Lecture 7 Flashcards
(18 cards)
What is repetitive DNA?
DNA that occurs in many copies in the genome
What are the 2 types of repeat?
Simple sequence repeats and transposons
What are simple sequence repeats?
Simple repeats -tandem arrays of short sequences
5% of human genome
What are transposons?
Mobile DNA elements -sequecnes can move from place to place in the genome.
Duplicate themselves and transpose into new sites in the genome
40% of human genome
What are the 2 major classes of transposons?
LINEs and SINEs
long interspersed elements and short
What is the difference between SINEs and LINEs?
LINEs: 6kbp. Some are transcribed and translated into proteins.
SINEs: 100-400bp transcribed but not translated
Which transposons transpose via an RNA intermediate?
LINEs, SINEs and retroviral-like elements.
DNA of the transposed element gets copied to RNA by RNA polymerase.
RNA is then copied to DNA by reverse transcription.
What do LINEs code for?
enzymes required for transposition.
RNA binding proteins and reverse transcriptase.
They have the genes for their own reverse transcriptase.
How many LINEs are active?
Only <100 out of >500,000
What class do Alu members belong to?
Part of the SINE class.
Make about 10% of human DNA
They are non-autonomous, transposition depends on LINE elements
In what way is the yeast genome very compact compared to human genome?
4% repetitive DNA -much less than humans
70% of genome consists of open reading frames -codes for proteins
Little space between genes
96% of genes have no introns
In what way is the human genome not as compact?
Less than 2% of the human genome codes for proteins
More than 50% is repetitive DNA
Genes commonly have multiple introns
What does synteny mean?
preservation of the order of genes in different organisms
-comparison -shows the order of genes in chromosomes is partly conserved through evolution
What are the essential sequences in chromosomes?
Multiple replication origins, 30,000 to 250,000 bases apart
Ends are called telomeres -defined by specific repetitive DNA sequences to which specific proteins attach
Specific repetitive DNA sequences with specific proteins attached define the centromeres
What is the basic building block of chromatin?
The nucleosome.
8 polypeptides: 2 copies each of histones H2A, H2B, H3 and H4
Structure of chromatin:
DNA forms 2 loops around the histones. Histones have a positive charge and DNA has a negative charge
What are histones?
There are 5 classes, and they are proteins that package and order the DNA into structural units called nucleosomes.
What are the further levels of packaging of DNA?
Chromosome is folded up not loops attached to a central scaffold.
