In bacteria, transcription and translation can occur...
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.
Are translation and transcription concurrent in Eukaryotic cells?
no, they are separated by time and space
What do tRNAs do?
act as adaptor molecules between amino acids and mRNA
Who proposed the idea that tRNA acts as an adaptor molecule ?
What did Francis Crick propose?
an adaptor molecule holds amino acids in place while interacting dierectly and specifically with a codon in mRNA
How many nucleotides make up tRNAs in length?
What is the secondary structure of of tRNA look like?
What did researchers noted about their experiment of having radioactive labeled lysine?
lysines binded to small RNA molecules (tRNAs)
What allows the tRNAs to hold its shape?
hydrogen bonds between sets of nucleotides
How many different tRNAs are present in a cell?
20 because there are 20 amino acids
(how amino acids are loaded onto tRNAs) 1.) What binds ATP and amino acid together?
an active site on aminoacyl tRNA synthetase (enzyme)
(how amino acids are loaded onto tRNAs) Are aminoacyl tRNA synthetase specific to one amino aicd?
(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
(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
(how amino acids are loaded onto tRNAs) 4th step (2)
-the tRNA synthetase and AMP leave
-Aminoacyl tRNA is ready to participate in translation
When the tRNA has an amino acid attached to it, what is it called?
How many types of tRNA synthetases are in a cell?
20 different types
The anticodon portion of the tRNA...
associates with the complementary bases pairs on mRNA
(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
(initiating translation) What are initiation factors?
- -help in associating mRNA to small ribosomal subunit
- *helps mRNA fit nicely
(initiating translation) IN eukaryotes, what do initiation factors bind to?
the 5' cap on the mRNA
What is a ribosome composed off?
- *they are made by an RNA polymerase II
(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
(initiating translation) 2nd step
the aminoacyl tRNA binds to mRNA to start codon
(initiating translation) 3rd step (2)
- -the large subunit of ribosome binds
- **this marks the beginning of translation
what are 3 compartments of large subunit of ribosome?
What does the a-site do?
-accepts the next tRNA
- **acceptor area
- ** Aminoacyl site
(elongation of polypeptides during translation) 1st step
-another aminoacyl tRNA comes into the A-site, where its anticodon pairs with the mRNA codon
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
(elongation translation) 2nd step
amino acid attached to tRNA in P site forms peptide bond with tRNA in A site
(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
(elongation translation) which direciton is ribosome traveling ?
it is moving to the right
(elongation translation) which direction is the mRNA moving as the ribosome moves to the right?
left in a 5' to 3' direction
(elongation translation) 4th step
new tRNA binds to the a-site binding its anticodon to the base pair in mRNA
(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
(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
How many amino acids are assocaited with the tRNA with the stop codon?
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
(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
(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
(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.
Can there by many ribosomes working on an mRNA at once?
yes there can be many working on the mRNA
Protein growth AND 5 prime to the 3 prime mRNA
-protein growth grows as they go from 5' to the 3' of mRNA
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