Overview of The Features and Functions of DNA You Can Demonstrate Using The DNA-Only Model
It is our intention that in using this model you and your students will be able to demonstrate all the basic parts and functions of the central molecules of life – and learn about them in a different and memorable way. We model creators especially remember the time during the building of the model when we got the angles between the bases and the sugars just right, and – in a kind of WOW! moment – saw the model twist into a helix. We also found that playing with the model raised questions about cellular information and machinery that we had never asked before.
Here’s what your students can discover with this model:
1. DNA Parts
The four different chemical components of a DNA strand are called nucleotides.
Each nucleotide, in turn, is made of a phosphate molecule, a sugar molecule, and one of 4 different base molecules: adenine (A), thymine (T), guanine (G), and cytosine (C).
2. DNA Bonding
- Nucleotides are linked one to another in two different ways – by chemical bonds between their sugars and their phosphates creating a backbone, and by chemical bonds between paired bases, creating a helix.
- The pairing of the bases is specific: A will only pair with T and G will only pair with C.
- The bonds that hold the bases together are weak (hydrogen bonds).
- The bonds holding the backbone sugars and phosphates together are strong (covalent bonds). Thus, the backbone remains intact when the bonds between the paired bases are broken.
- Covalent bonding requires energy. Each nucleotide entering the DNA strand arrives with two additional phosphates bonded to its single phosphate. The energy residing in that bond of two phosphates is used to create the new bond between the phosphate of the entering nucleotide and the sugar of the nucleotide just preceding it. The two extra phosphates are discarded in the process.
3. DNA Chain Orientation and Helix Formation
DNA exists in nature as long oppositely oriented chains held together by bonds between their paired bases. (The phosphate end of the chain is called the 5 prime (5’) end, and the sugar end is called the 3 prime (3’) end. The model cannot be assembled properly if this property is ignored.
The angle between the plane of the bases and the sugar to which each base is attached (36°) causes the double chain to take the form of a double helix, with ten pairs of bases per single turn of the helix (360°).
4. DNA Replication
A double helix is accurately replicated when proteins (represented by your hands):
- separate the two strands of a single DNA helix,
- attach new DNA nucleotide bases to their complements on the “mother” strands,
- and link the new DNA nucleotide sugar/phosphates one to another to form two new identical DNA molecules.
5. DNA as Information
The information for building proteins, cells, you, and every other living thing is encoded in DNA as sequences of nucleotides (Analogous to the sequences of letters in language, digits in programming and dots and dashes in Morse code.)
Over long periods of time, information is altered by mutations, which are changes in nucleotide sequences.
6. The Location in the Cell Where These Processes Occur
DNA replication takes place in the nucleus of cells that have a nucleus (eukaryotic cells),
And in the cytoplasm of cells that don’t (prokaryotic cells).
7. Genetic Mutation and Repair
Excision repair – when damaged, say by laser or radiation, a mutated nucleotide flips out, is removed and replaced by the correct nucleotide.
Non-excision repair –a mutated nucleotide flips out, is chemically modified and returns to bond with its complement.
8. Scale Dramatization
If the entire DNA in only one human cell were stretched out in one long strand it would be about 1 meter long. If the same amount were represented by the model and similarly stretched out, it would be about 93,000 miles long…
9. Genetic Chains are Looooong
The full length of human DNA is many millions of nucleotides long. The average gene is over one thousand nucleotides. A gene of that length would produce a protein over three hundred amino acids long. Some genes are more than three times that length. The model is designed to illustrate the principles, but obviously, it cannot convey the actual length of DNA molecules.
If you wish to go further and discover the forms and functions of RNA, tRNA and amino acids, and demonstrate not only DNA replication, but transcription and translation as well, contact TeachDNA at firstname.lastname@example.org.