99 Flashcards
(16 cards)
What is the main function of cell membranes?
Cell membranes separate the interior of the cell from the external environment and enclose organelles.
How do cell membranes facilitate communication?
Signal transfer occurs through receptors (transport proteins).
What factors affect the rate of diffusion across a lipid bilayer?
The rate depends on the size and solubility of the molecule; smaller and less polar molecules diffuse more rapidly.
What are the two types of transport across cell membranes?
1) Passive transport (does not require energy)
2) Active transport (requires energy).
What is passive transport?
Movement of molecules across a cell membrane that does not require energy, including simple diffusion and facilitated diffusion.
What is active transport?
Movement of molecules across a cell membrane that requires energy.
Why are lipid bilayers impermeable to solutes and ions?
The hydrophobic interior creates a barrier to most hydrophilic molecules, including ions.
What types of molecules can diffuse rapidly across lipid bilayers?
Small nonpolar molecules (e.g., O2, CO2) and uncharged polar molecules (e.g., H2O, ethanol) can diffuse rapidly.
What is osmosis?
Water diffuses across a membrane from lower solute concentration to higher solute concentration until equal.
What role does the Na+-K+ pump play?
It uses ATP energy to pump Na+ out of the cell and K+ into the cell against their electrochemical gradients.
What are integrins?
Integrins are transmembrane proteins that link the actin cytoskeleton to the extracellular matrix and relay signals.
What are the types of cell junctions?
1) Tight junctions
2) Adherens junctions
3) Gap junctions.
What is the function of tight junctions?
They form a seal between cells that prevents ions from passing across.
What do gap junctions do?
They allow small molecules and ions to move between adjacent cells, providing metabolic and electrical coupling.
How can membrane proteins be restricted in mobility?
Proteins can be tethered to the cell cortex, extracellular matrix, or other cells, and diffusion barriers can restrict them.
What is the role of the carbohydrate layer on the lipid bilayer?
It helps protect the cell surface from mechanical and chemical damage.
