Translation Questions in English

(A) The codon on $mRNA$ is $5' UAC 3'$.
According to the base-pairing rules,the anticodon on $tRNA$ is complementary to the codon on $mRNA$.
Complementary base pairing occurs in an antiparallel orientation ($5' \rightarrow 3'$ of codon pairs with $3' \rightarrow 5'$ of anticodon).
Given codon: $5' UAC 3'$.
The complementary sequence is $3' AUG 5'$.
By convention,anticodon sequences are written in the $5' \rightarrow 3'$ direction.
Reversing $3' AUG 5'$ gives $5' GUA 3'$.

(B) Translation is the process of protein synthesis.
$1$. Amino acids are joined by peptide bonds to form a polypeptide chain.
$2$. The formation of a peptide bond is an endergonic process,meaning it requires energy. This energy is provided by the activation of amino acids using $ATP$.
$3$. In bacteria,the $23S$ $rRNA$ (a ribozyme) acts as a catalyst for peptide bond formation.
$4$. Therefore,the statement that the formation of a peptide bond does not require energy is incorrect.

(D) Statement $(a)$ is correct: $\text{tRNA}$ contains an anticodon loop with bases complementary to the mRNA codon.
Statement $(b)$ is correct: $\text{tRNA}$ was previously known as soluble $RNA$ $(\text{sRNA})$ and was identified before the genetic code was fully understood.
Statement $(c)$ is incorrect: There are no $\text{tRNA}$ molecules for stop codons ($UAA$,$UAG$,$UGA$). Termination is mediated by release factors.
Statement $(d)$ is incorrect: The secondary structure of $\text{tRNA}$ is clover-leaf shaped,while the tertiary structure is inverted $L$-shaped.
Therefore,only statements $(a)$ and $(b)$ are correct.

(A) During the process of translation,$\text{rRNA}$ performs two primary functions:
$1$. Structural role: $\text{rRNA}$ forms the structural framework of the ribosome,which is the site of protein synthesis.
$2$. Catalytic role: The $23S$ $\text{rRNA}$ in bacteria (or $28S$ $\text{rRNA}$ in eukaryotes) acts as a ribozyme,specifically a peptidyl transferase,which catalyzes the formation of peptide bonds between amino acids during polypeptide chain elongation.

(A) $1$. Translation begins when the small subunit of the ribosome binds to the $\text{mRNA}$ at the start codon,making option $A$ the correct statement.
$2$. The formation of peptide bonds is catalyzed by the enzyme peptidyl transferase (a ribozyme),not peptidase.
$3$. $\text{UTRs}$ $(\text{Untranslated Regions})$ are present at both the $5'$-end (before the start codon) and the $3'$-end (after the stop codon) to ensure efficient translation,not between the start and stop codons.
$4$. At the end of translation,the release factor binds to the stop codon (not the initiation codon) to terminate the process.

(C) The anticodon loop of $tRNA$ contains a sequence of $3$ unpaired nitrogenous bases,known as the anticodon.
These bases are complementary to the specific codon present on the $mRNA$ strand during the process of translation.
Therefore,the correct option is $C$.

(A) The $tRNA$ molecule has a specific structure where the amino acid acceptor end is the $3'$ end.
This $3'$ end contains a conserved sequence of three unpaired bases,which is $CCA$.
This $CCA$ sequence serves as the binding site for the specific amino acid during the process of protein synthesis.
Therefore,$i$ corresponds to $3'$ and $ii$ corresponds to $CCA$.

(C) The process of translation,which is the synthesis of a polypeptide from an $mRNA$ template,occurs in three distinct stages:
$1$. Initiation: The ribosome assembles around the target $mRNA$ and the first $tRNA$ is attached to the start codon.
$2$. Elongation: The ribosome moves along the $mRNA$ strand,adding amino acids to the growing polypeptide chain one by one as specified by the codons.
$3$. Termination: When a stop codon is reached,the ribosome releases the completed polypeptide chain and dissociates from the $mRNA$.

(D) During protein synthesis,the elongation phase involves the following steps:
$1$. The first aminoacyl-$tRNA$ (initiator $tRNA$) carrying methionine binds to the '$P$'-site of the ribosome.
$2$. Subsequent charged $tRNA$ molecules,carrying specific amino acids,enter the ribosome at the '$A$'-site.
$3$. $A$ peptide bond is formed between the amino acid at the '$P$'-site and the amino acid at the '$A$'-site,a reaction catalysed by the $23S$ rRNA (ribozyme).
$4$. Translocation is the movement of the ribosome along the $mRNA$ in the $5' \rightarrow 3'$ direction,not $3' \rightarrow 5'$. Therefore,statement $D$ is incorrect.

