You’re going to explore what DNA is! By the end of this exercise, you’ll understand the statement below:
DNA is a strand of smaller molecules called nucleotides. Like a pearl necklace, nucleotides are strung together to form a strand of DNA. Two strands of DNA side-by-side bind together to form the double helix. A long DNA double helix can be called a chromosome, and all the DNA of an organism’s cell (one or many chromosomes) is what makes up a genome.
What is DNA made of?
DNA is made up of elements from the periodic table. Carbon, hydrogen, oxygen, phosphorous, and nitrogen (CHOPN) bond together create nucleotides, the building blocks of DNA.
Learn about nucleotides
Cells are able to put together atoms in the cell to first form molecules called Nucleosides, which are then later turned into Nucleotides. The Nucleoside molecules, Adenosine, Cytidine, Guanosine, and Thymidine are commonly abbreviated as A, C, G, T. If you look closely at these molecules, you won’t see any “P” (phosphorous) in them. Where is the phosphorous?
Lets see where nucleotides come from!
Make a DNA strand
To form a nucleotide, you also need phosphate!
Phosphate, is a molecule made up of phosphorus surrounded by oxygen atoms. When the cell adds a phosphate to a nucleoside, it can then be called a nucleotide. Nucleotides are what make up a DNA strand.
Drag Adenosine onto the correct point of the DNA Strand
Great! Now Drag Cytidine to the correct place
Nice one! Now Drag Guanosine to the correct place
Just about done! Drag Thymidine to the correct place
All nucleosides are in place! Bind them together with Phosphate. Notice the phosphate will bind to the ribose sugar rings, forming the sugar-phsophate backbone
Learn About Double Helix
Done! You’ve built a DNA strand that includes all four DNA nucleotides, Adenosine (A), Thymidine (T), Guanosine (G), and Cytidine (C).
Are you familiar with the term “Double Helix”?
Two DNA strands can come together to form “double stranded DNA”. This is also the infamous Double Helix structure that was discovered in 1953 at the University of Cambridge due to work by Francis Crick, James Watson, Rosalind Franklin, and Maurice Wilkens
How does your DNA strand form a double helix?
Build a Double Helix
All atoms can bond with other atoms. Bonding is an attractive force between atoms. One very important kind of bond is called a hydrogen bond. Hydrogen bonds make use of the fact that (+) charges are attracted to (-) charges.
Certain hydrogen atoms (H) in DNA are (+) charged and interact with other oxygen and nitrogen atoms in DNA, which are are (-) charged.
Two DNA Strands, like the one you made can zip together via hydrogen bonds.
View Hydrogen Bonds
Reference Material on Bonding: Chapter 6 of Zero to Genetic Engineering Hero
Rules of Zipping
There are rules on how two strands of DNA can "zip" together. Two strands together are called “Complementary Strands”.
Before the structure of DNA was discovered, a famous scientist called Erwin Chargaff discovered that the amount of A’s and T’s in organism's DNA were similar, and G’s and C’s were similar.
This led Francis Crick and James Watson to realize that, in a double helix:
A’s must bind T’s (and T’s bind A’s)
G’s must bind C’s (and C’s bind Gs)
All atoms can bond with other atoms. Bonding is an attractive force between atoms. One very important kind of bond is called a Hydrogen Bond.
Hydrogen bonds happen when Hydrogen atoms in molecules (which are slightly (+) chaged) interact with other atoms that are slightly (-) charged (like oxygen and nitrogen)
Two DNA Strands, like the one you make can zip together via hydrogen bonds.
Build a Complementary Strand.
Use Chargaff’s Rule
Place the “A” into the correct position
Place the “C” into the correct position
Place the “T” into the correct position
Place the “G” into the correct position
What about Genomes?
Nice Job! You’ve built two Complementary Strands of DNA.
When bound together, using Hydrogen bonding and following Chargaff’s Rule, they form a helical structure, called the Double Helix.
