Chapter 15 Flashcards
Operator
The “on-off switch! Of a segment of DNA
- positioned within the promoter
- controls the access of RNA polymerase to the genes
Operon
A unit of genetic function found in bacteria and phases consisting of a promoter, an operator and a coordinated regulated cluster of genes.
Represser
A protein that inhibits gene transcription.
In prok. Repressors bind to the DNA or near the promoter.
In euk. Repressors May bind to control elements within enhancers, to activators or other proteins to block activators from binding to DNA.
Blocks attachment of RNA polymerase
Regulatory gene
A gene that codes for a protein, such as a repressors, that’s controls the transcription of another gene or group of genes.
Some facts about repressors
Reversible
Operator alternates between repressive bound and non-repressors (bound is longer)
Repressors are allosteric (two alternative shapes)
Produced continuously with own promoter
Co repressors
A small molecule that binds to a bacterial repressors protein and changes the proteins shape, allowing it to bind to the operator and switch operon off
Inducer
A specific small molecule that binds to a bacterial repressors protein and changes the repressors shale so that I can not bind to an operator, thus switching operon on
Cyclic AMP
A ring-shaped molecule made from ATP that is a common intracellular signalling molecule in euk, cells, it is also a regulator of some bacterial operons.
Activator
A protein that binds to DNA and stimulates gene transcription. In prok. Activators bind in or near the promoter. In euk. Activators bind to control elements in enhancers.
Increases RNA POL affinity for the promoter
A typical human cell might express how much of its protein coding genes at any time?
20%
Differential gene expression
The expression of different sets of genes by cells with the same genome.
Histone acetylation
The attachment of an acetyl group to certain amino acids of histone proteins.
DNA methylation
The presence of methyl groups on the DNA bases (usually cytosine) or adding methyl groups to bases.
Epigenetic inheritance
Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome.
Can be altered, DNA methylation erased and reestablished on gametes
Methylation patterns inherited by parents
Control elements
A segment of non coding DNA that helps regulate transcription of a gene by serving as a binding site for a regulatory proteins such as transcription factor. Multiple control elements are on euk. Enhancers.
Can be anywhere, even in introns (distal enhancer)
Enhancers
A segment of euk. DNA. Containing multiple control elements, usually located far from the gene who transcription it regulates.
Specific transcription factors can function as repressors by
Binding directly to control elements to block activator
Interfere with activator itself
Alternative RNA splicing
A type of euk. Gene regulation at the RNA- processing level in which different mRNA molecules are produced from the same pre-mRNA depending on which RNA segments are treated as exons and which as introns.
MicroRNA (miRNA)
Small single stranded RNA, can degrade or prevent translation of an mRNA wi5 a complementary sequence
Small interfering RNA (siRNA)
Degrade or prevent translation of an mRNA with complementary sequence. Can also block transcription by promoting chromatin mod.
Block gene expression
Condensing of DNA
Reverse Transcriptase-Polymerase chain reaction
A technique for determining expression of a particular gene. It uses reverse transcriptase and DNA pol. To synthesize cDNA from the mRNA in a sample and then subjects the cDNA to PCR amplification.
mRNA —DNA—double stand—copied DNA —PCR to amplify
DNA microarray assays
A method to detect and measure the expression of thousands of genes at one time. Tiny amounts of a large number of single stranded DNA fragments are fixed to glass slide and tested for hybridization with samples of labelled cDNA.
Negative gene regulation
REPRESSORS!
And inducible operon
Repressor+co repressor= off
Determines if transcription is on or off
Positive gene regulation
ACTIVATORS
Determines rate at which transcription happens
Duel control
Genes with both positive and negative control
Co ordinated control
Interaction of multiple gene products is needed for appropriate control of transcription.
Ex: glucose is down= active CRP
Regulation of chromatin structure includes
- location of nucleosome
- degree of condensation (eu or hetero chromatin)
- chemical mod of DNA and histones
Methylation causes
While
Acetylation causes
Increases chromatin condensation= decrease transcription
Decreases condensation= increase transcription
Genes that are unexpressed and Barr bodies have high degree of what?
Methylation
General vs specific transcription factors
Low level rates of transcription on their own
Bind to control elements and act as either an activator or repressor
Piwi-associated RNA
Induce formation of heterochromatin to block expression
Used in reestablishing methylation patterns in gametes
