General Information

The DNA and RNA nucleotide subunits have three areas that represent the components of all nucleotides:

• Phosphate
  Circle area with raised arc, tactile diagonal lines, and a small round blank (place where the small round tab fits in)
• Sugar
  Diamond-shaped area with a small round tab (part that fits into the small round blank) denoting ribose or deoxyribose
• Nitrogenous base
  Rough-textured area with a large tab or blank, and a lower case braille and capital print letter in two orientations

DNA subunits are identifiable in the following ways:

• Black foam backing
• Smooth, diamond-shaped area (deoxyribose)
• Blue, yellow, white, and brown surface laminate

RNA subunits are identifiable in the following ways:

• White foam backing
• Raised circle in center of the diamond-shaped area (ribose)
• Blue, yellow, white, and orange surface laminate

Key to DNA Nucleotide Subunit Structures

The visual DNA nucleotide indicator is the black foam backing. The tactile DNA nucleotide indicator is the smooth, diamond-shaped area (deoxyribose).

White DNA Nucleotides - Adenosine monophosphate

Blue DNA Nucleotides - Guanosine monophosphate

Yellow DNA Nucleotides - Cytidine monophosphate

Brown DNA Nucleotides - Thymidine monophosphate

Key to RNA Nucleotide Subunit Structures

The visual RNA nucleotide indicator is the white foam backing. The tactile RNA nucleotide indicator is the raised circle in the diamond area (ribose).

White RNA Nucleotides - Adenosine monophosphate

Blue RNA Nucleotides - Guanosine monophosphate

Yellow RNA Nucleotides - Cytidine monophosphate

Orange RNA Nucleotides - Uridine monophosphate

Instructions

To link subunits together, press the tab or blank of one nucleotide down into the appropriate tab or blank of another nucleotide (see Figures 1 & 2).

To separate attached subunits, pull them apart horizontally in the plane of their attachment (see Figures 3-5 and 6-8).

• Photo: A yellow (C) and a blue (G) DNA nucleotide are linked together by the small round tab of the yellow (C) nucleotide and the small round blank of the blue (G) nucleotide.

  Figure 3.

• Photo: As the linked yellow (C) and blue (G) DNA nucleotides are pulled apart or separated in the plane of their attachment, a small gap remains between the small round tab of the yellow (C) nucleotide and the small round blank of the blue (G) nucleotide.

  Figure 4.

• Photo: The yellow (C) and blue (G) DNA nucleotides are completely separated.

  Figure 5.

• Photo: A yellow (C) and a blue (G) DNA nucleotide are linked together by the trapezoid blank of the yellow (C) nucleotide and the trapezoid tab of the blue (G) nucleotide.

  Figure 6.

• Photo: As the linked yellow (C) and blue (G) DNA nucleotides are pulled apart or separated in the plane of their attachment, a small gap remains between the trapezoid blank of the yellow (C) nucleotide and the trapezoid tab of the blue (G) nucleotide.

  Figure 7.

• Photo: The yellow (C) and blue (G) DNA nucleotides are completely separated.

  Figure 8.

These actions will cause the laminate to separate from the foam.

How to Form a Single Strand of DNA

• Photo: Two unlinked DNA nucleotides are lined up vertically, yellow (C) above blue (G). They are oriented so that small round tab projecting from the smooth diamond area of the yellow (C) nucleotide is just above where it will fit into the small round blank located in the circle area with tactile diagonal lines of the blue (G) nucleotide.

  Figure 11.

  1. Start with the first nucleotide oriented so that the sugar-phosphate side is on the left and the nitrogenous base blanks/tabs are on the right. In this orientation, the phosphate will be at the top left of the subunit (see Figure 11).

• Photo: Two linked DNA nucleotides are lined up vertically, yellow (C) above blue (G). They are linked by the small tab of the yellow (C) nucleotide and the small blank of the blue (G) nucleotide.

  Figure 12.

  2. A single strand of DNA is formed by linking nucleotides vertically, from the sugar (diamond shape) of one nucleotide to the phosphate (circle area with raised arc) of the next nucleotide. Note that free nucleotides are always added to the sugar end of a lengthening strand (see Figures 11 & 12).

