MB 207 – Molecular Cell Biology. From DNA to RNA The RNA world. The Nucleolus. Central Dogma of Molecular Biology. Transcription of DNA to RNA and then to protein Represented by 3 major stages. The DNA replicates itself: R eplication DNA transcribed to mRNA: T ranscription
Prokaryotes: Transcription takes place in cytoplasm. When transcription is completed, RNAs are ready for use in translation. Translation can even begin during transcription.
Summary of the steps leading from gene to protein in eukaryotes and bacteria
Initiation of transcription of a eukaryotic gene by RNA polymerase II
Binds to short sequences in DNA,
acting from a distance (thousands of nt pairs)
Eukaryotic mRNAs undergo extensive modifications to increase their stability and become biologically active.
The reaction that cap the 5’ end of each RNA molecule synthesized by RNA polymerase II
The structure of the cap at 5’ end
Structure of two human genes showing the arrangement of exonsand introns
Alternative splicing of the a-tropomyosin gene from rat
(regulates contraction in muscle cells)
A specific Adenine nucleotide in the intron sequence attacks the 5’ splice site
Creating a loop in the RNA molecule
For example: RNA splicing
Multiple RNA polymerase can transcribe the same gene at the same time
A cell can synthesize a large number of RNA transcripts in a short time
Transport of a large mRNA molecule through the nuclear pore complex.
The chemical modification and nucleolytic processing of an eukaryotic 45S precursor rRNA molecule into 3 separate ribosomal RNAsProcessing of rRNA
snoRNAs locate the sites of modification by base-pairing to complementary sequences on the precursor rRNA. The snoRNAs are bound to proteins and the ciplexes are calledsnoRNPs. snoRNPs contain the RNA modification activities
Sites of modification and cleavage of precursor to mature rRNAs are by a group of protein bound snoRNAs.
i) catalyze the attachment of amino acids to their corresponding tRNAs via an ester bond.
Amino acid activation