U4L1 Notes: Cell Communication/Signal Transduction

Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as MHC proteins and T cell receptors, mediate cell communication over short distances?

• The proteins receive electrical signals from nerve cells.

• The proteins leave the cell and travel in the bloodstream to other cells.

• The proteins interact directly with proteins on the surfaces of other cells.

• The proteins bind to molecules secreted by cells located in other parts of the body.

Notch is a receptor protein displayed on the surface of certain cells in developing fruit fly embryos. Notch’s ligand is a membrane-bound protein called Delta that is displayed on the surface of adjacent cells. When Notch is activated by its ligand, the intracellular tail of the Notch protein becomes separated from the rest of the protein. This allows the intracellular tail to move to the cell’s nucleus and alter the expression of specific genes. Which of the following statements best explains Delta’s role in regulating cell communication through the Notch signaling pathway?

• Delta transmits a chemical signal to all the cells of a developing embryo

• Delta allows the cells of a developing embryo to communicate without making direct contact.

• Delta restricts cell communication to short distances within a developing embryo.

• Delta determines which cells in a developing embryo express the gene that encodes the Notch protein.

Ethylene causes fruits to ripen. In a signaling pathway, receptors activate transcription factors, which ultimately leads to ripening. Which of the following best supports the claim that ethylene initiates the signal transduction pathway that leads to ripening of fruit?

• Ethylene is a simple gaseous molecule, which makes it easily detected by receptors

• Fruit will ripen in closed containers without exposure to air.

• Ethylene synthesis is under both positive and negative feedback regulation

• Loss-of-function mutations in ethylene receptors result in changes to the ripening process.