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It's one of the big mysteries of cell biology. Why do mitochondria-the oval-shaped structures that power our cells-have their own DNA, and why have they kept it when the cell itself has plenty of its own genetic material? A new study may have found an answer. Scientists think that mitochondria were once independent single-celled organisms until, more than a billion years ago, they were swallowed by larger cells. Instead of being digested, they settled down and developed a mutually beneficial relationship developed with their hosts that eventually enabled the rise of more complex life, like today's plants and animals.

In this video Paul Andersen explains how the mitochondria generates energy for the cell through aerobic respiration. He also explains how research into the organelle has shown its importance in eukaryotic evolution.

This case study introduces students to the structure and function of cellular organelles and seeks to show their importance by discussing diseases and disorders that can result when an organelle does not function as it should. The storyline follows a family whose joy at bringing home a new baby is soon altered by their child's sudden illness, which is eventually diagnosed as Leigh Disease. This disease occurs when defective mitochondria fail to produce energy needed by the cell, particularly affecting cells with high-energy needs like those in the brain, muscle, and gastrointestinal tract. The narrative also discusses some of the ways in which Leigh disease is inherited, treatment options, and the typical prognosis. The case was designed for an introductory non-majors biology course, but could also be used in other science or health related courses. Instructors also have the option of running the case in a "flipped classroom" in which students watch three recommended videos outside of class as a way of preparing for working on the case in class.

By early 2014, Flint, Kendler and a team of collaborators had analysed DNA sequences from 5,303 Chinese women with depression, and another 5,337 controls. As Flint expected, 85% of the depressed women had a severe form of the disorder called melancholia, which robs people of the ability to feel joy. "You can be a doting grandparent and your favourite grandchildren can show up at your door," says Douglas Levinson, a psychiatrist at Stanford University in California, "and you can't feel anything." The analysis yielded two genetic sequences that seemed to be linked to depression: one in a stretch of DNA that codes for an enzyme whose function is not fully understood, and the other next to the gene SIRT1, which is important for energy-producing cell structures called mitochondria. The correlations were confirmed in another set of more than 3,000 depressed men and women and over 3,000 controls.

Explore how ATP is made in 3 steps of aerobic cellular respiration with the Amoeba Sisters! This also compares this process to photosynthesis and introduces ATP structure. Most importantly, learn why all of this matters to you!

Paul Andersen explains how eukaryotic cells were formed through a process of endosymbiosis. He describes how aerobic bacteria became mitochondria and cyanobacteria became chloroplasts. He mentions an example of symbiosis that occurs today and mentions the importance of Dr. Lynn Margulis in the development of this modern theory.

This animation shows how glycolysis converts glucose into pyruvate through a series of enzyme reactions. It is the first of six animations about cellular respiration. These animations bring to life the molecular engines inside mitochondria that generate ATP, the main source of chemically stored energy used throughout the body.

Mitochondrial diseases are a group of disorders caused by genetic mutations. In this animation, Nature Video finds out how these diseases arise, and how new techniques can stop them being passed on from mother to child.

brief animations vividly illustrating cells and cellular processes

The behavior of a person's genes doesn't just depend on the genes' DNA sequence - it's also affected by so-called epigenetic factors. Changes in these factors can play a critical role in disease.

This PowerPoint-driven case study presents three different stories, each of which explores an aspect of membranes. The first (The Exploding Fish) covers diffusion, specifically addressing the question of why animal cells explode in freshwater but fish do not, and differences between saltwater and freshwater fish. The second case (The Pleasurable Poison) is designed to show that alcohol can slip across membranes and also highlights some of the problems of ingesting this toxin. The third case (The Dangerous Diet) explores a weight-loss drug, DNP, and how it operates in mitochondrial membranes. The first of these case studies also includes a number of "clicker" questions. These cases were originally designed for a semester-long, introductory biology course for non-majors, and instructors can choose to use one or all of the cases to suit their course.

video 13:35, In which Hank does some push ups for science and describes the "economy" of cellular respiration and the various processes whereby our bodies create energy in the form of ATP.