Download overview rna, transcription, translation

OVERVIEW RNA, TRANSCRIPTION, TRANSLATION
The RNA Molecule
RNA is structurally similar to DNA.
Overview: The Central Dogma
The central dogma of molecular biology describes the two-step process,
transcription and translation, by which the information in genes flows
into proteins: DNA to RNA to PROTEINS.
Transcription is the synthesis of an RNA copy of a segment of DNA. RNA is
synthesized by the enzyme RNA polymerase.
Transcription and translation are spatially and temporally separated in eukaryotic cells; that is,
transcription occurs in the nucleus to produce a pre-mRNA molecule.
The pre-mRNA is typically processed (introns removed, exons kept) to produce the mature
mRNA, which exits the nucleus and is translated in the cytoplasm.
The Transcription Process
RNA synthesis involves separation of the DNA strands and synthesis of
an RNA molecule in the 5' to 3' direction by RNA polymerase, using one
of the DNA strands as a template.
In complementary base pairing, A, T, G, and C on the template DNA strand specify U, A, C, and
G, respectively, on the RNA strand being synthesized.
Complete Transcription of an RNA Molecule
Transcription begins at the promoter, proceeds through the coding
region, and ends at the terminator.
RNA SPLICING
Introns removed and exons spliced, then sent to ribosome
Transcription copies the DNA code of a gene and converts it to messenger RNA (m RNA). The m
RNA will be used at the ribosome to make polypeptides (proteins). However all of the code
contained in the m RNA molecule is not needed to produce the polypeptide. The sections of m
RNA which do not code for translation of polypeptide are called introns. As the m RNA readies
itself to leave the nucleus, enzymes cut out and remove the introns. The remaining exons are
spliced back together again by a different enzyme. This modified m RNA is what comes to the
ribosome to be translated into polypeptides.
TRANSLATION Of mRNA into a PROTEIN
ISO
During translation, a small ribosomal subunit attaches to a mRNA molecule. At the same time,
an initiator tRNA molecule recognizes and binds to a specific codon sequence on the same
mRNA molecule. A large ribosomal subunit then joins the newly formed complex. The initiator
tRNA resides in one binding site of the ribosome called the P site, leaving the second binding
site, the A site, open. When a new tRNA molecule recognizes the next codon sequence on the
mRNA, it attaches to the open A binding site. A peptide bond forms connecting the amino acid
attached to the tRNA in the P site to the amino acid attached to the tRNA in the A binding site.
As the ribosome moves along the mRNA molecule, the tRNA in the P site is released and the
tRNA in the A site is translocated to the P site. The A binding site becomes vacant again until
another tRNA that recognizes the new mRNA codon takes the open position. This pattern
continues as molecules of tRNA are released from the complex, new tRNA molecules attach, and
the amino acid chain grows. The ribosome will translate the mRNA molecule until it reaches a
termination codon on the mRNA.