Cell Physiology Part 3

Question 1

What is one of the main functions of a plasma membrane?

Answer 1

To serve as a permeable membrane barrier, that is selective.

It allows lipid soluble molecules to diffuse through but other molecules must be transported across

Question 2

In regards to the plasma membrane, what kind of molecules can cross and what type cannot cross

Answer 2

Uncharged polar molecules can cross. Charged ions can’t cross.
Large ions dissolved in water cannot diffuse freely as well
Polar molecules can’t cross freely as well

Question 3

Why is water able to diffuse sometimes but other times not?

Answer 3

The cell membrane osmotic permeability caries from cell to cell, depending on the lipid bilayer and the presents of water selective pores, Aquaporins

Question 4

What are the four mechanisms a solute can move across membranes.

Answer 4

Simple diffusion across the bilayer
Simple diffusion thru channel
Facilitated diffusion thru passive transporters
Active transport (only one that requires energy)

Question 5

What do channel protein do?

Answer 5

Allow the transport of specific substance across a cell membrane-carrier mediated transport

Question 6

What is the affect of a molecules charge when trying to cross the membrane?

Answer 6

Neutral
-no effect on inward or outward transport
Cations
-favors inward transport and opposes outward transport
Anions
-opposes inward transport and favors outward transport

Question 7

What are the three types of channel proteins?

Answer 7

Ligand gated
Voltage gated
Stress gated

Question 8

What happens in passive transport by facilitated diffusion?

Answer 8

Solute binds transporter protein
So the transport is saturable
* NO energy required and molecules move down their concentration gradient*

Question 9

Describe the kinetics of carrier-mediated transport.

Answer 9

Transport relies on molecular binding between the cargo and membrane embedded channel or carrier protein. Second the rate of facilitated diffusion is saturable with respect to the concentration difference between the two phases;unlike free diffusion which is linear in the concentration difference. Temp dependence of facilitated diffusion is substantially different due to the presence of an activated binding event.

Question 10

How does diffusion work when it’s driven by concentration gradient?

Answer 10

A molecule that is free to move will diffuse from high concentration to low concentration until concentrations are equilibrated across the two areas

Question 11

What is the partition coefficient?

Answer 11

The relative lipid solubility of a molecule is expressed as the partition coefficient

Question 12

Which diffuses quicker across the membrane: O2 or CO2? And why?

Answer 12

CO2 diffuses Alta 20x higher rate than oxygen due to its higher solubility

Question 13

Define osmotic pressure

Answer 13

The amount of pressure required to oppose water movement from high to lower concentration (lower to high osmolarity)

Question 14

Hypertonic vs Hypotonic solutions

Answer 14

A hypotonic solution cause water to flow inside the cell causing it to swell and potentially burst
Hypertonic solution cause water to flow out of the cell causing it to shrivel

Question 15

Define facilitated transport

Answer 15

A substance is moved in the direction of its concentration gradient. This movement is facilitated by a transport or carrier protein

Question 16

Explain active transport

Answer 16

Substances are transported against their concentration gradient by active transport. Energy must be used to accomplish this. If energy is utilized directly by the transport protein the mechanism is termed primary active transport.

Question 17

Explain Secondary Active Transport

Answer 17

The transport of molecules into the cell is directly dependent on the expenditure of energy used to pump another molecule out of the cell. The inward movement of the second molecule down it’s concentration gradient is coupled to drive the movement of the second molecule up its concentration gradient.
Ex: Na+/glucose co transport

Question 18

What are ligand gated channels?

Answer 18

Transmembrane ion channel proteins which open to allow ions to pass through the membrane in response to the binding of a chemical messenger or ligand such as an neurotransmitter