Lecture 3 Flashcards
What is notable about eukaryotic genome size?
Eukaryote genomes are typically larger than prokaryote ones
There is no relationship between genome size and phenotypic complexity
There is relatively small gene density in many eukaryotes
What is notable about the number of genes seen in prokaryotes and eukaryotes?
Both prokaryotes and eukaryotes have highly variable numbers of genes
Eukaryotes typically have larger numbers of genes than prokaryrotes but still not as many as would be expected based on their genome size number of genes seems to be unrelated to phenotypical complexity and this may be due to the ability of organisms such as humans to splice exons in multiple ways
What are the three broad categories for DNA sequences?
Single copy functional genes, repetitive DNA, spacer DNA
What are the different functional repetitive DNA sequences?
Dispersed Gene families (which is when one original gene has become duplicated and the different copies may have diverged to cause the gene to have a slightly different function, or may have undergone an in activating mutation to from a pseudogene)
Tandem Gene families
(The genes have evolved in tandem arrays as the cell is required to produce large amounts of the gene products, these repeats are typically identical sequences and include the histone genes and rRNA genes seen in the nucleolar organizer)
Noncoding functional sequences such as telomeres
What is the function and mechanism of telomeres?
A repetitive tandem array of simple DNA sequences which acts as a cap at the end of a chromosome to stop it from becoming degraded
The G rich strand of the telomere typically protudes beyond the complementary C rich strand this can then be protected by specific proteins or invade an earlier region of the telomere to “tie off” the chromosome
What is the role of telomerase and its role cell degradation and aging?
The single protruding strand of the telomere can be extended by telomerase, however most somatic cells have little telomerase activity, this can result in the telomeres becoming shortened, after this reaches a critical point the chromosome will become unstable
What are centromeric repeats?
short AT rich sequences, flanking the centromeres in heterochromatin state
My use one several basic (under 10bp) repeat units
Originally called satellite DNA
Can potentially be highly abundant
They have no known function
What are variable number tandem repeats?
DNA tandem repeats with a high variability in the number of units between individuals in the population
Can be broken up into microsatellites (2-6bp) and minisatellites (15-100bp)
The most common microsatellite is CA-GT
These sequences are typically used for DNA fingerprinting and paternity tests
What are transposable elements?
Mobile DNA sequences from the genome of all oranisms, which can be highly abundant (45% human DNA)
Can usually insert themselves anywhere in the genome allowing them to cause mutation by disrupting genes or promoting chromosomal rearrangement
What are retrotransposons?
transposable elements which move through the genome by producing an RNA copy of themselves in a copy paste mechanism allowing rapid spread throughout the genome
Many are similar to retroviruses and they contain a wide variety of numbers of genes and tandem repeats
What is the key difference between a retrotransposon and a retrovirus?
The retrovirus has a gene that encodes for an envelope protein unlike a retrotransposon
What are DNA transposable elements?
Transposable elements that move within the genome through a similar mechanism to those used by bacteria, do not require and RNA intermediate and can therefore move by both cut and past and copy and paste mechanisms
Movment does require the transposase enzyme which is typically found in the transposon
What are the transposable elements in the human genome?
Typically two types of retrotransposons,
LINES- Long interrupted elements which have reverse transcriptase but lack LTRs
SINES- short interrupted elements, non autonomous lines
