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Mid Term 2 Cell biology
Terms in this set (18)
What are some of the major functions of Endoplasmic reticulum (ER)?
-is the site of production of all transmembrane proteins and lipids for most of the cell's organelles (ER itself, Golgi Apparatus, lysosomes, endosomes, secretory vesicles, and the plasma membrane.
-Here is where the production of mitochondrial lipids and peroxisomal membranes are made.
-Calcium storage/ Ca comes from cytosol
-Modification of proteins to create hormones
- contains enzymes what will help catalyze a serious of reactions for detoxification of toxins in cell membrane.
enzymes that carry out detoxification reactions by making toxin more water soluble.
what are polyribosome
and how do they influence the structure of
they are many ribosome that are bound to a single mRNA at the same times. A ER signal sequence binds to a SRP then it's directed to the a ER signal receptor. Once bound the mRNA molecule remains permanently bound to the ER memberane as part of a polyribosome giving that region the "rough" look.
What is signal hypothesis?
it is proposal that proteins destined for secretion are initially manufactured by a sequence of amino acids. The signal sequence is hydrophilic and is associated with ER membrane serves as a anchor while translocation of the protein occurs.
How did studies on ER import lead to the proposal of signal
hypothesis? Explain it explicitly.
In- vitro cell- free translation ( cell free is a cell that doesn't have all organelles a normal cell has. ribosomes, mRNA, amino acids, energy source and specific ions are needed).
I. no microsomes present- protein translation is happening with the absence of the ER. Translation happens with signal sequence still attached. Then you add ER membrane the fully formed polypeptide with signal attached isn't able to bind to in the ER membrane. You added the this to late. (Post translation)
II. When microsomes are present co translational. The polypeptide is able to bind to the microsomes transport of the protein inside the microsome happens. It's released inside the lumen of the microsome.
In the absence of microsomes and protease the added protease enzyme will digest the polypeptide. In the presents of microsome and add protease the polypeptide isn't degraded since the protease isn't able to cross the microsome membrane. No signal is present is present as well.
understand the steps (and all the molecular players
involved) involved in import of an
ER luminal protein
N- terminal signal sequence
- Ribosomes attach the mRNA producing a signal sequence of the growing peptide. A SRParticle is attached to prevent translation in the cytosol. The the complex is directed to the SRP receptor they are released once the mRNA is bound to the translocator in the ER membrane. Translation continues and translocation begins. Going into the ER lumen and eventually being released.
Explain insertion of single pass and multi-pass TMPs in to ER membrane.
- N-terminal ER sequence (start transfer signal) opens the translocator and translation is initiated. polypeptide contains a stop-transfer sequence (hydrophobic) and anchors protein into the membrane after the signal sequence has been cleaved off by a peptidase. The translocator opens at the seam and discharges the protein laterally into the lipid bilayer.
The hydrophobic region nearest to the N-terminal serves as a start-transfer sequence that allows the pass of this region to pass through the ER membrane. Subsequent hydrophobic sequences function in alternation as start and stop transfer sequences.
What is glycosylation in proteins?
the covalent addition of N-linked Oligosaccharide of the Asparagine side chain
What is the protein sequence need to attach the oligosaccharide?
X can never be proline.
What is the structure of N-linked Oligosaccharide
a group of N-acetylglucosamine
This happens in the ER
what is dolichol
What is the molecular basis (genetic) behind lysosomal storage disease?
the lack or defect function of HYDROLASES in lysosomes of cells leading to accumulation of undigested substrates in lysosomes and consequent cell pathology
what are lysosomal hydrolases composed of? why are they important?
a protein that contain signal patch, N-linked oligosaccharide with a terminal mannose residue.
How are lysosomal hydrolases recognized and selected in the TGN with the required accuracy?
They carry a unique marker in the forms of mannose 6 phosphate groups. This marker is attached to the N-linked oligosaccharide + protein. An enzyme recognizes the signal patch of the protein and binds to it. This enzyme is called GIcNAc phosphotranferase. A UDP- GIcNAc (U+ 2phosphates+GIcNAc) also binds to the enzyme. Catalytic rxn happens and A UMP (U+ 1phosphate) is released. Therefore (GIcNAc +P) is attached to the mannose. A second enzyme cleaves off the GIcNAc leaving the M6P exposed. This becomes a M6P signal to a M6P receptor protein in the TGN. They bind. The receptor are like claws inside the Golgi that have a stick in the luminal side. Adaptor proteins are attached to the stick and coat for clathrin and bud off and transported to early endosomes. The removal of the phosphate by the change of acidic pH happens.
What are the various types of coated vesicles involved in vesicular transport? List them
with specific examples of compartments that use them.
-clatharin-coated (transports material from the plasma membrane and between endosomal and Golgi compartments)
-COP1 (bud off from the Golgi compartments)
-COPII (bud off from the ER)
What is vesicle transport?
are containers that bud off from one compartment and fuse with another. They carry material as cargo from the lumen and membrane of the donor compartment to the lumen or membrane of the target compartment
Describe the molecular basis of clathrin
coated vesicle formation?
1. Cargo selection
specific signal sequences bind to cargo receptors. that are located on the donor lumen. Adaptor protein is attached to the cytosolic side of the cargo protein. coat protein bind to the adaptor proteins. adaptor protein select for specific set of transmembrane proteins that contain for specific vesicular transport pathways.
2. Vesicular budding- Dynamin buds off the vesicle. it's a GDPase to it hydrolysis GTP to GDP. The coating and adaptor protein disassociate. in result we have a naked vesicle.
3. Vesicle targeting and Fussion-
Remember that the naked vesicle contains vSNARS Rab GTPases( HELPS FACILITATE TRANSPORT TO THE SPECIFIC TARGET MEMBRANE AND IT SO HELPS VESICLE DOCK)
On the target membrane a tethering protein and a T-SNARE. Specific RabGTPase bind to specific tethering proteins. T and V-SNARS come together and fussion of membrane happen and cargo is sucessfully delivered.
How does phosphoinositide metabolism
regulate vesicular transport, specifically regarding site
of vesicle formation?
Local control of the PI and PIP kinase and PIP phosphatases can be used to rapidly control the binding of proteins to membrane or membrane domain. The membrane of secretory vesicle contain PIPs. When the vesicles fuse to plasma membrane a PI kinase converts PIPs to PIP2s (help recruit adaptor proteins) which help initiate the formation of clathrin coated pits. Once the clathrin coated vesicle is pinched off. PIP phosphotases the PIP2 and weakens the binding of adaptor proteins. promoting vesicle uncoating.