2.3.2 how DNA replicates Flashcards
DNA polymerase
enzyme that catalyses formation of DNA from activated deoxyribose nucleotides
–> using single-stranded DNA as template
helicase
enzyme that catalyses breaking of hydrogen bonds between nitrogenous pairs of bases in DNA molecule
semi-conservative replication
how DNA replicates
- results in 2 new molecules –> each contains 1 old strand & 1 new
- old strand is conserved in each new molecule
when does DNA replication occur
during interphase
(before the cell division)
to produce a new copy, the DNA molecule must:
- unwind = double helix is untwisted & catalysed by gyrase enzyme
- unzip = h bonds between nucleotide bases are broken - catalysed by helicase
^^ unzipping results in 2 single strands of DNA with exposed nucleotide bases
after unzipping/unwinding, what are the next steps in semi conservative replication
- free phosphorylated nucleotides (in nucleoplasm) bond to exposed bases
- DNA polymerase catalyses addition of new nucleotide bases to the single DNA strands –> uses each single strand of unzipped DNA as template
- leading strand synthesised continuously & lagging strand is in fragments that are later joined (catalysed by ligase enzymes)
- hydrolysis of activated nucleotides (release extra phosphate groups) = supplies energy to make phosphodiester bonds
which direction does DNA polymerase catalyse the addition of new nucleotide bases
5’ to 3’ direction
product of semi-conservative replication
2 DNA molecules identical to each other/parent molecule
^^each contain 1 old strand & 1 new strand
what other DNA replicates semi-conservatively
- loops of DNA in prokaryotes
- inside mitochondria/chloroplasts
how is the chance for mutation significantly reduced during replication
there are enzymes which proofread & edit out potential incorrect nucleotides
what are alleles/gene variants
different versions of particular gene
