Genes and How they Work

Chapter 15

The Nature of Genes

• Garrod

• Beadle and Tatum

• Francis Crick

Beadle and Tatum Experiment• Used Neurospora crassa

• One gene/one polypeptide hypothesis

Central Dogma of Molecular Biology

• DNA- RNA- Protein

• Transcription to translation

• Rule breakers? – Retrovirusese– Reverse Transcriptase

The Genetic Code

• Crick and Brenner– Codons– Spaced or Unspaced?– Frameshift Deletions

Nirenberg Deciphered the Code

• http://img.sparknotes.com/figures/1/132e5720f3b37836571a1aeb9d163ac3/genetic_code.gif

Genetic Code Almost Universal

• So where is it not the same?

Transcription

• Template Strand

• Coding Strand

• mRNA– Initiation– Elongation– Termination

Translation

• tRNA

• Takes place on the ribosome

• http://library.thinkquest.org/C004535/media/translation.gif

Types of RNA

• mRNA- make RNA from DNA template• rRNA- found in ribosomes• tRNA-adapter molecule between mRNA and

AA’s• snRNA’s- involved in the nuclear processing

of eukaryotic pre-mRNA• SRP RNA-mediate protein synthesis in

eukaryote• Micro-RNA- newly discovered

Eukaryotic vs. Prokaryotic Gene Expression

Characteristic Prokaryotes EukaryotesIntrons No introns Most genes have

introns

Number of genes in mRNA

Several for each mRNA Only one gene per mRNA

Site of Transcription and Translation

No membrane bound nucleus- t and t are coupled

Transcription in nucleus, outside nucleus for translation

Initiation of Translation Begins at AUG preceded by special sequence that binds the ribosome

Gegins at AUG preceded by the 5’ methylated GTP cap

Modification of mRNA after transcription

none Introns are removed, a 5; cap is added; poly A tail is added

Videos

• Eukaryotes vs prokaryotes

• Translation

• spliceosome

Words to know

• Promoter

• Terminator

• Operon

Spliceosome

• http://fig.cox.miami.edu/~cmallery/150/gene/sf13x8bc.jpg

Types of Mutations

• Point Mutations– Bases substitution

• Missense vs nonsense

– Frameshift

• Chromosomal Mutations– Deletions– Duplications– Inversions– Translocations

Point Mutations

• http://kvhs.nbed.nb.ca/gallant/biology/point_mutations.jpg

Chromosomal Mutations

• Page 300 in text