DNA and RNA_ The Nucleic acids

					      DNA and RNA: The Nucleic acids
Deoxyribonucleic acid, or DNA, is a complex molecule found in all living organisms. It
is the chemical that genes are made of. An understanding of the organization of this
molecule has answered many questions. Scientists now know how chromosomes can
duplicate during cell division and transfer their genetic information to new chromosomes.
Scientists also understand how chromosomes can direct the formation of specific proteins
outside the nucleus while still in the nucleus.
        In this investigation you will:
                 1) Construct a portion of a DNA molecule
                 2) Show the replication of DNA
                 3) Construct a portion of an RNA molecule
                 4) Compare and contrast DNA and RNA in terms of there structure and
                    function
Materials:
A bag filled DNA and RNA nucleotides.

Procedure

Part A. Structure of a DNA molecule
       The molecules that make up DNA are Deoxyribose, phosphoric acid and the four
nitrogen bases (adenine, thymine, cytosine, and guanine). Each molecule of deoxyribose
has one nitrogen base and one phosphoric acid chemically attached to it. The three
molecules together form a monomer called a nucleotide.

       Remove from your bag four different nucleotides for DNA.

       1) What is the only difference between the four nucleotides?
          _____________________________________________________

           _____________________________________________________
A DNA molecule is “ladder-like” in shape. Deoxyribose and phosphoric acid alternate to
form the sides (uprights) of the ladder and the nitrogen bases combine with each other to
form the steps of the ladder.

       Using the four nucleotides that you have already have, select two more and
       connect all six nucleotides together to form a row in the following order from top
       to bottom:
                       Cytosine nucleotide
                       Thymine nucleotide
                       Guanine nucleotide
                       Adenine nucleotide
                       Guanine nucleotide
                       Cytosine nucleotide

       Let this represent the left half of the “ladder-like” DNA molecule with one
       upright side and six half steps.
2) Name the two molecules that alternate to form the uprights side of the
   ladder.

   ____________________________________________________

3) Name the specific part of the nucleotide that the nitrogen bases attach to.

   ____________________________________________________

4) Name the molecules or parts of the nucleotide that form the half
   steps of the “ladder-like” DNA molecule.

   ____________________________________________________

   ____________________________________________________


Complete the “ladder-like” DNA molecule by adding the complementary
nucleotides to the right side. You will have to turn the new nucleotides so you
can see the lettering but it is upside down, in order for them to match up.
       Your completed model should look like a ladder with complementary
nitrogen bases pairs as steps.

       What are the names of the four nitrogen bases in DNA?

5) Is the order of nitrogen bases the same from top to bottom on the
   right side of the model as it is on the left side of the model? (look at the steps)

   ______________________________________________________

6) There are only two combinations of nitrogen bases that can
   make up the steps of the ladder. What are these two combinations?

   ______________________________________________________

   ______________________________________________________


7) Look carefully at the picture of the DNA molecule on Page 294 in
    your textbook. Look at the hydrogen bonds (doted lines) between adenine
   and thymine and between cytosine and guanine. Count the doted lines and
   explain why adenine can only bond with thymine and cytosine can only bond
   with guanine.

    _____________________________________________________

    _____________________________________________________

    _____________________________________________________
      8) In real life a Chromosome can be many thousands of nucleotide pairs long. If
         there were 9,478 adenine nucleotides in a strand of DNA, how many thymine
         nucleotides would you expect to find? ___________

      Count up the number of guanine nucleotides in your model. Then count up the
      cytosine nucleotides in your model and make sure it backs up your answer for
      question number 8.

      9) What are the three parts of a DNA nucleotide? (Use the specific names except
         for the nitrogen bases)


         ______________________________________________________

      10) The following is a list of the nitrogen bases on the left side of a DNA
          molecule. List the complementary bases that would make up the right side
          of the same DNA molecule.

                     Thymine                _____________________________

                     Adenine                _____________________________

                     Guanine                _____________________________

                     Guanine                _____________________________

                     Cytosine               _____________________________

                     Thymine                _____________________________

                     Cytosine               _____________________________

                     Adenine                _____________________________


Part B. DNA replication

      Your DNA model represents a very short piece of a chromosome but its
      replication is same as the replication of the chromosomes in the nucleus of a cell.

