1. DNA

2. DNA (Deoxyribonucleic acid) is a long polymer of repeating units. The monomers are called nucleotides. Each nucleotide has three components: A phosphate group A ring-shaped sugar, known as deoxyribose. A nitrogen-containing base

3. One molecule of DNA contains billions of nucleotides. However, there are only four nucleotides that make up DNA. The four nucleotides are: Cytosine Guanine Thymine Adenine

5. Thymine & Cytosine Single-ring structures Cytosine pairs with guanine Adenine & Guanine Double-ring structures Adenine pairs with thymine PYRMIDINESPURINES

6. In a single strand of DNA, nucleotides join together through covalent bonds. The sugar base of one nucleotide bonds to the phosphate group of another nucleotide.

7. D OUBLE H ELIX DNA forms a twisted staircase when the covalent bonds form. The structure of DNA is a double helix; meaning that the DNA is double stranded, with the two strands wrapping around each other.

8. The bases of each strand pair together through hydrogen bonds. A and T form two hydrogen bonds, while G and C form three hydrogen bonds.

10. DNA R EPLICATION Replication ensures that every cell has a complete set of identical genetic information. A single strand of DNA serves as a template to make another identical copy.

11. Proteins and enzymes do all the actual work of replication. Enzymes begin the process by unwinding the double strands of DNA. Specific proteins hold the DNA strands apart while each strand serves as a template. Free floating nucleotides in the nucleus can pair up with the existing strands. DNA polymerases bond the new nucleotides with the old strands.

12. The result is two new strands of genetically identical DNA

16. F AST & A CCURATE DNA replication occurs very quickly and accurately. In humans, about 50 nucleotides are added every second. Replication proceeds from hundreds of origins of replications along a chromosome. DNA polymerases are also able to detect errors, take out the incorrect nucleotide and replace it with the proper one.