Functions and dysfunction of genomic regulation Flashcards
why are mitotic chromosomes more condensed compared to interphase chormosomes?
To prevent physical damage to the DNA as chromosomes are separated and passed on to daughter cells
what are 20% of histone amino acid residues
lysine (lys) or arginine (Arg)
what residues in histone proteins are the target of post translational modifications?
lysine residues
what are two classes of proteins that bind to DNA?
1) histone proteins
2) non histone chromosomal proteins (TFs)
what are chromosome puffs?
unwound sections of DNA that are active in gene expressions
- ex of how steroid hormones work in body
euchromatin
- Lightly packed form of chromatin- (DNA, RNA and protein)
- Often (but not always) under active transcription
- Most active portion of the genome
- Approximately 92% of the human genome is euchromatic.
- Remainder is called heterochromatin
heterochromatin
-Heterochromatin is very condensed chromatin:
Stains darkly throughout the cell cycle, even in interphase
-Thought to be late replicating and genetically inactive
- Highly concentrated at centromeres and telomeres
- Contains very few active genes:
Position Effect:
-Activity a gene depends on relative position on
chromosome:
- Actively expressed genes will be silenced if relocated near heterochromatin
how many chromosomes does human genome have
46
2 copies of 23
how much of genome is responsible for coding
1.5 %
what do CGH arrays do?
- detect copy number variations
- used clinically to detect deletion of genes
- variations are basis for differences and disease states
RNAi
-A biological process in which RNA molecules (miRNA)
inhibit gene expression, or translation
- Neutralizes targeted mRNA molecules
Long terminal repeats (LTRs)
-Identical sequences of DNA
- Repeat hundreds or thousands of times
- Found at either end of retrotransposons (proviral DNA)
- Formed by reverse transcription of retroviral RNA
- Used by viruses to insert their genetic material into the
host genomes
what sequence do introns begin and end with
begin with GT and end with AG
what does HDAC do?
represses gene expressions (chromatin is compressed)
what does HAT do?
promotes gene expressions (open)
what enzyme is involved in methylation
methyl transferase
what does dna methylation do?
represses gene transcription when at a gene promoter
-essential for normal development
what does abnormal hypermethylation cause at promoter cPG islands?
- transcriptional silencing
- can be inherited by daughter cells
what does DNA polymerase require?
a primer with a free 3’-OH to begin processing
DNA helicase
-unwinds DNA (using ATP)
single stranded binding proteins
-binds to exposed ssDNA and stabilize and prevent hairpins
topoisomerase (DNA gyrase in bacteria)
relieves overwound supercoils
- breaks phosphodiester bond
- target of anti-cancer agents
UV radiation
causes covalent linkage with two adjacent pyrimidines
-pyrimidine dimers
