Lecture 10 Review
42 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the role of the SRP in protein translocation to the endoplasmic reticulum?

  • It synthesizes the entire protein before translocation.
  • It cleaves the signal sequence before translocation.
  • It facilitates the folding of the newly synthesized protein.
  • It binds to the ribosome and pauses translation. (correct)

What event occurs immediately after the SRP binds to the SRP receptor on the ER?

  • Translocation of the protein across the membrane begins.
  • Signal sequences are cleaved from the protein.
  • The SRP leaves the ribosome and translation resumes. (correct)
  • The ribosome detaches from the mRNA.

Which process describes the movement of the protein across the ER membrane during translation?

  • Non-cotranslational translocation
  • Post-translational translocation
  • Co-translational translocation (correct)
  • Transcriptional translocation

What happens to the N-terminal signal sequences after the SRP-mediated translocation process?

<p>They are cleaved on the lumenal side of the ER membrane. (C)</p> Signup and view all the answers

What is the function of the translocon during protein translocation?

<p>It acts as a channel for the newly synthesized protein to enter the ER. (B)</p> Signup and view all the answers

What happens to Ran when it is bound to the nuclear transport receptor?

<p>It accumulates in the cytosol. (C)</p> Signup and view all the answers

Where are most mitochondrial proteins encoded?

<p>In the nuclear genome. (B)</p> Signup and view all the answers

What occurs to proteins as they are translocated into mitochondria?

<p>They are unfolded during translocation. (D)</p> Signup and view all the answers

What function does the endoplasmic reticulum (ER) serve?

<p>Synthesis of secreted proteins. (A)</p> Signup and view all the answers

Which of the following is true about the nuclear transport receptor?

<p>It accumulates in the cytosol. (B)</p> Signup and view all the answers

Which process involves sorting proteins into chloroplasts?

<p>Translocation similar to mitochondrial import. (D)</p> Signup and view all the answers

What percentage of genes are involved in synthesis related to the ER?

<p>Approximately 30%. (A)</p> Signup and view all the answers

Which of the following is NOT a mechanism of protein sorting mentioned?

<p>Transport into lysosomes. (B)</p> Signup and view all the answers

What kind of proteins mainly require active transport to enter the nucleus?

<p>Large proteins like transcription factors (B)</p> Signup and view all the answers

Which protein family competes with cargo for binding to the import receptor?

<p>Ran GTPase (D)</p> Signup and view all the answers

What must occur for import to require high Ran-GTP levels in the nucleus?

<p>GTP hydrolysis must happen in the nucleus (B)</p> Signup and view all the answers

What role do GTP-binding proteins play in the context of nuclear transport?

<p>They act as molecular switches controlling transport. (B)</p> Signup and view all the answers

Which statement accurately reflects the process of cargo protein release from the import receptor?

<p>It requires binding of Ran GTPase to the receptor. (A)</p> Signup and view all the answers

What happens when Ran-GAP is depleted in a cell?

<p>Ran GTPase is unable to hydrolyze GTP effectively. (C)</p> Signup and view all the answers

What is the function of the GEF in relation to GTP-binding proteins?

<p>It promotes exchange of GDP for GTP. (B)</p> Signup and view all the answers

Which of the following accurately describes the nuclear pore complex?

<p>It has unstructured protein loops creating a diffusion barrier. (C)</p> Signup and view all the answers

What characterizes small GTP-binding proteins in their role as molecular switches?

<p>They activate pathways upon binding GTP. (A)</p> Signup and view all the answers

How do larger proteins typically enter the nucleus?

<p>Using nuclear transport receptors for active transport. (D)</p> Signup and view all the answers

What designation is given to the first signal sequence during protein translocation?

<p>Start-transfer sequence (C)</p> Signup and view all the answers

What is cleaved off by signal peptidase in the ER lumen?

<p>Signal sequences (B)</p> Signup and view all the answers

Which orientation results when the start-transfer sequence is positioned correctly?

<p>N-terminus in the lumen (B)</p> Signup and view all the answers

What is true regarding multipass membrane proteins?

<p>They comprise multiple stop-transfer and start-transfer sequences (B)</p> Signup and view all the answers

What type of glycosylation occurs on asparagine side-chains in the ER?

<p>N-linked glycosylation (D)</p> Signup and view all the answers

What is the primary role of signal sequences in protein sorting?

<p>They direct proteins to their specific cellular destinations. (A)</p> Signup and view all the answers

What is one function of protein glycosylation?

<p>Enhances protein folding and solubility (C)</p> Signup and view all the answers

What happens during the Ran-GTPase cycle regarding nuclear import of proteins?

<p>It regulates the transport of proteins into and out of the nucleus. (B)</p> Signup and view all the answers

How do proteins get targeted to mitochondria and chloroplasts post-translationally?

<p>By being tagged with a post-translational signal sequence. (A)</p> Signup and view all the answers

Where does glycosylation of proteins primarily occur?

<p>Only in the ER lumen (A)</p> Signup and view all the answers

What is the mechanism by which the signal recognition particle (SRP) functions?

