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Understanding Cancer: Unregulated Cell Division and DNA Synthesis

This chapter discusses the basics of cancer, including unregulated cell division, tumor formation, metastasis, and the risk factors associated with cancer. It also covers the processes of DNA synthesis, mitosis, and meiosis.

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Understanding Cancer: Unregulated Cell Division and DNA Synthesis

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  1. Chapter 5 • Cancer • DNA Synthesis, Mitosis, and Meiosis Figure 5.2

  2. 5.1 Chapter 5 Section 1 What Is Cancer? Figure 5.2

  3. 5.1 What Is Cancer? What Is Cancer? • Unregulated cell division • Tumor: mass of cells with no function Malignantif tumor invadessurrounding tissue(cancerous) Tumor Metastaticif individual cells breakaway and start a newtumor elsewhere(cancerous) Normalcell Potentiallycancerouscell Benignif tumor has noeffect onsurrounding tissue(noncancerous) Normal cell division Unregulated cell division Figure 5.2

  4. 5.1 What Is Cancer? Malignantif tumor invadessurrounding tissue(cancerous) Tumor Metastaticif individual cells breakaway and start a newtumor elsewhere(cancerous) Normalcell Potentiallycancerouscell Benignif tumor has noeffect onsurrounding tissue(noncancerous) Normal cell division Unregulated cell division • Benign tumor: doesn’t affect surrounding tissues • Malignant tumor: invades surrounding tissues; cancerous • Metastasis: cells break away from a malignant tumor and start a new cancer at another location Figure 5.2

  5. 5.1 What Is Cancer? Metastatic cells • Metastatic cells can travel throughout the body via the circulatory system or the lymphatic system. • Lymphatic system collects fluid that leaks from capillaries. • Lymph nodes filter the lymph. • Cancer cells found in lymph nodes indicate metastasis has taken place.

  6. 5.1 What Is Cancer? Cancer cells differ from normal cells: • Divide when they shouldn’t • Invade surrounding tissues • Move to other locations in the body

  7. 5.1 What Is Cancer? • Risk factors: increase a person’s risk of developing a disease • Tobacco use: tobacco contains many carcinogens (chemicals that can cause cancer) • Alcohol consumption: alcohol and tobacco increase risk in multiplicative manner • High-fat, low-fiber diet

  8. 5.1 What Is Cancer? - Risk factors Risk factors continued • Lack of exercise increases risk in two ways • Exercise keeps immune system healthy • Exercise helps prevent obesity • Increasing age • Immune system declines with age • Cumulative damage from carcinogens • Cells that divide frequently

  9. 5.1 End of Chapter 5 Section 1 What Is Cancer? Figure 5.2

  10. 5.2 Chapter 5 Section 2 Passing Genes and Chromosomes to Daughter Cells Figure 5.2

  11. 5.2 Passing Genes and Chromosomes to Daughter Cells Asexual reproduction: • Only one parent • Offspring are genetically identical to parent Sexual reproduction • Gametes are combined from two parents • Offspring are genetically different from one another and from the parents

  12. 5.2 Passing Genes and Chromosomes to Daughter Cells Before dividing, cells must copy their DNA • Gene: section of DNA that has the instructions for making one protein • One molecule of DNA is wrapped around proteins to form a chromosome containing hundreds of genes. • Different species have different numbers of chromosomes (we have 46).

  13. 5.2 Passing Genes and Chromosomes to Daughter Cells A A A b b b Replication Centromere Sisterchromatids C C C Unduplicatedchromosome Duplicatedchromosome • Chromosomes are uncondensed before cell division • They are duplicated through DNA replication • Duplicated chromosomes, held together at the centromere, are called sister chromatids Figure 5.6

  14. 5.2 Passing Genes and Chromosomes to Daughter Cells (a) DNA replication New strands Parental strands DNA Replication • DNA molecule is split up the middle of the helix • Nucleotides are added to each side • Result is two identical daughter molecules, each with one parental strand and one new strand (semiconservative replication) Figure 5.5a

