Membranes Flashcards
Membrane components
Composition
Membrane is mostly comprised of lipids.
Also a large component of cholesterol which allows for membrane fluidity.
Membrane components
Fluid mosaic model
The semisolid membrane is composed of a phospholipid bilayer.
Lipids can move freely within the membrane through lipid rafts. Larger molecules have restricted motion.
Membrane components
Flippases
Proteins that facilitate transport of phospholipids between layers of the membrane.
Membrane components
Glycoproteins
Proteins attached to carbohydrates. Perform various functions within the cell membrane including protection.
Membrane components
Cholesterol
Acts as a buffer for the effect of temperature on membrane fluidity.
At low temperatures, cholesterol leads to ↑ fluidity by preventing packing together of lipids.
Membrane transport
Active versus passive transport
- Active transport: moving against concentration gradient.
- Passive transport: moving with concentration gradient.
Membrane transport
Selective permeability
It is easier for small, nonpolar molecules to move through passive transport through the membrane.
Membrane transport
Types of passive transport
- Simple diffusion: Small, nonpolar molecules easily move from high to low concentration. Osmosis is diffusion of water.
- Facilitated diffusion: Movement with concentration gradient but aided by membrane proteins.
Membrane transport
Primary active transport
Uses ATP hydrolysis to transport against concentration gradient.
Membrane transport
Secondary active transport
Also called coupled transport. Uses energy of one molecule moving with its concentration gradient as energy source
Symport: molecules moving the same direction.
Antiport: moving opposite directions.
Membrane transport
Endocytosis and exocytosis
A form of transport where molecules are engulfed or ingested by cells.
Endocytosis = inward
Exocytosis = outward
Integral proteins
Definition
Proteins that are at least partially in the phospholipid bilayer.
Transmembrane proteins: Span the entire membrane.
Embedded proteins: Partially embedded in the membrane.
Integral proteins
Transmembrane proteins
Proteins that span the entire membrane.
The central portion (inside the bilayer) has hydrophobic amino acids; outer portions have hydrophilic amino acids.
Integral proteins
Embedded proteins
Proteins that are partially embedded in the membrane.
Often involved in cellular communication.
Embedded portion is generally hydrophobic.
Integral proteins
Peripheral proteins
Proteins that interact with the surface layer of the membrane and are not embedded.
Can interact with either side of bilayer.
Cell-cell junctions
Gap junctions
Junctions between cells that allow for rapid exchange of small molecules (like ions).
Cell-cell junctions
Tight junctions
Prevent leakage of solutes. Found in epithelial tissues.
Think of a “watertight” seal, like in the kidney.
Cell-cell junctions
Desmosomes
Hold cells together by anchoring to cytoskeleton. Found in barriers like skin.
