Biology chapter 18
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Why is gene expression so significant?
It allows only a few genes to create many different phenotypes.
- increased gene expression
- decreased gene expression
What is an OPERON?
What is its advantage?
A unit of genetic function found in bacteria and phages, consisting of a promoter, and operator, and a coordinately regulated cluster of genes whose products function in a common pathway.
It allows bacterial cells to use gene expression to respond quickly to environmental changes.
where RNA polymerase attaches and starts transcription
In bacterial DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of the repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.
part of the promoter, controls access of the RNA polymerase to the DNA transcript
differential gene expression
the expression of different sets of genes by cells with the same genome
All cells have same genome, differences in expression of genes llow them to have specialized functions.
What are the stages at which gene expression can be regulated in eukaryotic cells?
- cell signalling (hormones)
- modification of the chromatin structure
- transcription (transcription factors)
- post transscriptional modification --
- -- RNA manipulation
- -- mRNA degradation
- post-translational modification
- --protein manipulation
What is chromatin?
The complex of DNA and proteins (histones) that make up a eukaryotic chromosome. WHen the cell is not dividing, chromatin exists in its dipersed form, as a mass of very long, thin fibers that are not visable with a light microscope.
Why does chomatin need to be compacted?
- regulate gene expression
- protect the genome
- allow efficient movement during cell division
Name the four levels of chromatin packaging.
- 1st level: nucleosome
- 2nd level: solenoid
- 3rd level: scaffold proteins
- 4th level: metaphase
What is a histone?
A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role on chromatin structure.
How does chromatin packaging affect gene expression?
Genes are actively expressed in level 1, in level 2 can be easily moved back to level1. Level 3 contains unexpressed regions. Level four is metephase, no expression during replication.
What post-transcriptional modifications happen to mRNA in eukaryotes?
Why are they important?
- Alternative DNA splicing
- Results in many more proteins than there are genes in the genome.
alternative RNA splicing
- A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.
- Exons are spliced together.
What region of mRNA is most important for determining its longevity? What region binds proteins that can block translation?
the 3' UTR
What is microRNA? (miRNA)
A small single-stranded RNA molecule, generated from a hairpin structure on a precursor RNA transcribed from a particular gene. The miRNA associates with one or more proteins on a complex that can degrade or prevent translation of an mRNA with a complementary sequence.
What is RNAi?
What can it be used for?
- RNA interfernece: a technique used to silence the expression of selected genes: RNAi uses synthetic double stranded RNA molecules that match the sequence of a particular gene to trigger the breakdown of the gene's messenger RNA.
- It is used to study gene function and gene therapy
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