Transcription and Translation Exam 3

DNA -> RNA -> Protein

DNA to RNA (mRNA)

• 1.Initiation - recognize promoter region 
• 2.Elongation - make a RNA copy 
• 3.Termination - split from DNA

which one it copies varies but will always copy from 5' - 3' (DNA will be facing 3' to 5')

• Bacterial mRNAs can be used immediately Eukaryotic mRNAs  need to be cut and add cap and a tail
• Introns- spliced
• Exons- expressed

via splicesome (made of SnRNP)

rRNA and tRNA are self splicing via ribozymes

guanocine* added on 5' end NEEDED for mRNA to exit the nucleus

• Adenine added to the 3'
• Increases stability and lifespan in cytosol
• Not encoded in gene sequence

mRNA base triplets

DNA strand that will be turned into mRNA

more than one codon can specify the same amino acid

• 20 amino acids 
• 1 codon 1 amino acid but 64 possible codons

mRNA to protein

• clover structure (but L shaped b/c of hydrogen)
• has anticodon that matches the codon 
• acceptor stem for amino acid binding

• Catalyzes the attachment of amino acids to tRNA
• Reactions result in tRNA with amino acid attached or charged tRNA or aminoacyl tRNA

• ribosomal subunits (large and small) made of rRNA
• ribosome shape determined by rRNA

E (Exit), P (Growing Poplypeptide), A (Acceptor),  sites

• 1.Initiation - mRNA, first tRNA and ribosomal subunits
• assemble
• 2.Elongation - Synthesis from start codon to stop codon
• 3.Termination - Complex disassembles at stop codon
• releasing completed polypeptide

• mRNA binds to small ribosomal subunit
• facilitated by ribosomal-binding sequence
• Start codon a few nucleotides downstream
• Initiator tRNA recognizes start codon in
• mRNA
• Large ribosomal subunit associates
• At the end, the initiator tRNA is in the
• P site

3rd base in codon can be switched some and still make the same amino acid

start in eukaryotic cells

terminate transcription

translate a single mRNA simultaneously

make copies of polypeptide quickly

polypeptide is modified after translation and completed protein target specific sites in the cell

• free ribosomes make protein that function in cytosol
• bound make protein in ER that will be secreted from the cell 

they can switch!

• •Polypeptide
• synthesis always begins in the cytosol

• •Synthesis
• finishes in the cytosol unless the
• polypeptide signals the ribosome to attach to the ER

• •Polypeptides
• destined for the ER or for secretion are marked by a signal
• peptide