BIOLOGY 2B03 Chapter Notes - Chapter 6: Filopodia, Transmembrane Protein, Cell Signaling
17 Jun 2018
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BIOLOGY 2B03 - Module 6 Lecture I
Dictyostelium Cycle Between Uni- and Multicellular
Dictyostelium Discoideum: or slime mold, is a eukaryote that transitions from a collection of
unicellular amoebae into a multicellular slug and then into a fruiting body
● Aggregated amoebae: work together to form a multicellular slug that can migrate towards
heat, light, and humidity in a search for potential food
● Cells of slug will differentiate into prestalk and prespore cells
● In a suitable environment: the anterior end of the slug will form the stalk and the posterior
end will form the spores of the fruiting body which is about 2mm tall
Signal for Unicellular Aggregation : Starvation
● Dictyostelium feed on bacteria
● When food is abundant → mitosis
● Starvation → initiates a series of events that lead to the aggregation of unicellular amoebae
● cAMP: its production leads to aggregation response → forms a slug
○ Slug starts to differentiate when it founds suitable, nutrient-rich environment
○ Anterior cells → stalk, posterior cells → fruiting body
○ Fruiting body: contains spores with hard cell wall → spore to remain dormant for
extended periods
○ Spores will germinate to form new single celled amoebae when food is available
Aggregation is Chemotactic Response
Cyclic AMP: signal for aggregation
● G-protein coupled receptor or GPCR; is a transmembrane protein
● The extracellular domain of the receptor binds specifically to cAMP → active receptors
● Then cells reorganize their intracellular actin network to move towards the sources of the
signal
● Every cell is moving towards that ingle source of cAMP
Cell Movement Towards cAMP Signal
Researcher moves the pipette
● Every time the signal moves, the cell responds by changing the direction of movement
● Dynamic filopodia extends outward to allow movement
● Signalling initiates actin reorganization: nucleation, polymerization, and
depolymerization → enable movement
3-D Reconstruction of Crawling Cell
● Amoeba is moving towards the cAMP signal provided at the left side of the field of view
● Filopodia formation in the direction of movement
3-D REconstruction of cell that Cannot Respond to Signal
Dictyostelium carrying a mutation in the gene for the clathrin heavy chain
● Cells are unable to form the vesicles necessary for transport of proteins to cell membrane
● There is a signal, CAMP, and formation of filopodia, but no movement towards the source
● Absence of protein transport → the transmembrane G-protein coupled receptor is not
transported to the cell membrane
● No receptor for cAMP → no respond to that signal
find more resources at oneclass.com
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Document Summary
Dictyostelium discoideum: or slime mold, is a eukaryote that transitions from a collection of unicellular amoebae into a multicellular slug and then into a fruiting body. Aggregated amoebae: work together to form a multicellular slug that can migrate towards heat, light, and humidity in a search for potential food. Cells of slug will differentiate into prestalk and prespore cells. In a suitable environment: the anterior end of the slug will form the stalk and the posterior end will form the spores of the fruiting body which is about 2mm tall. Starvation initiates a series of events that lead to the aggregation of unicellular amoebae. Camp: its production leads to aggregation response forms a slug. Slug starts to differentiate when it founds suitable, nutrient-rich environment. Anterior cells stalk, posterior cells fruiting body. Fruiting body: contains spores with hard cell wall spore to remain dormant for extended periods. Spores will germinate to form new single celled amoebae when food is available.
