Cell Cycle

1
Cell Cycle
2
The Cell Cycle in Somatic Cells

• Sequence of growth and division
• Consists of interphase and the mitotic phase
• Produces 2 cells that are identical

3
(No Transcript)
4
Interphase Stage of Cell Cycle

• During interphase the cell carries on every life
  process except division.
• Metabolic reactions, increase in the number of
  organelles, DNA replication, protein synthesis,
  etc.
• Longest phase of cell cycle
• Interphase is made up of 3 phases
• G1 cytoplasmic growth
• S replication of chromosomes (DNA)
• G2 cytoplasmic growth

5
Replication of Chromosomes

• Doubling of genetic material during interphase.
  (S phase)
• DNA molecules unzip
• Semiconservative
• 2 complete identical DNA molecules formed

6
Chromosome number

• Human somatic cells contain 46 chromosomes or 23
  pairs of chromosomes
• The two chromosomes that make up a chromosome
  pair are called homologous chromosomes or
  homologs.
• A cell with a full set of chromosomes is called a
  diploid cell (2N) body cell.
• A cell with only one chromosome from each pair is
  termed haploid (N) gamete or sex cell.

7
Interphase

• A cell in interphase shows a distinct nucleus and
  the absence of chromosomes.

8
CELL DIVISION

• Cell division is the process by which cells
  reproduce themselves.
• nuclear division (mitosis and meiosis)
• cytoplasmic division (cytokinesis).
• Cell division that results in an increase in body
  cells is called somatic cell division and
  involves a nuclear division called mitosis, plus
  cytokinesis.
• Cell division that results in the production of
  sperm and eggs is called reproductive cell
  division and consists of a nuclear division
  called meiosis plus cytokinesis.

9
Mitotic Phase

• Mitosis is the distribution of two sets of
  chromosomes, one set into each of two separate
  nuclei.
• Stages of mitosis are
• Prophase
• Metaphase
• Anaphase
• Telophase

10
(No Transcript)
11
Prophase

• During prophase, the chromatin condenses and
  shortens into chromosomes.
• Nuclear envelope and nucleoli disappear.
• Centrosomes move to opposite ends of cell.

12
Metaphase

• During metaphase, the chromosomes line up at the
  exact center of the mitotic spindle, a region
  called the metaphase plate.

13
Anaphase

• Anaphase is characterized by the splitting of
  centromere and the movement of the two sister
  chromatids of each pair toward opposite poles of
  the cell.

14
Telophase

• Telophase begins as soon as chromatid movement
  stops the chromosomes uncoil to form chromatin
  form, microtubules disappear or change form, a
  new nuclear envelope forms, and new nucleoli
  appear.

15
Cytoplasmic Division Cytokinesis

• Cytokinesis is the division of a parent cells
  cytoplasm and organelles. The process begins in
  late anaphase or early telophase with a pinching
  of the plasma membrane to form a cleavage furrow
  in animal cells.
• Plant cells form a cell plate between the two
  cells becoming the cell wall.

16
Reasons for mitosis

• Growth of organisms
• Development of embryos
• Asexual reproduction
• Binary fission in bacteria (prokaryotes) p. 18

17
Control of Cell Destiny

• Cell death, a process called apoptosis, is
  triggered either from outside the cell or from
  inside the cell due to a cell-suicide gene.
• Necrosis is a pathological cell death due to
  injury.
• Tumor-suppressor genes can produce proteins that
  normally inhibit cell division
• The damage of this gene can result in the
  uncontrollable cell growth known as cancer.