Why Investigators Prefer DNA Sequences Rich in Tryptophan and Methionine Codons for PCR Primers
In selecting a DNA sequence to be used as a template for construction of PCR primers, many investigators look for sequences rich in codons for tryptophan or methionine because
A. Tryptophan and methionine have only one codon each (i.e., there is no wobble)
B. Tryptophan and methionine have three codon each
C. Codons for tryptophan and methionine abundantly present in mRNA
D. None.
Correct Answer: (A) Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Why Investigators Prefer DNA Sequences Rich in Tryptophan and Methionine Codons for PCR Primers
Polymerase Chain Reaction (PCR) is a powerful technique used to amplify specific DNA sequences. When designing PCR primers, selecting an optimal DNA template sequence is crucial for achieving high specificity and efficiency in amplification. One common strategy is to target sequences rich in codons for tryptophan (Trp) and methionine (Met).
Correct Answer Explained:
The correct answer is (A) Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Genetic Code and Codon Redundancy:
- The genetic code is degenerate, meaning that most amino acids are encoded by multiple codons due to the “wobble” effect at the third nucleotide position of the codon.
- However, tryptophan (Trp) is encoded by a single codon (UGG) and methionine (Met) is encoded by a single codon (AUG).
- This lack of redundancy reduces the chances of mismatched binding during primer design, improving the specificity and stability of the PCR reaction.
Why Other Options Are Incorrect:
- (B) Tryptophan and methionine have three codons each – This is incorrect because Trp and Met are each encoded by only one codon (UGG and AUG, respectively).
- (C) Codons for tryptophan and methionine are abundantly present in mRNA – Codons for Trp and Met are relatively rare in mRNA compared to other amino acids, so this statement is incorrect.
- (D) None – This is incorrect since option (A) is factually accurate.
Why Tryptophan and Methionine Codons Improve PCR Primer Efficiency:
-
No Wobble Effect:
- Since Trp and Met codons are not degenerate, there is no variability at the third codon position.
- This ensures that the primer sequence is highly specific to the target DNA.
-
Reduced Primer Mismatch:
- Single codon specificity reduces the possibility of mismatched primer binding.
- This improves the efficiency of primer annealing and amplification.
-
Higher Fidelity in Amplification:
- The absence of wobble effect minimizes off-target amplification.
- This leads to higher specificity and yield in PCR results.
Importance in Molecular Biology:
PCR primers rich in codons for Trp and Met are particularly useful for:
✅ Gene Cloning – High specificity ensures accurate gene amplification.
✅ Mutation Detection – Reduced variability leads to precise mutation identification.
✅ Protein Engineering – Ensures that target sequences are accurately amplified for recombinant protein expression.
Conclusion:
Investigators prefer sequences rich in tryptophan and methionine codons when designing PCR primers because these codons are uniquely encoded by a single nucleotide triplet (UGG and AUG, respectively). This reduces variability and enhances primer-target specificity, leading to more efficient and accurate PCR amplification.
Final Answer: (A) Tryptophan and methionine have only one codon each (i.e., there is no wobble).
70 Comments
Akshay mahawar
March 16, 2025Done 👍
Suman bhakar
March 17, 2025💯
Parul
March 22, 2025Done sir.
Abhilasha
March 25, 2025Ok sir
Nisha
March 27, 2025Done
Khushi Pareek
August 24, 2025tryptophan and methionine have only one codon
Mohd juber Ali
August 24, 2025Tryptophan and methionine have one codon
Tryptophan (UGG)
Methionine (AUG)
Sakshi yadav
August 24, 2025Methionine and tryptophan have one codon AUG , UGG
karishma don
August 24, 2025because tryptophan and methionine has only one codon each
Mansukh Kapoor
August 24, 2025The correct answer is option 1st
Tryptophan and methionine have only one codon each (UGG and AUG)
Neha Yadav
August 24, 2025Trp and met have only one codon each
Soniya Shekhawat
August 24, 2025Tryptophan and methionine have a one codon, tryptophan codon is a UGG methionine codon is AUG so is not part of wobble hypothesis.
Anurag Giri
August 24, 2025The correct answer is (A) Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Priyanka Choudhary
August 24, 2025A will bhi right answer,Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Khushi Agarwal
August 24, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Avni
August 24, 2025Tryptophan and methionine have only one codon each that are UGG and AUG, respectively
Aakanksha Sharma
August 24, 2025Bcz Tryp& met have 1codon each
Roopal Sharma
August 24, 2025Tryptophan and methionine has only one code so no wobble .
Dipti Sharma
August 24, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
So , it will be easier to predict DNA sequence more accurately .
Sheikh Aleen
August 24, 2025Correct ans is A- Tryptophan and methionine have only one codon each.
