ZIMA Lecture 4 Flashcards
Which compartment takes up the most volume/ is the largest in the cell?
What compartment is present in the greatest number?
Cytosol is the largest compartment/ takes up the most volume in the cell
Mitochondria are present in the greatest number
What is the fate of a protein with no sorting signal?
A protein with no sorting signal remains in the cytosol
Which organelles receive proteins via gated transport?
Which organelles receive proteins via transmembrane transport?
Which organelles receive proteins via vesicular transport?
Gated transport: nucleus
Transmembrane transport: Mitochondria, ER, peroxisomes and plasmids
Vesicular transport: Golgi, Lysosome Endosomes, Cell Exterior
Can you create an ER in a cell without an ER?
AKA can you create an organelle de novo?
NO, a new organelle cannot be made without an existing organelle. These organelles contain infor that is required for their construction.
What is the difference between the inner and outer membrane of the nucleus?
What is synthesized in the nucleus and sent out to the cytosol
vs
What is synthesized in the cytosol and brought into the nucleus?
Inner nuclear membrane contains specific proteins that act as anchoring sites for chromatin and nuclear lamina.
Outer membrane is continous with the ER.
tRNAs and mRNAs are made in the nucleus and sent out to cytosol
Histones, gene regulators, DNA and RNA Poly are made in cytosol and brought into nucleus
What structure is reponsible for the traffic of proteins and RNA between the nucleus and the cytosol?
What kind of molecules can get through?
The NUCLEAR PORE COMPLEX
Small molecules can freely diffuse through NPC, large proteins can;t oass NPC by passive diffucion they have special mechainism
Is transport of proteins in the nucleus pre translational, pretranscriptional, post transcriptional, post translational?
NUCLEUS: post translational
(fully folded proteins can be transported into the nucleus)
What is responsible for the selectivity of the nuclear import proces?
What structures recognize those specific signals?
Nuclear localization signals are responsible for the selectivity of the nuclear import process
Nuclear Import or Export Receptors bind to those localization signals
Where does the nucleus get the energy for transporting proteins in and out?
The energy for nuclear transport is obtained from GTP hydrolysis by Ran GTPase.
Where are Ran GAP and Ran GEF located?
Ran GAP is located in cytosol, it hydrolyses GTP to GDP and causes Ran-GDP to enter nucleus
Ran GEF is located in the nucleus, phosphorlyates the GDP into GTP and then causes RAN GTP to leave the nucleus
How does the Ran GTPase mechanism work
In the cytosol, RAN GDP binds to a nuclear import receptor. (remember ran gap converts gtp to gdp)
It then enters the nucleus, where Ran GTP binds to the nuclear imort receptor and the cargo protein is delievered to nucleus. (ran gef converts gdp to gtp)
It then leaves the nucleus and goes back into the cytosol.
Where do most of the proteins used in the mitichondria come from?
Most of the proteins come from the cytosol even though mitochondria have their own machinery to make proteins.
Can fully folded proteins enter the mitochondria?
No, mitochondrial proteins are first fully synthesized as precursor proteins in the cytosol ( a post translational mechanism). Then chaperon proteins bind to them as they enter the mitochondria. (not fully folded)
Define the role of the following structures:
TOM
SAM
TIM23
TIM22
OXA
TOM: protein transport through the outer membrane into the intermembrane space
SAM: folding of porin channels in the outer membrane (beta barrels)
TIM23: protein transport into matrix space and insertion of proteins into inner membrane
TIM22: insertion of proteins responsible for ATP-ADP transport of inner membrane
OXA: insertion of proteins that are synthesized into the inner membrane
Explain the mechanism of how proteins enter the mitochondria
Transport of Proteins into Mitochondria:
- The signal sequence on precursor protein binds to receptor on TOM complex
- Chaperone proteins Hsp70 are stripped off and then the protein chain is fed into translocation of TOM complex
- Protein first binds to the TIM 23 complex and passes through it
- Signal sequence removed by peptidases
What energy source is used in nuclear protein transport?
What energy source is used in mitochondrial protein transport?
Nucleus: GTP
Mitochondria: ATP
What two things fuel mitochondrial protein importation?
ATP hydrolysis both outside and in the matrix,
and the membrane potential (on inner memebrane) fuel mitochondrial protein import.
ATP gets hydrolyzed to pop off the chaperone proteins.
How are porins (pore forming proteins on the outermembrane of the mitochondria) transported into the mitochondria?
Porins are first transported through the TOM complex into the intermembrane space.
The SAM complex then inserts the porin proteins into the outer membrane and then helps to fold it properly
The ER is in charge of ____ & ____ synthesis and ___ storage
The ER membrane is continous with _____
The ER is in charge of protein and lipid synthesis and also calcium storage.
The ER membrane is continous with the outer nuclear membrane.
Rough ER vs Smooth ER
Proteins begin import into the ER before complete synthesis of the polypeptide chain - a _________ mechanism.
Rough ER: coated by ribosomes (protein synthesis)
Smooth ER: Lipid synthesis and calcium storage
Protein begin to import into the ER before complete synthesis of the polypeptide chain- a co-translational mechanism.
All proteins are directed to the ER membrane by a ________.
That ______ is cleaved off by a _____ in the ER membrane.
All proteins are directed to the ER membrane by an ER signal sequence.
The ER signal sequence is cleaved by a signal peptidase in the ER membrane.
What is SRP? What does it do?
SRP: made up of polypeptides and RNA
SRP guides signal sequence of a protein into the ER
SRP stops the process of protein synthesis, which gives the ribosome time to bind to the ER membrane before completion of the polypeptide chain,
Polypeptide chains are transferred across the ER membrane through a ______.
At rest that ____ is closed by a short helix
The growing polypeptide chain can remove that plug allowing a protein to transfer across the ER membrane
Polypeptide chains are transferred across the ER membrane through a translocator.
At rest, that translocator is closed by a short helix/”plug”
The growing polypeptide chain can remove the plug allowing a protein to go across
What does a protein need to have to become a transmembrane protein in the ER?
A start-transfer sequence is necessary for a protein to become a transmembrane protein in the ER
