Lect. 8 Membrane Transport - Energy and Metabolism Flashcards
Definition of something that is “selectively permeable”
It allows some substances to cross it more easily than others.
Generally, biological membranes are permeable to:
small molecules (H2O, O2, CO2) and lipid-soluble substances
they can penetrate the hydrophobic interior of the bilayer
A selectively permeable bilayer is permeable to:
- small uncharged molecules (O2)
- very small polar molecules (H2O, CO2)
- large non-polar molecules
urea, glycerol
A selectively permeable bilayer is impermeable to:
- large polar molecules (glucose)
- charged particles (ions: H+, Na+, Cl-, HCO-)
glucose, sucrose
Molecules enter/leave cells by: (5)
- diffusion
- osmosis (for water)
- facilitated diffusion
- active transport
- bulk transport: endocytosis & exocytosis
DOFAB
Water’s role in cells
- essential for survival
- prevents drying
- all chemicals that enter a cell can only do so if dissolved in water
all cells must live in a moist env
Diffusion is a ____ process. Does the cell have to expend energy to make it happen?
Diffusion is a passive process: the cell does not have to expend energy to make it happen.
Diffusion occurs when there exists a ____ until ____ .
Diffusion occurs when there exists a concentration gradient (CG) until equilibrium is reached.
What is a concentration gradient?
The difference in concentration b/w the high concentration vs the area of low concentration.
ex: - campfire: heat source; warm when close, cool when far; diff in temp represents a gradient
- perfume spray at one end of room; high fragrance next to spray, low at opp side of room; diff in fragrance represents a gradient
Concentration Gradient in a Cell
ex: A lipid-soluble substance moves through the lipid bilayer from ____ to ____ concentration.
A lipid-soluble substance moves through the lipid bilayer from high to low concentration.
As long as CG exists, net movement of molecules will be:
in direction of gradient.
Once equilibrium is reached, net movement stops but:
exchange still occurs on a molecule for molecule basis.
Diffusion: a physical process based on random motion
All atoms and molecules possess ____ above absolute 0.
All atoms and molecules possess kinetic energy above absolute 0. This is why there is random molecular motion in diffusion.
Factors that influence diffusion rate: (3)
- Concentration gradient
- Size and shape (small=more free mov, globular moves easier)
- Temp (kinetic E of the particles)
What are the 2 general principles that apply to diffusion and osmosis?
- concentration gradient
- equilibrium
Osmosis = fluid diffusion
Water’s net mov is from the side of ____ solute concentration to side of ____ solute concentration.
Water’s net mov is from the side of low solute concentration to side of high solute concentration.
Osmosis = fluid diffusion
Water’s net mov is from the side of ____ solvent concentration to side of ____ solvent concentration.
Water’s net mov is from the side of high solvent concentration to side of low solvent concentration.
An animal cell in a hypotonic solution will be:
While a plant cell is:
- lysed (pop)
- turgid (normal)
When an animal cell is normal in an isotonic solution, a plant cell is:
flacid.
In a hypertonic solution, an animal cell is:
and a plant cell is:
- shriveled/crenated
- plasmolyzed
tonicity in plant cells
ex: When water seeks to exit cell, solution surrounding cells is:
plant looks sad
hypertonic
no turgor pressure on cell wall
osmoregulation: control water balance
Paramecium is ____ to the pond in which it lives. To solve this problem, paramecium cells have a specialized organelle, the contractile vacuole, which functions as a pump to force water ____ the cell.
hypertonic, out of
Definition of “tonicity”
Tonicity is a measure of osmotic pressure related to the concentration of impermeable solutes in a particular solution.
hypotonic / hypertonic / isotonic
Definition of “osmolarity”
Osmolarity is a measure of molarity of all solutes (permeable + impermeable) dissolved in a particular solution.
hyperosmotic / hypo-osmotic / isosmotic
In facilitated diffusion, molecules that are too big (glucose or AA) and polar/charged molecules require ____ to get them through the cell membrane.
In facilitated diffusion, molecules that are too big (glucose or AA) and polar/charged molecules require protein molecules to get them through the cell membrane.
Types of transport proteins facilitate movement of molecules/ions across membranes: (2)
- channel proteins
(tunnel like gap junctions) - carrier proteins
down a concentration gradient
w/out carrier proteins, many molecules would not move across the membrane or would do so in such a slow fashion as to be useless to the cell
Channel proteins
Channel proteins provide ____ corridors for the passage of specific charge/polar molecules/ions.
