Regulation of Gene Expression (molecular biology)
MicroRNAs
(mRNAs) originate from DNA that is formed scattered across the genome
Short interfering RNAs
(siRNAs) are generated from dsRNA that originated outside the cell
What does the operon include?
-promoter -operator -structural genes -regulatory gene
What are two ways cell differentiate?
1. Cytoplasmic determinants 2. Cell-cell signals
Why is the regulation of gene expression in eukaryotic cells more complicated than in prokaryotes?
1. Multicellularity 2. Chromosome complexity 3. Uncoupling of transcription and translation
What are two types of proteins produced by regulatory genes?
1. Repressor protein 2. Activator protein
Transcription complex
A group of various proteins that are associated with RNA pol activity. Components of the complex include: 1. General transcription factors 2. Specific transcription factors 3. Coactivators and mediators
Corepressor
A molecule that binds to a repressor to activate it
Operator
A region engaged by a regulatory protein to either block or promote the action of the RNA polymerase
Inducible operons
A substance is required to induce (turn on) the operon
Operon
A unit of DNA that contains multiple genes whose products work together to direct a single metabolic pathway
Coactivators and mediators
Additional proteins that contribute to the binding of transcription complex components.
Protein degradation
As proteins age, they lose their functionality as their 3D shape changes.
RNA processing
Can produce different mRNAs by slicing the primary RNA transcript in different ways.
Histone modification
Changes in organization of histone proteins with DNA. Two types that can increase access to DNA transcription are acetylation and methylation.
X inactivation
Chromosome inactivation in females
Structural genes
Contain coding DNA - DNA that codes for various related enzymes that direct the production of some particular product
Determination
The series of events that lead to observable differentiation of a cell
RNA interference (RNAi)
Gene silencing caused by short RNA molecules that bing to complementary sequences of mRNAs in the cytoplasm and block their translation or cause their degradation (by cleavages). Two types are microRNAs and short interfering RNAs.
Homeotic genes
Genes that control pattern formation
What is an example of positive regulation?
Glucose repression because an activator protein is involved. When glucose is absent in the environment, CAP protein is activated and binds to operator, promoting RNA transcription of enzymes to occur.
What are two types of operons?
Inducible and repressible operons
Cytoplasmic determinants
Maternal substances in the egg that influence the course of early development. These are distributed unevenly in the early cells of the embryo and result in different effects.
DNA methylation
Methyl groups (-CH3) attach to DNA bases. This makes it more difficult for transcription factors to access the DNA.
Methylation
Methyl groups can be attached to histones. This can either increase or decrease transcription of genes. This is associated with repressed transcription.
Cell-cell signals
Molecules (like growth factors) produced by one cell influence neighbor cells, which causes cells to differentiate.
Regulatory genes
Produces the regulatory protein that engages the operator region and governs whether RNA pol can attach to the promoter region and being transcription. The protein becomes active or inactive only when they bind o some specific molecules.
Activator protein
Promotes the attachment of RNA pol to the promotor region. These proteins characterize positive regulation because they must be active in order for the transcription to occur.
Specific transcription factors
Proteins associated with regulating SPECIFIC transcription activities. Two types are activators and repressors.
General transcription factors
Proteins that are required by all transcription events to successfully initiate transcription by RNA polymerase
Promoter
Sequence of DNA to which the RNA polymerase attaches to begin transcription
Pattern formation
Sets up the body plan and is a result of cytoplasmic determinants and inductive signals. This determines the head, tail, and body orientation.
Repressible operons
Stop producing enzymes only in the presence of a repressor
Acetylation
The attachment of an acetyl group makes the histone molecules loosen their grip on the DNA molecule. This is associated with activated transcription.
Stem cells
These are cells in the early stages or embryonic development. When stem cells divide, the daughter cells have the potential to become any kind of cell.
Induction
The process by which molecules cause a cell response and causes cells to differentiate
What do specific transcription factors do?
They attach to enhancers (DNA binding sites), which can be thousands of nucleotides upstream/downstream from the gene. Because they can be so far away, the DNA segment containing the enhancer folds such that it can join the general transcription factors and RNA pol on the promoter
What do general transcription factors do?
They attach with the RNA pol to the promoter region upstream and adjacent to the gene to be transcribed
Lac operon
This controls the breakdown of lactose in E coli. A regulatory gene produces an active repressor that binds to the operator region --> RNA pol unable to transcribe genes. When lactose is available, some combines to inactivate repressor --> RNA pol able to transcribe genes that code for the enzymes the break down lactose. This is an example of negative regulation.
Transcription initiation
This is regulated by a transcription complex, and the makeup of the complex determines the degree to which transcription is activated or repressed.
mRNA degradation
This occurs as a result of RNAi, and because mRNAs are unstable molecules. Degradation of the poly A tail occurs as mRNA ages.
trp operon
This operon produces enzymes for the synthesis of the amino acid tryptophan. This is an example of negative regulation 1. A regulatory gene produces an inactive repressor that does not bind to the operator --> RNA pol transcribes genes and produces trp 2. Trp in environment --> E coli don't need to make it themselves 3. Induces some remade trp to react with the repressor to make it active (acts as a corepressor) 5. The active repressor binds to the operator region --> prevents transcription of genes
Repressor protein
This protein blocks the attachment of RNA pol to the promoter region. These characterize negative regulation because they must be inactive in order for transcription to occur.