BIOL 151 1st Edition Lecture 21 Outline of Last Lecture - Transcription unit- DNA sequence- Gene Definitiono Gene definition 2.0- MorpholinoOutline of Current Lecture - From genotype to phenotype- Point mutation- Insertion or deletion mutations- Controlling gene expression- Gene expression in bacteriao Repressible operono Inducible operonCurrent Lecture- Change to DNA = mutationo Chunks of DNA can be lost or addedo Single nucleotide changes (point mutations) DNA mutations in gametes are passed onto offspring- Genotype: DNA sequence- Phenotype: traito Change in genotypes can change phenotype- Possible outcomes of point mutationo Mutation type: single nucleotide pair is change or substituted  point mutation These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Possible effects on how mRNA is translated to amino acids (consequences of point mutation): Silent: no change in amino acid - Change in codon, but don’t get change in amino acid- No consequence- Okay because still codes for same amino acid- No change in amino acid, but change in DNA and mRNA Nonsense: codon changed from amino acid to STOP- Stops translation of mRNA prematurely- Codon for amino acid changed to stop codon=protein prematurely truncated- Severe effects since a lot less amino acid Missense: codon changed from 1 amino acid to another- Codon codes from 1 amino acid to another- Happens in sickle cell case- Sometimes no bad deal, sometimes disastrous- Single amino acid is changed; effect varies - If amino acids have similar structures, not a big deal, but if structures are very different, then could be disastrous- To determine severity of a missense mutation: amino acid conservationo Compares amino acid sequence in other specieso Conserved amino acid: common; if original amino acid is conserved, good chance that missense mutation disrupts protein function- Insertion or deletion mutations: non multiple of 3o Mutation type: non multiple of 3 bases inserted/deleted=frameshif in how mRNA codes for amino acidCODE CHANGES Every codon downstream has the potential to change what amino acid they code foro Possible consequences due to frameshif: can occur due to an insertion or deletion Nonsense: codon changed from amino acid to STOP Missense: a codon changed from one amino acid to another; can be multiple codons- Insertion or deletion mutations: multiple of 3o Insertion: frameshif to nonsense: inserted base shifs sequence and introduces a stop codon = protein prematurely truncated; shifs righto Deletion: framshif to missense: deleted base shifs sequence and changes most/all downstream codons 3 nucleotide deletion: missing AA deleted triplet= loss of AA; skips over codon- Controlling Gene Expression: DNA RNA  proteino Most cells in organisms have the same DNA.  But not all cells have different traits even if they have same information Every cell doesn’t express the same gene Each cell doesn’t make (“express”) functional proteins from all its DNAo Why does gene expression vary? Cell’s environment Cell’s identity Cell’s current tasko Why do bacteria regulate gene expression? Changes in the environment- Food availability- Bacteria chooses host environment- Needs to change gene expression to adopto How?- Transcription: turned on or off dependency on cell’s demand and environment’s supplyo Transcription OFF by trp operono Transcription ON by lac operon- Gene expression in bacteriao Gut: lots of tryptophan E. Coli doesn’t make tryptophano Gut: no tryptophan E. Coli makes tryptophan- Prefer to rely on environment for tryptophan, but when not possible, can make their own can do this by gene expressiono Tryptophan synthesis: precursor + 5 enzymes; trp genes code for these enzymes Regulate whether make own trp or not 5 trp genes are group on chromosome 1 on/off switch for trp gene cluster: operator- within the promotor- gatekeeper of RNA polymerase (part of flaky sequence)- operon: operator, promotor, genes controlled Trp operon: entire complex Repressor control of the operator switch:- Default mode: trp operator is ONo Cell transcribes trpA-trpE- Gut has tryptophan: trp operator turns OFF- REPRESSIBLE OPERON:o Under baseline conditions: trpR: always transcribed to mRNA - protein (inactive repressive)o When tryptophan binds to usually inactive protein, turns into active repressor, blocks switch no RNA made- INDUCIBLE OPERON:o Default mode: lac operator is offo Gut has lactose: lac operator turned ON and enzymes used to digest lactose are transcribedo Regulatory gene mRNA  protein is an active repressor  prevents operator  no RNA madeo Allolactose (inducer) binds to formerly active protein inactivates repressor allows operator switch to on  can transcribe, allows enzymes to digest lactose- Repressible v. inducible operonsRepressor trp operon Inducible lac operonOperator default mode ON OFFRegulatory gene default activityInactive repressor Active repressorEnvironmental stimulus + tryptophan = repressor active…trp genes off+lactose = repressor inactive..lac genes on (double negative)Bacterial gene expression regulated at transcriptional