamide adenine dinucleotide
What are mobile electron carriers?
Substances that shuttle e- between proton pumping complexes
Give 2 examples of mobile electron carriers in mitochondria
Ubiquinone
- carries e- from NADH dehydrogenase to cytochrome bc complex
Cytochrome c
- carries e- from cytochrome bc complex to cytochrome oxidase complex
What is chemisosmotic coupling?
What is this known as in mitochondria?
The linkage of e- transport, H+ pumping and ATP synthesis
Oxidative phosphorylation
What is redox potential?
The measure of tendency to acquire or lose e-
What is the redox potential of NADH?
What is the redox potential of H2O?
High e- transfer potential
= -ve value
Low e- transfer potential
= +ve value
What happens to the redox potential along the mitochondrial ETC?
Increases
(e- affinity increases)
From -ve to +ve
= good e- donor to good e- acceptor
How many carbons enter the Kreb’s cycle and how many leave?
What else is produced in each turn of the cycle?
2C enter in Acetyl CoA
2C released as CO2
3 NADH
1 GTP
1 FADH2
Give 2 examples of agents that interfere with oxidative phosphorylation
What do these do?
Cyanide
Carbon monoxide
Block passage of e- to O2
= ATP synthesis grinds to a halt
What do uncoupled mitochondria generate?
Heat
- H+ flow through mitochondrial membrane but NOT through ATP synthase
Why is light required for photophosphorylation?
H2O is a poor e- donor
-> requires lots of light energy to extract e-
How is the H+ gradient across the thylakoid membrane generated?
Proton pumping + protons released when e- are pulled off H2O
How are high energy e- produced by light energy?
What then happens to this energy?
Sunlight absorbed by chlorophyll
-> e- raised to higher energy level by photons
Channeled into special pair of chlorophyll molecules in reaction centre
What do photosystems consist of?
Antenna complex + a reaction centre
Describe the flow of e- through the 2 photosystems
e- extracted from water -> PSII -> Cytochrome b6-f complex -> PSI -> NADP reductase = NADPH
Give an example of a mobile electron carrier in chloroplasts
Plastoquinone
How do redox potentials change in photosynthesis?
e- moves from high to low energy
with boosts at PSI + PSII
In photosynthesis how many NADPH and ATP are produced for every 3C sugar produced?
What is this ATP + NADPH used for?
9 ATP
6 NADPH
Carbon fixation in the Calvin cycle
What does Rubisco stand for?
Ribulose bis phosphate carboxylase
What does Rubisco do?
Catalyses CO2 + RuBP
= Adds 1C + 5C
= 6C compound
-> cleaved into 2 x 3C compounds
What are the similarities between mitochondria + chloroplasts?
Use H+ gradients across membranes to produce ATP via ATP synthase
e- transport along ETC drives H+ pump
Cytochrome bc and b6f show sequence similarity
Ubiquinone + plastoquinone resemble one another
What are the differences between mitochondria + chloroplasts?
M: high energy e- from NADH
C: low energy e- from H2O but excited by light
M: ultimate e- acceptor = O2
C: “ = NADP+
M: chemical bond energy used in cellular processes
C: CB energy + reducing power used in C fixation
