lesson four structure of a gene. gene structure what is a gene? gene: a unit of dna on a chromosome...

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

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

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

Gene Structure A typical gene might look something like this:

This gene has 3 exons and 2 introns

----------

----------

= exon= intron

= promoter

= terminator

Lesson Five

Transcription

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)

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

Lesson Six

Translation

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

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

Protein Processing

Final transport

Primary control of gene expression

Genomics to Proteomics

Lesson Seven

Mutations

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)

Missense MutationSickle Cell Anemia