Mitosis - isgroeducationNSW

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Transcript Mitosis - isgroeducationNSW

Patterns in Nature
Topic 17: Mitosis
Part of the Patterns in Nature Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Point(s)
 Identify mitosis as a process of nuclear division and explain
its role
 Explain the need for cytokinesis in cell division
 Identify that nuclei, mitochondria and chloroplasts contain
The Role of Mitosis
In multicellular organisms, cell division is a process that leads
to the formation of new cells that form part of the organism
and, as a result, contribute to the growth and repair of damaged
The Role of Mitosis
The role of mitosis in multicellular organisms can be
summarised as follows:
 Growth
 Repair of damaged tissue and replacement of worn out cells
 Genetic stability: mitosis ensures the precise and equal
distribution of chromosomes to each daughter nucleus, so
that all resulting cells contain the same number and kind of
chromosomes as each other and as the original parent.
 Asexual reproduction: growing plants from cuttings
The Process of Mitosis
Mitosis is a highly co-ordinated process ensuring that the
replicated chromosomes separate and are equally
distributed to the daughter cells. Scientists have identified
several distinct stages in the process. We’ll look at these
Step 1 Interphase:
DNA replicates and
become double
Step 2 Prophase:
The DNA coils up
and the double
become visible. The
surrounding the
nucleus begins to
break down.
Step 3 Metaphase:
The Chromosomes
line up across the
equator (middle) of
the cell and a
network of fibres
appear, extending
from the poles of the
cell to each
Step 4 Anaphase:
The chromatids
separate to become
two independent
chromosomes. The
network of fibres
contracts, pulling the
chromosomes in
opposite directions.
Step 5 Telophase:
A nuclear membrane
encloses the
chromosomes and
two nuclei form, each
with the diploid
number of
Step 6 Cytokinesis:
The cytoplasm divides
and the result is two
identical daughter cells.
These cells grow in size
in preparation for the
next round of cell
The outcome at the end of mitosis and cytokinesis is two
daughter cells that have the identical chromosomes to
each other and to the original parent cell.
When the cytoplasm divides, the organelles such as
mitochondria and chloroplasts are distributed to the
daughter cells in approximately equal numbers.
It is then necessary for the organelles in the cytoplasm to
replicate so that they are not reduced in quantity.
Mitochondria and chloroplasts contain their own small
amounts of DNA and so they are able to replicate
By the time the daughter cells have grown to the size of
the original parent cell, they have a similar number or
organelles as the original cell had.