EUKARYOTIC CELL CYCLE.ppt (pharmacotherapeutics)

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Dr. Sarita Sharma

EUKARYOTIC CELL CYCLE

 Division cycle of most cells consists of four (4)
co-ordinated processes-
1. Cell growth
2. DNA replication
3. Distribution of duplicated chromosomes to
daughter cells
4. Cell division

 Eukaryotic cell cycle is more complex than
prokaryotic.
 Consists of overall 2 stages – mitosis (dividing stage) &
interphase (non-dividing or resting stage).
 Cells spend most of their life span in interphase  a
period of intense biosynthetic activity  cells double
in size & duplicate their chromosome.
 For some cells interphase is extremely prolonged
(circulating lymphocytes) or permanent (skeletal
muscle & nerve cells).

PHASES OF CELL CYCLE
 Four (4) discrete phases – M, G1, S, and G2.
 M - phase is usually followed by cytokinesis.
- M phase - mitosis
- G1 phase - interval (gap) between mitosis &
initiation of DNA replication
- S phase – synthesis of DNA
- G2 phase – 2nd gap between DNA synthesis &
initiation of mitosis
 For rapidly proliferating human cell of cycle time 24h-
* G1 – 11hrs, S – 8hrs, G2 – 4hrs, & M – 1hr.

EUKARYOTIC CELL CYCLE.ppt (pharmacotherapeutics)

 During G2 a cell contains two times (4n) the amount
of DNA present in the original diploid cell (2n).
 After mitosis the daughter cells again enter the G1
period and have a DNA content equivalent to 2n.

 Some cells divide occasionally to replace the dead
and injured cells, e.g, skin fibroblasts & cells of
some internal organs, such as liver.
 These cells exit G1 phase to enter a quiescent stage
of the cell cycle called G0.
 They remain metabolically active but no longer
proliferate unless called on to do so by appropriate
extracellular signals.

DETERMINATION OF CELLULAR DNA CONTENT
 More cells exist in the G1 phase with 2n DNA content
followed by cells in G2 phase with 4n DNA content.
 Cells in S phase have DNA contents between 2n & 4n
and are distributed between these two peaks.

CONDENSATION-DECONDENSATION
CYCLE OF CHROMOSOMES
 Eukaryotic chromosomes undergo condensation-
decondensation cycles at cell division.
 During interphase the chromosomes are
decondensed and cannot be distinguished under the
microscope.
 G1 chromosomes are completely dispersed; S-phase
duplication occurs; G2-condensation starts.
 At metaphase (M) and anaphase (A), the
condensation is maximal and the two centromeres
are clearly visible.

Condensation-decondensation cycle of chromosomes

The cell cycle is the process by which a cell grows and divides into two daughter cells. It consists of four main phases - G1 phase (cell growth), S phase (DNA replication), G2 phase (more cell growth), and M phase (mitosis and cytokinesis). In M phase, the cell divides into two identical daughter cells each with the same number and type of chromosomes as the original parent cell. The cell cycle allows for cell growth, replication, and replacement of old or damaged cells.

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EUKARYOTIC CELL CYCLE.ppt (pharmacotherapeutics)

1. EUKARYOTIC CELL CYCLE BY: DR SARITA SHARMA ASSOCIATE PROFESSOR DEPARTMENT OF PHARMACOLOGY MMCP, MMDU

2.  Division cycle of most cells consists of four (4) co-ordinated processes- 1. Cell growth 2. DNA replication 3. Distribution of duplicated chromosomes to daughter cells 4. Cell division

3.  Eukaryotic cell cycle is more complex than prokaryotic.  Consists of overall 2 stages – mitosis (dividing stage) & interphase (non-dividing or resting stage).  Cells spend most of their life span in interphase  a period of intense biosynthetic activity  cells double in size & duplicate their chromosome.  For some cells interphase is extremely prolonged (circulating lymphocytes) or permanent (skeletal muscle & nerve cells).

4. PHASES OF CELL CYCLE  Four (4) discrete phases – M, G1, S, and G2.  M - phase is usually followed by cytokinesis. - M phase - mitosis - G1 phase - interval (gap) between mitosis & initiation of DNA replication - S phase – synthesis of DNA - G2 phase – 2nd gap between DNA synthesis & initiation of mitosis  For rapidly proliferating human cell of cycle time 24h- * G1 – 11hrs, S – 8hrs, G2 – 4hrs, & M – 1hr.

6.  During G2 a cell contains two times (4n) the amount of DNA present in the original diploid cell (2n).  After mitosis the daughter cells again enter the G1 period and have a DNA content equivalent to 2n.

7.  Some cells divide occasionally to replace the dead and injured cells, e.g, skin fibroblasts & cells of some internal organs, such as liver.  These cells exit G1 phase to enter a quiescent stage of the cell cycle called G0.  They remain metabolically active but no longer proliferate unless called on to do so by appropriate extracellular signals.

8. DETERMINATION OF CELLULAR DNA CONTENT  More cells exist in the G1 phase with 2n DNA content followed by cells in G2 phase with 4n DNA content.  Cells in S phase have DNA contents between 2n & 4n and are distributed between these two peaks.

9. CONDENSATION-DECONDENSATION CYCLE OF CHROMOSOMES  Eukaryotic chromosomes undergo condensation- decondensation cycles at cell division.  During interphase the chromosomes are decondensed and cannot be distinguished under the microscope.  G1 chromosomes are completely dispersed; S-phase duplication occurs; G2-condensation starts.  At metaphase (M) and anaphase (A), the condensation is maximal and the two centromeres are clearly visible.

10. Condensation-decondensation cycle of chromosomes

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