Transcription

a. mRNA Composition and Structure

mRNA is an RNA copy of the genetic code in DNA in the process will then be translated into a sequence of amino acids.

mRNA is translated in groups of three nucleotides (codon) at the ribosome through pairing of tRNA anticodon with the mRNA codon.

• Informational RNA = protein-coding = messenger RNA

         – primary transcript in prokaryotes

         – processed transcript in eukaryotes

• 5’ and 3’ end modification

• Intron removal

       – generally transcribed by RNA polymerase II

       – translated into amino acid sequence
 

http://www.phschool.com/science/biology_place/biocoach/translation/init.html

b. tRNA and rRNA Composition and Structure

Karp-Cell and Mollecular Biology, 6th Ed

• tRNA structure

       Anticodon consists of 3 nucleotides.

• base pairs with codon in antiparallel fashion. 

       3’ acceptor end attaches amino acid.

• attachment catalyzed by aminoacyl-tRNA synthetases.
• one for each different tRNA.

• rRNA compotition

1. Ribosomal RNA is not involved in coding. 
2. The primary rRNA transcript is spliced and modified to produce mature rRNA molecules. 
3. rRNA molecules bind to proteins to form the large and small subunits of ribosomes. 

c.    Mechanism of Transcription

Transcription is the process by which nucleotide sequences in DNA are copied to a complementary  copy of messenger RNA. 

 Video of Transcription Process

Transcription in Prokaryotic Cell (Bacteria)

1. Promoter (elements), s factor (4 domains), aCTD, abortive intiation.
2. Structures accounting for formation of the closed complex, transitions to open complex and then stable ternary complex. 
3. Elongation and editing by polymerase (10^-4). 
4. Termination: Rho-independent and Rho-dependent mechanism.                                             

http://www.mun.ca/biology/scarr/Transcription_&_Translation_Prokaryotes.html

               

Transcription in Eukaryotic Cell

• Initiation

         – at 5’ end of gene

         – binding of RNA polymerase to promoter

         – unwinding of DNA

• Elongation

         – addition of nucleotides to 3’ end

         – rules of base pairing

         – requires Mg²⁺

         – energy from NTP substrates

• Termination

         – at 3’ end of gene

         – terminator loop (prokaryote) or processing enzyme

http://www.mun.ca/biology/scarr/Transcription_&_Translation_Eukaryotes.html