1. A Closer Look at DNA

2. Review Questions (Discuss the answers)
What are the 3 parts of a DNA nucleotide?
What is the technical term for the “twisted ladder” shape of the DNA molecule?
What makes up the “legs” of the DNA ladder?
What makes up the “rungs” of the DNA ladder?

3. Answers What are the 3 parts of a DNA nucleotide? 1. phosphate group
2. deoxyribose sugar
3. nitrogen base

4. Answers
What is the technical term for the “twisted ladder” shape of the DNA molecule?
double helix

5. Answers What makes up the “legs” of the DNA ladder?
The deoxyribose sugars and phosphate groups of the nucleotides bond together to form the “backbone” of the DNA molecule.

6. Answers What makes up the “rungs” of the DNA ladder? (AT & GC)
Pairs of nitrogen bases form the “rungs” of the DNA molecule.
(AT & GC)

7. Review: Patterns of Base Pairing
Base pairs are formed by the hydrogen bonding of A with T and G with C.
This pattern is constant for all organisms.
The sequence of bases in a nucleotide strand is different from one species to the next.

8. A Closer Look at DNA: Two Questions
How is DNA copied?
If a mistake occurs in the copy, how is it repaired?

9. DNA Replication…
…is the process by which DNA is duplicated prior to cell division.
2 Steps of DNA Replication
The two strands of DNA unwind and expose their bases.
Unattached nucleotides are paired with exposed bases.

11. Replication Enzymes DNA helicase: unwinds the double helix
DNA polymerase: assembles the nucleotides into chains
DNA ligase: seals sections of new DNA into continuous strands

12. “Semiconservative Replication”
DNA replication results in DNA molecules that consist of one “old” strand and one “new” strand.

13. “Semiconservative Replication”

14. DNA Repair…
…is the process by which enzymes remove and replace altered parts of the base sequence in one strand of DNA.
DNA polymerases, DNA ligases, and other enzymes are also involved in DNA repair.

15. Genes
Genes are portions of the DNA strand that tell the body what proteins to make. 
These proteins help carry out the functions of the cell.