Module 9 (Cell Signaling)

Question 1

What is cell signaling?

Answer 1

Transferring information from the outside of the cell to obtain a response inside the cell (by sending and receiving chemical signals)

Question 2

Elements for cell communication

Answer 2

• Signaling cell
• Signaling molecule
• Receptor molecule
• Receptor cell

Question 3

Signaling in bacteria

Answer 3

A small peptide was discovered to be continuously synthesized by pneumococcal bacterial cells, cells have a receptor for this peptide on the surface, when it binds then the bacterium expresses genes that enable it to take up DNA from the environment

Question 4

Receptor activation

Answer 4

Binding of signalling molecule

Question 5

Signal transduction

Answer 5

The transmission of signal into the cell

Question 6

Cellular response

Answer 6

It is specific for the target cell

Question 7

Signal Termination

Answer 7

Stops the response of the target cell

Question 8

Ligands

Answer 8

A specific molecule that is detected by receptors
- Sometimes crosses membrane to reach intracellular receptors

Question 9

How is a receptor turned on?

Answer 9

Turned on when the signaling molecule binds to the receptor (activated)

Question 10

What happens when a ligand binds to the ligand-binding site on its receptor?

Answer 10

A conformational change in the receptor triggers chemical reactions within the cytosol

Question 11

What happens in signal transduction?

Answer 11

Message is transmitted to cell through the cytoplasm, which can stay in the cytoplasm or go to the nucleus, and then a series of proteins are activated/inactivated in a particular sequence

Question 12

Once the signal has been received and acted upon, it is…

Answer 12

Terminated

Question 13

Endocrine Signaling

Answer 13

Long distance communication where the signaling molecules travel through the bloodstream
- Uses hormones

Question 14

Paracrine signaling

Answer 14

Short distance communication (approx 20 cells) where the signalling molecule travels via diffusion (usually small and water soluble)

Question 15

Autocrine signaling

Answer 15

When a cell secretes a signaling molecule and is also the target cell (helpful for embryonic development)

Question 16

Contact dependent signaling

Answer 16

A transmembrane protein on the surface of one cell acts as the signaling molecule, and a transmembrane protein on an adjacent cell acts as a receptor
Also known as juxtacrine signaling

Question 17

Intracellular receptors

Answer 17

• Only works with nonpolar signaling molecules
• located in the cytoplasm or nucleus

Question 18

Cell Surface Receptors

Answer 18

For polar signaling molecules
Contains three domains
- Extracellular domain
- Trans-membrane domain
- Cytoplasmic domain

Question 19

GPCR

Answer 19

G protein-coupled receptors
- Associate with G proteins and bind GTP and GDP in the cytoplasm

Question 20

Structure of G proteins

Answer 20

Alpha subunit
Beta subunit
Gamma subunit

Question 21

What happens when GDP binds to the alpha subunit of G proteins?

Answer 21

The three subunits of G proteins are bound together. When it is bound to GTP, the protein is active.

Question 22

What happens when a ligand binds to a GPCR

Answer 22

The binding activates a G protein by replacing GDP with GTP if the G protein is associated with the GPCR (active G protein)

Question 23

When a G protein is active…

Answer 23

The alpha subunit dissociates and binds to a target protein to activate the target protein

Question 24

How is heart rate influenced by GPCR systems?

Answer 24

When the G protein is active, it binds to adenylyl cyclase, which activates it and begins converting ATP into cyclic AMP. Cyclic AMP then activates Protein Kinase A, which phosphorylates proteins in heart muscle -> increases heart rate

Question 25

What is cAMP known as?

Answer 25

• cyclic adenosine monophosphate
• A second messenger molecule

Question 26

Protein Kinase A

Answer 26

Also known as PKA, and is an enzyme that phosphorylates proteins and increases the rate of contraction in the heart

Question 27

Signal Amplification

Answer 27

A small amount of ligand can create a large reaction
- multiple G proteins are activated with one receptor
- each adenylyl cyclase produces large amounts of cAMP
- Each active PKA activates multiple protein targets

Question 28

Binding Affinity

Answer 28

How tightly a receptor holds onto a ligand

Question 29

When the ligand leaves the receptor…

Answer 29

No longer able to activate other proteins, signal terminates.

Question 30

Phosphatases

Answer 30

Enzymes that dephosphorylate target proteins

Question 31

Receptor Kinases

Answer 31

Becomes active when a ligand bonds, receptors associate into dimers, and they phosphorylate another protein on the inside of the cell.

Question 32

Examples of receptor kinase signaling

Answer 32

Limb buds, Insulin signaling, wound healing

Question 33

PDGF

Answer 33

Platelet-derived growth factor
- stimulates repair of tissues
- binds to receptor kinases
- released by platelets

Question 34

MAP

Answer 34

Mitogen-Activated Protein

Question 35

Ras

Answer 35

The signaling protein that is activated in the MAP kinase pathway

Question 36

What happens when Ras is bound to GTP?

Answer 36

Triggers a kinase cascade
- At end of cascade, increased expression of cell division genes

Question 37

Ligand-Gated Ion Channels

Answer 37

Respond to binding of a signalling molecule

Question 38

Voltage-Gated Ion Channels

Answer 38

Respond to changes in voltage in the cell

Question 39

Mechanically-gated Ion Channels

Answer 39

Respond to force applied to the cell