Membrane Transport Flashcards
Plasma membrane is (3)
-semi fluid phospholipid bilayer
-hydrophilic heads at inner/outer surface
-hydrophobic tails in the middle
Two types of membrane proteins
-integral proteins
-peripheral proteins
Integral proteins (2)
-embedded in the membrane bilayer
-movement of compounds across the membrane
Peripheral proteins are
Bound to the inner or outer plasma membrane surface
Four roles of plasma membrane proteins include:
-transport across the membrane
-receptors involved in cell signalling
-enzymes that catalyze reactions
-anchoring of cells to one another and substrates
The lipid bilayer is not ___. This means ___
-miscible with extra/intracellular fluid.
-provides a barrier against movement of water and water-soluble substances between extracellular environment and cytoplasm of cell
Lipid soluble substances include (2) and they are able to ___
-Gases (O2, N2, CO2, etc)
-small, uncharged polar molecules (alcohols)
-diffuse directly across the lipid bilayer
Channel proteins (2)
-have a water-filled tunnel through the protein
-allow free movement of water, some ions and molecules
Carrier proteins (2)
-bind with ions or molecules
-undergo a conformational change in order to move the ion/molecule to the other side of the membrane
Transport across the membrane is via (2)
-active transport (requires ATP)
-passive transport (diffusion/osmosis and facilitated diffusion)
All molecules and ions in the body fluids are in
Constant random motion (called Heat or Brownian Motion)
Random motion of molecules/ions allows for
Diffusion
Brownian Motion states
The grater the temperature, the greater the motion. Motion only ceases at absolute zero
Molecules/ions diffuse across a membrane until
Equilibrium is reached
Fick’s Law of Diffusion (ie. factors that affect the net rate of diffusion) include: (5)
-concentration gradient
-permeability of membrane to substance
-surface area of membrane
-molecular weight of substance
-distance across which diffusion must occur
Fick’s Law of Diffusion: Concentration Gradient (2)
-the rate at which an ion/molecule diffuses INTO the cell is proportional to the concentration of that ion/molecule OUTSIDE the cell
-chemical driving force
Fick’s Law of Diffusion: Permeability of the membrane (2)
-the more lipid-soluble the molecule (ie. the fewer polar or ionized groups), the more easily it will traverse the membrane
-examples: O2, CO2, N2, alcohols, steroid hormones
Fick’s Law of Diffusion: Surface area of the membrane (2)
-the greater the surface area of the membrane, the greater the number of molecules that are able to hit the membrane and pass through
-limiting factor to cell size (as animals/cells get larger, the surface area:volume ratio get smaller)
Fick’s Law of Diffusion: Molecular weight of the molecule (3)
-larger molecules move more slowly
-larger molecules find it more difficult to pass through membrane protein channels
-example: water molecules move at 2500km/hr while glucose molecules move at 850 km/hr
Fick’s Law of Diffusion: Diffusion across which the molecules must travel (2)
-molecules travel at high velocities and collide with nearby molecules
-diffusion distributes molecules rapidly over short distances (ie. increasing a dose of a drug will NOT make it move faster)
The net rate of diffusion is proportional to (6)
-concentration gradient
-permeability of the membrane
-surface area of the membrane
-molecular weight of the molecule
-distance across which the molecules must travel
-membrane electrical potential
Two types of driving forces
-chemical driving force
-electrical driving force
The state of balance between two driving forces is called the
Equilibrium Potential
Membrane Electrical Potential (3)
-an electrical potential exists across a membrane on one side is relatively more positive and the other is more negative
-charged ions will move across the membrane (concentration gradient) to achieve a state of equilibrium
-electrical driving force
Equilibrium Potential is when ____ and is determined by the ____
-the electrical driving force is equal to and opposite to the direction of the chemical driving force
-Nernst Equation (important in neurophysiology)
Pressure is (3)
-the sum of all the forces of the different molecules striking a membrane
-greater on the side of the membrane with the most number of molecules
-creates a Pressure Gradient Force (ie. molecules move from side of high pressure to low pressure)
Diffusion of water is called
Osmosis
Water will move into the
Most concentrated solution (ie. where there is less water)
Tonicity refers to
The strength of a solution in relationship to osmosis
Isotonic solution (3) and example
-solute concentrations are the same on both sides of the cell membrane
