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You are studying a single spanning membrane protein that is normally located in ...

Jan 13, 2024

You are studying a single spanning membrane protein that is normally located in the plasma membrane. When cells are deprived of nutrients, this protein is endocytosed and accumulates in intracellular vesicles/compartments. You want to use an antibody to visualize the movement of the protein to these structures in live cells. You have two different fluorescently labelled antibodies that recognize the protein - one recognizes the N terminus and the other recognizes the C terminus of the membrane protein. When you carry out the experiment, you only see fluorescent signal (that moves from the plasma membrane to the internal structures after starvation is initiated) when you use the antibody that recognizes the C terminus of the protein. What is likely true about the membrane protein that could explain this? Select one: a. The protein is glycosylated. b. The protein is a type II membrane protein. c. The protein is a type I membrane protein. d. The cells are dying during the experiment.

Key Concept

Orientation of membrane protein termini

Explanation

In a type II membrane protein, the N terminus is located in the cytoplasm, while the C terminus is extracellular or in the lumen of organelles. Since the antibody recognizing the C terminus shows movement, it suggests that the C terminus is exposed to the extracellular space or vesicle lumen, allowing the antibody to bind, which is characteristic of type II membrane proteins.

Which of the following membranes would you expect to have the highest Tm? Select one: A. Membrane with short saturated hydrocarbon chains and no cholesterol B. Membrane with long saturated hydrocarbon chains and no cholesterol C. Membrane with short saturated hydrocarbon chains and some cholesterol D. Membrane with long saturated hydrocarbon chains and some cholesterol

Key Concept

Membrane fluidity and transition temperature (Tm)

Explanation

The transition temperature (Tm) of a lipid bilayer is the temperature at which the membrane transitions from a fluid state to a gel state. Membranes with long saturated hydrocarbon chains have higher Tm because the longer chains interact more strongly and pack together more tightly than shorter chains, making the membrane less fluid and increasing its Tm. The presence of cholesterol also increases Tm by stabilizing the membrane structure and making it less permeable and more ordered. Therefore, a membrane with long saturated hydrocarbon chains and some cholesterol would have the highest Tm.