Interactions Between Cells and the Extracellular Environment Part 3

Question 1

What factors play into the “negative pole” inside the cell and the “positive pole” outside the cell?

Answer 1

1. Fixed Anions- phosphate groups of ATP and other organic molecules are negatively charged at the PH of the cytoplasm. (Help make the Intracellular environment - )
2. The Na+/K+ pumps are pumping 3 + out for every 2+ in.
3. The permeability of the membrane to certain ions.

Question 2

What ion is the cell membrane most permeable to?

Answer 2

K+ …This also allows it to be drawn into the cell because of the negative charge created from fixed anions.

Question 3

What are the two things that play into the extent to which each ion contributes to the potential difference across the plasma membrane? (Membrane Potential)

Answer 3

1. Concentration Gradient

2. It’s permeability with the plasma membrane

Question 4

What is the membrane potential of a cell that is not producing impulses known as? What is the range for most body cells? and for Neurons?

Answer 4

Resting Membrane Potential
Range: -65mV to -80mV
Neurons: -70 mV

Question 5

Change in what ion extracellularly would have the greatest effect on the resting membrane potential?

Answer 5

K+ (but a change in the membrane permeability to any given ion will change the membrane potential)

Question 6

An increase in membrane permeability to Na+ will do what to the membrane potential?

Answer 6

It will drive the membrane potential towards +30 mV for a short time.

Question 7

What allows signals to travel directly from one cell to the next?

Answer 7

If the cells plasma membranes are very close together and their cytoplasm is continuous through tiny “gap junctions” that couple the cells together.

Question 8

What protein creates Gap Junctions?

Answer 8

Transmembrane “Connexin” proteins

Question 9

In most cases cells signal each other by releasing chemicals into the extracellular environment. What are the three types of this signaling?

Answer 9

1- Paracrine Signaling
2- Synaptic Signaling
3- Endocrine Signaling

Question 10

What is the term that is used to describe the difference in charges across the plasma membrane?

Answer 10

Potential Difference (measured in millivolts)

Question 11

The membrane potential is usually determined primarily by which ion’s concentration gradient?

Answer 11

K+ Potassium’s gradient.

Question 12

What kind of signaling is utilized when cells within an organ secrete regulatory molecules that diffuse through the extracellular matrix to nearby target cells?

Answer 12

Paracrine Signaling –considered local because it involves the cells of a particular organ.

Question 13

What signaling method has been discovered to be related to organ growth and coordinate the activities of the different cells and tissues within an organ?

Answer 13

Paracrine Signaling.

Question 14

What type of signaling do neurons use to regulate their target cells?

Answer 14

Synaptic Signaling

Question 15

What is Endocrine Signaling?

Answer 15

Endocrine signaling refers to the method cells of endocrine glands use to secrete chemical regulators, hormones, into the extracellular fluid and how they enter the blood and affect their target cells.

Question 16

In order for a target cell to respond to a hormone, neurotransmitter, or paracrine regulator it must have what?

Answer 16

It must have the specific receptor proteins for the molecule.

Question 17

Where can receptor proteins be located?

Answer 17

Receptor proteins may be located intracellularly in either the cytoplasm or nucleus, or on the outer surface of the plasma membrane of the target cell.

Question 18

What type of regulatory molecules can pass through the plasma membrane? Give three examples

Answer 18

If the regulatory molecule is nonpolar it can diffuse through the cell membrane and enter the target cell.
Ex’s: Steroid hormones, thyroid hormones, and nitric oxide gas ( a paracrine regulator).

Question 19

What type of regulatory molecules cannot pass through the plasma membrane? Give three examples.

Answer 19

Regulatory molecules that are large or polar. Ex: epinephrine (amine hormone), acetylcholine (amine neurotransmitter), and insulin (polypeptide hormone).
Require the assistance of secondary messengers.

Question 20

Secondary Messengers– what can they be?

Answer 20

1- Ions, most commonly Ca2+, that move into the cell from extracellular environment
2- Molecules produced within the cell cytoplasm in response to the binding of polar regulatory molecules to their receptor on the plasma membrane.

Question 21

cAMP

• What is it?
• What is it’s precursor?
• How does it work?

Answer 21

Cyclic Adenosine Monophosphate
1- It is a second messenger
2- The binding of the polar regulatory molecule indirectly activates an enzyme in the plasma membrane that produces cAMP from its precursor ATP.
3- cAMP concentrations increase, activating previously inactive enzymes in the cytoplasm, those enzymes activated by cAMP can then change the activities of the cell to produce the action of the regulatory molecule.

Question 22

Polar Regulatory Molecules indirectly activate enzyme proteins in the cytoplasm, what do they use to do this?

Answer 22

G-Proteins

Question 23

What are G-Proteins?

Answer 23

G-Proteins are “the thing” that travels between a receptor that has been activated by its polar reg. molecule and the target enzyme in the cytoplasm.
G-Proteins contain three protein subunits that shuttle between receptors and different membrane effector proteins, including specific enzymes and ion channels.

Question 24

What are the three subunits that make up a G-Protein?

Answer 24

Alpha, Betta, and Gamma

Question 25

Go through the steps G-Proteins take when they are activated.

Answer 25

1- Regulatory molecule binds to receptor which causes alpha subunit to dissociate from beta-gamma subunit. This dissociation of the alpha from the beta-gamma occurs because the alpha subunit releases GDP (guanosine diphosphate) and binds to GTP (guanosine triphosphate)
2- Alpha subunit, or the beta-gamma complex, moves through the membrane and binds to the effector protein, which is an enzyme or ion channel.
3- That temporarily activates the enzyme or opens/closes the ion channel.
4- Alpha subunit hydrolyzes the GTP into GDP+Pi which causes the three subunits to reaggregate and move back to the receptor protein.

Question 26

What embryonic tissue layer produces CNS and PNS glial cells?

Answer 26

Ectoderm