1.1 - Organisation of Genetic Information Flashcards
How is DNA packaged in eukaryotes?
- nucleosomes - DNA wrapped around a histone protein - basic unit of chromatin
histones are brought together in a spiral by histone 1 forming chromatin
there are different levels of condensation:
- euchromatin - least condensed, contains many genes
- heterochromatin - most condensed, mainly non-coding DNA
Different histone proteins are:
- H2A
- H2B
- H3
- H4
- H1
How is DNA packaged in prokaryotes?
DNA undergoes supercoiling.
supercoiling - coiling of a coil
supercoils can be positive (in the direction of the helix) or negative (the opposite direction from the helix)
Negative winding favours unwinding for transcription and replication
How are genes organised in prokaryotes?
- no introns as transcription and translation are coupled
- one copy of each gene
- operons - lots of genes are organised in the same cluster controlled by one promoter (lac operon)
plasmids - extrachromosomal DNA, include additional non-essential genes
How are genes organised in eukaryotes?
- genes have their own promoter
- introns and exons in each gene - alternative mRNA splicing - skipping
- introns can have transcription enhancers or repressors
How are Chromosomes organised in prokaryotes?
- circular
- no nucleus
- DNA is called the nucleoid
How are chromosomes organised in eukaryotes?
- linear and are in pairs (homologues)
pair of homologues - 2 sister chromatids joined by a centromere
2 copies of each gene found at the same locus
It was thought that chromosomes were arranged randomly in the nucleus, now looks like they have a chromosome territory.
What is a karyotype?
A lab made image of a complete set of chromosomes
chromosomes can be seen in prophase due to condensation of chromatin
Compare prokaryote and eukaryote genomes
prokaryotes - small, mainly protein coding genes, more gene dense
eukaryotes - large, lots of non-coding genes, less gene dense
Explain organisation of the human genome
- 21,000 functional genes
- > 98% is non coding genes
What is comparative genomics?
The comparison of the human genome to other species can hint at how species evolutionary diverged
How is comparative genomics carried out?
Genomes of two species arranged into blocks where the order of the genes is the same as their most recent ancestor - synteny
Light purple - direct block of synteny
Green - inverted block of synteny
