Polyteny Flashcards
What is the function of short non-coding RNA?
Silencing
What are the two types of RNA?
MiRNA (microRNA) and SiRNA (silencing RNA)
What does RISC stand for?
RNA
induced
Silencing
Complex
Why are polytonic chromosomes visible under a microscope?
They are so tightly packed and large
Would polytonic chromosomes be expressed? Why?
No, they are so tightly coiled that RNA cannot come and transcribe the chromosome (bands cannot be read)
What could be a reason for polytonic chromosomes?
Whenever there is a huge metabolic demand, the large presence of chromosomes amplify gene expression of inter-bands.
Why do polytonic cells often appear to have a haploid number of chomosomes?
The homologous chromosomes are so tightly paired and aligned
What structure connects polytene chromosomes?
The chromocentre
What is the puff mechanism?
When flies were exposed to high heat, a polytonic chromosome expanded (puffed) to be expressed more
What is the formation of polytene associated with?
The elimination of the mechanism of mitosis after DNA doubling
What phase is missing from the polytene cell replication cycle? What phase is the polytene cell “stuck” in?
The M phase is gone, so the cell is in a permanent “interphase”
What is intermediate polyteny?
Some phases of the cell are partially or completely bypassed, there may be some stages that occur such as multinucleate chromosomes
What chromosomal structures are very present in polytonic chromosomes?
Condensins and coheisins
What is a TAD polytonic band?
It is a region of tightly compacted chromatin that forms a visible band
What are interbands rich in?
euchromatin
What factors contribute to holding sister chromatids and homologous chromosomes togehter?
DNA coiling topological entanglement
Cohesin and Condensins pins
Packing of heterochromatin in dense bands
What two processes contribute to small numbers of transcripts needed in very large quantities or certain regions of the chromosome that do not need to replicate as fully?
Gene amplification or underreplication
Why are larger puffs directly related to increased transcriptional activity?
Greater accessibility for RNA polymerase enzymes
What does CDK stand for?
Cyclin dependent kinase
What triggers S and M phase initiation?
CDK activity
What type of cyclins and CDK induce S phase?
E or A type cyclins, and CDK2
What type of cyclins and CDK induce M phase?
B or A type cyclins and CDK1
In endocycling cells, how can we describe CDK activity?
It increases enough to reach the S phase threshold, but not the M phase
What does APC stand for?
Anaphase promoting complex
If you block the inhibition of APC, what happens?
It downregulates STG, which suppresses CDK1 which would suppress mitosis
What are polytonic genes responsible for functionally in fruit fly larvae salivary glands?
They overexpress the production of digestive enzymes like amylase.
What does polyteny allow for in giant trophoblasts?
The amplification of genes
Growth/metabolic activity
Support for placental development and integrity
Where is polyteny located in mammals generally? Why?
Mostly in the liver to be able to deal with higher levels of toxic substances
What is the mechanism called that protects against cancer? What is it?
Gene compensation is the presence of extra copies of genes that can buffer against loss or mutation of tumor suppressor genes
What is polyteny?
When a cell undergoes DNA replication without cell division
Why can’t thick polytene chromosomes undergo mitosis?
They are so tightly bundled it obstructs alignment/segregation
What is somatic synapsis?
Homologous and sister chromatids are synapsed
Where is polyteny observed?
In tissues and organs where there is need for rapid development and high levels of function
What is a polytene puff?
A site of decondensed chromatin where DNA is accessible for robust transcription