Channel proteins provide hydrophilic corridors for the passage of specific charge/polar molecules/ions.
Channel proteins
Name the specialized gated channel proteins that carry water rapidly across the membrane in response to osmolarity.
aquaporins
gated: responds to chemical or electrical stimulus
Carrier Proteins
Describe how a solute travels through carrier proteins
Carrier protein in the membrane selectively binds a solute particle and changes shape, opening a channel through the membrane. The solute can be transported into or out of the cell, but net mov is always from a region of higher to lower concentration.
Carrier proteins
The rate of transport depends on: (2)
- the number of carrier proteins
- how fast a solute travels through them
What are ion channels?
A specific category of protein that allow specific ions through, they function as gated channels.
Many ion channels are gated channels
Active transport requires: (2)
- energy (ATP) since it’s going away from equilibrium
- carrier proteins
transporting molecules against the chemical gradient
Active transport allows cell to maintain ____ internal conditions compared to external conditions.
Active transport allows cell to maintain different internal conditions compared to external conditions.
How does ATP supply its energy for active transport?
By phosphorylating (giving phosphate) to the carrier protein. It triggers the conformational change required to transport ions across membrane.
What is the sodium-potassium pump responsible for?
Creating/maintaining the membrane potential in neurons. It transports K+ in and Na+ out.
pump = active transport
sodium-potassium pump
The exchange is unequal: 2 K+ imported in for 3 Na+ exported. This creates:
a membrane potential; negative interior relative to a positive exterior.
Pumps that create membrane potentials are called:
electrogenic pumps
eletrically generating
Creating membrane potentials stores energy that can be harnessed for other reactions. What are the main electrogenic pumps in animal cells and {plants, fungi, and bacteria}?
animal: sodium-potassium pump
plants, fungi, and bacteria: proton pump to export H+ ions from cytoplasm
As a result of the membrane potential created via active transport, the passive transport of cations ____ the cell and anions ____ the cell is favoured.
As a result of the membrane potential created via active transport, the passive transport of cations into the cell and anions out of the cell is favoured.
The 2 forces (gradients) that drive ions towards equilibrium:
- Concentration gradient (applies to all molecules on either side of membrane)
- Electrical gradient (applies to charged particles)
The 2 combined are collectively called the electrochemical gradient.
Cotransport
ex: Plant cotransport proteins use the energy expended from H+ entering the cell (____ transport) to transport sucrose into the cell against its concentration gradient (____ transport).
Plant cotransport proteins use the energy expended from H+ entering the cell (passive transport) to transport sucrose into the cell against its concentration gradient (active transport).
Macromolecules (polymers: proteins, polysaccharides) and larger particles need to use what to enter the cells?
vesicles
Bulk Transport
Materials are transported out of the cell via:
exocytosis
ex: exit of insulin from pancreatic cells
- vesicle approaches plasma membrane
- fuses with it
- releases its contents outside
Bulk Transport
Materials are transported into the cell via:
endocytosis
Types of endocytosis:
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
How does Phagocytosis work?
“cell eating”
- cell wraps pseudopodia around particle and forms vacuole (large vesicle)
- vacuole then fuses with lysosome for digestion
ex: White blood cells phagocytize microbes constantly to protect the body from possible infection. Microbial debris are released by:
exocytosis
How does Pinocytosis work?
“cell drinking”
- cell takes in portions of extracellular fluid and all solutes dissolved in the solution
- non-specific mechanism (in comparison with receptor-mediated endocytosis)
How does Receptor-mediated Endocytosis work?
- A vesicle is formed when specific molecules attach to their respective surface receptors on the membrane
- specific mechanism compared to pinocytosis
- once the molecules exit the vesicle in the cell, the receptors are returned to the cell surface for reuse
ex: What is the mechanism used for the intake of LDLs?
receptor-mediated endocytosis
- blood cholesterol travels as lipoprotein
- LDL destined for uptake in cells
LDL’s bind to specific surface receptors
ex: What does influenza virus use for endocytosis?
Receptor-Mediated Endocytosis
Haemagglutinin is the protein responsible for both receptor binding and membrane fusion
