Transport Mechanisms Across Membranes Flashcards
What are the types of membrane proteins?
Integral and Peripheral
What are the functions of membrane proteins?
Transport, enzymatic activity, receptors for signal transduction, intracellular adhesion, cell-cell recognition, attachment to cytoskeleton and extracellular matrix.
What are the transport techniques?
Passive transport, Active transport, Vesicular (Bulk) Transport
What is simple diffusion?
Substances diffusing directly through lipid bilayer or diffuse through channel proteins.
What substances are transported through simple diffusion?
Lipid-soluble substances and ions
What are the factors affecting simple diffusion?
Concentration and electrical gradient
Surface area
Membrane thickness
Mass of diffusing molecule
Temperature
Why can’t ions pass directly through the phospholipid bilayer?
Because they are charged so they need ion channels
What are ion channels?
Transmembrane proteins that transport inorganic ions
What are two properties ion channels have?
Selectivity, only allowing certain ions.
Gating, ion channels open and close in response to a stimulus.
What are some examples of ion channels?
Na+ channel
K+ channel
Ca2+ channel
Cl- channel
What are the five types of gating?
Leak (non-gated) channels
Ligand-gated channels
Mechanically-gated channels
Voltage-gated channels
Temperature-gated channels
What do ligand-gated channels operate in a response to?
Extracellular mediators
Intracellular editors
What do mechanically-gated channels respond to?
Mechanical vibrations and pressure
What do voltage-gated channels respond to?
Direct change in the membrane potential
What is the function of voltage-gated channels?
Responsible for generation of action potential
What is osmosis?
Net diffusion if water across a selectively permeable membrane
How can water cross the plasma membrane?
Directly through the phospholipid bilayer,
Through H2O channels, called aquaporins
What is osmolarity?
The measure of solute concentration per unit of volume or mass of solvent
What is tonicity?
The measure of osmotic pressure gradient between two solutions
What does tonicity take into account?
Cell membrane permeability
Relative concentrations
How does osmolarity increase?
By decreasing water or increasing solute
What is facilitated diffusion?
Transport of larger molecules, requires carrier protein.
What characteristics does the carrier-mediated transport share?
Specificity,
Competition,
Saturation.
What is the transport maximum?
The number of carriers available in the plasma.
What is filtration?
The passage of water and solutes through a membrane by hydrostatic pressure.
How do substances move during filtration?
From higher pressure area to lower pressure area.
What is active membrane transport?
Requires carrier proteins and ATP to move solutes across a membrane.
How does primary active transport use ATP?
Hydrolysis of ATP
How does secondary active transport use ATP?
Exchange pump, not directly
What determines if it is secondary or primary active transport?
If Na+ is moving to outside then it is primary, also direct or indirect use of ATP.
What is bulk transport?
Transport of large particles and macromolecules across plasma membrane.
What are the types of bulk transport?
Phagocytosis,
Endocytosis,
Exocytosis.
Which bulk transport method is non-specific?
Pinocytosis (endocytosis)
What is manitol?
A carbohydrate that draws water from the cell.
