Structure of a chromosome
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Introduction-chromosomes
• Rod shaped structures
• Each consists of 2 sister chromatids
• These are joined together at the primary constriction or centromere
• This area is narrower and pale staining
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Introduction
• Each chromosome is a DNA – protein complex.
• It acts as a vehicle of heredity enabling transmission of genetic
material from one generation to another
• It is capable of self replication. Therefore enable reproduction and
maintenance of species
• The DNA within the chromosome is coiled many times over
• Length of human chromosome is 1/2mm but the total length of the
DNA within the chromosome is about 174cms
• Therefore, it is folded 10,000 times
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Orders of DNA coiling
• Primary coiling is the DNA double helix
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• Secondary coiling is when the double helix is wound around histone
beads. This is called nucleosomes
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• Tertiary coiling is when the nucleosomes are further wound about
themselves to form to form chromatin fibers. There are 6-7
nucleosomes in each turn
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• Quartenary coiling is when the chromatin fibers form loops or
domains surrounding a protein matrix or scaffold
• These loops are further tightly coiled to form the Solenoid Model of
the Chromosome
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