Biochemistry 3070 – Nucleic Acids 1 Nucleic Acids Biochemistry 3070.
Nucleic Acids 7.3 Translation. Recap video 4UUVHPQM 4UUVHPQM.
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Transcript of Nucleic Acids 7.3 Translation. Recap video 4UUVHPQM 4UUVHPQM.
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Nucleic Acids7.3 Translation
![Page 2: Nucleic Acids 7.3 Translation. Recap video 4UUVHPQM 4UUVHPQM.](https://reader030.fdocuments.in/reader030/viewer/2022032523/56649d895503460f94a6f655/html5/thumbnails/2.jpg)
Recap video http://www.youtube.com/watch?v=nHM4
UUVHPQM
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The Structure of the Ribosome
Proteins and RNA molecules (rRNA)
2 sub-units (large and small) 3 binding sites for tRNA on the
surface: E = exit site P = peptidyl site A = aminoacyl site
2 tRNA molecules can bind at the same time to the ribosome
Binding site for the mRNA on the surface
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The Structure of the Ribosome
Protein database http://www.rcsb.org/pdb/home/home.do
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Structure of tRNA
Loops: sections that become double stranded by base pairing
Base sequence CCA forms a site for attaching amino acid
Anti-codon: triplet of bases Part of a loop of 7
unpaired bases
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tRNA activating enzymes http://www.youtube.com/watch?v=KThCr1XdUGw
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Initiation of TranslationTo begin translation: An mRNA molecule binds to the small ribosomal subunit at
the mRNA binding site An initiator tRNA carrying Methionine (MET) binds to the
start codon “AUG” in the “P-site” The large ribosomal subunit binds to the small one
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Initiation of Translation The next codon signals another tRNA to bind in
the “A-site” A peptide bond is formed between the amino
acids in the P and A sites
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ElongationFollowing initiation The ribosome
translocates 3 bases along the mRNA Moving the tRNA in the
“P-site” to the “E-site” This tRNA is set free
A new tRNA with the correct anticodon binds to the next codon in the “A-site”
This series of steps repeats
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Termination of Translation The process continues until a stop
codon is reached The polypeptide is released The components disassemble
Note: direction of movement from 5’ to 3’
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What does 5’ to 3’mean?
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Free Ribosomes Free ribosomes synthesize proteins for
use primarily within the cell
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Bound Ribosomes Bound ribosomes synthesize proteins
primarily for secretion or for use in lysosomes
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Free vs Bound Ribosomes Proteins perform specific
functions. They must be sorted to go to the correct location.
Whether a ribosome is free in the cytosol or bound to the ER depends on a signal sequence in the polypeptide
The signal sequence is at the beginning of the polypeptide
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Free vs Bound Ribosomes As the signal
sequence is made it becomes bound to a signal recognition protein
Translation stops until the ribosome attaches to a receptor on the ER
Translation begins again, with the polypeptide moving into the lumen of the ER.
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Translation and Transcription in Eukaryotes vs Prokaryotes
Cellular function is compartmentalized
Nocompartmentalization
Modifications of mRNA after transcription before exiting nucleus
No modifications
Delay between transcription and translation
No delay
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Polysomes Polysomes are multiple ribosomes
attached to a single mRNA molecule.
Strings of polysomes attached to DNA molecule in a prokaryote
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Polysomes In prokaryotes, multiple
polysomes are visible associated with one gene.
In eukaryotes, polysomes occur on the cytoplasm and next to the ER.
Multiple ribosomes translating a single mRNA molecule with the cytoplasm. The polypeptides are longer the closer to the end of the mRNA.