Mito/Peroxisomes

Question 1

why do we need organelles? (4-and give an example for each)

Answer 1

1. separation of activities - ATP used in cytosol, made in mito
2. Concentration of activities - TCA cycle in mito
3. Sequestration of toxic molecules - hydrogen peroxide in peroxisomes
4. Microenvironments - H+ gradient across mito membrane

Question 2

why are organelles annoying? (4)

Answer 2

as a cell, you need to control their number and shape, you have to get molecules in and out of them, you have to control location, mvmt and inheritance, and you have to dedicate resources/energy to assemble them

Question 3

Mito structure

Answer 3

Be able to draw, label matrix, cristae, inner/outer membrane and intermembrane space

Question 4

Functions of mito and an example of each (5)

Answer 4

1. Energy production (ATP synthesis)
2. Catabolism (fatty acid oxidation)
3. Anabolism (fatty acid synthesis)
4. Heat (body temp control)
5. Signaling (apoptosis)

Question 5

Mito ATP production (3 overarching processes)

Answer 5

Sugars/amino acids/fats into TCA cycle, NADH into ETC, electrochemical gradient drives ATP synthase

Question 6

T/F. Mito inner membrane is impermeable, even to H+

Answer 6

True, thus requiring lots of special carriers

Question 7

T/F. Mito outer membrane is impermeable, even to H+

Answer 7

False, outer membrane is highly permeable with lots of B-barrel porins

Question 8

Examples of disease associated with mito dysfunction

Answer 8

heart problems, neurodegeneration, cancer, aging

Question 9

Gene composition of mtDNA

Answer 9

13 protein coding genes, 22 tRNAs, 2 rRNAs

Question 10

nucleoids

Answer 10

DNA-protein complexes where mtDNA is wrapped, several mtDNAs per nucleoid

Question 11

how is mtDNA weird? (3)

Answer 11

primarily maternal inheritance, genetic code diffs, 100s-1000s of copies in a cell

Question 12

steps for nuclear encoded mito proteins to reach and be function in mito

Answer 12

1. be targeted to mito
2. cross one or both mito membranes
3. sort themselves into OM, IM, IMS or matrix
4. often assemble with other subunits

Question 13

presequences

Answer 13

N-terminal signals on nuclear encoded mito proteins that are cleaved after their import. All presequences share a common 3D structure

Question 14

Mito import (7 steps)

Answer 14

1. Precursor binds cytoplasmic chaperones
2. Precursor binds to mito surface receptors
3. Precursor translocated across OM via TOM
4. Translocation across IM via TIM
5. Pulled through TOM-TIM complexes by matrix chaperon Hsc70
6. Presequence removed by processing protease in matrix
7. Imported protein folds with help of matrix chaperones

Question 15

Two types of protein sorting mechanisms in mito

Answer 15

OM and IM sorting, and IMS sorting, which use different machines and mechanisms

Question 16

nonbilayer phospholipids (2)

Answer 16

PE (phosphatidylethanolamine) and CL (cardiolipin)

Question 17

ER-mitochondrial crosstalk

Answer 17

PE made in mito IM by decarboxylation of PS, PS is made in the ER (like most lipids). CL is made in mito from PA, PS/PA are imported into mito from ER, and PE is exported to ER

Question 18

mitochondrial associated membranes (MAMs)

Answer 18

facilitate the exchange of lipids to and from the mito

Question 19

ER-mito tethers have roles in

Answer 19

crosstalk– involving calcium signaling, fission, apoptosis

Question 20

What (very broadly) controls number, size and shape of mitos in cell

Answer 20

regulated fusion and fission, mediated by a family of GTPases (Mfn/Opa1 fusion, Drp1 fission)

Question 21

What features delineate the sites of mito division

Answer 21

ER tubules and mtDNA

Question 22

T/F. Peroxisomes do not contain DNA and are surrounded by a lipid bilayer.

Answer 22

False, surrounded by a single membrane.

Question 23

Range of peroxisome counts in cells

Answer 23

From nearly undetectable to thousands of organelles, depending on metabolic demand

Question 24

Big ticket peroxisome function

Answer 24

Contain oxidases that produce H202 during lipid metabolism and catalase to degrade it

Question 25

Three other peroxisome functions

Answer 25

Lipid breakdown, lipid synthesis and bile acid synthesis/cholesterol

Question 26

T/F. Peroxisomes must import all their proteins

Answer 26

True

Question 27

Peroxisomal import machinery features (3)

Answer 27

1. C-terminal import signal PTS1
2. PTS1 signal recognition by cytosolic protein Pex5 which targets protein to surface
3. Peroxisomal membrane machinery form a pore to import protein

Question 28

T/F. Proteins translocated to the mito and to peroxisomes much be unfolded to be threaded through import pores

Answer 28

False, to the mito this is true, but peroxisomal proteins and sometimes even oligomers can be imported in a folded state.

Question 29

2 stages of peroxisomal assembly

Answer 29

1. de novo biogenesis

2. growth and division

Question 30

Where do the membranes for newly formed peroxisomes come from?

Answer 30

ER - and some peroxisomal proteins are inserted in the ER membrane and bud off in vesicles

Question 31

How do peroxisomes grow and divide?

Answer 31

Growth by uptake of peroxisomal proteins and lipids from cytosol, division by fission into daughter peroxisomes

Question 32

Mitochondrial derived vesicles

Answer 32

Vesicles with peroxisomal proteins that bud off the mito, then fuse with either ER-derived pre-peroxisomes, or a subclass of them

Question 33

T/F. Mito can be formed de novo.

Answer 33

False, they can arise only from growth and division of pre-existing mitos