• Photo: Four DNA nucleotides, oriented vertically, are shown linked together via their small round blanks and tabs in the following order: yellow (C), blue (G), white (A), and brown (T).

  Figure 13.

  3. Linking nucleotides this way demonstrates the formation of the sugar-phosphate "backbone" of DNA strands, which leaves the nitrogenous bases (blanks/tabs) available for base-pairing and the formation of a second, complementary strand (see Figure 13).

Note: For demonstration purposes, the sequence of nucleotides in a single strand does not have to follow a particular order.

Base-pairing Rules for Double-stranded DNA

The design of the nucleotides facilitates correct pairing of nitrogenous bases. Pairing of nitrogenous bases is horizontal and results in the formation of two attached strands of DNA that are complementary to each other.

How to Form a Double Strand of DNA

• Photo: Four DNA nucleotides, oriented vertically, are shown linked together via their small round blanks and tabs in the following order from top to bottom: blue (G), yellow (C), white (A), and brown (T).
  

  Figure 16.

  
  

  1. Form a single strand of DNA subunits making sure the sugar-phosphate "backbone" is on the left and the unpaired nitrogenous bases face right. Do this by linking the phosphate of each free nucleotide to the sugar (deoxyribose) of the previous nucleotide. In other words, always add free nucleotides to the sugar end of a lengthening strand. Any order of nucleotides is OK (see Figure 16).

• Photo: Five DNA nucleotides are shown linked together. Four of them are oriented vertically, and shown linked together via their small round blanks and tabs in the following order from top to bottom: blue (G), yellow (C), white (A), and brown (T). The brown (T) nucleotide is also linked horizontally to a white (A) nucleotide with large round tab and blank, respectively. This begins the formation of a second, right-hand strand.

  Figure 17.

  
  

  2. Select a free, unattached nucleotide that is complementary to the bottommost nucleotide in the single DNA strand just formed. Make sure the free nucleotide is oriented so that the sugar is up, the phosphate is down, and the base tabs/blanks face left. Then, press the base tab or blank of one nucleotide into the complementary base tab or blank of the other nucleotide (see Figure 17). This procedure ensures that the nucleotides of the second strand are added only to the sugar side of the growing DNA strand and demonstrates the directionality of nucleotides and DNA strand structure and formation.

• Photo: Six DNA nucleotides are shown linked together. Four of them are oriented vertically and linked together via small round blanks and tabs in the following order from top to bottom: blue (G), yellow (C), white (A), and brown (T). The brown (T) and white (A) nucleotides are also linked horizontally to white (A) and brown (T) nucleotides, respectively, forming a right-hand strand.

  Figure 18.

  
  

  3. Continue to link nucleotides upward until you have formed two complementary DNA strands that are attached via sugars and phosphates and between the bases (see Figures 18 and 19).

• Photo: Eight DNA nucleotides are linked to form a connected double strand; two sets of four vertically linked nucleotides are also linked horizontally in pairs. From top to bottom: blue (G) is linked with yellow (C), yellow (C) is linked with blue (G), white (A) is linked with brown (T), and brown (T) is linked with white (A).

  Figure 19.

Note: After the first complementary base is attached, subsequent nucleotides need to be linked between the nitrogenous bases and between the phosphate blank and the sugar tab (see Figures 18 and 19).

How to Demonstrate Semiconservative DNA Replication

• Photo: Eight DNA nucleotides are linked together to form a connected double strand; two sets of four vertically linked nucleotides are linked horizontally in pairs. From top to bottom: blue (G) is linked with yellow (C), yellow (C) is linked with blue (G), white (A) is linked with brown (T), and brown (T) is linked with white (A).

  Figure 20. One double strand of DNA

  
  

  1. Form a double strand of DNA with eight nucleotides using complementary base-pairing. The result is a double-stranded DNA molecule with four base pairs (see Figures 19 and 20).

• Photo: Four pairs of linked DNA nucleotides are shown being separated into two vertically linked strands, four nucleotides each.

  Figure 21. Separate the two strands and tighten links.

  Photo: Two separate strands of nucleotides, each one formed of vertically linked nucleotides. The left strand from top to bottom consists of a blue (G), yellow (C), white (A), and brown (T) nucleotide. The right strand from top to bottom consists of a yellow (C), blue (G), brown (T), and white (A) nucleotide.

