Ch.12: Transport Across Membranes Flashcards
Things unlikely to diffuse across the membrane?
Lipid bilayers are selectively permeable
- polar molecules: H2O, glycerol
- large molecules: amino acids, glucose
-ions: H+, Na+, K+, Ca2+
Things likely to diffuse across the membrane?
- small non polar molecules
ex. O2, CO2, N2, steroid, hormones
-simple diffusion
Cells build gradients
-concentration across membrane?
-what molecules?
- different conc. can be generated across a membrane
- only applies to molecules that can’t simply diffuse
Membrane potential
the voltage differences across the membrane
- building of ions across a membrane can generate
Resting Membrane Potential
=-20 to -200mV
- Inside of cell is more negative due to large amounts of negatively charged DNA and Proteins
Two main classes of membrane transport proteins?
- channel proteins
- transporter/carrier proteins
Channel Proteins
- selectivity
- shape
- molecules
- selectivity: size and charge
- shape: stay the same (pore)
- molecules:typically ions
Transporter (Carrier) Proteins
- selectivity
- shape
- molecules
- selectivity: binding site specificity
- shape: changes shape to transport molecules
- molecules: most other small molecules
- typically selective for one type of solute
Passive Transport
- Movement w/ respect to concentration:
- Energy Requirement:
- Proteins Types:
- Movement w/ respect to concentration: high to low only
- Energy Requirement: no
- Proteins Types: channel mediated or transporter mediated
Active Transport
- Movement w/ respect to concentration:
- Energy Requirement:
- Proteins Types:
- Movement w/ respect to concentration: low to high
- Energy Requirement: yes
- Proteins Types: pump (special transporters)
What effects movement of charged molecules?
- concentration gradient
- membrane potential/electrical charge
Aquaporins
channel proteins that greatly increase the rate of passage of water molecules
- up to 3 billion water molecules pass through a single aquaporin per second
Osmosis
water flows from low to high solute concentration
- dictates water flow in and out of cell
- cells have a higher concentration of solutes than their surroundings
- cells must protect themselves from swelling
Hypertonic Solution
As the solute concentration in the solution is greater than inside the cell
- water will exit and the water loss causes the cell to shrink in size
Isotonic Solution
No water is lost or gained as the concentrations of solutes are the same inside and outside of the cell
Hypotonic Solution
as the solute concentration in the solution is less than that inside the cell
- water will enter the cell and cause it to swell
- big problem because cell will burst
ATP-Driven Pump
uses energy released by ATP hydrolysis to curve uphill transport of solute
Glucose Transporter/Carrier Proteins
glucose transporters passively transport glucose down its concentration gradient
Gradient-Driven Pump
links uphill transport of one solute to the downhill transport of another
Transport against concentration gradient
requires a pump
Light-Driven
energy from sunlight drives transport (seen in bacteria)
Na+/K+ pump
an ATP-driven pump that moves Na out of the cell and K into the cell
- helps maintain Na/K gradient
- large amounts of sodium out side of cell and potassium inside the cell
What uses 30% of the ATP produced in the body?
Na/K pump
What do Gradient Driven Pumps do and what are the types?
pair transport of molecules
types: symport vs. antiport
symport vs antiport
symport: two molecules moving out/ moving in the same direction
antiport: two molecules moving in opposite directions
Ion channels and membrane potential
- What determines what can go through channels
- selectivity filter: based on diameter, shape, charge distribution
- gated: can be opened and closed
Different types of gated ion channels respond to different stimuli
- voltage gated
- ligand-gated (extracellular ligand)
- ligand-gated (intracellular ligand)
- mechanically gated
What is the sodium potassium pumps function?
it functions to move Na out of the cell and K into the cell to help maintain the Na/K gradient
What factors can ion channels gate for?
diameter, shape, and charge distribution
How many ion of each are transferred in one “pump” of the Na/K pump?
3 sodium ions leave the cell and 2 potassium ions enter the cell
Which type of proteins are used in active transport, carrier/transporter proteins or channel proteins? Why?
Because unlike channel proteins, carrier proteins close and open, binding to molecules and changing their shape to push the molecules across..
Explain how FRAP works?
In FRAP, cell membrane proteins were modified to glow fluorescent green. Then, a laser was shined on part of the cell membrane proteins which destroyed their ability to glow green. However, overtime the green proteins moved to the dark area and the non-green proteins spread out and the whole membrane was mostly green again.
