Chapter 4 - Cell Replication
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Transcript Chapter 4 - Cell Replication
Chapter 4 - Cell Replication
Area of Study One
Pages 75-92
Chapter 4 - Cell Replication
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Reproduction of Cells
New cells are constantly being produced in
multicellular organisms.
In mammals, red blood cells, skin cells and
gut cells are constantly being produced to
replace the cells that have died.
Replacement cells are produced only by
reproduction of existing cells.
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Reproduction of Cells
Eukaryote cells have a nucleus, which contains the genetic
material deoxyribonucleic acid (DNA).
DNA is found in thread like structures called
chromosomes.
As cells reproduce, it is critical that the genetic material is
also reproduced so that any new cells produced have the
same amount of genetic material as the parent cell.
The process that ensures that the genetic material is
transmitted from one generation to the next as cells
reproduce is called mitosis.
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Reproduction of Cells
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Mitosis
Mitosis is a process of nuclear division in which
the replicated genetic material is separated and
two new nuclei are formed.
There 5 distinct phases of mitosis (IPMAT).
These include:
1.
2.
3.
4.
5.
Interphase
Prophase
Metaphase
Anaphase
Telophase
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Mitosis
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Mitosis
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Cytokinesis
Once the nuclei have reproduced and separated
from mitosis – the rest of the cell forms during a
process know as cytokinesis.
As the two new nuclei form at the end of mitosis,
the cytosol and organelles such as mitochondria
and chloroplasts, surround each nucleus and
cytokinesis begins.
‘Cytokinesis brings the curtain down on the cell
cycle; it is the final dramatic act in which one cell
becomes two.’
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Cytokinesis
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Chromosomes –
‘gene carriers’
Genetic instructions are present in the DNA in the nucleus
of each somatic cell.
Genes are organised into larger structures known as
chromosomes with each chromosome carrying a large
number of genes.
Each species has a characteristic number of chromosomes
in its somatic cells – For humans this number is 46.
This number is often denoted as ‘2n’ and is referred to as
the diploid number.
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Chromosomes –
‘gene carriers’
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Human Chromosomes
Chromosome images are organised according to an international
convention to form a karyotype.
The 46 human chromosomes in a human male can be arranged
into 23 pairs. These have 22 ‘matched’ pairs and one ‘odd’ pair
consisting of an X and Y chromosome (XY).
In a human female the odd matched sex chromosomes are those
of two X’s (XX).
A shorthand way of denoting this is:
Male – 46 XY
Female – 46 XX
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Human Chromosomes
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Human Chromosomes
The 22 matched pairs of chromosomes present in both
males and females are called ‘autosomes’. These can be
distinguished by:
Their relative size,
The position of the centromere (near the middle of the
chromosome),
Patterns of light and dark bands that result from special
staining techniques.
Autosomes are identified by the numbers 1 to 22 in order of
decreasing size.
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Human Chromosomes
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Control Mechanisms Can Fail
As seen earlier, when a cell reaches the end of its
cell cycle, a programmed death instruction known
as ‘apoptosis’ is given.
Sometimes a breakdown in the processes of
apoptosis or mitosis can occur, which causes
severe outcomes for the organism.
If too much apoptosis occurs – a degenerative
disease will develop as too many cells die (ie
Alzheimer’s Disease).
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Control Mechanisms Can Fail
If too much mitosis occurs –
there will be a formation of
too many cells and a
cancerous tumour will form.
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Chapter Review
Bio-Challenge Questions
Chapter Review Questions
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