Cell membrane diseases often result in materials not being able to properly pass through cells. This lesson will discuss how different dysfunctions of the cell membrane can cause disease in a person.
The Cell Membrane
The cell membrane, also called the plasma membrane, separates the inside of the cell from the outside environment.
It acts like the walls of your house that keep the inside and outside apart. However, your house walls don’t always stay completely closed. You can open windows and doors to let people and things in and out.
The cell membrane is similar – it can allow certain things to move into and out of the cell through various means.The cell membrane is made up of a double layer of fats and phosphates as the foundation. This only allows small, uncharged molecules to get through. You can think of a leaky basement that only allows water to get in but stops bigger things like dirt, flies, and animals. Proteins in the membrane can act as tunnels for small things to go in and out of cells. This would be like a window with screens that can still let small fruit flies into your home.
In order for larger molecules to move in and out, the cell uses special processes analogous to eating. Opening a door for a human to get into your home would be like these processes.If the cell membrane is unable to do its job properly, this can cause the cell to stop working properly. If many cells have bad cell membranes, the disease can affect an entire organ or even the whole body. In many of these cell membrane diseases, proteins within the cell membrane don’t transport materials properly. It is not necessarily that the membrane itself disappears, rather that certain parts don’t work. Water, salt, and other nutrients can become imbalanced, leading to symptoms we’ll discuss later.
Going back to the house analogy, if you removed the doors to your house, animals could move in and cause damage. If all the houses in a neighborhood lost their doors as well, the neighborhood would have major pest management concerns.
Some membrane diseases are hereditary, meaning they are passed from parents to child. One example of a genetic disease that affects cell membranes is cystic fibrosis. Cystic fibrosis is a recessive genetic disease.
This means that both parents contribute one affected gene to the child. Cystic fibrosis is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein which helps move water and salt across the cell membrane.In a patient with cystic fibrosis, the cells do not secrete enough water. When this happens in the lungs, it causes the mucus to become extremely thick. Symptoms include wheezing, persistent cough, and exercise intolerance.
Besides making breathing difficult due to the buildup of mucus, it provides a good environment for germs to grow, making the patient prone to infection. Cystic fibrosis can also cause digestive problems, including lack of weight gain, constipation, and intestinal blockage.
Some diseases of the cell membrane are caused by infections from bacteria or viruses. One example is cholera, a disease caused by the bacterium Vibrio cholerae. Cholera is essentially the opposite of cystic fibrosis. In fact, in both conditions, the same protein, CFTR, is affected. During cholera infection, the CFTR protein is attacked so that the cell secretes too much water.
This results in severe diarrhea, and dehydration is a major concern.Some scientists suggest that the gene that causes cystic fibrosis has stayed in the population so long because it offers protection against cholera. If people have one copy of the normal CFTR gene and one copy of the cystic fibrosis CFTR gene, then they are somewhat resistant to cholera. They also don’t have cystic fibrosis, so they are more likely to reach adulthood and have children who may also become carriers of the cystic fibrosis CFTR gene.
Diseases with Unknown Causes
Alzheimer’s disease is a very serious condition that involves the build-up of plaques in the brain. While we don’t completely understand what causes the initial formation of these plaques, some evidence suggests that dysfunctional membrane proteins may play a role. This is further supported by evidence showing that unhealthy cholesterol levels are often found in Alzheimer’s patients.
Cholesterol is an important part of the cell membrane.
The cell membrane is responsible for determining what goes in and out of the cell, just as the doors, windows, and screens of a house determine what goes in and out of the house. When the cell membrane is not able to do its job properly, the body can experience serious effects.
Some cell membrane diseases, such as cystic fibrosis, are hereditary, meaning they are passed down from generation to generation. Other cells membrane diseases, like cholera, can be caused by infections from bacteria or viruses. Still others, as in Alzheimer’s, have an unknown cause. Regardless of what causes the defect, understanding how cell membranes function can help find treatments for diseases.