First, beta-secretase cut the peptide chain of APP outside the cell membrane at a certain length. Then the gamma-secretase makes a cut inside the membrane, releasing the beta-amyloid.
The beta-amyloid released will be in two forms, one which has 40 amino acids and another one with 42 amino acids. The beta-amyloid peptide with 42 amino acids is the one that will cause the Alzheimer’s disease.
Initially, beta-amyloid starts as a single molecule but tends to accumulate and gradually build up to become hard, insoluble plagues. These plagues may stick to the nerve cells, interfering with the cell-to-cell communication at the synapses, and eventually leads to the death of nerve cells.
Tau protein molecules that are found in the nerve cells function to stabilize the microtubules. Tau performs this function with the aid of a protein called tubulin along with its own isoforms and phosphorylation. However, when tau protein undergoes excess phosphorylation, which means excess phosphate groups bind to the specific sites of the tau protein’s molecular chain, causing the tau protein to be seperated from the microtubules and clumps together with other separated tau, forming neurofibrillary tangles. http://thebrain.mcgill.ca/flash/d/d_08/d_08_m/d_08_m_alz/d_08_m_alz_2a.jpg
Inside the brain, the microtubules act as a transport system that carries nutrients and other essential materials through the brain cells. This transport system is organized in a parallel strand and are maintained by the tau proteins. When the tau proteins are twisted into tangles, the strands collapse and this will lead to the failure of the transport system. Thus, nutrients and other crucial substances cannot be transported along the microtubules and the brain cells will eventually die.
At the early stage of Alzheimer’s, the most common symptom a person may be suffering from is memory lapses. Particularly, they may be facing difficulty in remembering recent events or conversation, or forgetting where they have place their belongings and even get lost in a familiar street or on the way home.
As the disease progress to a later stage, individuals will start facing problem with their intellectual skills. The part of the brain that store this skill is affected by the disease, therefore They may have an impaired language and speaking skills. For example, they will be struggling to follow a conversation or thinking of common words to say during a conversation.
They will be also facing difficulty in concentrating or thinking and reason even in the simplest matter. They are also likely to have a problem with making decisions and planning an activity. All of this will affect their daily lives as they are having problem with every single task which will be hard for them to perform their daily routine. They might even need someone else’s support to help them conduct their daily basis.
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Mayo Clinic. (2015, December 22). Alzheimer’s disease Symptoms and causes. Retrieved from http://www.mayoclinic.org/diseases-conditions/alzheimers-disease/symptoms-causes/dxc-20167103
What is Alzheimer’s Disease? Retrieved from https://www.alzheimers.org.uk/site/scripts/documents_info.php?documentID=100