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Lecture 10

BIOL 2P03 Lecture 10: Week 10 Screencast - The Eukaryotic Cell Cycle
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Department
Biology
Course
BIOL 2P03
Professor
Mark K Lukewich
Semester
Winter

Description
BIOL 2P03 Week 10 Scthencast – Thethukaryotic Cell Cycle March 20 – March 26 , 2017 Cell Division • Cell division refers to the creation of two daughter cells from one parent cell – Both daughter cells are identical to each other and to the parent cell • Cell division increases the number of cells in an organism – Required during growth and repair • Cell division is tightly regulated to prevent the overproduction of cells – Inadequate regulation can lead to diseases, such as cancer Cell Cycle • The term cell cycle refers to a series of stages that a cell progresses through before cell division can occur • The cell cycle consists of 4 sequential stages: – G 1 – S – G 2 – M G1 Phase • The purpose of the G p1ase is to prepare the cell for DNA replication • During the G 1hase, a cell will: – Grow in size – Synthesize mRNA and proteins required for DNA replication – Generate energy to fuel DNA replication • At the end of G1, the cell is committed to progress through the remainder of the cell cycle – Known as START S Phase • During the S (‘synthesis’) phase of the cell cycle, the parent cell’s DNA is replicated • Each chromosome is duplicated to produce 2 sister chromatids – Sister chromatids are held together by cohesins • Each chromosome contains a centromere – The centromere is the region where the kinetochore will form and microtubules will bind • The centrosome, which is a microtubule organizing centre, is also duplicated during S phase G2 Phase • During the G 2hase, the cell checks the newly replicated DNA for mistakes and attempts to repair them • At this point, the cell has finished duplicating its centrosome – One centrosome moves to each side of the cell to create 2 spindle poles • Microtubules grow from these centrosomes and attach to the kinetochores of the replicated chromosomes M Phase • During the G 2hase, the cell checks the newly replicated DNA for mistakes and attempts to repair them • At this point, the cell has finished duplicating its centrosome – One centrosome moves to each side of the cell to create 2 spindle poles • Microtubules grow from these centrosomes and attach to the kinetochores of the replicated chromosomes • Prophase – Chromosomes condense – Nuclear envelope retracts into the endoplasmic reticulum – Golgi breaks apart into vesicles – Microtubules form from each centrosome and extend toward the chromosomes • Creates the spindle poles – Kinetochore develops on each centromere – Microtubules attach to the kinetochore • Metapha se – Mic rot ubu les continue to develop until each chromosome is attached to two microtubules, one originating from each pole of the cell – The microtubules orient the chromosomes across the center of the cell • Anaphase – Cohesins present along the chromatids and within the centromere are degraded – Microtubules depolymerize to pull the sister chromatids towards the centrosomes – One chromatid from each pair is moved to each pole of the cell – This doubles the number of chromosomes in the cell • Telophase – Microtubules depolymerize – Chromosomes decondense – Nuclear envelope forms around each set of chromosomes at each pole • Cytokinesis divides the cell into 2 separate daughter cells G0 Phase • Some cells will exit the cell cycle a1 G and enter the0G phase • Postmitotic cells are cells in a multicellular organism that are unable to undergo cell division – These cells are typically highly differentiated • E.g. neurons in the brain – Postmitotic cells enter G a0d will remain there for the duration of their life • Some cells that are able to divide, will also enter0G for a portion of their lifespan – These cells can return to the cell cycle at a later time Regulation of Cell Cycle • Cell cycle is regulated by heterodimeric protein kinases that consist of: – A regulatory subunit known as cyclin – A catalytic subunit known as cyclin-dependent kinase (CDK) • Cyclin activates CDK and also determines which substrates CDK can phosphorylate • The amount of cyclin present in the cell changes throughout the cell cycle to regulate CDK activity • Mammalian cells express different isoforms of cyclins and CDKs – CDKs will only associate with one or a few cycl
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