D N A

DNAWhat are genes? (4 min)

http://www.youtube.com/watch?v=sf0YXnAFBs8&feature=relatedHistory of DNA

Deoxyribonucleic AcidDNA   is a complex molecule found in all living things. The primary function of DNA is to store and transmit genetic information   that tells cells which proteins to make and when to make them.

http://www.dnalc.org/home.html

In 1953, James Watson and Francis Crick proposed a model for the DNA molecule that consisted of two nucleotide chains that wrap around each other to form a double spiral. This shape is called a double helix.

An idea about size:   An average cell nucleus is about 6 micrometers in diameter.

The total length of the DNA in the human genome is 1.8 meters.

There must be several levels of coiling and supercoiling in DNA.

Chromosome: a coiled, double rod-shaped form of condensed DNA that forms during cell division.

DNA BASE PAIRS

What is a model?Why is modeling important to scientists?What are the advantages and/or disadvantages of using models?

Using Models

Build a Model of DNA using candy:

Task 1: Build a Model of DNA using candy.

KEY:Sugar – Twizzler (5 per side)

Phosphate- Marshmallow (5 per side)

Bases:

Adenine (A) – orange jelly

Thymine (T) – mango jelly

Cytosine (C) – grape jelly

Guanine (G) - strawberry jelly

Task 2: Label the plate of your candy DNA .

Note: Use string as backbone of ladder

Guide questions: Write your answers in

your notebook.

1. Draw and label your DNA candy model.

2. What molecules make up the sides of the ladder?

3. a. What molecules make up the rung (at the middle) of the ladder? b. How do the molecules in the rungs pair up? c. What side molecule are they attached to?

4. What is the sequence (code) of your DNA model?

A molecule of DNA (Deoxyribonucleic Acid) is composed of two backbones and four types of chemical bases.

Side of the Ladder:

•A chain of phosphate groups and sugars forms the sides of the ladder. •Each sugar molecule in the ladder provides anattachment site for one of the chemical bases.

DNA MODEL

Steps of the ladder:

The four types of chemical bases are: adenine, thymine, cytosine and guanine. They usually are represented by their first letters: A, T, C and G.

The bases form pairs in a very specific way:

A pairs with T, C pairs with G.

•The DNA sequence is the consecutive order of bases on one side, or strand, of the twisted ladder.

•The other strand has a complementary sequence determined by the basepairing rules.

DNA Model Kit1. Construct support stand. Attach 3 legs to black 4-

prong center and attach long green straw.

2. Construct 12 sets of sugar + base combination. Attach a base (A,T, C, G) to a black 3-prong center.

3. Construct 6 pairs of sugar + base combination. Insert 6 white 2-prong centerpiece to the long green straw. Connect each sugar and N-base combination to the white center. Note base pairings (A-T, C-G).

4. Construct phosphate group. Attach 2 yellow connectors to each end of red 2-prong center to make 6 sets. Connect the phosphates to each end of the sugars (black center).

5. End the chain. Attach a red center to the end of the sugars (end).

6. Make a double helix. Twist the chain by turning each white center and sliding it along the long green straw.

Steps: Legend:

Support: 1 Long Green Straw Support stand3 2” straw Support stand1 black 4-prong center Support stand

Bonds (Connectors):White 2-prong center (Sugar to base and Sugar to Phosphate connector)Yellow (Sugar to phosphate connector)

Nitrogen bases:Blue straw Adenine (A)Red straw Thymine (T)Grey Cytosine (C)Green Guanine (G)

Sugars: Black 3-prong center

Phosphate Group:Red 2-prong center

Base Pairs: A----TC----G

ADDITIONAL NOTES:

The specific matching of the base pairs, A with T and C with G, provides a way for exact copies of DNA to be made.

To make exact copies of DNA, the double helix ladder is untwisted and separates the two strands.

Next, two new strands are made by reading each side of the DNA ladder, one step (base) at a time. At each step, the matching base fills in (with its associated sugar and phosphate) to complete the rung and lengthen the new DNA strand.

When the process is complete, there are two identical DNA double helices, each containing one original and one new strand.

Copying of DNA is an important part in making new cells. Before a cell divides, it first duplicates its DNA so that the new cell will have the same genetic information.

The specific base pair matching during replication ensures that exact DNA copies are made.