1. DNA Replication

2. What is it? One Meter! 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. What if there is an error?
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

13. Write the complementary DNA strand for each of these DNA strands:
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. Grade 10 Biology MCAS OPEN RESPONSE QUESTION
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 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. Scoring Intro Let's see how well you did!
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. 4 What is a 4? This student earned a 
The response demonstrates a thorough understanding of Chargaff’s Rule and the composition of DNA .
What is a 4?

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

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

26. Sample Score 1 1 What is a 1? This student earned a 
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? This student earned a 
The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured.
What is a 0?

28. Rate Yourself!
EVALUATION
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. Take a break, you’ve earned it!
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. BINGO Spiral Staircase Parent Strand Deoxyribonucleic Acid
Sides of Ladder
Rungs of Ladder
Nitrogenous Base
Purine
Pyrimidine
Nucleotide
Complementary
Nucleus
Cytoplasm
Hydrogen Bonds
Covalent Bonds
Chargaff's Rule
Eukaryote
Daughter strand
Deoxyribonucleic Acid
Adenine
Guanine
Cytosine
Thymine
Base pairs
Sugar
Phosphate group
Deoxyribose
Double Helix
Chromosomes
Chromatin
Histones
Prokaryote
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