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Cell to Cell Communication

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Title: Cell to Cell Communication


1
Cell to Cell Communication
  • Chapter 11

2
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 ?.

3
Figure 11.0 Yeast
4
Figure 11.1 Communication between mating yeast
cells
5
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

6
Figure 11.3 Local and long-distance cell
communication in animals
7
Figure 11.4 Communication by direct contact
between cells
  • Cell junctions and cell-cell recognition

8
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

9
Figure 11.5 Overview of cell signaling (Layer 1)
10
Figure 11.5 Overview of cell signaling (Layer 2)
11
Figure 11.5 Overview of cell signaling (Layer 3)
12
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

13
Figure 11.10 Steroid hormone interacting with an
intracellular receptor
14
  • Cell Membrane Receptors found in cell membrane
  • Three major types
  • G-linked receptor
  • Receptor tyrosine kinase
  • Ligand-gated ion channel

15
Figure 11.6 The structure of a G-protein-linked
receptor
16
Figure 11.7 The functioning of a
G-protein-linked receptor
17
Figure 11.8 The structure and function of a
tyrosine-kinase receptor
18
Figure 11.9 A ligand-gated ion-channel receptor
19
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)

20
Figure 11.11 A phosphorylation cascade
21
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)

22
cAMP
  • Adenylyl cyclase an enzyme in cell membranes
    that converts ATP into cAMP
  • Phosphodiesterase an enzyme that converts cAMP
    into AMP

23
Figure 11.12 Cyclic AMP
24
Figure 11-12x cAMP
25
Figure 11.13 cAMP as a second messenger
26
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

27
Figure 11.14 The maintenance of calcium ion
concentrations in an animal cell
28
Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 1)
29
Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 2)
30
Figure 11.15 Calcium and inositol triphosphate
in signaling pathways (Layer 3)
31
Figure 11.16 Cytoplasmic response to a signal
the stimulation of glycogen breakdown by
epinephrine
32
Figure 11.17 Nuclear response to a signal the
activation of a specific gene by a growth factor
33
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

34
Figure 11.18 The specificity of cell signaling
35
Figure 11.19 A scaffolding protein
36
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

37
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