Exam 4 (Topic 19) Flashcards
Lipid-bilayers are impermeable to…
MOST molecules
Regulate what the cell gets rid of and takes in
Transporters and Channels
Very high in K+
Inside of the cell
Very high in Na+
Outside of the cell
Required to maintain difference of K+ and Na+
Membrane transport proteins
Create a barrier to the passage of most molecules
The lipid bilayer
The rate of passage varies depending on
Size and solubility (polarity or charge)
Readily diffuse across the bilayer
Small nonpolar molecules (O2, CO2)
Diffuse rapidly if the are small enough
Uncharged polar (H2O, Ethanol)
Very impermeable to diffusion across the lipid bilayer
Larger uncharged polar and Ions
Two classes of membrane transport proteins
- Channels
2. Transporters
Allow molecules of certain size or charge
Channel (if open, molecule can pass through)
Allow passage to those molecules that fit into its binding site
Transporters (bind with high specificity like enzymes)
Bind with high specificity like enzymes
Transporters
Membrane transport proteins are
Multipass transmembrane proteins
Solutes cross membranes by
Passive or Active Transport
Molecules move from a region of high concentration to a region of low concentration
Passive Transport
Molecules move down a concentration gradient
Passive Transport
Does not require any energy
Passive Transport
Sometimes called Facilitated Diffusion
Passive Transport
Another name for Passive Transport
Facilitated Diffusion
Molecules move from a region of low concentration to a region of high concentration
Active Transport
Molecules move up a concentration gradient
Active Transport
Requires energy
Active Transport
Must be couple to some other process that releases energy
Active Transport
Many active transport proteins are called
Pumps
The plasma membrane has transporters for
Nucleotide
Sugar (Glucose)
Amino Acids
Ions
The_________ uses transporters for H+ to keep the pH very low
Lysosome
Lysosome uses transporters for
H+ to keep the pH very low
The ___________ uses transporters for Pyruvate and ATP
Mitochondria
The mitochondria uses transporters for
Pyruvate and ATP
Glucose Transporter
(Glucose Uniporter) Found in the plasma membrane of many animal cells
Moves glucose down a concentration gradient
Passive Transport
Can switch reversibly between two different conformations
Protein
Once glucose binds, the protein
switches conformations and carries the glucose molecules inside the cell
Starvation
Low glucose outside the cell
Glucose is made in the cell through
gluconeogenesis
Glucose is transported out of the cell into the
Bloodstream down its concentration gradient
Does a glucose transporter require energy
No
Passive transport of charged molecules is dependent on
The electrochemical gradient
Electrochemical Gradient
- The concentration gradient
2. The membrane potential
Outside cell charge
Positive
Inside cell charge
Negative
***The cytoplasmic side of the plasma membrane
has a negative membrane potential relative to the outside
Charged ions will move
down their membrane potential
A negative ion will move
from inside the cell to outside
Membrane Potential
The difference in electrical charge on either side of the membrane
The difference in electrical charge on either side of the membrane
Membrane Potential
Passive transport of charged molecules is dependent upon
The electrochemical gradient
The movement of charged solute is dependent on
The sum of the concentration gradient and the membrane potential
When there is a lot of positive charges outside the cell, electrochemical gradient, when voltage and concentration gradients work…
In the same direction
When there is a lot of positive charges inside the cell, electrochemical gradient, when voltage and concentration gradients work…
In opposite directions
Na+ wants inside for
the negative charge
Ka+ doesn’t want to outside because of
the positive charge outside
When solutes move against their electrochemical gradient
Active Transport
Three ways cells use active transport
- Coupled transporters
- ATP-driven pumps
- Light driven pumps
Light driven pumps
found mainly in bacteria (bacteriorhodopsin)
Pumps both Na+ and K+ against their electrochemical gradient
Na+/K+ ATPase Pump
ATPase
can hydrolyze ATP itself for energy
NA+/K+ ATPase Pump is important for
keeping the cytoplasm low in Na+ and high in K+
Responsible for keeping the cytoplasm low in Na+ and high in K+
Na+/K+ ATPase Pump
Na+/K+ ATPase pump process
- Na+ binds inside the cell
- Na+/K+ pump phosphorylates itself
- Conformation changes and releases Na+
- K+ binds to pump
- Pump is dephosphorylated
- Conformation changes and K+ is released
The plasma membrane is permeable to
water
Water will flow from low solute (more water) to high solute (less water)
Osmosis
To facilitate osmosis, cells
Contain water channels called aquaporins
Water channels
Aquaporins
Allows water to move through the cell
Aquaporins
Osmosis is ________ transport.
Passive
Keeps the pH of the lysosome low
H+ ATPase pump
Regulate the pH of the cytoplasm by pumping H+ out of the cell
H+ ATPase Pump
Important for keeping the pH of the lysosome low by pumping H+ into the lysosome
H+ ATPase Pump
_______ is needed in lysosome to help degrade molecules
Low pH
Couple transport agains an electrochemical gradient with transport down an electrochemical grandient
Coupled Transporters
Two types of coupled transporters
- Symport
2. Antiport
When both solutes move in the same direction
Symport
When the two solutes move in opposite directions
Antiport
Do coupled transporters require energy
No
Gut epithelium is lined by
Intestinal epithelial cells
Epithelial cells in the lumen of the gut are separated by
Tight Junctions
Faces the gut lumen
Apical side
Faces the bloodstream and tissues
Basolateral Side
Epithelial cells have _________ on apical side to increase cell surface area
Microvilli
Increase surface area of the cell
Microvilli
Allows the import of glucose from the gut against its concentration gradient
Glucose-Na+ Symporter
Into the cell; Apical side
Regulates membrane potential
Na+/K+ pump (Basolateral Side)
Releases glucose to the blood stream if needed
Glucose uniporter (Basolateral Side)
Glucose-Na+ Symporter
Apical Side - into the cell
Na+/K+ pump
Basolateral Side
Glucose uniporter
Basolater Side
The energy comes from the Na+ electrochemical gradient
Active Transport
Allows cells to maximize glucose uptake, even if the cell or bloodstream is rich in glucose
Glucose-Na+ Symporter
Active Transport
During starvation conditions
Gut lumen = low in glucose
Cell = high in glucose (because of gluconeogenesis)
Bloodstream (Extracellular) = Low in glucose
What type of molecules most easily pass through the plasma membrane?
Small non polar
Molecules passing through the plasma membrane order
- small non polar (easiest)
- Uncharged polar
- Larger uncharged polar and ions (hardest)
Bacteriorhodopsin is _________ transport
Active
Pump: Up: Energy
Active Transport
NA + goes
Down gradient
Glucose goes
Up gradient
K+ goes
Up gradient