(D) During the process of translation in protein synthesis,the ribosome exists as two subunits: a smaller subunit and a larger subunit.
These two subunits remain separate in the cytoplasm when not involved in protein synthesis.
When the smaller subunit binds to the mRNA,the larger subunit attaches to it to form the functional ribosome complex.
This association of the two ribosomal subunits is dependent on the concentration of magnesium ions $(Mg^{++})$.
Therefore,$Mg^{++}$ ions are essential for the assembly of the functional ribosome.

(C) During the process of translation,the $mRNA$ codon pairs with the complementary $tRNA$ anticodon.
This interaction is mediated by the formation of $hydrogen$ bonds between the complementary nitrogenous bases (e.g.,$A$ with $U$,$G$ with $C$).
These $hydrogen$ bonds ensure the specificity and accuracy of the genetic code translation into a polypeptide chain.

(C) The formation of a polypeptide chain occurs during the process of translation.
Translation involves the synthesis of proteins from $mRNA$ templates.
$RNA$ polymerase is required for transcription (synthesis of $mRNA$ from $DNA$).
$DNA$ serves as the template for transcription,which provides the genetic code for the polypeptide chain.
Amino acids are the building blocks (monomers) required for the synthesis of the polypeptide chain.
$DNA$ polymerase is the enzyme responsible for $DNA$ replication,which is the process of copying $DNA$ molecules.
Therefore,$DNA$ polymerase is not involved in the process of protein synthesis (translation).

(B) The central dogma of molecular biology describes the flow of genetic information within a biological system.
$1$. $DNA$ acts as the master template and undergoes transcription to produce $mRNA$.
$2$. The $mRNA$ then undergoes translation at the ribosome to synthesize a specific polypeptide chain (protein).
$3$. Therefore,the correct sequence is $DNA \rightarrow$ Transcription $\rightarrow$ Translation $\rightarrow$ Protein.

(C) The start codon or initiation codon on $mRNA$ is $AUG$,which serves as the first codon to be translated during protein synthesis.
The anticodon on $t-RNA$ is complementary to the codon on $mRNA$ based on base-pairing rules ($A$ pairs with $U$,$U$ pairs with $A$,and $G$ pairs with $C$).
Therefore,the anticodon for the $AUG$ codon is $UAC$.

(D) $1$. The coding strand of $DNA$ has the sequence $ATG$ in the $5' \rightarrow 3'$ direction.
$2$. The $mRNA$ is transcribed from the template strand,which is complementary to the coding strand. Therefore,the $mRNA$ sequence will be identical to the coding strand,except that $Thymine$ $(T)$ is replaced by $Uracil$ $(U)$. Thus,the $mRNA$ codon is $AUG$.
$3$. During translation,the $t-RNA$ anticodon pairs with the $mRNA$ codon through complementary base pairing ($A$ pairs with $U$,$U$ pairs with $A$,$G$ pairs with $C$).
$4$. For the $mRNA$ codon $AUG$,the complementary anticodon on $t-RNA$ is $UAC$.

(A) To determine the number of amino acids,we must identify the Open Reading Frame $(ORF)$ starting from the initiation codon $(AUG)$ and ending at the termination codon ($UAA, UAG,$ or $UGA$).
The given $m-RNA$ sequence is: $5'-UUUUCUAUGCUGGUGGCUUGAUUUUCCCCU-3'$.
$1$. Locate the start codon $(AUG)$: The sequence contains $AUG$ starting at the $7^{th}$ position.
$2$. Identify the codons following $AUG$: $AUG$ (Met) - $CUG$ (Leu) - $GUG$ (Val) - $GCU$ (Ala) - $UGA$ (Stop).
$3$. The translation stops at the $UGA$ codon.
$4$. The codons are: $AUG, CUG, GUG, GCU$.
$5$. The $UGA$ codon is a stop codon and does not code for any amino acid.
$6$. Therefore,the polypeptide consists of $4$ amino acids (Methionine,Leucine,Valine,and Alanine).
Thus,the correct option is $A$.

(D) The figure shows a $tRNA$ molecule interacting with an $mRNA$ strand. The anticodon on the $tRNA$ is $UCA$,which base-pairs with the codon $AGU$ on the $mRNA$ strand.
According to the genetic code,the codon $AGU$ codes for the amino acid Serine (Ser).
Therefore,'$X$' represents the amino acid Serine (Ser).

(A) The $DNA$ template strand is $ATG$.
First,the $mRNA$ is synthesized from the $DNA$ template through transcription. According to the base-pairing rules ($A$ pairs with $U$,$T$ pairs with $A$,$G$ pairs with $C$),the $mRNA$ sequence will be $UAC$.
Next,the $t-RNA$ anticodon pairs with the $mRNA$ codon. The $mRNA$ codon is $UAC$.
The anticodon on $t-RNA$ is complementary to the $mRNA$ codon ($U$ pairs with $A$,$A$ pairs with $U$,$C$ pairs with $G$).
Therefore,the anticodon on $t-RNA$ will be $AUG$.

