DNA Replication

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!

Where does it happen?

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

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

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

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

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

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?

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

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

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

What’s in a chromosome? DNA + histone proteins

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

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

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’

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

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.

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!

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?

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.

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?

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?

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 .

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 .

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?

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?

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!

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