Explore a Stretch of Code

Resource for Grades 9-12

WGBH: Nova
Explore a Stretch of Code

Media Type:
Interactive

Running Time:
Size: 545.9 KB


Source: NOVA: "Cracking the Code of Life" Web site

This resource can be found on the NOVA: “Cracking the Code of Life" Web site.

Resource Produced by:

WGBH Educational Foundation

Collection Developed by:

WGBH Educational Foundation

Collection Credits

Collection Funded by:

National Science Foundation

Relative to the entire genome, genes are mere fragments of genetic code. But for the researchers who study the hundreds to millions of letters that can make up a single gene, they're big fragments. See for yourself in this interactive feature from the NOVA "Cracking the Code of Life" Web site.

open Background Essay

Genetic information is coded in DNA molecules. Every one of our cells (except red blood cells) contains a nucleus, and inside the nucleus are chromosomes. Chromosomes are built from long strands of a molecule called deoxyribonucleic acid (DNA). The twisted ladder-shaped DNA molecule is made of smaller molecules called nucleotides, or bases, that pair up and form the ladder's rungs. Though there are only four different types of nucleotides in a strand of DNA (usually referred to by the first letter of their chemical name -- A, T, C, and G), these molecules are repeated again and again -- three billion times in the human genome.

Genes are specific sequences of DNA that provide the code for building particular proteins, a two-step process. First, DNA is transcribed into a similar molecule called RNA. Then it is translated into a specific type of protein. In many cases, one gene codes for one type of protein. But that's not always the case. Humans, for example, have a low gene count relative to our high level of complexity. Higher animals like humans have evolved greater complexity, not by acquiring more genes, but by using their genes in multiple ways to create a wide variety of different kinds of proteins. About a third of all human genes code for several, sometimes many, different proteins through a process called "alternative splicing," which occurs as RNA is being translated into proteins.

To understand this process, think of a segment of RNA as a compound word: The word alternative, for example, can be read as a single word, or it can be split to form two new words, alter and native, that have entirely different meanings. Similarly, RNA can create proteins with its entire length, or with shorter sections that independently create their own proteins. This alternative splicing, in which one section of RNA is active at one time and another section is active at a different time, often corresponds to different stages in the growth of cells, as the protein needs of the cells change.


open Discussion Questions

  • What are some of the segments of DNA code that geneticists have identified, and what roles do these segments play?
  • Where is there evidence for our evolution in our DNA code?
  • What is the significance of the on-off switch and how might a mutation in that section lead to changes in the anatomy or physiology of an organism?

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