Chapter 8: Cell Communication

Question 1

What are the two reasons as to why cells need to respond to signals?

Answer 1

1. To respond to a changing environment
2. To communicate with other cells

Question 2

What is cell signaling?

Answer 2

A vital function of the plasma membrane that involves cells sending changes in their environment and communicating with each other

Question 3

Why is cell communication important?

Answer 3

All living organisms (bacteria, archaea, protists, fungi, plants, and animals) require cell communication to survive

Question 4

What are signals?

Answer 4

Chemical molecules or physical parameters like light or temperature

Question 5

What are the five ways cells communicate with each other?

Answer 5

1. Direct intercellular signaling
2. Contact-dependent signaling
3. Autocrine signaling
4. Paracrine signaling
5. Endocrine signaling

Question 6

What is direct intercellular signaling?

Answer 6

Cell junctions allow signals to directly pass from one cell to another

Question 7

What is contact-dependent signaling?

Answer 7

Molecules bound to the surface of cells serve as signals to other cells encountering them

Question 8

What is autocrine signaling?

Answer 8

Cells signaling molecules that bind to their own surface receptors

Question 9

What is paracrine signaling?

Answer 9

Cells release signals that affect nearby cells

Question 10

What is endocrine signaling?

Answer 10

Signals (called hormones) are released into the blood and affect target cells that are far away

Question 11

What are the three common stages of cell signaling?

Answer 11

1. Receptor activation
2. Signal transduction
3. Cellular response

Question 12

What is a signal transduction pathway?

Answer 12

A group of proteins that convert an initial signal to a different signal inside a cell

Question 13

What is a ligand?

Answer 13

A signaling molecule that binds to a receptor with high specificity

Question 14

What happens during receptor activation?

Answer 14

A ligand binds to a receptor; ligand binding triggers a conformational change in the receptor, transmitting the signal across the membrane

Question 15

Do receptors and ligands only function once?

Answer 15

The ligand-receptor complex is stable for a finite period of time; the complex will dissociate

Question 16

How fast do receptors and ligands bind and release?

Answer 16

Relatively rapid and will reach equilibrium

Question 17

What is the dissociation constant (Kd) used for?

Answer 17

It is used to quantify the affinity receptors have for their ligands; at equilibrium, the Kd = (koff/kon); reflects the ligand concentration where half of the receptors have bound ligand; greater the Kd, lower the ligand-receptor affinity

Question 18

What can we determine from comparing [ligand] and Kd value?

Answer 18

When [ligand] is greater than Kd value, most receptors are likely to have ligand bound to them; if [ligand] is substantially below Kd value, most receptors will not be bound to their ligand

Question 19

Why do signaling molecules need receptors?

Answer 19

Most signaling molecules are small and hydrophilic, or too large to get past the plasma membrane

Question 20

What are cell surface receptors?

Answer 20

Receptors found in the plasma membrane that enables a cell to respond to different kinds of signaling molecules

Question 21

What are extracellular signals?

Answer 21

Signals that come from outside of the cell

Question 22

What are the three different kinds of extracellular receptors?

Answer 22

1. Enzyme-linked receptors
2. G-protein-coupled receptors
3. Ligand-gated ion channels

Question 23

What are enzyme-linked receptors?

Answer 23

A receptor found in all living species that typically has two important domains: a extracellular domain and an intracellular domain

Question 24

What is an enzyme-linked receptor’s extracellular domain?

Answer 24

Receptor’s domain that binds to a signaling molecule

Question 25

What is an enzyme-linked receptor's intracellular domain?

Answer 25

Receptor's domain that has a catalytic function

Question 26

What are protein kinases?

Answer 26

Enzymes that transfer a phosphate group from ATP to a specific amino acid in target proteins

Question 27

What is phosphorylation?

Answer 27

The attachment of a phosphate to a molecule

Question 28

What are G-protein-coupled receptors (GCPRs)?

Answer 28

A common type of receptor found in the cells of eukaryotic species that interacts with G proteins to initiate a cellular response

Question 29

What are G proteins?

Answer 29

An intracellular protein that binds guanosine triphosphate (GTP) and guanosine diphosphate (GDP) and participates in intracellular signaling pathways

Question 30

What are ligand-gated ion channels (ionotropic receptors)?

Answer 30

A type of cell surface receptor that binds a ligand and functions as an ion channel; ligand binding either opens or closes a channel

Question 31

What are intracellular receptors?

Answer 31

Receptors that are found in the cytosol or nucleus, binding to small and hydrophobic signals; intracellular receptor activation typically leads to a change in gene expression