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In bacteria, transcription and translation can occur...
simultaneously
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In bacterial cells, do bacterial ribosomes wait for the RNA polymerase to finish transcribing to start translating mRNA?
No, they often begin translating mRNA while the RNA polymerase is still transcribing.
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Are translation and transcription concurrent in Eukaryotic cells?
no, they are separated by time and space
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What do tRNAs do?
act as adaptor molecules between amino acids and mRNA
***Transfer RNA
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Who proposed the idea that tRNA acts as an adaptor molecule ?
Francis Crick
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What did Francis Crick propose?
an adaptor molecule holds amino acids in place while interacting dierectly and specifically with a codon in mRNA
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How many nucleotides make up tRNAs in length?
75-85 nucleotides
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What is the secondary structure of of tRNA look like?
clover leaf
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What did researchers noted about their experiment of having radioactive labeled lysine?
lysines binded to small RNA molecules (tRNAs)
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What allows the tRNAs to hold its shape?
hydrogen bonds between sets of nucleotides
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How many different tRNAs are present in a cell?
20 because there are 20 amino acids
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(how amino acids are loaded onto tRNAs) 1.) What binds ATP and amino acid together?
an active site on aminoacyl tRNA synthetase (enzyme)
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(how amino acids are loaded onto tRNAs) Are aminoacyl tRNA synthetase specific to one amino aicd?
yes
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(how amino acids are loaded onto tRNAs) 2.) What happens After the aminoacyl tRNA synthetase binds ATP and amino acid? (3)
-2 phosphate groups are released
- -reaction leaves AMP(1 phosphate group) and amino acid bound to the enzyme
- ***amino acid is "activated" and as high potential energy
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(how amino acids are loaded onto tRNAs) 3rd step? (2)
- -activated amino acid is transferred from tRNA synthetase to the tRNA specific to that amino acid
- ***when this happens, AMP leaves
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(how amino acids are loaded onto tRNAs) 4th step (2)
-the tRNA synthetase and AMP leave
-Aminoacyl tRNA is ready to participate in translation
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When the tRNA has an amino acid attached to it, what is it called?
aminoacyl tRNA
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How many types of tRNA synthetases are in a cell?
20 different types
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The anticodon portion of the tRNA...
associates with the complementary bases pairs on mRNA
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(initiating translation) What is the Shine-Dalgarno region?
- portion of mRNA that initially binds to small ribosomal subunit (AGGAGGU)
- ***this part does not get translated into the protein
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(initiating translation) What are initiation factors?
- -help in associating mRNA to small ribosomal subunit
- *helps mRNA fit nicely
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(initiating translation) IN eukaryotes, what do initiation factors bind to?
the 5' cap on the mRNA
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What is a ribosome composed off?
- nucleotides
- *they are made by an RNA polymerase II
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(initiating translation) 1st step (2)
- -a ribosome binding site sequence binds to a complementary sequence in the RNA molecule in small subunit of the ribosome
- **with the help of initiation factors
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(initiating translation) 2nd step
the aminoacyl tRNA binds to mRNA to start codon
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(initiating translation) 3rd step (2)
- -the large subunit of ribosome binds
- **this marks the beginning of translation
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what are 3 compartments of large subunit of ribosome?
-A compartment
-P-compartment
-E- compartment
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What does the a-site do?
-accepts the next tRNA
- **acceptor area
- ** Aminoacyl site
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(elongation of polypeptides during translation) 1st step
-another aminoacyl tRNA comes into the A-site, where its anticodon pairs with the mRNA codon
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Why is a ribosome called a ribozyme? (2)
- the acitve site in the ribosome that catalyzes the peptide bond is all RNA
- ***this is a type of enzymatic actiivty by the the RNA
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(elongation translation) 2nd step
amino acid attached to tRNA in P site forms peptide bond with tRNA in A site
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(elongation translation) 3rd step
-ribosome moves mRNA down.
-tRNAs move down one spot to the left.
- A-site is empty because the tRNA attached to polypeptide moved to the P-site
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(elongation translation) which direciton is ribosome traveling ?
it is moving to the right
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(elongation translation) which direction is the mRNA moving as the ribosome moves to the right?
left in a 5' to 3' direction
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(elongation translation) 4th step
new tRNA binds to the a-site binding its anticodon to the base pair in mRNA
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(elongation translation) 5th step (2)
-peptide bond formation
-the polypeptide that was attached to the t-RNA is transferred to the aminoacyl tRNA in the A-site
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(elongation translation) step 6th (4)
-ribosome moves the mRNA down
-the tRNA attached to polypeptide chain moves into P-Site
- -empty tRNA from P-site moves down to E-site
- *it is ejected
-A-site empty again
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How many amino acids are assocaited with the tRNA with the stop codon?
0
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Does a tRNA show up when we reach stop codon?
- no, a protein release factor shows up.
- **it is not assocaited with any amino acids
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(termination of translation) 1st step (2)
- when translocation opens A-site and exposes a stop codon, a protein release factor fills the A-site
-release factor catalyzes the hydrolysis of the bond linking the tRNA in the p-site wth the polypetide chain
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(termination of translation) 2nd step (3)
-the hydrolysis reaction frees the polypeptide which is released from the ribosome
-empty tRNAs are released either along with the polypeptide or when;
- -the ribosome separates from the mRNA
- *the two subunits dissociate
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(termination of translation) 3rd step (2)
-two subunits of ribosomes dissociate
-subunits are ready to attach to the start codon of another message and start translation anew.
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Can there by many ribosomes working on an mRNA at once?
yes there can be many working on the mRNA
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Protein growth AND 5 prime to the 3 prime mRNA
-protein growth grows as they go from 5' to the 3' of mRNA
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Are all the ribosomes in the mRNA making the same protein?
- yes all the same protein because the mRNA is the same code
- **only way to get a different proteins is if you change the code
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