Podcast
Questions and Answers
What feature of the genetic code explains the AUC and AUA codons in mRNA both specify isoleucine?
What feature of the genetic code explains the AUC and AUA codons in mRNA both specify isoleucine?
How many nucleotides are in 12 mRNA codons?
How many nucleotides are in 12 mRNA codons?
Given 200 commonly occurring amino acids, what would be the shortest possible codon length?
Given 200 commonly occurring amino acids, what would be the shortest possible codon length?
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Discuss how degeneracy of the genetic code makes cells more robust to mutations.
Discuss how degeneracy of the genetic code makes cells more robust to mutations.
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Which subunit of the E. coli polymerase confers specificity to transcription?
Which subunit of the E. coli polymerase confers specificity to transcription?
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The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.
The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.
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If mRNA is complementary to the DNA template strand, why are the base sequences of mRNA and the DNA nontemplate strand not identical?
If mRNA is complementary to the DNA template strand, why are the base sequences of mRNA and the DNA nontemplate strand not identical?
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Describe the difference between rho-dependent and rho-independent termination of transcription in prokaryotes.
Describe the difference between rho-dependent and rho-independent termination of transcription in prokaryotes.
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Would you expect bacteria to transcribe a eukaryotic promoter spliced ahead of a bacterial gene?
Would you expect bacteria to transcribe a eukaryotic promoter spliced ahead of a bacterial gene?
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Which feature of promoters can be found in both prokaryotes and eukaryotes?
Which feature of promoters can be found in both prokaryotes and eukaryotes?
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What transcripts will be most affected by low levels of α-amanitin?
What transcripts will be most affected by low levels of α-amanitin?
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What kinds of mutations might lead to splicing errors, and what might be the outcomes?
What kinds of mutations might lead to splicing errors, and what might be the outcomes?
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Which pre-mRNA processing step is important for initiating translation?
Which pre-mRNA processing step is important for initiating translation?
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What processing step enhances the stability of pre-tRNAs and pre-rRNAs?
What processing step enhances the stability of pre-tRNAs and pre-rRNAs?
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What specific effect would you expect from antibiotics like tetracycline and chloramphenicol on protein synthesis?
What specific effect would you expect from antibiotics like tetracycline and chloramphenicol on protein synthesis?
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The RNA components of ribosomes are synthesized in the ________.
The RNA components of ribosomes are synthesized in the ________.
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In any given species, there are at least how many types of aminoacyl tRNA synthetases?
In any given species, there are at least how many types of aminoacyl tRNA synthetases?
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Transcribe and translate the following DNA sequence (nontemplate strand): 5'-ATGGCCGGTTATTAAGCA-3'. What is the resulting mRNA and protein?
Transcribe and translate the following DNA sequence (nontemplate strand): 5'-ATGGCCGGTTATTAAGCA-3'. What is the resulting mRNA and protein?
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Explain how single nucleotide changes can have vastly different effects on protein function.
Explain how single nucleotide changes can have vastly different effects on protein function.
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Study Notes
Genetic Code and Codons
- Degeneracy of the genetic code allows multiple codons to specify the same amino acid, such as AUC and AUA both coding for isoleucine.
- Twelve mRNA codons consist of 36 nucleotides since each codon is composed of three nucleotides (12 x 3 = 36).
- If there were 200 commonly occurring amino acids, a minimum codon length of four nucleotides would be necessary to provide sufficient combinations (4^4 = 256).
- Codons that specify the same amino acid usually vary by a single nucleotide, promoting functional redundancy and protecting against loss of protein function due to mutations.
Transcription and Promoter Functions
- The σ subunit of E. coli RNA polymerase is responsible for recognizing specific transcription start sites.
- Consensus sequences at prokaryotic promoters, such as the -10 and -35 elements, exhibit similarity across various bacterial species, rather than exact identity.
- mRNA sequences differ from DNA template and nontemplate strands due to the replacement of thymine (T) in DNA with uracil (U) in RNA, preventing identical base sequences.
Transcription Termination
- Rho-independent termination involves RNA forming a hairpin structure that disrupts RNA Polymerase, halting transcription, whereas rho-dependent termination relies on the rho protein to displace RNA Polymerase from the template.
Eukaryotic vs. Prokaryotic Transcription
- Bacteria have distinct promoter regions compared to eukaryotes; a eukaryotic promoter is unlikely to effectively drive transcription of a bacterial gene when spliced into a bacterial chromosome.
Pre-mRNA Processing
- Pre-mRNAs are significantly affected by α-amanitin, leading to reduced levels in transcripts compared to ribosomal RNAs.
- Splicing errors can result in retention of introns, excision of exons, or misplacement of splice sites, contributing to various diseases, including cancers.
- The 7-methylguanosine cap is crucial for initiating translation of processed pre-mRNAs.
- Methylation processes enhance stability of pre-tRNAs and pre-rRNAs, protecting them from degradation.
Protein Synthesis Inhibition
- Tetracycline specifically impacts tRNA binding to the ribosome, blocking amino acid addition, while chloramphenicol inhibits peptide bond formation, affecting the growth of the protein chain.
Ribosome RNA Synthesis
- Ribosomal RNA components are synthesized within the nucleolus, part of the cell's nucleus.
Aminoacyl tRNA Synthetases
- Each species has a minimum of 20 distinct types of aminoacyl tRNA synthetases to facilitate the correct pairing of amino acids with their corresponding tRNAs.
DNA Transcription and Translation
- The given nontemplate DNA sequence can be transcribed into mRNA: 5'-AUGGCCGGUUAUUAAGCA-3' and translated to produce the polypeptide sequence MAGY, with the sixth codon being untranslatable due to a preceding stop codon.
Effects of Nucleotide Changes
- Single nucleotide variations in the third position of codons often do not alter the resulting amino acid or protein function, illustrating the concept of redundancy in the genetic code.
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Test your knowledge with these flashcards from BIO 15, focusing on the genetic code and codon structure. Each card provides a key term along with a definition or question to enhance your understanding of molecular biology concepts. Perfect for quick revisions or exam preparation!