b2.1 membranes and membrane transport Flashcards
(28 cards)
How do phospholipids behave in water?
They naturally form continuous bilayers due to hydrophobic/hydrophilic interactions.
What is the primary function of the cell membrane?
Controls what enters and exits the cell.
Where are lipid bilayers found in cells?
- Plasma membrane
- Organelle membranes (nucleus, mitochondria, ER, Golgi)
Why does the hydrophobic core of a bilayer block hydrophilic particles?
Water-soluble molecules cannot pass through nonpolar lipid tails.
What are advantages of membranes as barriers?
- Compartmentalization of cell functions
- Selective transport
- Protection from environmental changes
What is simple diffusion?
Movement of molecules down their concentration gradient without energy use.
How does concentration gradient, particle size, and polarity affect diffusion?
- Higher gradient = Faster diffusion
- Smaller particles = Easier movement
- Nonpolar molecules = More permeable
Examples of simple diffusion?
- Oxygen enters cells (needed for respiration)
- Carbon dioxide exits cells (waste product)
Where are integral vs. peripheral proteins located?
- Integral proteins: Embedded in the bilayer
- Peripheral proteins: Attached to membrane surface
How do hydrophobic/hydrophilic regions affect anchoring?
Hydrophobic parts embed within bilayer, hydrophilic parts interact with water.
Six functions of membrane proteins?
- Transport (e.g., aquaporins)
- Enzymatic activity (e.g., ATP synthase)
- Signal reception (e.g., hormone receptors)
- Cell recognition (e.g., glycoproteins)
- Intercellular joining (e.g., tight junctions)
- Attachment to cytoskeleton (e.g., integrins)
Define osmosis.
Water movement across membranes from low to high solute concentration.
How does water move based on solute concentration?
Toward the side with higher solute concentration.
What is the function of aquaporins?
Protein channels allowing faster water transport across membranes.
What are channel proteins?
Membrane proteins forming selective tunnels for molecules to pass through.
Define facilitated diffusion
Passive transport using protein channels for larger or charged molecules.
How do channel proteins ensure specificity?
Only allow certain ions or molecules through.
Types of channel protein gates?
- Voltage-gated (opens with electrical signals)
- Ligand-gated (opens with molecule binding)
Example of facilitated diffusion?
Glucose transport via GLUT proteins.
What are pump proteins?
Membrane proteins moving molecules against concentration gradient using ATP.
Compare active transport vs. facilitated diffusion.
Active Transport: (Uses ATP - Moves with gradient - Pump proteins). Facilitated Diffusion: (No energy required - Moves against gradient - Channel proteins)
Define selective permeability.
Membrane controls which particles enter/exit based on properties.
Does simple diffusion show selectivity?
No—only depends on concentration gradient.
How does particle size affect permeability?
Smaller molecules pass more easily.
