Difference between revisions of "Laura"
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The genes that encode ribosomal RNA (rRNA) make up a multi-gene family. Ribosomal RNA genes are located in the nucleolus of the cell[http://www.britannica.com/EBchecked/topic/502158/ribosomal-RNA-rRNA 1]. Animal cells typically have 100-200 rRNA genes, while plants can have as many as 5,000. These genes are found in tandem arrays, which are comprised of a repeating unit. This unit is made of the rRNA genes that are transcribed as well as non-transcibed spacer sequences. The number of rRNA genes varies widely between and among species, espcially in plants because they can tolerate more variation than animals. This variation is caused by unequal crossover and mutations[http://www.molecular-plant-biotechnology.info/nuclear-genome/ribosomal-RNA-gene-families.htm 2]. | The genes that encode ribosomal RNA (rRNA) make up a multi-gene family. Ribosomal RNA genes are located in the nucleolus of the cell[http://www.britannica.com/EBchecked/topic/502158/ribosomal-RNA-rRNA 1]. Animal cells typically have 100-200 rRNA genes, while plants can have as many as 5,000. These genes are found in tandem arrays, which are comprised of a repeating unit. This unit is made of the rRNA genes that are transcribed as well as non-transcibed spacer sequences. The number of rRNA genes varies widely between and among species, espcially in plants because they can tolerate more variation than animals. This variation is caused by unequal crossover and mutations[http://www.molecular-plant-biotechnology.info/nuclear-genome/ribosomal-RNA-gene-families.htm 2]. | ||
| − | In eukaryotes, ribosomes contain four rRNA molecules: 28S, 5.8S, 5S, and 18S. The 18S, 5.8S, and 28S genes are found adjacent to each other in that order and are tandemly repeated from 100 to 1000 times. RNA polymerase I transcribes these genes to produce a pre-rRNA molecule. Ribonucleases then remove spacer sequences to make three rRNA molecules. The 5S genes are usually located somewhere else in the DNA and are transcribed by RNA polymerase III. These four rRNA types along with ribosomal proteins form a ribosome. | + | In eukaryotes, ribosomes contain four rRNA molecules: 28S, 5.8S, 5S, and 18S. The 18S, 5.8S, and 28S genes are found adjacent to each other in that order and are tandemly repeated from 100 to 1000 times. RNA polymerase I transcribes these genes to produce a pre-rRNA molecule. Ribonucleases then remove spacer sequences to make three rRNA molecules. The 5S genes are usually located somewhere else in the DNA and are transcribed by RNA polymerase III. These four rRNA types along with ribosomal proteins form a ribosome.[http://wps.aw.com/bc_russell_igen_mol_3/107/27559/7055294.cw/index.html 6] |
| − | + | [[Image:ribosome.jpg]] | |
== RBS for Eukaryotes == | == RBS for Eukaryotes == | ||
Revision as of 04:50, 18 January 2011
rRNA Genes
The genes that encode ribosomal RNA (rRNA) make up a multi-gene family. Ribosomal RNA genes are located in the nucleolus of the cell1. Animal cells typically have 100-200 rRNA genes, while plants can have as many as 5,000. These genes are found in tandem arrays, which are comprised of a repeating unit. This unit is made of the rRNA genes that are transcribed as well as non-transcibed spacer sequences. The number of rRNA genes varies widely between and among species, espcially in plants because they can tolerate more variation than animals. This variation is caused by unequal crossover and mutations2.
In eukaryotes, ribosomes contain four rRNA molecules: 28S, 5.8S, 5S, and 18S. The 18S, 5.8S, and 28S genes are found adjacent to each other in that order and are tandemly repeated from 100 to 1000 times. RNA polymerase I transcribes these genes to produce a pre-rRNA molecule. Ribonucleases then remove spacer sequences to make three rRNA molecules. The 5S genes are usually located somewhere else in the DNA and are transcribed by RNA polymerase III. These four rRNA types along with ribosomal proteins form a ribosome.6
RBS for Eukaryotes
A ribosomal binding site (RBS) is a sequence on the 5' untranslated region of mRNA that binds to the ribosome and orients it in the correct direction for translation 5. In prokaryotes, the RBS is usually 7 nucleotides before the start codon and is called the Shine-Dalgarno sequence. In eukaryotes, the 5' guanine cap of mRNA functions as the RBS. After recognizing the 5' cap and binding to the mRNA, the ribosome moves along the mRNA until it reaches the Kozak sequence, which has a similar function as the Shine-Dalgarno sequence, and the start codon 3 4.
