1. DNA Replication

2. The Structure of DNA DNA is a nucleic acid that is composed of nucleotides  DNA nucleotide = deoxyribose (a simple sugar), a phosphate group,and a nitrogen base

3. DNA Nucleotides In DNA there are 4 possible nitrogen bases – adenine (A), guanine (G), cytosine (C), and thymine (T)  which means there are also four possible nucleotides AdenineGuanineCytosineThymine Phosphate group Deoxyribose

4. The Double Helix In DNA, nucleotides combine to form two long chains, producing one large molecule These 2 chains form a structure similar to a ladder → the two strands are twisted, so its shape is called a double helix (similar to a spiral staircase)

5. Complementary Base Pairing In DNA, each strand that make up the double helix complement each other  This is shown by base pairing: Adenine (A) pairs with Thymine (T) Cytosine (C) pairs withGuanine (G)

6. The Double Helix Hydrogen bonds Nucleotide Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

7. Significance of DNA Replication Why does DNA have to be able to replicate (make copies of itself)?  Any time a cell divides (through mitosis or meiosis) each daughter cell needs a sufficient amount of genetic material

8. How does DNA Replicate? Brainstorm: Think of a process in which DNA could replicate itself  That is to say, you start with one molecule of DNA and end with two identical molecules of DNA (Hint: Could complementary base pairing be involved?)

9. DNA Replication If you know the order of bases on one strand of DNA, you can predict the order of bases on the other strand Predict the complementary strand: T C C A G T T A G C A A G A G G T C A A T C G T T C  During replication, each strand serves as a template to make a new DNA molecule

10. DNA Replication Four Key Steps to DNA Replication 1) DNA molecule “unzips” and the two strands unwind 2) Unwound strands of DNA serve as templates for new DNA 3) DNA polymerase joins individual nucleotides to produce a new strand 4) DNA polymerase proofreads the new strands

11. Section Quiz 1. DNA is a long molecule made of subunits called a. nucleotides. b. purines. c. pyrimidines. d. sugars.

12. Section Quiz 2. In DNA, the following base pairs occur: a. A with C, and G with T. b. A with T, and C with G. c. A with G, and C with T. d. A with T, and C with T.

13. Section Quiz 3. The first step in DNA replication is a. producing two new strands. b. separating the strands. c. producing DNA polymerase. d. correctly pairing bases.

14. Section Quiz 4. A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? a. GCGAATTCG b. CGCTTAAGC c. TATCCGGAT d. GATGGCCAG