BIO 15 Flashcards on Genetic Code

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?

36 (correct)

Given 200 commonly occurring amino acids, what would be the shortest possible codon length?

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

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

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

σ Signup and view all the answers

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

They are similar in all bacterial species 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?

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

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

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. Signup and view all the answers

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

No. Signup and view all the answers

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

TATA box Signup and view all the answers

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

pre-mRNAs Signup and view all the answers

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

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

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

7-methylguanosine cap Signup and view all the answers

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

Methylation Signup and view all the answers

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

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

The RNA components of ribosomes are synthesized in the ________.

Nucleolus Signup and view all the answers

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

20 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?

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

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

Changes in a nucleotide can lead to missense, nonsense, or silent mutations, significantly affecting protein structure and function. 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!