Translation Flashcards
what are three main things needed to translate mRNA into protein?
ribosomes, amino acids, and transfer RNA
what are the two subunits of the ribosome?
The 30S and 50S
how does the ribosome read the RNA
5’ to 3’
what are four general things that must happen before the polypeptide becomes a functional protein?
folding, joining with other subunits, identification tags added, and certain proteins cleaved from it
define the wobble hypothesis
tells us that the third nucleotide in the anticodon, when bound to the mRNA, does not have the same confines as the other two, allowing for non-specific base pairing. Therefore, codons with differing third nucleotides can code for the same amino acid
how many tRNAs are responsible for the 61 different codons?
45
what is the the role of tRNA?
It is responsible for carrying specific amino acids to the ribosome, each amino acid corresponding to a specific anticodon on the bottom of the tRNA
what is the name of the enzyme that binds tRNA to its corresponding amino acid?
aminoacyl-tRNA synthetase
what exactly does the enzyme do to the aa and the tRNA?
forms a covalent bond between the two
what is the driving source of energy for aminoacyl-tRNA synthetase?
ATP
where is the covalent bond made between the amino acid and tRNA?
on the 3’ end of the tRNA
what role does the 30S subunit play at the beginning?
It attaches to the mRNA strand at the start codon
where does the 30S subunit attach to the mRNA?
5’ Gcap
where will the beginning of translation always begin
in the cytosol
what are the three sites on the ribosome?
A, P, E
where is the tRNA received and matched with its appropriate codon?
A site
where do the peptide bonds form and the polypeptide snake out of?
P site
what elongation initiation factor is responsible for joining the new amino acid on the trna to the polypeptide chain?
peptidyl transferase
what is the difference between the n terminus and the C terminous
N terminus is the end that comes out first, the c terminus is at the end of the polypeptide strand
where are ribosomes manufactured
in the nucleolus
What is already part of the 30S subunit of the ribosome, allowing the subunit to find the start codon?
the anitcodon with methianie
what happens when a stoop codon is reached?
a release factor with corresponding anticodon binds at the E site
What makes the release factor able to release the polypeptide?
When transferase releases peptide bond on the previous tRNA, it tries to give it to the release factor, but it cant. So, the peptide is free to float away from the ribosome
How many aminoacyl transferases are there? Why?
- They need 20 because each amino acid is different and needs its own trnasferase to be able to move it
what is a big difference between euk and prok in regards to translation?
Eukaryotes can never carry out transcription and translation at the same time, while prok. can!
What signals the enzyme that takes the ribosome and mRNA to the ER?
signal peptide, made up of the first couple peptides synthesized in the chain
what is the protein family called that comes, recognizes the siganl peptide, and transports it to the ER?
signal recognition proteins
what happens once the recognition proteins bind to the signal peptide?
translation gets paused until the system reaches the ER
Once the ribosome reaches the ER, then what happens?
the signal recognition protein binds to an integral protein, and the way it binds also lines up the ribosome right on the opening of the integral protein
Once the signal recognition protein has bound to the pore, what does it do with the signal peptide?
It hands it over to the pore, and the pore anchors the signal (n terminus) to itself
Once the n terminus has been secured by the pore, and the ribosome is lined up, what will happen then?
The ribosome will once again contiue transcription, but this time the polypeptide will elongnate inside the ER
just before the ribosome finishes translation of sequence, what occurs?
a protein in the pore called peptidase cuts the peptide bond between the signal peptide and the first meaningful amino acid to the protein
What is important to remember in the relationship between the ribosome and the ER pore?
They are never attached to each other, just lined up
What is the initiation step to allow the making of a transmembrane protein
a seqeunce of polypeptides is recognized by the transmembrane protein, or pore.
What is the result of the initiation step in regards to making a transmembrane protein
a hydrophobic stop-transfer protein allows no more peptide through, and the rest of the polypeptide is translated and kept outside the ER membrane
why are chaperones needed?
polypeptides floating freely in the cytosol are vulnerable to degradation. chaperones keep that from happening
what are the two types of chaperones?
large and small
What are the characteristics of small chaperones? (2)
small chaperones interact directly with the protein
they maintain the structure of the polypeptide
what are the characteristics of large chaperones?
They completely engulf the polypeptide, creating a safe environment for the pp to begin folding
where does sorting occur in the golgi?
the last systernae
What are three postranslational additions to proteins?
glycocilation, acetylation, and lipidation
What is added to a protein if it is found to be faulty?
ubiquitone, which will send it to degradation
what are the two pathways by which proteins are secreted out of the cell?
constitutive and regulated
what kind of proteins are using the constitutive pathway?
Those that help maintain normal function, and plasma membrane proteins
what substances use the regulated pathway?
chemical messengers, such as insulin
what signals the release of vesicles in the regulatory pathway?
calcium
where do the regulated vesicles hang out?
they are docked on proteins just below the plasma membrane
Define point mutation
Where one nucleotide is changed in a sequence
what can cause mutations?
UV rays, free radicals, and exposure to dangerous chemicals
what is a missense mutation?
a point mutation that changes the codon so that it codes for different amino acid than it was supposed to
what is a nonsense mutation?
a point mutation that changes a codon into a stop codon
What is a silent mutation
A point mutation that results in third nucleotide in codon being switched, but the codon still codes for the same amino acid
what is frame shift mutation?
insertion or deletion of a single nucleotide, causing the reading frame to shift over one nucleotide
