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.

1. CELL CYCLE
Dr. M.Sankareswaran
Department of Microbiology

2. 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

3. CELL
 Cell is the basic structural, functional and biological
unit of all known living organisms
 Often called as building blocks of life.

4. 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

5. 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)

7. 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

8. 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

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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

16. 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.”

17. 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.

18. 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

19. 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.

20. 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.