Mitochondria Flashcards
Explain the Outer Membrane of the mitochondria ?
- Outer membrane contains porins, which act as a pore allowing some specific molecules to diffuse through, like channel proteins.
- Permeable to proteins 5kDa or less
Explain the Inner Membrane of the mitochondria ?
- The composition of this region is similar to the cytoplasm since the porins in the outer membrane are believed to be conduits for regulated water transport.
- This region has a higher protein composition than the matrix.
- The pH is lower than the matrix since protons are pumped across the inner membrane into this space.
Explain the Matrix of the mitochondria ?
- The matrix is viscous, containing less water than the cytoplasm.
- The matrix contains the DNA, ribosomes, enzymes, organic molecules, and inorganic ions.
- The enzymes in the matrix enable the reactions of the TCA cycle, beta oxidation of fatty acids and oxidative phosphorylation.
- The pH is more alkaline than the intermembrane space.
Explain the Cristae of the mitochondria ?
- The inner mitochondrial membrane is extensively folded into cristae.
- Cristae increase total membrane surface area, allowing more oxidative phosphorylation to occur (than if it were smooth).
- The inner membrane is freely permeable only to O2, CO2 and H2O, but less permeable to ions and small molecules than the outer membrane.
Explain the Cristae arrangements in different cell types ?
Liver - arranged like a series of shelves
Kidney - tightly packed like a stack of coins
Nerve - form network of tubes
Where did Mitochondrion originate from ?
Bacteria that were engulfed by an ancestral pre-eukaryotic cell and survived inside, living in symbiosis with their host.
1.5 billion years ago!
Evidence for Endosymbiotic theory ?
- The mitochondrion and chloroplast have many similarities
- A mitochondrion can divide like a bacterium (binary fission)
Explain Mitochondrial DNA?
- Mitochondria have their own circular DNA, which is extragenomic to the cells they are found in.
- Over time some of the mt genes have been moved to the host genome, but some have remained within the organelle.
- The mtDNA-encoded polypeptides are all subunits of enzyme complexes of the oxidative phosphorylation system.
- Mitochondria are not self-supporting; instead they require imported proteins from the cell.
Nuclear DNA vs Mitochondrial DNA (mtDNA)
Nuclear DNA - inherited from all ancestors
Mitochondrial DNA - Inherited from a maternal lineage
What are some functions of the Mitochondrion ?
- Aerobic carbohydrate metabolism via TCA cycle in matrix
- Fatty acid metabolism via TCA cycle in matrix
- ATP production via oxidative phosphorylation in inner mitochondrial membrane
What products do you get when at the end of one cycle of the TCA cycle ?
- 3 NADH
- 1 FADH2
- 1 ATP
- 2 CO2
Explain what β Oxidation does ?
- The triglycerides are broken into fatty acids and glycerol and can all be converted into Acetyl CoA
- One Actyl CoA is made per cycle, and this then enters the TCA cycle
What are the products of β Oxidation ?
- Acetyl CoA
- FADH2, NADH, H+
What do the reactions of the TCA cycle & oxidation of fatty acids produce ?
Activated electron carriers (reduced coenzymes) that are used in oxidative phosphorylation
What is Proton-motive force ?
Proton pumping creates an imbalance of protons (& a charge difference) between the matrix & intermembrane space
What is NADH reductase and what does it do (inner mitochondrial membrane)?
NADH reductase is an electron carrier (complex I) in the membrane & oxidises NADH to NAD+ + H+ + e. It simultaneously pumps protons to the intermembrane space & carries electrons to ubiquinone
What happens to FADH2 and what does it do (inner mitochondrial membrane)?
FADH2 is oxidised by complex II (succinate dehydrogenase) into FAD + 2H+ + 2e. It transfers the electrons to ubiquinone, but NOT THE H+
What do Complex III & IV pump ?
Complex III & IV pumps H+ ions con-currently with electrons. III receives electrons from ubiquinone, so the H+ ions will be displaced to the intermembrane space
Complex IV is the last electron carrier. What is the final electron acceptor ?
Oxygen
When protons have accumulated the proton motive force drives ?
Protons back to the matrix via the ATP synthase. This is coupled to ATP synthesis.
Explain Chemiosmosis ?
The pH gradient set up by pumping protons into the inner mitochondrial space is harnessed and used by ATP synthase in the inner mitochondrial membrane (IMM) to add phosphate onto ADP (ie make ATP)
What is the term given for disrupting oxidative phosphorylation ?
Uncoupling
What are some examples of Uncouplers ?
Aspirin and DNP (2,4-Dinitrophenol)
What do Uncouplers do ?
They act by binding to protons and effectively uncouples pH gradient from ATP synthesis, causing ATP depletion and for the energy generated by electron transfer to be lost as heat
