processes at membranes

Question 1

what are the two types of membrane transport

Answer 1

• passive and active transport

Question 2

what are the driving forces that drive diffusion

Answer 2

• chemical driving force (move down its concentration gradient)
• electrical driving force (movement of charged particles under the influence of an electrical potential difference)

Question 3

what is the two types of diffusion

Answer 3

• simple diffusion (through lipid bilayer)
• facilitated diffusion (requires carrier or channel proteins)

Question 4

what is the J diff equation

Answer 4

• measures how many substances that diffuse across per unit area per unit time
• Jdiff= K x A x D x (change in concentration/ change in diffusion distance)
• K= partition coefficient
• A= surface area
• D= diffusion coefficient which takes into account temperature and size and shape of particle/substance

Question 5

what determines the magnitude of driving force Jdiff

Answer 5

1. concentration difference (change in concentration)
2. membrane surface area (A)
3. membrane permeability ( K x D x (1/diffusion distance))

Question 6

what are the factors affecting membrane permeability

Answer 6

• lipid solubility of the diffusing substance (k)
• membrane thickness
• temperature and size and shape of the diffusing substance (D)

Question 7

what are the two proteins required for facilitated diffusion

Answer 7

1. carriers (single polypeptide, 12 or sometimes 14 transmembrane alpha helices)
2. ion channels

Question 8

what is the velocity for carrier proteins

Answer 8

• 1000 molecules per second

Question 9

what are the different types of carrier proteins

Answer 9

• uniporter (transports only one molecular species)
• cotransporter= divided into symporter (coupled transport of 2 different molecular species in the same direction), anti porter (coupled transport of 2 different molecular species in the opposite direction)

Question 10

what is an example of a uniporter prototype and its mechanism

Answer 10

• Glucose transporters such as GLUT1, 2, 4
• PASSIVE
• relies on concentration gradient
• ligand binding flips the transporter to be a different conformation, new conformation releases glucose on the other side of membrane, release allows it to flip back to repeat the cycle

Question 11

what is an example of a symporter prototype

Answer 11

• sodium glucose symporter (SGLT1)
• secondary active transport
• uses the gradient created by primary active transport to drive the process
• found in gut, kidneys
• sodium moves down its concentration gradient, and glucose moves against its concentration gradient, both move in same direction

Question 12

what is an example of an anti porter prototype

Answer 12

• band 3 protein HCO3-/CL-
• PASSIVE
• both go down their concentration gradient
• found in red blood cells
• when bicarbonate diffusion gradient is reverse the process reverses
• important for carbon dioxide transportation to lungs

Question 13

what is the transmission of ion channels

Answer 13

• 100 million ions per second

Question 14

what is the specificity of ion channels based off

Answer 14

• size
• charge
• note for potassium channels there is a filter for sodium ions because sodium ions are the same charge and are smaller, this filter can also be known as a gate

Question 15

what are some examples of gated ion channels and what are their features and stimuli

Answer 15

• gated ion channels open and close and need a stimuli to open them
• voltage gated ion channels (stimuli is a specific voltage threshold)
• ligand gated ion channels (can be intracellular ligand or extracellular ligand and the stimuli is the ligand)

Question 16

how do sodium voltage gated ion channels open and close

Answer 16

• has an activation gate which open when a specific voltage threshold is met
• inactivation gate closes the ion channels when it undergoes a conformational change in shape
• this prevent further influx of sodium ions and further increase in membrane potential of cell
• allows a short positive pulse of current into the cell

Question 17

what is an example of a ligand gated ion channel

Answer 17

• nicotinic cholinergic receptor (nicotinic acetylcholine receptor)

Question 18

what are the two types of active transport

Answer 18

• primary active transport (uses the energy source atp to directly transport molecules)
• secondary active transport (uses the energy of a concentration or electrochemical gradient created by primary transport

Question 19

why is the sodium potassium atpase pump essential for maintaining cellular osmotic balance

Answer 19

• pumps 3 sodium ions out of the cell, 2 potassium ions into cell
• makes the outside of the cell more positive
• this causes. excess water to move out of the cell
• absence of this pump would cause water to move into the cell causing it to swell and burst

Question 20

what Is the step by step mechanism of the sodium potassium pump

Answer 20

1. binding of cytoplasmic sodium to the pump protein stimulates phosphorylation by ATP
2. phosphorylation causes the protein to change its shape
3. the shape change expels sodium ions to the outside and extracellular potassium binds
4. potassium binding triggers release of phosphate group, loss of phosphate restores the original confirmation of the pump protein
5. potassium ions is released and sodium ions bind again

Question 21

what are some of the carrier proteins and channels found in the intestianal epithelium

Answer 21

• SGLT1 symporter which is used to transport glucose and sodium into the epithelial cell from the gi tract where glucose is transported against its concentration gradient
• glut proteins transports glucose passively from epithelial cell to extracellular fluid
• also a sodium potassium pump to maintain sodium concentration gradient and keep concentration of sodium low inside the cell which facilitates SGLT1 to work

Question 22

what are some other examples of primary active transport

Answer 22

• calcium ATPase
• hydrogen Atpase

Question 23

what are some other examples of secondary active transport

Answer 23

• sodium/calcium exchanger
• sodium hydrogen exchanger
• sodium bicarbonate exchanger

Question 24

how the plasma resting membrane potential maintained

Answer 24

• sodium potassium pump- makes the inside of the cell less positive than outside
• leaky potassium ion channels- allow potassium ions to diffuse out of the cell using a chemical driving force which increases negativity of the cell
• however potassium ions also diffuse into the cell due to the electrochemical gradient creating this potassium equilibrium potential

Question 25

what is the resting membrane potential of a cell

Answer 25

• between -90 to -40
• usually -70 mV

Question 26

what ions are the resting membrane potential affected by and why

Answer 26

• potassium ions affect membrane potential
• sodium ions do not impact resting membrane potential
• increasing sodium ion concentration has no impact on resting potential- due to sodium ion channels being closed
• increasing potassium ion concentration increases resting membrane potential due to the potassium ion channels being leaky

Question 27

what is the Nernst equation and what are some assumptions

Answer 27

• used to figure out voltage inside cell
• assumptions include one ion at a time, membrane must be completely permeable to that ion and ion must be at equilibrium

Question 28

how may subunits does a nicotinic choligernic receptor has

Answer 28

• pentameric
• five subunits

Question 29

what are some example of metabotropic receptors

Answer 29

• GABA beta
• dopaminergic receptors
• adrenergic receptors
• histaminergic receptors
• muscarinic cholinergic receptors
• metabotropic glutamate receptors

Question 30

what is the transmission of pumps

Answer 30

100 per second