Popular Posts

Popular Posts

Pages

Total Pageviews

Sunday, February 26, 2012

Time line of inventions..China 9th century AD


Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s.[2] It is a mixture of sulfurcharcoal, and potassium nitrate (saltpetre) - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer.[3]Because of its burning properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms and as a pyrotechnic composition in fireworks.
Gunpowder was, according to prevailing academic consensus, discovered in the 9th century in China, attributed to Chinese alchemists searching for an elixir of immortality.[4] This discovery led to the invention of fireworks and the earliest gunpowder weapons in China. In the centuries following the Chinese discovery, gunpowder weapons began appearing in the Arab worldEurope, and India. The consensus is that this was spread from China, through the Middle East, and then into Europe,[5] although there remains some dispute over the amount of Chinese influence on later advancements in gunpowder technology.[citation needed]
Gunpowder is classified as a low explosive because of its relatively slow decomposition rate and consequently low brisance. Low explosives deflagrate at subsonic speeds, whereas high explosives detonate, producing a supersonic wave. Ignition of the powder packed behind a bullet must generate enough pressure to force it from the muzzle at high speed, but not enough to rupture the gun barrel. Gunpowder is thus less suitable for shattering rock or fortifications. Gunpowder was widely used to fill artillery shells and in mining and civil engineering to blast rock roughly until the 2nd half of the 19th century, when the first high explosives (nitro-explosives) were discovered. Gunpowder is no longer used in modern explosive military warheads, nor is it used as main explosive in mining operations due to its cost relative to that of newer alternatives like ANFO.[6]
Black powder for muzzleloading rifles and pistols in FFFG granulation size. Coin(diameter 24 mm) for comparison.

The Nobel Prize in Physiology or Medicine 2006..Wikipedia


The Nobel Prize in Physiology or Medicine 2006

Andrew Z. Fire, Craig C. Mello

Andrew Z. Fire
Craig C. Mello

Andrew Z. Fire

Craig C. Mello

The Nobel Prize in Physiology or Medicine 2006 was awarded jointly to Andrew Z. Fire and Craig C. Mello "for their discovery of RNA interference
Andrew Zachary Fire
BornApril 27, 1959 (age 52)
Palo AltoCalifornia
ResidenceStanford, California
NationalityAmerican
FieldsBiologist
InstitutionsJohns Hopkins University
Stanford University
Alma materUniversity of California, Berkeley
Massachusetts Institute of Technology
Doctoral advisorPhillip Allen Sharp
Known forRNA interference
Notable awardsNobel Prize in Physiology or Medicine (2006)

























Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNAmolecules, 20-25 nucleotides in length, that play a variety of roles in biology. The most notable role of siRNA is its involvement in the RNA interference (RNAi) pathway, where it interferes with the expression of a specific gene. In addition to its role in the RNAi pathway, siRNA also acts in RNAi-related pathways, e.g., as an antiviral mechanism or in shaping the chromatin structure of a genome; the complexity of these pathways is only now being elucidated.
siRNAs were first discovered by David Baulcombe's group at the Sainsbury Laboratory in NorwichEngland, as part of post-transcriptional gene silencing (PTGS) in plants. The group published their findings in Science in a 1999 paper titled "A species of small antisense RNA in posttranscriptional gene silencing in plants".[1] Shortly thereafter, in 2001, synthetic siRNAs were shown to be able to induce RNAi in mammalian cells by Thomas Tuschl, and colleagues in a paper published in Nature.[2] This discovery led to a surge in interest in harnessing RNAi for biomedical research and drug development.
Mediating RNA interference in cultured mammalian cells.
RNA is an acronym for ribonucleic acid, a nucleic acid. Many different kinds are now known.[1]
The main function of RNA is to carry information of amino acid sequence from the genes to where proteins are assembled on ribosomes in the cytoplasm. This is done by messenger RNA (mRNA). The sequence of base pairs is transcribed from DNA by an enzyme called RNA polymerase and is reformed in the mRNA. Then the mRNA moves from the nucleus to the ribosomes in the cytoplasm to form proteins. The mRNA translates the sequence of base pairs into a sequence of amino acids to form proteins. This process is called translation.
RNA is physically different to DNA: DNA contains two intercoiled strands whereas mRNA only contains one single strand. RNA also contains different bases to DNA. It contains:
(A) Adenine (G) Guanine (C) Cytosine (U) Uracil
The first three bases are also found in DNA, but Uracil replaces Thymine as a complement to Adenine.
RNA also contains ribose as opposed to deoxyribose found in DNA. These differences result in RNA being chemically more reactive than DNA. This makes it the more suitable molecule to take part in cell reactions.
RNA is the carrier of genetic information in certain viruses, especially the retroviruses like the HIV virus. This is the only exception to the general rule that DNA is the hereditary substance.
Types of RNA.

Non-coding RNAs

Two kinds of non-coding RNAs help in the process of building proteins in the cell. They transfer RNA (tRNA) and ribosomal RNA (rRNA).

[change]tRNA

Transfer RNA (tRNA) is a short molecule of about 80 nucleotides which carries a specific amino acid to the polypeptide chain at a ribosome. Each one (there is a different tRNA for each amino acid) has a site for the amino acid to attach, and an anti-codon to match the codon on the mRNA. For example, codons UUU or UUC code for the amino acid Phenylalanine.

[change]rRNA

Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time.[2] rRNA is extremely abundant and makes up 80% of the 10 mg/ml RNA found in a typical eukaryoticcytoplasm.[3]

Regulatory RNAs

There are a number of RNAs which regulate genes, that is, they regulate the rate at which genes are transcribed or translated.[4]

[change]miRNA

Micro RNAs (miRNA) act by joining an enzyme and blocking mRNA, or speeding its breakdown. This is called RNA interference.

[change]siRNA

Small interfering RNAs (sometimes called silencing RNAs) interfere with the expression of a specific gene. They are quite small (20/25 nucleotides) double-stranded molecules. Their discovery has caused a surge in biomedical research and drug development.[5][6]