Genetic code Questions in English

(A) The concept of 'one gene-one enzyme' hypothesis was proposed by Beadle and Tatum.
It states that each gene is responsible for the synthesis of a single specific enzyme.
Therefore,one gene determines the synthesis of one enzyme.

(C) There are $3$ stop codons,also known as nonsense codons,which do not code for any amino acid. These are $UAA$,$UAG$,and $UGA$.

(B) The process of translation is terminated when the ribosome encounters a stop codon (also known as a termination codon) on the $mRNA$ strand.
There are three stop codons in the genetic code: $UAA$,$UAG$,and $UGA$.
These codons do not code for any amino acid and signal the release of the polypeptide chain from the ribosome.
Among the given options,$UAA$ is a stop codon.

(C) The original sequence is $AAC\ GAC\ AGC\ GGC\ ACA\ AAA$.
If the first base $(A)$ is deleted,the sequence becomes $ACG\ ACG\ AGC\ GGC\ ACA\ AA$.
This is a frameshift mutation. However,in the context of this specific question,if we consider the deletion of the first base of the first triplet,the reading frame shifts entirely.
Option $C$ is the most scientifically accurate description of a frameshift mutation,as the deletion of a single base changes every subsequent triplet codon,leading to a completely different sequence of amino acids in the resulting polypeptide chain.

(A) In eukaryotes,the chain initiation codon is generally $AUG$.
This codon codes for the amino acid methionine.
$UGA$ and $UAG$ are stop codons,while $GUG$ typically codes for valine.

(A) Exons are the coding sequences in $m-RNA$ that are expressed during protein synthesis.
Introns are the non-coding sequences that are removed during $RNA$ splicing.
Therefore,the exon part of $m-RNA$ contains the genetic code required for the synthesis of specific proteins.

(D) The genetic code is a triplet,meaning each codon consists of a sequence of three nitrogenous bases. Since there are $4$ types of nitrogenous bases $(A, U, G, C)$ in $RNA$,the total number of possible combinations is $4^3 = 4 \times 4 \times 4 = 64$. Thus,there are $64$ possible codons.

(A) Genes express their characters by synthesizing proteins,which often function as enzymes. This is based on the 'one gene-one enzyme' hypothesis proposed by Beadle and Tatum,which states that each gene is responsible for the synthesis of a single specific enzyme that catalyzes a particular biochemical reaction in the cell.

(D) The codons that cause chain termination are known as stop codons or nonsense codons.
These codons do not code for any amino acid during the process of protein synthesis (translation).
The three stop codons are $UAG$,$UGA$,and $UAA$.

(D) The process of translation begins at the initiation codon $(AUG)$ and terminates at a stop codon ($UAA$,$UAG$,or $UGA$).
For an $mRNA$ to be translated completely,the initiation codon must be present at the start,and the termination codon must be present at the very end of the sequence.
In option $(d)$,the sequence is $AUG \ UAU \ UUC \ UGC \ CUC \ UAG$. Here,$AUG$ acts as the initiation codon,and $UAG$ acts as the termination codon at the end of the sequence,allowing the entire segment to be translated.

(D) The correct answer is $D$. $A$ single amino acid is specified by a sequence of three nucleotides in $mRNA$,which is called a codon. Due to this triplet nature,the genetic code consists of $64$ possible codons $(4^3 = 64)$.

(C) George Gamow proposed the concept of the genetic code. He suggested that since there are $20$ amino acids and only $4$ bases,the code must be composed of a combination of bases. He proposed that the code was a triplet,meaning $3$ bases code for one amino acid. This is often referred to as the diamond code proposal.

(A) George Gamow,a physicist,was the first to propose that the genetic code must be a triplet of nucleotides. He reasoned that since there are only $4$ types of nitrogenous bases $(A, U, G, C)$ and $20$ amino acids to be coded,a single base $(4^1 = 4)$ or a doublet $(4^2 = 16)$ would not be sufficient to code for all $20$ amino acids. Therefore,a triplet code $(4^3 = 64)$ was necessary to account for all $20$ amino acids.

