Micro Biology > EXAMs > Chromosome Structure and Organelle DNA (All)
Chromosome Structure and Organelle DNA
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Chromosomes are structures that look like thread, which live in the nucleus (center) of cells. One molecule of DNA and one protein make up one chromosome. Chromosomes are different sizes, and proteins ... called histones allow them to pack up small enough to fit in a nucleus. Supercoiling- supercoiling: tertiary structure where DNA Helix is subjected to strain due to underwound or overwound- relaxed state: B-DNA (10bp per 360 rotation) - if energy is used to add or remove turns, strain is placed on molecule -> supercoil (twist on itself)- positive supercoiling: over-rotated (adding one bp per 360 rotation)- negative supercoiling: under-rotated (think of removing one bp per 360 rotation)- partial solution to packing problem since it occupies less space than relaxed DNA- takes place when strain cannot be compensated by turning the ends of double helix (as the case in circular DNA)- topoisomerases: enzyme that add or remove rotations by temporarily splitting nucleotide strands then rotates them -> rejoins them -> breaks tension)(watch bookmarked youtube video lol)- Most DNA is negatively supercoiled- two advantages: Makes separation of two strands of DNA easier during replication and transcription- under-rotated -> separation of strand uses less energy- can be packed into a smaller space [Show More]
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