Organelle and Function Quiz

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Questions and Answers

What role does COPII play in cellular transport?

Assists in the transport to the plasma membrane

Facilitates exit from the ER (correct)

Involved in protein folding within the ER

Mediates return of proteins from Golgi to ER

At what temperature does the Semliki Forest Virus (SFV) glycoprotein synthesis stop?

15 degrees Celsius (correct)

48 degrees Celsius

28 degrees Celsius

37 degrees Celsius

What does EndoH sensitivity indicate about protein localization?

Protein is processed in the Golgi apparatus

Protein is in the ERGIC

Protein is in the cytoplasm

Protein remains in the ER (correct)

How is the formation of ERGIC primarily driven?

Microtubule dynamics Signup and view all the answers

What characterizes the structural organization of the Golgi as opposed to ERGIC?

Pancake stack versus dot formations Signup and view all the answers

Which protein colocalizes with ERGIC53 at lower temperatures?

E1 Signup and view all the answers

What is the consequence of raising the temperature to 39 degrees Celsius for E1 protein?

Protein denatures and accumulates Signup and view all the answers

What happens to proteins modified by mannosidase II at lower temperatures?

They become EndoH resistant Signup and view all the answers

What is the primary role of Sar1P in the COPII pathway?

Acts as a GTPase that activates the COPII coat complex Signup and view all the answers

Which of the following signals directs the recognition of proteins by COPI for retrieval to the ER?

KDEL amino sequence Signup and view all the answers

What occurs to proteins as they move from the cis side to the trans side of the Golgi apparatus?

They are prepared for an acidic environment Signup and view all the answers

What does the term 'endo-H resistant' refer to in glycoproteins?

Glycoproteins that have been fully processed and glycosylated in the Golgi Signup and view all the answers

What is the function of the COPII protein complex during vesicle formation?

It drives the selection of proteins to be transported as cargo Signup and view all the answers

Which sequence in Type I proteins serves as a signal for COPI recognition?

Dilysine motif at the C-terminus Signup and view all the answers

What is the primary function of clathrin-coated pits in the transport process?

They facilitate the packaging of proteins for secretion Signup and view all the answers

What role do NSF and SNAPs play in vesicular transport?

They are required for SNARE protein recycling after fusion Signup and view all the answers

Study Notes

Organelle and Function

Organelles have distinct proteins and functions.
ERGIC (Endoplasmic Reticulum-Golgi Intermediate Compartment) plays a crucial role in protein transport.

Live Export and Examination

GFP-fusion proteins combined with viral proteins allow visualization of live export.
Swiss et al. noted that surface antigens in ERGIC are organized differently compared to the Golgi; Golgi has pancake stacks while ERGIC appears as dots.

Experimental Insights

Semliki Forest Virus (SFV) shows temperature sensitivity; performs poorly at high temperatures for glycoprotein creation.
E1, E2, E3 glycoproteins facilitate virulence by hijacking cellular components.
Protein denaturation at high temperatures leads to accumulation in the ER.
E1 prevents correct folding at high temperatures but refolds at lower temperatures, enabling antibody binding and surface synthesis.

EndoH Sensitivity

EndoH sensitivity indicates protein location; sensitive proteins are localized to ER or ERGIC, while resistant proteins are in the post-medial Golgi.
Temperature shifts influence protein behavior and EndoH sensitivity, with both wild-type and mutant proteins becoming sensitive at low temperatures.

Formation of ERGIC

E1 localizes with ERGIC53 at low temperatures, forming vesicles that aggregate to create the ERGIC.
The dynamics between ER, ERGIC, and Golgi depend on microtubule movement facilitated by the motor proteins dynein and kinesin.

Coat Protein Complexes

Coat proteins—COPII and COPI—regulate protein transport.
COPII drives exit from the ER, while COPI returns proteins from the Golgi to the ER.
Sar1P (GTPase) and Sec12p (GEF) coordinate COPII assembly and cargo selection.

Protein Fates in the ER

Proteins can be degraded (ERAD), retained, or exported to the Golgi.
COPI captures membrane proteins using specific signal sequences (KDEL or dilysine motifs).

Golgi Function

The Golgi synthesizes glycolipids and processes proteins, increasing acidity from cis to trans.
Cholesterol content rises while collagen moves through the Golgi.

KDEL Receptor Mechanism

KDEL receptor on resident proteins in the Golgi captures KDEL tagged proteins.
COPI interacts with the KDEL receptor, facilitating retrieval of proteins back to the ER.

Experimental Tools and Agents

GTP analogs influence COPII and COPI functions.
NEM, an alkylating agent, modifies active sites on cysteine residues and affects SNARE dynamics.
NSF and ATP hydrolysis are essential for regenerating SNARE complexes for future fusion events.

Key Points from Questions

GTPase activity (Sar1 for COPII, Arf for COPI) determines protein coating readiness.
Coat proteins dictate movement and transport fate of proteins.
Fluorescence microscopy excels in live imaging, providing specificity and detail in studying cellular processes.
Immunofluorescence reveals the localization and quantity of proteins at the cell surface.
EndoH resistance signifies that a glycoprotein has undergone specific glycosylation modifications, indicating its transit through the Golgi.

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Description

Test your knowledge on organelles and their functions, focusing on the role of ERGIC in protein transport. Explore concepts like live export visualization using GFP-fusion proteins and the behavior of glycoproteins under temperature variations. This quiz covers experimental insights into protein organization and EndoH sensitivity.