Cell to Cell Communication

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Cell to Cell Communication

• Chapter 11

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Example of Cell to Cell Communication

• Yeasts version of sex
• Two types of cells (a and ?)
• Each secretes a mating factor that binds to
  receptor on opposite cell
• Binding of mating factors lead to cell growth and
  fusion
• Nucleus of fused cell contains DNA from both a
  and ?.

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Figure 11.0 Yeast
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Figure 11.1 Communication between mating yeast
cells
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Local and Long Distance Signaling

• Local signaling influences cells in the nearby
  vicinity
• Paracrine signaling secreting cell releases a
  regulator in the the extracellular matrix
• Synaptic signaling nerve cell releases
  neurotransmitter into a synapse (space between
  nerves)
• Long Distance signaling can influence cells all
  over body
• Hormone signaling endocrine cells secrete
  hormones into blood where they can reach any cell

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Figure 11.3 Local and long-distance cell
communication in animals
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Figure 11.4 Communication by direct contact
between cells

• Cell junctions and cell-cell recognition

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Three Stages of Cell Signaling

• Reception target cells detection of a chemical
  signal
• Signal is detected when it binds to a receptor
• Ligand a signal molecule that binds to a
  receptor
• Transduction binding of signal to receptor
  stimulates a change in the receptor.
• The changed receptor triggers a step or many
  steps that lead to the cell response.
• Response end result the cell response

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Figure 11.5 Overview of cell signaling (Layer 1)
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Figure 11.5 Overview of cell signaling (Layer 2)
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Figure 11.5 Overview of cell signaling (Layer 3)
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Receptors

• Intracellular receptors found in cytoplasm or
  on nucleus so signal must pass through cell
  membrane first
• Ex. NO and steroid hormones like testosterone
• Testosterone receptor only found in certain cells
• An activated testosterone receptor acts as a
  transcription factor
• Transcription factors - turn on or turn off genes

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Figure 11.10 Steroid hormone interacting with an
intracellular receptor
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• Cell Membrane Receptors found in cell membrane
• Three major types
• G-linked receptor
• Receptor tyrosine kinase
• Ligand-gated ion channel

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Figure 11.6 The structure of a G-protein-linked
receptor
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Figure 11.7 The functioning of a
G-protein-linked receptor
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Figure 11.8 The structure and function of a
tyrosine-kinase receptor
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Figure 11.9 A ligand-gated ion-channel receptor
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Transduction

• Signal transduction pathways a chain of
  molecular interactions (like falling dominoes)
• Often involves protein phosphorylation and
  dephosphorylation
• Protein kinases enzymes that transfer phosphate
  groups from ATP to a protein
• Phosphorylation of protein often changes protein
  from inactive to active form
• Protein phosphatases enzymes that rapidly
  remove P (often turn off pathway)

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Figure 11.11 A phosphorylation cascade
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Second Messengers

• Second messengers small, nonprotein,
  water-soluble molecules or ions that are part of
  signaling pathways
• Two most common second messengers
• Ca2
• Cyclic adenosine monophosphate (cAMP or cyclic
  AMP)

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cAMP

• Adenylyl cyclase an enzyme in cell membranes
  that converts ATP into cAMP
• Phosphodiesterase an enzyme that converts cAMP
  into AMP

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Figure 11.12 Cyclic AMP
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Figure 11-12x cAMP
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Figure 11.13 cAMP as a second messenger
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Ca2

• Second messenger involved in growth factors, some
  hormones, muscle contractions, neurotransmitters,
  and cell division
• Ca2 levels are high in the blood, ER, and
  sometimes mitochondria and chloroplasts
• Low Ca2 cytosol concentration allows even small
  fluctuations to trigger pathways

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Figure 11.14 The maintenance of calcium ion
concentrations in an animal cell
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Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 1)
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Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 2)
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Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 3)
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Figure 11.16 Cytoplasmic response to a signal
the stimulation of glycogen breakdown by
epinephrine
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Figure 11.17 Nuclear response to a signal the
activation of a specific gene by a growth factor
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Fine Tuning of Response

• Signal Amplification number of activated
  products is much greater than in preceding step
• Specificity different cells have different
  proteins so two cells can respond to same signal
  in different manner
• Ex. epinephrine stimulates liver to break down
  glycogen and heart cells to contract faster
• Scaffolding Proteins large relay proteins to
  which several other relay proteins are attached

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Figure 11.18 The specificity of cell signaling
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Figure 11.19 A scaffolding protein
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Apoptosis

• Apoptosis - triggered by signals that activate
  cell suicide
• In C. elegans (small worm), death genes called
  ced. When activated they stimulate death by
  activating proteases and nucleases.
• Very similar genes found in other animals
  including humans
• Apoptosis problems are associated with cancer,
  Parkinsons, and alzheimers

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