Membrane Permeabilties And Action Potentials Flashcards
What type of molecules can diffuse through membranes?
Small, uncharged polar molecules (H20, urea) Hydrophobic molecules (O2, N2) Large uncharged but polar molecules can but very slowly
What is the permeability coefficient?
A measure of how quickly a substance will pass through a semi permeable membrane
What two factors does rate of passive transport depend on? is this fixed or will it change if you change other factors?
The concentration gradients and the permeability coefficient.
It will change, depending on specific membrane, specific substance and at differnt points over time- eg after depolarisation
What are the 3 models for facilitated diffusion proteins action?
Flip flop- carrier protein flips when ligand binds so it faces the inside of the membrane. However this uses lots of energy and only really seen during apoptosis
Ping Pong- When ligand binds conformational change exposes inner membrane and blocks extracellular space, only transports 1/2 molecules at a time though
Channels- Stimulus (voltage change, ligands (ach), ATP…) causes channels to open to allow ions to freely pass through to inside of cell
Is ∆G (gibbs free energy change) for active transport positive or negative?
Positive- as transport up a conc gradient is not thermodynamically favourable and requires energy
When calculating ∆G what can log10 be substituted for?
8.314
What is the difference between primary and secondary active transporters?
Primary uses energy directly from ATP to move substances up a conc gradient
Secondary uses conc gradients already set up by primary active transporters to move substances up a conc gradient
What are the two types of transport?
Uniport- one type of molecule at a time (PMCA only moves Ca2+)
Cotransport- moving two or more molecules at a time
What are the two types of cotransport? Give examples
Symport- moving two types of molecules at the same time in the same direction (Glucose and Na+ in gut epethilia)
Antiport- moving two types of molecules at the same time but in different directions (Na/K ATPase moves 2 Na out and 3 K in)
What is the concentration of Ca outside and inside the cell?
Out= 1mM In= 100nM
Is the concentrations of K, Na and Cl higher or lower outside the cell?
K+= lower outside the cell Na+= higher outside the cell Cl-= higher outside the cell
Describe the structure of the Na/K ATPase pump (P type)
The alpha subunit contains K, Na and ouabain (an inhibitor) binding sites. It crosses cell membrane. On the inside of the membrane there is an aspartate which ATP phosphorylates to create the conformational change to allow Na and K to move. There is a beta subunit which contains a glycoproteins which directs it to the cells surface
Why is the SERCA not a pump? What is it?
Because pumps are only found on the external plasma membrane of a cell. It is an ion transporter
What happens to the NCX in ischemia?
Inadequate blood supply to tissue means less ATP available. Therefor Na/K ATPase cannot function. Na therefor accumulates in the cell. This causes the NCX to reverse (3 Na out 1 Ca in), high Ca inside the cell is toxic to the cells.
How is pH of a cell in increased?
The NHE pushes one H+ out and one Na+ in, to increase the pH in the cell when it is too low. The NBC (sodium dependant chloride/ bicarbonate exchanger) uses Na moving in to move H+ out, Cl- out and HCO3- in (notice all charges balance so no electrical potential effect)
What pump is used to decrease pH of a cell?
The Cl-/ HCO3- anion exchanger (AE) removes Bicarbonate from the cell and bring one Cl- in down its concentration gradient.
How many water molecules move with K+, Na+ or Cl- when they move in/out the cell?
6
Name 3 transporters which remove water/ ions overall so resist cell swelling?
Cl- uniport active transporter move it out cell
K+ uniport facilitated diffusion moves it out cell
K+/ Cl- cotranpsorter moves both out cell at same time
Amino acids moved out
What activates and inhibits the NHE?
Activated by growth factors
inhibited by amiloride
name 3 mechanisms that resist cell shrinking?
NCX- 3 Na in and only 1 Ca out so overall inward movement of ions so overall inward movement of water
Na/ Cl symporter moves both Na and Cl- in down their conc gradient
Na and glucose both transported in together
Na/ Cl pump both with K coming in up its conc gradient with Na coming in down it.
How is glucose transported into the cells of the kidney and intestinal epithilium?
Na/ K ATPase moves Na out epithelial cell. Na+ conc in cell therefor lower than in lumen, Na/ Glucose symporter brings glucose in up conc gradient and Na in down conc gradient. GLUT2 transporter takes glucose out.
How is glucose transported into skeletal muscle, adipose tissue, liver and brain?
Insulin dependant- insulin must first bind to insulin receptor on cell membrane.
This activates a cascade
Which causes GLUT4 vesicle to fuse w/ plasma membrane
Glucose can therefor diffuse through GLUT4 uniporter
As it enter the brain it is phosphorylated to glucose-6- phosphate to maintain a concentration gradient. It is then converted into glycogen/ fats ect. This stops glucose leaving the cell when blood glucose levels drop.
Do all cells have negative resting potential?
yes but some larger than others
Erythrocyte= -9mv
Skeletal muscle= -95mV
How can the resting membrane potential be measured?
Microelectrode glass pipette is made by stretching heated glass to give it a tiny end
Glass pipette is filled with KCl to conduct charge and glass pipette penetrates cell membrane
Another electrode is placed outside cell in extracellular solution. voltmeter and wires passed between the two electrodes and voltmeter will detect the potential difference.
