Translation Flashcards
mechanism of protein synthesis, via a process in which the four-letter alphabet of nucleic acids is translated into the entirely different ____alphabet of proteins.
twenty-letter
transcribed to mRNA which is translated into protein with the help of
ribosomes
They transfer amino acids from cytoplasm to the ribosomal protein synthesizing machinery;
Since they are easily soluble, they are also referred to as soluble RNA or sRNA.
tRNA are present in
They are much shorter than mRNA molecules. each molecule is only ___ to___ nucleotides in length;
RNA molecules present in the cytoplasm.
73-93
When transcribed, the tRNA molecules are large and they undergo post-transcriptional
modifications.
The transfer RNAs show ______ base pairing and acquire clover leaf like structure
extensive internal
Features of trna
Considerably shorter than mRNA
Extensive internal base pairing, clover like structure
Under goes post-trancription
Contains plenty unusual base pairing like hypoxanthine, dihydrouracil, pseudoyridine
Moreover many bases are methylated.
Acceptor Arm is at the __’ end and it carries the
3
amino acid
This area has ___ base pairs and the end sequence is ‘.
tRNA
@ acceptor arm
7
CCA-3
The 3’ end hydroxyl group is forming an ester bond with the ___
@ acceptor arm
carboxyl end of amino acids
There are 64 possible combination of nitrogenous base
61 of 74 code for amino acids AUG = methionine
Remaining 3 doesn’t code dey stop d translation process
UGA
UAA
UAG
Anticodon complementary triplets of codon
@ anticodon arm of tRNA
Function
recognizes the triplet nucleotide codon present in mRNA
The specificity of tRNA resides in the _____ site,
anticodon
which has base sequences complementary to that of mRNA codon
For example, if the mRNA has a codon with the sequence UUU, the anticodon sequence of thetRNA will be_______
In this case, the UUU codon is translated as ____
AAA, by which it base pairs with mRNA codon.
So the specific tRNA can bind correctly to the mRNA codons.
phenylalanine
The tRNA molecule will show specificity in both aspects; in recognizing the mRNA codon as well as in accepting the specific amino acid coded by that codon.
The tRNAs act as _______molecules between mRNA and the amino acids coded by it.
adapter
Do nucleotides of codons have affinity for amino acids.
NO
So the tRNA molecules act as mediator between the mRNA and amino acids
The D arm or DHU region is so named due to the presence of ____
dihydro uridine in that area
____ arm serves as the recognition site for the enzyme which adds the amino acid.
The DHU
The opposite arm is called pseudouridine arm, as it contains a pseudouridine.
It is generally denoted with the Greek alphabet “ψ”
It is involved in binding tRNA to ribosomes.
ribosomal assembly is the protein synthesizing machinery
rRNA
rRNA
______ is the area where rRNA is synthesized and ribosomal assembly is produced.
Nucleolus
Components of rRNA
Components of rRNA
mammalian ribosome has a sedimentation velocity of 80S unit
It has a larger 60S subunit and another smaller 40S subunit.
They contain different rRNAs and specific proteins.
Ribosomal RNA has catalytic activity.
Peptidyl transferase activity is carried out by ___ RNA which acts as a ribozyme.
28S
Bacterial Ribosomes are Different
T or F
How?
Bacterial ribosomes are smaller than mammalian ones
Bacteria has 70S ribosomes; with 30S and 50S subunit
The rRNA is also synthesized as a 45S precursor which is cleaved to 28S, 18S, 5.8S and 5S
rRNAs.
The large ribosomal subunit has 28S, 5.8S and 5S rRNA and small ribosomal subunit has only
18S rRNA.
Genetic Code
A triplet sequence of nucleotides on the mRNA is the codon for each amino acid.
What are the features of genetic code
Triplets code
Code is on mRNA
Each code is a conservative sequence of 3 bases on mRNA
The codes are non overlaping
They are consecutive I.e the starting point is very important
codes are read one after another in a continuous manner,
Nonpunctuated
There is no punctuation between the codons.
It is consecutive or continuous.
E. G
AUG, CAU, GAU, GCA
There are 61 codes stand for the _____ amino acids.
20
So one amino acid has more than one codon.
For example, serine has __ codons; while glycine has ___ codons
This is called ______
6
4
degeneracy of the code.
