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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0:56 minutes

Problem 16

Textbook Question

Most proteins have more leucine than histidine residues, but more histidine than tryptophan residues. Correlate the number of codons for these three amino acids with this information.

Verified step by step guidance

Understand the genetic code: Each amino acid is encoded by one or more codons, which are sequences of three nucleotides in mRNA. The number of codons available for an amino acid can influence its frequency in proteins.

Identify the codons for leucine, histidine, and tryptophan: Leucine is encoded by 6 codons (UUA, UUG, CUU, CUC, CUA, CUG), histidine is encoded by 2 codons (CAU, CAC), and tryptophan is encoded by 1 codon (UGG).

Correlate codon availability with amino acid abundance: Amino acids with more codons are generally more abundant in proteins because there are more opportunities for their incorporation during translation. Leucine, with 6 codons, is expected to be more abundant than histidine, which has 2 codons. Similarly, histidine is expected to be more abundant than tryptophan, which has only 1 codon.

Relate this to the problem statement: The observation that most proteins have more leucine than histidine residues, but more histidine than tryptophan residues, aligns with the number of codons available for each amino acid. This suggests that codon availability plays a role in determining amino acid frequency in proteins.

Conclude the reasoning: The number of codons for leucine, histidine, and tryptophan directly correlates with their relative abundance in proteins, supporting the idea that the genetic code influences protein composition.

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Key Concepts

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

Amino Acid Composition

Amino acids are the building blocks of proteins, and their composition can influence protein structure and function. Leucine, histidine, and tryptophan are essential amino acids, each with distinct roles in protein synthesis. Understanding the relative abundance of these amino acids in proteins can provide insights into their biological significance and the evolutionary pressures that shape protein sequences.

Codon Usage

Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during protein synthesis. The number of codons available for each amino acid affects its frequency in proteins. Leucine has six codons, histidine has two, and tryptophan has one, which explains why leucine is often more abundant than histidine, and histidine is more common than tryptophan in proteins.

Genetic Code and Redundancy

The genetic code is degenerate, meaning that multiple codons can encode the same amino acid. This redundancy allows for variations in codon usage among different organisms and can influence the frequency of amino acids in proteins. The higher number of codons for leucine compared to histidine and tryptophan suggests that leucine is more readily incorporated into proteins, reflecting its greater availability in the genetic code.

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Related Practice

Textbook Question

A short RNA molecule was isolated that demonstrated a hyperchromic shift, indicating secondary structure. Its sequence was determined to be

5'-AGGCGCCGACUCUACU-3'

If the molecule were an internal part of a message, what amino acid sequence would result from it following translation?

440

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Textbook Question

A short RNA molecule was isolated that demonstrated a hyperchromic shift, indicating secondary structure. Its sequence was determined to be

5'-AGGCGCCGACUCUACU-3'

If the molecule were a tRNA fragment containing a CGA anticodon, what would the corresponding codon be?

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Textbook Question

The genetic code contains 61 codons to specify the 20 common amino acids. Many organisms carry fewer than 61 different tRNA genes in their genomes. These genomes take advantage of isoaccepting tRNAs and the rules governing third-base wobble to encode fewer than 61 tRNA genes. Use these rules to calculate the minimal number of tRNA genes required to specify all 20 of the common amino acids.

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Textbook Question

Shown here is a hypothetical viral mRNA sequence:

5'-AUGCAUACCUAUGAGACCCUUGGA-3'

Assuming that it could arise from overlapping genes, how many different polypeptide sequences can be produced? What are the sequences?

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Textbook Question

In an experiment to decipher the genetic code, a poly-AC mRNA (ACACACAC...) is synthesized. What pattern of amino acids would appear if this sequence were to be translated by a mechanism that reads the genetic code as

A quadruplet with overlaps?

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Textbook Question

A quadruplet without overlaps?

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Textbook Question

A triplet with overlaps?

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Textbook Question