Chapter 18: Gene Regulation Flashcards
What does bacteria must do in the environment?
they must respond quickly to changes in the environment
Why must bacteria need to stop production if they have enough of a product,
Waste of energy to produce more
How must bacteria need to stop production if they have enough of a product?
stop production of enzymes for synthesis
Why must bacteria need to utilize the new food/energy source, quickly if they find it?
metabolism, growth, reproduction
How must bacteria need to utilize the new food/energy source, quickly if they find it?
start production of enzymes for digestion
Feedback Inhibition
products acts as an allosteric inhibitor of 1st enzyme of in tryptophan pathway
What is the drawback of feedback inhibition?
Its a wasteful production of enzymes
Gene Regulation
blocks the transcription of genes for all enzymes in tryptophan pathways
What is the benefit of gene regulation?
Saves energy by not wasting it on unnecessary protein synthesis
How do cells vary the amount of specific enzymes ?
regulating gene transcription
Operon
genes grouped together w/ related functions
ex: all enzymes in a metabolic pathway
Promoter
RNA polymerase binding site, single promoter controls transcription of all genes in operon
Operator
DNA binding site of repressor proteins
How can genes be turned off?
the repressor protein can bind to DNA at operator site, blocking RNA polymerase, blocks transcription
Repressible Operon: Tryptophan
Synthesis pathway model
When excess tryptophan is present, it binds to tryp repressor protein & triggers repressor protein & triggers repressor to bind DNA
- blocks (represses) transcription
What happens when excess tryptophan is present
an active repressor protein will bind with the operator to stop the transcription of trytophan.
Inducible Operon: lactose
Digestive pathway model when lactose is present, binds to lac repressor protein & triggers repressor to release DNA
- induces transcription
What happens when lactose is present?
The inhibitor that blocks the lactase enzyme from being produced is unblocked allowing the production of lactase
Jacob & Monod
1st to describe operon system coined the phrase “operon”
How does E coli sense the glucose concentration is low?
Cyclic AMP (cAMP) concentration is high.
If glucose is low and lactose is present then lac operon is turned on
Repressible operon
usually functions in anabolic pathways
-synthesizing end products
when end product is present in excess,
cell allocates resources to other uses
Inducible operon
usually functions in catabolic pathways
-digesting nutrients to simpler molecules
produce enzymes only when nutrient is available
- cell avoids making proteins that have nothing to do, cell allocates resources to other uses
points of control
The control of gene expression can occur at any step in the pathway from gene to functional protein
What are the points of control?
- packing/unpacking DNA
- transcription
- mRNA processing
- mRNA transport
- translation
- protein processing
- protein degradation
How do you fit all that DNA into nucleus?
DNA coiling & folding
-double helix
-nucleosomes
-chromatin fiber
-looped domains
-chromosome
Nucleosome
“Beads on String”
1st level of DNA packing
histone proteins
- 8 protein molecules
- positively charged amino acid
-bind tightly to negatively charged DNA
What happens when DNA is tightly wrapped the histone?
no transcription, genes are turned off
Missense Mutation
a point mutation, switch between bases, that causes the wrong protein to be
Nonsense Mutation
a point mutation because it codes for a stop codon in the middle of the sequence causing the rest of the amino acids to not be coded
Silent Mutation
point mutation that has no effect on the amino acid sequence.
Methylation of DNA blocks transcription factors
no transcription
→ genes turned off
attachment of methyl groups (–CH3) to cytosine
C = cytosine
nearly permanent inactivation of genes
ex. inactivated mammalian X chromosome = Barr body
DNA Phosphorylation
addition of a phosphate group to an amino acid (phosphorylation) will prevent the chromatin from condensing
Acetylation of histones
unwinds the DNA
-loosely wrapped around histones, which enables transcription and turns on genes
attachment of acetyl groups (–COCH3) to histones
conformational change in histone proteins
transcription factors have easier access to genes
Epigenetics Inheritance
Mutations in the DNA are permanent changes….but modifications to the chromatin CAN BE reversed.
What is the 1st control of gene expression?
chromatin modifying enzymes by just making the area of DNA more or less accessible to the process of transcription
Promoter
nearby control sequence on DNA
binding of RNA polymerase & transcription factors
“base” rate of transcription
binds transcription factors that controls the initiation of transcription
Enhancer
distant control sequences on DNA
binding of activator proteins…brings it closer to promoter
“enhanced” (high level
Activator proteins
bind to enhancer sequence & stimulates transcription
Silencer proteins
bind to enhancer sequence & block gene transcription
Post Transactional Control
Alternative RNA splicing
-variable processing of exons creates a family of proteins
