CELL COMMUNICATION
Cellular Messaging
Epinephrine→triggers flight response
The same small set of cell-signaling mechanisms shows upn again ang again indiverse species.
Apoptosis→type of programmed cell death trhat integrates from multiple signaling pathways.
EVOLUTION OF CELL SIGNALING
Each typ eof cell secretes a specific factor that binds to receptros only on the other type of cell.
Alfa plus a =a/alfa cell
Signal transduction pathway
signaling mechanisms firstevolved in ancient prokaryotes.
Quorum sensins allows bacterial populationjs to coordinate their behaviours in numbers.
Biofilm is bacterial cells afhered to a surface.
LOCAL AND LONG-DISTANCE SIGNALING
paracrine signaling
involves the release of signaling molecules by a cell that affect nearby target cells, facilitating communication within a localized environment.
synaptic signaling
occurs in the nervous system, where neurotransmitters are released from a neuron and bind to receptors on adjacent neurons or muscle cells, enabling rapid and precise communication across synapses.
chemical signals are called hormones for long-distance signaling.
Endocrine signaling
involves the release of hormones into the bloodstream, allowing these chemical messengers to travel to distant target organs or tissues, thus regulating various physiological processes such as growth, metabolism, and mood.
Juxtacrine signaling
involves direct contact between neighboring cells, where signaling molecules pass through gap junctions or are presented on the cell surface to influence adjacent cells, facilitating processes like immune response and tissue repair.
THE THREE STAGES OF CELL SIGNALING: A PREVIEW
epinephirne causes the mobilization of fuel.
3 stages reception, transduction and response.
Reception→ targets cell deteciton of a signaling molecule coming from outside the cell.
Transduction→binding that changes the receptor protein in some way also amplifies the signal.
Response→ triggers a specific cellular esponse
The signal molecules are named ligands
RECEPTROS IN THE PLASMA MEMBRANE
GPCR, tyrosine kinases and ion channel receptors.
GPCR (G-Protein Coupled Receptors): These receptors activate intracellular signaling pathways through the binding of ligands, leading to various cellular responses.
Tyrosine Kinases: These receptors function by phosphorylating tyrosine residues on target proteins, which plays a critical role in regulating cellular processes such as growth and differentiation.
Ion Channel Receptors: These receptors allow ions to flow across the plasma membrane, contributing to changes in membrane potential and initiating rapid cellular responses.
Abnormal functionin gof the receptor tyrosine kinases is associated with many types of cancer.
INTRACELLULAR RECEPTORS
found either the cytoplasm or nucleus of target cells.
trsncription factors control which genes are turned on.
TRANSDUCTION:CASCADES OF MOLECULAR INTERACTIONS RELAY SIGNALS FROM RECEPTORS TO TARGET OLECULES IN THE CELL.
One benefit is the possibilityof greatly amplifying signals.
SIGNAL TRANSDUCTION PATHWAYS
relay molecules are proteins.
PROTEIN PHOSPHORYLATION AND DESPHOSPHORYLATION
protein phosphates are enzymes that can rapidly remove phosphate groups from proteins
SMALL M OLECULES AND IONS AS SECOND MESSENGERS
water-soluble molecules or ions called second messengers
they spread throughout the cell by diffusion
CYCLIC AMP
an enzyme embedded in the plasma membrane that converts ATP to cAMP in response to an extracellular signal.
CALCIUM IONS AND INOSITOL TRIPHOSPHATE
calcium ion is even more widely used than cAMP as a second messenger.
they are actively transported out of the cell.
IP3 AND DAG are produced by cleavafe of a certain kind of phospholipid in the plasma membrane
calcium in these pathways could be considered “third messenger”.
RESPONSE:CELL SIGNAING LEADS TO REGULATION OF TRANSCRIPTIONOR CYTOPLASMIC ACTIVITIES.
NUCLEAR AND CYTOPLASMIC RESPONSES
the final molecule may serve as a transcription facotr.
Signaling pathway regulates the activity of proteins rather than causing theirs synthesis by activating gene expression.
REGULATION OF THE RESPONSE
This regulation can occur through various mechanisms, including post-translational modifications, protein interactions, and feedback loops that ensure cellular responses are appropriately calibrated to external signals.
SINGAL AMPLIFICATION
activated products can be much greater than in the preceding step.
THE SPECIFICITY OF CELL SIGNALING AND COORDINATION OF THE RESPOSNE
two cell respond differently to the same thing.
SINALING EFFICIENY:SCAFFOLDING PROTEINS AND SIGNALING COMPLEXES.
scaffolding proteins large relay proteins to which several other relay proteins are simultaneously attached.
TERMINATION OF THE SIGNAL
signaling pathways only laast a shorty time.
When the number of active receptors falls the cellular response ceases.
APOPTOSIS INTEGRATES MULTIPLE CELL-SIGNALING PATHWAYS.
cells that are infected or daamged or have treached the end of their life undergo programmed cell death.
cellullar agents chop up the DNA and fragment the organelles and other cytoplasmic components
The cell shrinks and becomes lobes.
APOPTOSIS IN THE SOIL WORM CAENORHABDITIS ELEGANS
suicide proteins in cells destined ton die in c elegans.
ced-3 and ced4
The main protease of apoptosis is caled caspases
APOPTOTIC PATHWAYS AND THE SIGNAL THAT TRIGGERS THEM.
15 different capsapases can carry out apoptosis
These caspases are categorized into initiator caspases, which activate downstream effector caspases, and effector caspases, which execute the cell death program.
then ones that originate from inside the cell are coming from the nucles dna damge endoplasmic reticulkum when excessive protein misfolding ocurrs.