1. Mitochondria Guest lecturer: Chris Moyes, Dept of Biology
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2. Endosymbiosis
Mitochondria formed as a result of an endosymbiotic event around 2 billion years ago.

3. From: Gerhart and Kirschner: Cells, Embryos and Evolution

4. Mitochondrial compartments
Inner membrane
Respiratory chain and ATP synthase
impermeable to most charged molecules
highly folded into invaginations called cristae.
Outer membrane
Permeable to larger molecules
Matrix
Enzymes of the citric acid cycle, mtDNA
Intermembrane space
space between inner and outer membranes

5. Mitochondrial compartments

6. Mitochondrial morphology and movement
Mitochondria are dynamic organelles
they may exist as individual organelles
may become elaborate network
move throughout the cell on cytoskeleton
Changes in the network are mediated by fission and fusion proteins
Fuzzy Onion Protein (FZO) causes fusion
Dynamin-Related Protein causes fission

7. Mitochondrial reticulum

8. Fusion and fission proteins regulate network

9. Mitochondrial energy production
Three major steps in oxidative phosphorylation
1) Production of reducing equivalents (NADH, FADH2) from glycolysis, fatty acid oxidation, and the citric acid cycle
2) Electron transport and generation of proton motive force
3) Phosphorylation - Synthesis of ATP, driven by the proton motive force

10. Mitochondria make other products
Mitochondria produce biosynthetic precursors
OXPHOS also leads to the production of:
Superoxide: formed when O2 steals electrons from the ETC complexes
Heat: a by-product of the reactions of OXPHOS

11. Overview of energy production by OXPHOS
Show 14-10, gen overview

12. Reducing equivalents are produced in the oxidation of carbohydrate and lipid

13. Oxidation and Electron Transport
Electrons from NADH and FADH2 are passed down respiratory chain to O2
Electron transport expels protons, creating a proton gradient- the proton motive force (PMF)

14. Proton motive force (PMF)
The PMF is an electrochemical gradient of membrane potential (ΔΨ) and pH (ΔpH)

15. The PMF supplies the energy for active transport into the mitochondria

16. Phosphorylation The F1Fo ATPase (or ATP synthase) is a molecular motor
-it uses the PMF to make ATP
-it can also be reversed (using ATP hydrolysis to recharge the PMF)

17. Oxidation and phosphorylation are coupled by a shared dependence on the PMF

18. Because of this “coupling”, the two processes are interdependent
If the PMF is large, what would you predict about oxygen consumption?
If you took away oxygen, what would happen to the PMF?
What would an increase in [ADP] do to the oxygen consumption?
What would happen to ATP synthesis and oxygen consumption if the inner membrane became leaky?

19. Uncoupling proteins Many mammals warm vital tissues using brown fat
Adipose tissue with abundant mitochondria that possess a the protein thermogenin (or uncoupling protein 1).
UCP-1 short-circuits the proton gradient, increasing VO2 and heat production.
All eukaryotes have proteins related to UCPs, that are thought to prevent the PMF from “over-charging”, thereby reducing ROS production.

20. Mitochondrial biogenesis requires proteins encoded in 2 genomes (nucleus and mtDNA)
encodes few proteins
1000’s of copies per cell
genes transcribed as a polycistron
transcribed and translated directly in mitochondria)
Nucleus
encode most proteins
2 copies of each gene per diploid cell
genes regulated independently
proteins imported by post-translational import from cytoplasm

21. Peculiarities of mtDNA
mtDNA is a very compact genome
-genes attached end to end, with mRNA regions interspersed among rRNA and tRNA genes
-tRNA excision liberates protein-coding genes
-many genes lack a full termination codon (TAA)
Diversity
-maternal origin (most animals)
-many cells have multiple genotypes within a single cell (heteroplasmy)
-defects accumulate with age

22. Editing of mtDNA polycistron

23. Nuclear gene expression is coordinated by transcription factor networks

24. Mt enzyme synthesis requires coordinated gene expression and accessory factors