Download Cell Division - Mrs. Hayden, Science

Cell Cycle
1
What will we be talking
about for the next few
days?
CELL CYCLE
• Cells like people also
go through stages
which we call the CELL
CYCLE.
• During this cycle, cells
grow and mature until
they divide in half and
become two new cells.
• Unlike our life cycle,
the cell cycle happens
over and over again.
Picture from: http://www.smartdraw.com/examples/sciencebiochem/interphase_and_mitosis.htm
2
Our Focus
• Interphase is the longest stage of the cell cycle.
During this stage the cell grows and matures
and functions as a “normal, everyday” cell.
• We will focus on the last two stages of the cell
cycle: Mitosis and Cytokinesis.
• Mitosis is a short, but important, part of the cell
cycle because during this stage the cell creates
two copies of its control center, the nucleus.
• Cytokinesis is a process that actually splits the
cell into two halves.
3
Key Cell Terms You Need to Know
DNA: Deoxyribonucleic acid. The genetic
material that controls all the cell’s activities.
Also known as the building block of life.
Chromatin: The DNA contained in the cell’s
nucleus. DNA can be very loose and
unraveled or tightly wound.
Chromatid: condensed
Chromatin, and each identical
rod in a chromosome.
1 Chromatid & 1 Chromosome
Chromosome: two
double-rod structures
of condensed chromatin
connected by a centromere.
Picture from:
4
http://mywebpages.comcast.net/llpellegrini/meiosis.html
More new terms to know…
• Parent cell: A cell that has grown to the
proper size and is ready to divide.
• Daughter cells: Cells that have been
created as a result of cell division.
5
The Cell Cycle
• A single cell divides forming
2 cells.
• The 2 cells then divide and
form 4 cells, and so on.
• As you read this sentence,
many of the cells in your
body are undergoing cell
division!
6
The Cell Cycle
• The regular sequence of growth and division
that cells undergo is called the cell cycle.
There are 3 stages of the cell cycle:
Stage 1: Interphase: the cell grows, matures
and replicates (or copies) it’s DNA.
7
Stage 1: Interphase
• The period before cell division, and the
longest stage in a cells life.
• The cell grows to its mature size, makes a
copy of its DNA, and prepares to divide
into 2 cells.
Picture from:
http://mywebpages.comcast.net/llpellegrini/meiosis.html
8
During Interphase
• The cell makes a copy of the DNA in its nucleus in a
process called replication.
• The replication of DNA is very important, since each
daughter cell must have a complete set of DNA to
survive.
• At the end of DNA replication, the cell contains 2
identical sets of DNA.
• One set of DNA will eventually be distributed to each
daughter cell in the next stage of the cell cycle.
9
Stage 1: Interphase
• The cell grows and doubles in size.
Produces all the structures needed to
carry out its functions.
• Makes copies of all of the organelles, like
the ER, Mitochondria and chloroplasts
(only in a plant cell)
• The cell also produces structures it will
use to divide during the rest of the cell
cycle.
10
Stage 2:
Mitosis:
consists of 4
phases that
result in the
cell creating 2
copies of the
nucleus.
Picture from:
http://www.accessexcellence.org/R
C/VL/GG/mitosis.html
Almost 2
separate cells
11
Stage 2: Mitosis
• During mitosis, the cell’s nucleus divides
into 2 new nuclei.
• One copy of the DNA will be given to each
of the 2 new daughter cells that will be
formed during cytokinesis (end of the cell
cycle)
12
Phases of Mitosis
There are 4 phases of mitosis:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
To help remember, think P.M.A.T. or prometa-, ana-, telo13
Mitosis
• Prophase:
– The chromatin in the nucleus condenses to
form chromatids and then chromosomes.
– Spindle fibers form a bridge between the ends
of the cell.
– The nuclear membrane breaks down.
14
Mitosis
• Metaphase:
– Chromosomes line up across the center of the
cell.
– Each chromosome attaches to a spindle fiber
at its centromere.
15
Mitosis
• Anaphase:
– The centromeres split.
– The 2 chromatids separate from each
chromosome.
– Each chromatid moves to opposite ends of
the cell.
– The cell becomes stretched out as the
opposite ends pull apart.
16
Mitosis
• Telophase:
– The chromotids stretch out and lose their
rodlike shape.
– Occurs in the 2 regions at the ends (poles) of
the cell.
– A new nuclear membrane forms around each
region of the newly separated chromotids.
17
Stage 3: Cytokinesis
• The final stage of the cell cycle.
• Completes the process of cell division.
• The cytoplasm divides, distributing
organelles into each of the 2 new cells.
18
Cytokinesis
In animal cells:
• The cell membrane squeezes together
around the middle of the cell.
• The cytoplasm pinches into 2 cells with
half of the organelles in each daughter
cell.
19
Cytokinesis
In plant cells:
• The rigid cell wall cannot squeeze
together.
• So, instead, a cell plate forms across the
middle of the cell.
• The cell plate eventually develops into
new cell membranes between 2 daughter
cells.
• New cell walls form around the cell
membranes.
20
Cytokinesis
• The end of the cell cycle.
• 2 new cells have formed.
• Each daughter cell has the same number
of chromosomes as the original parent
cell.
• At the end of cytokinesis, each cell enters
interphase, and the cell cycle starts again.
21