Multicellularity and Choanoflagellates
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Questions and Answers

What characterizes true multicellularity?

  • An organism consists of more than one cell type. (correct)
  • An organism only has one cell type.
  • An organism is made entirely of bacteria.
  • An organism has only unicellular precursors.

    • How many times did true multicellularity evolve independently according to the content?

  • At least ten times. (correct)
  • Three times in fungi.
  • Only once in plants.
  • Four times in animals.

    • What is the primary function of the collar and flagellum in choanoflagellates?

  • Both structures are only used for cell-to-cell communication.
  • The collar helps in reproduction and the flagellum anchors the organism.
  • The collar captures light and the flagellum senses chemicals.
  • The collar traps bacteria and the flagellum is used for movement. (correct)

    • Which of the following statements about receptor tyrosine kinases is accurate?

    <p>They are important for cell-to-cell communication.</p> Signup and view all the answers

    What is a common result of the signal transduction cascade?

    <p>Phosphorylation, which can switch a protein on or off.</p> Signup and view all the answers

    Which component connects homotypic cell-cell adhesion molecules to actin filaments in animals?

    <p>Alpha and beta catenin.</p> Signup and view all the answers

    What can the phosphorylation of tyrosine residues achieve in enzyme function?

    <p>It can either activate or inhibit the function.</p> Signup and view all the answers

    How do choanoflagellates relate to sponges?

    <p>Choanoflagellates and sponges share a common ancestor.</p> Signup and view all the answers

    What was the initial evolutionary function of cadherins?

    <p>Bacterial capture</p> Signup and view all the answers

    Which statement accurately describes the body plan axes in animals?

    <p>Bilaterally symmetrical animals can have 2 or 3 axes.</p> Signup and view all the answers

    What occurs in the absence of WNT signaling?

    <p>Beta-catenin is degraded.</p> Signup and view all the answers

    What role do Wnts play in the development of radiata?

    <p>They establish the primary axis.</p> Signup and view all the answers

    Which feature is common among all bilaterally symmetrical animals?

    <p>Existence of nerves</p> Signup and view all the answers

    How are sensory cells in sponges proposed to relate to nerve cells?

    <p>They evolved into the first neurons in ctenophora.</p> Signup and view all the answers

    What is the consequence of inhibiting GSK3beta in the Wnt signaling pathway?

    <p>Activation of Wnt signaling pathway.</p> Signup and view all the answers

    What is the potential significance of having a high gradient of Wnt signaling?

    <p>It is crucial for your tail formation in vertebrate embryos.</p> Signup and view all the answers

    Study Notes

    Multicellularity

    • Multicellularity is defined as an organism consisting of more than one cell type.
    • True multicellularity evolved independently at least ten times: in animals (metazoa), six times in plants, and three times in fungi.
    • All multicellular organisms evolved from unicellular ancestors.

    Choanoflagellates

    • Choanoflagellates are single-celled organisms closely related to animals (metazoa).
    • They feature a collar region and a flagellum.
    • Choanoflagellates are heterotrophic, consuming bacteria.
    • The collar traps bacteria, and the flagellum propels the organism.

    Choanoflagellates vs. Sponges

    • Both choanoflagellates and sponges have choanocytes.
    • Choanoflagellates are single-celled, while sponges are multicellular.
    • Choanoflagellates are the sister lineage to all animals.
    • Choanocytes in sponges are specialized cells that resemble choanoflagellates.

    Cell to Cell Communication

    • Signal transduction cascades involve: transcriptional changes, cell shape alterations, and phosphorylation of proteins.
    • Phosphorylation is common in signal transduction, switching proteins on or off.
    • Key amino acids involved in phosphorylation are serine, threonine, and tyrosine.

    Cell-to-Cell Adhesion

    • Cell-to-cell adhesion involves homotypic molecules that connect to actin filaments.
    • Alpha and beta catenin mediate the connection between adhesion molecules and actin.
    • Evolutionarily, cadherin genes exhibit unique features in species like M. brevicollis compared to most animals. Specifically, cadherin genes lack certain domains present in animal cadherins.

    Body Plan Axes

    • Animals can have one or more body axes.
    • Radiata (e.g., jellyfish) have a singular anterior-posterior axis.
    • Bilateral animals (e.g., mammals) have multiple axes, including dorsal-ventral and left-right axes.

    Wnt Signaling

    • WNT is a secreted signaling ligand interacting with Frizzled receptors.
    • Wnt signaling cascade is complex and impacts cell adhesion, movement, and cytoskeleton rearrangement.
    • In the absence of WNT, GSK3β phosphorylates and degrades β-catenin, preventing it from entering the nucleus and regulating Wnt-responsive genes (which are "off").
    • Conversely, WNT binding to the receptors leads to the stabilization of β-catenin, which translocates into the nucleus and activates downstream Wnt-responsive genes.

    Radial Symmetry

    • WNT signaling plays a crucial role in establishing the primary body axes in radiata.
    • Wnts influence the development of anterior-posterior body axes.
    • High WNT gradients are implicated in tail development of vertebrates.

    Nerves

    • Sponges lack nerves.
    • All animals with bilateral symmetry possess nervous systems.

    Sensory Cells

    • Flask cells in sponges potentially evolved into neurons in other animals.
    • Flask cells in sponges exhibit functionalities akin to synapses.
    • The evolution of flask cells is speculated to have facilitated sensory diversification.
    • This evolution potentially laid the groundwork for more intricate environmental interpretation in nerve systems.

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    Multicellularity Study Guide PDF

    Description

    Explore the fascinating world of multicellularity and its evolution from unicellular ancestors. This quiz covers the characteristics of choanoflagellates and their significance as the closest relatives to multicellular animals. Compare the similarities and differences between choanoflagellates and sponges to deepen your understanding of cellular evolution.

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