1. Hereditary Molecules – DNA structure and Replication

2.  How is information passed down from parent to offspring?  Chromosomes are copied, separated, and packaged into new cells (mitosis and meiosis)

3.  Chromosomes are DNA wrapped around proteins  Each chromosome has many genes.  Genes hold the instructions for making proteins.  Proteins make you!

4. In order to understand how DNA holds instructions for making proteins, we need to understand the structure of DNA.

5.  DNA – Deoxyribonucleic Acid  Nucleic Acids are the fourth group of macromolecules!  Nucleic Acids are polymers  Nucleotides – the monomer of nucleic acids A polymer of DNA nucleotides One DNA nucleotide

6.  A 5-carbon sugar called deoxyribose  A phosphate group  One of four possible nitrogen-containing bases  Adenine  Thymine  Guanine  Cytosine Nucleotide 5-Carbon Sugar

7. There are four different possible Nitrogenous bases in DNA. Therefore, there are four different possible nucleotides – Adenine, Thymine, Guanine, and Cytosine.

8.  The phosphate of one nucleotide covalently bonds to the sugar of the next nucleotide. This continues until a long chain (polymer) is formed.  Here are four nucleotides bonded together – only the beginning of a polymer.  This is only one strand of nucleotides. DNA has two strands of nucleotides. One Adenine nucleotide One Thymine nucleotide

9.  Watson and Crick discovered how the two strands of DNA were bonded together.  The A from one strand bonds with the T on the other strand.  The C on one strand bonds with the G on the other strand.  The two strands are held together by hydrogen bonds.  The two strands run antiparallel to each other.  The two strands of DNA are complementary to each other – Not identical

10.  Watson and Crick used information from other scientists to help them discover the structure of DNA.  Erwin Chargaff  The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA.  The same thing is true for the other two nucleotides, guanine [G] and cytosine [C].  Called “ Chargaff’s Rules ”  A = T  C = G

11. If the sequence on one strand of DNA is A T C C A G T A C A G T T C A A G T A G G T C A T G T C A A G T T C What is the sequence on the complementary strand?

12.  Rosalind Franklin ’s research helped Watson and Crick to understand that DNA is a double- helix and that the two strands run antiparallel to each other.  Rosalind died with no credit for her contribution

13.  Now you will practice building DNA using the modeling components available.  Remember that A hydrogen bonds to T and C hydrogen bonds to G  Remember that the two strands need to run antiparallel to each other.

14.  All of the DNA in the nucleus of a cell must be copied before it can be divided into two new cells.  The process is called Replication.  Enzymes play an important role in the role of replication, especially DNA polymerase, and helicase

15. The two strands of DNA are pulled apart by an enzyme called helicase DNA polymerase brings new nucleotides to hydrogen bond with the exposed nucleotides This happens on both strands of DNA until two new double-stranded DNA molecules are made Chagaff’s rules are followed: A = T G = G

17.  Practice Replicating Practice Replicating  View an animation of Replicationanimation of Replication  Now practice replication with your own modeling components  View Crashcourse Biology Video on the structure of DNA and replication. Some of the details are more complex than we discussed, but it may still be helpful.Crashcourse Biology