Translation Flashcards
What is a codon?
Triplet of DNA that encodes amino acids
How many codons are there?
64
How many stop codons are there?
3
How many amino acid encoding codons are there?
61
What is the initiation codon?
AUG
What else does AUG encode for, other than being the initiation codon?
Met
What is degeneracy?
More than one codon for some amino acids
What does UUU code for?
Phe
What does CCC code for?
Pro
What does GGG code for?
Gly
What does AAA code for?
Lys
What are the three stop codons?
UGA
UAG
UAA
What is the open reading frame (ORF)?
The in-frame sequence between the initiation codon and the termination codon
What does the 5’ end of the mRNA correspond to?
The N-terminal of the protein (amino terminus)
What does the 3’ end of the mRNA correspond to?
The C-terminal (carboxy terminus)
Who discovered that protein synthesis begins at the amino terminal end of the nascent proteins?
Dintzis (1961)
What serves as the adapter molecules for specific amino acids, since mRNA templates can’t directly line up amino acids for protein synthesis?
tRNA - bind to specific codons on the RNA template
How are amino acids linked to tRNA molecules before being incorporated into the protein?
Amino acids are enzymatically to tRNA
Which undergoes more proofreading, translation, transcription or replication?
Replication
How many bases are found in tRNA?
73-93 (small)
All cells have at least ___ tRNAs.
32
What forms the wobble in the “wobble rules”?
The fact that some tRNAs can recognize more than one codon
What do most tRNAs have at the 5’ end?
G
What does the D arm of tRNA contain?
Dihydrouridine
What does the TpsiC arm contain?
The sequence ribothymidine (T) pseudouridin (psi) cytosine (C)
What is the anticodon? Where is it found?
A 3 base sequence
In the anticodon loop of tRNA
What does the anticodon of tRNA base pair with?
The codon in mRNA
What base does inositate contain?
Hypoxanthine
Some tRNAs contain what different nucleotide?
Inositate
Hypoxanthine can base pair weakly with which bases?
U, C, A
How many subunits make up ribosomes?
2 - a large and a small subunit
What is each ribosomal subunit made of?
An assembly of one or more rRNA molecules and many different proteins
What 3 sites do the ribosomal subunits form?
- Peptidyl (P) site
- Aminoacyl (A) site
- Exit (E) site
What occurs at the aminoacyl site?
It is the site where the amino acids come in
How big is a large bacterial ribosomal subunit?
50S
How big is a large eukaryotic ribosomal subunit?
60S
What size is the small bacterial ribosomal subunit?
30S
What size is the small eukaryotic ribosomal subunit?
40S
What are the 5 major stages of protein synthesis?
- Activation of amino acids
- Initiation
- Elongation
- Termination and ribosome recycling
- Folding and posttranslational processing
What occurs in stage on o protein synthesis?
The tRNA is “charged” with the proper amino acid
How and where are amino acids attached to the corresponding tRNA?
Via ester bonds to the 3’ OH
What is the reaction that attaches the amino acid to the tRNA?
Aminoacylation of the 3’ OH
What catalyzes the aminoacylation of the amino acid to the tRNA?
Amino acyl-tRNA synthetase
tRNA charging is highly ___.
Specific
Why is tRNA charging irreversible?
It uses 2 high-energy bonds
T or F: The identity of the amino acids attached to the tRNA are checked by the ribosome.
False
How do aminoacyl-tRNA synthetases recognize correct tRNAs? (4 ways)
Some recognize the anticodon
Some recognize 10 or more bases in tRNA
Some recognize one specific base pair
After tRNA is charged by a snthetase, the aminoacyl tRNA forms a complex with what molecule that will also bind one GTP molecule?
EF-Tu (elongation factor)
How many tRNAs do all organisms have for methionine?
2 - one for initiation, one for methionines within the polypeptide chain
In bacteria, how many components are required for initiation?
7
How many steps does it take for the 7 bacterial initiation factors to assemble?
3 steps
How is the initiation codon distinguished in step 1 of bacterial protein initiation?
By proximity to the Shine-Dalgarno sequence
In bacteria protein initiation, where is the P site placed?
Right over the AUG of the start site
What is the first step in bacterial mRNA initiation?
Small (30S) subunit positions itself on the mRNA template
What is step 2 in the initiation of protein synthesis in bacteria?
Initiator tRNA binds to the P site
What is step 3 in protein synthesis initiation in bacteria?
Large (50S) subunit binds to the complex
How many initiation factors or involved in the initiation of protein synthesis in eukaryotes?
At least 9
What is the Kozak sequence, that is found at many initiation sites?
5’-CCACCAUGG-3’
Do eukaryotes have a Shine-Dalgarno sequence?
No
How many ribosomes are found bound to each mRNA molecule?
10-100
What are the 3 steps of elongation?
Bind next aminoacyl-tRNA
Peptide bond formation
Translocation
Why are 2 steps used to move tRNAs?
Anchors one of of tRNA with the other moves
Prevents premature release of peptidyl-tRNA, enhances processivity
Proofreading on ribosomes is limited to what?
Codon-anticodon interactions
In termination, how is the peptide chain released from the ribosome?
Induce peptidyl transferase to transfer peptide chain to water
How many termination factors do eukaryotes have?
1
How much energy does protein synthesis take?
At least 4 high-energy bonds per peptide bond
Why is so much energy used in protein synthesis?
To maintain proper alignment of codon, tRNA and the growing end of the chain
Tetracycline and chloramphenicol are two drugs that do what?
Inhibit translation
What side affects can tetracycline have? (used to treat perio-disease)
Stain teel
How do tetracyclines inhibit translation?
Bind the A site
Block aa-tRNA binding
How does Ricin inhibit translation?
Inactivates the 60S subunit by depurinating the A residue of 28S rRNA - can’t bind TF
