CELL REPRODUCTION
THE CELL CYCLE
AND
MITOSIS
Lesson Objectives—Cell Cycle
• Describe the properties of cell division in prokaryotes.
• Describe cell division in eukaryotes. Explain the main
differences between cell division in prokaryotic and
eukaryotic cells.
• Describe the basic properties of chromosomes.
• Describe the key steps in the cell cycle.
• Identify and describe the main processes in mitosis.
• Describe how the cell cycle is controlled and define
cancer.
CELL REPRODUCTION
• Cell Division: process by which a cell divides to form
two new cells (daughter cells)
• Three types of cell division, or cell reproduction
– 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
Why do cells divide?
1: DNA Overload
– If cells grow without limit, an “information crisis”
would develop
– DNA cannot serve the needs of the increasing size of
cell
2: Exchange of materials
– Food and oxygen have to cross membrane very
quickly
– Waste must get out
– If cell is too large, this occurs too slowly and cell will
die
PROKARYOTIC CELL DIVISION
• Binary fission
– 3 main steps:
1: DNA Replication—DNA is copied, resulting in 2
identical chromosomes
2: Chromosome Segregation—2 chromosomes separate,
move towards ends (poles) of cell
3: Cytokinesis—cytoplasm divides, forming 2 cells
– Each new daughter cell is
genetically identical to parent cell
THE CELL CYCLE
G1 phase
M phase
S phase
G2 phase
CELL CYCLE-INTERPHASE
• Interphase: period of growth and DNA replication between
cell divisions
• Three phases:
– G1 Phase
• cell increases in size
– S Phase
• Replication of chromosomes
– Now two strands called sister chromatids joined by a centromere
– G2 Phase
• organelles double
• new cytoplasm forms
• All other structures needed for mitosis form
• DNA containing cell’s
genetic code
• Each chromosome has a
matching pair
-- Homologous Pair
• During interphase, each
chromosome copies
itself
EUKARYOTIC CELL DIVISION
• DNA found on chromosomes located in nucleus of cell
• Cell cycle continuous process
–
–
–
–
Cells grow
DNA replicated
Organelles duplicated
Divide to form daughter cells
– 2 Main steps:
1: Mitosis (4 steps—Prophase, Metaphase, Anaphase, Telophase)
Nucleus divides
2: Cytokinesis—Cytoplasm divide, forming 2 cells
Each new daughter cell is genetically identical to parent cell
• Mitosis = nuclear division
• Mitosis is followed by cytokinesis (cell division)
• The steps of mitosis ensure that each new cell
has the exact same number of chromosomes as
the original
MITOSIS
• Process that divides cell nucleus to produce two
new nuclei each with a complete set of
chromosomes
• Continuous process
• Four phases (PMAT)
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
•
•
•
•
(1)Prophase
(2)Metaphase
(3)Anaphase
(4)Telophase
Interphase
1
2
•PMAT
3
4
Cytokinesis
1. chromosomes visible (sister chromatids)
2. centrioles migrate to the poles (only in animals)
3. nuclear membrane disappears
4. spindle forms
1. chromosomes line up on the equator of the cell
2. spindles attach to centromeres
Equator
1. sister chromatids separate
2. centromeres divide
3. sister chromatids move to opposite poles
1. chromosomes uncoil • now chromatin
2. nuclear membranes reform
3. spindle disappears
-Occurs at end of Mitosis
--division of the cytoplasm to form 2 new daughter
cells
--organelles are divided
-Daughter cells are genetically identical
Cells return to interphase
Mitosis
1.Name the phases
starting at the top.
2.Name the phase
3.Identify X
4.Identify Y
5. Name the
phase
6. Name the
phase
Control of the Cell Cycle
• Regulatory proteins called cyclins control the cell
cycle at checkpoints:
• G1 Checkpoint—decides whether or not cell will
divide
• S Checkpoint—determines if DNA has been
properly replicated
• Mitotic Spindle Checkpoint—ensures
chromosomes are aligned at mitotic plate
Cell Cycle Checkpoints
CANCER CELLS
• Result of uncontrolled cell division of cells that
have lost ability to regulate cell cycle
• Reproduce more rapidly than normal cells
• Masses formed called ‘tumors’
Lesson Summary—Cell Cycle
• The cell cycle is a repeating series of events, characterizing the life of a eukaryotic cell.
• Binary fission is a form of cell division in prokaryotic organisms that produces identical
offspring.
• As a eukaryotic cell prepares to divide, the DNA and associated proteins coil into a
structure, known as a chromosome.
• The DNA copies during the S phase of the cell cycle, resulting in a chromosome that
consists of two identical chromatids, known as sister chromatids, attached at a region
called the centromere.
• Any cell containing two sets of chromosomes is said to be diploid; the zygote forms
from the fusion of two haploid gametes.
• The cell cycle has five phases: the first growth (G1) phase, the synthesis (S) phase,
the second growth (G2) phase, mitosis, and cytokinesis.
• Mitosis is the division of the nucleus; four distinct phases of mitosis have been
recognized: prophase, metaphase, anaphase, and telophase.
• Cytokinesis is the division of the cytoplasm.
• The cell cycle is controlled through feedback mechanisms.
• Cancer results from uncontrolled cell division, due to the loss of regulation of the cell
cycle.