Tightly. May be modified to counteract environmental changes or gene expression can change to change cell function
What are constitutive proteins
Proteins that are expressed all the time
What are inducible genes
Expressed only when they are needed to be induced
At what level can genes be regulated?
Gene expression begins when?
At the promoter, where the transcription is initiated
What happens in selective gene transcription
A decision is made about which genes to activate. And transcription factors control whether a gene is active
What are transcription factors
Regulatory proteins that bind to specific dna sequences near promoter
What are two types of regulation
Negative and positive
What is negative regulation
a repressor protein preventing transcription
what is positive regulation
an activator protein binding to stimulate transcription
how do acellular viruses use gene regulation to take over host?
They inject host cell with nucleic acid that takes over synthesis. New viral particles (virions) appear rapidly and are soon released from the now lysed cell
What is the lytic cycle
A typical viral reproductive cycle in a lysogenic phase. The viral genome is incorporated into the host genome and is replicated too
A bacteriophage may contain what two things
DNA and RNA and may not have a lysogenic phase.
What are the two stages of the lytic cycle?
Early stage and Late stage
What happens during the early stage of the lytic cycle
Promoter in the viral genome binds to host RNA polymerase and the nearby viral genes are ranscribed. Early genes shut down transcription and begin replicating themselves. Posttranscriptional mechanism shuts down host gene. The viral nucleus digests the hosts chromosome.
What happens during the late stage of the lytic cycle
It takes about 30 minutes, viral genes are now transcribe and they encode the viral capsid proteins and enzymes to lyse the host cell and release new virions
What is a retrovirus
HIV, a virus that encloses itself in the host cell. Fuses with its membrane and through reverse transcriptase, DNA synthesis directs RNA. Two strands of DNA are synthesized and they chill in the hosts chromosome as provirus.
Can some host cells reject invaders?
Some can. One such system is transcription terminator. Proteins that interfere with RNA polymerase but HIV counteracts this negative regulation with TAT.
What is TAT
Transactivator of transcription. It allows RNA polymerase to transcribe the viral genome
How do prokaryotes conserve energy?
They only make proteins when needed
At what level is the most efficient gene regulation
What does E. coli need to do
Adapt quickly to food supply changes. Glucose or lactose may be present
If lactose is predominant, what happens?
Then glucose is low and E. coli synthesizes all 3 enzymes
If lactose is removed, what happens?
The synthesis stops
What is an inducer
A compound that induces protein synthesis
What are two ways to regulate a metabolic pathway?
Gene expression and regulating enzyme activity
What are structural genes
They specify primary protein structure the amino acid sequence.
Tell me about the 3 structural genes for lactose enzymes.
They are adjacent on the chromosome, they share a promoter, and they are transcribed together. Their synthesis is ALL OR NONE
What is an operon
It is a gene cluster with a single operon; a short stretch of DNA near the promoter that controls transcription of structural gene. Lac operon encodes for lactose enzymes
How does an inducible operon work?
It is off unless needed (unless it needs to be induced)
How does a repressible operon work?
It is on until it needs to be repressed (off)
When is the lac operon transcribed
When B- galactoside predominates in the cell
What happens to the repressor in the presense of B-galactoside?
It detatches and allows RNA polymerase to initiate transcription.
What is the key to the lac operon regulatory system?
The repressor protein.
What happens when the repressor is bound to its operator
The repressible operon is OFF. But it only binds in the presence of a co-repressor
What is a co-repressor?
It causes a repressor to change shape in order to bind to the protmoter and inhibit transcription.
What is significant about tryptophan in regards to co-repressors?
It acts as its own repressor in the trp Operon.
What are two different types of operons
Inducible and repressible
How doe inducible systems work?
A metabolic substrate (inducer) interacts with a regulatory protein (repressor) the repressor then cannot bind and allows for transcription
How does a repressible system work
A metabolic product (co-epressor) binds to regulatory protein which then binds to operator and blocks transcription.