<p>It couples protein synthesis with their import into the endoplasmic reticulum. (C)</p> Signup and view all the answers

Which amino acid is specifically mentioned in the glycosylation sequence?

<p>Serine (A)</p> Signup and view all the answers

What role does protein glycosylation play in the endoplasmic reticulum?

<p>It facilitates the folding and stability of proteins. (B)</p> Signup and view all the answers

What role can protein glycosylation play in protein interaction?

<p>Facilitates protein sorting (A)</p> Signup and view all the answers

Which of the following correctly describes transmembrane proteins during their insertion into the endoplasmic reticulum?

<p>They are integrated into the membrane through a series of hydrophobic domains. (A)</p> Signup and view all the answers

Which statement about the sugar chain in glycosylation is incorrect?

<p>Occurs solely in the cytosol (D)</p> Signup and view all the answers

Which organelle is associated with post-translational import of proteins primarily via signal sequences?

<p>Mitochondria (D)</p> Signup and view all the answers

What determines whether a protein will remain in the cytosol or be directed elsewhere?

<p>The presence of signal sequences. (D)</p> Signup and view all the answers

What is the first step in the transport of a protein into the nucleus?

<p>Recognition of the nuclear localization signal by importins. (B)</p> Signup and view all the answers

Flashcards

Nuclear transport receptor

A protein that helps move molecules across the nuclear envelope.

Nuclear localization signal (NLS)

A sequence of amino acids on a protein that signals its entry into the nucleus.

Ran GTPase

A small GTP-binding protein that acts as a molecular switch, helping regulate nuclear transport.

GEF (Guanine nucleotide Exchange Factor)

An enzyme that helps Ran GTPase switch from its inactive GDP-bound state to its active GTP-bound state.

Signup and view all the flashcards

GAP (GTPase Activating Protein)

An enzyme that helps Ran GTPase switch from its active GTP-bound state to its inactive GDP-bound state.

Signup and view all the flashcards

Nuclear import

The process by which molecules are transported into the nucleus.

Signup and view all the flashcards

Nuclear export

The process by which molecules are transported out of the nucleus.

Signup and view all the flashcards

Nuclear pore complex

The region of the nucleus where the nuclear envelope is interrupted, allowing molecules to pass between the nucleus and the cytoplasm.

Signup and view all the flashcards

Diffusion barrier

The barrier formed by the nuclear pore complex that prevents large molecules from entering the nucleus.

Signup and view all the flashcards

Nuclear lamin

The protein that forms the nuclear envelope, providing structural support and regulating molecule movement.

Signup and view all the flashcards

Signal sequences

Short amino acid sequences that act as 'address labels', directing proteins to their correct destination within the cell.

Signup and view all the flashcards

Ran

A small GTPase protein that plays a central role in nuclear transport, shuttling proteins across the nuclear envelope.

Signup and view all the flashcards

Importin

A protein that binds to signal sequences and facilitates their transport into the nucleus.

Signup and view all the flashcards

Chaperone Protein

A molecular chaperone that helps guide proteins to their final destination within the cell, ensuring their proper folding and function.

Signup and view all the flashcards

Co-translational translocation

The process by which proteins destined for the endoplasmic reticulum (ER) are targeted to the ER during translation.

Signup and view all the flashcards

Signal recognition particle (SRP)

A protein complex that guides ribosomes carrying nascent proteins to the ER membrane.

Signup and view all the flashcards

Translocon

A tunnel-like structure in the ER membrane that allows proteins to cross the membrane.

Signup and view all the flashcards

Protein folding

The process by which proteins fold into their correct three-dimensional structure, often with the help of chaperone proteins.

Signup and view all the flashcards

ER Signal Sequence

A short sequence of amino acids at the beginning of a protein that acts as a signal, directing the protein to the endoplasmic reticulum (ER).

Signup and view all the flashcards

Cleavage of the Signal Sequence

The removal of the ER signal sequence from the protein once it has been translocated into the lumen of the ER.

Signup and view all the flashcards

Signal peptidase

An enzyme that cleaves off the signal sequence from a protein once it has reached the ER lumen.

Signup and view all the flashcards

Start-transfer sequence

The first signal sequence in a protein that initiates its translocation into the ER membrane.

Signup and view all the flashcards

Stop-transfer sequence

A second signal sequence in a protein that stops its translocation into the ER membrane, causing it to remain embedded in the membrane.

Signup and view all the flashcards

Protein Glycosylation

A type of protein modification where sugar molecules are covalently attached to amino acid side chains.

Signup and view all the flashcards

Where does Protein Glycosylation occur?

The process of protein glycosylation occurs in the ER lumen.

Signup and view all the flashcards

Which amino acid is involved in glycosylation?

The specific amino acid Asparagine (Asn) is involved in the attachment of the sugar chain during glycosylation.

Signup and view all the flashcards

Where on Asparagine is the sugar chain attached?

The sugar chain is attached to the Nitrogen atom on the Asparagine side chain.

