cell signaling
what is a ligand
a signaling molecule that binds to a specific receptor and initiates a cellular response
What is the movement of molecules from an area of high concentration to an area of low concentration called?
diffusion
where are receptors for hydrophilic signaling molecules typically located?
on the plasma membrane
what is one common second messenger?
cAMP
A person's body temperature rises above its normal set point. Which component of a homeostatic control system detects this change and initiates the response? what is this an example of?
the receptor that detects the change in temperature. negative feedback mechanism.
what happens when a ligand binds to a receptor
the receptor is activated and initiates a signaling pathway that leads to a cellular response
What is the difference between passive and active transport?
Passive transport does not require cellular energy and moves substances down their concentration/electrochemical gradient. Active transport requires energy and can move substances against their gradient.
what is the function of a receptor
To recognize and bind a specific signaling molecule and initiate a cellular response.
what is a second messenger?
a molecule inside the cell that relays or amplifies a signal from a membrane receptor.
A receptor detects that blood glucose levels have increased. The body then activates mechanisms that lower blood glucose back toward its normal range. What type of feedback is this, and why?
Negative feedback because the response opposes the original change and brings the variable back toward its normal range.
what are the three steps of cell signaling
reception, transduction, response
Does facilitated diffusion require ATP? Explain.
No. It uses membrane proteins to move substances down their concentration or electrochemical gradient.
Why do hydrophilic hormones usually need membrane receptors?
They cannot easily cross the hydrophobic interior of the plasma membrane
Put these steps in the correct order: cAMP, receptor, G protein, adenylyl cyclase, cellular response.
Receptor → G protein → adenylyl cyclase → cAMP → cellular response
Body temperature increases. Sweat glands are activated, causing heat loss and lowering body temperature. Identify the stimulus, receptor, control center, and effector.
Why can the same signaling molecule cause different responses in different cells?
Different cells can have different receptors, signaling proteins, or intracellular machinery, so they can respond differently to the same signal.
The sodium-potassium pump moves 3 Na⁺ out of the cell and 2 K⁺ into the cell. What type of transport is this? Why?
Primary active transport because it directly uses ATP.
Where are receptors for steroid hormones typically located, and why?
Inside the cell because steroid hormones are lipid-soluble and can cross the plasma membrane.
What would happen to the signaling pathway if adenylyl cyclase were inhibited?
Less or no cAMP would be produced, so the downstream signaling pathway would be reduced or stopped.
A patient is hypoventilating, causing CO₂ to accumulate in the blood. Using the carbonic acid reaction, explain step-by-step why this causes blood pH to decrease. Then explain how increasing ventilation would help restore pH toward normal.
Hypoventilation → CO₂ ↑ → reaction shifts toward H₂CO₃ → H₂CO₃ dissociates into H⁺ + HCO₃⁻ → H⁺ ↑ → pH ↓.
Increasing ventilation removes CO₂ from the blood, decreasing the amount available to form carbonic acid and ultimately decreasing H⁺ concentration, causing pH to move back toward normal.
A hormone binds to a receptor on the plasma membrane. The signal is then passed through several molecules inside the cell before producing a response. What process is occurring?
signal transduction
A Na⁺-glucose cotransporter moves glucose into a cell using the Na⁺ concentration gradient. Is this primary or secondary active transport? Explain.
Secondary active transport. It does not directly use ATP; it uses the energy stored in the Na⁺ gradient created by the sodium-potassium pump.
A hormone is unable to cross the plasma membrane but still causes a response inside the cell. Explain how this is possible.
The hormone binds to a membrane receptor, which activates an intracellular signaling pathway, often involving second messengers.
One signaling molecule binds to one receptor, but the cell eventually activates thousands of molecules. What concept does this demonstrate, and why is it important?
Signal amplification. It allows a small initial signal to produce a much larger cellular response.
A student says: “If CO₂ increases, blood pH decreases because CO₂ itself is an acid.” Is this explanation correct? Explain what is actually happening.
Not exactly. CO₂ itself is not the main reason for the increased acidity. CO₂ reacts with H₂O to form H₂CO₃, which can dissociate into H⁺ and HCO₃⁻. The increase in H⁺ is what directly lowers pH.