Cell Signaling

Simple nerve reflexes use signaling molecules called

• nitric oxides
• G proteins
• neurotransmitters
• proteases

Which of the following is true about a hydrophilic signaling molecule?

• Its receptor is located in the cytosol of the target cell
• It might trigger a signal cascade that causes some effect in a cell
• Since it can enter the cell, it directly affects some specific cell process
• It is a steroid

A signal molecule that binds to a plasma-membrane protein is a

• ligand
• second messenger
• protein kinase
• receptor protein

Which of the following can activate a protein by transferring a phosphate group to it?

• cAMP
• G Protein
• protein kinase
• protein phosphatase

What do second messengers do?

• transport a signal through the lipid bilayer
• relay a signal from the outside to the inside of the cell
• relay message from the inside of the mebrane throughout the cytoplasm
• dampen the message

What does a protein phosphatase do?

• removes phosphates
• transfers phosphates from ATP to proteins
• activates an enzyme with a signal molecule

What does a protein kinase do?

• removes phosphates
• transfers phosphates from ATP to proteins
• activates an enzyme

Which of the following is a chemical message that usually travels through the bloodstream to target cells?

• hormone
• local regulator
• endocrine cell

When epinephrine binds to cardiac (heart) muscle cells, it speeds their contraction. When it binds to muscle cells of the small intestine, it inhibits their contraction. Which of the following best accounts for the fact that the same hormone can have different effects on muscle cells?

• Cardiac cells have more receptors for epinephrine than do intestinal cells
• Epinephrine circulates to the heart first and thus is in higher concentration around cardiac cells
• The two types of muscle cells have different signal transduction pathways for epinephrine and thus have different cellular responses
• Cardiac muscle is stronger than intestinal muscle and thus has a stronger response to epinephrine

Which of the following can activate a protein by transferring a phosphate group to it?

• cAMP
• G Protein
• protein kinase
• protein phosphatase