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What is selective permeability?
Allowing some substances to cross it more easily than others.
What is the cell membranes composed of?
Composed of a fluid-mosaics of lipids and proteins. Phospholipids are the most common lipid.
What type of molecules are phospholipids? what does it mean?
Phospholipids are amphipathic molecules which means they contain hydrophobic and hydrophilic regions.
Can phospholipids in the plasma membrane move within the bilayer? If so, how?
Yes they can. Most of the lipids and some protein drift laterally. Rarely do they flip-fop.
What may cause a flip-flop to occur?
Membranes rich in ___________ are more fluid than those rich in ___________ .
unsaturated fatty acids, saturated fatty acids.
What are the different effects that cholesterol has on membrane fluidity at different temperatures?
- At warm temperatures, cholesterol retains movement of phospholipids.
- At cool temperatures, it maintains fluidity by preventing tight packing of phospholipids
- -cholesterol (only in animal cells) acts as a buffer
What determines most of the membrane's specific functions?
Define peripheral proteins.
They are bound to the surface of the membrane. (more hydrophobic)
Define integral proteins.
- penetrate the hydrophobic core.
- embedded through the bilayer. amphipathic molecule
What functions do membrane proteins perform? (6)
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachment to the cytoskeleton and the ECM
What function does carbohydrates play in the plasma membrane?
Cells recognize each other by binding to carbohydrates on the plasma membrane.
What are the two membrane carbohydrates and how are they bonded?
Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
What types of substances would you expect to easily pass through the lipid bilayer?
- nonpolar (hydrophobic) molecules such as hydrocarbonspolar molecules DO NOT cross
What is passive transport?
It's diffusion of a substance across a membrane with no energy investment.
What is diffusion?
- It's the tendency for molecules to spread out evenly into the available space.
- moves from an area of high concentration to low concentration
What are the movements of substances in passive transport?
Substances diffuse down their concentration gradient, from an area where its MORE concentrated to where it's LESS concentrated with no energy.
Define Osmosis. (2)
- It's the diffusion of water across a selectively permeable membrane.
- diffuses from the region of lower solute concentration to the region of higher solute concentration.
What is tonicity?
It's the ability of a solution to cause a cell to gain or lose water.
what is hypertonic?
- It's when a solution has a higher solute concentration than cell
- causes cell to lose water and shrivel
What is hypotonic?
- Solution has a lower solute concentration than the cell
- causes cell to gain water and burst
What is isotonic?
Solution and cell have equal solute concentrations.
When animal cell bursts from a hypotonic solution, what is it called?
What happens to a plant cell when it's in a hypotonic solution?
- swells until the walls opposes uptake
- cell is now turgid (firm)
What happens to a plant cell when it's in a isotonic solution?
- no net movement of water into the cell
- cell becomes flaccid (limp) and plant may wilt
What happens to a plant cell when it's in a hypertonic solution?
- plant cells lose water
- eventually membrane pulls away from the wall, an effect called plasmolysis
What happens in facilitated diffusion?
when transport proteins speed the passive movement of molecules across the plasma membrane.
What are transport proteins?
They are transmembrane proteins that allow passage of hydrophilic substances across the membrane.
What are channel proteins?
- They have hydrophilic channel that certain molecules or ions can use as a tunnel.
- includes aquaporins
What facilitated transport/diffusion?
Its a passive transport aided by proteins.
What are ion channels?
Channels that open and close in response to stimulus. (gated channels)
What are carrier proteins?
These proteins bind to molecules and change shape to shuttle them across the membrane.
What is active transport?
- Moves substances against their concentration gradient
- requires energy, usually in the form of ATP
What is the sodium-potassium pump? (3)
- one type of active transport system
- shuttles 3 Na+ OUT and 2 K+ INTO the cell
- both move against their gradients
Define membrane potential.
voltage difference across a membrane
What is a electrogenic pump?
a transport protein that generates voltage across a membrane
What is the major electrogenic pump in plant, fungi, bacteria and animal cells?
- Animals cells: sodium-potassium pump
- Plant, fungi, and bacteria cells: Proton pump
Occurs when active transport of a solute indirectly drives transport of another solute.
What is bulk transport? (2)
- It's the crossing of a membrane in a bulk via vesicles for big molecules like macromolecules.
- requires energy
Transport vesicles migrate to the membrane, fuse with it, and release their contents to the outside of the cell.
Define endocytosis. what are the three types?
- The cell takes in macromolecules by forming vesicles from the plasma membrane. It includes:
- receptor-mediated endocytosis
Define pinocytosis. (2)
- Molecules are taken up when extracellular fluid is "gulped" into tiny vesicles.
- for small molecules
- Cell engulfs a particle in a vacuole.for big molecules
What is endosome?
Vesicle that's formed from the membrane.
Define receptor-mediated endocytosis.
- binding of ligands (any molecule that binds specifically to a receptor site) to receptors triggers vesicle formation
- for specific molecules