Jumat, 17 Agustus 2012

Gregor Mendel: The Father of Modern Genetics

Gregor Mendel is usually considered to be the founder of modern genetics. Though farmers had known for centuries that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity. An Augustinian monk living in what is now the Czech Republic, Mendel had access to an experimental garden in which he could breed “true” lines of pea plants and patiently wait for them to crossbreed in specified combinations. He worked with seven characteristics of pea plants: plant height, pod shape and color, seed shape and color, and flower position and color. Using the example of seed color, his results showed that when a yellow pea and a green pea were bred together their offspring plant was always yellow. However, in the next generation of plants, the green peas reappeared at a ratio of 1:3.

To explain this phenomenon, Mendel coined the terms “recessive” and “dominant” in reference to certain traits. (In the preceding example, green peas are recessive and yellow peas are dominant.) He published his work in 1866, demonstrating the actions of invisible “factors”—what we now call genes —in providing for visible traits in predictable ways.
Mendel never enjoyed recognition in his lifetime. In fact, it was more than three decades later, in 1900, that three scientists doing agricultural research discovered his 1866 paper. Erich Tschermak, Hugo de Vries, and Carl Correns independently verified several of Mendel's experimental findings, and the age of "genetics was" born. In the next several decades, scientists would learn more about genes and the special substance called DNA that carried each living thing's specific traits.

Sumber : http://history.nih.gov/exhibits/nirenberg/HS1_mendel.htm
Photograph of Gregor Mendel.
Gregor Mendel.

Drawing of a pea plant.
Mendel used pea plants in his experiments.

Amino acid

Amino acids are molecules that are the building blocks of proteins. They have a specific chemical makeup and can be produced by cells or ingested through diet. By the 1950s, scientists had agreed upon a list of twenty amino acids. That list still stands today, though it is possible that more will be discovered and named.
List of Amino Acids:
  • alanine
  • phenylalaline
  • lysine
  • proline
  • threonine
  • cysteine
  • glycine
  • leucine
  • glutamine
  • valine
  • aspartic acid
  • histidine
  • methionine
  • arginine
  • tryptophane
  • glutamic acid
  • isoleucine
  • asparagine
  • serine
  • tyrosine

A nucleotide base (guanine, adenine, cytosine, and thymine) is one of the building blocks of DNA, along with phosphates and sugar. These substances will join together to determine the order of proteins in each organism. Codon
A codon is a triplet series of bases linked together during protein synthesis to form an amino acid. Each codon carries the code for a specific amino acid.
“Central Dogma”
Francis Crick's “central dogma” of molecular biology, put simply, is: DNA makes RNA makes protein. This general rule emphasized the order of events from transcription through translation and provided the basis for much of the genetic code research in the post double-helix 1950s. The central dogma is often expressed as the following: “DNA makes RNA, RNA makes proteins, proteins make us.”
DNA, deoxyribonucleic acid, and RNA, ribonucleic acid, are molecules that hold the genetic information of each cell. The DNA strands store information, while the RNA molecules take the information from the DNA, transfer it to different places in the cell, and decode or read the information.
DNA takes the form of a double helix, with repeated sugar-phosphate backbones on the outside and paired bases making up the “steps” in the middle. DNA makes up genes, each of which contains enough information to make a specific protein. The mixture and order of these genes make up each organism.
Though DNA, then called nuclein, was first isolated back in 1869, it was not until the second half of the twentieth century that scientists began to fully understand the importance of DNA and its relationship to hereditary characteristics.
Escherichia coli
Escherichia coli, or E. coli as it is usually known, is a one-celled organism. The cell has no nucleus, and its DNA is in the form of one long looping molecule. E. coli is a commonly available bacterium, plentiful in the human colon, and therefore often used for experimental purposes.
A genome is the name for the entire set of unique DNA that makes up a particular organism.
A protein is a molecule that performs chemical reactions necessary to sustain the life of an organism. One cell can contain thousands of proteins.
The ribosome is the place in the cell where groups of bases called codons are translated into amino acids.


Transcription is the process by which information is transferred from the DNA to the messenger RNA (mRNA) in preparation for the RNA to translate the information into specific proteins. The DNA is made up of two strands, linked together in the shape of a double helix. During transcription, the two strands separate, and two strands of mRNA form against them. The RNA simply copies the information into its own system of bases. Like a Xerox machine, the RNA does not need to understand the information—it simply copies the information for future use. The new mRNA then moves on to the ribosome area of the cell where translation will take place.
At the ribosome in the cell's cytoplasm, the mRNA translates the information it has gleaned from the DNA into amino acids and then proteins. The mRNA is divided into codons, three-letter “words” made up of nucleotide bases, and each codon matches up with a particular transfer RNA (tRNA). The tRNA then takes the codon—now known as an amino acid—and links it together with other amino acids in a protein chain. The order of the amino acids in the chain is dictated by the sequence of codons in the mRNA. When the protein is completed, a “stop codon” will indicate that the protein chain can detach from the ribosome. It is now a fully functioning molecule of protein.
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