DNA Replication

1. DNA Replication

2. What is it? • DNA Replication • Process of copying the DNA in a cell before it divides • How much DNA do we need to copy? • bacteria: 3 million base pairs • humans: 3 billion base pairs One Meter!

3. Where does it happen?

4. Why does it happen? • So daughter cells have a complete copy of the parent DNA ? ? ? ?

5. When does it happen? • Remember synthesis phase in mitosis? • Interphase • S phase = Synthesis

6. How does DNA replicate? TEMPLATE “semi-conservative”: half of each new strand is the old strand

7. How does DNA replicate? 1. Replication Fork • Site where DNA is separated and copied

8. The Enzymes 2. Helicase: separates or “unzips” the 2 strands of the double helix • Breaks Hydrogen Bonds

9. The Enzymes 3. DNA polymerase: inserts appropriate bases • Proofreads the bases to make sure that they are paired correctly What if there is an error?

10. How does DNA replicate? 4. Replication Fork • Nucleotides are added in 5’3’ direction • Anti-parallel • Okazaki Fragments

11. Video Clip • http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

13. Write the complementary DNA strand for each of these DNA strands: • DNA • GAATTACA • CCAATTAG • ATAGACAG • CCAGTACA • DNA • CTTAATGT • GGTTAATC • TATCTGTC • GGTCATGT

14. What’s in a chromosome? • DNA + histone proteins

15. What’s in a chromosome? • DNA + Histone = chromatin • Chromatin beads  nucleosome • Nucleosome packed and coiled  Chromosome

16. DNA Replication Review • Each strand of the double helix of DNA serves as a __________ or model, for the new strand • Sites where DNA separation & replication occur are called: __________ __________ • DNA separates into two strands by the enzyme called __________. template replication forks helicase

17. DNA Replication Review 4) The enzyme ________________ adds bases along the original DNA strand. • Two new strands form, following the rules of __________ 5) Nucleotides are added in direction DNA polymerase base pairing 5’-->3’

18. DNA Replication Review chromatin 6) DNA + Histone = _______________ 7) Chromatin beads  _______________ 8) Nucleosome packed and coiled  _______________ nucleosome chromosomes

19. INTRODUCTION Grade 10 Biology MCAS OPEN RESPONSE QUESTION The following is an Open Response question. It is important to practice answering these types of questions in preparation for the state mandated MCAS. This exercise will walk you through the process. There will also be some reference links to assist you.

20. How to answer HOW TO ANSWER AN OPEN RESPONSE QUESTION • Be sure to... • Read all parts of each question carefully. • Make each response as clear, complete and accurate as you can. • Proofread your work!

21. In 1950, Erwin Chargaff and colleagues examined the chemical composition of DNA and demonstrated that the amount of adenine always equals that of thymine, and the amount of guanine always equals that of cytosine. This observation became known as Chargaff's rule. • Based on current knowledge of the structure of DNA, explain the basis of Chargaff's rule. • The diagram below represents a single-stranded segment of DNA. In your Student Answer Booklet, write the complementary DNA strand that would form from this strand during replication. Use the letters A, C, G, and T to designate the bases: A = adenine; C = cytosine; G = guanine; T = thymine. • Why is Chargaff's rule so important to DNA's ability to replicate itself accurately?

22. Now that you’ve finished the problem, Scoring Intro Let's see how well you did! MCAS Open Response questions are graded as either a 4,3,2,1 or 0 with 4 being the best possible score. The following pages are examples of work done by other students who earned those scores. Please use the example of a 4 to check your answers.You will also see the guidelines that were used to grade these answers. As you look over these pages, try to rate your own answer as a 4,3,2,1or 0.

23. What is a 4? The response demonstrates a thorough understanding of Chargaff’s Rule and the composition of DNA . This student earned a  4

24. What is a 3? The response demonstrates a general understanding of Chargaff’s Rule and the composition of DNA . This student earned a  3

25. Sample Score 2 What is a 2? This student earned a  2 The response demonstrates a limited understanding of Chargaff’s Rule and the composition of DNA .

26. Sample Score 1 What is a 1? This student earned a  1 The response demonstrates a minimal understanding of understanding of Chargaff’s Rule and the composition of DNA .

27. Sample Score 0 What is a 0? The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured. This student earned a  0

28. EVALUATION Rate Yourself! Now that you’ve seen how the scores are graded, how did you do? Try to rate yourself. Would you say that you earned a 4,3,2,1, or 0?

29. CONCLUSION Hopefully, this has been a helpful experience for you. The only way to improve is to practice, and there are other problems like this one available for you to try if you are up to the challenge! -- or -- • Call a friend, have them do the same problem and you can talk about it. -- or -- • Take a break, you’ve earned it!

30. Deoxyribonucleic Acid Adenine Guanine Cytosine Thymine Base pairs Sugar Phosphate group Deoxyribose Double Helix Chromosomes Chromatin Histones Prokaryote Spiral Staircase Sides of Ladder Rungs of Ladder Nitrogenous Base Purine Pyrimidine Nucleotide Complementary Nucleus Cytoplasm Hydrogen Bonds Covalent Bonds Chargaff's Rule Eukaryote Daughter strand BINGO • Parent Strand • Replication Fork • DNA helicase • DNA polymerase • 5’ to 3’ • 3’ to 5’ • Okazaki Fragments • Leading strand • Lagging strand • Anti-parallel • Semi conservative • Nucleosome • Beads • S phase • Interphase