Scientists have pinpointed how toxic protein deposits kill off nerve cells in the brains of people with Alzheimer's disease.
Alzheimer's is linked to cell death
The international team hope the breakthrough, published in Science, could lead to new treatments.
Alzheimer's is linked to the build up of amyloid protein plaques.
The new study has shown that these plaques inflict damage by interacting with an enzyme produced in the cell's energy-producing power plants.
The interaction damages these tiny structures - known as mitochondria - and causes toxic substances to leak out into the rest of the cell, leading to its destruction.
It is thought that this loss of cells directly leads to the memory less and other symptoms associated with Alzheimer's.
The new findings are based on an analysis of brain tissue from Alzheimer's patients, and genetically engineered mice.
The researchers hope that it may eventually be possible to block or reduce the interaction between the amyloid plaques and the mitochondrial enzyme.
Dr Susanne Sorensen, head of research at the Alzheimer's Society, described the research as "very exciting".
"The link between the occurrence of amyloid plaques in the brain and the death of nerve cells has seemed obvious for many years, but there has been no clear experimental evidence for a mechanism that would explain how amyloid beta cause the death of nerve cells.
"This paper provides a possible explanation of how amyloid beta may cause cell death and points towards potential targets for drug therapy. This is very basic, but very important research.
"There is currently no real treatment for Alzheimer's disease that halts or reverses the disease."
Harriet Millward, deputy chief executive of the Alzheimer's Research, said there was some controversy over whether the enzyme - ABAD - has a role in the damage which occurs to nerve cells in an Alzheimer's brain.
She said: "More research needs to be done, but if the work from these scientists is confirmed then this enzyme could offer a route for the development of new treatments.
"This is a good progress, but unfortunately Alzheimer's is a very complex condition and much more work needs to be done before we will have an answer to this awful disease."