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Uploaded byDr.M.SANKARESWARAN
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Cell cycle

El ciclo celular es una serie de eventos que una célula atraviesa desde su formación hasta su división, que incluye las fases de interfase y mitosis. La regulación del ciclo celular se realiza a través de puntos de control que utilizan señales químicas, garantizando que las células se dividan solo cuando sea apropiado. Este proceso es fundamental para el crecimiento celular y se aplica en áreas como el tratamiento del cáncer.

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CELL CYCLE Dr. M.Sankareswaran Department of Microbiology
Objectives and student outcome:  To learn about the cell growth and the phases of cell cycle and its regulations and check points. Purpose and benefits to the students:  The Purpose and the process to control the cell growth. Prior Assignment:  Index of Cell Cycle And Its Control Points Prerequisite And Prior Knowledge:  Cell Cycle Kinetics  Cyclin Control cell division
CELL  Cell is the basic structural, functional and biological unit of all known living organisms  Often called as building blocks of life.
CELL CYCLE  A cell cycle is a series of events that a cell passes through from the time until it reproduces its replica.  Howard and Pelc (1953) first time described it.  It is the growth and division of single cell into daughter cells and duplication (replication).  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
PHASES OF CELL CYCLE  It consists of 2 major activities.  INTER PHASE (90% of cell cycle) G1 (pre-synthetic phase) S (DNA synthesis) G2 (pre-mitotic phase)  CELL DIVISION (MITOTIC PHASE) (10% of cell cycle)
Interphase  It is the period between the end of one cell division to the beginning of next cell division.  It is also called resting phase or not dividing phase.  In this phase the cell becomes enlarged in size due to high growth rate.  It is the longest phase. In a typical human cell, out of the 90h, interphase lasts for 89h
Stages of Interphase  G1 phase/ Post mitotic/ Pre-DNA synthetic phase /First Gap  S-phase/ Synthetic phase  G2-phase/ Pre mitotic/ Post synthetic phase / Second Gap
G1 phase  The G1 phase follows mitosis and is the period in which the cell is synthesizing its structural proteins and enzymes to perform its functions.  In this phase, the cell increases in mass in preparation for cell division.
S phase  In S phase, the DNA within the nucleus replicates.  During this process, each chromosome is faithfully copied, so by the end of the S phase, two DNA molecules exist for each one formerly present in the G1 phase.  Human cells contain 92 chromosomes per cell in the S phase.  A regular cell cycle exists only for growing cells, the differentiated cells do not enter into S phase, stopped dividing and arrested in non-cycling state called G0 state (Quiscent phase). Eg: Neurons – animal nerve cells – do not divide.
G2 phase  In the G2 phase or Pre-mitotic phase - the cell prepares for mitosis.  The G2 phase is the gap period between S-phase and mitotic (M) phase of a cell cycle.  It is a period of rapid cell growth and protein synthesis which the cell ready itself for mitosis.  The nucleus increases in volume.  Metabolic activities essential for cell division, occur during this phase.
M-phase/Dividing phase/Mitotic phase  Mitosis is the distribution of the two sets of chromosomes into two separate and equal nuclei.  This is the division phase.  During this phase the cell divides. Nuclear division i.e. karyokinesis occurs in 4 phases – prophase, metaphase, anaphase and telophase.  This phase has a short duration.  A typical human cell cycle has duration of 90h. Of these the M phase has duration of 45 to 60min.
Duration of cell cycle  It depends on the type of cell and external factors such as temperature, food and oxygen.  Time period for G1, S, G2 and M-phase is species specific under specific environmental conditions.  Example: 20 minutes for bacterial cell, 8-10 hours for intestinal epithelial cell, and 20 hours for onion root tip cells.
The Cell Cycle Control System  The cell cycle control system is regulated by both internal and external controls  This cell cycle has specific checkpoints where the cell cycle stops until a go-ahead signal is received
Regulation of cell cycle  Organisms need to be able to stop cell division when the cell in question is damaged, or when there isn’t enough food to support new growth; they must also be able to start up cell division when growth or wound healing are needed.  The cells use a variety of chemical “signal cascades” that a single protein may change the function of many other protein. Example:  Cyclins and cyclin-dependent kinases – to act as “stop points.”
Cell Cycle Checkpoints  A checkpoint in the cell cycle is a critical control point where stop and go-ahead signals regulate the cycle.  Many signals registered at checkpoints come from cellular processes and sometimes the checkpoints register signals from outside the cell. Three main types of checkpointsare:  DNA damage checkpoint,  DNA replication checkpoint,  Spindle checkpoint.
Function of Cell Cycle  Cell cycle is important in cell growth and cell division.  If cells did not grow in between divisions, each generation of “daughter” cells would be only half the size of the parent generation.  In order to accomplish this growth and prepare for cell division, cells divide their metabolic activities into distinct phases of Gap 1, Synthesis, Gap 2 between cell divisions
Keywords:  Cell, Phases Of cell cycle, regulations, check points. Areas of application:  Cell division  Cell study in the treatment of cancer  Therapeutic applications Assessment and questions: 1.Define interphase 2.Explain cell cycle 3.Detail about the regulations and check points of cellcycle.
Post session assignment/ Closure:  Cell cycle  Cell cycle regulations  Cell cycle check points  Functions of cell cycle. References:  David R Hyde (2010). Genetics and Molecular biology. Special Indian edition, Tata Mc Graw Hill P.Ltd., New Delhi.  Ramawat and Shaily goyal (2010). Molecular biology and Biotechnology. First edition S.Chand & Co.Ltd., New Delhi.  Peter Paolella (2010). Introduction to Molecular Biology. First edition, Tata Mc Graw-Hill P. Ltd., New Delhi.  Mahabal Ram (2010). Fundamentals of Cytogentics and Genetics. First edition, PHI Learning P.Ltd., New Delhi.  Ajoy Paul (2007). Text Book of Cell and Molecular Biology. First edition, Books Allied (P) Ltd., Kolkata.  Peter Snustad D and Michael J Simmons (2003). Principles of Genetics. Third edition, John Wiley and Sons, Inc. publication, New Delhi.
Cell cycle