The Cell Cycle and Cancer

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The Cell Cycle and Cancer

  1. 1. 1 The Cell Cycle, Cancer, and Mutations
  2. 2. 2 In Unit 6, you discovered that, in mitosis, you have a number of phases in the division process in which identical daughter cells are made. Those stages are: 4 Stages: “PMAT” 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Quick Review!
  3. 3. 3 Phases of the Cell Cycle • The Cell Cycle, which includes cellular division, also involves the processes occurring during interphase. A cell is actually in interphase most of the time! Look at the image below: • Interphase – G1 – primary growth – S – DNA replicated – G2 – secondary growth • M – mitosis (PMAT) • C – cytokinesis
  4. 4. 4 Interphase • G1 – Cells undergo majority of growth • S – The genome (DNA) is replicated (Synthesized) in this phase along with other small organelles needed for mitosis later. NOTE: The S Phase is where most mutations can occur as DNA is being replicated. Nucleic Acid mismatches can occur at this time. • G2 – Assembles sub-cellular machinery such as the spindles to prepare for Mitosis.
  5. 5. 5 G2 of Interphase • A nuclear envelope bounds the nucleus. • The nucleus contains one or more nucleoli (singular, nucleolus). • Two centrosomes have formed by replication of a single centrosome. • In animal cells, each centrosome features two centrioles. • Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed. G2 OF INTERPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane
  6. 6. 6 Checks and Balances • As mentioned in the Amoeba Sister’s Video, cells have checks and balances that are constantly accessing their health. Special proteins called cyclins monitor the cell’s health. • Cells determined unhealthy self-destruct in what is called “apoptosis”. In fact, our cells die quite often for many reasons. Cancer cells however, have lost this ability.
  7. 7. 7 Pause, Think, and Share • What phase is a cell in the longest period of time? Interphase • Replication occurs during what period of interphase? S-Phase • Mutations of a base would most likely occur during which phase? S-Phase Interphase
  8. 8. 8 • For many cells, the G1 checkpoint seems to be the most important • If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide • If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a non-dividing state called the G0 phase Checks and Balances (cont..)
  9. 9. 9 • Most cells in your body can detect when they are overcrowding and signals are produced to stop dividing. • Your cells also know to only grow in certain areas and on particular substrates. • Cancer cells ignore these signals. Checks and Balances (cont..)
  10. 10. 10 Cancer • Cancer is a disease of uncontrolled cell division. It starts with a single cell that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and can potentially kill the host. • Normal cells are controlled by several factors. They stay in the G1 stage of the cell cycle until they are given a specific signal to enter the S phase, in which the DNA replicates and the cell prepares for division. Cancer cells enter the S phase without waiting for a signal. • Another control: Normal cells are mortal. This means that they can divide about 50 times or so and then they lose the ability to divide and eventually die. This “clock” gets re-set during the formation of the gametes. Cancer cells escape this process of mortality: they are immortal and can divide endlessly.
  11. 11. 11 • Cancer cells that are not eliminated by the immune system form tumors, masses of abnormal cells within otherwise normal tissue • If abnormal cells remain only at the original site, the lump is called a benign tumor • Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors
  12. 12. 12 • Recent advances in understanding the cell cycle and cell cycle signaling have led to advances in cancer treatment. • Cancer.org features a number of treatments that are currently available to treat a wide variety of cancers: • http://www.cancer.org/treatment/treatm entsandsideeffects/treatmenttypes/
  13. 13. 13 All cancer is genetic, in that it is triggered by altered genes. Genes that control the orderly replication of cells become damaged, allowing the cells to reproduce without restraint. Cancer usually arises in a single cell. The cell’s progress from normal to malignant to metastatic appears to follow a series of distinct steps, each controlled by a different gene or set of genes. Many Mutations Can Lead to Cancer
  14. 14. 14 Even though all cancer is genetic, just a small portion—perhaps 5–10% —is inherited. Most cancers come from random mutations that develop in body cells during one’s lifetime— either as a mistake when cells are going through cell division or in response to injuries from environmental agents such as radiation or chemicals.
  15. 15. 15 Pause, Think, and Share • Normal cells have checks and balances that regulate cell________ Growth • Most cancers are caused by genetic_________. Mutations • Most cells live only a short while, but cancer cells are virtually _________. Immortal
  16. 16. 16 Mutations Mutations are a kind of genetic change.
  17. 17. 17 As was mentioned before, cancer, is caused by a number of mutations. These mutations can effect a number of genes. These almost always include: • Mutations in genes that are involved in mitosis • Genes that regulate apoptosis • Genes that regulate growth and aging • Genes that stimulate new blood vessel growth • And genes that keep cells in particular areas • Let’s look a few ways that mutations can happen.
  18. 18. 18 A Few types of Mutations
  19. 19. 19 Kinds of Mutations Gene Mutations * Gene mutations involving a change in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. Point mutations include substitutions, insertions, and deletions.
  20. 20. 20 Kinds of Mutations Substitutions usually affect no more than a single amino acid. Only one amino acid will not be produced. The remaining sequence is fine. Hopefully, the protein created still works. 
  21. 21. 21 Kinds of Mutations The effects of insertions or deletions are more dramatic. The addition or deletion of a nucleotide causes a shift in the grouping of codons (groups of 3 nucleotides). Changes like these are called frameshift mutations. Not good! The entire reading frame has shifted!
  22. 22. 22 Kinds of Mutations Chromosomal Mutations * Chromosomal mutations involve changes in the number or structure of chromosomes. * Chromosomal mutations include deletions, duplications, inversions, and translocations. Extra Chromosome – Down Syndrome (Trisomy 21)
  23. 23. 23 Kinds of Mutations Deletions involve the loss of all or part of a chromosome.
  24. 24. 24 Copyright Pearson Prentice Hall Kinds of Mutations Duplications produce extra copies of parts of a chromosome.
  25. 25. 25 Copyright Pearson Prentice Hall Kinds of Mutations Inversions reverse the direction of parts of chromosomes.
  26. 26. 26 Copyright Pearson Prentice Hall Kinds of Mutations Translocations occurs when part of one chromosome breaks off and attaches to another.
  27. 27. 27 Copyright Pearson Prentice Hall Significance of Mutations Significance of Mutations Many mutations have little or no effect on gene expression. Some mutations are the cause of genetic disorders. Polyploidy is the condition in which an organism has extra sets of chromosomes.
  28. 28. 28 Pause, Think, and Share • Mutations are a kind of genetic ________. change • Insertions and deletions of nucleotides can cause _______ mutations. Frameshift • Replacing a single nucleotide is called a ________ mutation. Point
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