Regulation of Transcription

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Regulation of Transcription 1.) Sigma
factors 2.) Other DNA binding proteins A.)
Negative, block RNA polymerases access to
DNA --- lac repressor B.) Positive,
enhance recruitment of RNA polymerase ---
catabolite activation --- sometimes both
negative and positive systems compete to operate
on the same set of genes --- genes in bacteria
are often grouped into regulatory elements called
operons (groups of genes controlled by the same
operator), this saves time and energy for the cell
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Lactose Operon in E. coli
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Tryptophan Operon
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Positive Regulation The Maltose Operon
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Catabolite Activation, dual regulation
(positive negative) in the lac operon
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Two Component Systems
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Translation Requires 1.) Ribosomes 2.)
charged tRNAs 3.) mRNA 4.) accessory factors
(initiation factor, elongation factor,
etc.) 5.) ATP GTP Based on Genetic
Code --- need at least 20 words so must have
3 nucleotide codons --- code is degenerate,
multiple codons specify the same amino acid,
effects A.) reduces likelyhood of mutational
damage B.) codon useage can vary between
different organisms
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Translation
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Other Tidbits RNA interference --- Use
non-coding (ncRNA) to block translation or
trigger destruction of mRNA Quorum
Sensing --- Small rapidly diffusing molecules
are used to measure cell density --- Often
used by pathogens to time toxin release
for maximum effect
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Mutation --- a change in the genetic
information (DNA sequence) of an organism ---
cells spend considerable energy fixing
mutations --- preventing all mutation would
actually be a bad idea, WHY? Types of
Mutation A.) Base Substitution swap one base
for another 1.) Transition change from one
purine or pyrimidine base to another (A?G or
T?C) 2.) Transversion change from a purine to
a pyrimidine or a pyrimidine to a
purine --- only possibility of change to AA
sequence of protein, WHY?
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Types of Mutations (Continued) B.) Insertion/
Deletion add or remove one or more base
pairs --- these types of mutations can cause a
frameshift, changing the reading frame of the
rest of the gene (often results in a
premature stop codon). --- What is one case
where there would be almost no effect of a
frameshift mutation?
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Mutagens and Mutagenesis Mutagen something
that causes DNA damage 1.) Chemicals, chemical
modification of DNA bases can easily result in
mutation 2.) DNA intercalators, aromatic
compounds that can form p-stacking
interactions with bases, are often read as
additional bases, creating insertion
mutations 3.) UV- induced thymine
dimers 4.) Ionizing radiation, creates double
stranded DNA breaks, can be difficult to
repair and may still result in an insertion or
deletion --- mutagenesis is the process of
purposely mutating an organism, wreck and
check strategy of protein study
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The Ames Test --- measuring how mutagenic
a substance is