Chapter 23 - Signal Transduction Mechanisms

Question 1

How do cells produce signals?

Answer 1

Signals are produced by cells by displaying molecules on their surface that are recognized by receptors on the surfaces of other cells. Requires cell to cell contact.

Question 2

How can multicellular organisms control the activities of specialized cells?

Answer 2

Through the release of chemical messengers.

Question 3

How are signaling molecules classified?

Answer 3

Based on the distance between their site of production and the target tissue(s) it acts upon.

Question 4

What are endocrine signals?

Answer 4

(Greek: “to secrete into”) Messenger signals (hormones) that are produced at great distances from target tissues and are carried by the circulatory system to various sites in the body.

Question 5

What is an example of paracrine signals?

Answer 5

Growth factors.

Question 6

What are paracrine signals?

Answer 6

(Greek: “beside”) Signals that are diffusible and act over a short range. Signals that are released locally where they diffuse to act at a short range on nearby tissues from where they are released.

Question 7

What are juxtacrine signals?

Answer 7

Signals sent at a short range that require physical contact between the sending and receiving cells.

Question 8

What are autocrine signals?

Answer 8

Local mediators (signals) that act on the same cell that produces them.

Question 9

What are receptors?

Answer 9

A protein that contains a binding site for a specific signaling molecule.

Question 10

What is a ligand?

Answer 10

A substance that binds to a specific receptor thereby initiating the particular even or series of events for which that receptor is responsible.

Question 11

What happens once a messenger reaches its target cell/tissue?

Answer 11

It binds to receptors on the surface of the target cells, which initiates the signaling process.

Question 12

What does a ligand do?

Answer 12

It often binds to a receptor embedded within the plasma membrane of the cell receiving the signal. In other cases, the ligand binds to a receptor inside the cell.

Question 13

How do cells distinguish messengers from the multitude of other chemicals in the environment or from messengers intended for other cells?

Answer 13

Based on the highly specific way the ligand binds to the receptor. The ligand forms noncovalent chemical bonds with the receptor proteins.

Question 14

What is a binding site?

Answer 14

A site that allows a receptor to make numerous bonds with its ligand that also allows the messenger molecule to fit closely.

Question 15

What is the first step in cell-cell signaling?

Answer 15

Ligand binding is the first step which leads to production of additional molecules or ions within the cell.

Question 16

What are second messengers?

Answer 16

Transmit signals from extracellular signaling ligands to the cell interior, which initiates a cascade of changes within the receiving cell. Often affects the expression of specific genes within the receiving cell.

Question 17

What is signal transduction?

Answer 17

Mechanisms by which signals detected at the cell surface are transmitted into the cell’s interior, resulting in changes in cell behavior and/or gene expression.

Question 18

What enables the receptor to distinguish its specific ligand from thousands of other chemicals?

Answer 18

The combination of binding site shape and the strategic positioning of amino acid side chains.

Question 19

What is the first step of cell signaling?

Answer 19

Bing of a ligand to its receptor, in which the ligand is a “primary messenger”.

Question 20

What does the binding of a ligand do to a receptor?

Answer 20

Can cause a change in the receptor conformation or causes receptors to cluster together or for both to happen.

Question 21

What are examples of second messengers?

Answer 21

cyclic AMP, calcium ion, inositol trisphosphate, and diacylglycerol and other several substances

Question 22

What happens once changes take place due to the binding of the ligand to the cell?

Answer 22

The receptor initiates a preprogrammed sequence of signal transduction events inside the cell.

Question 23

What does “preprogrammed” mean?

Answer 23

Cells have a greater repertoire of functions than are in use at any particular time and many remain unused until particular signals are received that trigger them. Specific preprogrammed responses of a cell depends on the past history of the cell.

Question 24

How is a cell able to sense that the appropriate ligand has successfully bound to its associated receptor?

Answer 24

The production of additional molecules and ions within the cell after receiving the signal.