dna Flashcards
semi- conservative replication
-two parental DNA strands separate due to the breaking of hydrogen bonds between complementary bases
-both strands act as templates for the synthesis of new complementary DNA strands
-each new DNA molecule consists of one original DNA strand and one newly synthesised DNA strand
why replication only occurs in the 5’ to 3’ direction
- the shape of the active site of DNA polymerase, and its enzyme specificity allows DNA polymerase to work only one direction from 5’ to 3’
- DNA polymerase can only add DNA nucleotide to the free 3’ -OH end of an existing strand
leading strand
leading strand is synthesised continuously because the DNA polymerase is moving in the same direction as the unwinding and unzipping of DNA
how replication of the lagging strand template occurs
lagging strand synthesised discontinuously resulting in okazaki fragments as the two parental DNA strands are anti-parallel
– shape of the active site of DNA polymerase and its enzyme specificity allows DNA polymerase to work in only one direction from 5’ to 3’
-DNA polymerase can only add DNA nucleotides to the free 3’ –OH end of an existing strand
- each fragment is initiated by an RNA primer before the addition of DNA nucleotide
why 1 leading + 1 lagging strand
-the shape of active site of DNA polymerase and its enzyme specificity only allows DNA polymerase to work only in one direction from 5’ to 3’
- DNA strands are antiparallel. one runs in the 5’ to 3’ direction while the complementary strand runs in the 3’ to 5’ direction
DNA and RNA differences
- DNA is double stranded while RNA is single- stranded
- pentose sugar in DNA nucleotide is deoxyribose pentose sugar while pentose sugar in RNA nucleotide is a ribose
- nitrogenous bases in DNA can only be adenine, thymine, cytosine, guanine while nitrogenous bases in RNA can only be adenine, uracil, cytosine, guanine
formation of phosphodiester bond
-forms between the -OH group on C3 of the pentose sugar of one nucleotide and the phosphate group on C5 of the pentose sugar of the adjacent nucleotide
- condensation with the removal of the water molecule
- catalysed by DNA polymerase
explain the reason for production of okazaki fragments
- shape of the active site of DNA polymerase and its enzyme specificity allows DNA polymerase to work in only one direction from 5’ to 3’
DNA polymerase can only add DNA nucleotide to the free 3’ OH end of an existing strand - two parental DNA strands are anti-parallel