3. What is a notochord and what tissue layer does it develop from? Why is the de

Question

3. What is a notochord and what tissue layer does it develop from? Why is the development of a notochord important? (2 points) 4. What is a somite and what tissue layer does it develop from? What type of embryonic tissue is the somite made of? In humans, what do the somites develop into? (2 points) 5. Name the three domains of life. Which two contain prokaryotes? Identify one characteristic that can be used to distinguish between all members of these two prokaryotic domains (eg name one way all members of one prokaryotic domain are different from all members of the second). (3 points)

Explanation / Answer

3. The notochord is a defining structure forming in all chordate embryos. It is an early forming midline structure in the trilaminar embryo mesoderm layer initially ventral to the ectoderm, then neural plate and finally neural tube. This is a transient embryonic anatomy structure, not existing in the adult, required for patterning the surrounding tissues. The patterning signal secreted by notochord cells is sonic hedgehog (SHH). This secreted protein binds to receptors on target cells activating a signaling pathway involved in tissues differentiation and development, this protein regulates the development of surrounding tissues (neural plate, somites, endoderm and other organs).

The notochord and has essential roles in vertebrate development. It serves as a source of midline signals that pattern surrounding tissues and as a major skeletal element of the developing embryo.

4. Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somite can be defined as any a series of dorsal paired segments of mesoderm occurring along the notochord in vertebrate embryos. It develops into muscle and bone in the adult animal. Somites are transient structures that will give rise to cells of the vertebrae and ribs, dermis of the dorsum, skeletal muscle of the body wall, back and limbs.

5. The three domains of life are: Archaea, Bacteria and Ekarya. Archaea and bacteria are prokaryotic that are single celled and without nucleus.

Bacteria and archaea, however, differ in cell wall characteristics and membrane lipid composition. They also differ in RNA polymerase structure and, therefore, protein synthesis. Unlike bacteria, archaea cell walls do not contain peptidoglycan. Archaea have unique phospholipids in their plasma membrane and hydrocarbon tails that contain isoprene.

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