STOCKHOLM — Japanese biologist Yoshinori Ohsumi won the Nobel Prize in medicine on Monday for discoveries on how cells break down and recycle content, a garbage disposal system that scientists hope to harness in the fight against cancer, Alzheimer's and other diseases.

The Karolinska Institute honored Ohsumi for "brilliant experiments" in the 1990s on autophagy, a phenomenon that literally means "self-eating" and describes how cells gobble up damaged content and provide building blocks for renewal.

Disrupted autophagy has been linked to several diseases including Parkinson's, diabetes and cancer, the prize committee said.

"Intense research is now ongoing to develop drugs that can target autophagy in various diseases," it said in its citation .

Ohsumi, 71, from Fukuoka, Japan, is a professor at the Tokyo Institute of Technology. In 2012, he won the Kyoto Prize, Japan's highest private award for global achievement.

Ohsumi said he never thought he would win a Nobel Prize for his work, which he said involved studying yeast in a microscope day after day for decades.

"As a boy, the Nobel Prize was a dream, but after starting my research, it was out of my picture," he told reporters in Tokyo.

"I don't feel comfortable competing with many people, and instead I find it more enjoyable doing something nobody else is doing," Ohsumi added. "In a way, that's what science is all about, and the joy of finding something inspires me."

Nobel committee secretary Thomas Perlmann said Ohsumi seemed surprised when he was informed he had won the Nobel Prize.

"The first thing he said was 'ahhh.' He was very, very pleased," Perlmann said.

Nobel judges often award discoveries made decades ago, to make sure they have stood the test of time.

Though scientists have known that autophagy exists for more than 50 years, its fundamental significance was only recognized after Ohsumi's "paradigm-shifting research" on yeast in the 1990s, the committee said.

"Thanks to Ohsumi and others following in his footsteps, we now know that autophagy controls important physiological functions where cellular components need to be degraded and recycled," it said.

The term autophagy was coined in 1963 by Belgian scientist Christian de Duve, who shared the 1974 Nobel Prize in medicine for discoveries on cell structure and organization.

But before Ohsumi's research, scientists "didn't know what it did, they didn't know how it was controlled and they didn't know what it was relevant for," said David Rubinsztein, deputy director of the Institute for Medical Research at the University of Cambridge.

Now "we know that autophagy is important for a host of important mammalian functions." For example, it protects against starvation in the period when a newborn animal hasn't yet started breastfeeding, by providing energy, he said.

It also removes proteins that clump together abnormally in brain cells, which is important in conditions like Huntington's and Parkinson's diseases and some forms of dementia. If autophagy didn't do that job, "the diseases would appear more early and be more aggressive," he said.

Animal studies suggest that boosting autophagy can ease and delay such diseases, said Rubinsztein, whose lab is pursuing that approach for therapy.

"As time goes on, people are finding connections with more and more diseases" and normal cellular operations, he said.

In 1993 Ohsumi published his "seminal discovery" of 15 genes crucial to autophagy, and cloned several of those genes in yeast and mammalian cells in subsequent studies, the Nobel committee said.

"He actually unraveled which are the components which actually perform this whole process," said Rune Toftgard, chairman of the Nobel Assembly. "Having those components at hand were also important tools to ... do functional experiments to understand how important it was for different types of processes in the body."

In Tokyo, Ohsumi said many details of autophagy are yet to be understood and that he hoped younger scientists would join him in looking for the answers.

"There is no finish line for science. When I find an answer to one question, another question comes up. I have never thought I have solved all the questions," he said. "So I have to keep asking questions to yeast."

It was the 107th award in the medicine category since the first Nobel Prizes were handed out in 1905.

Last year's prize was shared by three scientists who developed treatments for malaria and other tropical diseases.

The announcements continue with physics on Tuesday, chemistry on Wednesday and the Nobel Peace Prize on Friday. The economics and literature awards will be announced next week.

Each prize is worth 8 million kronor ($930,000). The awards will be handed out at prize ceremonies in Stockholm and Oslo on Dec. 10, the anniversary of prize founder Alfred Nobel's death in 1896.

Associated Press writers Keith Moore in Stockholm, Malcolm Ritter in New York and Mari Yamaguchi in Tokyo contributed to this report.