AKANKSHA RAJPUT
August 24, 2025The correct answer is (A)
Aafreen Khan
August 24, 2025Tryptophan and methionine have only one codon each, there is no wobble
anjani sharma
August 24, 2025Answer a
Methionine and tryptophan have one codon each AUG , UGG
Khushi Mehra
August 24, 2025Tryptophan and methionine coded by only single-single codon
Tryptophan= UGG
methionine= AUG
Neelam Sharma
August 24, 2025Methionine and tryptophan have one codon AUG , UGG
Tanvi Panwar
August 24, 2025Tryptophan and methionine have only one codon that is there is no wobble.
Heena Mahlawat
August 24, 2025Methionine and tryptophan doesn’t show redundancy ,they show only one specific codon
Arushi Saini
August 24, 2025Trp and met have only one codon which reduces the mismatch pairing between template and primer in primer synthesis by protein
MOHIT AKHAND
August 24, 2025Done sir ✅
Sneha Kumawat
August 24, 2025Tryptophan and methonoine have only one chodon
UGG AND AUG
Santosh Saini
August 24, 2025Tryptophan (UGG) and methionine (AUG start codon) have only one code each (there is no wobble)
Bhawna Choudhary
August 24, 2025Tryptophan and methionine has only one codon
Dharmpal Swami
August 25, 2025Tryptophan and methionine have only one codon
Ayush Dubey
August 25, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Divya rani
August 25, 2025Tryptophan and methionine has only one codon which is not wobble.
Aman Choudhary
August 25, 2025Option A is correct
Tryptophan and methionine have only one codon each (i.e., there is no wobble)
shruti sharma
August 25, 2025Tryptophan and methionine has only one code so no wobble .
Payal Gaur
August 25, 2025Tryptophan (UGG) and methionine (AUG) only one codon sequance so no wobble.
Pallavi Ghangas
August 25, 2025No wobble for tryptophan and methionin
Bhavana kankhedia
August 26, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Vanshika Sharma
August 26, 2025Tryptophan and methionine have only one codon each
Bhavana kankhedia
August 26, 2025Tryptophan and methionine have only one codon each so no wobble
Minal Sethi
August 26, 2025Met and Trp have only one codon each so that the number of different primers reduces
Bhavana kankhedia
August 26, 2025Tryptophan and methionine have only one codon each and no wobble
Shivani
August 26, 2025(A) Tryptophan and methionine have only one codon each.
Rishita
August 26, 2025Opt a is correct
Surendra Doodi
August 26, 2025Tryptophan and methionine have only one codon
Alec
August 26, 2025Tryptophan and methionine have only one codon thus there is no wobble.
Simran Saini
August 26, 2025Tryptophan and methionine have only one codon each (I.e. there is no wobble).
Samiksha bajiya
August 27, 2025Tryptophan and methionine have only one codon each so no wobble
Devika
August 27, 2025Tryptophan and methionine have only one codon
Rakesh Dhaka
August 27, 2025The correct answer is option 1st
Tryptophan and methionine have only one codon each (UGG and AUG)
Mitali saini
August 28, 2025Correct Answer: (A) Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Kanica Sunwalka
August 28, 2025done
Nilofar Khan
August 28, 2025Correct answer is a
Tryptophan and methionine have only one codone each.
Methionine (AUG)
Tryptophan (UGG)
Deepika Sheoran
August 28, 2025Option A is correct
Tryptophane and Methionine have only one codon each (UGG and AUG)..
Mohini
August 28, 2025Tryptophan and Methionine have only one codon each. and they are less found in sequence,
Khushi Vaishnav
August 28, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Muskan singodiya
August 29, 2025Tryptophan and methionine have only one codon each
Parul Yadav
August 29, 2025Tryptophan and Methionine are coded by one codon only.
Neeraj Sharma
August 29, 2025Option A as tryptophan and methionine have only one codon each so sequencing will be easy
Anisha Beniwal
August 29, 2025Option A – methionine and tryptophan are have one codon each AUG&UGG
Priya dhakad
August 29, 2025Tryptophan and methionine have only one codon each.
Asha Gurzzar
August 30, 2025Tryptophan and methionine have only one codon
Khushi Singh
August 30, 2025Tryptophan methionine has only 1 codon
Kirti Agarwal
August 31, 2025Tryptophan and methionine have only one codon
Kajal
August 31, 2025correct answer is (A) Tryptophan and methionine have only one codon each (there is no wobble)
Neelam Sharma
September 9, 2025Tryptophan and methionine have only one codon each (i.e., there is no wobble).
Neelam Sharma
September 9, 2025Tryptophan and methionine have only one codon each (there is no wobble)
Muskan Yadav
September 17, 2025Tryptophan and methionine have only one codon each there is no wobble .