Organelle Ecology - the Mitochondria

Question 1

Structure

Answer 1

1. Intro to mitochondria
2. Mitochondrial fission
3. Mitochondrial fusion

Question 2

Mitochondrial structure

Answer 2

• OMM
• crista space
• IMM
• cristae
  -crista junction
• matrix

Question 3

Mitochondrial organisation

Answer 3

• motile
• networking
• tubular, fusing, branching structure
• can be tissue specific

Question 4

Cell specificity

Answer 4

animal mitochondria vary in morphology as independent ovoids or reticulate networks

Question 5

Mitochondrial fission mechanism

Answer 5

1. Fis1 tethers Dnm1 to the OMM
2. Mdv1 coassembly: active fission apparatus
3. GTP hydrolysis

Question 6

Dnm1

Answer 6

dynamin 1

Question 7

Mdv1

Answer 7

mitochondrial division membrane 1

Question 8

ER-mitochondrial encounter structure

Answer 8

• ERMES
• bridges the ER, mitochondria and actin

Question 10

mitofusin GTPases

Answer 10

• Mfn1/2: OMM fusion
• Opa1: IMM fusion

Question 11

Regulation of fusion

Answer 11

stochiometry of L-Opa1 to S-Opa1; controlled by RNA splicing

Question 12

L-Opa1

Answer 12

long isoform

Question 13

S-Opa1

Answer 13

short isoform

Question 14

What happens to membrane potential during fission/fusion?

Answer 14

• drops and repolarises

Question 15

What roles do fission and fusion play?

Answer 15

1. QC
2. heteroplasmy
3. metabolic efficiency

Question 16

Mitochondrial QC

Answer 16

• fission segregates impaired mitochondria from healthy ones (autophagy)
• fusion dilutes and buffers damage

Question 17

Mitochondrial DNA

Answer 17

• multi-copy nucleoids through the network
• highly compacted within the matrix

Question 18

nuceoids

Answer 18

• punctate mtDNA-protein complices

Question 19

mtDNA replication

Answer 19

• uncoupled from cell cycle

Question 20

Heteroplasmy

Answer 20

• in plants
• coexistence of mitochondria containing various amounts of DNA within a single cell
• suggests mitochondrial fission w/ unequal DNA distribution

Question 21

What are the advantages of having a mitochondrial network?

Answer 21

• mitochondria close to the cell surface decrease the diffusion distance from metabolites and oxygen
• the resulting proton motive force can be transported for use in the distal network and inner cell
• this is faster than diffusion

Question 22

What is the right size for a cell?

Answer 22

• v. small: macromolecular crowding; slow diffusion
• v. large: large diffusion distance

Question 23

Optimal cell size

Answer 23

minimal characteristic diffusion time (tau)

Question 24

Tau models

Answer 24

• eukaya: 15.7 micrometres
• prokaryotes: 1.1 micrometres

Question 25

Mitochondria early

Answer 25

structural perspective

Question 26

Universal Scaling Laws

Answer 26

- fitness is maximised by metabolic capacity

Question 27

metabolic capacity

Answer 27

the rate at which energy and material resources are taken up from the environment, and allocated to some combination of survival and reproduction

Question 28

The West, Brown, Enquist (WBE) model

Answer 28

stresses the importance of branching networks for internal transfer

Question 29

What does the WBE model demand?

Answer 29

a space-filling, fractal-like, branching pattern; to minimise the energy required to distribute resources to supply an entire organismal volume