-no net gain or loss of water
-cells neither swell nor shrink
Example: RBCs are isotonic in 0.9% NaCl
Hypotonic Solution (3) and example
-solution has a LOWER concentration of solute (ie. more water) than the cell
-water enters the cell
-cell swells (turgor) and may burst (lysis)
Example: RBCs in less than 0.9% NaCl will undergo haemolysis
Hypertonic Solution (3) and example
-solution has a HIGHER percentage of solute (ie. less water) than the cell
-water leaves the cell
-cell shrinks and appears crenated
Example: RBCs in solution with a concentration HIGHER than 0.9% NaCl will shrink
The movement of water from a hypotonic to a hypertonic solution will cause
An increase in Hydrostatic Pressure in the Hypertonic Compartment
The most abundant substance to diffuse across the cellular membrane is
Water
Diffusion can be
-simple
-facilitated
Channel proteins are ___ diffusion
Simple
Simple diffusion can occur through (2)
-the interstices of the lipid bilayer (ie. lipid soluble ions/molecules)
-hydrophilic channel proteins (ie. water and water soluble molecules
Three examples of channel proteins include
-Potassium Channel
-Sodium Channel
-Calcium Channel
Carrier proteins are used for ___ diffusion
Facilitated
Channel Proteins (5)
-simple diffusion
-integral proteins (ie. span the cell membrane)
-narrow, hydrophilic central canal called a Pore
-selectively permeable
-can be opened/closed by gates
Channel proteins are selectively permeable based on (3)
-diameter of pore
-electrical charge
-protein structure
An Aquaporin is
A type of channel protein that allows for the passage of water
Na+, K+, and Ca2+ channels are examples of
Channel proteins
Potassium Channel (3)
-type of channel protein
-permits the passage of K+ OUT of the cell (unidirectional)
-consists of 4 protein subunits surrounding a central pore
At the surface of the Potassium Channel pore are ___. Their purpose is ___
-Pore Loops
-lined with carbonyl oxygens that selectively filter (strip water and allow only K+ to pass through)
Sodium Channel (4)
-type of channel protein
-inner surface is lined with negatively charged amino acids
-pull small Na+ away from water molecules
-K+ is too large to fit
Gating of protein channels (3)
-controls the permeability of channels
-conformational change of the [protein either opens or seals the pore (ie. opens or closes the gate)
-controlled by two mechanisms (voltage gating and ligand/chemical gating)
Two mechanisms that control opening/closing of protein channel gates
-voltage gating
-ligand (chemical) gating
In general, cells have a small net excess of ___ clustered beneath the ___. This means ___
Negative ions; Plasma Membrane. The inside of the cell is slightly more negative
Voltage gating and examples
-if the cell is polarized, the differential between the inside and outside of the cell is reduced —> causes gate to open and ions to enter
Examples: Sodium and Potassium Channels (neurons and muscle cells), Calcium Channel (neurons)
In voltage gating, the molecular conformation of the gate responds to
The electrical potential across the cell membrane
Ligand (chemical) Gating and an example
-gates are opened by the binding of another molecule which causes a change in conformation or chemical bonds
Example: Neurotransmitter Channels in nerve and muscle cells
Facilitated Diffusion is also called
Carrier-Mediated Diffusion
Facilitated Diffusion uses ___
Carrier Proteins
Both simple and facilitated diffusion are
Down a concentration gradient (passive)
Facilitated Diffusion differs from Simple Diffusion in two ways
-the net rate of diffusion is proportional to the number of carrier proteins available (saturation of carrier proteins = Vmax)
-similar molecules can compete for binding with the carrier protein (ie. presence of molecule A can limit the rate at which molecule B enters the cell)
Simple diffusion uses ___ proteins while Faciliated diffusion uses ___ proteins
Channel; Carrier
Active Transport is when
Molecules/ions move against their concentration, electrical, or pressure gradients (ie. need energy/ATP)
K+ has high concentrations ___ while Na+ has high concentrations ___
Intracellularly; extracellulary
Similar to Facilitated Diffusion, Active Transport requires
Carrier Proteins
Two types of active transport are
-Primary (energy is derived from the breakdown of ATP)
Secondary (energy is stored as ionic concentration gradient, derived originally from primary active transport)
An example of Primary Active Transport is ___. Explain how it works
Sodium-Potassium Pump:
-ATP pumps Na+ out of the cell while simultaneously pumping K+ into the cell (both are going against their concentration gradients)