Suggested Reference Material:
Chapter 1 of Zero to Genetic Engineering Hero
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Made with help from Wikipedia
Congratulations! You built your first DNA strand!
Extract DNA from Strawberry
The Nucleotide molecules, Adenosine, Cytidine, Guanosine, and Thymidine are commonly abbreviated as A, C, G, T. These are the "Building Blocks" of DNA
How do they fit together?
Note: Nucleotides have a phosphate, nucleosides, do not
Next: Plant Genome
Locate Genome In Human Cell
Humans are made up of an estimated one trillion cells. There are hundreds to thousands of different types of cells that make up the human body.
With the exception of mature Red Blood Cells, each human cell has a copy of that person’s genome.
Human cells are much more complicated than bacteria cells and this shows in the size of a human genome. The human genome is about 3,000,000,000 base pairs long. This is about 1000x larger than bacterial genomes!
Unlike how an E. coli bacterium genome is one chromosome, a human genome is made up of 46 chromosomes.
You just built a short double stranded DNA molecule that has four nucleotides in each strand. Complementary pairs of nucleotides (e.g. A-T, C-G) are sometimes called basepairs. In other words, your double stranded DNA was four base pairs long.
Long strings of double stranded DNA are what make up plasmids and chromosomes. Some organisms (like humans) have many chromosomes of DNA. All of the DNA in an organism make up its genome.
A virus is a microscopic infectious agent that is only able to “grow” and replicate when it is inside the cell of a living organism (such as bacteria, plant cells, or human cells). Viruses are non-living.
The Lambda Phage is a virus that infects bacteria. The genome of Lambda Phage is 48,502 base pairs long. That is more than 10,000 times longer than the DNA you created!
You’ve probably heard of viruses like Chicken Pox. Like Lambda Phage, they have their own genomes of comparable sizes.
Locate Viral Genome
Next: Bacteria Genome
Locate Bacterium Genome
Next: Human Genome
Bacteria are more complicated than viruses. Bacteria are able to grow and function independently.
Bacteria, like E. coli bacteria have a single large chromosome that is 4,600,000 base pairs long and is responsible for growth and maintenance of the cell. E. coli and other bacteria can also have extra small circular pieces of DNA called plasmids that are ~5,000 base pairs long. These plasmids can have extra information that give the bacteria an advantage, such as antibiotic resistance.
The E. coli genome is about 100x larger than a viral genome.
Locate Genome in Plant Cell
Paris japonica Genome
The largest known genome is 150,000,000,000 base pairs. Thats right, the largest genome we know of is in a plant!
This genome is 50 times larger than the human genome.
Take me back
DNA is made up of elements from the periodic table. Carbon, hydrogen, oxygen, phosphorous, and Nitrogen (CHOPN - remember “chopping”)) together create nucleotides, the building blocks of DNA
DNA is a string of smaller molecules called nucleotides. Like a pearl necklace, nucleotides are strung together by a cell to form a strand of DNA. Two strands of DNA side-by-side can bind together to form a double helix. A long DNA double helix can be called a chromosome, and all the DNA of an organism’s cell (one or many chromosomes) is what makes up an organisms genome.
Do you remember what CHOPN stands for? Say it out loud!
Show me the Backbone!
A DNA strand is a string of nucleotides. The A’s, T’s, C’s, and G’s can go in any order and the DNA strand can be hundreds of millions of nucleotides long! The order of the nucldeotides is the secret information that the cell knows how to read and write.
The phosphate of one nucleotide becomes bonded to the ribose sugar ring of another nucleotide. This often referred to as the sugar-phosphate backbone.
Start Building a Strand!
When a cell assembles DNA using a protein enzyme called “DNA polymerase”, it assembles nucleotides (which have phosphates attached).
In the following exercise, you’ll be building a DNA strand, but the phosphate is separated from the nucleotides. This is only to emphasize the sugar-phosphate backbone!