(B) The process of protein synthesis involves two main steps: transcription and translation.
$1$. During transcription,the template strand of $DNA$ $(ACG)$ is transcribed into $mRNA$. According to the base-pairing rules ($A$ pairs with $U$,$T$ pairs with $A$,$C$ pairs with $G$,and $G$ pairs with $C$),the $mRNA$ codon will be $UGC$.
$2$. During translation,the $tRNA$ carries an anticodon that is complementary to the $mRNA$ codon.
$3$. Since the $mRNA$ codon is $UGC$,the complementary anticodon on the $tRNA$ will be $ACG$ ($U$ pairs with $A$,$G$ pairs with $C$,and $C$ pairs with $G$).
Therefore,the correct option is $B$.

(C) The correct answer is $C$.
In a $tRNA$ molecule,the amino acid binding site is located at the $3'$ end.
This end contains a conserved sequence $CCA$ where the specific amino acid is attached via an ester bond to the $3'-OH$ group of the terminal adenosine residue.

(B) The given $DNA$ template strand sequence is: $3$' $TAC$ $ATG$ $GGT$ $CCG$ $5$'.
During transcription,the mRNA is synthesized complementary to the $DNA$ template strand in the $5$' to $3$' direction.
The mRNA sequence will be: $5$' $AUG$ $UAC$ $CCA$ $GGC$ $3$'.
The codons on the mRNA are $AUG$,$UAC$,$CCA$,and $GGC$.
The anticodons on the tRNA molecules that bind to these codons are $UAC$ (for $AUG$),$AUG$ (for $UAC$),$GGU$ (for $CCA$),and $CCG$ (for $GGC$).
Comparing the given tRNA complexes:
- $A$: $AUG$ (Anticodon for $UAC$)
- $B$: $UAC$ (Anticodon for $AUG$)
- $C$: $CCG$ (Anticodon for $GGC$)
- $D$: $GGU$ (Anticodon for $CCA$)
The sequence of binding to the mRNA codons ($AUG$,$UAC$,$CCA$,$GGC$) is $B$,$A$,$D$,$C$.

(C) $mRNA$ contains Untranslated Regions $(UTRs)$ which are sequences of $RNA$ that are not translated into proteins.
These $UTRs$ are present at both the $5'$-end (before the start codon $AUG$) and the $3'$-end (after the stop/terminator codon).
They are not translated but are required for the efficient translation process and stability of the $mRNA$ molecule.

$(A)$ Statement $A$ is wrong because a monocistronic mRNA, typically found in eukaryotes, contains the genetic information for only a single polypeptide chain.
Polycistronic mRNA, which is common in prokaryotes, is the type that can produce multiple polypeptide chains from a single mRNA strand.
Statement $B$ is correct because the process of translation is terminated by the presence of specific stop codons (terminator codons like $UAA$, $UAG$, or $UGA$) on the mRNA molecule, which signal the release of the polypeptide chain from the ribosome.

(A) $tRNA$ (transfer $RNA$) acts as an adapter molecule during protein synthesis.
It contains an anticodon loop,which consists of a sequence of three nitrogenous bases that are complementary to the specific codon present on the $mRNA$ strand.
During translation,the anticodon of the $tRNA$ base-pairs with the codon of the $mRNA$,ensuring that the correct amino acid is incorporated into the growing polypeptide chain.
Therefore,the correct region is the anticodon loop.

(D) $tRNA$.
Transfer $RNA$ $(tRNA)$ acts as an adapter molecule.
It has an anticodon loop that base pairs with the codon on $mRNA$ and a $3'$ acceptor end that carries a specific amino acid to the ribosome for protein synthesis.

(D) The correct answer is $D$.
Untranslated regions $(UTRs)$ are specific sequences present on the $mRNA$ that are required for efficient translation but are not translated into proteins.
These regions are located before the start codon at the $5'$-end and after the stop codon at the $3'$-end.

(B) The genetic code is read in the $5' \rightarrow 3'$ direction on $mRNA$.
$AUG$ is the start codon that codes for Methionine.
The anticodon on the $tRNA$ is complementary to the codon on the $mRNA$ and is read in the $3' \rightarrow 5'$ direction.
According to the base-pairing rules ($A$ pairs with $U$,$U$ pairs with $A$,$G$ pairs with $C$,and $C$ pairs with $G$):
- The complement of $A$ is $U$.
- The complement of $U$ is $A$.
- The complement of $G$ is $C$.
Therefore,the anticodon for the $AUG$ codon is $UAC$.

(B) $UTR$ stands for Untranslated Regions.
These are sequences present at the $5'$ and $3'$ ends of $mRNA$ that are not translated into proteins but are crucial for translation regulation.