Cell Growth & Division PDF

Cell Growth and Division Dr Humaira Khan [email protected]  Session Aims By the end of today’s lecture, you should be able to: ✓ Understand the significance of cell growth and division ✓ Describe the stages of the cell cycle ✓ Explain the process of DNA...

Cell Growth and Division Dr Humaira Khan [email protected]  Session Aims By the end of today’s lecture, you should be able to: ✓ Understand the significance of cell growth and division ✓ Describe the stages of the cell cycle ✓ Explain the process of DNA replication ✓ Understand the significance of cell senescence and apoptosis ✓ Describe the signals which induce somatic cell division ✓ Look at cell cycle disruption and its pathological implications  Self-Directed Study ✓ Lecture slides and notes- annotate effectively ✓ Core textbooks ✓ Additional sources of information- Review articles, Governmental citations (Cancer Research UK, National Cancer Institute, WHO) 3  Cell Division ▪The cell cycle is the orderly sequence of events required for the duplication of a eukaryotic cell into two genetically identical daughter cells. ▪The cell undergoes nuclear division (mitosis) and a cytoplasmic division (cytokinesis) ▪Essential process to replace dead/injured cells from wear & tear, stress, chemical damage and adds new ones in tissue growth ▪A human being goes from 1 cell to around 75 trillion  Cell Division is tightly controlled Cell division must be a controlled sequence of events Cells have a finite number of divisions Controlled by activation of ‘suicide genes’ Between 50 and 70 billion cells die each day due to apoptosis in the average human adult **There must be a delicate balance between cell division and cell death**  Cell Growth vs Cell Death ATROPHY- tissue waste away as a result of the degeneration of cells. DYSPLASIA- the presence of additional cells of an abnormal type within a tissue, which may signify a stage preceding the development of cancer. HYPERPLASIA- the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells, often as an initial stage in the development of cancer  Cell Division- Mitosis Cells must first replicate all their homologous (same relation, relative position or structure) chromosomes Cell replication has 2 main stages: ✓ Interphase (when the cell is not dividing) ✓ The mitotic (M) phase when a cell is dividing  Interphase ▪ It is the phase between two successive mitotic divisions ▪ During this phase the cell grows and prepares itself for division ▪ Subdivided into – *G1 phase- Gap 1 or presynthesis stage – S phase and- synthesis stage – *G2 phase- Gap 2 or postsynthesis stage ▪ Busiest time in the cell cycle; longest ▪ *important checkpoints here ▪ Most cells only spend a small amount of time dividing ▪ An interphase cell in G0 is not dividing or preparing to divide e.g. neurons  G1 phase- initiation stage ✓ Cells do not pass G1 without growth factors ✓ Strictly controlled; one of the important check points ✓ Lasts for about 8-10 hours of a 24 hour ✓ cycle ✓ High rate of metabolism, protein synthesis and growth ✓ Duplicates most organelles  S phase- DNA replication ✓ Lasts for about 8 hours ✓ DNA replicates ✓ Precise and accurate DNA replication is necessary to prevent genetic abnormalities which often lead to cell death or disease.  G2 Phase ✓ It lasts for 4-6 hours ✓ Synthesis of enzymes and proteins essential for cell division ✓ Replication of centrioles completed (form the spindle apparatus associated with the movement of DNA) http://essayweb.net/biology/images/celldivision/interphase.png  Mitotic phase Characterised by: – Karyokinesis: Division of nucleus and – Cytokinesis: Division of cytoplasm It is a continuous process but for the sake of convenience is described in four phases. – Prophase – Metaphase – Anaphase and – Telophase LASTS