1. THE STRUCTURE OF DNA Chapter 12… section 12.1 & 12.2

2. What do we know about DNA? What is the importance of DNA?

3. Chromosomes contain many genes made of DNA. A gene is a segment of DNA that codes for a particular trait.

4. GENES (and DNA) DO 3 CRITICAL THINGS …. 1. carry information from one generation to the next 2. determine the inheritable characteristics of an organism 3. can be easily copied

5. Deoxyribonucleic Acid (DNA) DNA is a long thin molecule in a human cell with over 6 billion nucleotides.

6. DNA- is a long molecule made up of units called nucleotides. - Determines the production of proteins. A nucleotide has 3 parts: 1. Deoxyribose Sugar 2. Phosphate Group 3. Nitrogenous Base

7. There are 4 kinds of nitrogenous bases in DNA….. 1. Adenine (A) 2. Guanine (G) 3. Cytosine (C) 4. Thymine (T)

8. Adenine and Guanine are PURINES and have a “double” ring structure

9. Thymine and Cytosine are PYRIMIDINES and have a “single” ring structure

10. DNA looks like a twisted ladder…. the sides (BACKBONE) are composed of alternating… deoxyribose sugars and phosphate groups (Covalently bonded together) the steps (RUNGS) are composed of …. complementary pairs of nitrogenous bases

11. “untwisted” “twisted”

12. The nucleotides can be joined in any order…. this means that, ANY SEQUENCE of N bases is possible… thereby allowing for great diversity in living things – even among members of the same species

13. Watson and Crick – determined the structure of DNA to be a DOUBLE HELIX in which two strands were wound around each other DNA is like a spiral staircase

14. HYDROGEN BONDS… bond between a positive H atom of one molecule and a negative atom of another molecule; intermolecular force weak bond no electrons involved Form between the N bases in DNA provide enough force to hold the 2 strands of DNA together

15. Hydrogen Bonds form between certain base pairs ADENINE (purine) and THYMINE (pyrimidine) – 2 H bonds GUANINE (purine) and CYTOSINE (pyrimidine) – 3 H bonds because the N bases can only pair in a certain way this is called….. COMPLEMENTARY BASE PAIRING a purine will always bond with a pyrimidine

16. HYDROGEN BONDS

17. Chargaff’s Rule (because of complementary base pairing) for every adenine there is exactly 1 thymine for every cytosine there is exactly 1 guanine

18. Covalent Bonds – occur when 2 atoms share electrons; intramolecular force strong bonds that are not easily broken found between… the sugars and phosphates the sugars and nitrogen bases maintain the…. backbone (sides) of the DNA molecule the integrity of the DNA code (sequence of N bases)

19. DNA Structure- 10 base pairs make up one full twist of DNA

20. What is the complement? If the sequence of N bases on 1 strand of DNA is…. A T C G G C T T A A T A T C G What is the sequence on the other strand? REMEMBER…DNA is a double stranded molecule T A G C C G A A T T A T A G C

21. During most of the cell cycle chromosomes are not visible, instead the DNA is seen in a form called chromatin. During cell division, the chromatin condenses and coils around proteins (called histones) to form chromosomes.

22. Semiconservative DNA REPLICATION…. (hyperlink)hyperlink making an exact copy of DNA occurs before cell division (mitosis + meiosis) - interphase highly accurate MUTATIONS may occur …. changes in the (sequence of nucleotides) DNA Watson and Crick realized that each strand of a DNA molecule has all the information needed to RECONSTRUCT THE OTHER STRAND

23. DNA Replication a simplistic view….

24. DNA Replication – 3 Steps 1. UNWINDING … DNA Helicase (enzyme) separates the DNA molecule at Hydrogen bonds 2. BASE PAIRING… DNA Polymerase (enzyme) adds new nucleotides forming new strands of DNA 3. JOINING… DNA ligase (enzyme) connects new “daughter” strands together

25. The sites where separation and replication occur are called replication forks

26. DNA replication produces …. 2 new complementary strands(of DNA) Following (Chargaff’s) rules of base pairing

28. Each “parental” (old) strand of DNA serves as a template (pattern) for the making of (2) “daughter” (new) strands When DNA replication is complete…. 2 molecules of DNA are made Each molecule is composed of… 1 old strand and 1 new strand

29. Prokaryotic Cells…. have no nucleus have no membrane bound organelles… mitochondria, golgi bodies, vacuoles,… DNA is in the cytoplasm have a single, circular chromosome DNA replication begins at a single point and often proceeds in 2 directions until the entire DNA is replicated

30. Eukaryotic Cells… have a nucleus have membrane bound organelles… mitochondria, golgi bodies, vacuoles,… DNA is in the nucleus have more DNA…. DNA replication occurs at hundreds of places and produces segments called OKAZAKI FRAGMENTS replication proceeds in both directions until the DNA is completely copied

31. DNA is usually in a form called CHROMATIN But during cell division, the chromatin Condenses and coils around proteins (called histones) to form CHROMOSOMES (of DNA and protein)

32. chromosome chromatin