A portion of the carrier protein in the Sodium Potassium Pump has ___ receptor sites located on the ____for Na+ and ___ receptor sites located on the ___ for K+
Na+ = 3 receptor sites on inside of cell
K+ = 2 receptor sites on outside of cell
When Na+ binds Intracellularly…. (5)
-ATPase enzyme cleaves ATP generating ADP and a single phosphate group (this releases energy)
-released energy causes a conformational change in the Sodium-Potassium Pump Carrier Proteins
-Na+ is released extracellularly
-the extracellular K+ binds, triggering the release of the phosphate group and causing a conformational change
-K+ is released intracellularly
In nerve cells, ~70% of the cell’s energy is used to
Drive the Sodium Potassium Pump
The Na-K Pump is responsible for (3)
-maintaining concentration gradients (and negative electrical voltage within the cell)
-transmitting nerve impulses
-controlling cell volume
__ Na+ are expelled for every __ K+ gained which equals __
3:2, net loss of ions —> osmosis of water OUT of cell
Calcium Pump/Uniport (3)
-primary active transport mechanism
-Ca2+ is extremely low inside the cell
-pumps Ca2+ out of the cell and into the sarcoplasmic reticulum of muscle cells and mitochondria
When Na+ is transported of the cell by primary active transport it creates (2)
-large concentration gradient (Na+ wants to go back into cell and will pull other molecules with it)
-large energy store
Two forms of Secondary Active Transport
-co-transport
-counter-transport
An example of co-transport secondary active transport is the
Sodium-Glucose Symport (both sodium and glucose move INTO the cell)
Following active transport, in order for Na+ to reenter the cell via the Sodium-Glucose Symport,
Na+ AND Glucose must both bind the Symport in order to cause a conformational change and enter the cell
Sodium-Glucose Symport is important in
Intestinal and Renal Cells
An example of counter-transport secondary active transport is the
Sodium-Calcium Antiport (molecules move in OPPOSITE directions)
The Sodium-Calcium Antiport/Exchanger ()
-occurs in all cells
-moves Na+ into cell
-moves Ca2+ out of cell
A Uniport is (2) and an example is __
-specific to one molecule
-used in primary active transport and facilitated diffusion
Example: Calcium Uniport
A Symport is (2) and an example is __
-used in primary and secondary active transport
-transport 2 molecules in the SAME direction (ie. co-transport)
Example: Sodium-Glucose Symport
An Antiport is (2) and examples are __
-used in primary and secondary active transport
-transport 2 molecules in DIFFERENT directions (counter-transport)
Examples: Sodium-Potassium Pump, Sodium-Calcium Antiport
Transport of materials into or out of the cell is via
Vesicles
Endocytosis is moving materials
Into the cell
Three types of Endocytosis are
-phagocytosis
-pinocystosis
-receptor-mediated
Materials moving out of the cell is done via
Exocytosis
Exocytosis can be (2)
-constitutive
-regulated
Transport of materials into the cell is done via
Endocytosis
Two main roles of Endocytosis include
-cell signalling
-cellular defense
In Endocytosis, ingested products can be (3)
-degraded
-recycled
-stored
Phagocytosis (3)
-type of Endocytosis
-“cell eating” of large particles (pathogens, damaged/apoptotic cells, debris)
-few, specialized cells perform phagocytosis —> Phagocytes, Macrophages and Neutrophils
Pinocytosis (4)
-type of Endocytosis
-“cell drinking” of extracellular fluid & solutes, and large proteins
-occurs continually in most cells
-rate varies between cells
Transport from within the cell to the extracellular environment is called
Exocytosis
Receptor-Mediated Endocytosis (3)
-highly specific
-allows for ingestion of minor components of the extracellular fluid
-specific receptors located on membrane surface
Exocytosis (3)
-transport from within the cell to the extracellular environment via the Trans Face of the Golgi apparatus to the cell membrane
-vesicles contain synthesized proteins and waste products
-vesicles formed by membrane proteins and lipids from the Golgi apparatus
Constitutive Exocytosis (5)
-occurs in all cells
-components of the extracellular matrix
-takes out waste products
-initial packaging in the Endoplasmic reticulum, modified and repackaged in the Golgi apparatus
-replenishes lipids and proteins of the cell membrane
Regulated Exocytosis (3)
-used for hormones, digestive enzymes, and neurotransmitters
-products are stored for release at a specific time via receptors on the cell’s surface
-vesicle membrane does NOT replenish the cell membrane
Solutes are pumped into the extracellular/interstitial fluid and returned to ___ via the ___
The vascular system via the lymphatic system
Which type of transport requires energy?
Primary and Secondary Active Transport
