Chapter 15 Flashcards
Natural selection has favored bacteria that produce?
only the gene products needed
Gene expression in bacteria is controlled by a mechanism known as?
operon model
operon
a single promoter serves a set of functionally related genes
The functionally related genes of an operon can be coordinately controlled by?
a single on “on-off” switch
operator
segment of DNA that is a regulatory switch
The operon stretch of DNA includes?
operator, promoter, genes that promoter/operator control
How can operon be switched off?
protein repressor
The repressor binds to the ___ and ____
operator, blocks the attachment of RNA polymerase
The repressor is the product of?
a seperate regulatory gene not part of the operon
repressor can be in ___ or __
inactive or active form
corepressor
molecule that cooperates with a repressor to switch operon off
example of repressible operon
tryptophan
The trp operon is ___ and the genes for trp synthesis are ___ because ___
on, transcribed, it is an amino acid and bacteria need proteins
When trp is present, it binds to the ___ protein which then turns ___
trp repressor, the operon off
A repressible operon is one that is usually __
on
A inducible operon is one that is usually __
off
example of inducible operon
lac operon
By itself, the lac repressor is __ and switches __
active, the lac operon off by binding to operator
inducer
inactivates the repressor to turn the lac operon off
lac operon inducer is?
allolactose
Inducible enzymes
enzymes of lactose pathway
Repressible enzymes
enzymes of trp pathway
repressible enzymes usually function in ___ and their synthesis is ___
anabolic pathways, repressed by high levels of their end product
inducible enzymes usually function in?
catabolic pathways
regulation of lac and trp operons involves ___ of genes because operons are ___
negative control, switched off by active form of repressors
When glucose is scarce, __ acts as an ___
cAMP receptor proteins, activator of transcription
CRP is activated by binding with?
cyclic AMP
Differences between cell types result from?
differential gene expression
differential gene expression
expression of different genes by cells with same genome
Gene expression is regulated at many?
stages
gene expression is commonly controlled at?
transcription
Greater complexity provides opportunities for regulating?
gene expression at stages other than transcription
What can influence gene transcription?
location of gene promoter relative to nucleosomes
Genes within ___ are usually not expressed?
heterochromatin
histone acetylation
acetyl groups attach to amino acids in histone tails
DNA methylation
addition of menthyl groups which can lead to reduced transcription.
Once methylated genes usually?
remain menthylated through cell divisions
After replication, enzymes methylate the correct daughter strand so that?
methylation pattern is inherited
epigenetic inheritence
inheritence of traits transmitted by mechanisms not directly involving nucleotide sequence
epigenetic modifications can be?
reversed
Associated with most eukaryotic genes are multiple?
control elements
control elements
segments of noncoding DNA that serve as binding sites for transcription factors
control elements and transcription factors are critical for?
precise regulation of gene expression
general transcription factors act at?
promoter of all genes
some genes require?
specific transcription factors that bind to control elements
distal control elements are ___ and proximal control elements are ___.
enhancers, promoters
In eukaryotes, the precise control of transcription depends on?
binding of activators to control elements
eukayotic genes that are ___ are not ____.
co-expressed, organized into operons
eukayotic coexpressed genes are?
scattered over different chromosomes
To mark a particular protein for destruction, the cell commonly attaches molecules of?
Ubiquitin
Protein coding DNA accounts for only __ of the human genome
1.5%
What plays a crucial role in regulating gene expression?
large and diverse population of RNA molecules
Micro RNAs
small, single stranded RNA molecules that can bind to mRNA sequences
miRNAs can ___ mRNA or block its ___.
degrade, translation
What is another class of small RNAs?
small interfering RNAs (siRNAs)
siRNAs and miRNAs are similar but?
form from different RNA precursors
RNA interference
phenomenon of inhibition of gene expression by siRNAs
In some yeasts siRNAs are required for the formation of?
heterochromitin at centromeres of chromosomes
siRNA system interacts with ___ and ____.
noncoding RNAs, chromatin-modifying enzymes
What also induces formation of heterochromatin?
piwi-associated RNAs (piRNAs)
piwi-associated RNAs (piRNAs)
block expression of transposons
Most straight forward way to discover which genes are expressed by cells of interest?
identify the mRNAs being made
We can detect mRNA in a cell using?
nucleic acid hybridization
nucleic acid hybridization
base pairing of a strand of nucleic acid to its complementary sequence
nucleic acid probe
complementary molecule or a short stranded DNA or RNA
in situ hybridization
The nucleic acid probe is tagged with fluorescence which allows us to see the mRNA.
Another method used for comparing the amounts of specific mRNAs?
reverse transciptase-polymerase chain reaction (RT-PCR)
Reverse transcriptase-polymerase chain reaction (RT-PCR)
turns sample set of mRNAs into double stranded DNAs
complementary DNA (cDNA)
DNA copy of an mRNA
DNA microarray assays
tiny amounts of many single stranded DNA fragments on a slide in a grid are studied for genome-wide expression
RNA sequencing (RNA-seq)
sequence cDNA samples from different tissues or stages to discover which genes are expressed.