Generally speaking, if the amino acid has more than one codon, what will happen
the first two bases in the codon will be the same
It is only the third one that is different and this reduces the effect of mutations
Amino acids such as_____ , ____&____ are specified by six codons each
leucine,arginine, and serine
The number of codons for a particular amino acid correlates with its frequency of occurrence in proteins
Codons that specify the same amino acid are called synonyms. For example, ___&____ are
synonyms for histidine
CAU and CAC
Features of genetic code
Triplet Codons
Nonpunctuated
Degenerate
Unambiguous
Universal
Wobbling Phenomenon
Terminator Codons
Genetic code are Unambiguous
That is, one codon stands only for one amino acid
Genetic code are Universal
The codons are the same for the same amino acid in all species
What’s Wobbling Phenomenon
Inosine is complementary to ___, ___&___
The reduced stringency between the third base of the codon and the complementary nucleotide in the anticodon is called wobbling
It decreases the risk of mutation
Uracine, Adenine, Cytosin
Translation process is commonless
I.e it reads 3 then 3 and so on
Except viruses
Overlapping is common in viruses
Isoluceine has how many codon namely
3
AUC
AUA
AUU
____&____ only has one codon
Methionine AUG
tryptophan UGG
The T arm function
It’s near the 3 • end
joins the tRNA to the ribosomes
D ram function
allows the identification of the tRNA by tRNA synthetase enzymes
3° end helps in interaction with AA by the use of ___
CCA
The pairing of codon and anticodon can wobble at the third letter. For example, ___, ___&___are the codes for glycine;
three will pair with the anticodon
GGU, GGC and GGA
CCI (I =
Inosinic acid)
The _____ of genetic code and ______ together will reduce the effect of
mutations.
degeneracy & wobbling phenomenon
There are three codons which do not code for any particular amino acids.
nonsense codons”, more correctly termed as punctuator codons or terminator codons.
These three codons are
U Go Away
U Are Away
U Are Gone
UGA is a stop codon; but in special circumstances, it stands for
_______ (the “21st” amino acids)
seleno-cysteine
In most of the cases, AUG acts as the initiator codon. AUG also acts as the codon for methionine.
In a few proteins, _____ may be the initiator codon.
GUG(Valine)
Mitochondria have different codes
The protein synthesising machinery of mitochondria is distinct from that in the cytoplasm.
There are only about ___tRNAs in mitochondria; but there are ____tRNA species in cytoplasm
22 tRNA in mitochondria but 31 tRNA in cytoplasm
Translation occur at____
Cytoplasm
In the polypeptide chain synthesized, the first amino acid is the amino terminal one i.e the chain growth is from
The chain growth is from amino terminal to carboxyl terminal
The process of translation can be conveniently divided into the phases of:
• A. activation of amino acid
• B. initiation
• C. elongation
• D. termination and
• E. post-translational processing.
• Activation of Amino Acid (Charging reaction)
The enzymes ________activate the amino acids.
By reacting it with ATP to form
aminoacyl tRNA synthetases
Aminoacyl tRNA and AMP
The enzymes aminoacyl tRNA synthetases activate the amino acids.
The enzyme is highly selective in the recognition of both the amino acid and the transfer RNA
acceptor.
There is atleast one tRNA for each of the 20 amino acids.
The D arm of tRNA is very important
for the recognition by the enzyme
The CCA 3’terminus of the acceptor arm carries amino acid
Amino acid is first activated with the help of ATP
Then the ____ group of the amino acid is esterified with 3’ hydroxyl group of tRNA.
carboxyl
Activation of AA is a 2 step reaction
The first rxn is
The second rxn is
The formation of AMP-amino acid-enzyme complex
In the second reaction, this activated amino acid is transferred to the corresponding tRNA & AMP is released
• B. Initiation of Protein Synthesis occur in ___ steps
4
Recognition
Formation of pre initiation complex( binding ternary complex of met-tRNA, GTP and eIF-2 to 40S ribosome.)
Binding of mRNA to the pre-initiation complex to form 43S initiation complex
The 43S initiation complex is combined with the 60S ribosomal subunit to form 80S initiation complex.
Eukaryotic ribosomes have ____ large subunit and ____ smaller subunit
Size
Rokaryoteic ribosomes have ____ large subunit and ____ smaller subunit
Size
60s and 40s together called 80S
60s 30s together called 70s
In prokayotic cells drugs like aminoglycoside e.g gentomisin,
Tetracycline e.g deoxycycline, minocycline,
Macrolites e.g azythromysin, clarithromysin,
target the ribosomes by affecting the ____ subunit
30S
Macrolites = 50S
Start codon in prokayotic cells is
AUG called N-formyl matheinen
Elongation Process of Translation are of ___ steps namely
3 steps
Binding of aminoacyl tRNA to the A site
Peptide bond formation
Translocation of the ribosome on the mRNA
For each peptide bond formation, ___ high energy phosphate bonds are used
4
two for the ____ and one for ______and one for _____
initial
activation
EF-1 step (GTP to GDP)
EF-2 step (GTP to GDP).
