Download Cell Cycle & Division

Mitosis
• The form of cell division by which a
eukaryotic somatic cell duplicates.
• Mitosis is asexual reproduction.
• Cell division is the continuation of life
based on the reproduction of cells.
Somatic Reproduction
• Most eukaryotic cells reproduce asexually by
mitosis.
• Somatic cells are all body cells (like nerve, liver,
etc...) except sperm and ova (egg).
• All Somatic cells have the same number of
chromosomes.
Cell Division
Cell Division:
• All cells are derived from
preexisting cells (Cell Theory)
• Cell division is the process by
which cells produce new cells
• Cell division differs in
prokaryotes (bacteria) and
eukaryotes (protists, fungi, plants,
& animals)
• Some tissues must be repaired
often such as the lining of gut,
white blood cells, skin cells with a
short lifespan
• Other cells do not divide at all
after birth such as muscle &
nerve
Reasons for Cell
Division:
• Cell growth
• Repair & replacement of
damaged cell parts
• Reproduction of the species
Copying DNA
• Since the instructions for
making cell parts are
encoded in the DNA, each
new cell must get a
complete set of the DNA
molecules
• This requires that the
DNA be copied
(replicated, duplicated)
before cell division
Chromosomes & Their Structure
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The plans for making cells are coded in DNA
DNA is a long thin molecule that stores genetic information
DNA is organized into giant molecules called chromosomes
Chromosomes are made of protein & a long, single, tightlycoiled DNA molecule visible only when the cell divides
When a cell is not dividing the DNA is less visible & is
called chromatin
DNA in eukaryotic cells wraps tightly around proteins called
histones to help pack the DNA during cell division
Centromeres hold duplicated chromosomes together before
they are separated in mitosis
When DNA makes copies of itself before cell division, each
half of the chromosome is called a sister chromatid
Chromosome Numbers
• Humans somatic or body cells • Human reproductive cells or
gametes (sperms & eggs) have
have 23 pairs of chromosomes
one set or 23 chromosomes
or 46 chromosomes (diploid or
(haploid or n number)
2n number)
• Every organism has a specific
• The 2 chromatids of a
chromosome number
chromosome pair are called
homologues (have genes for the
Organism
Chromosome
same trait at the same location)
Number (2n)
Human
46
Fruit fly
8
Lettuce
14
Goldfish
94
• Fertilization, is the joining
of the egg & sperm cell
• Sex chromosomes, either X or
Y, determine the sex of the
organism
• Two X chromosomes, XX,
will be female and XY will
be male
• All other chromosomes,
except X & Y, are called
autosomes
• Chromosomes from a cell
may be arranged in pairs by
size starting with the longest
pair and ending with the sex
chromosomes to make a
karyotype
• A human karyotype has 22
pairs of autosomes and 1 pair
of sex chromosomes (23 total)
Human Male Karyotype
Cell division in Prokaryotes
DNA of prokaryotes (bacteria) is one,
circular chromosome attached to the
inside of the cell membrane
• Prokaryotes divide into two identical new
cells by the process of binary fission
• Binary fission is an asexual method of
reproduction
Occurs in 3 steps:
 The chromosome, attached to cell
membrane, makes a copy of itself
 The cell grows to about twice its normal
size
 Next, a cell wall forms between the
chromosomes & the parent cell splits
into 2 new identical daughter cells
(clones)
Binary Fission
• Bacteria, cyanobacteria, and most single celled
organisms reproduce by binary fission.
bacteria
chromosome
plasma membrane
Asexual
Reproduction
Cell Cycle
S
phase
G1
interphase
Mitosis
-prophase
-metaphase
-anaphase
-telophase
G2
Cell Cycle:
• The phases of life of a cell are called THE CELL
CYCLE
• The cell cycle includes 2 main parts --- interphase
and cell division
• Cell division includes mitosis (nuclear division)
and cytokinesis (division of the cytoplasm)
• Interphase is the longest part of a cell's life cycle
and is called the "resting stage" because the cell
isn't dividing
• Interphase consists of 3 parts: G1, S, & G2 phases
Interphase
1. G1 (gap) phase:
 First growth stage
 Cell increases in size
 Cell prepares to copy its DNA
2. S phase:
 Copying of all of DNA’s instructions
 Chromosomes duplicated
3. G2 (gap) phase:
 Time between DNA synthesis & mitosis
 Cell continues growing
 Needed proteins produced
Cell Cycle
 Stages in growth &
division
 G1 Phase
 S Phase
 G2 Phase
 M Phase
 Cytokinesis
Cell Division in Eukaryotes:
• Eukaryotes have a nucleus & •
membrane-bound organelles
which must be copied exactly •
so the 2 new cells formed
from division will be exactly •
alike
• The original parent cell & 2
new daughter cells must have
identical chromosomes
• Both the nucleus (mitosis) and
the cytoplasm (cytokinesis)
must be divided during cell
division in eukaryotes
Stages of Mitosis:
Division of the nucleus or
mitosis occurs first
Mitosis is an asexual method of
reproduction
Mitosis consists of 4 stages --Prophase, Metaphase,
anaphase, & Telophase
Prophase
• Longest phase
• Nucleolus disappears
• Chromatin material condenses into chromosomes,
consisting of two sister chromatids.
• Centrioles move apart (not found in plants).
• Spindle fibers form and attach from
centrioles to centromeres by kinetochores.
• Nuclear envelope fragments and disappears.
Prophase
early prophase
late prophase
centrioles
spindle fibers
aster
fibers
nuclear envelope
disappearing
centromere
Metaphase
• Shortest phase
• Centrioles are at opposite ends of the cell and
attached with aster fibers.
• Chromosomes move to the metaphase plate
(equatorial plate - center of cell).
Metaphase
centrioles
aster
fibers
spindle fibers
metaphase plate
Anaphase
• Sister chromatids separate and move apart.
• After separation, chromatids are now considered
chromosomes.
• During this phase, the cell contains twice the
normal number of chromosomes.
• Cell begins to elongate.
• At the end, there are equal numbers of
chromosomes at the poles.
Anaphase
No longer sister chromatids, now chromosomes
aster
fibers
spindle fibers
centrioles
Telophase
• Nuclear membrane & nucleolus reappears.
• Chromosomes uncoil.
• In the end, two genetically identical nuclei are
present.
Telophase
cleavage furrow (cytokinesis)
nuclear membrane reforming
nucleolus reappears
Cytokinesis
• Cytoplasmic division
• Cleavage furrow develops
in animal cells
(Cytokinesis begins).
• Cell plate develops in
plants (no cleavage
furrows in plants).
• Nucleolus reappears.
cell plate
cell plate
Parent cell
Chromosomes are
copied and double
in number
Chromosomes
now split
2 daughter cells
identical to original
Question:
• A cell containing 20 chromosomes at the
beginning of mitosis would, at its completion,
produce cells containing how many chromosomes
each?
Answer:
• 20 chromosomes
• Cancer is Uncontrolled
Mitosis:
• Mitosis must be
controlled, otherwise
growth will occur
without limit (cancer)
• Control is by special
proteins produced by
oncogenes