Genes for functional RNA

Genes for rRNAs and tRNAs, or genes for functional RNAs, encode ribonucleic acids that have a significant role in the process translation but do not rewrite themselves into proteins. In a cell, these types of RNA have a relatively high proportion - tRNAs account for 15% of the total amount of cellular RNA and there are more than 40 of its families, rRNAs occur in three types in Prokaryota-prokaryont and four in eukaryont and, in terms of quantity, the highest - over 80% of the RNA (just 5% is the mRNA that encodes the proteins).

tRNA

Transfer RNA is around 80 nucleotides long. It is tasked with assigning a specific amino acid to an emerging peptide chain based on the complementary nature of its anticodone-codon-translated mRNA. Amino acid binds to the aminoacyl (acceptor) arm involving the aminoacyl-tRNA transferase enzymes, which are able to recognize the anticodone and thus bind only the amino acid that corresponds to the anticodone. There are 64 possible combinations of codon (= triplet bases). But because there is a phenomenon called fluctuating base pairing, the required number of molecular types of tRNA and therefore the genes that encode them is shrinking. Transcription of tRNA takes place using the enzyme DNA-dependent RNA-polymerase III. Individual tRNAs are first transcribed in the form of pre-tRNAs, then by post-transcription adjustments a functional tRNAs are obtained that leave the nucleus. The motors recognized by polymerase III are specific to the fact that they are not located in front of transcription units, but within them, unlike those for polymerases I and II.

rRNA

There are 4 types of ribosomal RNA in the eukaryotic cell. Together with proteins, they form small and large subunits of ribosomes. A large subunit contains 3 rRNA molecules, a small one. Active rRNA transcription takes place in the nucleus, where the genes that actively transcribe the rRNA are concentrated. In humans, genes that encode rRNAs are found on short arms of acrocentric chromosomes in their end regions called satellites. Genes for rRNA synthesis are estimated to be 400-500. The transcript is done using DNA-dependent RNA-polymerase I. More than one nucleus may be present in the nucleus of each cell. It depends on how translatable the cell is and how many ribosomes it needs. We can theoretically find up to 10 nuclei in the nuclei of human cells. This is because there are 5 pairs of acrocentric chromosomes in the human caryotype that contain satellites. Most often, however, the nucleus tends to be only one in a cell, possibly a few. If there is a deletion of the short arm of the acrocentric chromosome (e.g. in Robertson translocations), most of the time the synthesis of rRNA is taken over by another acrocentre without any complications.

References

Related Sites

• RNA

External links

• http://www.osel.cz/1209-chybejici-trna-geny-u-mini-archei-odhaleny.html
• https://ublg.lf1.cuni.cz/heslo/priklady/files/genova exprese.htm
• http://biology.ujep.cz/vyuka/file.php/1/opory/Genetika.pdf

Literature

• KOČÁREK, Eduard – PÁNEK, Martin – NOVOTNÁ, Drahuše. Klinická cytogenetika I.: Úvod do klinické cytogenetiky, vyšetřovací metody v klinické cytogenetice. 1. edition. Prague : Karolinum, 2006. 120 pp. ISBN 80-246-1069-8.

• GOETZ, Peter. Vybrané kapitoly z lékařské biologie, díl 2. 1. edition. Praha. 2002. 139 pp. ISBN 80-246-0320-9.