Gene Expression Regulation Mutations from Gene to Protein

Lecture 18 – June 2nd , 2016

Gene Expression Regulation Mutations From Gene to Protein

Central Dogma

Replication

RNA DNA Transcription Translation PROTEIN

RNA Viruses: genome is RNA  Protein Reverse  Transcriptase (RT) DNA Inserts into host (e.g. human cell) genome (INTEGRATION)

RT mRNA cDNA (Complementary DNA) From Gene to Protein: Mutations

DNA* RNA* PROTEIN* Mutation are changes in genetic material of a cell.

Chromosomal Mutations: (e.g. Duplications and deletions) large-scale mutations: multiple genes are affected  Multiple phenotypes

Point Mutations: 1 base pair (bp) substitution  in one gene

Missense mutation  1 bp change  different a.a. encoded

UGC (cys)  UGG (trp)

Nonsense mutation  1 bp change  STOP codon

UGC (cys)  UGA (STOP)

Silent mutation  1 bp change  codon is the same (due to wobble)

UGC (cys)  UGU (cys) From Gene to Protein: Mutations

DNA* RNA* PROTEIN* Frameshift Mutations:

Insert or Delete a basepair

1 1  Frameshift in ORF

2 2  Frameshift in ORF

3 3  Insert or delete an a.a. From Gene to Protein: Mutations

(silent) From Gene to Protein: Mutations

What about mutations that are not in the coding sequence?

Affect mRNA synthesis - promoter - termination - splicing

Affect Translation - mutation in RBS (Prok) - Stability of mRNA (3’UTR polyAAA tail) Regulation of Gene Expression

Every cell in the body has the same DNA

So how can cells be so different from one another?? (cell shape, function, etc)

Gene Regulation!!! DNA Transcription RNA Regulation of Gene Expression

Transcriptional UNIT (DNA!)

1st base of mRNA Promoter Terminator P T Start Stop

Coding Region 3’ UTR 5’ UTR

Promoter is very important RNA polymerase binds choses sense/template strand Can Determine how active a gene will be!! Regulation of Gene Expression

Promoters – DNA sequence that RNA polymerase binds

“Good” Promoter  RNA Pol binds tightly and lots of mRNA is made

“Poor” Promoter  RNA Pol binds poorly and little of mRNA is made

Encoded in the DNA of the promoter how often a gene is transcribed

Promoter sequences are constantly changing from: good to poor HOW?

Allosteric Regulation!!

Regulation of RNA polymerase Transcriptional Activator: Recruit RNA polymerase to a promotoer: ON!

Transcriptional Repressor: Block RNA polymerase: OFF! Regulation of Gene Expression

Transcriptional Activators and Repressors

Repressor (TR) can bind at the promoter or a nearby sequence and block RNA pol : turns gene OFF!

RNA Pol P ORF Regulation of Gene Expression

Transcriptional Activators and Repressors

Repressor (TR) can bind at the promoter or a nearby sequence and block RNA pol : turns gene OFF! RNA Pol TR X P ORF

RNA Pol TR X P ORF

Binding site for repressor TR RNA Pol X P ORF Regulation of Gene Expression

Transcriptional Activators and Repressors

Activator (TA) Binds to specific sequence, next to promoter, recruits RNA pol to that promoter – turns gene ON!

TA RNA Pol P ORF

Binding site for activator Regulation of Gene Expression

Prokaryotic Gene Regulation A typical scenario:  An individual bacteria can respond to environmental change by regulating gene expression

How can negative feedback inhibition affect more than one gene? Regulation of Gene Expression: Prokaryotic

Prokaryotic Gene Regulation

Normal food is glucose; Lactose is polymer of galactose-glucose

so the amount of lactose permease (a receptor molecule which brings lactose inside cell) is normally low at the cell surface

Lactose ( ) is low Lactose ( ) is high

Allosteric Regulation! Bacteria will induce multiple genes which take advantage of lactose as a food source Regulation of Gene Expression: Prokaryotic