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Unformatted text preview: iments to determine the
molecular nature of the gene and, ultimately, the genetic code. ~ “We Can Sleep Later”, Edited by Franklin W. Stahl CSHL Press Alfred Hershey and Raquel Rotman
• Looked at two loci in T2
• h+: able to infect and lyse type
B, but not type B/2 E. coli cells.
• Produce cloudy plaques if
plated on a lawn with both
B and B/2 cells.
• h - : infects and lyses both B
and B/2 E. coli.
• Produces clear plaques Alfred Hershey and Raquel Rotman • r+: wild-type small, (fuzzybordered) plaques.
• r - : abnormal large (distinctbordered) plaques Hershey and Rotman’s
experiment to map phage genes 42
on same chromosome 12
12 76% 24% Lecture 13:
Bacterial and Viral Genetics
July 29, 2013
• Gene regulation (Chapter 16)
• Elements common to bacteria and eukaryotes
– Genes and regulatory elements
– Levels of gene regulation
– DNA-binding proteins
• Gene regulation in prokaryotes
• The lac and trp operons
– Catabolite repression
– Antisense RNA Regulation of gene expression
in prokaryotes • E. coli respond to their environment through regulation of gene
expression: • E. coli responds to the presence or absence of glucose
• If glucose is present, E. coli uses it to generate ATP
• If there is no glucose, it utilizes other sugars, such as lactose AA can be harvested from medium or from food source, anything else can
be synth if not avail. Regulation of gene expression
• E. coli respond to their environment through regulation of gene
expression: • E. coli responds to the availability of amino acids
• If amino acids are available, E. coli uses them to synthesize
proteins • If a particular amino acid is absent, E. coli produces the
enzymes necessary for synthesizing the amino acid Regulation of gene expression
in prokaryotes • Why don’t E. coli produce all the enzymes they need for all
circumstances all the time? energetically costly • E. coli (and all organisms) carry the genes for most proteins/
enzymes they need Text • but only express (transcribe and translate) them when needed Regulation of gene expression
in prokaryotes • Regulation of gene expression is also critical in eukaryotes (Ch 17)
• Cells need to respond to their environment
• They also need to differentiate - e.g. neurons express different
genes than blood cells. Genes and Regulatory Elements • Many aspects of gene regulation are similar in bacteria and
eukaryotes both have genes • Genes
• A gene is any sequence that is transcri...
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