Eukaryotic Genome Organisation Flashcards
how do cells have diff functions?
they have the same genome but different gene expression
chromatin (definition, diff forms)
equal amount of DNA and protein
histone protein packages DNA and regulates expression
euchromatin during interphase when not dividing, 10% active euchromatin transcribed and 80% inactive, and 10% heterochromatin which is condensed and not transcribed
euchromatin decondenses during interphase
heterochromatin condensed so few expressed sequences and stabilises nucleus
histones
small, highly conserved
solenoid structure with DNA wound round core and linker DNA between 2 histones
very +ve because DNA -ve so stick together
nucleosome - 2 molecules of H2A, H2B, H3, H4 and 1 molecule of H1
H4 and H3 make H3-H4 tetramer
H2A and H2B make dimer
protrusions of N-terminal is important to function
2 dimers and 1 tetramer forms histone octamer
packaging
nucleosomes condense and histones bunched in interphase
are chromosomes when about to divide and unwound when not dividing
nucleosome
consisting of a length of DNA coiled around a core of histones
modifications to genome organisation (what’s modified, how, what’s the effect, hypoacetylation)
histones modified at N-terminal tails, mod depends on AAs in the tail and can be acetylated, methylated, phosphorylated, ubiquitylated
makes it more packaged or less
if it is open then can be transcribed
hypoacetylation - sir proteins bind histones and interact with each other and package DNA tight
chromosome structure
lecture 11
origin of replication in middle between telomere and centromere: essential for cell cycle
kinetochore associated with centromere
origin of replication
recognised by ORC (origin recognition complex)
cofactors and helper proteins bind to complex so helicase can bind and open DNA and replication starts
kinetochore
in centromere
microtubules of spindle bind to it during cell division
human centromere
variant of histone 3 arranged differently
kinetochore bind to H3 variant and separate chromosomes
telomeres
non-coding repetitive sequences that vary in size but usually long
TTAGGG repeated in vertebrates
ends shrink with each replication because pol doesn’t have space to fill the end gap because no space for primer before it
telomerase
overhang to generate additional DNA so enough space for pol to bind and fill gap but doesn’t work fully
telomere rejuventation
convert back to stem cells by adding telomeres so young again
bigger genomes have more….
non-coding/repetitive DNA
gene dense regions
gene poor regions
1 gene per 20kb
1 gene per 200kb
