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)
What is cancer?
Changes in cell division/cell cycle
Oncogenes
Abnormal mutated cancer-causing genes
Mutagens and carcinogens
Anything that leads to a mutation
Cancer-causing substances
Proto-oncogenes
Code for proteins that stimulate normal cell growth and division (normal)
Tumor-suppressor genes
Code for proteins that inhibit cell division (normal)
How is cell division controlled by these genes?
Signal pathways
The discovery of viruses
TMV- tobacco mosaic virus
Why aren’t viruses living things?
- Cannot reproduce on their own
- Cannot perform protein synthesis so can’t grow
Obligate Intracellular Parasites- requires a host for survival
Restriction enzymes
Enzymes that cut apart viral DNA, restrict virus’ ability to infect bacteria
Lytic Cycle
- Attachment- tail fibers connect with receptors
- Entry- nucleic acid through capsid, degrades host’s DNA
- Synthesis- uses host’s contents and enzymes to copy genome and make proteins
- Assembly- create heads, tails, etc. packs genome into capsid
- Release- enzyme damages walls, allows fluid into cell which cause cell to burst
Lysogenic cycle
- Entry- factors decide whether lytic or lysogenic cycle
- Combination- viral DNA with host’s DNA, creating a prophage
- Cell division- creates large population of cells with prophages
- Result- daughter cells with prophages
Triggers- an environmental/chemical signal that causes a change from the lysogenic cycle to the lytic cycle
What phases can be replicated by both the lysogenic and the lytic cycles?
Temperate phages (phage lambda)
Retroviruses - RNA virus
Reverse transcriptase - an enzyme which transcribes mRNA into DNA
What is an example of this?
HIV- human immuno deficiency that attacks white blood cells, destroying immune system, this can be inactive in your body for long time but then replicates, is activated, and turns into AIDS (acquired immuno deficiency syndrome)
How do viruses make you sick?
Cell/tissue destruction
Release toxins
How are viruses treated?
Vaccination programs and antiviral drugs
How do viruses spread?
Indirect- coughing, sneezing
Direct- touch
