Related topics: genes , genome , y chromosome , protein , cells
Chromosome
hideA chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes. Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000 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. Furthermore, 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 the cell cycle. Chromosomes are the essential unit for cellular division and 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 (copied during synthesis phase) contain two 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). 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 undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.
However, in practice "chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
For more information about Chromosome, read the full article at
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News tagged with chromosomes
Longevity tied to genes that preserve tips of chromosomes
Nov 11, 2009 |
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A team led by researchers at Albert Einstein College of Medicine of Yeshiva University has found a clear link between living to 100 and inheriting a hyperactive version of an enzyme that rebuilds telomeres - the tip ends ...
Male sex chromosome losing genes by rapid evolution, study reveals
Jul 17, 2009 |
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Scientists have long suspected that the sex chromosome that only males carry is deteriorating and could disappear entirely within a few million years, but until now, no one has understood the evolutionary ...
Two from one: new research maps out evolution of genders from hermaphroditic ancestors
Biology /
Nov 20, 2008 |
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Research from the University of Pittsburgh published in the Nov. 20 edition of Heredity could finally provide evidence of the first stages of the evolution of separate sexes, a theory that holds that males and females develo ...
Down Syndrome becoming more prevalent in the U.S.
Dec 02, 2009 |
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(PhysOrg.com) -- A new study, aimed at estimating the prevalence of Down Syndrome in newborns, children and teenagers in 10 areas of the U.S., has found an increase in prevalence of more than 30 percent over ...
Panda genome resembles dog: Chinese media
Dec 13, 2009 |
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A detailed genome map of the giant panda completed by Chinese scientists has shown that the notoriously shy animal is genetically similar to the dog, state media reported Sunday.
US trio win Nobel Medicine Prize for research into ageing (Update 3)
Oct 05, 2009 |
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Australian-American researcher Elizabeth Blackburn and Carol Greider and Jack Szostak of the United States won the Nobel Medicine Prize on Monday for identifying a key switch in cellular ageing.
Researchers rapidly turn bacteria into biotech factories
Jul 26, 2009 |
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High-throughput sequencing has turned biologists into voracious genome readers, enabling them to scan millions of DNA letters, or bases, per hour. When revising a genome, however, they struggle, suffering from serious writer's ...
Discovery pinpoints new connection between cancer cells, stem cells
Jul 01, 2009 |
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A molecule called telomerase, best known for enabling unlimited cell division of stem cells and cancer cells, has a surprising additional role in the expression of genes in an important stem cell regulatory pathway, say researchers ...
Parasite breaks its own DNA to avoid detection
Apr 15, 2009 |
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The parasite Trypanosoma brucei, which causes African sleeping sickness, is like a thief donning a disguise. Every time the host's immune cells get close to destroying the parasite, it escapes detection by rearranging its DN ...
Researchers discover mechanism that prevents two species from reproducing
Oct 26, 2009 |
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Cornell researchers have discovered a genetic mechanism in fruit flies that prevents two closely related species from reproducing, a finding that offers clues to how species evolve.
Important new model shows how proteins find the right DNA sequences
Mar 16, 2009 |
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(PhysOrg.com) -- Researchers at Uppsala University and Harvard University have collaboratively developed a new theoretical model to explain how proteins can rapidly find specific DNA sequences, even though ...
When is a stem cell really a stem cell?
Nov 24, 2009 |
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(PhysOrg.com) -- Induced pluripotent stem (iPS) cells -- adult cells reprogrammed to look and function like versatile embryonic stem cells -- are of growing interest in medicine. They may provide a way to ...
How does a worm build a throat? Tackling the 'organ formation puzzle'
Oct 06, 2009 |
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(PhysOrg.com) -- Mention worms to most people, and they probably think of fishing, gardening, or trips to the vet. Mention them to Susan E. Mango, and she begins telling you how “absolutely beautiful” they ...
Scientists identify key component in cell replication
Jan 29, 2009 |
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Last week, a presidential limousine shuttled Barack Obama to the most important job in his life. Scientists at the Stanford University School of Medicine have now identified a protein that does much the same for the telomerase ...
Genetic conflict in fish led to evolution of new sex chromosomes
Oct 01, 2009 |
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University of Maryland biologists have genetically mapped the sex chromosomes of several species of cichlid (pronounced "sick-lid") fish from Lake Malawi, East Africa, and identified a mechanism by which new ...
