L7 - Repetitive DNA Flashcards
What is Repetitive DNA?
DNA that occurs in many copies (generally similar, not identical, to one another) in the genome
Do smaller genomes have more or less repetitive DNA?
Amount of repetitive DNA varies among organisms; smaller genomes contain less than larger genomes
How much of the human genome does repetitive DNA make up?
> 50%
What are Transposons?
Much of repetitive DNA (about 40% in humans) consists these:
Transposons: mobile DNA elements
Essentially molecular parasites, that duplicate themselves and transpose into new site in the genome
Describe the 2 main classes of transposons in humans
LINEs: long interspersed elements (around 6000bp)
SINEs: short interspersed elements (about 100-400bp)
What is the mechanism of transposition?
1) LINEs, SINEs, and retroviral-like elements all transpose via an RNA intermediate
(DNA –> RNA –> DNA).
2) RNAP copies DNA to RNA.
3) The RNA is copied to DNA by reverse transcription catalysed by reverse transcriptase.
What do LINEs code for?
LINEs code for enzymes required for transposition (RNA bonding protein, reverse transcriptase)
How many out of all LINEs are active?
<100 out of >500,000 in the genome are active
Estimated current transposition rate in humans: 1 insertion for ever 20-200 births
WHat are Alu elements?
An Alu element is a short stretch of DNA originally characterized by the action of the Arthrobacter luteus restriction endonuclease.
Alu elements are the most abundant transposable elements, containing over 1,000,000 copies dispersed throughout the human genome.
Where did Alu elements come from?
They are derived from the small cytoplasmic 7SL RNA, a component of the signal recognition particle.
Alu elements are highly conserved within primate genomes and originated in the genome of an ancestor of Supraprimates.
Alu elements apparently evolved about 80 million years ago. Transposition activity peaked about 40 million years ago
How can Alu elements cause disease in humans?
Alu elements are a common source of mutation in humans, but they are often confined to non-coding regions where they wont cause an effect.
Alu insertions are sometimes disruptive and can result in inherited disorders. However, most Alu variation act as markers for disease so the presence of a particular Alu allele does not mean that the carrier will definitely get the disease.
The following human diseases have been linked with Alu insertions:
Breast cancer Ewing's sarcoma Familial hypercholesterolemia Hemophilia Neurofibromatosis Diabetes mellitus type II
What is the genome of yeast like?
Very compact:
- approximately 4% repetitive DNA
- little space between genes
- 96% of genes have no introns
- genes that do have introns usually only have 1
WHat percentage of the human genome codes for proteins?
less than 2%
averagely 1 gene per around 90kbp
How long in humans is the average:
a) primary transcript
b) coding sequence
a) 30kbp
b) 1.4kbp
Define Synteny
Comparison of genomes of different organisms shows that the order of genes in chromosomes is partly conserved through evolution
