Cell Cycle

Page 1

CELL DIVISION

• The process by which a cell divides to form two new

cells

• Three types of cell division or cell reproduction in

organism

• Prokaryotes (bacteria)

— Binary fission

• Divides forming two new identical cells

 Eukaryotes

— Mitosis

• Cell or organism growth

• Replacement or repair of damaged cells

— Meiosis

• formation of sex cells, or gametes

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WHY DO CELLS DIVIDE?

• Cells divide for growth, development, repair of worn-out tissues

and reproduction

• To facilitate the exchange of materials

• To control DNA overloading

Page 3

PROKARYOTIC CELL DIVISION

1. Binary Fission

• Three (3) major steps;

• DNA Replication

DNA is copied resulting into two identical chromosomes

• Chromosome Segregation

Chromosomes separate and move towards ends (poles) of cell

• Cytokinesis (Separation)

Cytoplasm divides forming two (2) cells

• Each new daughter cell is Genetically Identical to parent cell

EUKARYOTIC CELL DIVISION

• Cell division that results in two daughter cells each having the same

number and kind of chromosomes as the parent cell

1. MITOSIS

• Two (2) main steps:

1. Mitosis

Fours steps; [Prophase>Metaphase>Anaphase>Telophase]

2. Cytokinesis

Cytoplasm divides forming two new daughter cells

• Each daughter cell is Genetically Identical to parent cell

• Cell division that results in four daughter cells

2. MEIOSIS

• Two (2) major steps:

1. Mitosis

Fours steps; [Prophase>Metaphase>Anaphase>Telophase]

2. Cytokinesis

Cytoplasm divides forming two new daughter cells

• Each daughter cell is NOT Genetically Identical to parent cell

Page 4

THE CELL CYCLE

• The sequence of events from the time a cell first arises as a result of cell division

until the time when that cell itself divides.

• Arise – Divide

• This consist of periods of;

• Growth and Development

• DNA Replication

• Preparation For Division

• Cell Division

• Cell after division begins a new cycle

- Consist of two(2) main

periods;

I. Interphase

II. Mitotic Phase

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CELL CYCLE - Interphase

• Interphase: period of growth and DNA

replication between cell divisions

• Three (3) phases:

• G1 Phase

‒ Cell increases in size

• S Phase

‒ Replication of DNA

‒ Two sister strands of DNA called chromatids

are produced

• G2 Phase

‒ Organelles double

‒ New cytoplasm forms

‒ All other structures needed for mitosis form

Page 6

CELL CYCLE – Mitotic Phase

• Mitotic phase is the stage when a cell divides

• Mitosis – the division of a single nucleus into two genetically

identical daughter nuclei

• This division involves two(2) processes;

‒ Division of the nucleus

‒ Separation of the cytoplasm and the new nuclei into daughter cells

• Divided into two (2) mitotic phases

• 1st MP contain four stages (P-MAT)

‒ Prophase, metaphase, anaphase and telophase

• 2nd MP is cytokinesis

Page 7

Mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

•P-MAT

Early Prophase:

• Chromatids condense becoming

chromosomes

• Nucleolus disappears

• Centrioles separate and start moving

to opposite ends of the cell

• Spindle begins to form

Late Prophase: • The nuclear membrane

fragments and the

microtubules invade the

nuclear area

• Centrioles have moved to the

opposite poles

• The spindle is completely

formed