DNA replication-Medicine, Study notes of Medicine

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3/8/25, 9:05 PM about:blank DNA replication DNA and replication Semi-conservative replication — one original strand is maintained in the new replicated double helix. Two strands in DNA replication — leading and lagging. DNA polymerase only works in 5 prime to 3 prime direction Leading ~ 5 to 3 prime directions Lagging — 3 to 5 prime direction (wrong way for DNA polymerase) Lagging strand the DNA is copied in chunks as so: DNA is unwound making it available for an RNA primer is synthesised via DNA alpha which then in. Turn initiates DNA replication via DNA polymerase. This produces a series of DNA fragments (called Okazaki fragments)which are joined together via DNA ligase. DNA takes a few different types of helixes Normally DNA is found as B-DNA (canonical) it has 10.5 bases per turn and is right handed. Very neat and orderly. A-DNA is believed to be when DNA is bound in a protein complex. It is also right handed but has 11 bases per tum with a slightly irregular double helix. Perhaps to protect the DNA more. Z-DNA is left handed not right. Tend to be found when gene regulation is occurring, the bases are not as easily paired with lots of DNA instability. DNA is wound round histones which then form chromatic fibre of packed nucleosides Mitotic cell cycle — G0 — most cells sit in this stage until they need to divide. G1 — cell growth where preparation for DNA synthesis occurs G1 check point - RB and p53 proteins regulate this check point. S—DNA replication Intra-S checkpoint — validates replication has occurred with high fidelity (no errors). 12