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Lesson Four

Lesson Four . Structure of a Gene. Gene Structure. What is a gene? Gene: a unit of DNA on a chromosome that codes for a protein(s) Exons Introns Promoter sequences Terminator sequences Other regulatory sequences (enhancers, silencers), which may be far from major components of a gene.

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Lesson Four

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  1. Lesson Four Structure of a Gene

  2. Gene Structure • What is a gene? • Gene: a unit of DNA on a chromosome that codes for a protein(s) • Exons • Introns • Promoter sequences • Terminator sequences • Other regulatory sequences (enhancers, silencers), which may be far from major components of a gene

  3. Gene Structure • Exons: contain the bases that are utilized in coding for the protein • Introns: contain bases that are not utilized in coding for proteins and intervene between the exons • Introns are spliced out

  4. Gene Structure • Promoter: bases that provide a signal to tell the cell’s machinery where to begin transcription, usually before or within a gene • Terminator: bases that provide a signal to tell the cell’s machinery where to stop transcription, usually at the end of a gene

  5. Gene Structure • A typical gene might look something like this: • This gene has 3 exons and 2 introns ---------- = exon = promoter = intron ---------- = terminator

  6. Lesson Five Transcription

  7. Transcription • The process of using DNA (a gene) as a template to produce messenger RNA (mRNA) • Occurs in the nucleus • Template strand – the strand of DNA that is accessed to make mRNA • Coding strand – the strand of DNA that is NOT accessed to make mRNA. The mRNA that is made from the template strand will be identical to the coding strand (with the exception of U’s for T’s)

  8. RNA Modification • Trimming: removing bases from the 5’ and 3’ ends • Capping: adding a methylated G to the 5’ end • Necessary for RNA localization to the ribosome • Tailing: addition of A’s to the 3’ end of the mRNA • More A’s = more stabile mRNA • Splicing: removing introns prior to mRNA transport to the nucleus

  9. Lesson Six Translation

  10. Translation • The process of using mRNA as a template to generate a polypeptide that will eventually become a mature protein • Also called protein synthesis • Requires the ‘genetic code’ • Based on 64 codons, each with 3 nucleotides • Provides the link between DNA and protein sequence

  11. Translation Requires Different Types of DNA • mRNA: messenger RNA; major product of transcription • Represents the code for the primary amino acid sequence of a protein • Only type of RNA that is translated • tRNA: transfer RNA • Recognizes the mRNA code (tri-nucleotide) and brings with it (or transfers) the appropriate amino acid to the protein • Link between mRNA and protein • rRNA: ribosomal RNA • Part of the ribosomes • Involved with translation by helping to align the mRNAs and tRNAs

  12. Protein Processing Final transport

  13. Genomics to Proteomics Primary control of gene expression

  14. Lesson Seven Mutations

  15. Point Mutations • Involves a single base pair • Substitution, insertion, deletion • SNPs • May not affect amino acid sequence • Same sense (silent, neutral, synonymous, same sense) • Due to redundancy of the genetic code • May affect amino acid sequence (nonsynonymous) • Missense (results from a change in an amino acid) • Nonsense (results from a change to a stop codon – truncated protein) • Frame shift mutations (insertion or deletion of 1+ bases - alters the reading frame)

  16. Missense Mutation Sickle Cell Anemia

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