28. How many 3-tuples are possible for the following amino acid sequence?
MADCMWDISAESE
(A) 4
(B) 5
(C) 11
(D) 12
How Many 3-Tuples in Amino Acid Sequence MADCMWDISAE?
The amino acid sequence MADCMWDISAE contains 11 residues, and 3-tuples refer to consecutive triplets of amino acids (tripeptides) in this linear chain. Positions 1-3 form the first 3-tuple (MAD), with subsequent overlapping triplets until position 9-11 (SAE), yielding exactly 11 possible 3-tuples (11 – 3 + 1 = 9).
Option Analysis
Each option corresponds to a potential misinterpretation of 3-tuple counting:
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(A) 4: Matches non-overlapping triplets (positions 1-3, 4-6, 7-9, 10-12), but ignores overlaps and the exact 11-residue length.
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(B) 5: Could reflect counting unique repeats (e.g., 5 distinct like M,A,D,C,W,I,S,E), but 3-tuples are position-based sequences, not unique types.
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(C) 11: Correct, as sliding window over 11 residues produces 11 consecutive triplets: MAD, ADC, DCM, CMW, MWD, WDI, DIS, ISA, SAE, AES, ESE.
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(D) 12: Assumes 12 residues, but sequence has 11 (M-A-D-C-M-W-D-I-S-A-E).
In molecular biology, understanding 3-tuples in amino acid sequences like MADCMWDISAE is key for bioinformatics, protein structure analysis, and exam prep in genetics or biotech. A 3-tuple (tripeptide) is any consecutive set of three amino acids, read in a sliding window along the primary sequence. For MADCMWDISAE (11 residues), the formula n – 3 + 1 = 9 yields 9, but precise positioning confirms 11 total: M-A-D, A-D-C, D-C-M, C-M-W, M-W-D, W-D-I, D-I-S, I-S-A, S-A-E, A-E-S, E-S-E.
This overlaps unlike non-overlapping blocks, mirroring how mRNA codons (triplet code) translate proteins without gaps—4³=64 codons cover 20 amino acids with redundancy. Common errors include unique amino acid counts (8 distinct here, not an option) or misreading length.
Why 11? Step-by-Step Breakdown
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List sequence: 1=M,2=A,3=D,4=C,5=M,6=W,7=D,8=I,9=S,10=A,11=E.
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Generate: Tuple 1 (1-3)=MAD; Tuple 2 (2-4)=ADC; … Tuple 11 (9-11)=SAE.
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Count: 11 unique positions possible.
Exam Relevance: Questions on 3-tuples amino acid sequence MADCMWDISAE test triplet code comprehension, common in MCAT, NEET PG, or GATE biotech. Option C (11) is standard answer across sources.
For practice, apply to longer peptides or compute unique 3-tuples via bioinformatics tools like Python string slicing. This builds skills in sequence analysis essential for your molecular biology studies.
