Transcript From DNA to Protein

From DNA
to Protein
Chapter 14 Part III
Translation
• review of RNA
• translation: process of
converting information in
mRNA into sequence of amino
acids to make a protein
• occurs at the ribosomes in the
cytoplasm or on the
endoplasmic reticulum
The Cell
Players in Translation
• tRNA – each tRNA carries one amino
acid on one end of the compound
•An anticodon on the other end
identifies the codon in mRNA that
codes for the amino acid
•rRNA makes up the ribosomes and
provides the bonding sites
•E (for exit) site
•P (for peptide) site
•A (for amino acid or acceptor) site
Transfer RNA
Ribosomal RNA
Step #1 of Translation: Initiation
• Parts needed:
• ribosome (large and small)
• initiation factors (proteins), and
• mRNA and initiator tRNA
•UAC anticodon; carries met
• small rRNA attaches to mRNA (at
start codon – AUG)
• Initiator tRNA attaches to P site
• large rRNA joins small rRNA
Initiation
Step #2 of Translation: Elongation
• growth in length of the polypeptide
• tRNA bring amino acids to ribosome
• ribosome reads codon in mRNA
•allows 1 tRNA with anticodon
complementary to mRNA codon
to bring amino acid
•joins the ribosome at A site
• methionine of initiator is
connected to amino acid of 2nd
tRNA by peptide bond
Elongation continued
• next tRNA moves to P site
(translocation)
• initiator moves to E site and exits
• ribosome reads the next codon
• allows 1 tRNA to bring its amino
acid (anticodon matches mRNA
codon) and joins the ribosome at
it’s A site
• dipeptide on 2nd amino acid is
connected to amino acid of 3nd
tRNA by peptide bond
Elongation
Step #3 of Translation: Termination
• previous tRNA moves to P site
• spent tRNA moves to E site (exits)
• ribosome reads STOP codon
• UAA, UAG, UGA – no amino acid
• polypeptide (protein) released by
release factor
• ribosome releases mRNA and
dissociates into subunits
• mRNA can read by another
ribosome
Termination
Final Thoughts
• DNA makes RNA makes
proteins
• mRNA strands can be read
several times to make proteins
• Proteins must fold in a specific
way to fit their function
• Proteins go anywhere in the
cell to provide structure or act
as enzymes
THE END