Actual peptide bond formation (peptidyl transferase step) does not require any energy, because
the amino acids are already activated.
T or F
Further, 1 ATP is used for _____; 1GTP for ________and 1
GTP
initiation complex formation
GTP for 80S ribosome formation
for termination.
Termination Process of Translation
After successive addition of amino acids, ribosome reaches the terminator codon sequence which are
on the mRNA
UAA,
UAG or UGA)
Since there is no tRNA bearing the corresponding anticodon sequence, the “A” site remains free
Post translation processing
Example of Proteolytic cleavage Modification of polypeptides by partial proteolysis, is?
pro-insulin to insulin
Modifications of amino acids
Examples are?
Hydrogenation of proline & lysin in collagen with the help of vit C
Gamma carboxylation of glutamic acid residues of prothrombin:
Phosphorylation of hydroxyl groups of serine, threonine, or tyrosine by kinases:
Cotranslational glycosylation:This refers to the addition of carbohydrate molecules to specific amino acids during the process of protein synthesis.
types of glycosylation are
O-glycosidic linkages–Carbohydrates are attached to serine or threonine residues through O-glycosidic linkages. This means that a carbohydrate molecule is bonded to the amino acid through a specific type of chemical bond.
N-glycosidic linkages–Carbohydrates are attached to asparagine or glutamine residues through N-glycosidic linkages. Similarly, a carbohydrate molecule is bonded to the amino acid through a specific type of chemical bond.
Subunit aggregation e.g
immunoglobulin, hemoglobin and maturation of collagen
What are the examples of reversible and irreversible post translation
Reversible
Disulfide bridge
Glycosylation
Phosphorylation
Acylation
N-acylation
ADP ribosylation
I reversible
Proteolysis
Ubiquitination
Lysin hydroxylation
Methylation
Examples of Failure of post-translational modification
cross-linking of collagen in scurvy, since ascorbic acid is required for the hydroxylation of proline and lysine.
One eukaryotic ribosome can synthesise 5 to 6 peptide bonds per second.
What’s poly ribosomes or polysome
When many ribosomes work on the same mRNA molecule simultaneously
In such cases each ribosome will be about 80 to 100 nucleotides apart on the mRNA.
______ may be attached on the walls of the endoplasmic reticulum to form the rough ER .
The proteins are then transported through cisternal space to Golgi apparatus, where they are temporarily stored
Polyribosomes
Cytoplasmic proteins are synthesized by ribosomes that __
exist free in cytoplasm.
The modern medical practice is heavily dependent on the use of antibiotics.
They generally act only on bacteria and are nontoxic to human beings.
This is because mammalian cells have ____ ribosomes, while bacteria have ribosomes
80S
70S
Reversible Inhibitors in Bacteria eg & how
Tetracyclins which bind to the 30S subunit of bacterial ribosome and so inhibit attachment of aminoacyl tRNA to the A site of ribosomes.
Chloramphenicol inhibits the peptidyl transferase activity of bacterial ribosomes
Erythromycin (macrolides) and clindamycin prevent the translocation process.
Irreversible Inhibitors in Bacteria eg & how
These antibiotics are bactericidal.
Streptomycin and all other aminoglycoside antibiotics bind to 30S subunit of bacterial ribosomes
They cause misreading of mRNA and at high concentrations, they completely inhibit the initiation
complex formation and totally inhibit protein synthesis
Inhibitors of Protein Synthesis in Mammals e.g & how
They are not suitable for clinical use; but the are used as research tools
Puromycin is structurally similar to tyrosine-tRNA and gets attached to the “A” site of the ribosome
Hence, the incomplete peptide is released.
It acts both in bacterial and mammalian cells
Cycloheximide inhibits peptidyl transferase in 60S subunit and it acts only on eukaryotic cells.
Diphtheria
Which mammalian inhibitor works only on eukaryote
Cycloheximide inhibits peptidyl transferase in 60S subunit and it acts only on eukaryotic cells.
Diphtheria toxin is produced or liberated by the bacteria, Corynebacterium diphtheria, causes inactivation of EF-2 by attachment of ADP to EF-2 and consequent inhibition of protein
biosynthesis in mammalian systems.
Inhibitors of transcription will also in turn inhibit translation process
