DNA REPLICATION Chapter 11, Section 1

DNA Review What is the building block of DNA? Nucleotides What is the shape of DNA? Double Helix What holds together the two strands of DNA? Hydrogen bonds between complimentary nitrogen base pairs During what part of the Cell Cycle does DNA replicate (copy itself)? Interphase (S phase) What pairs with Guanine? Adenine? Guanine & Cytosine, Adenine & Thymine What are the complimentary bases for the following sequence? AATCCGC TTAGGCG

How DNA Replicates DNA has to be replicated before a cell divides (during S phase of interphase). New cells at the end of Mitosis need identical strands of DNA

One strand of DNA gets used as a template (pattern) to make a new strand that matches up with it. This is called semi-conservative replication, one strand is new and the other is old. Special enzymes are required for DNA replication

Steps of DNA Replication 1. Replication begins with the unwinding & separation of the DNA double helix by enzymes called helicases –The process is like unzipping a zipper

2. New strands are formed by enzymes called DNA polymerase which adds complimentary nucleotides to the original strands

Each new strand compliments one of the original strands (one new strand and one old strand; semi- conservative replication) 2 identical DNA double helix strands are the result of DNA replication

Uneven formation of DNA When DNA is replicating one strand forms continuously and the other strand forms in chunks (Okazaki fragments) with spaces that need to be filled in. This is because they form in opposite directions Continuously = leading strand Chunks= lagging strand

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