structure of gene in prokaryotes
Draw out structure
define: gene, operons, promotor
highlight: transcription and translation
check notes
- gene: seq of DNA that encodes a trait; unit of heredity
- operons: set of coordinately controlled genes (only in bacteria); multiple gene products controlled by a single regulatory region
draw and explain the strucutre of gene in eukaryotes
check notes
- more complex gene regulation
- promoters tend to be weak
- defult gene expression is OFF
- regulation is controlled by upstream regulatory elements (URE); eg. enhancer elements and repressor elements
- eg. euk promoter: TATA box or CpG
how is the gene regulated?
explain H-bond acceptors donors
- genes are controlled by DNA binding proteins
- recognize info in the major and minor grooves of DNA (usually in major grooves)
- reads the DNA
- bases H-bond donors and acceptors that associate with R groups of polar a.a
explain positive vs negaitve regulation
ex. MyoD (eukaryotes), LocI
- bind to DNA to promote transcription
- MyoD: binds to the minor grooves
vs - bind to DNA and prevent transcription
- more common in bacteria
- LacI: heterodimer; binds to seqs in DNA (operator) and causes DNA to loop; somehow represses LOC operon expression
What is the Lac Operon
draw it out and it’s parts
- coordinated regulation of gene involved in metabolism of lactose by E.coli
- genes for Lactose metabolism are ONLY needed if glucose is lacking and lactose is present
- Lac Z encodes bgal
- Lac Y = permiase - allows transport of lactose into cell
- Lac a: no known fxn in operon
Explains what happens to the Lac Operon in the absence of Lactose
draw it out, repression
- where there is no lactose in cell; no operon expression
- no Z,Y and A genes are expressed
- expression of LacI is constitutive (always on)
- binds to the operator and represses transcription = negative regulation
- inhibits either by:
1. preventing RNA poly from binding promoter
2. preventing RNA poly from moving off promoter
Explain what happens in the Lac operon in the presence of lactose
draw it
- repressor with induce bound can no longer bind to operator
- Z, Y and A genes can be expressed
- Lac I has a DNa binding domain that recognizes the operator and a Lactose binding domain so when Lactose is bound it causes an allosteric shift (shape change) and Lac I can no longer bind to the operator
How do we study the Lac Operon?
- using X-galactosidase (X-gal); changes color to blue to show cells have active Lac Operon expression
F-plasmids and th Lac operon
Describe the relationship b/w a plasmid and Lac Operon in genomic DNA
draw it out, Lac I and P O
Plasmids:
- found floating freely in cytoplasm
- naturally occuring
- often contain extra genes
- can be altered to introduce gens into a host cells
- Lac I protein is a trans acting factor therefor can influence expression in both gDNA copy and plasmid copy
- P and O are cis acting factors: only influence expression on same strand that they are located on