(B) The genetic code is said to be $Non-ambiguous$ because one specific codon always codes for only one particular amino acid. This means there is no ambiguity in the translation process,as a single codon cannot code for two different amino acids.

(B) The genetic code was first deciphered by Nirenberg and Matthaei in $1961$. They used a cell-free system to synthesize proteins from synthetic $RNA$ and experimentally proved that the genetic code is triplet in nature.

(B) The genetic code is said to be degenerate because some amino acids are specified by more than one codon. Since there are $64$ possible codons and only $20$ standard amino acids,the number of codons exceeds the number of amino acids. This redundancy ensures that multiple codons can code for the same amino acid,which provides a buffer against mutations.

(C) The genetic code is generally considered universal,meaning it is the same in most organisms. However,there are exceptions to this universality.
In human mitochondria $(mtDNA)$,the genetic code differs from the standard nuclear genetic code.
For example,the codons $AGG$ and $AGA$ normally code for arginine,but they function as stop signals in human mitochondria.
Additionally,the codon $UGA$,which is a standard termination codon,codes for tryptophan in mitochondria,and the codon $AUA$,which normally codes for isoleucine,codes for methionine in human mitochondria.

(A) The genetic code is described as degenerate because some amino acids are encoded by more than one codon.
Since there are $64$ possible codons and only $20$ amino acids,the genetic code exhibits redundancy.
This means that multiple codons can specify the same amino acid,which is the definition of degeneracy in the genetic code.

(B) The genetic code is a triplet code,meaning that a sequence of three nitrogenous bases,known as a codon,specifies a particular amino acid during the process of protein synthesis (translation).
There are $64$ possible codons,out of which $61$ code for amino acids and $3$ act as stop codons.

(A) During the process of viral replication,the virus hijacks the host cell's machinery to synthesize its own components.
The genetic information required to code for viral proteins (which are composed of amino acids) is stored in the viral genome.
The viral genome consists of nucleic acids,either $DNA$ or $RNA$.
Therefore,the genetic code for the synthesis of viral proteins is carried by the virus's own nucleic acid.

(B) Hargobind Khorana,along with Marshall Nirenberg and Robert Holley,was awarded the Nobel Prize in Physiology or Medicine in $1968$ for their interpretation of the genetic code and its function in protein synthesis.
Specifically,Khorana's work involved the chemical synthesis of oligonucleotides,which helped in deciphering the genetic code and understanding how specific sequences of bases code for specific amino acids.

(B) George $Gamow$ was the first to suggest that the genetic code must be a triplet,meaning three nucleotides code for one amino acid. He argued that since there are only $4$ bases and $20$ amino acids,a triplet code ($4^3 = 64$ codons) is the minimum required to code for all $20$ amino acids. While $Nirenberg$ and $Matthaei$ experimentally proved the triplet nature of the code using synthetic $mRNA$ (poly-$U$),the theoretical possibility was first pointed out by $Gamow$.

(A) Dr. Hargovind Khorana was awarded the Nobel Prize in Physiology or Medicine in $1968$ for his work on the interpretation of the genetic code and its function in protein synthesis.
He is specifically recognized for his pioneering work in the synthesis of the first artificial gene,which involved the chemical synthesis of a functional gene for a transfer $RNA$ (tRNA) molecule.

(B) The genetic code is defined by the sequence of nitrogenous bases in $mRNA$.
In $mRNA$,the nitrogenous bases are Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Uracil $(U)$.
Thymine $(T)$ is present in $DNA$ but is replaced by Uracil $(U)$ in $RNA$.
Since the coding dictionary (genetic code) is based on the sequence of codons in $mRNA$,Thymine is absent in the coding dictionary.

(B) The genetic code is degenerate,which means it lacks specificity,and one amino acid is often encoded by more than one codon triplet.
This phenomenon is also known as the redundancy of the genetic code.
Only methionine and tryptophan are encoded by a single triplet codon.

(D) The Wobble hypothesis was proposed by $F. H. C. Crick$ in $1965$.
This hypothesis explains that the third base of a codon (at the $3'$ end) can form non-standard base pairs with the first base of an anticodon (at the $5'$ end),allowing a single $tRNA$ to recognize more than one codon.

