CHROMOSOMESuuu
A chromosome is a structure of DNA, protein, and RNA found in cells. It is a single piece of coiled DNA containing manygenes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. Chromosomal DNA encodes most or all of an organism's genetic information; some species also contain plasmids or other extrachromosomal genetic elements.
Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 100,000 to over 3,750,000,000[1][2] Nucleotides in a long chain. Typically, eukaryotic cells (cells with nuclei) have large linear chromosomes and Prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Cells may contain more than one type of chromosome; for example,mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through thecell cycle. Chromosomes are even more condensed than chromatin and are an essential unit for cellular division. Chromosomes must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated. Unduplicated chromosomes are single linear strands, whereas duplicated chromosomes contain two identical copies joined by a Centromere.
Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right) if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends. Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergomitotic catastrophe and die, or it may unexpectedly evade apoptosis leading to the progression of cancer. JCDIQBAL@GMAIL.COM
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