Lecture 4

Question 1

structure of gene in prokaryotes

Draw out structure

define: gene, operons, promotor
highlight: transcription and translation

check notes

Answer 1

• 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

Question 2

draw and explain the strucutre of gene in eukaryotes

check notes

Answer 2

• 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

Question 3

how is the gene regulated?

explain H-bond acceptors donors

Answer 3

• 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

Question 4

explain positive vs negaitve regulation

ex. MyoD (eukaryotes), LocI

Answer 4

• 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

Question 5

What is the Lac Operon

draw it out and it’s parts

Answer 5

• 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

Question 6

Explains what happens to the Lac Operon in the absence of Lactose

draw it out, repression

Answer 6

• 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

Question 7

Explain what happens in the Lac operon in the presence of lactose

draw it

Answer 7

• 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

Question 8

How do we study the Lac Operon?

Answer 8

• using X-galactosidase (X-gal); changes color to blue to show cells have active Lac Operon expression

Question 9

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

Answer 9

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