BIOLOGY 151 Chapter Notes - Chapter 4: Transcription Preinitiation Complex, Start Codon, Messenger Rna
13 Jun 2018
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TRANSLATION: DNA TO mRNA TO PROTEIN
● To express a gene:
○ First: the info in DNA is transferred to a messenger RNA molecule by a way of a
process called transcription
■ TRANSCRIPTION: the DNA of a gene serves as a template for
complementary base pairing and an enzyme, RNA polymerase II catalyzes
the formation of a pre-mRNA molecule which is then processed to form
mature mRNA
■ The resulting mRNA is a single stranded copy of the gene which must
then be translated into a protein molecule
○ Second: TRANSLATION: the mRNA is “read” according to the genetic code,
which relates the DNA sequence to the amino acid sequence in protein
■ Each group of 3 bases in mRNA has a codon and each one specifies a
certain amino acid
WHERE TRANSLATION OCCURS
● w/in all cells, the translation machinery resides within the ribosome
● In eukaryotes: mature mRNA molecules must leave the nucleus and travel to the
cytoplasm where the ribosomes are
● In prokaryotic organisms: ribosomes can attach to mRNA while it’s being transcribed
● tRNA: adaptor molecules and have one end that can read the triplet code in the mRNA
through complementary base pairing and another end that attaches to a specific amino
acid
THE BEGINNING OF mRNA IS NOT TRANSLATED
● There is an area near the 5’ end of the molecule known as the untranslated region or
leader sequence and is located between the first nucleotide that’s transcribed and the start
codon of the coding region
● UTR: contains a ribosome binding site
○ In bacteria: this site is known as the Shine-Dalgarno box (AGGAGG)
■ Here, the 5’ UTR is normally short
TRANSLATION BEGINS AFTER THE ASSEMBLY OF A COMPLEX STRUCTURE
● First, three initiation factor proteins (IF1, IF2, IF3) bind to the small subunit of the
ribosome
○ The preinitiation complex and a methionine-carrying tRNA then behind to the
mRNA near the AUG start codon which forms the initiation complex
● When translation begins, the small subunit of the ribosome and an initiator tRNA
molecule assemble on the mRNA transcript
○ The small subunit of the ribosome has 3 binding sites, an amino acid site, and
polypeptide site, and an exit site
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Document Summary
First: the info in dna is transferred to a messenger rna molecule by a way of a process called transcription. Transcription: the dna of a gene serves as a template for complementary base pairing and an enzyme, rna polymerase ii catalyzes the formation of a pre-mrna molecule which is then processed to form mature mrna. The resulting mrna is a single stranded copy of the gene which must then be translated into a protein molecule. Second: translation: the mrna is read according to the genetic code, which relates the dna sequence to the amino acid sequence in protein. Each group of 3 bases in mrna has a codon and each one specifies a. W/in all cells, the translation machinery resides within the ribosome. In eukaryotes: mature mrna molecules must leave the nucleus and travel to the cytoplasm where the ribosomes are.
