The baby in Figure \(\PageIndex{1}\) has a lot of growing to do before they are as big as their mom. Most of their growth will be the result of cell division. By the time the baby is an adult, their body will consist of trillions of cells. Cell division is just one of the stages that all cells go
through during their life. This includes cells that are harmful, such as cancer cells. Cancer cells divide more often than normal cells and grow out of control. In fact, this is how cancer cells cause illness. In this concept, you will read about how cells divide, what other stages cells go through, and what causes cancer cells to divide out of control and harm the body. The Cell CycleCell division is the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells. How this happens depends on whether the cell is prokaryotic or eukaryotic. Cell division is simpler in prokaryotes than eukaryotes because prokaryotic cells themselves are simpler. Prokaryotic cells have a single circular chromosome, no nucleus, and few other organelles. Eukaryotic cells, in contrast, have multiple chromosomes contained within a nucleus and many other organelles. All of these cell parts must be duplicated and then separated when the cell divides. Cell division is just one of several stages that a cell goes through during its lifetime. The cell cycle is a repeating series of events that include growth, DNA synthesis, and cell division. The cell cycle in prokaryotes is quite simple: the cell grows, its DNA replicates, and the cell divides. This form of division in prokaryotes is called asexual reproduction. In eukaryotes, the cell cycle is more complicated. Eukaryotic Cell CycleFigure \(\PageIndex{2}\) represents the cell cycle of a eukaryotic cell. As you can see, the eukaryotic cell cycle has several phases. The mitotic phase (M) includes both mitosis and cytokinesis. This is when the nucleus and then the cytoplasm divide. The other three phases (G1, S, and G2) are generally grouped together as interphase. During interphase, the cell grows, performs routine life processes, and prepares to divide. These phases are discussed below. InterphaseThe Interphase of the eukaryotic cell cycle can be subdivided into the following phases (Figure \(\PageIndex{2}\)).
Mitotic PhaseBefore a eukaryotic cell divides, all the DNA in the cell’s multiple chromosomes is replicated. Its organelles are also duplicated. This happens in the interphase. Then, when the cell divides (mitotic phase), it occurs in two major steps, called mitosis and cytokinesis, both of which are described in greater detail in the concept Mitotic Phase: Mitosis and Cytokinesis.
Control of the Cell CycleIf the cell cycle occurred without regulation, cells might go from one phase to the next before they were ready. What controls the cell cycle? How does the cell know when to grow, synthesize DNA, and divide? The cell cycle is controlled mainly by regulatory proteins. These proteins control the cycle by signaling the cell to either start or delay the next phase of the cycle. They ensure that the cell completes the previous phase before moving on. Regulatory proteins control the cell cycle at key checkpoints, which are shown in Figure \(\PageIndex{3}\). There are a number of main checkpoints:
Cancer and the Cell CycleCancer is a disease that occurs when the cell cycle is no longer regulated. This happens because a cell’s DNA becomes damaged. This results in mutations in the genes that regulate the cell cycle. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor (see Figure \(\PageIndex{4}\)). The rapidly dividing cells take up nutrients and space that normal cells need. This can damage tissues and organs and eventually lead to death. When uncontrolled cell division happens in the bone marrow, abnormal and nonfunctional blood cells are produced because the division is happening before the cell is ready for division. In these types of cancer, there is not any evident tumor. Figure \(\PageIndex{4}\): Gross appearance of an opened large intestine specimen containing an invasive colorectal carcinoma and two adenomatous polyps. The cancer cells have grown out of control and forming a tumor.Feature: Human Biology in the NewsHenrietta Lacks sought treatment for her cancer at Johns Hopkins University Hospital at a time when researchers were trying to grow human cells in the lab for medical testing. Despite many attempts, the cells always died before they had undergone many cell divisions. Mrs. Lacks's doctor took a small sample of cells from her tumor without her knowledge and gave them to a Johns Hopkins researcher, who tried to grow them on a culture plate. For the first time in history, human cells grown on a culture plate kept dividing...and dividing and dividing and dividing. Copies of Henrietta's Lacks cells — called HeLa cells for her name — are still alive today. In fact, there are currently many billions of HeLa cells in laboratories around the world! Figure \(\PageIndex{5}\): Fluorescently dyed HeLa Cells. The woman named Henrietta Lacks died in 1951 of an unusual form of cervical cancer, she was just 31 years old. A poor, African-American tobacco farmer and mother of five, she (or at least her cells) would eventually be called immortal.Why Henrietta Lacks' cells lived on when other human cells did not is still something of a mystery, but they are clearly extremely hardy and resilient cells. By 1953, when researchers learned of their ability to keep dividing indefinitely, factories were set up to start producing the cells commercially on a large scale for medical research. Since then, HeLa cells have been used in thousands of studies and have made possible hundreds of medical advances. For example, Jonas Salk used the cells in the early 1950s to test his polio vaccine. Over the decades since then, HeLa cells have been used to make important discoveries in the study of cancer, AIDS, and many other diseases. The cells were even sent to space on early space missions to learn how human cells respond to zero gravity. HeLa cells were also the first human cells ever cloned, and their genes were some of the first ever mapped. It is almost impossible to overestimate the profound importance of HeLa cells to human biology and medicine. You would think that Henrietta Lacks' name would be well known in medical history for her unparalleled contributions to biomedical research. However, until 2010, her story was virtually unknown. That year, a science writer named Rebecca Skloot published a nonfiction book about Henrietta Lacks, named The Immortal Life of Henrietta Lacks. Based on a decade of research, the book is riveting, and it became an almost instantaneous best seller. As of 2016, Oprah Winfrey and collaborators planned to make a movie based on the book, and in recent years, numerous articles about Henrietta Lacks have appeared in the press. Ironically, Henrietta herself never knew her cells had been taken, and neither did her family. While her cells were making a lot of money and building scientific careers, her children were living in poverty, too poor to afford medical insurance. The story of Henrietta Lacks and her immortal cells raises ethical issues about human tissues and who controls them in biomedical research. However, there is no question that Henrietta Lacks deserves far more recognition for her contribution to the advancement of science and medicine. Review
Explore MoreThe video below discusses the cell cycle and how it relates to cancer. Attributions
What are the two division of eukaryotic cells?the actual division of the nucleus, called mitosis; 2.) the division of the cytoplasmic material— cytokinesis—into two daughter cells after the nuclear division; and 3.) the interphase just before and after division. The division to produce sex cells ( gametes) is called meiosis and involves still other complications.
What is prokaryotic cell division?The cell division process of prokaryotes (such as E. coli bacteria) is called binary fission. For unicellular organisms, cell division is the only method to produce new individuals. The outcome of this type of cell reproduction is a pair of daughter cells that are genetically identical to the parent cell.
What is prokaryotic and eukaryotic cell division?Definition. Prokaryotic cell division refers to the process responsible for the production of new cells through binary fission while eukaryotic cell division refers to the process responsible for the production of new cells either through mitosis or meiosis.
What are the three main divisions of a eukaryotic cell?The three main parts of a eukaryotic cell are the cell membrane, the cytoplasm and the nucleus.
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