BCOR 103 1st Edition Lecture 20 Outline of Last Lecture I CDK Regulation Phosphorylation Dephosphorylation II Transition Points in Cell Cycle III Rb Phosphorylation Defines Restriction Point IV CDK Activation and Inhibition Regulates G1 S Transition Outline of Current Lecture I Regulation of Transitions II Meiosis III Stem Cells Current Lecture Regulation of the G2 M Transition o Cells monitor replicated DNA and cell size before committing to M phase o M phase CDKs phosphorylate multiple substrates to prepare for chromosome separation nuclear division and cytokinesis o CDKs Aurora kinases and Polo like kinases function in positive feedback loop to regulate entry into M phase Early Events in G2 M Transition o Nuclear envelope breakdown requires phosphorylation of nuclear lamina Sister Chromatid Cohesion and Condensation o Cohesin proteins connect sister chromatids together o Condensin proteins condense sister chromatids for faithful segregation of chromosomes in mitosis Loss of M phase CDK triggers Phosphatases o Inactivation of M phase CDKs triggers phosphatases to stimulate myosindependent contractile ring closure Meiotic Recombination These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Meiotic recombination allows for exchange of genetic information DNA between homologous chromosomes o Synaptonemal complex protein complex that keeps homologous chromosomes closely aligned through pachytene stage Mos Kinase a Component of the CSF o CSF Cytostatic Factor o Mos Kinase inhibits a kinase cascade that inhibits the APC Differentiation of Human Cells and Tissues o Rapid proliferation of embryonic cells differentiation tissues organs o 100 trillion cells in adult human body Classified into 20 different categories based on structure and function Cell Types are determined during Embryonic Development o Cellular differentiation must occur at right time and place within embryo o Must have coordination between cell cycle regulation mRNA transcription and protein synthesis o Once differentiated most cells will maintain a G0 arrest regardless of their location or environment o Radical de differentiation is very unusual but modulations of a differentiated state can occur depending in environmental cues Usually requires alternate protein synthesis Cells in Different Tissues have Different Fates o Some cells never reproduce and cannot be replaced if they are lost E g nerve cells heart muscle cells eye lens cells o Most cells are continually dying and must be replaced Some cells are replaced by duplication of already differentiated G0 cells E g epithelial cells of liver endothelial cells of blood vessels skin fibroblasts wound repair Some cells are replaced by differentiation of stem cells E g gut epithelial cells blood cells Properties of Stem Cells o Defining properties of stem cells 1 It is not terminally differentiated 2 Proliferation It can divide without limit for lifetime of host 3 Each daughter cell has a choice A remain a stem cell self renewal B undergoes irreversible terminal differentiation Pluripotent Stem Cells o Pluripotent stem cells Can differentiate into wide variety of cells Embryonic stem cells have the broadest differentiative capacity Embryonic Stem Cells in Therapeutic Cloning o Nucleus from patients somatic cell is transferred to enucleated egg o Embryonic stem cells from this early embryo can be differentiated into desired cell type and put back into patient o This type of transplant avoids complications associated with immune system rejection