 Turn in your mutations packet.  When your partner arrives – finish your lab activity from yesterday.  Due by 11:05

 Agenda: ◦ Finish Model ◦ Chapter 18 Regulation  Trp and Lac ◦ Chrome Books: Lac Operon  HW: Finish Lac Operon Pkt  Reminder: Test Tuesday Ch 16-18

Chapter 18

Transcription

 Natural selection has favored bacteria that can conserve resources and energy  E.Coli / Human Intestine ◦ Obtains nutrients from the erratic eating habits of its host ◦ Needs the amino acid tryptophan  Without it  Synthesize its own tryptophan  Host consumes a meal w/ tryptophan  Stop producing tryptophan

Enzyme 1 is inhibited by the end product of the pathway. If Trp accumulates, it shuts down the synthesis of more Trp by inhibiting it Feedback Inhibition Operon Model

 Cells can adjust the production level of enzymes ◦ By regulating the genes that code for those enzymes  If the gut has a lot of tryptophan  The cell stops making the enzymes that synthesize tryptophan ◦ During transcription

Operon Operon: entire stretch of related genes required for enzyme production Three Parts: 1.Promoter – where RNA polymerase attaches 2.Operator – “on/off”, controls access of RNA poly to the genes 3.Genes – code for related enzymes in a pathway

The operon is always turned on. Unless….. A repressor is present.

 Trp repressor is the protein product of a regulatory gene trpR, has its own promotor ◦ Located upstream of the trp operon ◦ Continuously transcribed at a low rate, inactive ◦ Becomes active if it binds with tryptophan to change its shape  Tryptophan is called a co-repressor in this example

trp operon

 Trp Operon: Repressible: Usually on, but can be inhibited or repressed by a repressor Comparison  Lac Operon: Inducible: Usually off, but can be turned stimulated or induced when a molecule interacts with a regulatory protein

)  E.Coli and Lactose (Dissacharride)  Lacl regulatory gene upstream of the promoter  The lac repressor is active alone.  Lactose act as an inducer  Binds to the repressor to inactivate it  Now the lac operon can be transcribed

lac operon

off  Negative control of genes: operons are switched off by active form of repressor protein ◦ Eg. trp operon, lac operon increase  Positive control of genes: regulatory protein interacts directly with genome to increase transcription ◦ Eg. cAMP & CAP

 E.Coli prefers glucose over lactose ◦ How does it sense the concentration of glucose and relay this to the lac operon?  Allosteric regulatory protein: CAMP  Accumulates when glucose is scarce

 Glucose levels high, CAMP Low, CAP Inactive  Decrease RNA Polymerase Affinity

 cAMP accumulates when glucose is scarce  cAMP binds to CAP (catabolite activator protein) ◦ ↑ affinity of RNA polymerase ◦ ↑ transcription  Start using lactose again. cAMP + CAP = Positive Control

PROG Promotor, Repressor, Operator, Genes

 Agenda: ◦ Chapter 17 Check for Understanding ◦ Eukaryotic Gene Regulation ◦ Epigenetics Video Clips  HW: Honors Biology Test Practice

Many stages

 Typical human cell: only 20% of genes expressed at any given time  Constantly switched on/off  Example: Cell Specialization ◦ Different cell types (with identical genomes) turn on different genes to carry out specific functions differential gene expression  Differences between cell types is (not due to different genes) but is due to differential gene expression

Example: Regulation of Chromatin Structure:  Organization of chromatin and chemical modification to chromatin can influence gene expression

 Modifications on chromatin can be passed on to future generations  Changes gene expression, not the underlying DNA  Effects phenotype not genotype

Genetic Science Learning Center

Transcription Initiation:  Specific transcription factors (activators or repressors) bind to control elements (enhancer region)  Activators: increase transcription  Repressors: decrease transcription

Activators bind to enhancer regions + other proteins + RNA polymerase

Cell type-specific transcription

Regulation of mRNA: micro RNAs (miRNAs) small interfering RNAs (siRNAs) micro RNAs (miRNAs) and small interfering RNAs (siRNAs) can bind to mRNA and degrade it or block translation

I am after school until 2:15 today.