Molecular Structure of Genes and Chromosomes 1 (L8) Flashcards
simple transcription unit - what can a mutation in an intron region cause?
affects splicing
simple transcription unit - what can a mutation in a regulatory region cause?
gene not expressed when and where it should be
complex transcription unit - what can a mutation cause?
different outcomes in multi-exon genes
what is the origin of exon duplication?
unequal crossing over
what are transposons?
segments of DNA that can move around to different positions in the genome of a single cell
effects of transposons
- can cause mutations
- can increase or decrease amount of DNA in genome of a cell
movement of DNA transposons? what enzyme do they require?
“cut and paste” - require transposase
functional significance of alternative splicing and example
different final product from genes in same DNA segment - rearrange exons to make variety of end products
-example: dscam and down syndrome
example of functional significance of gene duplication
beta-globin gene cluster
homolog
gene related to a 2nd gene by descent from a common ancestral DNA sequence
ortholog
gene in different species that evolved from a common ancestral gene by speciation - have same function
paralog
genes related by duplication within a genome - evolve new functions
tubulin example of gene duplication
2x copies of same gene with some sequence variation -> eventually give rise to multiple species
hox clusters
duplications of same sequences
BLAST
basic local alignment search tool - tells you which bases or sequences are similar or identical; measured in %
example of sequence alignment and clinical problems
NF1
non-coding RNAs
don’t code for protein, but have physiological fxn:
-rRNA, tRNA, snRNA, miRNA, telomerase RNA
microsatellites
short tandem repeats of nts - repeating sequences of 2-5 bp of DNA
mechanism of microsatellite expansion
backward slippage during replication (get n+1)
retrotransposons
“copy and paste” - the copy made is RNA, not DNA - copies then transcribed back into DNA by reverse transcriptase
end result of DNA transposons vs. retrotransposons
same end result but different methods of insertion
origin of DNA transposon duplication
one copy of transposon before S phase -> S phase: DNA replication and DNA transposition -> after S phase, one daughter molecule has two copies of transposon
two types of retrotransposon
with and without LTR - a direct repeat
what is LTR a characteristic of?
integrated retroviruses
what do retrotransposons encode for in retroviruses?
all proteins except envelope proteins
non-LTR retrotransposons
don’t have long terminal repeats like most A/T rich regions
non-LTR retrotransposon steps
- Nicking
- Priming of reverse transcription by chromosomal DNA
- Reverse transcription of LINE RNA by ORF2
- Copying of chromosomal DNA by ORF2
- Insertion completed by cellular enzymes
DNA now contains LINE DNA b/w direct repeats
what are LINE?
long interspersed elements
ORF1
RNA binding protein
ORF2
DNA endonuclease and reverse transcriptase
examples of LINE in humans
L1, L2, L3
SINE
short interspersed elements - bare bone LINE, don’t encode proteins
what do SINE depend on?
LINE protein machinery
examples of SINE in humans
Alu elements
exon and promoter shuffling via..
homologous recombination (double crossover b/w Alu elements)
when can transposase recognize two transposons?
when they are close enough together
origin of mitochondria
endosymbiosis
mitochondrial genome
have own genome that uses atypical codons
mitochondrial inheritance
cytoplasmic
heteroplasmy
presence of a mixture of more than one type of an organellar genome w/i a cell or individual - factor in severity of mitochondrial diseases
maternal inheritance
traits of offspring are maternal in origin due to expression of extranuclear DNA present in ovum during fertilization
one example of a mitochonrial disease
LHON
