Where is the start codon located?
a. At the start (5′ end) of the mRNA
b. In the DNA just upstream of where transcription starts
c. At the downstream end of the 5′ untranslated region (UTR)
d. At the upstream end of the 3′ untranslated region (UTR)

검증된 단계별 안내

Understand the role of the start codon: The start codon is a specific sequence of three nucleotides (AUG in most cases) that signals the beginning of translation, where the ribosome starts synthesizing a protein.

Recall the structure of mRNA: mRNA has a 5′ untranslated region (UTR), a coding sequence, and a 3′ untranslated region (UTR). The start codon is part of the coding sequence, not the untranslated regions.

Identify the location of the start codon: The start codon is located at the downstream end of the 5′ untranslated region (UTR), marking the transition from the UTR to the coding sequence.

Eliminate incorrect options: a) The start codon is not at the very start (5′ end) of the mRNA, as the 5′ UTR precedes it. b) It is not in the DNA upstream of transcription, as the start codon is part of the mRNA. d) It is not at the upstream end of the 3′ UTR, as the 3′ UTR is downstream of the coding sequence.

Conclude that the correct answer is c) at the downstream end of the 5′ untranslated region (UTR), as this is where the start codon is located in the mRNA.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Start Codon

The start codon is a specific sequence of nucleotides in mRNA that signals the beginning of translation. It is typically the codon AUG, which codes for the amino acid methionine. The presence of the start codon is crucial for ribosomes to initiate protein synthesis.

mRNA Structure

Messenger RNA (mRNA) is a single-stranded molecule that carries genetic information from DNA to the ribosome, where proteins are synthesized. The 5' end of mRNA is capped, and it contains a 5' untranslated region (UTR) before the start codon, which plays a role in the regulation of translation.

Transcription and Translation

Transcription is the process by which DNA is copied into mRNA, while translation is the subsequent process where ribosomes read the mRNA sequence to synthesize proteins. The start codon is essential in translation as it marks the site where the ribosome begins to assemble amino acids into a polypeptide chain.