Lecture 2

Question 1

Cell Membrane composed of

Answer 1

Phospholipid Bilayer - Hydrophilic outside and hydrophobic inside

• barrier for water and water-soluble molecules
• proteins - Allows for movement of substances through membrane

Question 2

5 types of Proteins within bilayer of the Membrane

Answer 2

1. Ion channels
2. Carrier proteins (picks up a substance at one side of a protein and drops it at the other)
3. Pumps (uses energy because against concentration gradient)
4. Receptors (allow for communication between cells)
5. Enzymes

Question 3

2 Types of transport through a membrane

Answer 3

1. Diffusion (no energy required)
2. Active transport (energy required)

Question 4

Diffusion

Answer 4

Random movement in all directions

2 types - simple diffusion and facilitated diffusion

Question 5

Simple diffusion

Answer 5

Movement through membrane, channel protein, or pore

Question 6

Selectivity of channels

Answer 6

Highly selective permeability due to different composition

Gated channels are unique to specific ions.

Na+ gated, Ca+ gated, etc.

Question 7

Ungated vs Gated Channels

Answer 7

1. Ungated channels - always open (specific ion is always diffusing through pore); leak channels (important for electrical signals)
2. Gated channels - Open and close in response to a stimulus

Question 8

Facilitated Diffusion

Answer 8

Required interaction of transported molecule with a carrier protein which aids passage

Diffusion because it still doesn’t require ATP

Question 9

How do the two types of diffusion, facilitated and simple, differ?

Answer 9

Simple diffusion = exponential rate

Facilitated Diffusion = logarithmic increase (dependent on the rate at which carrier protein can change conformation due to stimulus; Vmax cannot be greater than the rate of this change in conformation)

Question 10

Net Diffusion

Answer 10

Average direction of diffusion

Question 11

2 factors that affect the net rate of diffusion

Answer 11

1. Concentration gradient (down concentration gradient)
2. Membrane electrical potential - electrical potential across membrane is equal in magnitude but opposite in direction to the concentration force (Nernst Potential - EMF (mV) = +/- 61 log (Co/Ci) )
   
   1. (+) and (-) ions will affect the rate of diffusion

Question 12

Osmosis

Answer 12

Net diffusion of water

Question 13

Osmostic Pressure

Answer 13

Amount of pressure required to counter osmosis (i.e. higher osmolarity = higher osmotic pressure)

In other words, how much pressure is needed to stop osmosis

Question 14

Lipid-soluble molecules - how do they interact with the cell membrane?

Answer 14

move readily through the membrane (rate depends on lipid solubility) - oxygen, carbon dioxide, alcohol, and steroid hormones

Question 15

How does water interact with the cell membrane?

Answer 15

Water can pass freely through any channel or pore

Question 16

Water-soluble ions - how do they interact with the cell membrane?

Answer 16

cross via SPECIFIC water-filled channels or pores

Question 17

What are the two types of gated channels?

Answer 17

1) Voltage-gated channels - sensitive and dependent; dependent on differences in electrical potentials across the membrane (gate is opened to restore potential difference)
2) Chemical (Ligand)-gated channel - open and close when stimulated by chemical binding (ex: Acetylcholine)

Question 18

Osmotic pressure determined by

Answer 18

the number of particles present in a solution REGARDLESS of the size or mass

Ex: 1 M of glucose vs. 1 M of albumin. Albumin may be a larger protein, but the osmotic pressure is the same!

Question 19

Diffusion of water is always from _____ concentration to _____ concentration.

Answer 19

High –> Low

Question 20

Skeletal muscle nerves will release Acetylcholine which allows sodium to come into the cell. This interaction is an example of what type of gated channel?

Answer 20

Chemical Gated Channel