USABO 11: Cell Communication

Introduction

  • quroem sensing: bacterai senseing the concentration of signaling molecules allows bacteria to monitor their own local cell dencity

  • biofilm is an aggregation of bacteria cells attatched to a surface by molecules secreted by the cells after the cells have reached a certain density

  • a signal tranduction pathway is a pathway

Yeast Production

  • a yeast cells and alpha yeast cells are the two sexes

    • each releasese specifi cators that bind only to recepters on the other type of cell, providing advantages to the cell descendants

  • a/alpha cells are fused/mated yeast cells that contain genes of both the invidual cells

Local and Long Distance Signaling

  • paracine signaling is a type of local signaling animals where signaloing nolecules travel only short distances to influence neabry cells

  • growth factors are a class of local regulators in animals that stimulate nearby target cells to grow and divide

  • synaptic signaling is a specialized type of local signaling occuring in the animal nervous system involving an electric signal traveling along a nerve cell triggering neurotransmitter secreation

  • hormones are molecules used by plants and animals for long distance signaling

  • encocrine signaling is hormone signaling in animals where specialized cells release that travel through the circulatory system to other parts of the body where they reach target cells

    • many plant hormones reach distant targets by traveling through cells, so many are small and nonpolar

    • insulin regulates sugar levels in blood and is a protein with thousands of atoms

Three Stages of Cell Signaling

  • Signal Reception is the target cell’s detection of a signaling molecules coming outside the cell, when a signaling molecule binds to a receptor protein located at the cell’s surface

  • Signal transduction is the stage of cell signaling where the signal is converted to a form that can bring about a specific cellular response after binding to a receptor protein

    • A signal transduction pathway is the sequence of changes in aseries of different molecules

    • Can lead the the amplification of a signal, where there is a geometric increase in the number of activated molecules

  • Cellular Response is the stage of cell signaling where the trabsducted signal triggers a specific cellualr response

Signal Reception

  • ligands are molecules that specficallt bind to another molecuekes

    • signaling moelcules act as ligands that bind to a receptor protein which causes it to change it’s shape

  • GCPRs, or G protein coupled receptors are the largest family of cell surface receptors that work with the help of a G protein

    • G proteins are proteins that work in GCPRs and binds the energy rich molecule GTP

  • Receptor Tyrosine Kinases are membrane receptors that attach phosphate groups to tyrosines triggering a transduction pathway

    • protein kinases are enzymes that catalyze the transfer of phosphates groups from ATP to another protein

    • dimerization is the provess where two receptor monomers assosciate closely with eachother after the binding of signaling molecules forming a complex known as a dimer

  • Ligand gated ion channel is a type of membrane channel receptor featuring a region that acts as a gate that opens or closses the channel when a signaling molecules binds to the ligand

Intracellular Receptors

  • Intracelluaar receptors proteins are receptors proteins foun din the cytoplasm or nuclus of target cells

  • generally small and non-polar

Transcription factors are special proteins that control which genes are turned on

Signal Transduction

  • Protein Kinase are enzymes that transfer phosphate groups from ATP to a protein

  • A phosphorylation cascade is a signal transduction pathway where a series of different proteins are phosphorylated in turn, each protein adds a phosphate group to the next one in line

    • causes a shape change from the interaction of teh phosphate group with charged or polar amino acids, often activaying it

  • Protein phosphatates are enzymes that can rapidly remove phosphate groups from proteins in dephosphorylation to turn off signal trandsduction pathways.

    • make portein kinases available for reue

Secondary Messengers

  • Secondary messegers are small, water-soluble molecules or ions that are components of signal transduction pathways

    • cyclic AM{ and calcium ions are the two most popular ones

      • increasing cytosolic calcium ion concentration leads to muscle cell contraction, exocytosis, and a vaiety of other actions

      • calcium ion concentration in cyctosol is generally much lower than outside the cell, activelt imported into ER and sometimes mitochondria

  • cyclic AMP(cAMP) is a secondary messenger produced from ATP in the epinephrine signal pathway

    • broadcasts the signal to the cytoplasm

    • Phosphodeiestere is an enzyme that converts cAMP to AMP

  • Adenylyl cylclase is an enzyme embedded in the plasma membrane that converts ATP to cAMP in response to an extracellualar signal

    • once epineprine binds to a g portein it activates adenylyl cylase

  • inositol triphosphate(IP3) is a secondary messenger that binds to an IP3 gated ion channel in the ER triggering an influx of calcium ions in the cytosol which serve as secondary messengers

Cellular Response

Different kinds of cekls have different collections of proteins because of they turn on different kinds of genes so they have different responses to stimuli

  • Signal Amplification is the amplification of a signal during signal trandsuction as each step produces a greater number of activated products

    • occurs due to proteins existing in their active state for long enough to process multiple rounds of substartes

  • Scaffolding proteins are large relay proteins to which severak relay proteins are simultaneously attached that help speed up signal transfer

    • speeds up signal transfer because protein-protein interactyion isn’t limited by difussion

Apoptosis

  • Apoptosis is controlled cell suicide that occurs when cells are damaged, infected, or have the reached the end of their life span

    • cellular agents chop up the DNA, fragemnt the organelles, and the cell shrinks and becomes lobed.

    • can occur afte DNA has been damaged and protein-protein interactions pass along a signal that trigegrs cell death

  • Caspases are the main proteases/enzymes that cut up proteins and DNA of apoptosis in mammals