Chapter 11 - Cell Communication

Question 1

What is cellular messaging?

Answer 1

External signals are converted to responses within the cell.

Cell junctions allow molecules to pass between adjacent cells

Two cells may communicate with molecules protruding from their surfaces.

Question 2

What are the two types of cell signaling?

Answer 2

Local and long distance

Question 3

What are implied within local signaling?

Answer 3

Paracrine signaling - secretory cells release signaling molecule to near by cells

Synaptic signaling -Nerve cell releases neurotransmitter into synapse to propagate a nerve impulse

Question 4

What is Long-Distance signaling?

Answer 4

The signal will come from cells that are at a further distance away from the target cell; in our bodies it is often found in the form of a hormone and will travel through the blood.

Question 5

What are the three stages of cell signaling?

Answer 5

1. Reception
2. Transduction
3. Response

Question 6

What is Reception?

Answer 6

The target cell will detect signaling molecule from outside the cell.
- the signaling molecule will behave as a ligand

Question 7

What is a Ligand?

Answer 7

A molecule that binds to another, often larger.

Question 8

What is a receptor?

Answer 8

It usually is a transmembrane protein.

• G protein-coupled receptors
• Receptor tyrosine kinase
• Ion channel receptors

Question 9

How does the G protein-coupled receptor work?

Answer 9

a signaling molecule will tell the G protein-coupled receptor to start a cellular response by sending GTP to an inactive enzyme on the cell membrane. This will trigger a cellular response.

Question 10

How does the Receptor tyrosine kinase work?

Answer 10

A ligand (signaling molecule) will bind to the binding sites found on top of the Receptor tyrosine kinase proteins (pillar like structures with 6 tyrosine molecules). After ligand binds to the two proteins they will combine to make a dimer 6 ATP will then bind to add phosphates to each tyrosine. Inactive proteins will then bind to the phosphorylated tyrosine and trigger a cellular response.

Question 11

How does the Ion channel receptor work?

Answer 11

A signaling molecule will attach to the ligand-gated ion channel receptor. The signaling molecule with open the gate which will let the ions in to the cell and then the cellular response can happen.

Question 12

What are Intracellular Receptors?

Answer 12

They are receptor proteins found in either the cytoplasm of nucleus of target cells. To reach such a receptor, a signaling molecule passes through the target cell’s plasma membrane.

Question 13

How does the Intracellular Receptor work?

Answer 13

1. The steroid hormone aldosterone passes through the plasma membrane. (they can pass through the membrane because they are hydrophobic enough or small enough to pass through the membrane)
2. Aldosterone binds to a receptor protein in the cytoplasm, activating it.
3. The hormone receptor complex enters the nucleus and binds to specific genes.
4. The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA.
5. The mRNA is translated into a specific protein.

Question 14

What is Transduction?

Answer 14

They are cascades of molecular interactions that relay signals from receptors to target molecules in the cell.

Question 15

What molecules/enzymes can be found in a Transduction stage?

Answer 15

Protein Kinase - enzymes that transfer a phosphate group from ATP
Protein phosphatase - rapidly removes phosphate groups from proteins
First messenger - Signaling molecule or ligand (i.e. a hormone)
Second Messenger - A small, non-protein, water soluble molecule or ion which is used in the cascade to propagate signal.

Question 16

What is Phosphorylation Cascade?

Answer 16

The “cascading” of different types of protein kinase to get an specific active protein.

Question 17

What happens in a Phosphorylation Cascade?

Answer 17

A signaling molecule will activate a relay molecule.

1. A relay molecule activates protein kinase 1.
2. Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase.
3. Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3.
4. Finally, active protein kinase 3 phosphorylates a protein that brings about the cell’s response to the signal.
5. Enzymes called protein phosphatases catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse.

Question 18

What are cyclic AMP (cAMP)?

Answer 18

They are second messenger molecules that aid in activating proteins to start a cellular response. Example: Epinephrine without passing through the plasma membrane of a cell causes glycogen breakdown. This is done because second messengers will transmit the signal from the plasma membrane to the metabolic machinery in the cytoplasm.

Question 19

What are calcium ions?

Answer 19

Ions that also aid in cellular response by acting as a second messenger.

Question 20

How can Calcium ions act as a second messenger?

Answer 20

PIP2 is split into diacyglycerol and IP3 which is a second messenger. Because of the Ca2 gradient (lower concentration of calcium in the cytosol) When the IP3 molecule binds with an IP3 gated channel, it will open and move Ca2 out of the ER and will then become a 2nd messenger.

Question 21

What is Response?

Answer 21

A response is the regulation of one or more cellular activities after a signal transduction occurs.

• The response may occur in the nucleus or in the cytoplasm.
• Many signaling pathways lead to the regulation of protein synthesis.
  
  • Activation of a transcription factor will turn on a gene.

Question 22

What is apoptosis?

Answer 22

• Controlled cell death
• they will happen via signaling pathways
• During the process cellular agents will chop up DNA and break apart organelles and other cell components (stops growth of the cells in that region and causes the space between fingers)
• All parts get engulfed by vesicles
• Consumed by specialized scavenger cells