1-29 Organelles and Protein Sorting Flashcards
targeting of newly synthesized enzymes to mitrochondria involves which transport mechanisms?
transmembrane transport
proteins encoded by the mitochondrial genome (synthesized where)? carry out functions in which compartment of the mitrochondria?
synthesized in matrix, transported to inner membrane. they are all components of the ETC or ATP synthase complex (both localized in inner membrane)
the mitochondrial genome encodes
rRNAs, tRNA,s and mRNAs
where is the mito genome located?
in the mito matrix
how many copies of mito genome are in each mitro?
several copies
mito uses a ____________ than the nuclear genome
slightly different genetic code
What is synthesized in the mito?
ATP (atp synthatase), DNA (during replication), RNA (when transcribed into 2 giant strands), Proteins (13 are synthesized within mito)
what is NOT synthesized in mito?
oligosaccharides. they are synthesized in the ER and Golgi
ETC occurs in which compartment?
the inner membrane
proteins are imported into the mito matrix _______
post-translationally
What effect does maternal inheritance of mito genes have on mutation frequency?
no effect.
synthesis of mtDNA encoded proteins occurs in the
mitochondrial matrix
x-linked adrenoleukodystrophy is caused by defects in
the fatty acid transporter in peroxisomal membranes.
a defect leads to a build up of long fatty acids in cytoplasm - toxic- leads to demyelination of neurons.
golgi
proteins synthesized in the ER are modified here
worn out organelles are digested in the
lysosomes
where are mitochondria located?
either in areas that need lots of ATP or around the cell along microtubules
structure of mitochondria from outside to inside
Outer membrane, intermembrane space, matrix, inner membrane
Matrix space
large internal space
lots of enzymes for breaking down fatty acids and citric acid cycle
contains mito genome with machinery
inner membrane
encloses matrix
convoluted cristae to increase SA for ETC and ATP synthetase (both necessary for oxid phosp)
Electrochemical gradient that powers ATP syntehsis is established across the membrane by the ETC
outer membrane
separates the mito from cytosol
contains porins across lipid bilayer, permeable to small molecules
intermembrane space
small space between inner/outer membrane
contains cytocrome C component of ETC, also gets released signaling apoptosis
final destination of proteins depends on
amino acid sequences which may contain sorting signals, directing them to an organelle
no sorting signal - stay in cytosol
three mechanisms of protein transport
nuclear pores (GAF/GEF), protein translocators (co-translation or translationally, and vesicles (ER to Golgi to PM/extracellular space/lysosomes
three mechanisms of protein transport
nuclear pores (GAF/GEF)
protein translocators (co-translation or translationally
vesicles (ER to Golgi to PM/extracellular space/lysosomes
SRP
signal recognition particle - recognizes the signal sequence, directs it to correct organelle
process of importing proteins to mitochondria
Transport mediated by two protein translocators (TOM & TIM complexes) located in outer and inner membranes
- Precursor protein binds its recept sequence to receptor on TOM
- Precursor protein and TOM move laterally across outer membrane until encouters TIM complex
- Unfolded precursor protein translocates across both membranes, signal sequecne first. Chaperone proteins in matrix help pull the protein across the two membranes
- Signal sequence cut off by microchondrial signal peptidase - protein unfolds to active confirmation with help for other chaperone proteins
structure of peroxisomes
small multifucntional organelles found in all eukaryotic cells.
Major site of oxygen utilization, contains high concentrations of oxidatize enzymes used in reactions that break down molecules includig toxins, alcohol, and fatty acids, also synthesize special phospholipids.
Cells have hundreds
3 functions of peroxisomes
Oxidative degradation - remove hydrogen atoms from organic substrates to produce hydrogen peroxide. Catalase uses h2o2 to oxidize/detox molecules
Beta oxidation (break down of fatty acids)
Synthesis of cholestrol, bile acids, some lipids - essential for making the plasmologens of myelin sheaths
describe the mitochondrial genome
i. Very small circular ds DNA
ii. 37 genes for 2 rRNAs, 22 tRNAs, and 13 polypeptides
iii. Very little non-coding (junk) sequences
iv. No introns
v. Genetic code varies slightly from nuclear
Each mito contains 10-20 copies of the genome. Each cell therefor has thousands of copies
Mitochondrial replication
a. Replication - occurs throughout cell cycle, on average the total number of mtDNA molecules doubles with each cell cycle
mitochondrial transcription
both strands of mtDNA transcribed from single promoter region on each strand. Produces 2 giant rna molecules, each cleaved to give 2 rnas, 22 trnas, and 13 mRNA’s.
mitochondrial translation
occuring in matrix using tRNAs and rRNAS encoded by mito genome. Produces only 13 pp, all of which involved in eT and oxidative phos
basic principles of mito genetics and inheritance
maternal inheritance
heteroplasmy/threshold effect - homoplasmy penetrance can decrease due to environmental factors
mtDNA has high mutation rate
mutation rate of mtDNA?
much higher than normal
- no introns = all mutations are within a coding sequence
- no protective histones
- inefficient repair
- mtDNA is exposed to oxygen free radicals
describe mito disorders
often late onset due to increasing mutations over time. Broad range of tissues but usually those that require most oxidative phosphorylation - neuropathies, myopathies, etc..
release of cytochrome c
triggers a caspase cascade creating lots of proteolytic enzymes that cause apoptosis
catlase
uses hydrogen peroxide to oxidize substrates. Important in detoxifying areas of teh body like kidney and liver cells.
synthesis of mtDNA encoded proteins occurs in the..
mitochondrial matrix
What is the role of the mitochondria in the intrinsic pathway of apoptosis?
Releases cytochrome c from the intermembrane space into the cytosol which triggers activation of the caspase cascade
What is the caspase cascade?
Triggered by the release of cytochrome c from the intermembrane of the mitochondria into the cytosol, the caspase cascade is an intracellular proteolytic cascade responsible for cleaving key cellular proteins
What are TOM/TIM and what do they do?
TOM-protein Translocator located in Outer Membrane
TIM-protein Translocator located in Inner Membrane
Precursor protein binds to a receptor associated with TOM (must reach outer membrane first), via signal sequence. This complex will diffuse laterally until they reach TIM…protein is in folded state at this point, then chaperone proteins in the matrix pull protein through two membranes
What do chaperone proteins do?
located in the mito matrix, they pull the protein being translocated through TOM/TIM into the matrix…where the mito signal sequence is cleaved off by mito signal peptidase and protein re-folds into its final conformation
if you destroy the electrochemical gradient across the inner membrane, what happens to protein transport?
It stops.
DNA replication is limited to the S phase in both nuclear DNA and mito DNA replication
False…mito DNA replication occurs throughout cell cycle
Where does translation of mito proteins occur? How many polypeptides are made and where do they go after translation?
Occurs in mito matrix, synthesizes 13 polypeptides that all go to the inner membrane to function in the ETC and oxidative phosphorylation
What is heteroplasmy and the threshold effect?
Heteroplasmy is when mutant and WT mtDNA both express in cells at different percentages…resulting in variable espressivity…differences in severity of disease. A phenotype will not be apparent until a threshold is reached…known as the threshold effect.
What is homoplasmic?
Homoplasmic is when all of a woman’s mtDNAs carry a particular mutation…in this case, all of her children will inherit the mutation and any disease associated with with it
What is N-linked glycosylation and where does this occur?
N-linked glycosylation is a protein modification that occurs in the ER. A preformed oligosaccharide (sugar) of 14 sugars is attached to a.a. residues during translocation (co-translationally).
N-linked glycosylation modification begins in the ER, but continues in the golgi
