Unit 4
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Importance of cell communication
Cell specification: Development of cells so they can do their job and cells become the right type of cell needed Receive signals for cell division Receive signals for cell death Cell mating in yeast
What types of cells communicate
Single and multi-celled organisms
Quorum sensing
communication among bacteria to benefit population Small signaling molecules used by bacteria to measure population
Importance of quorum sensing
resistance to antibiotics promote motility Most often- change gene expression to benefit their life cycle
Forms of intracellular signaling
Contact dependent signaling Paracrine Endocrine synaptic
Contact dependent signaling
signaling molecule presented as a transmembrane protein Cells have to be in contact with each other
Paracrine and autocrine signaling
binding to nearby cells; secreting molecule, released and binding to receptors on neighboring cells autocrine: signaling molecule comes back to stimulate same cell
Endocrine signaling
signaling cell releases molecule enter bloodstream and reaches target cell Transfer over long distances hormones
Synaptic signaling
Neurotransmitter binds to target cell Signals within neuron travels long distances because of length of axon
Types of ligands
Cell surface-bound Secreted and bind cell surface receptors Hydrophobic small ligands diffuse across the membrane and bind to intracellular receptors (inside the cell)
Morphogens
Specialized type of ligand
What do morphogens’ effects depend on
Depend on how much of them are around High levels- become cell type A Medium levels- become cell type B Low levels- become cell type C
What does the reaction depend on in a cell
It can react in different ways depending on combination of signals that a cell receives
How multiple signaling molecules regulate cells
Survive grow and divide differentiate die
Why does one signaling molecule have varied responses
Different receptors Different intracellular signals with the same receptor but different intrcellular events Different responses to different levels or amount of ligand present
Endocrine speed, affininty, concentration of signaling
Takes more time with slower responses Ligand acts at low concentrations receptors have high affinity for ligand meaning it binds strongly
Synaptic speed, affinity, concentration of signaling
Faster response Ligand acts at high concentrations Receptors have lower affinity for ligand
What does the speed of signaling responses depend on
How far signal travels and how well receptors bind to signaling molecule
Speed of signaling response in altering protein function
Fast Ex: binding event or adding phosphate group
Speed of signaling response in altering protein synthesis
Slow Ex: making protein like Transcription, translation, folding
Molecular switches
Protein kinases: add phosphate groups Protein phosphatase: remove phosphate group GEF: GTP binding by releasing GDP turns things on GAP: binds GDP by GTP hydrolysis turns things off
What turns proteins on and off for protein kinases and phosphatases
Either one
What turns proteins on and off for GAP and GEF
GEF turns things on GAP turns things off
What are G protein-coupled receptors signaling molecules responsible for
Taste and smell neurotransmitters hormones light