Mitochondria

Question 1

What is the structure of mitochondria?

Answer 1

• outer membrane
• intermembrane space
• inner membrane
• matrix
• cristae for higher surcafe area
• ribosomes
• mtDNA
• small granules

Question 2

What is the function of mitochondria? Briefly comment on the processes taking place within.

Answer 2

TCA/Kreb’s cycle/citric acid cycle (more elaborately in biochemistry, check later)

Cells utilize sugars (predominantly, can be sourced from amino acids and fatty acids too) and turn the into pyruvate. Pyruvate enters mitochodria and gets converted into acetyl CoA. As a side product, NADH (from NAD+) and FADH2 (from FAD+) which get synthesized carry electrons (in a form of H+) into the electron transport chain also termed oxidative phosphorylation because of the O2 presence demand which drive the ATP pums in the cristae of the inner membrane that create ATP (24+4 molecules from glycolysis/pyruvate).

Question 3

Where are the Kreb’s cycle enzymes?

Answer 3

matrix

Question 4

Where does the electron transport chain take place?

Answer 4

cristae

Question 5

Where are the ATP synthase pumps?

Answer 5

in the cristae protrusions

Question 6

Name an example of cells requiring a lot of mitochondria

Answer 6

muscle cells

Question 7

What does elevated occurance of mitochondria indicate?

Answer 7

Excessive proliferation of mitochondria is a sign of disease. Mitochondria are damaged or mutated and fail to produce ATP. This induces the cell to make more copies of mitochondria or increase the number of cristae to compensate for the loss.

Question 8

How do mitochondria replicate?

Answer 8

furrowing and fission in the cell interphase (before nuclear DNA rep.)

Question 9

Define mtDNA.

Answer 9

Located in so called nucleoid regions with 4-5 copies of mtDNA in the matrix. 16kBP encoding for 2 rRNAs, 22 tRNAs and 13 proteins, other proteins have to be imported into the mitochondria. Some subunits of the proteins that are synthesized are:

• cytochrome oxidase
• ATPase
• CoQH2 cytochrome C reductase
• NADH-CoQ reductase

Question 10

What is the evolutional origin of mitochondria?

Answer 10

Most probably prokaryotic origin. Aerobic bacteria (mitochondria) were engulfed by anaerobic cells and existed in endosymbiosis. Present day anaerobis eukaryots with a distant evolutional pathway found. Supporting arguments: presence of own mtDNA, ribosomes have a different encoding pattern from the cytosolic ribosomes (read the sequences differently), when treated with some ATB targeting protein synthesis, mitochondria may be rendered unable to synthesize their own proteins.

Question 11

Explain the import of proteins into mitochondria.

Answer 11

Outer membrane = aqua. porins, small proteins can enter
Inner membrane = cardiolipin, makes the membrane impenetrable
Complex and selective protein complexes

CYTOSOL-OM.
Proteins with mitochondrial import sequence on the N-terminus are bound with chaperones to prevent them from folding. Recognized by TOM (translocator in the outer membrane) and translocated into the intermemrabe space. 1) stay there and fold, 2) are recognized by SAM and get embedded into the outer membrane space

INTERM-IM.
3) travel to matrix by TIM23 translocator in the inner membrane that spans both outer and inner membrane with a hydrophobic a-helical protrusion, import sequence gets cleaved off and proteins mature 4) are recognized by TIM22 and get embedded in the inner membrane

MATRIX-IM.
Proteins encoded in the matrix that are destined to be embedded to the inner membrane are integrated by OXA