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What is osmosis?
Diffusion of water across a selectively permeable membrane.
What is the difference between hypotonic and hypertonic solutions.
A hypotonic solution has a lower solute concentration than the cell causing water to move into the cell and make it swell while a hypertonic solution has a higher solute concentration than the cell causing water to move out of the cell and make it shrink.
What are aquaporins?
Channel proteins that allow rapid movement of water across membranes.
Steroid hormones can enter a cell by simple diffusion. Therefore steroids __________.
do not initiate cell signaling by interacting with a receptor in the plasma membrane
A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to __________.
lower activity of protein kinase A
What are the 3 stages of cell signaling?
Reception, Transduction, Response
What is the fluid mosaic model ?
A model describing the membrane as a fluid phospholipid bilayer with proteins embedded and moving within it like a mosaic.
What makes up the majority of membranes?
Phospholipids, proteins, and some carbohydrates.
What are channel proteins?
Proteins that form hydrophilic tunnels allowing specific molecules or ions to cross the membrane.
What is facilitated diffusion?
Passive movement of substances across the membrane using transport proteins without energy.
What is active transport?
Movement of substances against their concentration gradient using energy (ATP).
What is the sodium-potassium pump?
A transport protein that uses ATP to pump Na⁺ out and K⁺ into the cell.
What does “amphipathic” mean?
A molecule that has both a hydrophilic (water loving) and hydrophobic (water fearing) region.
How can one hormone molecule affect millions of molecules?
Through signal amplification
What is exocytosis
a process to move products out of the cell.
The general name for an enzyme that transfers phosphate groups from ATP to a protein is __________.
protein kinase
What is diffusion?
Movement of molecules from high concentration to low concentration.
What is the role of cholesterol in membranes?
It regulates membrane fluidity by reduces fluidity at high temperatures and prevents solidification at low temperatures.
A G protein is active when __________
GTP is bound to it
How can a single hormone molecule lead to a large cellular response?
Through signal amplification in cascades where each step activates many molecules in the next step.
Why is the original signaling molecule usually not passed along the pathway?
Because it only binds to the receptor on the cell surface and does not enter the cell; it only triggers changes inside the cell.
What is endocytosis
The procedure that cells use to import large molecules across their plasma membrane.
What is the difference between reception and transduction in cell signaling?
Reception is when the signal molecule binds to the receptor, while transduction is the series of steps that relays and converts the signal inside the cell.
What is a concentration gradient?
A difference in concentration of a substance across a space or membrane.
Why is phosphorylation important in signal transduction?
It changes protein shape and activity, often switching proteins on or off.