Groovy DNA Beads

Celestine M. Jeffreys Hales Franciscan High School
4930 South Cottage Grove
Chicago IL 60615
(312) 285-8400 x69

This lesson is designed for 7th - 10th graders. The main objective of this
mini-teach is provide students with a hands-on experience matching DNA
nitrogenous base pairs, arranging nucleotides into codons, and visualizing the
size of a single gene.

Materials Needed:
(For Pairs of Students)
--Plastic beads (the type which you can string), approximately 1,000. You
should have 6 distinctly different colors.
--String (3 strings per group), approximately 2.5 feet long.
--Plastic baggies (1 for each group).

Note: place at least 42 beads in each bag, making sure that you've given each
pair of students a wide variety of all 6 colors. You must give out all 1,000 of
the beads in the baggies. Place the three strings in the baggie. Although I've
used green, pink, blue, yellow, orange and purple in this write-up, you aren't
limited to these colors. But you need to choose the colors which will represent
each nitrogenous base.

A nucleotide of DNA is made of three parts: a nitrogenous base (the part we're
going to work on); a 5-carbon sugar called deoxyribose; and a phosphate group.
There are four nitrogenous bases of DNA A, G, C, T (Adenine, Guanine, Cytosine
and Thymine).

1) The beads in your plastic bag represent one of the four nitrogenous bases.
For now, set aside the orange and purple beads.
2) Green represents A; pink represents G; blue represents C; yellow represents
T. So each color represents a nitrogenous base of DNA. Write the colors in
the space below:

A = _____________ G = _____________ C = _____________ T = ______________

3) Take both of the strings out of your bag and tie a knot in one end of the
string. The knot should be secure, but not tight.
4) In a reasonably random order (in other words, don't string AGCTAGCT), string
21 beads on one of your strings. In the space below, write the nitrogenous
bases you have strung together.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
(string #1)

DNA stands for deoxyribonucleic acid and is unique in a few ways: A, G, C, T
(adenine, guanine, cytosine and thymine) are the nitrogenous bases; it is inside
the nucleus; it is always double stranded. Now that you have made one strand of
DNA, you are going to make its complementary strand. In order to make a
complementary strand of DNA, you need to know that green and yellow (adenine and
thymine) are base pairs; blue and pink are base pairs (cytosine and guanine).

5) In the space below, write the color of the other part of the nitrogenous
base pair. The first one is written for you.

A = green ----> T = yellow G = pink ----> C = _________
T = yellow ----> A = _______ C = blue ----> G = _________

6) On the first line, again write the nitrogenous bases you strung together.
On the second line, write the other part of the nitrogenous base pair. In
other words, if you strung together ACCGTTA on the first line, then on the
second line you'd write TGGCAAT. This is called base pairing because the
nitrogenous bases A and T (adenine and thymine) are paired, as are C and G
(cytosine and guanine).

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
(string #1)

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
(string #2)

7) Now that you've written the complementary strand of DNA, use the other
string in your bag to string together the beads that represent each
nitrogenous base. Put a loose knot at the other ends of both strings.
8) Hold both strings at both ends. Make sure that the base pairs are touching.
Gently twist the two strands to the right. You've created a double helix.

MAKING A COMPLEMENTARY STRAND OF RNA RNA stands for ribonucleic acid. RNA is similar to DNA with two differences:
the 5-carbon sugar is a ribose instead of deoxyribose; and RNA does not have
thymine, instead RNA has uracil. So, green is paired with purple (adenine with
uracil); yellow is paired with green (thymine in DNA is paired with adenine in
RNA); and pink is still paired with blue (guanine with cytosine).

1) You'll now use the purple beads which will represent U (uracil).
2) In the space below, write the color of the other part of the nitrogenous
base pair. The first one is written for you.
DNA RNA A = green --------> U = purple G = pink ------> C = _________ C = blue ------> G = _________ T = yellow ------> A = _________ 3) On the first line below, again write the nitrogenous bases (string #1) of DNA. On the second line, write the corresponding RNA strand. So that if you string together ACCGTTA, you'd write UGGCAAU. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- (DNA string #1) -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- (RNA string #1) 4) String the beads which represent the nitrogenous bases of RNA.

CODONS DNA transcribed into RNA will (eventually) make proteins. Proteins are
important because they control biochemical pathways within the cell, direct the
making of essential compounds like lipids, carbohydrates and nucleotides, and
are responsible for the structure and movement of the cell. A protein "begins"
as a sequence of codons. Codons are 3 nucleotides of RNA. So that if you had
UGGCAAUCG --> UGG is a codon; CAA is another codon; UCG is the third codon in
this string of RNA.

1) Again write down the RNA strand (RNA string #1) you've made and put a slash
between each codon.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
(RNA string #1)

2) Separate the codons on your string by making a 1/4" - 1/2" space in between
the beads.
3) How many codons did you get? ________________

THE GREAT LEAP FORWARD Now that we've been working with nitrogenous bases, let's take a leap into chromosomes. 1) Using all three strings, string all of the beads in the baggie (in random order). 2) Put a loose knot on both ends of the strings. 3) Have the students hold each string horizontally. They should stand next to one another with the ends of the strings touching. They are representing one strand of the double-stranded DNA. 4) We have approximately 75,000 to 100,000 genes in human cells. A single human gene has about 10,000 nitrogenous base pairs. If the class holds only 1,000 base pairs, how many more classes and how many more beads would we need in order to represent a single human gene? __________ and __________ 5) EXTRAPOLATION: how is it possible to get all that genetic information inside one chromosome? (answer: genes portions of DNA which is coiled
inside a chromosome)

Performance Assessment:
Students will be able to:
identify the four nitrogenous bases of DNA;
identify the two base pairs of DNA;
describe the shape of a DNA strand;
identify the four nitrogenous bases of RNA;
identify the two base pairs of RNA/DNA;
explain the size of a codon;
explain and visualize the size and number of human gene(s).

The concept of DNA/RNA base pairing and formation of codons is difficult for
students to understand and visualize. This activity is inexpensive and easy.
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