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Animations
(Animation Requirements)

• Nine Animations

Reading DNA
In this exercise, you can explore how regulatory proteins "read" DNA, design proteins with different structural motifs, and test these hypothetical proteins against particular DNA sequences.

Gene Regulation
This exercise explores the various strategies employed by organisms to regulate the transcription of genes. You can examine bacterial gene regulation and eukaryotic gene regulation.

Ribosomes Are Ribozymes. The machine within the cell that manufactures proteins is a complex of proteins and RNA molecules called a ribosome. Because the enzymes of the cell are proteins, it had been commonly assumed that the proteins of the ribosomes did the actual chemistry of protein synthesis, the RNA molecules carrying out secondary roles. Recently scientists completed the first detailed analysis of the structure of a ribosome at atomic resolution, and they had quite a surprise. The researchers found that the many proteins of a ribosome are scattered over its surface like decorations on a Christmas tree, linking RNA strands together at key positions like spot-welds. Inside, where the protein-building takes place, there are no proteins, just twists of RNA. It is this RNA that catalyzes the linking together of amino acids to make a new protein. The RNA of the ribosome is acting like an enzyme — "ribozyme."

1. The fact that ribosomes carry out catalysis may shed light on the origin of life.

Unraveling the Mystery of DNA
The realization that Mendel's patterns of heredity can be explained by the segregation of chromosomes in meiosis raised a question that occupied biologists for 50 years: What exactly is the nature of the connection between hereditary traits and chromosomes? In this lecture we recount the chain of experiments that led to our current understanding of the molecular mechanisms of hereditary. The experiments are among the most elegant in science. Just as in a good detective story, each conclusion has led to new questions. The intellectual path has not always been a straight one, the best questions not always obvious. But however erratic and lurching the course of the experimental journey, our picture of heredity has become progressively clearer, the image more sharply defined. As we have mastered the details of what a gene is, and of how genes do their job of dictating what we are like, DNA has become a household word, and its study the core of the new science of molecular biology. Little of biology, from taxonomy and botany to genetics and cell biology, can be properly understood except in the context of DNA.

Cyanobacteria Control Heterocyst Pattern Formation Through Intracellular Signaling
The regulation of pattern formation in an organism is a fundamental aspect of its development. Pattern formation is under strict genetic regulation, whether in large multicellular organisms or simple bacteria. Studying simple systems is a good way to uncover basic mechanisms. Cyanobacteria, for example, are photosynthetic prokaryotic cells that grow together in filaments. These cyanobacterial filaments exhibit a simple developmental pattern: single heterocysts (specialized nitrogen-fixing cells) are separated by approximately ten photosynthetic vegetative cells. James Golden and Ho-Sung Yoon at Texas A&M University have identified a small gene, called patS, that appears to be crucial for the formation and maintenance of proper pattern formation of heterocysts and vegetative cells. To investigate how patS controls heterocyst pattern, Golden and Yoon examined the effects of different levels of patS transcription on heterocyst formation. They found that the patS gene makes a diffusible protein that inhibits the formation of adjacent heterocysts, in this way maintaining a minimum number of ten vegetative cells in between heterocysts.