Gene Expression Flashcards
How is gene expression controlled in bacteria?
Genes are turned on and off by starting or stopping transcription.
What are operons?
a unit of genetic function which consists of a promoter, operator, and genes that are grouped together based on their job
What are the two types of negative gene regulation (feedback)?
repressible and inducible operons
Explain repressible operons.
- transcription is usually on but can be turned off
- function in anabolic pathways (building large molecules)
- regulatory gene codes for a repressor upstream from the operon and makes it when there is enough of a protein, a corepressor (the protein) then binds to a repressor which activates it and causes it to bind to the operator which inhibits RNA polymerase from binding to the operon
Explain inducible operons.
- transcription is usually off but can be turned on
- function in catabolic pathways (break down molecules)
- when a repressor is made, it is immediately activated and attaches to the operator, preventing the binding of RNA polymerase. The presence of a substance (the inducer) then attaches to the repressor and deactivates it. RNA polymerase is then free to bind and transcribe.
How is positive gene regulation controlled?
an activator (protein) binds to the promoter and stimulates transcription of a gene by attracting RNA polymerase
Give an example for a repressible operon, an inducible operon, and positive gene regulation.
- tryptophan synthesis
- Lac operon- makes enzyme (B-galactosidase) that breaks down lactose (inducer)
- CAP (catabolite activator protein) which is activated by cAMP
What are the 7 places gene expression can be controlled in humans?
Chromatin modification, DNA methylation, Regulation of transcription initiation, Alternative RNA splicing, mRNA Degradation, Regulatory proteins, Protein Degradation
Chromatin modification
Loosens the chromatin (loosens the DNA from the proteins) in a nucleosome, structure of 8 histone proteins with DNA coiled around twice. This is done by histone modification - that addition of acetyl groups
-encourages gene expression
DNA methylation
Inactivates the DNA
- addition of methyl groups
- how x inactivation happens
Epigenetic inheritance
The inheritance of traits not directly involved DNA
- the way genes expressed are affected by chemicals so they are different
- even identical twins look different this way
- different genes are expressed at different times
Regulation of transcription initiation
Transcription factors called activators attach to control elements called enhancers upstream from the genes both of which are specific to each gene. Control elements are non-coding segments of DNA. The activators are attracted to other transcription factors on the promoter with mediator proteins with the help of a DNA-bending protein. The combination of these proteins allows RNA polymerase to transcribe.
How is the regulation of transcription initiation an example of cell type-specific transcription?
Gene expression varies from cell to cell because different activators are available in different cells so liver proteins may be expressed in one cell but eye proteins may be expressed in another.
Alternative RNA splicing
Different mRNA molecules can be made from the same portion of DNA depending on which introns are spliced out
mRNA degradation
mRNA can last days or weeks. This controls how many proteins are made from that strand.
Regulatory proteins
Can block the attachment of mRNA to ribosomes thus preventing translation, enzymes controlling a feedback mechanism
Protein degradation
By proteasome, broken into pieces
What are noncoding RNAs and what are the two types?
ncRNA's Do not help protein synthesis MicroRNAs - miRNA -break down mRNA -block translation Small interfering RNA's - siRNAs -block translation
Why is regulated gene expression especially important in an embryo?
Differentiation
Morphogenesis by homeotic genes and cytoplasmic determinants
Differential gene expression
Expression of different genes by different types of cells that all have the same genome
Differentiation
The process by which your cells become specialized in structure and function
Morphogenesis
Creation of form - to change shape
The physical process that gives and organism it’s shape
Cytoplasmic determinants
Substances in cytoplasm of mom’s egg cell that influence early gene expression in an embryo
Homeotic genes
Pattern formation in late embryo and larvae (head, bone, tissue, etc.) and (head, thorax, abdomen)
