Teaching the Concept of DNA Replication and Repair

By: Jessica JosephSunita Bali

IntroductionWe have seen detectives on TV

and movies getting excited about finding hair or skin or other body cells on the crime scene. Why?

Exactly the same DNA is contained in every single cell in our bodies! Have you ever wondered how that is possible?

Cells are capable of giving rise to a new generation of cells by undergoing DNA replication and cell division. We are going to study how DNA is replicated so that each new cell gets the same copy in its nucleus.

Lesson Sequence Lesson 1: Discovery of DNA: A Review

Scientists and experiments leading to the discovery of DNA

Lesson 2: DNA Structure: A Review The Chemical Composition of DNA, The Double Helix

Lesson 3: DNA Replicates Semi-Conservatively The Meselson and Stahl Experiment

Lesson 4: The Process of DNA Replication Separating the DNA Strands, Building the

Complementary Strands, DNA Repair Lesson 5: Assessment

Curriculum Expectations

Overall ExpectationsD2. investigate, through laboratory activities, the structures of cell components and their roles in processes that occur within the cell;D3. demonstrate an understanding of concepts related to molecular genetics, and how genetic modification is applied in industry and agriculture.

Specific ExpectationsD2.2 analyse a simulated strand of DNA to determinethe genetic code and base pairing of DNA (e.g., determine base sequences of DNA for a protein; analyse base sequences in DNA to recognize an anomaly) [AI]D3.1 explain the current model of DNA replication, and describe the different repair mechanisms that can correct mistakes in DNA sequencing

Discovery of DNA Scientists such as Hammerling, Griffith,

Hershey and Chase, Chargaff, Franklin and Wilkins, Watson and Crick conducted experiments that led to better understanding of DNA and its structure. Slides with M/C questions and clickers may be used to review this information with the students.

Students complete a DNA timeline scavenger hunt at› http://www.dnai.org/timeline/index.html

Composition and Structure of DNA: A Review

Students are shown the following video› http://www.youtube.com/watch?v=ZGHkHMoyC5I

Students build DNA molecules in pairs (Activity # 1)

Teacher goes over discussion questions with the class. Any gaps in knowledge are filled and misconceptions are corrected.

DNA Replicates Semi-Conservatively

What is semi-conservative replication?› What do you notice?

› Based on your knowledge of DNA structure, how do you think this occurs?

Semi-Conservative Replication:

Meselson and Stahl Experiment Hypothesis

Objective: Is DNA replication conservative, semi-conservative or dispersive?

Conservative Semi-Conservative Dispersive

Meselson and Stahl Experiment (Continued)

Experiment explained using overhead

Following animation explaining experiment shown:› http://highered.mcgr

aw-hill.com/olc/dl/120076/bio22.swf

Students complete the virtual lab and assessed (quiz #1)› http://www.sumanasi

nc.com/webcontent/animations/content/meselson.html

DNA Replication:Separating the DNA Strands

Key Enzymes: DNA Helicase, Single Stranded Binding Proteins (SSBs), DNA Gyrase

Replication Fork vs. Replication Bubble

DNA Replication:Building the Complementary Strands

Key Enzymes: DNA Polymerase I and III, Primase, DNA Ligase

Key Terms: RNA Primers, Leading and Lagging Strands, Okazaki Fragments

DNA Replication:Building the Complementary Strands

Synthesis of Lagging Strand

DNA Repair Key Enzymes: DNA polymerase I and III

act as exonuclease

DNA Replication Summary

The students will be shown animations:› http://highered.mcgraw-hill.com/olc/dl/120

076/micro04.swf› http://highered.mcgraw-hill.com/olc/dl/120

076/bio23.swf Whole-Class Replication Role-Play

› Each student acts as a nucleotide. Hands are used to form bonds. (Explained fully in summary)

DNA Replication: Differentiated Assessment

1) Visual: Students will make a sketch or diagram of the process of DNA replication. (K/I)2) Musical: Students will listen to the DNA replication song and write another verse for

the song. (K/I/C/A)http://www.youtube.com/watch?v=dIZpb93NYlw3) Kinesthetic: Students will design an explanation for DNA replication using body/hand

actions. (K/I/C/A)4) Linguistic: Students will imagine being a DNA molecule and write a story explaining

how they are copied. (K/I/C)5) Intrapersonal: Students will write explaining what they found to be fascinating about

DNA replication. (K/I/C/A)6) Interpersonal: Students will explain their understanding of DNA replication to their

partners. (K/I/C)7) Logical: Students will perform the DNA replication gizmo at http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=439Students will be given a copy of the ‘Student Exploration Sheet’ found on the website.

(K/I/C/A) Summative Assessment will take place at the end of the genetics unit in the form of a

Unit Test.

Potential Student Difficulties and Solutions• The students may find it difficult to understand the procedure and conclusions of the Meselson and Stahl experiment

• Explain each step in detail using illustrations and drawings• The students may have a difficult time visualizing the concept of DNA replication

• Show the animations multiple times• The students may have difficulty keeping track of all the enzymes involved in replication

• Create a word wall with all the important terms• The students may get confused about the lagging strand replication

• Emphasize that DNA strands are antiparallel and DNA polymerase III synthesizes only in the 5’ to 3’ direction.

• The following tutorial can be used to reiterate concepts:http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html

Safety Considerations• There is a lot of computer/internet use in the lessons. Students should be made aware of proper computer lab behaviour.• The class should be cleared and clear instructions given during the role play activity.• Assessment stations should be monitored for smooth performance and minimum issues.

Accommodations for ELL and Special Needs Students

Model building, role play and animations will help the entire class including ELL and special needs students to visualize the abstract structure of DNA.

Posting a word wall with the new vocabulary related to DNA structure and replication process will help the ELLs and special need students in writing tasks.

Extra attention and time will be given to ELLs and special needs students during classroom discussions and in computer lab.

Peer assistant will be encouraged in the classroom assignments by heterogeneous grouping of students.

Practical Applications

• DNA analysis can be used to:• Solve crimes (homicide)• Identify human remains (missing persons,

disasters)• Determine relationship between family

members (paternity, child abductions)• Medical Research (genetic diseases,

drugs)• Agriculture and Horticulture (genetically

modified organisms)• Animal Husbandry (genetically modified

animals)

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Thomson Nelson Limited. (2003). Biology 12. Toronto, Ontario: Author.This textbook was the source for background information and was also used for organizing the lessons.  http://www.accessexcellence.org/RC/AB/WYW/wkbooks/SFTS/activity2.phpThis website was used to form Activity # 1 that is used in reviewing DNA composition and structure. http://highered.mcgraw-hill.com/olc/dl/120076/bio22.swfThis animation was used to explain the Meselson and Stahl Experiment. http://www.sumanasinc.com/webcontent/animations/content/meselson.htmlThis virtual lab was used as assessment for the Meselson and Stahl Experiment. http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swfhttp://highered.mcgraw-hill.com/olc/dl/120076/bio23.swfThese animations were used in summarizing DNA Replication http://www.youtube.com/watch?v=dIZpb93NYlwThis video shows the DNA replication song that was part of assessment. http://www.explorelearning.com/index.cfm?method=cResource.dspDetail&ResourceID=439This gizmo was used as an assessment tool at the end of the lessons. http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.htmlThis tutorial was used to clear any student misconceptions and reiterate the whole process of DNA replication