Apoptosis can occur when a cell is damaged beyond repair, infected with a virus, or undergoes stress conditions such as starvation. DNA damage from ionizing radiation or toxic chemicals can also induce 1) ___ via the actions of the tumor-suppressing gene p53, also known as protein 53 (TP53), which regulates the cell cycle and hence functions as a tumor suppressor. If the TP53 gene is damaged, tumor suppression is severely reduced. The “decision” for apoptosis can come from the cell itself, from the surrounding tissue, or from a cell that is part of the 2) ___ system. In these cases apoptosis functions to remove the damaged cell, preventing it from sapping further nutrients from the 3) ___, or to prevent the spread of viral infection. Apoptosis also plays a role in preventing cancer. If a cell is unable to undergo apoptosis, due to mutation or biochemical inhibition, it can continue dividing and develop into a 4) ___. For example, infection by papilloma viruses causes a viral gene to interfere with the cell’s p53 protein, an important member of the apoptotic pathway. This interference in the apoptotic capability of the cell plays a critical role in the development of 5) ___ cancer. Apoptosis is a form of programmed cell death in multicellular organisms. It is one of the main types of programmed cell death (PCD) and involves a series of biochemical events leading to a characteristic cell morphology and death. Processes of disposal of cellular debris whose results do not damage the organism differentiates apoptosis from necrosis, which is a form of traumatic cell death, resulting from acute cellular injury. Apoptosis confers advantages during an organism’s life cycle. For example, the differentiation of fingers and toes in a developing human embryo occurs because cells between the fingers apoptose; the result is that the digits are separate. Between 50 billion and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day. In a year, this amounts to the proliferation and subsequent destruction of a mass of cells equal to an individual’s body weight. Research on apoptosis has increased substantially since the early 1990s. In addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in an extensive variety of diseases. where an insufficient amount results in uncontrolled cell proliferation, such as 6) ___.

ANSWERS: 1) apoptosis; 2) immune; 3) organism; 4) tumor; 5) cervical; 6) cancer