Multicellularity

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Multicellularity

• Colonies cyanobacteria and choanoflagellates
• Sponges as organisms

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Cyanobacteria - among the oldest fossils
Stromatolite section
Stromatolites colonies of cyanobacteria
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Figure 26.3x2 Filamentous cyanobacteria from the
Bitter Springs Chert
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Figure 26.2 Clock analogy for some key events in
evolutionary history
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Figure 27.11 The cyanobacterium Anabaena and its
nitrogen-fixing heterocysts
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Development and communication in Anabaena
Crucial components need to be identified to
understand the process of heterocyst cellular
differentiation. What is the switch that commits
a cell to differentiate? How is transcription
controlled at different stages of development? Is
there a single master transcriptional regulatory
control or do several regulators work in
parallel? What mechanisms are involved in
expression of the nitrogen-fixation genes?
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Figure 26.1 Some major episodes in the history
of life
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Figure 32.8 Animal phylogeny based on sequencing
of SSU-rRNA
colonial choanoflagellate
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Enzymes typical of true animals (metazoans) are
found in their colonial protist anscestors, e.g.
tyrosine kinase is found in choanoflagellates.
tyrosine
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Multicellularity

• Colonies cyanobacteria and choanoflagellates
• Sponges as organisms

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Figure 33.2 Sponges
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Figure 33.3 Anatomy of a sponge
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Its whats between cells that defines
multicellularity in animals.
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Integrins are cell-surface proteins that sense
the extracellular protein (matrix) environment
and signal to the cell to control
differentiation, survival and migration of cells.
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Figure 26.2 Clock analogy for some key events in
evolutionary history
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Multicellularity

• Colonies cyanobacteria and choanoflagellates
• Sponges as organisms