MCDB 50 Midterm Study Guide

MCDB 50 Midterm Study Guide - Stem cell

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Study Guide What is an Embryo + Introduction to Stem Cells 1. When fertilization occurs, a “zygote” is formed. It starts to divide rapidly, skipping the synthesis portions of the cell cycle. This is called “cleavage.” The 2 nd and 3 rd day results in a ball of 8-32 blastomeres, called a morula. As this travels down the fallopian tube on the way to the uterus, the morula continues to cleave and eventually takes up fluid from its surroundings, becoming a hollow ball with an outer layer of cells and a bundle of cells inside called the Inner Cell Mass. The outer layer is called the trophoblast, which later develops into the placenta. The Inner Cell Mass, or ICM, is a mass of pluripotent cells which will develop into the embryo proper. On the 5 th to 6 th day and during the second week, the trophoblast cells burrow into the wall of the uterus, implanting the blastocyst and officially initiating the pregnancy. During the 3 rd week, gastrulation occurs. The primitive streak forms and the epiblast invaginates and the 3 germ layers form. During week 4 the primitive heart forms and the organ buds become clearly visible during weeks 5 and 6. The embryo becomes clearly human during weeks 7 and 8 when the head becomes larger and the fingers appear. 2. The developmental stage after week 8 is called the fetal stage. 3. The Holmgren Lab website defines an embryo as the completion of the pre- implantation stage, from conception to the eighth week of pregnancy. Kiessling & Anderson’s Human Embryonic Stem Cells defines it as the developmental stage that follows implantation and precedes organogenesis. 4. In vitro refers to “in glass,” or done in the lab. In vivo refers to “in life.” 5. The defining characteristics of stem cells include: the ability to self-renew ( reproduce without changing developmental potential) and differentiate (give rise specialized cell types). They have high telomerase activity, a normal karyotype, can be maintained after successive passages, and have the proper self-renewal markers. 6. They help repair damaged tissues and replace old cells. PGCs and shit 7. For symmetric self renewal, an undifferentiated stem cell will divide into two undifferentiated stem cells. During asymmetric self renewal, an undifferentiated stem cell divides into two daughter cells: one still undifferentiated and the other a differentiated mature cell.
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8. The different stem cell fates include: two undifferentiated stem cells, two differentiated mature cells, one stem cell and one mature cell, no division at all, resulting in a quiescent stem cell, and apoptosis, or cell death. 9. Totipotency: can be part of an extra-embryonic structure or any germ layer in the embryo proper. This can be a blastomere when the embryo is in the 2-8 cell stage. Pluripotency: can form any part of any germ layer. An example is a cell from the ICM.
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MCDB 50 Midterm Study Guide - Stem cell

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