The base sequences in mRNA that code for certain amino acids...

The base sequences in mRNA that code for certain amino acids are Glu: $\quad$ GAA, GAG Val: GUU, GUC, GUA, GUG Met: AUG Trp: UGG Phe: UUU, UUC Asp: GAU, GAC These sequences are complementary to the sequences in DNA. a. Give the corresponding sequences in DNA for the amino acids listed above. b. Give a DNA sequence that would code for the peptide trp-glu-phe-met. c. How many different DNA sequences can code for the butapeptide in part b? d. What is the peptide that is produced from the DNA sequence $\mathrm{T}-\mathrm{A}-\mathrm{C}-\mathrm{C}-\mathrm{T}-\mathrm{G}-\mathrm{A}-\mathrm{A}-\mathrm{G} ?$ e. What other DNA sequences would yield the same tripeptide as in part $\mathrm{d}$ ?

The base sequences in mRNA that code for certain amino acids are
Glu: $\quad$ GAA, GAG Val: GUU, GUC, GUA, GUG Met: AUG Trp: UGG Phe: UUU, UUC Asp: GAU, GAC
These sequences are complementary to the sequences in DNA.
a. Give the corresponding sequences in DNA for the amino acids listed above.
b. Give a DNA sequence that would code for the peptide trp-glu-phe-met.
c. How many different DNA sequences can code for the butapeptide in part b?
d. What is the peptide that is produced from the DNA sequence $\mathrm{T}-\mathrm{A}-\mathrm{C}-\mathrm{C}-\mathrm{T}-\mathrm{G}-\mathrm{A}-\mathrm{A}-\mathrm{G} ?$
e. What other DNA sequences would yield the same tripeptide as in part $\mathrm{d}$ ?

Key Concepts

Reading Frame

The reading frame is the way nucleotides in an mRNA or DNA sequence are divided into consecutive non-overlapping triplets or codons during translation. The correct reading frame is crucial because starting the translation at the wrong nucleotide can lead to a completely different amino acid sequence, as the triplet grouping of bases shifts. Understanding the reading frame is essential when deciphering how a given nucleotide sequence translates into a functional peptide.

Codon Degeneracy

Codon degeneracy refers to the redundancy of the genetic code; that is, multiple codons can encode the same amino acid. This feature has implications for mutation tolerance and the design of synthetic genes because small changes in the nucleotide sequence might not necessarily alter the amino acid sequence in the protein, leading to different nucleotide sequences that still produce the same peptide sequence.

Transcription

Transcription is the biological process in which a segment of DNA is used as a template to produce a complementary RNA sequence. During this process, the base pairing rules ensure that adenine in DNA pairs with uracil in RNA (instead of thymine), while cytosine pairs with guanine. This process is fundamental to translating genetic information into a form that can be used by the ribosome during protein synthesis.

Genetic Code

The genetic code is the set of rules by which information encoded in messenger RNA (mRNA) sequences is translated into proteins. It specifies which combinations of three nucleotides, called codons, correspond to specific amino acids. This code is degenerate, meaning that most amino acids are specified by more than one codon, allowing for some flexibility and redundancy in the DNA and mRNA sequences.

Complementary Base Pairing

Complementary base pairing is the principle that dictates how nucleotides pair with one another in DNA and RNA. In DNA, adenine (A) pairs with thymine (T) and cytosine (C) with guanine (G). In RNA, adenine pairs with uracil (U) instead. This specificity ensures accurate replication and transcription, where the mRNA sequence is the complement of the DNA template strand.

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