BIOL 2P03 Lecture Notes - Lecture 11: Nuclear Dna, Nuclear Pore, Signal Recognition Particle

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turquoiseskunk573

27 Feb 2016

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Lecture 11 protein import into organelles (rest of chapter 13) The rough er appears rough because it is dotted with ribosomes. Proteins to be synthesized in the er contain an n-terminal targeting sequence. Recognized during cytosolic translation, and the cytosolic ribosome is moved to the er. Proteins to be synthesized in the er include: Those that will be secreted from the cell. Those that will be packaged into membranes and delivered as vesicles within the cell. Those that need to be post-translationally modified with a sugar (glycosylation) disulphide bond other. Cotranslational translocation refers to fact that ribosomes are moved to the er as they are translating a protein recognized as needing to be made in the er. How it works: mrna/ribosome/emerging protein recognized and bound by srp (signal recognition particle, delivered to srp receptor and translocon in er membrane, growing protein goes right through translocon and into er lumen as it is being translated.

Related Questions

6. True or false

a_______ Nuclear pore complexes are specialized so that some mediate import and others mediate export

b_______ Membrane-bound and free ribosomes, which are structurally and functionally identical, differ only in the proteins they happen to be making at a particular time.

c_______ Some proteins can be made as either free or membrane-bound proteins. They have the same mRNA but different splicing and poly-adenylation patterns

d_______ a protein that does not have a sorting signal will be tagged for destruction by ubiquitin

e_______ when the hydrophobic signal peptide emerges from the ribosome, it is bound by SRP, which causes a pause in protein synthesis. Synthesis resumes when the ribosome with a bound SRP then binds to the SRP receptor on the cytosolic surface of the rough ER.

f________ A protein cannot leave the ER unless it is correctly folded

g________ All of the glycoproteins and glycolipids in intracellular membranes have their oligosaccharide chains facing the cytosolic side, and all those in the plasma membrane have their oligosaccharide chains facing the outside of the cell.

Which of the following statements about secreted proteins is/are correct? Choose all that apply. Which of the following statements about secreted proteins is/are correct? Choose all that apply.

Secreted proteins travel directly from the rough endoplasmic reticulum into the trans face of the Golgi apparatus.

Secreted proteins are likely to have received N-linked glycosylation in the rough ER.

Secreted proteins are the only proteins that receive sugar modifications in the Golgi.

Secreted proteins that are constitutively expressed are exported as they are prepared, as opposed to being released as a response to a signal.

Secreted proteins are synthesized on membrane-bound ribosomes, not free cytosolic ribosomes.

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1. Which cytosolic factor is most likely to associate with the signal sequence of a protein that is targeted co-translationally to the ER?

A chaperone of the Hsp70 family

The translocation channel

The ribosome

Signal recognition particle (SRP)

Signal peptidase

2. What is the most likely fate of a protein with an N-terminal hydrophobic sorting signal and an additional internal hydrophobic domain of 22 amino acids?

The protein stays in the cytosol

The protein is transported to mitochondria

Because the protein has an N-terminal sorting signal, the protein is translocated all the way into the ER lumen

The hydrophobic domain is recognized as a transmembrane domain once it is in the translocation channel and released sideways into the membrane

The hydrophobic domain is cleaved off by signal peptidase

3. Which of the following statements best describes N-glycosylation? N-glycosylation refers to........

the addition of a pre-formed sugar tree to a serine or threonine present in the cytosolic domain of a protein

the addition of a pre-formed sugar tree to a phospholipid to make a glycolipid

the addition of individual sugars to selected amino acids on a protein

the addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in an ER lumenal domain of a protein

the addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in a cytosolic domain of a protein

4. What is the most likely fate of a protein in which a mutation has led to misfolding in the ER?

It is sequestered by the proteasome in the cytosol

It is first tagged with ubiquitin in the ER and then degraded by the proteasome in the cytosol

It is first moved out of the ER, tagged with ubiquitin in the cytosol and then degraded by the proteasome in the cytosol

It associates with many chaperones in the ER, which guarantee its correct folding

Its misfolded state is recognized by chaperones in the ER, which will induce the protein's degradation by the proteasome in the ER.

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BIOL 2P03 Lecture Notes - Lecture 11: Nuclear Dna, Nuclear Pore, Signal Recognition Particle

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