Biology Reference
In-Depth Information
Box 2.2 Key Points Regarding Transcription and Translation of DNA
Transcription
Protein-coding genes are transcribed into pre-mRNA that must be processed in the nucleus into mRNA
before going to the cytoplasm for translation.
Transcription requires RNA polymerase, but no primer; transcription of the coding strand of DNA occurs
from the 5
′
to the 3
′
end. Ribonucleotides include A, C, G, and U.
Processing of mRNA involves splicing out the introns in a spliceosome, capping and methylation of the 5
′
end, and adding a poly(A) tail at the 3
′
end.
mRNA for protein-coding genes also includes a leader sequence and a trailer segment.
Genes for rRNA, tRNA, and other small RNAs are used directly without translation into proteins.
Translation
Protein-coding genes are translated in the cytoplasm on the ribosomes
, which consist of rRNAs and
proteins. The rRNAs are ribozymes.
tRNAs have an anticodon complementary to the codon of the mRNA
.
tRNAs have a three-dimensional structure and contain an amino-acid attachment site
where the amino
acids are attached by specific enzymes.
tRNAs carry a specific amino acid to the ribosome
where they bind to the mRNA molecule based on
complementary base pairing.
mRNA is monitored and destroyed if it is damaged
.
The
stability of mRNA is regulated
so that specific proteins are produced in appropriate amounts at the
appropriate location to ensure normal development and metabolic activities are accurately maintained.
form (
Baker 2000
). The ability to predict protein structure and folding mecha-
nisms is very difficult, but this information helps in understanding how the pro-
tein functions (
Lee et al. 2007, Chouard 2011
).
See
Box 2.2
for key points regarding transcription and translation of DNA.
2.9 RNA Surveillance: Damage Control
It is very important that mRNA be accurately produced; otherwise, damaged
or truncated proteins are produced (
Hilleren and Parker 1999, Maquat and
Carmichael 2001, Doma and Parker 2007
).
mRNA surveillance
systems in eukary-
otes monitor pre-mRNA processing and RNA translation (
Doma and Parker
2007
). mRNAs that are translated aberrantly, or that have no stop codons, or
that produce a stall in elongation, or that translate beyond the normal stop
codon into the 3
′
untranslated region are detected by specific machinery that
eliminates defective mRNAs (
Doma and Parker 2007
). mRNA surveillance
