1. DNA – The building blocks of life

2. DNA stands for Deoxyribonucleic Acid and is responsible for: a) storing and passing on genetic information from one generation to another. b) Provides the instructions for creating proteins.

3. The DNA structure is shaped like a spiral staircase, or twisted ladder. The outer parts of the ladder are made of sugars called deoxyribose which are connected by phosphate groups. The rungs of the ladder are made of pairs of nitrogen bases held together by hydrogen bonds.

4. There are four possible DNA bases 1. Adenine – A 2. Guanine – G 3. Thymine – T 4. Cytosine - C There is only one way these bases can bond together. A C C G T T T T G A C A C A T G G C A A A A C T G T G T Purines -have a double ring base Pyrimidines - have a singe ring base Adenine pairs with Thymine Guanine pairs with Cytosine.

5. It is the order of these nitrogen bases that produces the genes for a trait. The specific sequence of the nitrogen bases are instructions (or a code) for making proteins which in turn present as a particular trait. Because there can be so many different combinations of the bases, the code can be limitless.

6. DNA Replication Replication is the process where DNA molecules form exact duplicates. Replication is essential for cellular division so that new daughter cells will have a complete copy of the genetic information.

7. DNA Replication Simply stated: 1. The ladder splits 2. Free floating nitrogen bases pair with the opened strand 3. Two new DNA strands are formed.

8. Now more details With the help of the helicase enzyme, the double helix is rotated and uncoiled. The bonds between the complementary bases are then broken, splitting the double helix up the middle – like a zipper unzipping starting at one end and moving towards the other producing a Replication Fork

9. This exposes the two stands as single bases needing complements. These 2 single strands act as a template for constructing a new double helix and are held apart by single strand binding proteins.

10. Replication can not begin with out an identified starting point. An enzyme called Primase is “tags” the DNA template to initiate the synthesis of the new DNA segment.

11. New nucleotides are brought from a pool of free nucleotides present in the cytoplasm to bind with the complimentary bases. The new strand is assembed by the enzyme DNA polymerase which is guided along the chain by a sliding clamp. DNA polymerase proof-reads the new strand – 1 error in about 10 billion.

12. The RNA primers created to initiate replication are eventually removed by the enzyme RNase H leaving gaps between segments on the lagging strand. These segments are known as Okazaki fragments Once replication is complete, DNA ligase join the segments together, sealing the double chain and reforming the helix.

13. DNA Replication Animation Tutorial http://www.wiley.com/college/pratt/047139 3878/student/animations/dna_replication/ http://www.wiley.com/college/pratt/047139 3878/student/animations/dna_replication/