Summary Biol 275 Exam 2 Study Guide

Regulation of Gene Expression:
● Master blueprint - contractors carry out specific jobs
● Workers interact and adjust with instructions for them
● Master genome - cells carry out specific jobs
● 2 copies of human genome - 1 from mom and 1 from dad
● All cells have same set of genes, but different functions

Every cell has complete copy of genome
Different cell types use different sets of genes to define how they appear, where they reside,
and how they function

Gene Regulation: Selective control by cell of how to use genes in genome

Drosophila and Hox Genes:
● Embryos stained by fluorescent antibodies
● Color is antibody against different Hox (early development) protein
● Homeobox Genes = Hox genes - important in bilateral symmetry
● Homeobox proteins are coded for by homeobox genes
● Deletion / Removal of Hox genes changes the body plan

Human vs. Drosophila Genome:
● Human - 3.2 billion bp and 20,000 genes
● Drosophila - 122.7 million bp and 15,500 genes
● Humans have 30X larger physical genome than fly, but only 1.3X more genes
● It is not the amount of genes that determines complexity, but how the cells use the genes
● Much human genome is regulatory, not coding

Prokaryotic Gene Regulation:
● E. coli - genome is 5.44 million bp and 5,400 genes

Metabolism Involves Gene Expression in Balance:
● Catabolism: breaking down of molecules for raw materials
● Lactose pathway is good model for regulation
● Production of pathway proteins must be coordinates




Lactose Pathway:

, 1. Galactoside permease brings lactose to cell
2. Trans-acetylase adds acetyl group to lactose
3. B-galactosidase breaks down lactose into simple sugars




Breaks glycosidic bond between sugars into galactose and glucose



Genes in Bacterial Lactose Pathway:
● Operon: Genes with related function grouped together under same control
● Allows genes to be turned on or off in synchronized fashion - on/off expression of
pathway components
● lacZ gene encodes B-galactosidase
● lacY gene encodes galactosidase permease
● lacA gene encodes transacetylase (adds Ac to lactose)
● All 3 genes located s group as lac operon
● Promoter: where RNA Polymerase 2 is recruited by transcription factor proteins
● RNA Pol 2 makes mRNA strand




Expression from Lac Operon is Stimulated by Lactose:

, ● Most time, lac operon is turned off
● lacI gene is usually transcribed into lacI mRNA and then into repressor protein - binds to
DNA in promoter region bound to operator
● If repressor protein binds to operator, it stops RNA Polymerase 2 from transcribing lacA,
Y, and Z genes
● Repressor protein by lacI inhibits RNA pol activity




If Lactose is Present:
● It will bind to the repressor protein to make it inactive
● Lactose deactivates inhibitor




Cyclic AMP:
● Enhances lac operon activity
● Cyclic adenosine monophosphate (cAMP)
● Catabolite Activator Protein (CAP)
● Encourages DNA to unwind
● Encourages RNA polymerase to transcribe the operon

, ● Glucose inhibits cAMP formation
● Cells prefer glucose to lactose - saves resources

1. CAP - cAMP complexes bind to CAP recognition site ( C ) by promoter of lac operon
2. Promoter becomes more readily bound by RNA polymerase
3. RNA polymerase starts transcribing lac operon




Structure of lac Operon:
● Repressor binding causes DNA to loop
● In looped shape, RNA Pol cannot bind
● CAP is ready to help RNA Pol when lactose releases repression