(D) The genetic code is degenerate,which means that more than one codon can code for the same amino acid.
Since there are $64$ possible codons and only $20$ amino acids to be coded,some amino acids are specified by more than one codon.
This redundancy or degeneracy ensures that the genetic code is robust against mutations.
Therefore,the correct answer is $D$.

(A) The genetic code is degenerate,meaning that some amino acids are encoded by more than one codon.
Both $UGC$ and $UGU$ are codons that code for the amino acid $Cysteine$ $(Cys)$.
Therefore,$UGU$ codes for the same information as $UGC$.

(B) The correct matches are as follows:
$1. \; AUG$ codes for $\text{Methionine}$ (start codon).
$2. \; UAA$ is a stop codon, which signals $\text{Termination}$ of protein synthesis.
$3. \; UUU$ codes for $\text{Phenylalanine}$.
$4. \; UGG$ codes for $\text{Tryptophan}$.
Therefore, the correct matching is $A-2, B-4, C-1, D-3$.

(A) The coding strand sequence is alternating $C$ and $U$ residues,which can be represented as $...CUCUCU...$.
During transcription,the $mRNA$ formed from this coding strand will have the same sequence: $...CUCUCU...$.
The genetic code is read in triplets (codons). The possible codons from this sequence are $CUC$ and $UCU$.
According to the genetic code table,$CUC$ codes for the amino acid Leucine $(Leu)$ and $UCU$ codes for the amino acid Serine $(Ser)$.
Therefore,the resulting polypeptide will contain alternating Leucine and Serine residues.

(B) The genetic code is degenerate and specific.
- $UUA$ codes for Leucine.
- $AAA$ codes for Lysine.
- $AUG$ codes for Methionine (it also acts as a start codon).
- $CCC$ codes for Proline.
Therefore,the pair $AAA$-Lysine is correctly matched.

(C) The genetic code is a triplet code. Three adjacent nitrogenous bases on the messenger $RNA$ $(mRNA)$,termed a codon,specify one amino acid. The sequence of these bases is read in the $5'$ to $3'$ direction.

(B) The relationship between the sequence of nucleotides in $mRNA$ and the sequence of amino acids in a polypeptide chain is described as colinear. This means that the linear sequence of codons in the $mRNA$ corresponds directly to the linear sequence of amino acids in the protein synthesized. Therefore,both $mRNA$ and proteins exhibit a linear arrangement of their respective components.

(B) The genetic code is described as $Degenerate$ because some amino acids are coded by more than one codon. Since there are $64$ possible codons and only $20$ amino acids,multiple codons can specify the same amino acid. This property is known as the degeneracy of the genetic code.

(A) The genetic code is the set of rules by which information encoded in genetic material ($mRNA$ sequences) is translated into proteins (amino acid sequences) by living cells.
During the process of translation,the sequence of nucleotides in $mRNA$ is read in groups of three,known as codons.
Each codon corresponds to a specific amino acid,which is brought to the ribosome by $tRNA$ molecules containing the complementary anticodon.
Thus,the genetic code effectively translates the language of $RNA$ into the language of proteins.

(A) triplet codon is defined as a sequence of three consecutive nitrogenous bases on $mRNA$ that codes for a specific amino acid during the process of protein synthesis (translation). This triplet sequence is known as a codon. While $tRNA$ contains an anticodon (a sequence of three bases complementary to the codon),the term 'codon' specifically refers to the sequence found on the $mRNA$ strand.

(B) The genetic code is present on the $mRNA$ molecule,which dictates the specific sequence of amino acids to be incorporated into the polypeptide chain during translation. Since the $mRNA$ template is derived from $E. coli$,the resulting polypeptide will correspond to the proteins synthesized by $E. coli$ cells,regardless of the source of the $tRNA$ or ribosomes,as the genetic code is universal.

(C) The genetic code is a triplet,meaning $3$ nitrogenous bases code for $1$ amino acid.
To code for the $N$-terminal amino acid (which is the $1$st amino acid) and the next $13$ amino acids,we need to code for a total of $1 + 13 = 14$ amino acids.
Since each amino acid requires $3$ bases,the total number of bases required is $14 \times 3 = 42$ bases.
Therefore,the correct option is $42$.

