#14 & # 15 Transcription and Translation

#14 Eukaryotic transcription- is more complex than prokaryotic transcription. For instance, in eukaryotes the genetic material (DNA), and therefore transcription, is primarily localized to the nucleus, where it is separated from the cytoplasm (in which translation occurs) by the nuclear membrane. DNA is also present in mitochondria in the cytoplasm and mitochondria utilize a specialized RNA polymerase for transcription. This allows for the temporal regulation of gene expression through the sequestration of the RNA in the nucleus, and allows for selective transport of RNAs to the cytoplasm, where the ribosomes reside.
The basal eukaryotic transcription complex includes the RNA polymerase and additional proteins that are necessary for correct initiation and elongation.

Transcription process:

Eukaryotes have three nuclear RNA polymerases, each with distinct roles and properties:

Name	transcribed
RNA Polymerase I (Pol I, Pol A)	nucleolus	Larger ribosomal RNA (rRNA) (28S, 18S, 5.8S)
RNA Polymerase II (Pol II, Pol B)	nucleus	messenger RNA (mRNA) and most small nuclear RNAs (snRNAs)
RNA Polymerase III (Pol III, Pol C)	nucleus (and possibly the nucleolus-nucleoplasm interface)	transfer RNA (tRNA) and other small RNAs (including the small 5S rRNA)

There are many eukaryotes that differ from the canonical presentation of the roles of RNA polymerasespossess four distinct RNA polymerases. Other organisms utilize RNA polymerase I to transcribe certain protein-coding genes in addition to rRNAs.

Transcription regulation:
The regulation of gene expression is achieved through the interaction of several levels of control including the regulation of transcription initiation. Most (not all) eukaryotes possess robust methods of regulating transcription initiation on a gene-by-gene basis. The transcription of a gene can be regulated by cis-acting elements within the regulatory regions of the DNA, and trans-acting factors that include transcription factors and the basal transcription complex.

#15 TRANSLATION-is the third stage of protein biosynthesis (part of the overall process of gene expression). In translation, messenger RNA (mRNA) produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein. In Bacteria, translation occurs in the cell's cytoplasm, where the large and small subunits of the ribosome are located, and bind to the mRNA. In Eukaryotes, translation occurs across the membrane of the endoplasmic reticulum in a process called vectorial synthesis. The ribosome facilitates decoding by inducing the binding of tRNAs with complementary anticodon sequences to that of the mRNA. The tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is "read" by the ribosome.


             short animation:   http://www.biotopics.co.uk/genes/translation.html