Chapter 6: Cellular Interactions and Communications

Question 1

Define extracellular environment.

Answer 1

• Includes all constituents of body outside the cells
• 20% of ECF is blood plasma
• 80% of ECF is interstitial fluid (fluid that surrounds the cells) contained in a gel-like matrix (semi-solid) i.e. cartilage or connective tissue

Question 2

Discuss extracellular matrix.

Answer 2

-meshwork of collagen and elastin fibers linked to molecules of gel-like ground substance

Question 3

Discuss the components of a solution.

Answer 3

Solution consists of a solvent (water) and a solute (molecule dissolved in water)

• i.e. salt water
  
  • solvent: water
  • solute: salt

Question 4

Discuss diffusion.

Answer 4

• Random movement of particles will establish equilibrium if there is a difference in concentration in two regions
  i. e. food coloring dropped into water
• Movement of MOLECULES (not water) from an area of high concentration to an area of low concentration
• No energy required

Question 5

Discuss ion channels.

Answer 5

• For bigger, charged ions
• Still diffusion just with a special gate
• Particles still moving from high concentration to low concentration

Question 6

Simple vs Facilitated Diffusion

Answer 6

Simple Diffusion: Passive movement of small, non-polar modules from high to low concentration

Facilitated Diffusion: Passive movement of bigger, polar molecules from high to low concentration via use of protein carriers

• No ATP required
• CANNOT transport molecules against the concentration gradient; must ALWAYS go high to low, NEVER low to high

Question 7

List the circumstances that effect the rate of diffusion. (4)

Answer 7

1. Degree of disparity in concentration (steepness of gradient)
2. Permeability of membrane
3. Temp
4. Surface area of membrane (i.e. microvilli)

Question 8

Discuss osmosis.

Answer 8

• WATER moves across the membrane NOT the molecules

- Movement is still passive; no ATP required

Question 9

Define osmolality.

Answer 9

• measure of concentration
• high concentration = high osmolality
• low concentration = low osmolality

Question 10

Discuss tonicity including isotonic, hypertonic, and hypotonic.

Answer 10

• the effect of a soln on osmotic movement of H2O
• Think “osmosis”

Isotonic: solns have same osmotic pressure

Hypertonic: solns have higher osmotic pressure
- i.e. RBC in salt water, cell will shrink because H2O from inside the cell will leave to try and dilute the surroundings

Hypotonic: solns have lower osmotic pressure
- i.e. RBC in distilled water, cell will burst because distilled H2O comes into the cell to try and even out distribution of particles

Question 11

Discuss Carrier-Mediated Transport and the 3 characteristics they exhibit.

Answer 11

• molecules too large or polar to diffuse across the membrane are transported via protein carriers (can be passive or active)

Characteristics:

1. Specificity (only transport 1 or 2 specific molecules)
2. Competition (among substrates for transport if more than 1 kind)
3. Saturation (when all carriers are occupied - “transport maximum”)

Question 12

Discuss active transport.

Answer 12

• Uses pumps to move molecules and ions against the concentration gradient (from lower concentration to higher concentration)
• Requires ATP

Question 13

Discuss primary active transport and the Na+/K+ pump.

Answer 13

• Uses ATP to move 3 Na+ out and 2 K+ in against their concentration gradients
• Molecule binds to recognition site, bonding stimulates breakdown of ATP, carrier changes shape, protein releases transported molecule to the other side of the membrane

Question 14

Discuss secondary active transport.

Answer 14

• ATP is used move one ion against the concentration gradient but once there, it uses the energy created from the natural inclination of that molecule to get something else to move. It’ll either pull it along or push it through

Question 15

Discuss bulk transport.

Answer 15

• Moves large molecules and particles across the plasma membrane
• Occurs by endocytosis and exocytosis

(endocytosis - bringing things IN to the cell)
(exocytosis - sending things OUT of the cell)

Question 16

Discuss membrane potential.

Answer 16

• Results from unequal distribution of charges
• More negative inside the cell, more positive not he outside of the cell and we want to keep it that way
• Important for transmission of nerve impulses and muscle contraction

Question 17

Discuss resting membrane potential.

Answer 17

• Not producing impulses
• Resting cell is more permeable to K+ than Na+
• Average resting membrane potential of -65 to -85 mV

Question 18

Discuss cell signaling and the 3 types.

Answer 18

• How cells communicate with each other
• Some use gap junctions (signals pass directly from one cell to another)
• Some use chemical communication where they release a chemical that binds to receptors on the target cell or enters the target cells

3 Types:
1. Paracrine Signaling - cells secrete chemicals that diffuse to NEARBY target cells

2. Synaptic Signaling - 1 neuron sends neurotransmitter messages to another cell via synapse
3. Endocrine Signaling - cells secrete chemical (hormone) that moves through the blood stream to distant target cells

Question 19

What are G-proteins?

Answer 19

• G-proteins are the shuttle between receptors and enzymes (like a middle man)
• Used because receptor protein and enzyme are in diff locations in the membrane.