genetics 6 Flashcards
where does mRNA transcription start
transcription start site
what is the pribnow box essential for
transcription initiation
what is the 35 region used for
high transcription rate
what is prokaryotic genes regulated by
- promotor
- operator
- enhancers
- silencers
what can related genes be arranged by
operons
what does polycistronic mean
multiple protein encoding regions in a single mRNA
what does the TATA box do
- in many eukaryotic promotors
- TATA binding proteins
what does the CAAT box do
- site for CAAT-enhanced binding proteins
what do introns almost always have
- begin with GU
- end with AG
what is the characteristics of bacterial chromosomes
- large - 3.6-3.9 million
- circular DNA molecules
- nucleoid - where most DNA resides, has nucleoid associated proteins and domains (supercoiled loops)
what are the characteristics of bacterial plasmids
- small (160,000- 1.8 million base pairs)
- circular DNA molecules
- separated from chromosomal DNA
- replicate independently
- supercoiled
what are bacterial plasmids genes for
- antibiotic resistance
- horizontal transfer
what % of components make up DNA
- 75% genome
- 1-2% encodes proteins - exons
- rest is introns and intergenic
what are the types of DNA repeats
- dispersed repetitive DNA
- satelite DNA - repeats cluster together
- tandem repeats
what are transposable elements and what are the forms
- type of dispersed repeat
- short interspersed elements (SINE’s) - 90-500 bp
- long interspersed elements (LINE’S) - up to 7000bp
what are alpha satellite DNA repeats
- 171bp repeats
- 10% of the genome
- all centromeres
- high order repeat units (HORs)
what do high order repeats do in satellite DNA repeats
HOR arrangement —-> chromosome specificty
- transcribed and large protein transcriptome
what does VNTRs stand for
variable number of tandem repeats
what are minisatellite repeats
- 10-60bp
- repeated 5-50 times
- GC rich - 3hb so much stronger
- many parts of genome
- centromeres and sub telomeric regions
- genetic fingerprinting
what are microsatellite repeats
- short tandem repeats or simple sequence repeats
- <10bp repeats
- repeated 5-50 times
- telomeres - humans
what are transposable elements
- DNA sequences that can change its position within a genome
what do short interspersed elements do - SINE’s
- 90 to 500bp
- Alu repeats - contains Alu restriction sites
- adenine rich tail
- insertions —-> many diseases
what do long interspersed elements do - LINE’s
- up to 7000bp
- adenine rich 3’ tail
what do LTR- retrotransposons do
- gag gene expression —> virus like particles
- reverse transcriptase of RNA to cDNA
- integration into genome
- requires intergrase
what do transposons do
- variable in size
- contain transposae gene
- tandem inverted repeats
- short tandem site duplication
what is the structure of nucleosomes
- 146 bp around histone
- 8 histone protein
- 2 x H2A, H2B, H3, H4
- 20-60 bp spacer
what is the structure of chromatosomes
- histone 1 protein links nucleosomes to form a string of chromatosmes - 166bp
what is the core histones functions
- H2A,H2B,H3 and H4
- wrap DNA
- form nucleosomes
- left handed superhelical ramp
- amino-terminal tail extension
what are linker histones and what is their function
- H1 and H5
- higher order DNA structures
- bind nucleosomes at DNA entry and exit sites
why to histones have variations
- specific functions
- insertion into nucleosomes at specific sites
- require ATP-dependent chromatin remodelling enzymes
how are histones modified
- often N-terminal histone tails modified
- acetylation of lysines
- mono, di or tri methylation of lys/arg
- phosphorylation of serines
- lysine ubiquitylation
- mutually exclusive modifications
what is ubiquitylation
- adds ubiquitin - 76 amino acid protein
what are the reasons for histone modification
- recruit other structural proteins
- regulation of expression - loose/ tight structure
- cell memory - some modification kept
where does topoisomerase 1 act
- tyrosine active site
- DNA nicked to allow rotation
what does DNA topoisomerase do
- prevents DNA tangles
what doe topoisomerase 2 do
- two circular DNA double helices that are interlocked
- cut to allow seperation
- allows strands to move over eachother
what does topoisomerase 1 inhibitors do and what is the limitations
- mainly prevent colorectal and ovarian cancers
- examples - lamellarin D, irinotecan (CPT11), topotecan, and camptothecin
limitations - inactivation in the blood, internal target - transporter expression required
what are examples of topoisomerase 2 inhibitors
- etoposide and teniposide
what do antibiotics do to topoisomerase inhibitors
- target topoisomerase 2 in bacteria
- examples - quinolones - milidixic acid and ciproflaxacin
- binds to cleavage-ligation active site leading to chromosomal breakages and excess DNA repair leading to cell death
