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24 Cards in this Set
- Front
- Back
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What do ribosomes assemble mRNA with?
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Assembles mRNA together with tRNAs.
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tRNA?
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Translates mRNA codons into amino acids.
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Anticodon?
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Each tRNA has one at the bottom. Whatever it compliment (for example, if anti is UUC, it complements AAG, which is and makes phenylalanine) that is the amino acid it constributes to the polpeptide chain.
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Two functional sites of a tRNA?
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Anti codon site on the bottom, and AA attachment site on the top (where the amino acids being made are added).
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How many tRNAs? And how does this work?
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There are 45 tRNAs to translate 61 codons into 20 amino acids... this means that several tRNAs have to recognize more than one codon.
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How can it accommodate more than one codon? What is Inosine?
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Because it can flex/wobble! The wobble site is the furthest to the right of the 3 code, and it can "wobble" between different recognizations. If its uracil, it can bind Adenine or Guanine.
If it's a special nucleotide called Inosine (I), it can bind U, C, or A. |
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How do amino acids bind to tRNA?
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Via the enzyme aminoacyl-tRNA synthetase. There is a different one of these for every AA.
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How do the different synthesases distinguish the 45 tRNAs?
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Differences in the variable loop nucleotides (the red dots in the picture).
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Two parts of a ribosomes? What are they made of?
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Large and small subunit (small on the bottom). Each made of rRNA plus protein.
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What do they do?
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They assemble the mRNA together with AA carrying tRNAs.
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Three "sites" on the large subunit?
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EPA
E- Exit site -- where it exits out. P - Polypeptide site -- where they growing polypeptide happens A -- AA entry site -- next AA to be added to polypeptide chain enters here. |
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Site on the small?
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mRNA binding site.
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Are prokar and eukar ribosomes the same?
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No. Similar, but distinct.
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First three steps in Initiation of Translation by a small ribosomal sub-unit & initiator tRNA?
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(1) small ribosome subunit attaches to 5’ methylguanine cap (Eukaryote)
or "leader nucleotides" (a sequence motif in prokaryote mRNA) |
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What else is needed?
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Initiation factors and GTP for energy.
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Last step in initation?
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(4) After initiator tRNA is added
the large Ribosome sub-unit joins the small subunit & completes initiation. Thus, we can now begin with the elongation! |
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3 steps of elongation?
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(1) Codon recognition -- required energy.
(2) peptide bond formation between the incoming amino acid, and the ones that are already there. (3) tRNA translocation -- requires energy. Boot out the tRNA on the left that now has no amino acids bound to it. |
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Termination? How does it happen, and what happends?
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Happens once a stop codon is reached at the A site. (UAA, UGA, UAG). Will add a -OH instead of a AA, which dissembles the whole ribosomal translation complex.
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Polyribosomes? What do they do, and where are they?
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simultaneous translation of mRNA by multiple successive ribosomes
occurs in cytoplasm or on rough ER of eukaryotic cells |
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who uses the polyribosomes? and why?
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Prokary! Maximal use of the short lived mRNA.
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Polypeptide trafficking?
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using Signal Peptides (aka Leader peptides)
to direct polypeptides to the endoplasmic reticulum (or to non-endomembrane organelles) |
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Post-translational mods? Three common types?
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Modifications for their final functioning done after translation.
(1) Proteolysis -- directed degradation.. changes shape and size. (2) Glycosylation -- adding glucose molecules (3) Phosphorylation |
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How do anti-biotics work in light of this information?
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They target the parts of this process that are unique to prokar cells. i.e., RNA polymerases, Ribosomes, other transcrption/translation proteins, etc
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What do they attack the most?
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Mostly target the unique bacterial ribosomes (involved in translation).
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