Chapter 7: Cell Membrane Flashcards
Selective Permeability
Cell allows some substances to travel “across” the membrane
Amphipathic
When a molecule has hydrophobic AND hydrophilic regions (exp phospholipid bilayer; most common kind of membrane lipid)
Most cell membrane proteins and lipids are amphipathic
Fluid mosaic model of cell membranes
Made of mosaic of protein molecules bobbing in a fluid bilayer of phospholipids
Proteins occur in patches based on shared, specialized function
More densely packed in some areas of the membrane than others
Fluid phospholipid bylayer
Must be fluid to work properly
Membrane lipids can move about the membrane laterally; they don’t have to stay in the same position.
Held together primarily by hydrophobic interactions
Fluid becomes more rigid/solid as temp drops (unless it’s made of phospholipids with kinked/unsaturated tails)
Cholesterol “fluidity buffer” in the membrane
Found in the cell membrane
Makes the membrane less fluid at lower temperatures bc it impedes the close packing of lipids; helps membrane resist temp-based changes in fluidity
2 major membrane proteins
Integral Protein
Peripheral Protein
Integral (membrane) protein
Proteins that penetrate the hydrophobic interior of the phospholipid bilayer (transmembrane)
Peripheral Proteins
Loosely bound to the surface of cell membrane
Sometimes bound to the exposed part of integral proteins
Integrin
Type of integral transmembrane protein
Enhances strength of the membrane
Transmembrane Protein Structure
May have N terminus region (sticking out of the membrane), secondary alpha helix region (within the hydrophobic part of the bilayer) and a C terminus (inside the cell cytosol)
p/ 129 bacteriorhodopsin
Glycolipids and glycoproteins
Types of molecular markers used by cells to identify one another
Nonpolar molecules vs phospholipid bilayers
Non polars like hydrocarbons, CO2, and O2 can dissolve in the bilayer and pass through it without any help from the cell
polar molecules vs phospholipid bilayers
Polars can’t get through the hydrophobic part of the bilayer without help from transport proteins
Passive transport
Transport/Channel Proteins
Help materials pass through the membrane:
exp. Aquaporins: used to transport H2O
Tonicity
The ability of a surrounding solution to cause a cell to gain or loose water
Depends on the concentration of solutes that cannot pass through the cell membrane
If there is a higher concentration of non penetrating solutes in the surrounding solution, water will tend to leave the cell and vice versa;
Free water goes to where the solutes are
Plasmolysis
When the environment around the PLANT cell wall is hypertonic and the water leaves the cells, causing the membrane to shrivel but the cell wall stays in tact.
Causes plants to wilt
Facilitated Diffusion/Passive Transport:
Channel Proteins
No energy req by the cell; materials being moved DOWN their concentration gradients
Basically and open protein gate that material can flow through to pass through the cell membrane
exp. aquaporins transport water
ion channels transport ions (some have gates)
Facilitated Diffusion/Passive Transport:
Carrier Proteins
No energy req by the cell; materials being moved DOWN their concentration gradients
Change shape to allow materials to travel through the membrane
Active transport
Energy IS req by the cell; materials being moved UP their concentration gradients
ATP may give up a phosphate group to activate the transport protein, which changes shape to facilitate the transport exp NaK pump
Membrane potential
Potential energy of the cell membrane
Requires active transport the maintain desired balance of negative and positively charged ions inside and outside of the cell
Involves effects of ions’ concentration gradient and electrochemical gradiant (charge attractions/repulsion)
Electrogenic Pump
Transport protein that generates voltage across the cell membrane (by pumping ions in or out of the cell)
exp. NaK pump in ANIMALS
Proton pump in PLANTS, FUNGI, BACTERIA (transports hydrogen ions)
Cotransport
When the activity of a one pump or some passive transport of a material down its concentration gradient indirectly drives the active transport of some other material
???
Bulk transport
Active, req energy, transport of large materials like proteins and polysaccharides
Exocytosis: when vesicle buds OFF the golgi and travels along the microtubules to the plasma membrane where it can fuse with in and then pass on its contents; exportation
Endocytosis: reverse of exocytosis
3 types of endocytosis
phagocytosis: Eating
Pinocytosis: Drinking
receptor mediated endocytosis: cholesterol processing
Ligand
Any molecule that binds specifically to a receptor site of another molecule
Involved in receptor mediated endocytosis
What can pass/diffuse through the membrane without help
Nonpolar molecules (like hydrocarbons, CO2, H2O)
Partly because they are small enough to fit but mostly because they are hydrophobic
What can NOT pass/diffuse through the membrane without help
Polar/hydrophilic molecules (like mean polar bears and sugars) and ions
These diffuse very slowly and need help to move through the membrane
