Constructing a DNA Model

Introduction:

DNA is a complex molecule that is found in all living organisms.  Constructing DNA models is a great way to learn about DNA structure, function and replication. DNA contains the genetic information for the reproduction of life. Its structure is that of a twisted double helix that is composed of long strands of alternating sugars and phosphate groups, as well as nitrogenous bases (adenine, thymine, guanine and cytosine). The basic unit of structure for a DNA molecule is the nucleotide. A nucleotide is composed of a phosphate, a deoxyribose sugar molecule, and a nitrogen-containing base (A, T, C, or G). The instructions carried on DNA are used to make proteins from amino acids in the cytoplasm. RNA must first make a copy of DNA in the nucleus before the proteins can be built by ribosomes in the cytoplasm. The following activity will introduce you to the structure of DNA and how to determine the amino acids it will code for in protein construction.

Objectives:

Materials:

Procedure:

PART A - Building DNA

  1. Cut out all of the units needed to make the nucleotides from the patterns provided (see table 1 for quantity needed)

  2. Color code the Nitrogenous bases, phosphorus, and sugars:          Adenine (Blue), Guanine (Green), Thymine (Yellow), Cytosine (Red), Phosphate (Black), and Deoxyribose (Purple)

  3. Construct a NUCLEOTIDE by gluing or taping a phosphate, sugar, and one base together (see Diagram 1)

  4. Finish constructing the other 23 nucleotides (24 Total)

BASE PAIRING RULE For DNA:

A   pairs with   T

C   pairs with   G

  1. Use 12 of your nucleotides to make the LEFT STRAND of your DNA model by taping the phosphates of ONE nucleotide to a deoxyribose sugar of ANOTHER nucleotide

  2. When you have completed the left side of your model (12 nucleotides), RECORD the BASE SEQUENCE starting with the TOP base in Table 2.

  3. Use your other 12 nucleotides to construct the COMPLEMENTARY RIGHT STRAND of DNA (A with T and C with G)

  4. Record the sequence of your Right Strand in Table 2.

  5. You now should a model of DNA that looks like a ladder.

  6. Use string to attach your DNA model to the bottom of a coat hanger for hanging.

TABLE 1

Nucleotide Component Quantity Color
Thymine 6 YELLOW
Adenine 6 BLUE
Cytosine 6 RED
Guanine 6 GREEN
Phosphate 25 BLACK
Deoxyribose Sugar 25 PURPLE

Diagram 1

 

Table 2

Base Sequence LEFT Strand Base Sequence Right Strand
   
   
   
   
   
   
   
   
   
   
   
   

 

PART B - Determining DNA's Amino Acid Sequence

  1. Using the Base Sequence of ONLY the LEFT STRAND of DNA, write the bases in order (top to bottom) in Table 4. (12 bases)

 

BASE PAIRING RULE For RNA:
(Remember that uracil replaces thymine)

A   pairs with   U

C   pairs with   G

  1. Now determine the mRNA Bases that would match up with your DNA sequences & write these bases in Table 4. (mRNA "reads" DNA so ribosomes can put amino acids in the right order when proteins are made.)

  2. Use the mRNA codon table (Table 3) to write the 4 Amino Acids that your DNA strand codes for when a protein is being made.

Table 3 - mRNA Codons

Amino Acid

Codons

Amino Acids

Codons

Alanine GCU, GCC, GCA, GCG Leucine UUA, UUG, CUU, CUC, CUA, CUG
Arginine CGU, CGC, CGA, CGG, AGA, AGG Lysine AAA, AAG
Asparagine AAU, AAC Methionine AUG
Aspartic Acid GAU, GAC Phenylalanine UUU, UUC
Cysteine UGU, UGC Proline CCU, CCC, CCA, CCG
Glutamine CAA, CAG Serine UCU, UCC, UCA, UCG, AGU,AGC
Glutamic acid GAA, GAG Threonine ACU, ACC, ACA, ACG
Glycine GGU, GGC, GGA, GGG Trpytophan UGG
Histidine CAU, CAC Tyrosine UAU, UAC
Isoleucine AUU, AUC, AUA Valine GUU, GUC, GUA, GUG
Start AUG, GUG Stop UAG, UGA, UAA

 

Table 4

DNA Bases, mRNA codons, and Amino Acids
DNA                        
MRNA                        
Amino Acids        

Conclusion:

1. Name the 4 DNA nucleotides.

 

2. What 2 molecules make up the sides of DNA.

 

3. Your DNA model appeared ladder-like. What is the true shape of a DNA molecule?

 

4. What nitrogen base is on DNA, but not on RNA? What base replaces it?

 

5.What mRNA codon starts the making of a protein?

 

6. What codons stop the making of a protein?

 

7. Where in a cell would you find DNA? RNA? Amino Acids?

 

8. If 25% of DNA is Adenine, what percent is Cytosine?

 

9. What would happen if RNA made mistakes when it copied DNA's instructions?

 


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