My AP Biology Thoughts  Unit 2 Cell Structure and Function

Welcome to My AP Biology Thoughts podcast, my name is Sid and I am your host for episode #64 called Unit 2 Cell Structure and Function: Why Apoptosis? 

Segment 1: Introduction to Apoptosis

Apoptosis is when a cell undergoes a programmed death. This is different from necrosis which is when cells die from injuries. Apoptosis is the most convenient way for an organism to remove cells that need to be removed.

 Segment 2: More About Apoptosis

In apoptosis a cell commits suicide for a variety of reasons. One reason could be because some cells need to be removed in order to shape a structure. For most organisms, especially those with hands and feet, apoptosis is necessary for proper growth and development. For organisms with hands and feet, the hands and feet start off as a block of tissue that needs to have some cells removed so it can take a shape where it can be useful. To the organism. An example of this comes from the human hand. Hands are formed from larger blocks of tissue. Some parts of this larger block need to be removed so the block of tissue can take the structure of a hand. The cells that need to be removed go through apoptosis. This process also happens on other structures like the tails of tadpoles. Another reason why cells may need to go through apoptosis is because they are damaged or infected. If the DNA in a cell is damaged, this could potentially negatively affect the entire organism. Because of this the cell will go through apoptosis to ensure it won’t do any damage to the organism. Another way the cell could be damaged is by viral infections. If a virus has infected a cell, the cell will undergo apoptosis. Apoptosis also happens when cells need to be taken away to maintain balance, or if the cell was somewhere for a temporary task and is no longer needed.

What happens to a cell that undergoes apoptosis? They start off by shrinking while bubble-like structures form around the surface of the membrane. The DNA as well as organelles then get cut into smaller pieces. These pieces end up trapped in membranes which then signal phagocytic cells to come to them. What’s different about the membranes, that the pieces are enclosed in, is that there is a lipid called phosphatidylserine (fosfa-tidal-serine) that’s on the surface when it’s usually on the inside of the membrane. This lipid allows the phagocytic cells to envelop them.

Another reason that apoptosis is important is because it helps prevent cancerous, infected cells or damaged cells from damaging the organism by killing those cells before they can do any harm. When a cell’s DNA is damaged, it can go through repairs to fix it, but these repairs can only go so far. If the DNA is damaged to the point where it cannot be repaired, the cell undergoes apoptosis. Now on to cancerous cells. Before cells become cancerous, they normally use internal apoptosis cues which allows them to die off before any harm is done. Sometimes though, the cancerous cells can avoid the internal apoptosis cue and will not die. If this happens, then immune cells can detect them and force the cell to go through apoptosis through an external cue. If a cancerous cell is somehow able to avoid both the cues, then it will be able to divide and mutate which could be harmful or fatal to the organism.

Segment 3: Connection to the Course

Apoptosis is one of the most...