Semester 1 Final: Cell Communication Flashcards
Local & Long Distance Signaling
• Cells use chemical signals for means of communication
– Chemical messengers may travel a very short distance or throughout an entire organism to reach their target cell
Local Regulators
For communication with cells that are touching (juxtacrine) or within a very short distance (paracrine)
• These messages can reach several local cells quickly to elicit a response
– The chemical messenger will be short lived & degraded easily
• Examples:
– Growth factors released to induce cell growth & division
– Neurotransmitters crossing the synapse
Long Distance Signaling
Hormones are used to send messages throughout animals to target specific cells (endocrine signaling)
– These travel great distances & create responses in multiple cells simultaneously
– Moved by the circulatory system
– Do not degrade quickly
G-Protein-Linked Receptors
A receptor protein that works with the help of a G protein
– G proteins bind the energy-rich molecule GTP
• A signaling molecule bonds to the extracellular side of the receptor which will become activated & change shape
• The cytoplasmic side of the receptor binds & activates a G protein which carries GTP
• The activated G protein leaves the receptor & diffuses along the membrane until it binds to an enzyme
• The activated enzyme can then trigger the next step in the transduction pathway
• All these processes are reversible & all molecules will inactivate for reuse
Receptor Tyrosine Kinases
Receptors that can trigger more than one signal transduction pathway at once by phosphorylating multiple relay molecules
– 10 or more pathways can be activated simultaneously
• A ligand will bond to the active site on both individual proteins which causes them to form a dimer (work together)
• The dimerization activates the tyrosine-kinase region adding a phosphate from ATP to each tyrosine
• The fully activate protein is recognized by relay proteins
which bind to the
phosphorylated tyrosine becoming active & triggering a transduction pathway
Ion Channel Receptors/Ligand-gated ion channels
A membrane receptor that has a gate that blocks the passage of ions until a ligand bonds to the receptor to open/close the gate
– The gate will return to its original position once the ligand dissociates
– Crucial in the nervous system
Phosphorylation Cascade
A relay molecule is activated by a ligand bonding to the receptor which will activate protein kinase 1
• Protein kinase 1 will activate protein kinase 2 by adding a phosphate group
– This process continues until the protein that regulates the cellular response is activated
• Protein phosphatases removes the phosphates from the activated proteins to return them to an original state
– When multiple protein kinases act upon each other a phosphorylation cascade can be created
Second Messengers
Many signal transduction pathways utilize small, water soluble molecule or ions to relay messages within the cytoplasm
• Two most common:
– Cyclic AMP
– Calcium (Ca2+)
Cyclic AMP
A ligand (epinephrine) will bond to a G-protein-linked receptor which activates adenylyl cyclase that will convert ATP into cyclic AMP
• Large quantities of cAMP are quickly produced to broadcasts the message
through the cell
• cAMP is short lived and converted to AMP
• The typical cAMP pathway will stimulate a protein kinase which phosphorylates another molecule
Calcium
The goal is to increase calcium concentration in the cytoplasm
– This creates a cellular response such as muscle contraction, secretion of neurotransmitters, & the trigger of transduction pathways
• Calcium is released from the endoplasmic reticulum in response to a transduction
pathway that open a calcium gated ion channel
Cellular Response
The ultimate goal is the cellular response
• In the cytoplasm:
– Cellular response may regulate the activity of a protein
• In the nucleus:
– Many pathways regulate gene expression
– Activated molecules may act as a transcription factor (which can regulated numerous genes)
