Translation Flashcards
______ three nucleotide codons in mRNA encode 20 amino acids + start and stop codons; most amino acids have multiple codons; codons are read in the _____ direction with the ___ terminal nucleotide at the left
64 codons; 5’ to 3’, 5’ at left
The conversion of information in RNA to protein = ______
Translation (of one language to another)
one codon– _____ – acts as both initiation signal and methionine
AUG
There are three possible reading frames in protein synthesis; RNA can be translated 3 different ways. What can go wrong..?
(one base pair mutation), single deletion, single addition= shifted reading frame
*as long as non multiple of 3
______ match amino acids to codons in mRNA
tRNA
tRNA recognizes 5’ codon on mRNA and binds/recognizes a specific _______ at the 3’
amino acid
The Anticodon of tRNA is :
set of 3 consecutive nucleotides that pairs with the complementary codon on the mRNA
the short, single stranded region on the 3’ end of tRNA….
recognizes and binds a SPECIFIC amino acid that corresponds to the condon
Some tRNAs only require accurate base-pairing only …..position of the codon and can tolerate a mismatch (WOBBLE) at the _____ position
first two positions must be accurate, third can wobble
Wobble base-pairing explains….
why so many alternative codons for AA differ only in their third nucleotide
Recognition and attachment of the correct AA to a tRNA depends on enzymes called _________ which:
amionacyl-tRNA synthetases: covalently couple AA to appropriate tRNA
**one for each AA (20)
Synthetases use ______ to produce a high-energy bond between the ____ end of the tRNA and an amino acid. The energy of this bond is used at a later step to link…
ATP hydrolysis ; 3’ end
NRG used to link AA covalently to growing peptide chain
Amino acids are added to the ____-terminal end of a growing polypeptide chain
C-terminal
Fundamental Reaction of Translation:
Formation of peptide bond between Carboxyl-group (o-c=o) at the end of the growing polypeptide chain and the free amino group (NH2) on the incoming amino acid
**nucleophilic attack
A protein is synthesized from its _____ end to its ______ end
N to C
Each amino acid carries within it the activation energy for the addition of the next amino acid from the breaking of the….
covalent linkage between the tRNA and the carboxyl end of the polypeptide chain
The formation of each peptide bond is energetically favorable because…
the growing C-terminus has been activated by the covalent attachment of the tRNA molecule
The ______ subunit of ribosomes recognizes mRNA and only once correctly position, the ____ subunit is added
Small recognizes, then large is added
Ribosomes are made of:
proteins (1/3) ++++ RNA molecules (rRNA) (2/3)
The small subunit of ribosomes:
matches tRNA to the codon of the mRNA
The large subunit of ribosomes:
catalyzes formation of peptide bonds
_______ form the E, P, and A tRNA binding sites
rRNA
Prokaryotic Ribosome (70S) Large subunit (50s) ------ Small subunit (30S) 5S+23S+ proteins= 50S 16S+ proteins=30S
Look at a picture
Eukaryotic Ribosome= 80S
Large subunit=60S ——- Small subunit= 40S
5S+28S+5.8S+ proteins= 60S
18S+ proteins= 40S
Look at picture
Three tRNA binding site:
A=
P=
E=
A= incoming aminoacyl-tRNA ===tRNA + amino acid P= existing peptidyl-tRNA bond E= exiting of tRNA
Translation begins with the ____ codon, thus all new proteins have ______ at their _____ terminal (which is usually removed)
AUG–> Methionine which is at N terminus
(eukaryotes) the initiator tRNA is first loaded onto the small subunit with proteins called ______
eukaryotic initiation factors (eiFs)
After tRNAi binds with eiFs, the small subunit binds the 5’ end of mRNA which is recognized by….and it then proceeds to look for first AUG (assisted by helicases)
the 5’ cap and eiFs
After the small subunit finds AUG start site…..
eiFs dissociate, allowing for large subunit to join
**tRNAi now occupies P site, A site awaits next aminoacyl-tRNA
The start codon selection in bacteria is different since bacterial mRNA don’t have a 5’ cap, instead they….
have a specific sequence called the Shine-Delgarno sequence
bacterial mRNAS are ________ whereas eukaryotic mRNAS generally only encode for a single protein
polycistronic
Three major steps of Elongation:
1)
2)
3)
1) new tRNA binds to A site (codon base pairing)
2) carboxyl end (o-c=o) of peptide chain released from it’s tRNA (in P site) by breaking high energy bond–>followed by joining peptide chain to free AA linked to tRNA in A site (peptidyl transferase)
3) conformational change moves mRNA exactly 3 nucleotides through ribosome to prepare ribosome for next aminoacyl-tRNA
REPEAT
_________ are necessary for moving the mRNA forward through the ribosome in translation
elongation factors (EFS)
The end of the protein-coding message is signaled by the presence of one of three stop codons:
UAA, UAG, UGA
Release factors bind the ribosome with the stop codon in the A site and forces peptidyl transferase to….
add a water molecule instead of an amino acid to the peptidyl tRNA (c terminal) thereby freeing the carboxyl end of the chain
- **released into cytoplasm
- **Large and small subunits separate with the help of a divorce attorney
Protein synthesis can occur in the _______ in addition to the ________
Rough Endoplasmic Reticulum (RER) + cytosol
**translation in RER allows for quick packaging and transportation in vesicles
Tetracycline
blocks binding of aminoacyl-tRNA to A site of ribosome
Streptomycin
prevents the transition from translation initiation to chain elongation and also causes miscoding
Chloramphenicol
blocks the peptidyl transferase reaction on ribosome
Erythromycin
binds in the exit channel of the ribosome (E) and thereby inhibits elongation of peptide chain
Rifamycin
block initiation of RNA chains by binding to RNA polymerase thus preventing RNA synthesis
