The document discusses the eukaryotic cell cycle, detailing its phases (G1, S, G2, and M) and the types of cells involved (labile, stable, and permanent). It explains the process of mitosis and the stages within it (prophase, metaphase, anaphase, and telophase), as well as the significance of cell checkpoints and regulators like cyclins and cyclin-dependent kinases (cdks) in regulating cell division. The overview highlights the importance of these mechanisms for proper cellular function and division.

1. CELL CYCLE , CELL CHECKPOINTS , CELL CYCLE
REGULATORS –CYCLINS AND CDKS
PRESENTATION BY –SHIVALIKA (130) AND ANSHIKA (003,B.ED)

2. CELL CYCLE !!

3. EUKARYOTIC CELL
 Cells contain- Cell Membrane, Nucleus (DNA), Cytoplasm
 Type of cells on the basis of the division
 Labile (Proliferative cell)-
• Epithelium of skin
• GI, Urinary tract
• Hematopoietic Cell
 Stable Cells- ( Grow, when stimulus is there)
• Hematopoietic cells (Liver)
• Epithelium of kidney tubules
• Lungs Cells
 Permanent Cells (amitotic cells)-never go into mitosis
• Neurons
• Skeletal Muscle
• Cardiac Muscle

4.  Synthesis Phase (S phase)-
• DNA replication
• DNA Polymerase (I & III)
 Gap Phase -2 (G2)-
• Cell Growth
• Cytoplasm increases
 Interphase- G1,S & G2
 Gap Phase -1(G1)-
• Most of the cells reside in the G1 phase
• Make more organelles
• Synthesizing protein & Enzymes
• Repair Thymidine dimer (repair
process)
 Gap Phase 0(G0)-
• Terminal differentiation
• Cells are destined never to divide again
. Eg-nerve cells

5. MITOSIS
• The mitosis is a part of somatic cell division which includes
the division of the nucleus (called mitosis or karyokinesis)
and the division of the cytoplasm (called cytokinesis).
• Strasburger (1875), a German botanist, was the first to work
out the details of mitosis. Mitosis can be studied best in the
root tip and shoot tip of several plants. But the most
favourable material is the apices of onion roots.
• In mitosis, the metabolic nucleus passes through a
complicated system of changes in the form of four different
stages, viz., prophase, metaphase, anaphase and telophase.

6. PROPHASE
Prophase:
1. It is the first and the longest phase in the mitotic cell division.
2. Chromosomes become visible in the nucleus as short, thick, helically coiled
threads.
3. Each chromosome splits into two chromatids joined at the centromere.
4. Nuclear membrane starts dissolving.
5. Nucleolus also starts dissolving and disappearing.
6. Prophase changes into next stage called metaphase.
4. Chromosomes become shorter and thicker.

7. METAPHASE:
1.Nuclear membrane disintegrates and disappears completely.
2. Nucleolus disintegrates and disappears completely.
3. Spindle fibres start appearing and these fibres get attached to
chromosomes at centromeres.
4. Chromosomes become shorter and thicker.
5. Chromosomes arrange themselves in the center or on the equator of
spindle.
6. At the end of metaphase, two chromatids of each chromosome also start
separating.
7. Metaphase changes into the next stage called anaphase.

8. ANAPHASE
1. Chromatids separate from each other at centromere and called
daughter chromosomes.
2. Daughter chromosomes move to the opposite poles of the spindle.
3. Daughter chromosomes appear ‘V’, ‘U’ or J-shaped during their
movement towards poles.
4. Anaphase changes into the next stage called telophase.

9. TELOPHASE:
1. Daughter chromosomes are now at the end of the spindle, i.e., present on two opposite poles.
2. Nuclear membrane reforms around each group of daughter chromosomes.
3. Nucleolus reforms and two nuclei are thus organised, one at each pole of the parent cell.
4. Chromosomes begin to loose their compact structure.
5. Spindle fibres disappear gradually.
6. Thus formed two daughter nuclei are exactly similar to the parent nucleus.

10. MITOTIC PHASE

11. CELL CHECKPOINTS
 A checkpoint is a stage in the eukaryotic cell cycle at which the cell
examines internal and external cues and "decides" whether or not to move
forward with division.
 There are a number of checkpoints, but the three most important
ones are:
• The G1checkpoint, at the G1/S transition.
• The G2checkpoint, at the G2/M transition.
• The spindle checkpoint, at the transition from metaphase to
anaphase.

12. CELL CYCLE REGULATORS
 Cyclins
 Cyclins are among the most important core cell cycle regulators. Cyclins are a group of related proteins,
and there are four basic types found in humans and most other eukaryotes: G1 cyclins, G1/S cyclins, S
cyclins, and M cyclins.
 each cyclin is associated with a particular phase, transition, or set of phases in the cell cycle and helps drive the
events of that phase or period.
 G1 cyclins – cyclin D
 G1/s cyclins – cyclin E
 S cyclins – cyclin A
 M cyclins – B cyclin

14.  Cyclin-dependent kinases
 Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent
kinases (Cdks)
 A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify
target proteins.
 How does this work? Cdks are kinases, enzymes that phosphorylate (attach phosphate groups to) specific target
proteins. The attached phosphate group acts like a switch, making the target protein more or less active.