Mito/Peroxisomes Flashcards
why do we need organelles? (4-and give an example for each)
- separation of activities - ATP used in cytosol, made in mito
- Concentration of activities - TCA cycle in mito
- Sequestration of toxic molecules - hydrogen peroxide in peroxisomes
- Microenvironments - H+ gradient across mito membrane
why are organelles annoying? (4)
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
Mito structure
Be able to draw, label matrix, cristae, inner/outer membrane and intermembrane space
Functions of mito and an example of each (5)
- Energy production (ATP synthesis)
- Catabolism (fatty acid oxidation)
- Anabolism (fatty acid synthesis)
- Heat (body temp control)
- Signaling (apoptosis)
Mito ATP production (3 overarching processes)
Sugars/amino acids/fats into TCA cycle, NADH into ETC, electrochemical gradient drives ATP synthase
T/F. Mito inner membrane is impermeable, even to H+
True, thus requiring lots of special carriers
T/F. Mito outer membrane is impermeable, even to H+
False, outer membrane is highly permeable with lots of B-barrel porins
Examples of disease associated with mito dysfunction
heart problems, neurodegeneration, cancer, aging
Gene composition of mtDNA
13 protein coding genes, 22 tRNAs, 2 rRNAs
nucleoids
DNA-protein complexes where mtDNA is wrapped, several mtDNAs per nucleoid
how is mtDNA weird? (3)
primarily maternal inheritance, genetic code diffs, 100s-1000s of copies in a cell
steps for nuclear encoded mito proteins to reach and be function in mito
- be targeted to mito
- cross one or both mito membranes
- sort themselves into OM, IM, IMS or matrix
- often assemble with other subunits
presequences
N-terminal signals on nuclear encoded mito proteins that are cleaved after their import. All presequences share a common 3D structure
Mito import (7 steps)
- Precursor binds cytoplasmic chaperones
- Precursor binds to mito surface receptors
- Precursor translocated across OM via TOM
- Translocation across IM via TIM
- Pulled through TOM-TIM complexes by matrix chaperon Hsc70
- Presequence removed by processing protease in matrix
- Imported protein folds with help of matrix chaperones
Two types of protein sorting mechanisms in mito
OM and IM sorting, and IMS sorting, which use different machines and mechanisms
nonbilayer phospholipids (2)
PE (phosphatidylethanolamine) and CL (cardiolipin)
ER-mitochondrial crosstalk
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
mitochondrial associated membranes (MAMs)
facilitate the exchange of lipids to and from the mito
ER-mito tethers have roles in
crosstalk– involving calcium signaling, fission, apoptosis
What (very broadly) controls number, size and shape of mitos in cell
regulated fusion and fission, mediated by a family of GTPases (Mfn/Opa1 fusion, Drp1 fission)
What features delineate the sites of mito division
ER tubules and mtDNA
T/F. Peroxisomes do not contain DNA and are surrounded by a lipid bilayer.
False, surrounded by a single membrane.
Range of peroxisome counts in cells
From nearly undetectable to thousands of organelles, depending on metabolic demand
Big ticket peroxisome function
Contain oxidases that produce H202 during lipid metabolism and catalase to degrade it
Three other peroxisome functions
Lipid breakdown, lipid synthesis and bile acid synthesis/cholesterol
T/F. Peroxisomes must import all their proteins
True
Peroxisomal import machinery features (3)
- C-terminal import signal PTS1
- PTS1 signal recognition by cytosolic protein Pex5 which targets protein to surface
- Peroxisomal membrane machinery form a pore to import protein
T/F. Proteins translocated to the mito and to peroxisomes much be unfolded to be threaded through import pores
False, to the mito this is true, but peroxisomal proteins and sometimes even oligomers can be imported in a folded state.
2 stages of peroxisomal assembly
- de novo biogenesis
2. growth and division
Where do the membranes for newly formed peroxisomes come from?
ER - and some peroxisomal proteins are inserted in the ER membrane and bud off in vesicles
How do peroxisomes grow and divide?
Growth by uptake of peroxisomal proteins and lipids from cytosol, division by fission into daughter peroxisomes
Mitochondrial derived vesicles
Vesicles with peroxisomal proteins that bud off the mito, then fuse with either ER-derived pre-peroxisomes, or a subclass of them
T/F. Mito can be formed de novo.
False, they can arise only from growth and division of pre-existing mitos