How do inducible systems control catabolic pathway
They are turned on when the substrate is available
How do repressive systems control anabolic pathways
They are turned on UNTIL the product concentration becomes excessive
What are sigma factors
Other proteins that bind to RNA polymerase and direct it to specific promoters
What are two kinds of sigma factors
Global gene regulation and sporulation
What is global gene regulation
Genes that encode protein relate functions may have different locations but they hav the same promoter sequence- they are on at the same time
What is sporulation
This occurs when nutrients are depleted and genes are expressed sequentially, directed by a sigma factor.
What are eukaryotic promoters
Transcription factors. Each promoter contains a core promoter sequence where RNA polymerase binds.
Name a common core promoter sequence.
TATA box. Rich in a-t base pairs. Only after general transcription factors bind to the core promoter, RNA polymerase II bind and initiate transcription
What are enhancers?
DNA sequences that bind activators.
What are silencers. Those DNA sequences that bind repressors
What determines the rate of transcription
The combination of factors present
What are NFATs
Nucear factors of activated t-cells. They are transcription factors and they control genes in the immune system.
How can gene expression be coordinated?
Even if the genes are far apart on different chromosomes. They have regulatory sequences that bind the SAME transcription factors.
How do plants use coordinated gene expression?
They use the dehydration response element. A transcription factor changes shape and binds to this element during a drought
How can gene transcription be regulated by reversal alterations
Reversal alterations to DNA or chromosomal proteins can be passed on to daughter cells. These epigenetic changes are different from mutations because they are reversible
How can DNA be modified with methyl group
In cytosine, methyl group is covalently added to 5 carbon to form 5-methylcytosine. DNA methyltransferase catalyzes this reaction.
What kind of DNA change is heritable
A covatlent one.
Tell me about methylase and demethylase
When dna replicates, maintenance methylase catalyzes formation of 5 methylcytosine in new strand and demethylase catalyzes the removal of this extra methyl group
What are the effects of DNA methylation
Can bind proteins involved in repression of transcription and genes tent to be silenced (inactive); patterns of DNA methylation can include large regions or whole chromosomes.
Two kinds of chromatin that are visible during interphase
Euchromatin and heterochromatin
What is euchromatin
It is diffuse and light staining; contains DNA and mRNA transcription
What is Heterochromatin
It is condensed, dark staining; and containes genes not transcribed
What is a type of hetero chromatine
Inactive X chromosome in mammals. The barr body is identifiable during interphase and can be seen in cells of human females.
What is chromatin remodeling
A mechaninism for epigenetic regulation; it is the lalteration of the chromatin structure.
What happens in chromatin remodeling
Histones acetyltransferases change charge by adding acetyl groups and histone loses affinity for DNA. It can activate transcription
What is histone deactylase
Another kind of chromatin remodeling protein that can remove acetyl groups from histones thurs, repressing transcription
What plays an important role in epigenetic modifications?
Environment; twins can show different methylation after living in different environments.
What can alternative splicing do
It can make different mRNAs from the same gene.
Can gene expression be regulated?
Yep! After the initial gene transcript is made.
What are microRNAs
Small molecules of noncoding RNA. They are important regulators of gene expression
What role do lin-14 mutations have iin C. elegans
They cause larvae to skip the first step; normally, they would be involved in it
What does lin 4 mutation do
It causes the cell to repeat stage one events.
How come mRNA transcriptions can be regulated
Protein and mRNA concenrations are not consistently related- they are governed by factors after mRNA is made. They can be blocked or altered as to how long they persist in cell
What are 3 ways to regulate mRNA translation
Inhibition of translation with miRNAs, modification of 5cap end of mRNA or repressor proteins can block translation (translational repressors).
How does Creb regulate the expression of many genes?
Creb fam of transcription factors can activate or repress genes by binding to cAMP response element (CRE). It has been linked to addiction and memory tasks as well as metabolism.