Membrane Transport Flashcards
Boundary that separates the living cell from its surroundings. Exhibits selective permeability. Allows some substance to cross the membrane more easily than other substance
Plasma membrane
Most abundant lipid in the plasma membrane
Phospholipids
Contain both hydrophilic and hydrophobic regions
Amphipathic molecules
can exist as a stable boundary between 2 aqueous compartments
phospholipid bilayer
A membrane that is a fluid structure with a “mosaic” of various proteins embedded in it. Proteins are not randomly distributed in the membrane
Fluid Mosaic Model
direction where lipids, and some proteins drift
laterally
determine most of the membrane’s specific functions
Membrane protein
Proteins Bound to the surface of the membrane
Peripheral protein
Proteins that Penetrate the hydrophobic core
Integral proteins
Integral proteins that span the membrane
Transmembrane protein
6 major function of membrane proteins
transport, enzymatic activity, signal transduction, cell to cell recognition, intercellular joining, attachment
Role of Membrane Carbohydrates in Cell-Cell Recognition
Cells recognize each other by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
Membrane carbohydrates may be
covalently bonded to lipids (glycolipids) or more commonly to proteins (glycoproteins)
Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual
Can dissolve in the lipid bilayer and pass through the membrane rapidly
Hydrophobic
Includes ions and polar molecules that do not pass the membrane easily
Hydrophilic
Allows the passage of hydrophilic substance across the membrane
Transport Proteins
With hydrophilic channel that certain molecules can use as a tunnel (transport protein)
Channel proteins
Facilitate the passage of water (under channel protein)
Aquaporins
Bind to molecules and change shape to shuttle them across the membrane, uses energy (transport protein)
Carrier proteins
Movement of molecules from an area of higher concentration to an area of lower concentration without any energy investment
The tendency for molecules to spread out evenly into the available space
Diffusion
Substances diffuse down their concentration gradient
No work must be done to move the substances down the gradient (type of transport)
Passive Transport
Diffusion of water across the selectively permeable membrane from the region of lower solute concentration to the region of higher solute concentration until the concentration is equal on both sides
Osmosis
Ability of a surrounding solution to cause a cell to gain or lose water
Tonicity
Solute concentration is the same as inside the cell. No net movement of water across the membrane
Isotonic solution
Solute concentration is greater outside the cell
Cell loses water, Cell becomes shrivelled
Hypertonic solution
Solute concentration is less than the inside of cell. Cell gains water, Cell may swell or burst
Hypotonic solution
Control of solute concentrations and water balance
Needed for organisms that has problems with the hypertonic or hypotonic environments
Osmoregulation
Transport proteins speed up the passive movement of molecules across the plasma membrane
Facilitated Diffusion
Undergo subtle change in shape that translocates the solute-binding site across the membrane (facilitated diffusion)
Carrier proteins
Provide corridors to allow specific molecules to cross the membrane (facilitated diffusion)
Channel proteins
Facilitate diffusion of water
Aquaporin
Facilitate diffusion of ions. Some are known as gated channels. They open and close in response to a stimulus (facilitated diffusion)
lon channel
Moves substances against their concentration gradient
Requires energy, usually in the form of ATP
Performed by specific proteins embedded in the plasma membrane
Allows cells to maintain concentration gradients that differ than their surroundings
Sodium-potassium pump is one type of the active transport
Active Transport
Voltage difference across a membrane Created by differences in the distribution of positive and negative ions across a membrane
Membrane Potential
2 combined forces, Drive the diffusion of ions across a membrane
Electrochemical Gradient
lon’s concentration gradient (force)
Chemical force
Effect of membrane potential on the ion’s movement (force?
Electrical force
A transport protein that generates voltage across the membrane, Help store energy that can be used for cellular work
Electrogenic Pump
Major electrogenic pump for animal cells
Sodium-potassium pump
Major electrogenic pump for plants, fungi, and bacteria
Proton pump
Coupled transport by a membrane protein
Occurs when active transport of a solute indirectly drives transport of
Cotransport
same direction of passage in cotransport
Symport
opposite direction of passage in cotransport
antiport
Movement of proteins or macromolecules into and out of the cell, Requires energy
Bulk Transport
2 types of Bulk Transport
- Exocytosis
- Endocytosis
Transport vesicles migrate to the
membrane, fuse it, and release their
contents outside the cell
* Many secretory cells use exocytosis to export their products
Exocytosis
Cells take in macromolecules by forming vesicles from plasma membrane
Endocytosis
3 types of Endocytosis
Phagocytosis, Pinocytosis, Receptor-mediated endocytosis
cellular eating, Cell engulfs a particle in a vacuole. The vacuole fuses with a lysosome to digest the particle
Phagocytosis
cellular drinking, Molecules dissolved in droplets are taken up when extracellular fluid is “gulped” into tiny vesicles
Pinocytosis
Binding of ligands to receptors triggers vesicle formation
Receptor-mediated endocytosis
Any molecule that binds specifically to a receptor site of another molecule
Ligand
2 HIV receptors
CD4 and CCR5
