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The Central Dogma: DNA to RNA to Protein

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20 Questions

What is the primary flow of genetic information in the Central Dogma?

DNA is used to make RNA is used to make Protein

What is the function of the transcribed region in a gene?

It serves as a template for the transcribed RNA

What is the primary mechanism of gene regulation in prokaryotes?

Negative regulation using repressor proteins

What is the function of basal transcription factors in eukaryotes?

They recruit RNA polymerase to the promoter

What is the role of enhancers in gene regulation?

They greatly increase transcription when bound by transcriptional activators

What is the function of the transcription start site in a gene?

It corresponds to the first nucleotide at the 5' end of the RNA product

What is the primary difference between prokaryotic and eukaryotic gene regulation?

Prokaryotes use negative regulation, while eukaryotes use positive regulation

What is the function of regulatory transcription factors in eukaryotes?

They bind to proximal control elements to modify transcription

What is the role of the promoter in gene regulation?

It recruits basal transcription factors to initiate transcription

What is the function of the 5' end of the RNA product in a gene?

It corresponds to the transcription start site

What is the primary function of RNA polymerase in transcription?

To unwind DNA and assemble complementary RNA nucleotides

What is the purpose of the 5' cap and 3' polyA tail in mRNA?

To protect the mRNA and aid in export to the cytoplasm

What is the result of splicing in mRNA processing?

Removal of introns and ligation of exons

What is the function of tRNA in translation?

To hydrogen bond with the proper codon on mRNA

What is the purpose of the ribosome in translation?

To enzymatically assemble polypeptides

What is the result of translation initiation in eukaryotes?

The small ribosomal subunit binds to mRNA at the 5'-cap

What is the function of the release factor in translation?

To halt translation when a stop codon is reached

What is the purpose of the promoter in transcription?

To recognize the RNA polymerase and initiate transcription

What is the result of transcription termination?

The RNA polymerase releases the RNA transcript

What is the difference between a replication bubble and a transcription bubble?

A replication bubble is formed during DNA replication, while a transcription bubble is formed during transcription

Study Notes

The Central Dogma

  • DNA is used to make RNA, which is used to make Protein

Gene Structure

  • A gene has a transcription start site (+1) at the 5' end of the RNA product
  • A transcribed region is located downstream of the transcription start site (positive base positions)
  • A regulatory domain called a promoter is located upstream of the transcription start site (negative base positions)

Regulation of Gene Expression

Prokaryotes

  • Rely largely on negative regulation using repressor proteins

Eukaryotes

  • Rely on positive regulation of gene expression
  • Use transcription factors as activators or repressors of RNA polymerase activity
  • Basal transcription factors bind to the promoter to recruit RNA polymerase, acting as an on/off switch for transcription
  • Regulatory transcription factors (activators and repressors) bind to proximal control elements, modifying transcription
  • Enhancers greatly increase transcription when bound by transcriptional activators

Transcription

  • One strand of DNA acts as a template for RNA production by RNA polymerase
  • RNA polymerase:
    • Unwinds DNA locally
    • Assembles complementary RNA nucleotides along the DNA template strand
    • Links nucleotides with phosphodiester bonds into a polynucleotide
    • Can only add to the 3'-end of the growing polymer
    • Doesn't require a primer

Stages of Transcription

  • Initiation: RNA polymerase interacts with the promoter at the TATA box to establish a transcription complex
  • Elongation: RNA polymerase extends the new RNA by adding to the 3' end
  • Termination: A sequence in the DNA (terminator) halts transcription

Eukaryotic Transcription

  • Produces pre-mRNA that must be processed to mature mRNA for translation
  • Processing involves:
    • Adding a 5' cap
    • Adding a 3' polyA tail
    • Splicing to remove introns and ligate exons
  • Mature mRNA is exported to the cytoplasm for translation

Translation

  • mRNA has a protein coding sequence using codons
  • Codons are translated using tRNA and enzymes for each of the 20 amino acids
  • tRNA hydrogen bonds with the proper codon on mRNA through its anti-codon
  • Codons represent a degenerate code, with more than one codon representing the same amino acid
  • Reading codons in order determines the polypeptide sequence

Ribosome and Translation

  • Translation occurs in the ribosome, a large multi-protein complex
  • Initiation: the small ribosomal subunit binds to mRNA near the 5'-end
  • Elongation:
    • A charged tRNA enters the A-site
    • Ribosomal enzymes cut the growing polypeptide free from the P-site tRNA
    • Attach the polypeptide to the new amino acid on the tRNA in the A-site with a peptide bond
    • The ribosome slides down the mRNA one codon, shifting the tRNAs over (P to E, and A to P)
    • The process repeats until a stop codon lines up with the A-site and binds to a release factor, halting translation

Test your understanding of the Central Dogma, the process by which DNA is used to make RNA, and RNA is used to make proteins. This quiz covers the basic structure of genes on DNA, including transcription start sites, transcribed regions, and regulatory domains.

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