Question

Draw an integral membrane protein extending from partway through the ER membrane into the ER lumen. Next, draw the protein where it would be located in a series of numbered steps ending at the plasma membrane. Would the protein contact the cytoplasm or the extracellular fluid? Explain.

Answer 1

Sure! I'll describe the integral membrane protein and its location in a series of steps. The protein will start from the endoplasmic reticulum (ER) and end up at the plasma membrane. Please note that I'll provide a simplified representation, and the actual structure of a protein can vary.

Step 1:

In the ER membrane, draw a transmembrane protein represented by a squiggly line passing through the lipid bilayer. The squiggly line indicates the hydrophobic regions of the protein that embed within the membrane, while the loops represent the hydrophilic regions that face the ER lumen.

Step 2:

The protein undergoes proper folding and processing in the ER, with any necessary post-translational modifications. It remains within the ER membrane but may undergo additional interactions and modifications.

Step 3:

The ER membrane forms transport vesicles that bud off, carrying the protein along with other cargo molecules. Draw a vesicle budding off from the ER membrane, with the protein embedded in it.

Step 4:

The vesicle moves towards the Golgi apparatus. Draw the vesicle approaching the Golgi, and the protein still present within the vesicle membrane.

Step 5:

At the Golgi apparatus, the protein undergoes further processing and sorting. Draw the protein embedded in the Golgi membrane, indicating its movement through the Golgi compartments (cis, medial, and trans).

Step 6:

Transport vesicles bud off from the Golgi and carry the protein towards the plasma membrane. Draw a vesicle containing the protein moving away from the Golgi.

Step 7:

The vesicle fuses with the plasma membrane, releasing its contents into the extracellular fluid. Draw the vesicle fusing with the plasma membrane, with the protein now embedded in the plasma membrane.

Step-by-step explanation:

Regarding your question about whether the protein contacts the cytoplasm or the extracellular fluid, it depends on the orientation of the protein. Integral membrane proteins can have different domains facing different compartments. In this case, the hydrophilic loops of the protein would face the ER lumen, Golgi lumen, and extracellular fluid, while the hydrophobic regions (transmembrane segments) would be embedded within the lipid bilayers of the ER membrane, Golgi membranes, and plasma membrane. Therefore, the protein would contact the extracellular fluid once it reaches the plasma membrane, while its hydrophilic regions would remain exposed to the lumen of the organelles (ER, Golgi) during the transport process.

Answer 2

Regarding the question of whether the protein would contact the cytoplasm or the extracellular fluid, it depends on the specific location along the pathway. Initially, within the ER, the protein is in contact with the cytoplasm. However, as it moves through the secretory pathway, it eventually reaches the plasma membrane, where it would be in contact with the extracellular fluid.

In order to draw an integral membrane protein extending from partway through the ER membrane into the ER lumen, we can imagine a protein structure embedded within the ER membrane. This structure would consist of a hydrophobic region, which spans the membrane, and hydrophilic regions, which face the ER lumen.

Now, let's consider the protein's location in a series of numbered steps ending at the plasma membrane:

1. The protein is synthesized in the rough endoplasmic reticulum (ER) and begins to be inserted into the ER membrane.
2. As the protein continues to be synthesized, it extends further into the ER lumen, forming a hydrophilic region within the lumen.
3. The protein may undergo modifications within the ER, such as folding or glycosylation, before it is transported further.
4. Next, the protein moves from the ER to the Golgi apparatus through vesicle transport.
5. Within the Golgi apparatus, the protein undergoes additional modifications and is sorted for transport to its final destination.
6. The protein may be packaged into vesicles and transported to the plasma membrane.
7. Finally, the vesicle fuses with the plasma membrane, releasing the protein and inserting it into the membrane.