1. Chapter 11 DNA and Genes Section 1 DNA: The Molecule of Heredity

2. What does DNA do? Determine an organism’s traits. Determines the structure of proteins. –Enzymes, a special type of protein, control the chemical reactions needed for life.

3. What is DNA, again? Polymer composed of repeating subunits called nucleotides. –Every nucleotide has three parts: A simple sugar. A phosphate group. A nitrogenous base.

4. Nucleotide Parts Simple Sugar Deoxyribose Phosphate Group One atom of phosphorous surrounded by four oxygen atoms. Nitrogenous Base A carbon ring structure that contains one or more atoms of nitrogen. In DNA, there are four possible nitrogenous bases.

5. Four Possible Nitrogenous Bases Adenine (A) Guanine (G) Cytosine (C) Thymine (T)

6. Four Possible Nitrogenous Bases –Because there are four possible bases, there are four different nucleotides which make up DNA.

7. Structure of DNA The phosphate group of one nucleotide bonds to the deoxyribose sugar of an adjacent nucleotide to form the backbone of a long chain.

8. Structure of DNA The nitrogenous bases stick out of the long chain like the teeth of a zipper. –The amount of adenine in DNA is always equal to the amount of thymine. –The amount of guanine in DNA is always equal to the amount of cytosine. (Complementary Base Pairs)

9. Structure of DNA Two of these long chains of nucleotides “zip” together to form DNA. –The nitrogenous bases on each nucleotide chain bond with each through weak hydrogen bonding to hold the two chains together. –However, adenine can only bond to thymine, and cytosine can only bond to guanine, so the two nucleotide chains must complement (run opposite of) each other.

10. Structure of DNA

11. The two chains of nucleotides coil around each other to form a “double helix”.

12. Structure of DNA The order of nucleotides on the chains determine the genetic make-up of the organism. –The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

13. Replication of DNA Before a cell can divide by either meiosis or mitosis, it must first make a copy of its chromosomes. The DNA in the chromosomes is copied in a process called DNA replication. –Without DNA replication, new cells would only have half the DNA their parents had.

14. DNA Replication During replication, each strand of the DNA serves as a template to make a new DNA molecule.

15. DNA Replication Step 1: –An enzyme breaks the hydrogen bonds between the bases that hold the two strands together. Step 2: –As the DNA unzips, nucleotides that are floating free in the surrounding medium are attached to their base pair by hydrogen bonding. Step 3: –Another enzyme bonds these nucleotides into a chain.

16. DNA Replication The process of unzipping and re-bonding continues until the entire molecule has been unzipped and replicated. Each new strand that is formed is a complement of one of the original strands. The end product of replication is two DNA strands that are identical to the original, or parent, DNA strand.

17. DNA Replication Animation DNA Replication