Lecture 13 - mitochondria and chloroplasts

Question 1

What is the endosymbiont theory?

Answer 1

first eukaryotic common anscestor - formed from engulfed prokaryotic ancestor cell developing internal membrane compartments
common ancestor cell engulfed and maintained endosymbiotic organism and other additional changes gave rise to cellular features now common in all eukaryotic cells

Question 2

What is the function of mitochondria?

Answer 2

double membrane-bound organelle that plays a role in energy production derived from carbohydrate and lipid catabolism (oxidative phosphorylation)

Question 3

What is the function of chloroplast?

Answer 3

energy production and carbohydrate synthesis via photosynthesis

Question 4

What is unique about mitochondria and chloroplast?

Answer 4

• contain their own DNA
• partake in organelle biogenesis - includes protein targeting, membrane assembly, morphology, motility, replication, degradation and inheritance during cell division
• semi-autonomous - organelle rep controlled by both nuclear genome and organelle genome
• arise only from pre-exisitng organelles

Question 5

What are the two membranes of the mitochondria?

Answer 5

outer membrane
inner membrane

Question 6

What does the outer membrane of mitochondria contain?

Answer 6

porins - barrel shaped integral membrane proteins with large internal channel

Question 7

What is the outer membrane of mitochondria permeable to?

Answer 7

ions and small molecules

Question 8

What is the pH in the intermembrane of mitochondrial space?

Answer 8

high [H+] - low pH

Question 9

What does the inner membrane of the mitochondria form?

Answer 9

lies adjacent to outer membrane, forms folds (cristae) that extend into organelles interior - provides increased SA

Question 10

Is the inner membrane of the mitochondria permeable?

Answer 10

No it is impermeable, contains H+ gradient and in the site of ATP synthase

Question 11

What is the mitochondrial matrix?

Answer 11

aqeuous interior
- site of TCA cycle, ATP from oxidative phosphorylation
- contains mitochondrial genome (circular DNA)
- contains ribosomes (used for translation of mitochondrial genome encoded proteins)

Question 12

Are mitochondrial proteins encoded by nuclear genes?

Answer 12

mostly, they are targeted post-translationally to mitochondria

Question 13

What is something we’ve recently discovered about mitochondria?

Answer 13

not a bean shaped organelle but it possesses a wide range of shapes and sizes, forms a mitochondrial network - highly branched long and interconnected series of tubules

Question 14

How can we view th ‘bean shaped’ mitochondria we know under he microscope?

Answer 14

through sectioning of a single tubule of mitochondrial network

Question 15

What can mitochondrial tubules undergo?

Answer 15

fusion and fission

Question 16

How does fusion and fission occur in the mitochondria?

Answer 16

response to environmental stimuli, developmental status or overall energy requirements of the cell

Question 17

What do rates of fission versus fusion control?

Answer 17

number, size and extent of inter-connections of mitochondrial network

Question 18

What are fission and fusion controlled by in the mitochondria?

Answer 18

distinct protein machineries

Question 19

What are the steps to mitochondrial fission?

Answer 19

1. ER tubules encircle mitochondrion at future fission site and initiate constriction = ER subdomain MAM
2. Drp1 recruited from cytoplasm to constriction site and assemble into helices (DRP1 ring) around surface of mitochondrial outer membrane
   - recruitment of Drp1 mediated by lipid microdomain in mitochondrial outer membrane which is enriched with cardiolipin, Drp1 interacts with cardiolipin at constriction site
3. conformational change in Drp1 ring due to GTP hydrolysis results in further membrane constriction and fission - formation of two daughter mitochondrion