      Separate the two halves of your DNA strand in to left and right where the nitrogen
      bases come together. A chromosome untwists and unzips
      like this with the help of an enzyme called DNA HELICASE.

      Using the left half of your model as a pattern, connect new complementary
      nucleotides to form a new right half to complete a DNA strand.

      Build a second DNA model by using the right half of the original model as a
      template (pattern), add new complementary nucleotides to form a new left half.
       11) Do the two new ladder-like molecules contain the same number of steps?

               _______________

       12) Is the order of nitrogen base pairs the same for each DNA model from top to

           bottom? __________________________

       13) Are the two DNA molecules exact copies of each other?

       ____________________________________________________


       14) What is it about the nitrogen bases that ensures that when DNA replication
           occurs, the two new DNA strands are identical to the original?

           __________________________________________________

           __________________________________________________

           __________________________________________________

           __________________________________________________

Part C. Structure of RNA and RNA transcription

        Besides ensuring the exact replication of chromosomes, complementary base
pairing and the order of the nitrogen base pairs also serves a code that contains the
instructions for directing the cells activities, and for what characteristics an organism will
have. How does a cell “read” and “translate” the message held in the order of the
nitrogen base pairs of DNA? That is where ribonucleic acid (RNA) comes in.
        RNA is also made up of nucleotides. (What are the three parts of a nucleotide?)
The differences between DNA and RNA are that Ribose is the sugar group in RNA
rather than Deoxyribose, and RNA has Uracil as a nitrogen base instead of Thymine,
and RNA is made up a single strand of nucleotides instead of a double strand. It looks
like half of the “ladder-like” structure.

       15) Determine the molecular formulas for Ribose and Deoxyribose. (How many
           carbons, hydrogens, and oxygens are in each) Refer to the diagrams of the
           structural formulas for ribose and deoxyribose on the next page of this lab and
           count the C’s, H’s, and O’s. Add the proper subscripts to the letters below.
           (H2O)

               Ribose:   C H O                 Deoxyribose:   C H O
       16) How are these two sugars different from each other?
17) Examine the shape of a uracil nucleotide. With which nitrogen base can uracil
    match up to form a complete step of the ladder?

       _______________________________________



The process of making RNA is called Transcription. Choose one of the two
DNA strands in front of you and take it apart. With the DNA strand that is left
you are going to construct an RNA molecule. Separate the DNA strand into left
and right where the nitrogen base pairs come together.

During transcription, an enzyme called RNA POLYMERASE untwists and
unzips the DNA to separate the two halves like you just did.

Using the right side of your DNA strand as a template (pattern) match up RNA
nucleotides with their complements on the DNA strand.

18) Is the order of nitrogen bases in the RNA strand the same as the order of
    nitrogen bases in the unused left side of the original DNA strand? (with the
    exception of uracil replacing thymine) ________________

19) Do the RNA half-rung nitrogen bases pair up exactly as they
       Would if this was DNA replication? (with the exception of uracil
       replacing thymine) __________________________

Move the RNA strand to the side and move the two halves of the DNA strand
back together. (during transcription, the DNA strands are separated only
temporarily)

After the single stranded RNA is completed it leaves the nucleus and travels to the
ribosomes to deliver the message from the DNA.

20) What are the three parts of an RNA nucleotide? (be specific)

       ______________________________________


21) What is it about the nitrogen bases that ensures when RNA Transcription
    happens, the new RNA strand will carry the correct DNA message to the
    ribosomes?
    _____________________________________________________

   _____________________________________________________

   _____________________________________________________

   _____________________________________________________
Analysis

   1) Complete the following table by using an X to indicate which nucleic acid each
      characteristic applies to.

                                                         DNA              RNA
               Ribose
            Deoxyribose
          Phosphoric acid
              Adenine
              Thymine
               Uracil
              Guanine
              Cytosine
   Double strand of nucleotides
   Single strand of nucleotides
        Leaves the nucleus
       Stays in the nucleus
            Replication
           Transcription

   2) Explain how the pairing of nitrogen bases ensures that the DNA code is
      accurately passed from one cell to the next through DNA replication.




   3) We know that messenger RNA (mRNA) passes the message from the DNA to
      the rest of the cell. How do you know that by reading the mRNA the ribosome
      will know what the original DNA strand looked like?

				
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