Mitochondria

What is the mitochondrial genome like? For what does it encode?

A circular DNA molecule that encodes for rRNA, tRNA, and 12 polypeptide subunits for inner membrane proteins. Any other proteins are encoded for the in the nucleus, translated in the cytosol and imported to the mitochondria.

What facilitated the increase in complexity in eukaryotic organisms?

Aerobic bacteria carry out cellular respiration on their outer plasma membrane, while eukaryotic organisms do this on their highly folded inner mitochondrial membranes. The increased surface area provided by the mitochondria allows for an increased capacity to make ATP.

Why does fine control of ATP production increase efficiency?

Because it reduces the likelihood that oxidative phosphorylation will mess up and produce ROS and delays aging.

Why can large eukaryotic cells survive?

Because they compartmentalize their energy production in mitochondria with elaborate cristae, that have much more surface area for production of ATP.

Why can't large bacterial cells survive?

Because they don't have a larger enough surface area to volume ratio to be able to produce enough ATP to support life.

What is the exception to strictly maternal transmission of mtDNA in animals?

Bivalves -- display doubly uniparental inheritance (DUI)

What are some secondary roles of the mitochondria?

Calcium storage, apoptosis pathway, heat generation, synthesis/modification/breakdown of molecules.

Why do mitochondria have their own genes?

Maintaining key genes allows eukaryotic cells to finely control the rate of respiration, so that mitochondrial genes can be turned on and off in response to cellular needs.

What is doubly uniparental inheritance?

Male and female mtDNA lineages gradually diverge in DNA sequence over time. Females of different species from the same ancestor are more closely related than the male counterpart of the same species from the same ancestor.

What are the TWO powerhouses of the cell?

Mitochondria and chloroplasts

Why are mitochondria inherited through females?

Mitochondria in the sperm do not enter the egg, or are destroyed soon after.

What is the role of mitochondria? Do all cells have the same amount?

Perform cellular respiration (burning of glucose) to generate cellular ATP; more active cells require more mitochondria.

The more surface area of the mitochondrion, the higher capacity to ________.

Produce ATP

Proteins in what space play a role in apoptosis?

Proteins in the inter membrane space of the mitochondria.

What are ROS?

Reactive oxygen species -- damage DNA, lipids, and other biomolecules.

Explain in depth the process of protein sorting to the mitochondrial matrix.

See slide 35 ppt RHE mitochondria.

Explain the ox-tox hypothesis.

Symbiont de-toxifed the cytoplasm of the host by consuming oxygen; proteins encoded by host genome allowed transport of ATP from mitochondria to host.

What are porins?

Transmembrane channel proteins (outer membrane of mitochondria) --allow free movement of small molecules and ions.

What are cristae? Why are they important? Why are they necessary?

Cristae are the distinctive infoldings of the inner membrane of the mitochondria. They are important because they vastly increase the organelle's surface area, which is necessary to accommodate the large number of protein complexes required for electron transport and ATP synthesis.

What is in the matrix of the mitochondria?

Gel-like consistency; contains many water soluble proteins and contains many enzymes, DNA molecules and ribosomes.

Explain the energy cycle.

Light energy is used to create glucose (photosynthesis), energy stored in glucose is used to make ATP (respiration), energy stored in ATP is used by cell (work).

What is the role of the inner membrane of the mitochondria?

Partitions the organelles into two separate compartments with different composition -- intermembrane space and the matrix.

How do proteins marked for the matrix get there?

Pass through points where the membranes come into contact with each other.

Why aren't male mitochondria normally inherited?

1) uniparental inheritance prevents possible "cytoplasmic warfare" between maternal and paternal mitochondria 2) maternal inheritance limits damage to mtDNA in embryos because eggs have much lower respiration rates then sperm

How do eukaryotic cells prevent age-related damage from being passed to the next generation?

Early in development, we set aside healthy mitochondria with healthy tDNA in germ line tissue, which will produce gametes at maturity. Mitochondria in germ cells remain dormant during development, limiting damage from ROS.

What was like the endosymbiont of the mitochondria? The host?

Endosymbiont: likely an alpha-proteobacteria. Host: likely methanogenic symbiont (more controversial)

Explain the hydrogen hypothesis.

Endosymbiosis was supported by the transfer of hydrogen from a hydrogen producing bacterium to a hydrogen dependent host.

What was the key to eukaryotic evolution and diversification?

Endosymbiotic mitochondria.

What is the mitochondrial theory of aging?

Even with fine control, eventually damage will occur. (oxidative damage/mutation/mitochondrial dysfunction)

What is another advantage of removing oxidative phosphorylation from the PM?

It frees up space for other specialized functions to occur on the PM (ie. phagocytosis).

What makes an organelle semi-autonomous?

It has its own DNA, can replicate divide and grow, and contains the machinery for transcription and translation... but must import materials and proteins from other parts of the cell.

What is the role of chaperone proteins?

Keep the protein unfolded until it is transferred successfully from the cytosol to the matrix, at which point it can assume its 3D shape.

Was the process of endosymbiosis abrupt?

No, it was a gradual process.

What are the two theories of endosymbiosis of mitochondria?

Ox-tox and hydrogen.

What is the purpose of apoptosis?

The breakdown of the parts of a cell so they can be used to form new cells.

Where do we inherit our mitochondria from?

The egg cell of our mother during fertilization.

How is the mitochondrial shape dynamic?

The mitochondria are in a constant state of flux, with fission and fusion occurring often.

How do proteins being sorted by the mitochondria know where to go?

There are different protein sorting signals for the outer membrane, intermembrane space, inner membrane and matrix.

Why does the inner membrane have so many proteins embedded in it?

They are required for the breakdown of glucose and production of ATP that occurs during cell respiration (ie. ATP synthase)