SCIE1106 Lecture Notes - Lecture 10: Inosine, Transfer Rna, Polyadenylation
L10 Transcirption 2 (Products of Transcription)
• Pro + eu mRNA diff
• tRNA fx & structure
• aminoacyl-tRNA synthases fx
• pro + eu ribosomes diff
• roles of ribosomes binding sites in translation
of mRNA
→
protein
1. mRNA – codes for protein
2. tRNA – small adaptor molecules, align specific
a.a opposite triplet codon in mRNA
molecules, during (translation of mRNA → a.a
→ proteins)
3. rRNA – part of ribosomes, important in
protein/a.a synthesis machinery
Eukaryotes
• transcription / translation occur separately
• transcription occurs in nucleus, translation in
cytoplasm
• separated processes enables greater control
(easier to control 1 process, and then another
process, rather than controlling 2 processes at
the same time )
Prokaryotes
• transcription + translation occur at the same
time and are coupled
• nucleic acid floats free in the cytosol
Eukaryotic mRNA
• whats the diff between eu mRNA and pro
mRNA?
o Pro mRNA does not have
cap/polyadenylation
• are modified by 5’ capping + 3’
polyadenylation
o transport of mRNA from nucleus →
outside
o protect mRNA from degradation in
cytoplasm increase half life
o enables binding of
ribosomespromote translation
• cap – 7-mthylguanosine ( G – CH3 – PPP) at 5’
end
• poly-A tail – series of Adenosines linked to
RNA’s 3’ ed
o is not incorporated/encoded in the
DNA sequence
o AAAAAA – is a binding site for some
proteins – some transport proteins
need to recognize this mRNA and
transport it outside of the nucleus
into the cytoplasm
tRNA
• Brings a.a opposite their triplet codon, during
translation
• AGCU present in tRNA
• Inosine, psedouridine, dihydrouridine (as a
result of post-transcriptional modification) are
present in tRNA
• Anticodon sequence determines mRNA
codon binding
• a.a binds to 3’ ed
• 3D shape of tRNA determines correct a.a
attachment, by aminoacyl-tRNA synthesases
• different tRNA 3D shapes allows itself to bind
to the correct aminoacyl-tRNA syntehsase
• linkage of a.a to tRNA needs ATP
2 adaptors translate genetic code
1. aminoacyl-tRNA synthesase – couples a.a
to its tRNA
2. tRNA – anticodon forms codons of mRNA
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Document Summary
Proteins: rrna part of ribosomes, important in protein/a. a synthesis machinery. Eukaryotes transcription / translation occur separately transcription occurs in nucleus, translation in cytoplasm separated processes enables greater control (easier to control 1 process, and then another process, rather than controlling 2 processes at the same time ) Prokaryotes transcription + translation occur at the same time and are coupled: nucleic acid floats free in the cytosol. 2 adaptors translate genetic code: aminoacyl-trna synthesase couples a. a to its trna, trna anticodon forms codons of mrna. Large subunit catalyses peptide bond formation: both large & small move to next codon, ribosomes 1 mrna binding site, 3 trna binding sites trna binding sites. A= aminoacyl-trna (a. a with trna linked): new trna enters ribosomal complex. E= exit : empty trna , exists ribosomal complex ( goes out and reused by being recognized by trna synthesase: aminoacyl-trna binds to a-site, spent trna leaves.