  Figure 22. One double DNA strand, separated

  2. Separate the two strands by pulling them apart horizontally between the base pairs, leaving some space between the left and right single strands of DNA (see Figures 21 and 22). The links holding the sugar-phosphate backbone together may need to be tightened.

• Photo: Two growing strands of DNA nucleotides, each one formed of vertically and horizontally linked nucleotides. The left strand from top to bottom consists of a blue (G), a yellow (C), a white (A), and a brown (T) nucleotide; the (bottom) brown (T) nucleotide is connected horizontally to a white (A) DNA nucleotide. The right strand from top to bottom consists of a yellow (C), a blue (G), a brown (T), and a white (A) nucleotide; the (top) yellow (C) nucleotide is connected horizontally to a blue (G) DNA nucleotide.

  Figure 23. Add nucleotides to each strand.

  Photo: Two growing strands of DNA nucleotides, each one formed of vertically and horizontally linked nucleotides. The left strand from top to bottom consists of a blue (G), a yellow (C), a white (A), and a brown (T) nucleotide; the (bottom) brown (T) nucleotide is connected horizontally to a white (A) DNA nucleotide, and the white (A) nucleotide above it is connected horizontally to a brown (T) DNA nucleotide. The right strand from top to bottom consists of a yellow (C), a blue (G), a brown (T), and a white (A) nucleotide. The (top) yellow nucleotide (C) is connected horizontally to a blue (G) DNA nucleotide, and the blue (G) nucleotide below it is connected horizontally to a yellow (C) DNA nucleotide.

  Figure 24. Nucleotides are added only to the sugar end of a growing strand.

  3. Using free nucleotides and base-pairing rules, form new strands of DNA that are complementary to the left and right strands of the original DNA molecule. Start at the bottom of the left strand and progress up as you link the nucleotides together. Start at the top of the right strand and progress down as you link the nucleotides together (see Figure 23). This demonstrates the directionality of nucleic acid strands: Nucleotides are added only to the sugar end of a growing nucleotide strand (see Figure 24).

• Photo: Two sets of eight linked nucleotides, each one consisting of two sets of four vertically linked nucleotides that are also linked horizontally in pairs. From top to bottom, each set of eight linked nucleotides consists of blue (G) linked with yellow (C), yellow (C) linked with blue (G), white (A) linked with brown (T), and brown (T) linked with white (A).

  Figure 25. Two identical double strands of DNA

  
  

  4. Continue adding nucleotides to each strand until two identical double strands of DNA are formed (see Figure 25). This demonstrates semiconservative DNA replication: Each of the two new double-stranded DNA molecules are composed of one "parent" strand from the original DNA molecule and one new strand formed from free nucleotides.

Base-pairing Rules for Transcribing DNA to RNA

How to Demonstrate Transcription

Transcription is the formation of a single strand of messenger RNA (mRNA) from a (single) template strand of DNA.

• Photo: Two strands of six vertically linked DNA nucleotides that are also linked horizontally in pairs. The left strand consists of three blue (G) nucleotides followed by a yellow (C), a white (A), and a brown (T) nucleotide from top to bottom. The right strand consists of three yellow (C) nucleotides, followed by a blue (G), a brown (T), and a white (A) nucleotide from top to bottom.

  Figure 28. Double strand of DNA

  Photo: Six pairs of horizontally linked DNA nucleotides are shown being separated into two vertically linked strands, six nucleotides each. The left strand consists of three blue (G) nucleotides followed by a yellow (C), a white (A), and a brown (T) nucleotide from top to bottom. The right strand consists of three yellow (C) nucleotides, followed by a blue (G), a brown (T), and a white (A) nucleotide, from top to bottom.

  Figure 29. Separate the strands.

  
  

  1. Form a double-stranded DNA molecule using DNA base-pairing rules at least six base pairs long (Figure 28). Separate it into two single strands and choose one to be the template strand (Figure 29).

• Photo: Nine linked nucleotides form a partial double strand with six vertically linked DNA nucleotides on the left: three blue (G) nucleotides, one yellow (C), one white (A), and one brown (T) from top to bottom. The bottom three DNA nucleotides of this strand are linked to RNA nucleotides from bottom to top: brown (T) DNA nucleotide with white (A) RNA nucleotide, white (A) DNA nucleotide with orange (U) RNA nucleotide, and yellow (C) DNA nucleotide with blue (G) RNA nucleotide.

