Membrane Structure & transport, intracellular compartments & protein sorting. An
ID: 82384 • Letter: M
Question
Membrane Structure & transport, intracellular compartments & protein sorting. An extensive carbohydrate layer is found on the outer surface of all eukaryotic cells. Name two functions of this carbohydrate layer. Do cells need membrane transport proteins for oxygen? Briefly explain why or why not. Can the Mediator complex, which functions in transcription, passively diffuse through the nuclear pore? Briefly explain why or why not. The following diagram depicts the topology of a multipass transmembrane protein in the endoplasmic reticulum (ER) membrane. Which helices (1-6) act as stop-transfer signals in this protein? What are the three main tasks of the signal recognition particle (SRP)?Explanation / Answer
Answer 1.
An extensive carbohydrate layer composed of a variety of different monosaccharides is present on outer surface of eukaryotic cells. The layer and forms a cell coat or glycocalyx outside the cell membrane.
The layer plays an important role in protection and cell recognition.
Answer 2.
No, membrane transport proteins don’t require oxygen. Oxygen (along with water and carbon dioxide) is a simple molecule that can cross the cell membrane by diffusion and hence, doesn’t require membrane transport proteins.
Answer 4.
Second helical region
Normally, the first helical domain is an internal uncleaved signal-start sequence that commences the transfer of the protein. The second helical region acts as a stop-transfer signal and prevents further transfer of the polypeptide. The result is the insertion of a hairpin loop across the membrane.
Answer 5.