Chapter 18: gene expression regulation Flashcards
metabolic control
- cells adjust activity of already-active enzymes
- cells adjust production levels enzymes
coordinately controlled
group of genes controlled by one “switch”
operator
segment of DNA within promoter controlling access of RNA polymerase to group of genes
operon
operator, promoter, genes they ctonrol
repressor
binds to operator and blocks attachment of RNA polymerase to promoter
regulatory gene
gene located away from operon with its own promoter. codes for repressor protein
corepressor
small molecule that works with repressor protein to turn off operon
Trp operon
has genes for tryptophan synthesis
tryptophan absent: repressor inactive, operon on
tryptophan present: repressar active, operon off
repressible operon
transcription usually on but can be repressed when specific molecule binds allosterically to regulatory protein (ex: tryptophan operon)
inducible operon
transcription usually off but can be stimulated when specific molecule interacts with regulatory protein (ex: lac operon)
β-galactosidase
enzyme catalyzing hydrolysis of lactose into glucose and galactose
lacI
regulatory gene that codes for allosteric repressor protein for lac operon
inducer
specific small molecule that inactivates repressor
allolactose
inducer of lac operon. isomer of lactose (indicates lactose is present)
lac operon
has genes for lactose metabolism
lactose absent: repressor active, operon off
lactose present: repressor inactive, operon on
lac operon genes
lac Z: β-galactosidase
lac Y: permease
lac A: transacetylase
negative regulation
operons switched off by active rterpressor protein
cyclic AMP
accumulates when glucose is scarce
CAP (catabolite activator protein)
regulatory protein activated by cAMP. attaches upstream to lac promoter, increasing affinity of RNA polymerase to promoter. stimulates gene expression (of lac operon)
positive gene regulation
regulatory protein interacts with genome to switch transcription on (ex: CAP and lac operon)
activator
protein that binds to DNA and stimulates transcription of a gene
differential gene expression
expression of different genes by cells with the same genome
histone acetylation
acetyl groups attached to lysines in histone tails. neutralizes positive charges and promotes looser chromatin. (makes transcription easier)
methylation of histone
addition of methyl to histone tails promotes condense chromatin
histone phosphorylation
addition of phosphate to amino acid next to methylated amino acid in histone tail promotes loose chromatin
histone code hypothesis
modifications to histone tails can affect chromatin structure and gene expression
DNA methylation
important for long term inactivation of genes
genomic imprinting
regulation of whether or not maternal or paternal allele of a gene is expressed through DNA methylation. Methylation patterns are usually passed on for each DNA replication
epigenetic inheritance
transmission of traits not directly involving nucleotide sequence
control elements
segments of noncoding DNA in eukaryotes that serve as binding sites for transcription factors
proximal control elements
located close to promoter
distal control elements
located far from poromter
enhancers
groups of distal control elements
activation domains
structure in protein that bind other regulatory proteins or transcription stuff
mediator proteins
interact with bound activators on control elements and proteins at promoter
DNA bending protein
bends DNA to bring bound activators closer to promoter
silencing
repressors recruit proteins that deacetylate histones, leading to reduced transcription
coordinately controlled eukaryote genes
depends on specific combination of control elements with every gene in dispersed group
alternative RNA splicing
different mRNA produced from same transcript
mRNA degradation
mRNA degraded within a few minutes for bacteria, sometimes up to weeks in multicellular organisms
utr
untranslated regions at 5’ or 3’ end. regulatory proteins can bind to those regions and block ribosome attachment
ubiquitin
marks proteins for destruction
proteasomes
recognize ubiquitin-tagged proteins and degrades them
ncRNA
non coding RNA. can regulate gene expression pathway
miRNA
single-stranded ncRNA. forms a complex with other proteins and binds to mRNA molecule with complementary sequence. degrades target mRNA or blocks translation..
miRNA synthesis
- long RNA precursor folds into hairpins
- Dicer enzyme cuts out double stranded hairpins
- one strand of hairpin degrades
remaining strand is miRNA
RNA interference
injecting double-stranded RNA turns off expression of genes with same sequence as RNA
siRNA
blocks translation of mRNA with the same sequence as it. multiple siRNA formed from long, linear, double-stranded RNA molecule
piRNA
ncRNA that induces formation of heterchromatin, blocking expression of transposons
transposons
parasitic DNA
differention
process by which cells become specialized in structure and function
morphogenesis
physical processes that give an organism its shape
cytoplasmic determinants
maternal substances in egg that influence development (unevenly distributed substances in unfertilized egg)
induction
process of signals causing changes in target cells
determination
events that lead to observable differentiation of a cell
tissue-specific proteins
give cell its characteristic structure and function
myoD
master regulatory gene encoding myoD protein, a transcription factor for many genes. turns cells into myoblasts (muscle cells)
pattern formation
development of spatial organization of tissues and organs
positional information
molecular cues controlling pattern formation
homeotic gene
control pattern formation in late embryo, larva, and adult Drosophila
emybronic lethals
mutations with phenotypes causing death at early stage
maternal effect gene
if mutant in mother, always results in mutant offspring
egg-polarity genes
maternal effect genes. control polarity of embryos
bicoid
gene controlling body axes of drosophila. highly concentrated at anterior end.
2 mutant alleles: posterior at both ends
morphogen gradient hypothesis
gradients of morphogenes establish an embryo’s axes and other form features
oncogenes
cancer-causing genes
proto-oncogenes
normal versions of oncogenes
tumor-suppressor gene
makes proteins that help prevent uncontrolled cell growth
proto-oncogene -> oncogene pathways
- translocation/transposition: gene moved to new locus under new controls
- gene amplification
- point mutation: within control element or gene
ras gene
makes Ras protein, a G protein for a pathway (with protein kinase cascade) that synthesizes a protein that stimulates cell cycle
p53 gene
tumor-suppressor gene that encodes transcription factor for cell-cycle inhibiting protein genes
p21
gene whose product halts cell cycle by binding to Cdks.
APC gene
tumor suppressor gene. often mutated in colon cancer patients
BRCA1/BRCA2 gene
genes often mutated in breast cancer patients.
p53 functions
- activates p21
- activates miRNAs that can inhibit cell cyle
- turns on genes for DNA repair
- activates suicide genes for irreparable DNA damage
