2. Reproduction requires life to replicate its DNA. DNA replication DNA replication is the process in which one DNA strand becomes two.

3. This means that both sides of the DNA ladder and all of the intervening steps must be replicated.

4. one side of the original DNA ladder The two DNA strands that emerge from this process receive one side of the original DNA ladder. synthesised during replication The other side is synthesised during replication.

5. Original strand Newly synthesised stand Semi-conservative model

6. DNA polymerase This process is controlled by a protein called DNA polymerase. This protein untwists the ladder, and then it uses each side as a template.

7. New sides are added to this template. DNA polymerase moves along the entire chromosome until every step has been replicated.

8. proof-reading DNA polymerase has proof-reading mechanisms built into it. If it adds the wrong step by mistake, it can remove it, and replace it with the correct step.

9. DNA polymerase As a result, this process is very accurate. DNA polymerase rarely makes a mistake. Before a cell can divide it must replicate all of its genes.

10. mitosis meiosis Each chromosome must be duplicated. Thus, DNA replication always precedes both mitosis and meiosis.

11. DNA Replication A portion of the double helix is unwound by the enzyme helicase. The Steps:

13. DNA polymerase 3' to 5' direction A molecule of DNA polymerase binds to one strand of the DNA and begins moving along it in the 3' to 5' direction, using it as a template for assembling a leading strand of nucleotides and reforming a double helix.

15. 5' to 3’ direction Because DNA synthesis can not occur in the 5' to 3’ direction, a second DNA polymerase molecule is used to bind to the other template strand as the double helix opens.

16. Okazaki fragments This molecule must synthesise discontinuous segments of polynucleotides (called Okazaki fragments).

18. DNA ligase Another enzyme, DNA ligase then stitches these together into the lagging strand.

19. DNA Replication

20. There are several enzymes that are involved in replication

21. 5' 3' The DNA is always replicated from the 5' end to the 3' end. This is based on the numbering of the carbon atoms in the deoxyribose molecule.

22. The phosphate attaches to the number 1 Carbon atom. The nucleotide base attaches to the number 5 Carbon atom.

24. antiparallel leading strand lagging strand DNA Ligase enzyme Because the two strands are antiparallel, this means there's a "leading strand", which just keeps on going, and a "lagging strand" which consists of small fragments that must later be linked together (by DNA Ligase enzyme).

26. Central Dogma of Molecular Biology