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
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New cells are constantly being produced in
multicellular organisms.
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In mammals, red blood cells, skin cells and
gut cells are constantly being produced to
replace the cells that have died.
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Replacement cells are produced only by
reproduction of existing cells.
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Reproduction of Cells
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Eukaryote cells have a nucleus, which contains the genetic
material deoxyribonucleic acid (DNA).
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DNA is found in thread like structures called
chromosomes.
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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.
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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
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Mitosis is a process of nuclear division in which
the replicated genetic material is separated and
two new nuclei are formed.
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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
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Once the nuclei have reproduced and separated
from mitosis – the rest of the cell forms during a
process know as cytokinesis.
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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.
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‘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’
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Genetic instructions are present in the DNA in the nucleus
of each somatic cell.
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Genes are organised into larger structures known as
chromosomes with each chromosome carrying a large
number of genes.
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Each species has a characteristic number of chromosomes
in its somatic cells – For humans this number is 46.
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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
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Chromosome images are organised according to an international
convention to form a karyotype.
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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).
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In a human female the odd matched sex chromosomes are those
of two X’s (XX).
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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
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The 22 matched pairs of chromosomes present in both
males and females are called ‘autosomes’. These can be
distinguished by:
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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.
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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
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As seen earlier, when a cell reaches the end of its
cell cycle, a programmed death instruction known
as ‘apoptosis’ is given.
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Sometimes a breakdown in the processes of
apoptosis or mitosis can occur, which causes
severe outcomes for the organism.
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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
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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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