  Figure 30. Add RNA nucleotides starting from the bottom of the left template strand.

  
  

  2. Using free RNA nucleotides and base-pairing rules for transcribing DNA to mRNA, form a complementary mRNA strand along the DNA template. A left-hand template strand (bases point right) begins transcription at the bottom of the DNA strand; add RNA nucleotides from the bottom up (Figure 30). A right-hand template strand (bases point left) begins transcription at the top of the DNA strand; add RNA nucleotides from the top down. This demonstrates the directionality of nucleic acid strands: Nucleotides can only be added to the sugar end of a growing nucleotide strand.

• Photo: Six vertically linked DNA nucleotides form the left strand: three blue (G), one yellow (C), one white (A), and one brown (T) from top to bottom. Six vertically linked RNA nucleotides form the right strand: three yellow (C), one blue (G), one orange (U), and one white (A) from top to bottom. Both strands are linked horizontally forming pairs: three blue (G) with three yellow (C) nucleotides, one yellow (C) with a blue (G) nucleotide, one white (A) with an orange (U) nucleotide, and one brown (T) with a white (A) nucleotide, from top to bottom.

  Figure 31. Complementary mRNA strand attached to DNA template

  Photo: A single strand of vertically linked RNA nucleotides: three yellow (C), one blue (G), one orange (U), and one white (A) from top to bottom.

  Figure 32. mRNA ready for translation

  
  

  3. After forming the complementary mRNA strand (Figure 31), separate it from the DNA template. A single strand of mRNA remains (Figure 32) and is ready to demonstrate translation.

Note: The figures here demonstrate the start codon of mRNA (AUG) and the codon for proline (CCC). The DNA template strand reads TACGGG, which is transcribed to AUGCCC. This mRNA sequence codes for the amino acid methionine first and then proline in the transcribed mRNA. Translation typically begins with the amino acid methionine. All 64 combinations of nucleotide triplets code for either start (AUG), stop (UAA, UAG, UGA), or one of the remaining 19 different amino acids (see Universal Genetic Code here).

Universal Genetic Code

Messenger RNA (mRNA) Codons and Amino Acids

Alignment With Disciplinary Core Ideas—Life Sciences
A Framework for K-12 Science Education Standards¹

Life Science 1.A: Structure and function
How do the structures of organisms enable life’s functions?

All cells contain genetic information in the form of DNA. Genes are specific regions within the extremely large DNA molecules that form the chromosomes. Genes contain the instructions that code for the formation of molecules called proteins, which carry out most of the work of cells to perform the essential functions of life.

Life Science 3.A: Inheritance of traits
How are the characteristics of one generation related to the previous generation?

DNA molecules contain four different kinds of building blocks, called nucleotides, linked together in a sequential chain. The sequence of nucleotides spells out the information in a gene. Before a cell divides, the DNA sequence of its chromosomes is replicated and each daughter cell receives a copy. DNA controls the expression of proteins by being transcribed into a "messenger" RNA, which is translated in turn by the cellular machinery into a protein.

¹ National Research Council. (2012). A Framework for K-12 Science
 Education: Practices, Crosscutting Concepts, and Core Ideas. Committee
 on a Conceptual Framework for New K-12 Science Education
 Standards. Board on Science Education, Division of Behavioral
 and Social Sciences and Education. Washington, DC: The National
 Academies Press. www.nap.edu/catalog.php?record_id=13165

Back to Introduction

Suggested Websites

Howard Hughes Medical Institute: BioInteractive DNA: Animations
www.hhmi.org/biointeractive/dna/animations.html

National Institutes of Health, U.S. National Library of Medicine: Genetics Home Reference Handbook: Cells and DNA - What is DNA?
ghr.nlm.nih.gov/handbook/basics/dna

DNA from the Beginning
www.dnaftb.org/

Understanding Evolution: DNA, the Language of Evolution: Francis Crick & James Watson
evolution.berkeley.edu/evolibrary/article/history_22

DNA-RNA Kit

Catalog Number 1-08979-00

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