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From Gene to Protein
Transcription &
Translation
AN OVERVIEW
Mobility Problem
• DNA cannot leave the nucleus.
• Proteins are made in the cytosol
• How to connect the 2?
Transcription
• RNA can leave the nucleus.
• Similar structure to DNA, except
– Only one-stranded
– Does not have Thymine (T). Has
Uracil (U) instead.
– Ribose for its sugar instead of
deoxyribose.
mRNA (messenger RNA) is transcribed
according to instructions of the coding
strand of DNA.
mRNA can then carry the message of the
DNA to the ribosome in the cytosol!
Language Problem
• Language of DNA- 4 bases, A, T,
G, & C
• Language of Proteins- 20 amino
acids.
• How to translate?
Translation
• Synthesis of a polypeptide,
under the direction of the
translatorRNA
• Occurs in cytosol, at the
ribosome.
Every 3 nucleotides code for the
production of a specific amino acid.
Transcription
A Closer Look
1. RNA polymerase separates 2
strands of DNA
a) It then hooks RNA nucleotides
together as they match to DNA
template.
b) 5’3’
2. Polymerase attaches to
sequence of DNA called
promoter.
3. Sequence that signals end of
transcription is called
terminator.
Which strand of DNA to
transcribe?
Modifying RNA
• Both ends of the RNA sequence
are altered.
– 5’ end is capped with a modified
Guanine
– 3’ end is capped with a poly-A tail.
More Modification
• RNA splicing
– Initial RNA sequence is
approximately 8,000 nucleotides
– Generally, only approx. 1,200 are
needed, though.
– Noncoding areas are found in
between coding areas
Introns
- Noncoding region
Exons
- Coding region of
nucleic acid
How are introns found & cut
out?
• snRNPs (“snurps”) recognize the
end of an intron
• They then form a spliceosome
with other proteins and cut out
that intron
Translation
A closer look
What’s a triplet code?
• Flow of information from gene
(DNA) to protein is a triplet code
• Every 3 nucleotides will code for
the production of a specific
amino acid.
• mRNA base triplets are called
codons.
The purpose of tRNA.
• Interpreter of the mRNA codons
is tRNA (transfer RNA)
• Each tRNA molecule has a
section called the anticodon.
• tRNA grabs a specific amino
acid & brings it to the ribosome
How do mRNA & tRNA work
together to get the correct
amino acid?
• Anticodon of tRNA meets with
the codon of mRNA at the
ribosome.
– Ex- mRNA codon UUU
- tRNA anticodon- AAA
- tRNA will have phenylalanine to
add to the polypeptide
• First
• Study
ribosomes, p.
316.
• Second
• Study Building a
Polypeptide, p.
317-318