Transcript 5-3 “The Cell Cycle”

Chapter 5 Section 3
Cell Division
“The Cell Cycle”
The cell cycle is the regular sequence of
growth and division that cells undergo
One “parent” cell divides into two identical
“daughter” cells
The length of the cell cycle depends on the
type of cell. Some cells such as the human
brain cells, never divide.
The Cell Cycle-Stage 1: Interphase
Interphase is the period before cell division
occurs
The cell grows to its mature size, makes a
copy of its DNA, and prepares to divide
into two cells.
Growth
*during the 1st part of interphase, the cell
doubles in size and produces all the
structures needed to carry out its function
Stage 1: Interphase
Growth
*the cell enlarges its endoplasmic
reticulum, makes new ribosomes, and
produces enzymes. Both mitochondria
and chloroplasts make copies of
themselves. The cell matures and grows
to its full size.
Stage 1: Interphase
DNA Replication-The next part of interphase
*replication-the cell makes a copy of its nucleus in
this process
* DNA is a nucleic acid found in the chromatin in a
cell’s nucleus
* DNA is the genetic material that holds all the
information that a cell needs to carry out its
functions
*Each daughter cell must have a complete set of
DNA to survive
*At the end of DNA replication, the cell contains two
identical sets of DNA-one for each daughter cell
Interphase
Stage 2: Mitosis
Mitosis-the stage in which the cell’s
nucleus divides into two new nuclei.
During mitosis, one copy of DNA is
distributed into each of the two daughter
cells.
Mitosis is divided into 4 parts or phases:
Prophase, Metaphase, Anaphase, and
Telophase
Prophase
During this stage the chromatin in
the cell’s nucleus begins to
condense and coil, like fishing line
wrapping around a ball.
The condensed chromatin looks like
tiny rods which doubled during DNA
replication
Each double rod of condensed
chromatin is called a chromosome
Each rod/strand of the chromosome
is called a chromatid.
The two strands are held together by
a structure called a centromere
Prophase
Metaphase
Metaphase-the
chromosomes line up
across the center of
the cell. Each
chromosome attaches
to a spindle fiber at its
centromere, which
still holds the
chromatids together.
Metaphase
Anaphase
The centromere split
and the two
chromatids separate.
The chromatids move
along the spindle fiber
to opposite ends of
the cell
The cell becomes
stretched out as the
opposite ends pull
apart.
Anaphase
Telophase
The chromosomes
begin to stretch out
and lose their rod-like
appearance .
Occurs at the two
regions at the ends of
the cell.
A new nuclear
membrane forms
around each region of
chromosomes
Telophase
Stage 3: Cytokinesis
During cytokinesis, the
cytoplasm divides,
distributing the
organelles into each of
the two new cells.
Cytokinesis usually
starts about the same
time as telophase.
Cytokinesis
*Animal Cells -the cell membrane squeezes
together around the middle of the cell. The
cytoplasm pinches into two cells with about half
of the organelles in each daughter cell.
*Plant Cells – a plant cell’s rigid cell wall can’t
squeeze together, instead a structure called a
cell plate forms across the middle of the cell.
The cell plate gradually develops into new cell
membranes between the 2 daughter cells, then
new cell walls then form around the cell
membranes.
Cytokinesis
The Entire Cell Cycle
DNA Replication
Ensures that each daughter cell will have
all of the genetic information it needs to
carry out its activities.
James Watson and Francis Crick, figured
out the structure of DNA.
The Structure of DNA
DNA molecules look like a twisted ladder,
or spiral staircase.
Often called a “double helix”
The two sides of the DNA ladder are made
up of molecules of a sugar called
deoxyribose, alternating with molecules
known as phosphates.
The Structure of DNA
Each rung of the DNA ladder is made up of a
pair of molecules called nitrogen bases.
Four kinds of nitrogen bases: Adenine (A),
Thymine (T), Guanine (G) and Cytosine (C)
Adenine only pairs with Thymine
Guanine only pairs with Cytosine
The Structure of DNA
The Replication Process
DNA replication begins
when the two sides of a
DNA molecule unwind
and separates or “unzips”
between the paired
nitrogen bases on each
rung. New bases pair
with the base on each
strand. As a result, two
identical DNA molecules
form.