BIO 15 Flashcards on Genetic Code
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Questions and Answers

What feature of the genetic code explains the AUC and AUA codons in mRNA both specify isoleucine?

  • Universality
  • Degeneracy (correct)
  • Nonsense codons
  • Complementarity
  • How many nucleotides are in 12 mRNA codons?

  • 24
  • 12
  • 48
  • 36 (correct)
  • Given 200 commonly occurring amino acids, what would be the shortest possible codon length?

    5

    Discuss how degeneracy of the genetic code makes cells more robust to mutations.

    <p>Degeneracy allows mutations in the third position of codons to not result in changes to the amino acid, thereby maintaining protein function.</p> Signup and view all the answers

    Which subunit of the E. coli polymerase confers specificity to transcription?

    <p>σ</p> Signup and view all the answers

    The -10 and -35 regions of prokaryotic promoters are called consensus sequences because ________.

    <p>They are similar in all bacterial species</p> Signup and view all the answers

    If mRNA is complementary to the DNA template strand, why are the base sequences of mRNA and the DNA nontemplate strand not identical?

    <p>Because T in DNA is replaced with U in RNA.</p> Signup and view all the answers

    Describe the difference between rho-dependent and rho-independent termination of transcription in prokaryotes.

    <p>Rho-independent termination involves the formation of a hairpin structure in RNA that displaces RNA Polymerase, while rho-dependent termination requires the rho protein to disassociate RNA Polymerase from the template.</p> Signup and view all the answers

    Would you expect bacteria to transcribe a eukaryotic promoter spliced ahead of a bacterial gene?

    <p>No.</p> Signup and view all the answers

    Which feature of promoters can be found in both prokaryotes and eukaryotes?

    <p>TATA box</p> Signup and view all the answers

    What transcripts will be most affected by low levels of α-amanitin?

    <p>pre-mRNAs</p> Signup and view all the answers

    What kinds of mutations might lead to splicing errors, and what might be the outcomes?

    <p>Mutations in splice sites or regulatory regions could lead to introns being retained or exons being excised, potentially resulting in truncated or dysfunctional proteins.</p> Signup and view all the answers

    Which pre-mRNA processing step is important for initiating translation?

    <p>7-methylguanosine cap</p> Signup and view all the answers

    What processing step enhances the stability of pre-tRNAs and pre-rRNAs?

    <p>Methylation</p> Signup and view all the answers

    What specific effect would you expect from antibiotics like tetracycline and chloramphenicol on protein synthesis?

    <p>Tetracycline would directly affect tRNA binding to the ribosome; chloramphenicol would affect growth of the protein chain.</p> Signup and view all the answers

    The RNA components of ribosomes are synthesized in the ________.

    <p>Nucleolus</p> Signup and view all the answers

    In any given species, there are at least how many types of aminoacyl tRNA synthetases?

    <p>20</p> Signup and view all the answers

    Transcribe and translate the following DNA sequence (nontemplate strand): 5'-ATGGCCGGTTATTAAGCA-3'. What is the resulting mRNA and protein?

    <p>mRNA: 5'-AUGGCCGGUUAUUAAGCA-3'; Protein: MAGY.</p> Signup and view all the answers

    Explain how single nucleotide changes can have vastly different effects on protein function.

    <p>Changes in a nucleotide can lead to missense, nonsense, or silent mutations, significantly affecting protein structure and function.</p> Signup and view all the answers

    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!

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