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Overview of Cell Cycle and Division
Sep 10, 2024
Cell Cycle and Cell Division Lecture
Introduction
Definition of
Cell Cycle
: Self-regulated sequence of events for cell growth and division into two daughter cells.
Continuous process: Cells divide and daughter cells begin the cycle again.
Major Phases of the Cell Cycle
Interphase
Definition
: Period between two successive cell divisions.
Function: Cell growth and replication of genetic material.
Sub-phases of Interphase
:
G1 Phase (Gap 1)
:
Occurs immediately after cell division.
Cell growth and nutrient accumulation.
Preparation of DNA replication machinery.
Critical for successful cell division; defects can lead to cancer.
S Phase (Synthesis)
:
DNA replication occurs, doubling genetic material.
Formation of chromatids for each chromosome.
Checkpoints for DNA integrity and repairs.
G2 Phase (Gap 2)
:
Follows DNA replication.
Continued cell growth and organelle reorganization.
Centrioles formation crucial for cell division.
M Phase (Mitotic Phase)
Definition
: Period of actual cell division.
Includes nuclear and cytoplasmic division.
Stages of Mitosis
:
Prophase
:
Condensation of genetic material into visible chromosomes.
Disintegration of nuclear envelope.
Movement of microtubules and centrioles.
Metaphase
:
Chromosomes align at the cell equator.
Ideal for karyotyping.
Anaphase
:
Separation of sister chromatids to opposite poles.
Telophase
:
Cytoplasmic division.
Reconstitution of nuclear envelope.
Importance of Mitosis
Increases cell number rapidly (e.g., blood cells).
Growth and development of organisms and organs.
Repair and replacement of worn-out tissues.
Maintains genetic consistency—daughter cells identical to parent cell.
Meiosis
Occurs only in germ cells (sperm and oocytes).
Involves two phases:
Meiosis I
and
Meiosis II
.
Meiosis I
: Separation of homologous chromosomes, reducing chromosome number to haploid (23 chromosomes).
Meiosis II
: Similar to mitosis but with haploid cells.
Purpose
:
Achieves haploidy for fertilization, restoring diploid state in offspring.
Genetic variation through crossing over.
Cells in G0 Phase
Description
: Cells that have exited the cycle, lost division capacity.
Termed as "quiescent" stage or terminal differentiation.
Examples: Mature red blood cells, skeletal muscle cells, most neurons, many cardiac muscle cells, osteocytes.
Conclusion
The lecture covered the cell cycle's role in growth, division, and maintaining genetic integrity.
Importance of mitosis and meiosis in cell proliferation, organism development, and genetic consistency and variation.
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