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This is a DNA molecule. It is what contains the 

genetic material of every living thing. It is in all of 

your cells, and tells them what to do. There are 6 

feet of DNA in each and every one of your 

hundreds of trillions of cells. 

Shown on the right is a nucleotide. 

DNA molecules are a string of these. 

The sugar and phosphate are the 

"backbone" of the molecule, 

represented as the D and P on the 

molecule diagram. The nitrogenous 

bases are what line up in the middle.

A-Adenine

G-Guanine

T-Thymine

C-Cytosine

The nitrogen bases can be any of the 

molecules listed. When they attach, 

adenine joins with thymine, and 

guanine joins with cytosine. The 

sequence of nitrogenous bases 

determines everything about you.

Check Your Understanding

What are the different parts of a 

nucleotide?

What are the four nitrogen bases 

called?

Check Your Understanding

The phosphate, sugar, and nitrogen 

base.

Adenine, Guanine, Thymine, and 

Cytosine.

For a cell to reproduce, it must first 

duplicate its DNA. To do this, first an 

enzyme called helicase splits the strand 

in half. Then, another enzyme, called 

DNA polymerase, creates new strands. 

The result is two new molecules that 

are identical to the original.

Pictured here is a strand of RNA. 

You'll notice it's similar to DNA, with 

one key difference -- it has only one 

strand. RNA is copied from the DNA 

in a process called transcription. 

This is transcription. RNA polymerase 

splits the DNA, creates a corresponding 

RNA strand, and rejoins the DNA.

As you can see, there is another key 

difference in the RNA structure -- there 

is no thymine. Instead, where there 

would be a T, there is a U for uracil.

What is transcription?

What difference is in the nitrogenous 

bases of DNA and RNA?

The process of creating RNA from 

DNA

DNA has thymine; RNA has uracil.

RNA's job is to make protein. There is 

one more step it must undergo to do 

this. It is called translation. The RNA 

strand we have been discussing, called 

mRNA (messenger RNA), holds the 

code. A ribosome reads the code to 

make protein using rRNA (ribosomal 

RNA).

The molecule above is called tRNA 

(transfer RNA). Beneath it is a set of 3 

nitrogen bases on mRNA, called a codon. 

The codon on the mRNA matches with a 

corresponding anticodon on the tRNA. The 

amino acid then detaches. This continues 

with many codons to make a polypeptide 

chain, which forms a protein.

What does translation create?

Name the molecules involved.

Protein.

mRNA, tRNA, rRNA, amino acids

Sometimes something goes wrong 

during translation and one of the 

nitrogen bases is misread. This is called 

a mutation. There are several different 

kinds of mutations.

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