Chromosome Structure, Shape, composition and organisation | Video 1

Just before a eukaryotic cell divides, a number of threadlike structures called chromosomes gradually become visible in the nucleus. They are easily seen, because they stain intensely with particular stains. They were originally termed chromosomes because ‘chromo’ means coloured and ‘somes’ means bodies.
In eukaryotes, the genome consists of several double-stranded linear DNA molecules. Each species of eukaryotes has a characteristic number of chromosomes in the nuclei of its cells. Human body (somatic) cells have 46 chromosomes, while human gametes (sperm or eggs) have 23 chromosomes each. A typical body cell contains two matched or homologous sets of chromosomes (one set from each biological parent)—a configuration known as diploid. (Note: The letter n is used to represent a single set of chromosomes; therefore, a diploid organism is designated 2n.) Human cells that contain one set of chromosomes are called gametes, or sex cells; these are eggs and sperm, and are designated 1n, or haploid.
Upon fertilization, each gamete contributes one set of chromosomes, creating a diploid cell containing matched pairs of chromosomes called homologous (“same knowledge”) chromosomes. Homologous chromosomes are the same length and have specific nucleotide segments called genes in exactly the same location, or locus. Genes, the functional units of chromosomes, determine specific characteristics by coding for specific proteins. Traits are the variations of those characteristics. For example, hair color is a characteristic with traits that are blonde, brown, or black, and many colors in between.
Chemical Composition of Chromosome:
DNA — 40%
Histone (Protein) — 50%.
Non-Histone (Protein) — 10%
Structure of Chromosome

Chromosomal satellite- is the term given to that part of the end of a chromosome that is separated from the rest of the chromosome by a secondary constriction.
Telomeres- They function to protect the ends of chromosomes from sticking to each other. They also protect genetic information during cell division because a short piece of each chromosome is lost every time DNA is replicated. Cells use a special enzyme called telomerase to keep dividing, which lengthens their telomeres.
The primary constriction- refers to the region of the chromosome occupied by the centromere.
Kinetochore- A complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach.

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