Exam 1 lecture 1

Question 1

What is the physical make up of a plasma membrane?

Answer 1

50% lipids and 50% protein

Question 2

What is the function of the plasma membrane?

Answer 2

• Separates intra and extracellular compartments
• Barrier to the free diffusion of water-soluble solutes
• Electrically excitable in nerve and muscle cells.
• Tranduces electrical, chemical and mechanical signals into a specific cellular response.

Question 3

What goes through the lipid membrane easiest?

Answer 3

• Gases: CO2, N2, and O2
• Small Uncharged particles such as ethanol
• Water and Urea through special mechanisms

Question 4

What is blocked from going through the lipid membrane?

Answer 4

• Large uncharged polar molecules such as glucose
• Ions
• Charged polar molecules such as amino acids, ATP and Glucose-6-phosphate.

Question 5

What are the two types of transport proteins?

Answer 5

-Carrier proteins and Channel proteins

Question 6

What are the distinguishing features of carrier proteins?

Answer 6

• They’re like revolving door: so they’re not opened simultaneously to both sides in and out
• Have two mechanisms: Primary active transport and secondary active transport.

Question 7

Whats the difference between primary active transport and secondary active transport in carrier proteins?

Answer 7

• Primary: directly use of energy

- Secondary: Indirect use of energy.

Question 8

What are the distinguishing features of channel proteins?

Answer 8

• They’re like a doorway (either opened on both sides or closed)
• Facilitate diffusion through a pore in the membrane along a gradient.

Question 9

What dictates the diffusion of molecules through channels in the plasma membrane?

Answer 9

The pores only allow molecules to go through but the directions are dictated by concentration gradients and electrochemical gradients for ions.

Question 10

Can carrier protein control direction unlike channel proteins?

Answer 10

Yes.

Question 11

How does primary active transport work in a carrier protein in the plasma membrane?

Answer 11

-Carriers can use the energy of ATP concentration to concentrate molecules on one side of the membrane.

Question 12

How does secondary active transport work in a carrier protein in the PM?

Answer 12

• The carriers use the potential energy of concentration gradient of one molecule to move another.
• Very often the first molecule is sodium.

Question 13

What is the difference between carrier proteins and channel proteins in terms of controlling directionality of diffusion?

Answer 13

• Carrier proteins can control the direction and send molecules against their concentration gradient or electrochemical gradient.
• Channel proteins can’t do that. the direction for channel proteins is dictated by electrochemical gradient or concentration gradient.

Question 14

What is the sodium-potassium pump?

Answer 14

its an active transport mechanism that utulizes ATP and work through series of conformational changes in a transmembrane protein.

Question 15

What are the steps of the sodium-potassium pump?

Answer 15

1) 3 Na ions bind to the cytoplasmic side of the protein. changing the conformation to allow it to be phosphorylated by ATP.
2) This conformational change closes the pump from the cytoplasmic side and opening to the extracellular side and in this conformation it has low affinity for Na ions and it translocates them to the outside.
3) The new conformation has high affinity to K+ ions and now they bind from the extracellular side of the protein into their specific binding sites.
4) This new binding of K ions causes the originally bound phosphate from ATP to dissociate and reverts the protein back to its original conformation.
5) The potassium is exposed to the cytoplasmic side and in this conformation (the original conformation) it has a low affinity to potassium and translocates K+ into the cytoplasm.

Question 16

What provides energy for most secondary active transport mechanisms?

Answer 16

-The potential energy from the extrusion of sodium.

Question 17

What is the estimated consumption for the Na-K pump in the whole body? The brain?

Answer 17

it’s 25% of the whole body and 70% of the brain energy consumption.

Question 18

What is the effect of the Na-K pump being electrogenic?

Answer 18

• It contributes a small amount to resting negative membrane potential for neurons.
• Contributes about half of the negative resting membrane potential for smooth muscle.

Question 19

What are the function and use of secondary active transport?

Answer 19

• a substance is pumped from a region of lower concentration to an area of higher concentration but that requires energy since it’s against the concentration gradient.
• Using a symport pump of Na and the potential energy it creates, we move glucose against its concentration gradient but since ATP is originally used to pump Na and not glucose, its considered secondary active transport.

Question 20

What is the function of Sodium-calcium exchanger?

Answer 20

• Its an example of the linkage between primary and secondary active tranpsort.
• The sodium pump keeps pumping sodium out which creates a huge gradient for sodium.
• Taking advantage of the sodium gradient since it desprately wants to go into the cell and link it with Calcium to get Ca+ out its gradient.

Question 21

What happens if we inhibit the sodium-potassium pump? what drug inhibits or blocks the function of the Na-K pump?

Answer 21

• The inhibitors are called digitalis or ouabain.
• This increases intracellular Na since the pump is not translocating it outside of the cell which affects the concentration gradient that the sodium-calcium exchanger relies on.
• this means the extrusion of calcium will be slowed down or inhibited which increases Ca+ concentration inside the cell.

Question 22

How are electrical potentials are produced in the cell?

Answer 22

• First we make different concentration of ions inside and outside of the cell.
• Open channels that allow certain types of ions to go in and out and this will create different charge in and out of the cell (voltage).

Question 23

Electrical terms:

• What is a charge?
• What is current?
• What is voltage?
• What is conductance?

Answer 23

• Charge is ions (Na+, Cl-… etc)
• Current: flow of Ions/sec in and out of the cell
• Voltage: energy to move the charge.
• Conductance: ease of moving across the membrane so 1/resitance.

Question 24

What is a resting voltage (resting membrane potential)?

What is excitation and inhibition of cells?

Answer 24

• Approximately -70 mV. it’s still considered strong in relevance to the distance it’s working with.
• Less negative inside or positive this would be exciting the cell. Because this cell will be more likely produce an action potential. (Depolarization)
• More negative inside the cell is inhibition. (hyperpolarization) by removing positive charge or introducing negative charges.

Question 25

What is the function of aquaporin channels? How are they structured? Where are they most prominent?

Answer 25

• Allow passage of water, glycerol, ammonia and urea.
• Do not allow passage of charged molecules

-Structure: 6-transmembrane proteins and are most prominent in the kidneys.

Question 26

What drives osmosis (Diffusion of water)? How can you increase osmotic pressure?

Answer 26

The difference in concentration of water and solutes in and out of the cellular membrane.

• When water move into an area, it expands its area and when the pressure exerted due to the increase of size, we create the osmotic pressure.
• Since water will move the area with higher solute, the area of higher solute will have higher osmotic pressure/

Question 27

What is osmolarity?

Answer 27

-Concentration or molarity of solute particle dissociating in solution.

Question 28

What is tonicity?

Answer 28

-How fat or skinny the cell is due to how the medium changing its volume.

Question 29

What is isotonic?
Hypotonic?
Hypertonic>

Answer 29

• Isotonic: If cells volume doesn’t change then the solution is isotonic
• Hypertonic: if cell volume decreases then solution is hypertonic
• Hypotonic: If cell volume of cell increases then the solution is hypotonic (If cell is very hypotonic or fat it will get lysed or burst).