Cell Communication and Signal Transduction
Overview
How do cells communicate?
Ligand binds to receptor and signals a response within the cell.
Forms of Signaling
Autocrine - cell targets itself
Paracrine - cell targets a nearby cell
Endocrine - cell targets a distant cell (using chemical messengers known as hormones)
Direct Signaling - connections between cells
Gap Junction - cell targets a connected cell (animals)
Plasmodesma - connecting between neighboring cells (plants)
Holly plants switch to spiky phenotype when they are nibbled at by predators. Upper leaves may stay smooth, while lower leave become spiky. Type of communication - paracrine
Negative Feedback Loops
- returns body to set point
- maintains homeostasis
- Example: maintaining temperature or blood glucose levels
Positive Feedback Loops
- increase activity
- Example: uterine contractions during labor
Chemical Signaling Pathway
1. Reception
2. Transduction
3. Response
Types of Receptors
a) Ion channel linked receptor
b)
G protein linked receptor
c)
Enzyme linked receptor
Action of Epinephrine
1. Hormone binds to receptor
2.
G protein dissociates
3.
GTP activates adenylyl cyclase
4. ATP catalyzes formation of cAMP
5.
cAMP triggers cell response
G protein coupled receptors (GPCR)
- activate secondary messengers in the cell
- involved in responses to sensory input, hormones, and nerve transmission
- three subunits: alpha, beta, gamma
Cell Signaling
a) outside cell - b) membrane -c) inside cell
1. Ligand 2. Receptor 3. G protein 4. GTP 5. Adenylyl Cyclace
6. ATP 7. cAMP 8. Kinase 9. Cell Response
Cholera and Cell Signaling
1. Toxin binds to receptor
2.
CAMP activation
3.
CFTR channel opens
4.
Water leaves the cell
Classroom Resources
Laboratory Investigation – Taste and Signal Transduction with Gymnema Tea
In this lab, students taste samples that are salty, sweet, bitter, and sour. After swishing Gymnema tea in their mouth, their taste receptors are altered. They can no longer taste sweet! The reason is that the tea interferes with the signal transduction pathway.
Negative Feedback Loops with Glucagon and Insulin – explores how the pancreas and liver maintain homeostasis by regulating the amount of glucose on the blood
Cell Signaling – How Glucose is Taken Up by the Cells – shows a graphic with a glycoprotein receptor and how insulin triggers the transport of Glut-4 to the cell membrane.
Cell Signaling – Epinephrine – shows a graphic with G proteins, adenylyl cyclase, cAMP, and PKA. Examines how a stimulus triggers the “fight or flight” response.
Signal Transduction – a final review of the processes showing graphics of signal transductions, phosphorylation cascade, and cytokine signaling. Great for a final review!