Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

11. Translation

The Genetic Code

Genetics

11. Translation

The Genetic Code

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1:28 minutes

Problem 32

Textbook Question

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′

Locate the start codon and stop codon in this sequence.

Verified step by step guidance

Identify the start codon in the mRNA sequence. The start codon in eukaryotic mRNA is typically AUG, which codes for methionine. Scan the sequence from the 5' end to locate the first occurrence of AUG.

Determine the reading frame starting from the identified start codon (AUG). This means grouping the nucleotides into codons (triplets) starting from the AUG.

Search for the stop codon within the same reading frame. The stop codons in mRNA are UAA, UAG, and UGA. These codons signal the termination of translation.

Verify that the stop codon is downstream of the start codon and within the same reading frame. Ensure that the sequence between the start and stop codons is divisible by three, as codons are read in triplets.

Record the positions of the start codon (AUG) and the stop codon (UAA, UAG, or UGA) within the sequence. These positions will indicate the boundaries of the coding region of the mRNA.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

mRNA Structure

mRNA, or messenger RNA, is a single-stranded molecule that carries genetic information from DNA to the ribosome for protein synthesis. It features a 5' cap that protects the RNA from degradation and aids in ribosome binding, and a 3' poly(A) tail that enhances stability and translation efficiency. Understanding the structure of mRNA is crucial for identifying functional elements like start and stop codons.

Start Codon

The start codon is a specific sequence of three nucleotides (AUG) that signals the beginning of translation in protein synthesis. It is recognized by the ribosome, which assembles around the mRNA to initiate the process of translating the genetic code into a polypeptide chain. Locating the start codon is essential for determining where the protein-coding sequence begins.

Stop Codon

A stop codon is a nucleotide triplet (UAA, UAG, or UGA) that signals the termination of protein synthesis. When the ribosome encounters a stop codon during translation, it releases the newly synthesized polypeptide chain, concluding the process. Identifying the stop codon is vital for understanding where the coding sequence ends and for predicting the length of the resulting protein.

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Related Practice

Textbook Question

M. Klemke et al. (2001) discovered an interesting coding phenomenon in which an exon within a neurologic hormone receptor gene in mammals appears to produce two different protein entities ( and ALEX). Following is the DNA sequence of the exon's end derived from a rat.

5'-gtcccaaccatgcccaccgatcttccgcctgcttctgaagATGCGGGCCCAG

The lowercase letters represent the initial coding portion for the protein, and the uppercase letters indicate the portion where the ALEX entity is initiated. (For simplicity, and to correspond with the RNA coding dictionary, it is customary to represent the coding (non-template) strand of the DNA segment.)

Locate the initiator codon within the XLαs segment.

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Textbook Question

M. Klemke et al. (2001) discovered an interesting coding phenomenon in which an exon within a neurologic hormone receptor gene in mammals appears to produce two different protein entities ( and ALEX). Following is the DNA sequence of the exon's end derived from a rat.

5'-gtcccaaccatgcccaccgatcttccgcctgcttctgaagATGCGGGCCCAG

The lowercase letters represent the initial coding portion for the protein, and the uppercase letters indicate the portion where the ALEX entity is initiated. (For simplicity, and to correspond with the RNA coding dictionary, it is customary to represent the coding (non-template) strand of the DNA segment.)

Convert the coding DNA sequence to the coding RNA sequence.

433

views

Textbook Question

M. Klemke et al. (2001) discovered an interesting coding phenomenon in which an exon within a neurologic hormone receptor gene in mammals appears to produce two different protein entities ( and ALEX). Following is the DNA sequence of the exon's end derived from a rat.

5'-gtcccaaccatgcccaccgatcttccgcctgcttctgaagATGCGGGCCCAG

The lowercase letters represent the initial coding portion for the protein, and the uppercase letters indicate the portion where the ALEX entity is initiated. (For simplicity, and to correspond with the RNA coding dictionary, it is customary to represent the coding (non-template) strand of the DNA segment.)

Are there any evolutionary advantages to having the same DNA sequence code for two protein products? Are there any disadvantages?

484

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Textbook Question

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.

579

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Textbook Question

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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Textbook Question

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.

438

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Textbook Question

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.

436

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Textbook Question

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.

341

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