Jun 10, 2010

Chromosomes - Their Organization

Chromosomes are structures made of DNA and proteins that carry genetic information in the form of genes. In eukaryotic cells, chromosomes are located in the nucleus and are visible during cell division.

The organization of chromosomes is hierarchical, with the DNA packaged into progressively smaller units:

DNA Double Helix: The basic unit of DNA is the double helix, which consists of two complementary strands of nucleotides.

Nucleosomes: The DNA is wrapped around histone proteins to form nucleosomes, which are the building blocks of chromatin. Nucleosomes help to compact the DNA and regulate gene expression.

Chromatin: The nucleosomes are further coiled and compacted into chromatin fibers, which are visible as light-staining regions in the nucleus.

Chromosome: The chromatin fibers are organized into discrete chromosomes, which are visible as distinct structures during cell division.

The number and shape of chromosomes vary between different organisms. For example, humans have 23 pairs of chromosomes, while dogs have 39 pairs. The shape of chromosomes can also vary, with some organisms having linear chromosomes and others having circular chromosomes.

During cell division, the chromosomes condense and become visible as distinct structures. This allows the cell to accurately divide the genetic material between the daughter cells. After cell division, the chromosomes decondense and return to their more relaxed chromatin state.

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