dna replication
http://www.2shared.com/complete/orl_79PE/Replication_of_DNA.html
DNA is replicated once per each cell division.
The Template/Parental DNA has to be unpackaged by the “helicase” and then separated into two different strands by a DNA fork. Two strands are then formed which are derived from the DNA. The DNA at the site of replication resembles a fork, where the two strands of the DNA are split apart to be copied.
The new strand of DNA is made by placing the complementary nucleotides opposite each nucleotide in the parental strand. If the parental strand reads ‘CTA’ for example, then a ‘GAT’ will be bonded next to it.
Sometimes there are mistakes, such as T may be paired with C rather than A. Or G may be paired with A rather than C. These mistakes are detected by enzymes referred to as “proof reading enzymes”, in biological terms referred to as Polymerase III Holoenzyme.
The two strands of DNA are mirror images of each other, this makes the replication a complicated process. This is due to the structure of the Deoxyribose in the DNA backbone. Deoxyribose contains five carbon atoms, which are usually numbered 1 to 5.
The phosphate upstream is attached to carbon atom number 3, the phosphate downstream to carbon atom number 5. The 3’ bond in one strand of the double helix is opposite the 5’ bond in the other strand.
DNA polymerase (enzyme which brings about the formation of a particular polymer) creates new strands only in the 5 à 3 directions. Basically it is function to copy from left to right and is unable to copy from right to left. The second strand (the lagging strand) must be done is small sections as the direction of replication must still be 5' to 3'. Thus, you get these fragments of DNA called Okazaki fragments. These are then later joined together using the enzyme DNA ligase (facilitates the joining of DNA strands together by catalysing the formation of a phosphodiester bond forming a complete new strand of DNA.
DNA is replicated once per each cell division.
The Template/Parental DNA has to be unpackaged by the “helicase” and then separated into two different strands by a DNA fork. Two strands are then formed which are derived from the DNA. The DNA at the site of replication resembles a fork, where the two strands of the DNA are split apart to be copied.
The new strand of DNA is made by placing the complementary nucleotides opposite each nucleotide in the parental strand. If the parental strand reads ‘CTA’ for example, then a ‘GAT’ will be bonded next to it.
Sometimes there are mistakes, such as T may be paired with C rather than A. Or G may be paired with A rather than C. These mistakes are detected by enzymes referred to as “proof reading enzymes”, in biological terms referred to as Polymerase III Holoenzyme.
The two strands of DNA are mirror images of each other, this makes the replication a complicated process. This is due to the structure of the Deoxyribose in the DNA backbone. Deoxyribose contains five carbon atoms, which are usually numbered 1 to 5.
The phosphate upstream is attached to carbon atom number 3, the phosphate downstream to carbon atom number 5. The 3’ bond in one strand of the double helix is opposite the 5’ bond in the other strand.
DNA polymerase (enzyme which brings about the formation of a particular polymer) creates new strands only in the 5 à 3 directions. Basically it is function to copy from left to right and is unable to copy from right to left. The second strand (the lagging strand) must be done is small sections as the direction of replication must still be 5' to 3'. Thus, you get these fragments of DNA called Okazaki fragments. These are then later joined together using the enzyme DNA ligase (facilitates the joining of DNA strands together by catalysing the formation of a phosphodiester bond forming a complete new strand of DNA.