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					                                     Biology (Science II)

Unit VI: Genetics

Time Frame:         2 weeks


Competencies

       1.   Understand the chromosomal basis of inheritance and the role of DNA as a blue
            print of life

            1.1 Explain the chromosomal basis of inheritance
            1.2 Give the importance of DNA in the transmission of traits

Lesson 2. DNA Replication

I.     Subject Matter: DNA Replication

       Time Frame: 1 period

       References:

       Suggested Textbook:

            University of the Philippines National Institute for Science and Mathematics
                Education Development. (In Press). Sourcebook on practical work for
                teachers: High school biology. (Vol 3). Quezon City: Author.

II.    Objectives:

       1.   Use models to construct a molecule of DNA
       2.   Manipulate models to demonstrate how DNA replicates

III.   Materials:

       A.   For Teaching:

            Diagram of DNA replication (transparency or drawn in manila paper)
            Overhead projector (if transparency will be used)

       B.   For Student Activity:

            Paper nucleotides
            Scissors
            Crayons




214                                                           BSE-Department of Education
IV. Lesson Proper:

    A.   Recall

         What is the pairing arrangement of nitrogen bases?
         Adenine pairs with thymine and guanine pairs with cytosine.

    B.   Motivation

         Show a zipper to the class to represent a DNA molecule. Ask them if they can see
         any similarities between the zipper and the DNA molecule.

    C.   Activity

         Photocopy enough copies of paper models for the whole class.
         Assign students to color and cut out the paper models a day before the activity.

    D.   Postlaboratory Discussion

         Answers to Developmental Questions in the Activity.

         Question 1.      Do the two new DNA molecules contain the same number of
                          adenine and thymine molecules?
              Answer:     Yes

         Question 2.      Are the two DNA molecules exact copies of each other?
           Answer:        Yes

    E.   Generalization

         1.   DNA produces an exact copy of itself through the process of replication.
         2.   During replication, the two DNA chains separate. Each DNA chain acts as a template.

    F.   Valuing or Application

         The discovery of the molecular structure of DNA, its replication mechanism and the
         process of protein synthesis allowed for the biochemical manipulation of this molecule.
         Cells (human, plant, animal, bacterial) are being studied for the better understanding of
         molecular processes which could then be harnessed to benefit humans, other organisms
         and the environment.




BSE-Department of Education                                                                   215
      G.   Assessment

           The left chain of a DNA molecule has the nucleotide sequence CCGTAGGCC.
           What is the sequence of the right chain of the DNA molecule?
                     GGCAUCCGG



V.    Agreement

      Read on the process of protein synthesis.




216                                                      BSE-Department of Education
                         Activity 2. Investigating DNA Replication

When Watson and Crick discovered the structure of DNA, they stated in their paper that the
DNA structure suggests a mechanism for replication. In this activity, the process of DNA
replication will be investigated through the use of paper nucleotides.

Objectives

1. To identify the molecules which make up DNA
2. To use models to construct a molecule of DNA

Materials

     Paper nucleotides
     Scissors
     Crayons

Procedure

1.   Color and cut out the nucleotides.

2.   Construct a DNA model using the paper nucleotides. Fit nucleotides together to form a
     row in the following sequence from top to bottom:

            TAC CAG CGG CGT GCC ACT

     Let this arrangement represent the left half of the DNA molecule.
     Complete the right side of the DNA molecule by matching the bases of other
     nucleotides.

3.   Unzip (open) the DNA molecule along the base pairs.

4.   Separate the two halves of the DNA molecule.

5.   Make a new DNA molecule by adding new nucleotides to the left half of the DNA. Build
     a second DNA molecule by adding new nucleotides to the right half of the DNA.

     Question 1. Do the two new DNA molecules contain the same number of adenine and
                 thymine molecules?
                 ____________________________________________

     Question 2. Are the two DNA molecules exact copies of each other?
                 _____________________________________________




BSE-Department of Education                                                           217
      A   T           C              G


          DNA nucleotides




218                         BSE-Department of Education

				
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