Nucleic acids and chromosomes Flashcards
explain the packaging of DNA into nucleosomes and relate this to chromosome structure
DNA (150 bp per histone - core DNA) is coiled histone octamer - called nucleosome - lowest level of packaging - bead on chain
many nucleosomes mean the chromosome is condense - 7 fold condensation
Histone + charge so associate with - charged phosphate
one additional histone attached
nucleosomes condense further - 6 nucleosomes coil and stack - 40 fold condensation
chromatin fibre folded into loops
entire mitotic chromosome - 10 000 fold condensation
Tightly packaged - chromatin
summarise the human karyotype
organised profile of chromosomes 46 22 pairs 2 sex chromosomes. see abnormalities
Describe the difference between DNA in interphase and the mitotic phase
less compact in interphase
chromatin more extended in interphase
Explain the structure of DNA
RH Double helix - secondary structure sequence of deoxynucleotides - primary structure antiparallel complementary nucleosides A--T, C---G Phosphodiester backbone - nucleosides linked by 3' OH to phosphate group phosphate outside - negative base inside - perp to chain deoxyribose - oxygen missing from Carbon-2 major and minor groove associated with histones - major groove linear polymer
explain the structure of RNA
similar to DNA
ribose instead of deoxyribose
U instead of T
doesn’t have to be double helix
Which bases are purines
A G
Which bases are pyrimidines
C T
Explain Watson Crick base pairing
complementary nucleotides are held together with H bonds chains same distance apart A and T C and G always pair AT 2 H bond CG 3 H bond Purine always with pyrimidine
Explain the melting and reannealing of complementary strands
melting - break the hydrogen bonds, high temperatures (near boiling) and low salt
reannealing/hybridisation - cool or low salt
