Chapter 9

Question 1

cell communication

Answer 1

The process by which cells can detect, interpret, and respond to signals in their environment. In multicellular organisms, cell communication is also needed to coordinate cellular activities within the whole organism.

Question 2

signal

Answer 2

Regarding cell communication, an agent that influences the properties of cells.

Question 3

receptor

Answer 3

1. A cellular protein that recognizes a signaling molecule and becomes activated or inhibited in response to it. 2. A structure capable of detecting changes in the environment of an animal, such as a touch receptor.

Question 4

Knowledge of the dissociation constant of ligands and their receptors allows researchers to predict when a signaling molecule is likely to cause a(n)

Answer 4

cellular response

Question 5

cellular response

Answer 5

Adaptation at the cellular level that involves a cell responding to signals in its environment.

Question 6

Why do Cells Need Signals?

Answer 6

Responding to Changes in the environment
Cell to Cell communication

Question 7

cell-to-cell communication

Answer 7

A form of cell communication in which cells share information with each other.

Question 8

Signals are relayed between cells in five common ways, all of which involve a cell that produces a signal and a target cell that receives the signal.

Answer 8

Direct intercellular signaling
Contact-dependent signaling
Autocrine signaling
Paracrine signaling
Endocrine signaling

Question 9

Direct intercellular signaling

Answer 9

Signals pass through a cell junction from the cytosol of one cell to adjacent cells.

Question 10

Contact-dependent signaling

Answer 10

Membrane-bound signals bind to receptors on adjacent cells.

Question 11

Autocrine signaling

Answer 11

Cells release signals that affect themselves and nearby target cells.

Question 12

Paracrine signaling

Answer 12

Cells release signals that affect nearby target cells.

Question 13

Endocrine signaling

Answer 13

Cells release signals that travel long distances to affect target cells.

Question 14

Stages of Signal Transduction

Answer 14

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

Question 15

1. Receptor activation

Answer 15

The binding of a signaling molecule causes a conformational change in a receptor that activates its function.

Question 16

2. Signal transduction

Answer 16

The activated receptor stimulates a series of proteins that forms a signal transduction pathway.

Question 17

3. Cellular response

Answer 17

The signal transduction pathway affects the functions and/or amounts of cellular proteins, thereby producing a cellular response.

Question 18

signal transduction pathway

Answer 18

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

Question 19

ligand

Answer 19

An ion or molecule that binds to a protein, such as an enzyme, a receptor, or a channel.
is a signaling molecule that binds to a receptor.

Question 20

ligand * receptor complex

Answer 20

The structure formed when a ligand and its receptor bind noncovalently to each other.

Question 21

1. Ligands binds noncovalently to their receptor with high _____
2. Binding and release between receptor and ligand relatively _____
3. Ligand binding changes receptor structure – this ____ _____ transmits the signal across the membrane
4. Once a ligand is released, the receptor reverts andis ____ again

Answer 21

1. specificity
2. rapid
3. conformational change
4. inactive

Question 22

cell surface receptor

Answer 22

A receptor found in the plasma membrane that enables a cell to respond to different kinds of extracellular signaling molecules.

Question 23

Cell Surface Receptors

Answer 23

enzyme-linked receptor
G-protein-coupled receptor (GPCR)
ligand-gated ion channel

Question 24

enzyme-linked receptor

Answer 24

A receptor found in all living species that typically has two important domains: an extracellular domain, which binds a signaling molecule, and an intracellular domain, which has a catalytic function.

Question 25

G-protein-coupled receptor (GPCR)

Answer 25

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

Question 26

ligand-gated ion channel

Answer 26

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 27

What produces the cellular response to signals?

Answer 27

Typically, the signaling molecule binds to cell surface receptor and the conformation change stimulates a signal transduction pathway
Signal transduction pathways may involve a cascade of intracellular kinases, or generation of intracellular signals called second messengers

Question 28

receptor tyrosine kinase

Answer 28

A type of enzyme-linked receptor found in animals and choanoflagellates that can attach phosphate groups to tyrosines in the receptor itself or in other cellular proteins.

Question 29

Cellular Response - Receptor Tyrosine Kinases

Answer 29

1. Receptor activation: Two EGF molecules bind to 2 EGF receptor subunits, causing them to dimerize and phosphorylate each other on tyrosines.
2. Relay between the receptor and protein kinase cascade: Grb binds to the phosphorylated receptor and then to Sos. Sos stimulates Ras to release GDP and bind GTP.
3. Protein kinase cascade:Ras activates Raf, which starts a protein kinase cascade in which Raf phosphorylates Mek, and then Mek phosphorylates Erk.
4. Activation of transcription factors: Erk enters the nucleus and phosphorylates transcription factors, Myc and Fos.
5. Cellular response: Myc and Fos stimulate the transcription of specific genes. The mRNAs are translated into proteins that cause the cell to advance through the cell cycle and divide.

Question 30

protein kinase cascade

Answer 30

The sequential activation of multiple (three) protein kinases.

Question 31

Second Messengers: Signal transduction via cAMP

Answer 31

Signals binding to cell surface are “first messenger”
Many signal transduction pathways lead to production of second messengers that relay signals inside of the cell.
cAMP = Cyclic Adenosine Monophosphate

Question 32

cAMP has two advantages

Answer 32

1. Signal amplification
   Binding of signal to one receptor can cause the synthesis of many cAMP molecules that activate PKA, and each PKA can phosphorylate many proteins
2. Speed
   In one experiment a substantial amount of cAMP was made within 20 seconds after addition of signal

Question 33

Epinephrine

Answer 33

Fight-or-flight hormone
Different effects throughout body
Airways of the lungs relax to provide more oxygen
More glycogen breakdown in skeletal muscle
Heart muscle cells beat faster
This explains effect of caffeine
Caffeine inhibits phosphodiesterase, the enzyme that removes cAMP once the signal is gone
Inhibition causes cAMP to persist, so heart beats faster even with low epinephrine

Question 34

A Cell’s Response to Signaling Molecules Depends on the Proteins It Makes

Answer 34

One hormone causes different effects in different cell types
Differential gene expression – all cells contain the same genome but only express particular genes
Can effect cellular response in a variety of ways:
Receptor may not be expressed
Different receptors for same signal
Different affinities for signal
Signal transduction pathways different

Question 35

Apoptosis: Programmed Cell Death

Answer 35

1. Cell shrinks and forms rounder shape due to destruction of nucleus and cytoskeleton
2. Plasma membrane forms blebs – irregular extensions that break away

Question 36

extrinsic pathway

Answer 36

One of two different pathways for apoptosis that involves the activation of death receptors.

Question 37

death receptor

Answer 37

A type of cell surface receptor found in eukaryotic cells that can promote apoptosis when it becomes activated.

Question 38

Apoptosis - Extrinsic Pathway

Answer 38

1. A signaling molecule, which is a trimer, binds to 3 death receptors, causing them to aggregate and exposing the death domain.
2. Adaptor proteins and initiator procaspase bind to the death domain, forming a death-inducing signaling complex.
3. The initiator procaspase is cleaved, and a smaller active initiator caspase is released.
4. The initiator caspase cleaves the executioner procaspase, making it active.
5. The executioner caspase cleaves cellular proteins, such as actin filaments, thereby causing the cell to shrink and eventually form blebs.

Question 39

apoptosome

Answer 39

A complex of proteins that promotes apoptosis via the intrinsic pathway by activating caspases.