5

Animations
(Animation Requirements)

• Eight Animations

Art Labeling Activities

• Five Art Labeling Activities

Explorations

Enzymes in Action: Kinetics
In this exercise, you can compare catalysis ability and the effectiveness of binding a substrate among ten different enzymes.

Oxidative Respiration
In this exercise, you can vary oxygen levels, food supply, and ATP levels and explore the effects on the mitochondrial membrane.

Aging. Given enough food to live on, and protection from infectious disease, humans live quite a long time, often for 80 years or more. But they do eventually die. Is this merely a matter of our bodies wearing out, or is our eventual death somehow programmed into the human blueprint? Theories abound. Many involve the progressive accumulation of damage to DNA, as genes that prolong life often affect DNA repair processes. Other theories involve the progressive loss of telomeric DNA from the ends of chromosomes with successive cell divisions. Still other theories focus on caloric restriction, arguing for prolonging life by reducing the efficiency with which energy is gleaned from food.

1. Aging may be the body's way of preventing the development of cancer.
2. Unraveling the mystery of aging.
3. A gene mutation called "I'm not dead yet" may hold the secret of longer life.

Aging: Does Metabolism Limit Life Span?
All the activities of life — growth, communication, reproduction — require energy. It thus should come as no suprise that researchers now suggest aging is related to changes in the way we process metabolic energy. All humans die. After puberty, the rate of death increases exponentially with age. A variety of theories have been advanced to explain why. The oldest theory of aging is simply that cells accumulate mutations as they age. Other related theories focus on the idea that cells wear out over time, accumulating damage until they are no longer able to function. Free radicals produced as a by-product of oxidative metabolism can be quite destructive in a cell. Also, every time a cell divides, it loses material from the tips of its chromosomes; eventually so much is lost that the chromosome can no longer divide. Some investigators argue that a gene clock controls aging. Single gene mutations can double the life span of fruit flies. When researchers isolated the gene involved, it proved to encode a protein involved in moving preliminary products of food metabolism across membranes to where the food's processing takes place. Surveys of very-long-lived humans also point to a single gene, whose function is being eagerly sought.

How Do Proteins Help Chlorophyll Carry Out Photosynthesis?
Great advances in biology have been made in recent years, some more quietly than others. Among these has been unmasking the underlying mechanism of photosynthesis. Plants possess two kinds of photosystems (I and II) that work together to harvest light energy. In the reaction center of photosystem I, a pair of chlorophyll molecules act as the trap for photon energy, passing an excited electron onto an acceptor molecule outside the reaction center. Two proteins (PsaA and PsaB) act as scaffolds to hold the chlorophyll molecules in place. A single amino acid of the PsaB protein, dubbed His-656, has become the focus of efforts to clarify how proteins help chlorophyll carry out photosynthesis. To determine the importance of His-656, Andrew Webber of Arizona State University, working with an international research team, set out to change the animo acid located at position 656 of PsaB in order to see what effects the change might have on photosynthesis. If His-656 indeed plays a critical role in modifying the chlorophylls, then a different amino acid at that position should have profound effects.