Skip to 0 minutes and 15 seconds Welcome to the next video for ‘Cancer in the 21st century; The Genomic Revolution’. Previously we’ve looked at cells, their components, and how they work and are controlled by genes under normal conditions. So we can now move on to thinking about how cells grow and divide and how these processes are normally regulated, before we begin to consider how these processes are interrupted in cancer cells. So what is the cell cycle? In most eukaryotic cells there is a series of events which must occur in a particular order which ultimately results in the cell’s division and duplication or replication.
Skip to 0 minutes and 58 seconds The phases or steps in the cycle are controlled by checkpoints, which prevent the cell cycle progressing to subsequent stages until all the necessary molecular events have occurred. Cells begin the cycle by entering interphase. Interphase is where the cell prepares for division by growing and duplicating it’s DNA. Interphase can be further broken down into three discrete phases– G1, S, and G2. In G1, normal cellular functions occur, as well as cell growth where organelle and cytoskeletal components increase. S is the synthesis stage. Nuclear DNA replicates producing two identical copies of each chromosome. During the G2 phase, the cell continues to grow and prepare for mitosis and cell division.
Skip to 1 minute and 58 seconds Mitosis– or the M-phase– can be further subdivided into prophase, metaphase, anaphase, and telophase. During prophase, the chromosomes become visible and condense. Each identical copy of a single chromosome is known as a sister chromatid. At this point the nuclear envelope breaks down, and spindle fibres form as microtubules from the centriole structures which move to opposite poles of the cell. During metaphase, the chromosomes line up along the equator of the cell also known as the metaphase plate. The spindle fibres are fully formed, and the microtubules attach to each sister chromatid. The next phase of mitosis is anaphase, which occurs when the chromosomes begin to move away from each other along the spindle fibres and towards the poles.
Skip to 2 minutes and 59 seconds Finally in telophase, the two groups of chromosomes reach the opposite poles of the cell, and a new nuclear envelope begins to form. The chromosomes then uncoil and the spindle disappears.
Skip to 3 minutes and 14 seconds The division of the cytoplasm and other cellular organelles is called cytokinesis. The result of mitosis and cytokinesis is two genetically identical daughter cells. Some cells, following M-phase, enter a resting phase known as G0, where the cell has left the cycle and has stopped dividing.
Skip to 3 minutes and 39 seconds To ensure that only those cells which are fit for division progress through the interphase to M-phase, there are a series of checkpoints throughout the different phases.
Skip to 3 minutes and 52 seconds The three major cell cycle checkpoints are G1/S– which monitors factors such as cell size, growth factors, nutrients, and DNA damage; G2/M– where cell size, successful and complete replication and DNA damage after S-phase are assessed; and finally the M-phase checkpoint where the attachment of chromosomes to spindle in anaphase is monitored.
Skip to 4 minutes and 24 seconds The control and regulation of the cell cycle is essential in ensuring genomic integrity from cell division to cell division and is the process whereby a single fertilised embryo can develop and grow into mature organism. It is easy to see why mutations in essential genes required for regulation of this cycle– for example P53 or RB– can contribute to tumour formation as the cells leave this normal cycle. Now that we understand the basics of how the cell controls these processes, we can go on to look at cancer as a multi-state process involving mutations in different genes some of which have a known relationship and role within the cell cycle.
All under control: the cell cycle and checkpoints
Kathleen Murphy describes the basics of the cell cycle, providing us with fundamental knowledge, key to understanding how a normal cell controls growth and division.
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