L2 pdf.pdf

L2 Cell cycle, mitosis and their regulation Dr. Preetha J Shetty Associate Professor Biomedical Sciences September 3, 2019 www.gmu.ac.ae...

L2 Cell cycle, mitosis and their regulation Dr. Preetha J Shetty Associate Professor Biomedical Sciences September 3, 2019 www.gmu.ac.ae COLLEGE OF MEDICINE Learning Objectives At the end of this lecture, students will be able to Identify the phases of the eukaryotic cell cycle; Outline the phases of mitosis; Explain how the cell cycle is controlled. Cell Cycle A cell cycle is a series of events that a cell passes through from the time until it reproduces its replica. In prokaryotic cells, the cell cycle occurs via a process termed binary fission. In eukaryotic cells, the cell cycle can be divided in two periods- a) interphase b) mitosis  The Cell Cycle The cell cycle is divided into two halves Interphase - period of the cell cycle between cell divisions M phase – period of time when mitosis and cell division occurs  Parts of Interphase G1 Phase Growing Synthesize new proteins and organelles Doing their jobs Longest phase of cell cycle S Phase Chromosomes(DNA) are replicated Key proteins associated with replication are made (centromeres) G2 Phase Shortest of the 3 phases of interphase Organelles and molecules for cell division are produced (centrioles) Check-up phase before mitosis  Checkpoints A checkpoint in the cell cycle is a critical control point where stop and go signals regulate the cycle. 3 major checkpoints are found in the G1, G2, and M phases Regulation of the cell cycle Cell cycle checkpoints How do cells know when to divide and when not to? Cell Cycle Regulation The Cell Cycle Is Regulated by Protein Kinases. The mechanism regulating the progression of cells through their division cycle is highly conserved in evolution, and plants have retained the basic components of this mechanism. The key enzymes that control the transitions between the different states of the cell cycle, and the entry of nondividing cells into the cell cycle, are the cyclin- dependent protein kinases, or CDKs Internal regulators (proteins that respond to events inside the cell) Cdk (cyclin dependent kinase, adds phosphate to a protein), along with cyclins, are major control switches for the cell cycle, causing the cell to move from G1 to S or G2 to M. MPF (Maturation Promoting Factor) includes the CdK and cyclins that triggers progression through the cell cycle p53 is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is severe this protein can cause apoptosis (cell death). p27 is a protein that binds to cyclin and cdk blocking entry into S phase. Cyclins G2 Checkpoint G2 checkpoints controlled by Maturation promoting factor (MPF) Active MPF = Mitotic CDK + Mitotic Cyclin MPF controls G2 M by phosphorylating and activating proteins involved in: G1 Checkpoint G1 checkpoint is controlled by G1 Cdks-cyclin G1 cyclin levels also vary with the cell cycle Many additional levels of phosphorylation, dephosphorylation regulate. Cyclin-dependent kinases(CDKs) Cell division is a vital process that requires orderly progression. Endogenous hormones such as auxin, cytokinins, abscisic acid, gibberellins and brassinosteroids as well as environmental factors all regulate progression through the cell cycle. Cell cycle events take place with clock-like precision. Recent studies have demonstrated that cell cycles in plants and animals are regulated by similar mechanisms. A group of highly conserved serine/threonine kinases called cyclin-dependent kinases(CDKs) has been found to play a key role in guiding the cell cycle process. Cyclins Four classes of cyclins : 1. G1-cyclins — help to promote passage through “ Start” or the restriction point in late G1 2. G1/S-cyclins — bind Cdks at the end of G1 and commit the cell to DNA replication 3. S-cyclins – binds Cdks during S phase and are required for the initiation of DNA replication 4. M-cyclins — promote the events of mitosis  External Regulators External regulators - Proteins that respond to events outside the cell are called external regulators. External regulators direct cells to speed up or slow down the cell cycle. Growth factors are among the most important external regulators, which tell cells to speed up division. When is this important? Molecules found on the surfaces of neighboring cells often have an opposite effect, causing cells to slow down or stop their cell cycles. Uncontrolled Cell Growth Cancer cell The common thread in all cancers is that control over the cell cycle has broken down. Over 50% of cancer cells have a defect in the p53 gene. Mitosis Prophase Metaphase Anaphase Telophase Mitosis - Interphase  Prophase Chromatin condenses into chromosomes. Nucleoli and nuclear envelope break down. Spindle fibers grow from centrioles Centrioles migrate to opposite poles of cell. Mitosis- Metaphase Mitosis- Anaphase Mitosis- Telophase  Cytokinesis Cytoplasmic division and other changes exclusive of nuclear division that are a part of mitosis or meiosis.  1. The break down of a cell’s entire life is the _______ ________. 2. The phase of the cell cycle when the cell is growing, replicating DNA and getting ready for mitosis is _____________. 3. What are the four phases of Mitosis? 4. The process of a cell actually splitting in two is called _______________.