Transcript Cell Division

The Cellular Basis of Inheritance
Repair and Growth
Reproduction
Asexual: process in which a single cell or
set of cells produces offspring that inherit all
their genetic material from one parent
 Sexual: process in which genetic material
from two parents combines and produces
offspring that differ genetically from either
parent

Chromatin
DNA is located in the nucleus
 In the nucleus, they are found on long,
thin fibers called Chromatin
– Chromatin consists of DNA wound
around proteins called histones
– Next the DNA is wrapped into a tight
helical formation

Chromosomes
When a cell is preparing to divide,
chromatin condense into chromosomes
 The human somatic cell (body cell) has
46 chromosomes = diploid
– An egg and sperm cell only has 23 =
haploid
 Each chromosome may contain
thousands of genes

Chromosomes
Before a cell divides, it replicates all of
its chromosomes
 Each chromosome now consists of 2
identical joined copies called sister
chromatids
 Each sister chromatid is joined by a
centromere

Chromosome
The Cell Cycle


Describes the process of cell division
Begins with interphase, followed by mitosis
and cytokinesis
Cell Cycle and Mitosis

The eukaryotic cell cycle is divided into two
major phases: interphase and cell division.
A. Interphase

Ninety percent or more of the cell cycle is
spent in interphase. During interphase,
cellular organelles double in number, the
DNA replicates, and protein synthesis
occurs. The chromosomes are not visible
and the DNA appears as uncoiled chromatin
Interphase
 Interphase
is divided into the
following stages:
– G1
S
– G2
–
G1 phase
 During
G1 phase, the period that
immediately follows cell division,
the cell grows and differentiates.
New organelles are made but the
chromosomes have not yet
replicated in preparation for cell
division.
S phase
 DNA
synthesis occurs during S
phase. The chromosomes
replicate in preparation for cell
division
G2 phase
During
G2 phase,
molecules that will be
required for cell replication
are synthesized.
Cell Division
 Cell
division consists of nuclear
division and cytoplasmic
division. Nuclear division is
referred to as mitosis while
cytoplasmic division is called
cytokenesis

Interphase in a plant
cell:

Interphase in an
animal cell
Mitosis (nuclear division)

Mitosis is the nuclear division process
in eukaryotic cells and ensures that
each daughter cell receives the same
number of chromosomes as the original
parent cell. Mitosis can be divided into
the following phases: prophase,
metaphase, anaphase, and telophase.
Prophase

During prophase, the chromatin
condenses and the chromosomes
become visible. Also the nucleolus
disappears, the nuclear membrane
fragments, and the spindle appartus
forms and attaches to the centromeres
of the chromosomes.
Prophase

Prophase in a
plant cell

Prophase in an
animal cell
Metaphase
 During
metaphase, the
nuclear membrane
fragmention is complete and
the duplicated
chromosomes line up
along the cell's equator.
Metaphase

Metaphase in a
plant cell

Metaphase in an
animal cell:
Anaphase

During anaphase, diploid sets of
daughter chromosomes separate and
are pushed and pulled toward
opposite poles of the cell. This is
accomplished by the polymerization
and depolymerization of the
microtubules that help to form the
spindle apparatus.
Anaphase

Anaphase in a
plant cell:

Anaphase in an
animal cell
Telophase
 During
telophase, the nuclear
membrane and nucleoli reform,
cytokinesis is nearly complete, and
the chromosomes eventually uncoil
to chromatin. Usually cytokinesis
occurs during telophase.
Telophase

Telophase in a
plant cell

Telophase in an
animal cell
Cytokinesis (cytoplasmic division)
 During
cytokinesis, the
dividing cell separates
into two diploid daughter
cells..
Cytokinesis (cytoplasmic division)

In animal cells, which lack a cell wall
and are surrounded only by a
cytoplasmic membrane,
microfilaments of actin and myosin
attached to the membrane form
constricting rings around the central
portion of the dividing cell and
eventually divide the cytoplasm into two
daughter cells
Cytokinesis (cytoplasmic division)

In the case of plant cells , which are
surrounded by a cell wall in addition to
the cytoplasmic membrane,
carbohydrate-filled vesicles
accumulate and fuse along the
equator of the cell forming a cell
plate that separates the cytoplasm into
two daughter cells.
Cytokinesis in plants vs. animal cells

In animal cells,
cytokinesis begins in
anaphase and
continues until the
cytoplasm has
completely divided
equally.
– Indentation is
caused by the
contraction of
microfilaments just
under the plasma
membrane

In plant cells, a disk
containing cell wall
material called a cell
plate forms inside
the cell and grows
outward
– Eventually the
cell wall divides
into 2
Mitosis
2
diploid cells are produced
 Somatic body cells
 Genetically identical cells
produced
Cancer

Caused by uncontrolled
cell reproduction
(mitosis) and severe
disruption of the
mechanisms that
control mitosis

These cells form a
mass called a tumor
–
Benign tumor: abnormal
mass of normal cells

Malignant tumor: abnormal mass of cancer
cells
–
–
–
Malignant tumor displaces the normal tissue as it
grows
If it is not removed, the cells can break off and
spread to other areas of the body via blood or
lymph
The spread of cancer cells beyond their original
site is called metastasis
Karyotype


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Typical human cell has 46 chromosomes
A display of the all 46 chromosomes is called
a karyotype
Each person has 2 twin chromosomes called
homologous chromosomes
–
Where do you think each came from?
Homologous chromosomes


Each homologous chromosome carries the
same sequence of genes controlling a
characteristic, but different versions
Example:
–

Eye color is located on the same place, but may
be different versions (blue, brown, hazel)
Different from sister chromatids because the
material is genetically different



Humans have 23 homologous pairs of
chromosomes
The 23rd pair are called sex chromosomes
All chromosomes look the same except for
the sex csomes
–
–
Males have XY
Females have XX
Meiosis

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Sexual reproduction that involves formation
of sex cells (Chromosome 23)
4 haploid cells are produced
Sex cells (gametes)
All 4 cells genetically different