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ORGANISATION OF EUK. GENOME (NON-CODING DNA (PROMOTER (RNA polymerase and…
ORGANISATION OF EUK. GENOME
NON-CODING DNA
Regulatory sequences: regions of DNA sequence where gene regulatory proteins bind to control the rate of assembly of protein complexes required for gene expression
PROMOTER
contains TATA box
located upstream from transcriptional start site
RNA polymerase and GTFs bind to promoter
forming a transcription initiation complex
CONTROL ELEMENTS
DISTAL
enhancers
bind to activators
silencers
bind to repressors
PROXIMAL
bind to GTFs
part of TIC
UNTRANSLATED REGIONS
5' UTR IN MRNA
regulate mRNA's stability for translation
starts at the 1+ position of DNA
ends one nucleotide before the start codon
3' UTR IN MRNA
regulate mRNA's stability for translation
found after the polyadenylation signal sequence
REPETITIVE DNA
CENTROMERES
region where two sister chromatids are joined in a replicated chromosome during cell division
STRUCTURE
made up of repetitive AT-rich sequences
FUNCTIONS
sister chromatid adhesion
site of assembly of kinetochore
ensures proper segregation
TELOMERES
STRUCTURE
single-stranded 3' overhang invades upstream telomeric repeat
displaces the same sequences
C' base pairs to complementary strand
forms a t-loop
located at the two physical ends of a linear euk. chromosome
FUNCTION
protect the 3' single-stranded overhangs and 5' ends from degradation by exonucleases
confers stability by preventing the chromosome tips from fusing to other chromosomes
protects the organism's genes from the END REPLICATION PROBLEM after each replication
regulating replicative cell senescence
STRUCTURE
FIRST LEVEL OF CONDENSATION
DNA molecule coils around an octamer of histone proteins
forming a
nucleosome
multiple nucleosomes are packed together to produce the 10-nm chomatin fibre, aka
nucleosome fibre
interaction between neg.-charged DNA sugar phosphate backbone and pos.-charged lysine residues on histone tails
'beads-on-a-string' look
SECOND LEVEL OF CONDENSATION
DNA is further colied
30-nm chromatin fibre, aka
solenoid
involves Histone H1 and linker DNA in coiling
THIRD LEVEL OF CONDENSATION
solenoid fibres are condensed into
looped domanins
by scaffold proteins
in mitotic and meiotic chromosomes, the looped domains coil further, making
chromatids
visible
700-nm in width
ROLE OF CONDENSATION
organise
pack
facilitates segregation