Transcript 07 Cell Division lesson

Cell Division:
Cell Division:
why?
cells wear out & must be replaced
organisms grow & so need more cells
when?
cells have different life spans
Cell type
Cell life span
Stomach lining cells
Sperm cells
Platelets
Skin epidermal cells
days
weeks
Lymphocytes
Red blood cells
months
Macrophages
Pancreas cells
Bone Cells
years
Cell Cycle:
The process of a cell growing
and preparing for cell division
Phases of the Cell Cycle:
G1 - (Growth Phase 1)
cell grows larger
cell organelles duplicate
S - (Synthesis Phase)
the DNA is duplicated
G2 – (Growth Phase 2)
the DNA is checked for errors
cell is prepared for division
M – Phase  Mitosis
a process to separate the DNA
packaged in chromosomes
into two identical cells
Terms
chromatin  a mixture of DNA and proteins found
in the interphase nucleus
chromosome  condensed chromatin
chromatid  one arm of a
double-stranded chromosome
centromere a structure that holds
two sister chromatids together
single-stranded chromosome
 a chromatid after it has been separated from
its sister chromatid
chromosome
centromere
chromatids
Summary of the Phases of Mitosis:
Prophase  prepare
Metaphase  middle
Anaphase  separate
Telophase  finish
Interphase  between
Prophase
cell membrane
cytoplasm
1. Chromosomes condense &
become visible
2. Nuclear membrane
breaks down
3. Spindle fibres connect the
two centrioles
4. Centrioles separate & move
to each pole of cell
Metaphase
1. the centrioles are at the poles
2. the spindle fibres pull the
centromeres into line
3. the double-stranded chromosomes
align at the cell equator
4. the centromeres now divide
Anaphase
1. the spindle fibres contract & pull the
centromeres to the poles
2. the chromatids of the
double-stranded chromosomes
now separate
3. Now called single-stranded
chromosomes they are pulled
to opposite poles
Telophase
1. the nuclear membrane reforms
2. the ss chromosomes now uncoil
and will disappear
Cytokinesis
3. The cell membrane pinches inward
4. The result is the separation of genetic
material into two identical parts
Interphase
1. The chromatin is uncoiled
2. The nuclear membrane
is fully intact
3. Two almost identical cells are
produced
4. The cell now starts to go
through G1, S and G2 again
Problems with mitosis
What if a cell does not stop dividing?
cancer
Why is this a problem?
cancer takes away things from normal cells
cancer takes space
cancer takes blood
this means oxygen
and nutrients
Now let’s look at mitosis under the microscope
After we learn some things about microscpes
key parts of a microscope
ocular lens
course
adjustment
fine
adjustment
objective lens
slide stage
Rules for microscopes
when on high power
only use the fine
adjustment to focus
on low power, focus
down and away from
the objective lens with
the course adjustment
always use two hands to carry a
microscope and do not swing it
these microscopes are parafocal and
so once they are in focus on low
power, little adjustment is needed on
medium or high power
only move a slide on or off a
microscope with it on low
power
Onion root tip
Cells undergo mitosis in
this section of the root tip