Ch. 9 - The Molecular Biology of Translation

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172당신이 사용하는 게 아니라요?교과서 변경

Sanders 3rd Edition

Ch. 9 - The Molecular Biology of Translation

문제 35a

9장, 문제 35a

Table D lists α-globin and β-globin gene sequences for the 11 or 12 nucleotides preceding the start codon and the first nucleotide following the start codon (see Problem 34). The data are for 16 vertebrate globin genes reported by Kozak (1987). The sequences are written from -12 to +4 with the start codon sequence in capital letters. Use the data in this table to:
Determine the consensus sequence for the 16 selected α-globin and β-globin genes.

검증된 단계별 안내

Step 1: Understand the problem context. You are given sequences of nucleotides from 16 vertebrate α-globin and β-globin genes, spanning positions from -12 to +4 relative to the start codon. The start codon (usually 'AUG' in mRNA, 'ATG' in DNA) is capitalized and located at positions +1 to +3. Your goal is to find the consensus sequence, which represents the most common nucleotide at each position across all sequences.

Step 2: Organize the data by position. For each nucleotide position from -12 to +4, list all nucleotides found in the 16 sequences. This means creating a column for each position and noting the nucleotide from each gene sequence in that column.

Step 3: Count the frequency of each nucleotide at every position. For each position, tally how many times each of the four nucleotides (A, T, C, G) appears among the 16 sequences. This will help identify which nucleotide is most common at each position.

Step 4: Determine the consensus nucleotide at each position. For each position, select the nucleotide with the highest frequency count. If there is a tie, consider biological context or note ambiguity. The consensus sequence is formed by stringing together these most frequent nucleotides from position -12 through +4.

Step 5: Write out the consensus sequence clearly, indicating the start codon in capital letters at positions +1 to +3. This consensus sequence represents the typical nucleotide pattern found in the α-globin and β-globin genes around the start codon.

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주요 개념

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Consensus Sequence

A consensus sequence represents the most common nucleotide or amino acid found at each position in a set of aligned sequences. It summarizes conserved regions that are functionally or structurally important, such as promoter elements or start codon contexts. Identifying consensus sequences helps reveal patterns critical for gene expression or protein function.

Start Codon and Flanking Regions

The start codon (usually AUG) signals the beginning of translation in mRNA. Nucleotides immediately upstream (-12 to -1) and downstream (+1 to +4) of the start codon influence translation efficiency. These flanking sequences often contain regulatory motifs, such as the Kozak sequence, which affect ribosome recognition and initiation.

Sequence Alignment and Comparative Analysis

Sequence alignment arranges DNA or RNA sequences to identify regions of similarity and difference. Comparing multiple globin gene sequences from different species allows detection of conserved nucleotides, aiding in consensus sequence determination. This comparative approach highlights evolutionary conservation and functional importance.

관련 실천

교과서 질문

In terms of the polycistronic composition of mRNAs and the presence or absence of Shine–Dalgarno sequences, compare and contrast bacterial, archaeal, and eukaryotic mRNAs.

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교과서 질문

The six nucleotides preceding the start codon and the first nucleotide after the start codon in eukaryotes exhibit strong sequence conservation as determined by the percentages of nucleotides in the to positions and the position (see Problem 34). Use the data given in the table for Problem 35 to determine the seven nucleotides that most commonly surround the start in vertebrates.

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교과서 질문

Table D lists α-globin and β-globin gene sequences for the 11 or 12 nucleotides preceding the start codon and the first nucleotide following the start codon (see Problem 34). The data are for 16 vertebrate globin genes reported by Kozak (1987). The sequences are written from -12 to +4 with the start codon sequence in capital letters. Use the data in this table to:

Compare the consensus sequence for these globin genes to the consensus sequence derived from the larger study of 699 vertebrate genes in Problem 34.

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교과서 질문

A eukaryotic mRNA has the following sequence. The 5' cap is indicated in italics (CAP), and the 3' poly(A) tail is indicated by italicized adenines.

5′-CAPCCAAGCGUUACAUGUAUGGAGAGAAUGAAACUGAGGCUUGCCACGUUUGUUAAGCACCUAUGCUACCGAAAAAAAAAAAAAAAAAAAAAAAA-3′

Determine the amino acid sequence of the polypeptide produced from this mRNA. Write the sequence using the three-letter and one-letter abbreviations for amino acids.

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교과서 질문

Diagram a eukaryotic gene containing three exons and two introns, the pre-mRNA and mature mRNA transcript of the gene, and a partial polypeptide that contains the following sequences and features. Carefully align the nucleic acids, and locate each sequence or feature on the appropriate molecule.

a. The AG and GU dinucleotides corresponding to intron-exon junctions
b. The +1 nucleotide
c. The 5' UTR and the 3' UTR
d. The start codon sequence
e. A stop codon sequence
f. A codon sequence for the amino acids Gly-His-Arg at the end of exon 1 and a codon sequence for the amino acids Leu-Trp-Ala at the beginning of exon 2

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교과서 질문

Table C contains DNA-sequence information compiled by Marilyn Kozak (1987). The data consist of the percentage of A, C, G, and T at each position among the 12 nucleotides preceding the start codon in 699 genes from various vertebrate species and at the first nucleotide after the start codon. (The start codon occupies positions +1 to +3 and the first nucleotide immediately after the start codon occupies position +4) Use the data to determine the consensus sequence for the 13 nucleotides ( -12 to -1 and +4) surrounding the start codon in vertebrate genes.

645

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