Signup and view all the flashcards

What are the functions of Protein Glycosylation?

Protein glycosylation plays a crucial role in protein folding, solubility, protection, and even protein sorting.

Signup and view all the flashcards

Nuclear Pore Complex (NPC)

The protein complex that forms channels through the nuclear envelope, allowing transport of molecules between the nucleus and cytoplasm.

Signup and view all the flashcards

Nuclear Envelope

The double membrane surrounding the nucleus, with nuclear pores that regulate the passage of molecules between the nucleus and the cytoplasm.

Signup and view all the flashcards

Nucleolus

The region within the nucleus where ribosomal RNA is synthesized and assembled with ribosomal proteins to form ribosomes.

Signup and view all the flashcards

Study Notes

Protein Sorting Overview

  • Eukaryotic cells have membrane-bound organelles
  • Proteins are sorted by different mechanisms:
    • Transport through nuclear pores
    • Transport across membranes
    • Transport by vesicles

Learning Objectives

  • Understand mechanisms for protein targeting to various cellular compartments
  • Understand signal sequences
  • Understand how proteins are targeted post-translationally to mitochondria and chloroplasts
  • Understand how SRP couples translation and translocation of proteins into the endoplasmic reticulum
  • Understand how proteins with multiple transmembrane regions are inserted into the endoplasmic reticulum
  • Understand protein glycosylation and folding in the ER

Nuclear Envelope Architecture

  • The nuclear envelope comprises an outer and inner membrane
  • The space between the two nuclear membranes is called the perinuclear space
  • Contains nuclear pores
  • The inner membrane and outer membrane are linked by nuclear pores
  • Nuclear pores allow the transport of molecules between the nucleus and the cytoplasm
  • Small proteins can passively diffuse
  • Larger proteins need an active process for transport
  • Nuclear transport receptors move molecules through the nuclear pores

Nuclear Pore Complexes

  • Unstructured protein loops create a diffusion barrier
  • Very small proteins (<5 kD) can passively diffuse through nuclear pores. Larger proteins require an active transport process.
  • Many proteins enter the nucleus through these pores requiring an active shuttling process

Nuclear Transport Receptors

  • Prospective nuclear protein (cargo) binds to the nuclear import receptor
  • The nuclear import receptor "lets go" of cargo protein in the nucleus
  • GTP-binding proteins (GTPases or monomeric GTPases) are molecular switches
    • The "GEF" (guanine nucleotide exchange factor) triggers GTP binding.
    • The 'GAP' (GTPase-activating protein) triggers GTP hydrolysis.
  • GTP hydrolysis drives nuclear transport
  • Ran GTPase competes with cargo for binding to the receptor

Mitochondrial Protein Import

  • Most mitochondrial proteins are encoded in the nuclear genome
  • Proteins are unfolded as they are translocated across both membranes simultaneously
    • Binding to import receptors in the outer membrane
    • Protein translocator in the inner membrane
  • Proteins are then translocated into the matrix
  • Proteins are refolded within the mitochondrion

ER Protein Import - SRP and Co-translational translocation

  • SRP (signal recognition particle) binds signal sequence and slows/pauses translation
  • SRP binds to the SRP receptor on the ER
  • SRP leaves and ribosome engages translocation channel (aka "translocon")
  • Translation resumes and protein is translocated across the bilayer
  • Signal sequence is cleaved off protein by signal peptidase
  • Protein folds in the ER lumen

Transmembrane Proteins

  • Proteins with transmembrane segments are directed into the ER membrane in a "co-translational translocation"
  • First segment (start-transfer sequence)
  • Second segments (stop-transfer sequence)
  • The mechanism dictates the direction of the protein in the membrane (N-terminus in the lumen)

Glycosylation

  • Many proteins undergo glycosylation (N-linked) in the ER
  • Sugar chains attach to asparagine in the ER
  • Never occurs in the cytosol

Multipass Membrane Proteins

  • Multipass membrane proteins contain multiple stop-transfer and start-transfer sequences
  • These sequences relate to translocation and not translocation.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Protein Sorting in Eukaryotic Cells (Lecture Notes) PDF

Description

Test your knowledge on the mechanisms of protein translocation and sorting within cellular organelles such as the endoplasmic reticulum, mitochondria, and chloroplasts. This quiz covers key concepts including the role of the signal recognition particle (SRP), translocon function, and the transport receptors involved in protein import. Dive into the complexities of cellular transport processes!

More Like This

Lodish Ch 13 TB MC
41 questions

Lodish Ch 13 TB MC

TenaciousNephrite186 avatar
TenaciousNephrite186
Lodish Ch 13: Moving Proteins into Membranes and Organelles
30 questions

Lodish Ch 13: Moving Proteins into Membranes and Organelles

TenaciousNephrite186 avatar
TenaciousNephrite186
Protein Translocation and TIM23 Complex
48 questions

Protein Translocation and TIM23 Complex

RockStarLobster8287 avatar
RockStarLobster8287
Use Quizgecko on...
Browser
Open
Browser
Browser