Ctb003 - Mitochondria

Front 1

What are mitochondria?

Back 1

Vital organelles in eukaryotic cells

Front 2

What kind of relationship was established when an aerobic microorganism invaded an anaerobic host (to eventually form mitochondria)?

Back 2

Endosymbiosis

Front 3

Where is mitochondria found? What is it often associated with?

Back 3

Found near sites of high ATP utlization. Often associated with microtubules.

Front 4

Coordination of mtDNA and nuclear DNA is required for what?

Back 4

Synthesis, assembly and functioning of respiratory chain enzymes

Front 5

Coordination of mitochondria and the nucleus is required for what?

Back 5

Proper functioning

Front 6

What are the two major functions of mitochondria?

Back 6

1) complete oxidative metabolism of carbs, amino acids, fatty acids

2) coupling of ETC and oxidative phosphorylation for ATP generation

Front 7

What are the four compartments of mitochondria?

Back 7

1) outer mitochondrial membrane
2) intermembrane space
3) inner mitochondrial membrane
4) mitochondrial matrix

Front 8

What are the components of the outer mitochondrial membrane?

Back 8

1) porins or voltage-dependent anion channel (make OMM like sieve, allows small molecules to go through)
2) receptors
3) translocases of OMM (help translocation of proteins to various mitochondrial compartments)

Front 9

What are the two components of the intermembrane space?

Back 9

1) cytochrome c (usually stays within the space)
2) adenylate kinase (balances ADP, ATP ratio)

Front 10

What are the components of the inner mitochondrial membrane?

Back 10

1) cardiolipin (→ phosphorylates creatine kinase → energy reserves)
2) respiratory chain enzymes (complexes I - V)
3) transport proteins:
- ATP-ADP translocase (import ADP, export ATP)
- translocases of IMM (help import proteins to IMM or to matrix)

Front 11

What are the components of the mitochondrial matrix?

Back 11

1) Krebs cycle enzymes
2) peptidases
3) mtDNA (several copies)
4) ribosomes
5) Ca-2+

Front 12

Describe the electrical gradient of mitochondria.

Back 12

Inside of mitochondria is negative. This is the basis for the membrane potential (large force) and proton gradient (small force).

Front 13

How do mitochondria multiply?

Back 13

Binary fission.

Front 14

What does the negative electrical gradient inside mitochondria do?

Back 14

Drives:
- ADP/ATP transport
- proton/phosphate transport
- proton/pyruvate symport
- various translocases on OMM & IMM for protein import

Front 15

Describe human mitochondrial DNA.

Back 15

- double stranded (heavy and light)
- closed circular DNA
- no introns
- encodes rRNAs, tRNAs, 13-polypeptide-encoding RNAs (complex I-IV subunits)
- D-loop contains the origin of replication for the heavy strand (1), heavy and light strand promoters (2), 3 conserved sequence blocks (3) and termination association sequences (4).

Front 16

How does mtDNA replicate?

Back 16

Replication is bidirectional, asynchronous and semiautonomous.

Front 17

How does mtDNA transcribe?

Back 17

Transcription occurs symmetrically from the 2 promoters in the D-loop

rRNA transcripts outnumber the other transcripts

Front 18

What are the unique codons for mitochondria?

Back 18

AGA, AGG: STOP (normal: arginine)
AUA: methionine (isoleucine)
UGA: tryptophan (STOP)

Front 19

How is mtDNA inherited?

Back 19

X-linked/maternal.

Front 20

Does mtDNA undergo replicative segregation? If so, when?

Back 20

mtDNA DOES undergo replicative segregation and it occurs during mitosis and meiosis

Front 21

What is the mutation rate of mtDNA?

Back 21

10-20x higher than nuclear DNA

Front 22

Does mtDNA have threshold expression?

Back 22

Yes, when the threshold is crossed, the organ suffers.

Front 23

How many copies of mtDNA are present in mitochondria?

Back 23

2-10 copies.

There is a lot of cytoplasmic inheritance in each cell.

Front 24

What is the role of the nuclear genome in regards to mitochondrial biogenesis and nuclear-mitochondrial interactions?

Back 24

1) specifies all enzymes of mitochondrial matrix
2) cooperates with mitochondrial genome in assembling oxidative phosphorylation multisubunit enzyme complexes
3) encodes components of protein & small RNA import machinery (TOMS, TIMS)
4) encodes transcription factors for mtDNA transcription, replication, and proteins that target the mitochondria
4.5) controls the translation of specific mitochondrial mRNAs
5) controls the processing of specific mtRNA precursors

Front 25

What percentage of proteins have to be imported in to mitochondria?

Back 25

90+% (around 99%)

Front 26

Describe the mechanism of protein import into the mitochondria (9 steps).

Back 26

1) targeting sequence targets protein to mitochondria
2) cytosolic chaperones (Hsp70) unfold the protein (need ATP)
3) import receptors on OMM attach to the protein. (SAM complex is necessary for assembling complex OMM proteins)
4) general import pore or channels on OMM match up with channels in IMM -- translocation of protein occurs via contact sites between OMM & IMM
5) "machinery for protein import and assembly" pathway proteins and small intermembrane space proteins assist in sorting and assembly of proteins in the intermembrane space and inner mito membrane
6) need proton-motive force to transport proteins across the inner membrane space
7) translocation motors need mtHsp70 and ATP
8) proteolytic processing of matrix-targeting signals
9) refolding, assembly and intramitochondrial sorting (need Hsp60 and ATP)

Front 27

What are three possible sources of mutations?

Back 27

1) nuclear DNA (Mendelian inheritance)
2) cytoplasmic DNA (mtDNA) (maternal transmission)
3) x-linked

Front 28

What are some reasons for mtDNA mutations?

Back 28

1) mtDNA is attached to inner mito membrane and is the source of oxygen radicals
2) mtDNA lacks protective histones
3) mtDNA has a limited repair system

Front 29

What kinds of mutations occur in mtDNA?

Back 29

1) missense mutations (amino acid substitutions)
- LHON: Leber's Hereditary Optic Neuropathy

2) biogenesis mutations (tRNA point mutations; affect protein synthesis)
- MERRF: Myoclonus Epilepsy and Ragged Red Fibers
- MELAS: Mitochondrial encephalomyopathy, lactic acidosis, stroke-like symptoms)

3) insertion-deletion mutations
- flanked by direct repairs of nucleotides
- no family history
- most deletions are new mutations occur during development
- size and position of deletion can differ among patients
- KSS (Kearns Sayre Syndrome)
- PEO (Progressive External Ophthalmoplegia)

4) copy number mutations

Front 30

What aging diseases are associated with mitochondrial dysfunction?

Back 30

1) normal aging
- reactive oxygen species are major mtDNA-damaging agents
- mtDNA deletions accumulate with age
- oxidative phosphorylation normally declines with age

2) Parkinson's disease

3) Alzheimer's disease

Front 31

What is the relationship between mitochondria and apoptosis?

Back 31

cytochrome c release → binds to Apaf 1 → binds caspase 9 → activates caspase 9 → activates caspase 3 → triggers apoptosis

Front 32

Describe the relationship between BCL-2 family proteins and mitochondria.

Back 32

BCL-2 and BCL-XL block the release of cytochrome c from mitochondria and promote cell survival.