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Gene Expression at the Molecular Level - Coggle Diagram
Gene Expression at the Molecular Level
Central dogma
Transcription (produces RNA copy of gene, mRNA specifies amino acid sequence)
Translation (synthesising polypeptide on ribosome using mRNA template)
Transcription
Initiation (recognition step, sigma factor cause RNA polymerase to recognise promoter region)
Elongation (RNA polymerase synthesises mRNA, template used, 5' to 3', uracil instead of thymine)
Termination (termination sequence, polymerase & DNA transcript dissociate from DNA)
Eukaryotic transcription
RNA polymerase I - transcribes rRNA.
RNA polymerase II – transcribes mRNA.
RNA polymerase III – transcribes tRNA.
RNA polymerase II requires 6 general transcription factors (TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIH) to initiate transcription
RNA Processing in Eukaryotes
Introns (transcribed but not translated)
Exons (found in mature mRNA)
Spliceosome, removes introns precisely
Alternative splicing, can occur more than one way to produce different products
rRNA & tRNA are ribozymes, self-splicing
Capping, modified guanine attached to 5' helps mRNA leave nucleus
Poly A tail, adenine nucleotides added to 3' increased stability & lifespan in cytosol
Translation & genetic code
Read in groups of three nucleotide bases or codons
Degenerate in nature
Has stop (UAA, UAG, UGA) & start codons (AUG)
mRNA, identical to coding strand, has codon set of 3 RNA nucletoides
tRNA, identical to non-coding strand, anticodon has 3 RNA nucleotides (cloverleaf structure, anticodon, acceptor stem for amino acid binding) carries serine
Aminoacyl-tRNA synthetase (catalyses attachment of amino acids to tRNA, results in tRNA with amino acid attached)
Ribosomes
Prokaryotes have one type, while eukaryotes have different types
Composed of large and small subunits
Bacterial (small 30S, large 50S, assembled 70S)
Eukaryotic (small 40S, large 60S, assembled 80S)
P site – Peptidyl site
A site – Aminoacyl site
E site – Exit site
Stages of translation
Initiation (mRNA, first tRNA and ribosomal subunits
assemble)
Elongation (synthesis from start codon to stop codon, codon-anticodon recognition)
Termination (complex disassembles at stop codon releasing the completed polypeptide) stop codons are UAA, UAG, UGA, recognised by release factors
Instead of a ribosomal-binding sequence, mRNAs
have guanosine cap at 5’ end.
Position of start codon more variable.