Lesson Four Structure of a Gene Gene Structure

Lesson Four Structure of a Gene

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

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

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

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

Lesson Five Transcription

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

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

Lesson Six Translation

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

Translation Requires Different Types of DNA n m. RNA: 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 n t. RNA: transfer RNA n r. RNA: ribosomal RNA – Recognizes the m. RNA code (tri-nucleotide) and brings with it (or transfers) the appropriate amino acid to the protein – Link between m. RNA and protein – Part of the ribosomes – Involved with translation by helping to align the m. RNAs and t. RNAs

Protein Processing Final transport

Genomics to Proteomics Primary control of gene expression

Lesson Seven Mutations

n Point Mutations Involves a single base pair – Substitution, insertion, deletion – SNPs n May not affect amino acid sequence – Same sense (silent, neutral, synonymous, same sense) – Due to redundancy of the genetic code n 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)

Missense Mutation Sickle Cell Anemia