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
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 ...
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 ...
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.
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 ...
Sex Talk Revelations of the Lonely Y Chromosome
Sep 09, 2009 |
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(PhysOrg.com) -- In the week that the University of Leicester celebrates the 25th anniversary of the discovery of DNA fingerprinting (Thursday September 10) new findings from the world-renowned University of Leicester Department ...
Researchers examine mechanisms that help cancer cells proliferate
Sep 01, 2009 |
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A process that limits the number of times a cell divides works much differently than had been thought, opening the door to potential new anticancer therapies, researchers at UT Southwestern Medical Center report in the Aug. ...
After dinosaurs, mammals rise but their genomes get smaller
Jul 27, 2009 |
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(PhysOrg.com) -- Evidence buried in the chromosomes of animals and plants strongly suggests only one group -- mammals -- have seen their genomes shrink after the dinosaurs' extinction. What's more, that trend continues today, ...
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 ...
Genes that influence start of menstruation identified for first time
May 17, 2009 |
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Researchers from the Peninsula Medical School, along with collaborators from research institutions across Europe and the United States, have for the first time identified two genes that are involved in determining when girls ...
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 ...
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 ...
Researchers identify potential cancer target
Jan 16, 2009 |
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(PhysOrg.com) -- Dartmouth Medical School researchers have found two proteins that work in concert to ensure proper chromosome segregation during cell division. Their study is in the January 2009 issue of ...
'Scrawny' gene keeps stem cells healthy
Biology /
Jan 07, 2009 |
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(PhysOrg.com) -- Stem cells are the body's primal cells, retaining the youthful ability to develop into more specialized types of cells over many cycles of cell division. How do they do it? Scientists at the ...
Scientists suggest certain genes boost chances for distributing variety of traits, drive evolution
Dec 14, 2009 |
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Genes that don't themselves directly affect the inherited characteristics of an organism but leave them increasingly open to variation may be a significant driving force of evolution, say two Johns Hopkins scientists.
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.
