Chromosomes

A chromosome is an organized structure of DNA and proteins in cells. This is one piece spiral of DNA contains many genes, regulatory elements and other sequences of nucleotides. Chromosomes also contain DNA-bound proteins, which are used for packaging of DNA and control its functions. The chromosome comes from the Greek (chroma, color), (soma, body) due to their property to be strongly colored by certain dyes.

Chromosomes are highly variable among different organisms. The DNA molecule can be circular or linear and may be composed of 10,000 billion nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nucleus) smaller circular chromosomes, but there are many exceptions to this rule. In addition, cells can contain more than one type of chromosome, for example, in most eukaryotic mitochondria and chloroplasts in plants have their own small chromosome.


In eukaryotes, nuclear chromosomes are packaged by proteins in a structure called chromatin condensed. This allows very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies during the cell cycle. Chromosomes are the essential unity of cell division and must be replicated, divided, and successfully passed his daughter cells to ensure genetic diversity and survival of their offspring. Chromosomes may exist as duplicates or no duplicates, without duplicating the single-stranded chromosomes are linear, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a kinetochore. Compaction of the duplicated chromosomes during mitosis and meiosis in the results of the classical structure with four arms (see photo at right). chromosomal recombination plays a key role in genetic diversity. If such structures are handled incorrectly, through a process known as chromosomal instability and translocation.