(A) monocistronic $mRNA$ is a type of messenger $RNA$ that encodes information for the synthesis of only one specific polypeptide chain or protein molecule.
In eukaryotes,most $mRNA$ molecules are monocistronic,meaning each $mRNA$ transcript contains the genetic information for a single protein.
In contrast,polycistronic $mRNA$,commonly found in prokaryotes,contains the genetic information for multiple proteins.

(A) The "one gene one enzyme" hypothesis was proposed by George Beadle and Edward Tatum in $1941$.
They conducted experiments on the bread mould $Neurospora crassa$.
They demonstrated that genes act by regulating definite chemical events, specifically that each gene is responsible for the synthesis of a single enzyme.

(B) The correct statement is $B$. According to the 'one gene-one polypeptide' hypothesis,a single gene is responsible for the synthesis of a single polypeptide chain. Since many proteins are composed of multiple polypeptide subunits,a single gene does not necessarily code for an entire protein molecule.

(A) The 'one gene one enzyme' hypothesis,proposed by Beadle and Tatum,states that each gene is responsible for the synthesis of a single specific enzyme.
This concept implies that a gene controls a structural or functional trait by regulating the synthesis of a specific protein or enzyme.

(A) Beadle and Tatum proposed the 'one gene-one enzyme' hypothesis based on their experiments with the bread mold $Neurospora crassa$.
They demonstrated that specific mutations in genes resulted in the loss of specific enzymatic activities, thereby proving that a single gene is responsible for the synthesis of a single specific enzyme (or protein).

(A) The production of human gene products in genetically engineered bacteria is possible primarily because the genetic code is universal.
This means that the same codons in $DNA$ or mRNA specify the same amino acids in both prokaryotes (like bacteria) and eukaryotes (like humans).
Therefore,when a human gene is inserted into a bacterial plasmid,the bacterial machinery can correctly translate the human genetic sequence into the corresponding human protein.

(B) Har Gobind Khorana was a Nobel Prize-winning biochemist who is renowned for his pioneering work in the synthesis of the first artificial gene. He successfully synthesized the gene for yeast alanine transfer $RNA$ $(tRNA)$ in the laboratory,which was a landmark achievement in the field of molecular biology and genetic engineering.

(A) The genetic code is a triplet,meaning that $3$ nitrogenous bases constitute a single codon on $m-RNA$. Each codon specifies a particular amino acid during the process of protein synthesis (translation). Therefore,$m-RNA$ contains sequences of $3$ bases that act as codons.

(B) The genetic code is a set of rules by which information encoded in genetic material ($DNA$ or $mRNA$ sequences) is translated into proteins (amino acid sequences) by living cells. Each codon,consisting of a triplet of nucleotides,corresponds to a specific amino acid. Therefore,the genetic code dictates the sequence of amino acids in a polypeptide chain.

(C) The genetic code has several key characteristics:
$1$. It is $Triplet$: Each codon consists of three nitrogenous bases.
$2$. It is $Universal$: The same codon codes for the same amino acid in almost all organisms (from bacteria to humans).
$3$. It is $Unambiguous$ (Non-ambiguous): One codon codes for only one specific amino acid.
Since the option $Ambiguous$ is incorrect (the code is non-ambiguous) and the code is both $Triplet$ and $Universal$,the question implies identifying the correct properties. However,in standard multiple-choice formats,if $Triplet$ and $Universal$ are both correct,the question structure often points to the most defining feature. Given the options,$Triplet$ is a fundamental property,but since $Universal$ is also correct,and $Ambiguous$ is false,'All of the above' is technically incorrect. The most accurate single answer is $Triplet$.

(C) The genetic code is based on $4$ nitrogenous bases $(A, U, G, C)$.
If the code is a triplet,the number of possible codons is $4^3 = 64$.
If the genetic code were a tetraplet (four-letter code),the number of possible codons would be $4^4$.
Calculating this: $4 \times 4 \times 4 \times 4 = 256$.
Therefore,there would be $256$ possible codons.