BIO 111

• DNA


  The info stored in DNA is coded for by specific sequences of A, C, G, & Ts along the DNA strands
• Central dogma of biology


  1. DNA

  2. RNA

  3. PROTEIN
• Gene


  A specific sequence of nucleotides on a strand of DNA that typically lead to the production of a specific protein product
• Beadle & Tatum's experimental findings
• Beyond one gene-one enzyme
• Genetic code


  The nucleotide sequence prescribes the amino acid and protein sequence
• Redundancy


  Multiple codons can code for the same amino acid or one codon can have more than one amino acid
• Universality of the genetic code
• Reading the genetic code


  1. Start codon

  2. Stop codons

  3. Reading frame
• Transcription


  Synthesis of mRNA under the direction of DNA
• Translation


  The synthesis of a protein under the direction of an mRNA
• Prokaryotic gene expression


  • Gene expression occurs solely in the cytoplasm
  • Prokaryotes do NOT require RNA transcript processing
• Transcription


  1. Initiation

  2. Elongation

  3. Termination
• Promoter sequence


  A stretch of DNA that serves as a binding/recognition site for Transcription factors and RNA polymerase
• Transcription factors


  Proteins that aid in the initiation and regulation of transcription
• RNA polymerase


  Enzyme that carries out transcription
• Transcription elongation


  1. RNA polymerase unwinds DNA to access the template strand

  2. Links ribonucleotides using DNA as a template

  3. Produces the RNA transcript in a 5' to 3' direction

  4. Typically producing the RNA transcript at 15-50 nucleotides per second
• Terminator sequences


  A sequence of DNA at the end of a gene that is transcribed and signals the RNA transcript is complete
• Differences in transcription termination between prokaryotes and eukaryotes
• Post-transcriptional processing in eukaryotes


  1. 5' cap added

  2. 3' poly A tail added

  3. Introns removed
• 5' cap


  Modified guanine added to the 5' end of the pre-mRNA
• 3' poly A tail


  Poly-adenosine tail added to the 3' end of the pre-mRNA
• Introns


  Non-coding regions of the gene that are removed from the pre-mRNA
• Exons


  Coding regions of the gene that remain in the mature mRNA
• Spliceosomes


  Complexes of proteins and small nuclear RNAs that remove introns from pre-mRNA
• Evolutionary importance of alternative splicing
• Transcription Termination


  1. RNA polymerase reaches and transcribes the termination sequence

  2. The RNA transcript is released by RNA polymerase

  3. RNA polymerase detaches from the DNA, officially ending transcription
• Post-transcriptional Processing in Eukaryotes


  Eukaryotic cells must modify RNA after transcription & before translation
• Alteration of mRNA Ends (5' and 3')


  1. The 5' end receives a modified guanine (5' cap)

  2. The 3' end receives a poly-adenosine tail (3' poly-A tail)

  3. Both protect the RNA as it enters the cytoplasm and undergoes translation
• 5' Cap


  • A modified guanine nucleotide added to the 5' end
• 3' Poly-A Tail


  • 50 to 250 adenine nucleotides added to the 3' end
• Post-transcriptional Processing: RNA Splicing


  1. Cuts out introns (noncoding sequences) and links together exons

  2. Accomplished using specialized proteins complexes known as spliceosomes
• Spliceosomes


  • Complexes made of protein and catalytic RNA (ribozymes)
• Introns


  Noncoding sequences
• Exons


  Coding sequences
• Functional & Evolutionary Importance of Introns


  • Allow for alternative splicing
  • Polypeptides within proteins often have discrete functional and structural regions called domains
• Alternative Splicing


  Process of selecting different combos of splice sites within a pre-mRNA to produce multiple spliced mRNAs
• Domains


  Discrete functional and structural regions within proteins
• DNA is transcribed into RNA, which is then translated into protein
• Codon


  3 base sequence in mRNA that codes for a specific amino acid