Cells in a multicellular organism communicate by __________ ___________.
chemical messengers
How might animal cells communicate in local signaling
direct contact, or cell-cell recognition
Describe local regulators
messenger molecules that travel short distances
Describe paracrine signaling
local regulator released directly onto one cell by another
Describe synaptic signaling
a nerve signal triggers the release of a local regulator onto a near by cell
What are hormones?
chemical messengers that travel long distance
Describe signal transduction pathway
a set of step that trigger a certain response from a cell after a signal is received
What are the 3 steps of signal transduction pathway
- Reception
- Transduction
- Response
What is reception
delivery of a signal to a cell
What are ligands
Signal molecules
How to certain ligands go through the cell membranes?
Water soluble ligands must bind to receptor proteins in the cell membrane
Non-polar or small ligands can travel directly in the cell
What is a G protein-coupled receptor
membrane receptor that activates a G protein when a ligand is present
What process do G protein-coupled receptors start
transduction
How does a G protein work?
when activated, it uses energy from GDP becoming GTP to turn on an enzyme
Describe receptor tyrosine kinase
membrane receptors that attach phosphates to tyrosines.
How is a dimer made
When the ligand is present, the two kinases form
What does a dimer do
trigger multiple transduction pathways
Describe a ligand-gated ion channel
receptor opens like a gate when a ligand is present to allow ions in
Small or hydrophobic ligands go inside a cell how?
they travel directly through the cell membrane
What is a hormone receptor complex
a ligand and internal receptor binded together
What process does a hormone receptor complex start?
transduction
Signal transduction usually involves multiple steps that includes what to get a response from a cell?
turning a sequence of proteins on and off
What is phosphorylation
adding a phosphate (turns proteins on)
What is dephosphorylation
removing a phosphate (turns proteins off)
Phosphorylation is done by what types of proteins?
Protein kinases
Dephosphorylation is done by what types of proteins?
Protein phosphatases
Describe second messengers
Small, water soluble molecules or ions, which rapidly relay the signal from the membrane-receptor-bound “first messenger” into a cell’s interior
What are types of second messengers?
cAMP (made from ATP), IP3, Ca+, DAG
Cell usually respond by doing what?
synthesizing enzymes or proteins, or turning genes on or off
What is apoptosis?
A response that is a programmed or controlled cell suicide
How does apoptosis work?
A cell is chopped and packaged into vesicles that are digested to prevent enzymes from leaking out and damaging other cells
Apoptosis can be triggered by:
An extracellular death-signaling ligand
DNA damage in the nucleus
Protein misfolding in the endoplasmic reticulum
List two advantages of a multistep pathway in the transduction stage of cell signaling
- amplification to produce a large cellular response and also provide opportunity for regulation and coordination.
- easier to regulate or shut off the system since there are more targets.
Explain how an original signal molecule can produce a cellular response when it may not even enter the target cell
The signal molecule binds a receptor on the surface of the cell. This receptor is embedded in the cell membrane. Upon binding of a signal molecule the receptor will become active and will be able to activate proteins in the cytoplasm. This in turn will affect other proteins eventually resulting in a cell response.
Explain how signals can be sent through direct contact
They may be communicated between cells through direct cytoplasmic connections (gap junctions or plasmodesmata) or through contact of surface molecules (cell-cell recognition in animal cells).
How do second messengers function in signal transduction pathways
Second messengers participate in pathways initiated by both G protein-coupled receptors and receptor tyrosine kinases. Commonly used second messengers are cAMP and calcium ions.
Explain why different types of cells may respond differently to the same signal molecule
each type of cell has its own complement of proteins
