Topic 7- Signaling and Response

Question 1

Why do cells need to communicate?

Answer 1

• embryo patterning: tells cells what organism/tissue they are apart of.
  -coordination among cells: For cells to function together they need to be on the same page.
  -Motility: if there is an issue they can communicate an flee
  -environmental sensing: To identify what’s going on around it so they can react accordingly.

Question 2

What are the two forms of direct signal transfer?

Answer 2

Direct signal transfer is communication between adjacent cells.
-Gap junctions: protein tunnels in animal cells that let small ions and molecules get passed from one cell to another.
-Plasmodesmata: Holes in the cell wall that allows plant cells cytoplasm to be interconnected thus molecules can flow freely through.

Question 3

Describe local/paracrine signaling.

Answer 3

Cell releases signaling molecules to be detected by near by cells. The signal molecules are loaded into vesicles in order to pass through the memebrane.

Question 4

Describe distance/endocrine/hormonal signaling

Answer 4

A gland or structure will release signaling molecules into your blood stream which will spread throughout your body.

Question 5

Describe the generic signaling pathways.

Answer 5

1. Reception- membrane proteins receptors will detect the signaling molecule when it binds to the protein.
2. Transduction- series of proteins send the message from one protein to another until it reaches the nucleus. This is called a phosphorylation cascade.
3. Response- usually will be gene transcription which tells a cell to make more or less of a specific protein.

Question 6

Describe the 3 forms of Reception in the signaling pathway.

Answer 6

G-protein coupled receptors:
1. Signaling molecule binds to the receptors which activates it.
2. Activated receptor makes the G protein swap the GDP for GTP which activates the G protein.
3. Activated G protein travels along the membrane surface until it bumps into target enzyme which activates it.
4. The active enzyme then starts transduction. After the G protein leaves it turns into GDP.

Ion Channel receptors
1. the signaling molecule (ligand) bonds with the protein receptor which opens up a ligand gate allowing ions to diffuse in which triggers a cellular response. Ions get pumped out to build a gradient

Intracellular receptor: receptor protein is inside the cells cytoplasm.
1. Nonpolar signal molecule gets through the membrane and binds to the protein which has a transcription factor and can facilitate a response itself.

Question 7

Kinase vs. phosphatase. Why are they important?

Answer 7

Kinase adds a phosphate group and phosphatase removes a phosphate group.

Adding a negatively charged phosphate group changes a proteins shape making it active.

Question 8

Describe a phosphorylation cascade.

Answer 8

1. activated relay molecule binds to kinase 1 making it active
2. Kinase 1 takes a phosphate group for ATP and uses it to activate Kinase 2.
3. Eventually the last Kinase in the chain activates a a protein which triggers a response.

Meanwhile phosphatase roams around and deactivates the Kinases.

Question 9

How does signal amplification occur?

Answer 9

At every step that does not rely on 1 to 1 contact. the signal is amplified so you can get a robust response at the cellular level.
ex. one signal receptor can activate several G proteins

Question 10

How is the the signal passed from the receptor to the phosphorylation cascade.

Answer 10

When the target enzyme of the G protein is Adenyl Cyclase, it removes to phosphate form ATP to create Cyclic AMP (adenosine monophosphate) which goes on to start the phosphorylation cascade.