Name: ______Period: ______
DNA & RNA Nucleotide Modeling Activity
Background:
Deoxyribonucleic acid (DNA) is a molecule that carries most of the genetic instructions used in the development, functioning and reproduction of all known living organisms and many viruses. Most DNA molecules consist of two strands coiled around each other to form a double helix. The two DNA strands are composed of simpler units called nucleotides. Each nucleotide is composed of a nitrogen-containing base—either cytosine (C), guanine (G), adenine (A), or thymine (T), as well as a monosaccharide sugar called deoxyribose and a phosphate group. Nitrogenous bases can be further classified as pyrimidines (single carbon ring) or purines (double carbon rings). The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next. This results in an alternating sugar-phosphate backbone to the DNA molecule. According to Chargaff’s rules of base pairing A pairs with T, and C pairs with G. Hydrogen bonds bind the nitrogenous bases of the two separate strands to make double-stranded DNA. Both strands of the double-stranded structure store the same biological information. Biological information is replicated as the two strands are separated.
Purpose:
a) To re-enforce the names of the molecules that make up DNA.
b) To use models to construct DNA and shoe how it replicates.
c) To re-enforce the differences and similarities of DNA and RNA
d) To use models to show how the base sequences code in DNA and are exactly transcribed to RNA.
Materials: scissors, colored pencils, DNA paper models, RNA paper models
Procedure:
Part A: Structure of DNA Nucleotides:
Two important molecules which make up DNA are deoxyribose and phosphoric acid. These models and structural formulas are shown here. Deoxyribose is a carbohydrate. Phosphoric acid is a molecule in ATP. Deoxyribose is a carbohydrate. Phosphoric acid was studied previously as a molecule in ATP.
1. Give the molecular formula for the following items. Use the picture on the right to help you à à à à(a) Deoxyribose-- C______H______O______
(b)Phosphoric acid-- H ______P ______O______/
In addition there are 4 molecules called bases. There structural formulas and models are shown here.
2a. Of the 4 bases, which other base does adenine most resemble in structure? ______
2b. Of the 4 bases, which other base does thymine most resemble in structure? ______
2c. What is the classification of the bases in 2a? ______In 2b? ______
A molecule of deoxyribose joins with phosphoric acid and any one of the four bases to form a chemical compound called a nucleotide. A nucleotide is named for the base that joins with the deoxyribose. For example if thymine attached to deoxyribose, the molecule is called a thymine nucleotide.
è Use the nucleotides of the previous page to answer the following questions.
3. List the 4 nucleotides of DNA. ______, ______, ______, ______
4. Use the lines below to explain the similarities and differences in the chemical structure of the bases.
Similarities: ______
______
Differences: ______
______
Part B: Structure of a DNA Molecule
A DNA molecule is like a twisted ladder. Deoxyribose and phosphoric acid molecules join to form the sides or uprights of the ladder. Base molecules form the rungs of the ladder.
è Color the parts of nucleotides as indicated below:
o Cytosine = orange
o Thymine = green
o Adenine = purple
o Guanine = blue
o Phosphoric acid = yellow
o Deoxyribose = red
è Cut out the nucleotide molecules that are needed (see below). CUT ONLY ON THE SOLID LINES OF THE DIAGRAM.
è Fit 6 nucleotides together in a puzzle like fashion to form a row in the following sequence from top to bottom.
o cytosine nucleotide
o thymine nucleotide
o guanine nucleotide
o adenine nucleotide
o guanine nucleotide
o cytosine nucleotide
è Tape these nucleotides down onto the middle left of the page labeled DNA MODEL in your packet. This is the LEFT half of the DNA ladder molecule. It should consist of one side / upright and 6 rungs.
5. If DNA is ladder-like which two molecules form the sides of the DNA?______, ______
6. To which molecule does each base attach? ______
7. If DNA is ladder-like which molecule form the rungs of the DNA?______
Complete the RIGHT side of the DNA ladder by matching the bases of other nucleotides to form complete rungs. The ends of each base will allow only a specifically shaped matching new base to fit exactly. Once finished, tape the right side next to the left side that you have taped on DNA MODEL sheet. Your completed model should look like a ladder with matched bases as the rungs. Besides being shaped like a ladder, a DNA molecule is twisted. It looks like a spiral staircase. However, your paper model cannot show this shape.
8. Look at the DNA model. Only 2 pairings are possible list them here:
______matches with ______
______matches with ______
9. If you notice that there are 4 guanine bases on a DNA model how many cytosine should there be? ______
10. In your DNA model there are 4 guanine bases. Is your prediction from # 9 correct? YES / NO
11. Complete the base pairs for the set shown on the right. à à à à / ThymineAdenine
Guanine
Cytosine
Part C: RNA Structure
Besides ensuring the exact replication of chromosomes, the sequence (order) and pairings of bases are a genetic code of the instructions for the entire cell. How does a cell “read” the chemical message coded in its DNA in the form of specific base sequences? Part of the answer lies with a second molecule in the nucleus of cells called ribonucleic acid (RNA).RNA is similar to DNA in that its molecules are also formed from nucleotides. However, deoxyribose and thymine are not found in RNA. Two other molecules, ribose and uracil, are present. Ribose replaces deoxyribose, and uracil replaces thymine. Looking at their structural formulas and models, you will see certain similarities between the molecules that they replace. Formulas and models are shown to the right. /
è Color the parts of nucleotides as indicated below:
o Cytosine = orange
o Uracil = brown
o Adenine = purple
o Guanine = blue
o Phosphoric acid = yellow
o Ribose = red
è Cut out the nucleotide molecules that are needed (see below). CUT ONLY ON THE SOLID LINES OF THE DIAGRAM.
è Build the RNA strand using the following sequence from top to bottom.
o cytosine nucleotide
o uracil nucleotide
o guanine nucleotide
o adenine nucleotide
o guanine nucleotide
o cytosine nucleotide
è Tape these nucleotides down onto the middle of the page labeled RNA MODEL in your packet.
12. In RNA, the thymine base is replaced by ______and the deoxyribose sugar is replaced with ______.
Analysis:
Complete the following table by placing a check in the box next to each characteriatic indicating if it is true of DNA, RNA or place a check in both columns to indicate it is true of both. USE YOUR TEXT AND MODELS TO HELP YOU!
DNA / RNADeoxyribonucleid acid
Ribonucleic acid
Ribose present
Deoxyribose present
Phosphoric acid present
Adenine present
Thymine present
Uracil present
Guanine present
Cytosine present
Formed from nucleotides
Double stranded
Single stranded
Remains in nucleus
Moves out of nucleus
Contains a chemical message or code
DNA MODEL
RNA MODEL
DNA Nucleotides
RNA Nucleotides