Chapter 11: Cell Communication Flashcards
Most cell signals
Chemicals
Saccharomyces cerevisiae
Type of yeast that uses chemical signaling for mating
Quorum sensing
Allows bacterial populations to coordinate their behaviors in activities that require a given number of cells
Biofilm
Example of quorum sensing
Bacterial cells come together to get nutrients off of surface they are on
Slimy coating on leaves, logs, and teeth
Evolution and cell communication
Same set of signaling mechanisms show up in a variety of species
Signal transduction pathway
Convert signals received at cell’s surface into cellular responses
Local signaling
Animal and plant cells can communicate by direct contact
Cell Junctions
Found in animal and plant cells to coordinate signaling
Signaling molecules in cytosol pass freely between one another
Gap junction
Cell Junction in Animals
Plasmodesmata
Cell Junction in Plants
Growth factors
Stimulate nearby target cells to grow and divide
Paracrine signaling
Paracrine signaling
numerous cells can respond to signal molecules
local signaling
growth factors
Synaptic signaling
animal nervous system when a neurotrasmiter is released in response to an electric signal
Hormones
Both animals and plants use for long distance signaling
Endocrine signaling
Specialized endocrine cells secrete hormones into body fluids (blood)
Hormones reach all body cells but are only picked up by some
Earl W. Sutherland
Discovered how the hormone epinephrine works on cells
EXPAND ON!!!!!!
3 Stages of Cell Signaling
- Reception
- Transduction
- Response
Reception
Signaling molecule binds to a receptor protein on target cell
Transduction
Concerts the signal to a form that can bring about a specific cellular response
Response
Transduced signal finally triggers a specific cellular response
Examples of cellular response
Catalysis of an enzyme
rearrangement of cytoskeleton
activation of a certain gene through transcription
Ligand
Signal molecule
Are receptors specific?
Yes they are highly specific
Initial transduction of a signal
Shape change in the receptor
What are most signal receptors?
Plasma membrane proteins
3 Types of Membrane Receptors
G-Protein Coupled Receptors
Receptor tyrosine kinases
Ion channel receptors
G protein
Bind the energy rich GTP
G proteins are all very similar in structure
Study the diagram for more information
Receptor tyrosine kinases
Membrane receptors that attach phosphates to tyrosine
Can trigger multiple signal transduction pathways at once
What does abnormal RTK contribute to?
Cancer
Ligand gated ion channel
Gate when receptor changes shape
Specific ions flow through a channel in the receptor
Intracellular Receptors
Found in cytoplasm or nucleus of target cells
Small hydrophobic chemical messengers cross the plasma membrane and activate them
Can act as a transcription factor
Ex: steriod and thryoid hormones
Multistep transduction pathways…
can amplify a signal
provide more opportunities for coordination and regulation of the cellular response
What happens at each step of the signal transduction pathway?
Signal is transduced into another form
Usually a shape change in protein
Protein kinases
Transfer phosphates from ATP to protein
Can transfer phosphate to another protein kinase
Called phosphorylation
phosphorylation cascade
many relay molecules in signal transduction pathways
Protein Phosphates (PP) Molecules
Take away phosphate from activated protein kinase
Dephosphorylation
How do phoshorylation and dephosphorylation work?
As a switch that can turn activities on and off or up and down as required
Second messengers
Small, non protein water soluble molecules that spread through a cell by diffusion
Cyclic AMP
Second messenger
activates protein kinase A
Adenylyl cyclase
Enzyme in plasma membrane
Converts ATP to cAMP
Can be triggered by G-protein or RTK
What is import in regard to cAMP
Important to have a different signaling molecule that inhibits adenylyl cyclase
Activates a g-protein to inhibit
Ca concentration in the cell
Low in the cytosol
High in the ER and the mitochondria
Ca concentration in the cell
Low in the cytosol
High in the ER and the mitochondria
Ca pumps
Require ATP to pump Ca from low concentration to high concentration
Located on ER and Mitochondria
IP3 and DAG
Additional second messengers that signal calcium to release
Produced by cleavage of a certain phospholipid in the membrane
Phospholipase C
Appears to create IP3 and DAG
Output response
Cell’s response to an extracellular signal
How do cellular responses work?
Normally occur in the cytoplasm or nucleus
A lot of times they turn genes on or off to regulate enzyme and protein production
OR they regulate the activity of enzymes directly
Transcription Factor
Final activated molecule in the signaling pathway
Turns genes on or off
Four aspects of signal regulation
- Amplification of the signal
- Specificity of the response
- Overall efficiency of response
- Termination of the signal
MIGHT BE MORE THAN JUST ON OR OFF
Enzyme cascades
Amplify the cell’s response to the signal
Specificity of cell signaling and response
All cells have different proteins
They recieve different signals
Even the same signals act differently in different cells depending on the internal proteins and pathways
Cross Talk
Pathway branching
Help the cell coordinate incoming signals
Scaffolding Proteins
Large relay proteins to which other relay proteins are attached
Increase the efficiency of the signal transduction
Termination of the signal
Once ligand concentration falls, fewer receptors will be bound (epinephrine wearing off)
Unbound receptors revert to an inactive state
What types of cells undergo apoptosis?
Cells that are infected or damaged
Apoptosis
Cell suicide for the greater good
What happens in apoptosis?
Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells
Enzymes can’t leak out and harm neighboring cells cause it gets cleaned up
How is apoptosis triggered?
By signals
Once the signal is recieved a cascade of caspase proteins occurs
Chief caspase in apotosis in nematodes
Ced-3
How many caspases do humans have
15
Internal signals for apoptosis (not a ligand)
Result from irreparable DNA damage or excessive protein misfolding
Kill yourself cause you screwed up
When is apoptosis essential?
In early development and maintenance of all animals
Normal part of development of human hands and feet not to be webbed
