Chapter 21 Essay

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Chapter 21 * Cells undergo cell differentiation where cells become specialized in structure and function; organized into tissues and organs. * In plants and animals the morphogenic ways are different in many ways. * In animals movement of cells and tissues are necessary to transform the early embryo into the characteristic 3-D form of the organism. * In plants morphogenesis and growth in overall size are not limited to embryonic and juvenile periods but occur throughout the life of the plant. * Animals begin with a zygoteEight cellsBlastula(Sphere of cells)Gastrula(When Gastula folds inward)Adult Animal (Cell differentiation at this stage is for replacement of lost cells) * Plants begin with Zygote2 cells Embryo inside seed Plant forms (apical meristem’s are structures that continue to help the growth and function of the tips and roots of plants. ) * Through experiments on carrots done at Cornell, it was shown that differentiated cells taken from the root and put into a medium were able to grow into normal plant cells, almost identical to the parent plant. * In plants at least, mature cells can dedifferentiate and give rise to all the specialized cell types of the mature organism- and cell with this potential is totipotent. * Animal scientists used a different approach to see if animals were totipotent. * They used nuclear transplantation where an egg or zygote was replaced with the nucleus of a differentiated cell. * *If the nucleus would be able to retain its full genetic capability then it could direct development of egg into all proper tissues. * The frog experiment proved this theory to be true as the transplanted nucleus was able to support the development from an egg to a tadpole. * With this experiment scientists concluded that cell types of the body differ in structure and function not because they contain different genes; but because they express different genes from a common genome. * Dolly did have the same chromosomal DNA as to the nucleus donor( the mitochondrial DNA came from the egg donor), but problems went wrong most likely in incomplete reprogramming of the original transplanted nucleus. * After the cell from a mammal sheep is fused with the nucleus of an egg cell, it is grown in culture and implanted into a 3rd sheep which then produces the baby, Dolly. * In human cloning eggs were able to reach blastocyst stage (similar to blastula stage) but wouldn’t go beyond that stage. * Since only a small subset of genes are actually turned on, this results in many abnormalities. * Misplaced methyl groups in DNA donor nuclei may interfere with pattern of gene expression necessary for normal embryonic development. * Stem cells in adults replace nonproducing specialized cells as needed, or otherwise known as pluripotent- able to give rise to multiple but not all cell types. * Hope is that stem cells can repair damaged tissues. * MyoD protein is extremely powerful as it can change fully differentiated nonmuscle cells into fat or liver cells. * Other cells lack a particular combination of regulatory proteins making it that other cells can’t respond to MyoD. * Two important sources of information in development is egg cell’s cytoplasm containing both RNA and protein molecules encoded
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