  15. 5.2 Passing Genes and Chromosomes to Daughter Cells (b) The DNA polymerase enzyme facilitates replication. Unwound DNA helix DNA polymerase DNA polymerase Free nucleotides • DNA polymerase: the enzyme that replicates DNA • Forms covalent bonds between nucleotides on the new strands • Forms hydrogen bond between nitrogenous bases Figure 5.5b

  16. 5.2 Passing Genes and Chromosomes to Daughter Cells PLAY Animation—The Structure of DNA

  17. 5.2 End of Chapter 5 Section 2 Passing Genes and Chromosomes to Daughter Cells Figure 5.2

  18. 5.3 Chapter 5 Section 3 The Cell Cycle and Mitosis Figure 5.2

  19. 5.3 The Cell Cycle and Mitosis Cell cycle: the “lifecycle” of the cell • Three steps: • Interphase: the DNA replicates • Mitosis: the copied chromosomes are moved into daughter cells • Cytokinesis: the cell is split into 2 daughter cells

  20. 5.3 The Cell Cycle and Mitosis - Interphase Interphase has three phases: • G1: cell grows, organelles duplicate • S: DNA replicates • G2: cell makes proteins needed to complete mitosis • Most of the cell cycle

  21. 5.3 The Cell Cycle and Mitosis - Mitosis Mitosis • Produces genetically-identical daughter cells • Sister chromatids are pulled apart • Four stages: • Prophase • Metaphase • Anaphase • Telophase

  22. 5.3 The Cell Cycle and Mitosis - Mitosis • Prophase: cell prepares for division • Replicated chromosomes condense • Nuclear envelope disappears • Microtubules pull the chromosomes toward the middle of the cell • In Animal cells, microtubules are attached to centrosomes at the poles of the cell

  23. 5.3 The Cell Cycle and Mitosis - Mitosis • Metaphase: chromosomes prepare for separation • chromosomes are aligned across the middle of the cell

  24. 5.3 The Cell Cycle and Mitosis - Mitosis • Anaphase: chromotids separate • centromeres split, • sister chromatids are pulled apart toward opposite poles

  25. 5.3 The Cell Cycle and Mitosis - Mitosis • Telophase: cells finalize nuclear division • Nuclear envelopes reform around chromosomes • Chromosomes revert to uncondensed form

  26. 5.3 The Cell Cycle and Mitosis PLAY Animation—Mitosis

  27. 5.3 The Cell Cycle and Mitosis - Cytokinesis Cytokinesis • Stage in which two daughter cells are formed from the original one • In Plants, a new cell wall forms between the cells, built from cellulose

  28. 5.3 The Cell Cycle and Mitosis - Cytokinesis Cytokinesis • Animals: • Don’t have a cell wall • Proteins pinch the original cell into two new cells • After cytokinesis, cells reenter interphase.

  29. 5.3 The Cell Cycle and Mitosis Mitosis

  30. 5.3 End of Chapter 5 Section 3 The Cell Cycle and Mitosis Figure 5.2

  31. 5.4 Chapter 5 Section 4 Cell Cycle Control and Mutation Figure 5.2

  32. 5.4 Cell Cycle Control and Mutation Control of the Cell Cycle • Cell division is a tightly controlled process • Normal cells halt at checkpoints • Proteins survey the condition of the cell • Cell must pass the survey to proceed with cell division

  33. 5.4 Cell Cycle Control and Mutation 3 checkpoints during the cell cycle • G1 checkpoint: are growth factors present? • Cell must also be large enough and have enough nutrients • G2 checkpoint: has DNA replicated properly? • Metaphase checkpoint: have all chromosomes attached properly to microtubules?

  34. 5.4 Cell Cycle Control PLAY Animation—The Cell Cycle

  35. 5.4 Cell Cycle Control and Mutation Cell Cycle Control and Cancer Two important genes • Proto-oncogenes • Tumor-suppressor genes

  36. 5.4 Cell Cycle Control and Mutation Proto-oncogenes • Proto-oncogenes are genes that code for the cell cycle control proteins • Many proto-oncogenes encode for growth factors • Mutation: a change in the sequence of DNA • This changes the structure and function of the protein • Mutations may be inherited or caused by carcinogens

  37. 5.4 Cell Cycle Control and Mutation (a) Mutations to proto-oncogenes Mutated proto-oncogene(oncogene) Proto-oncogene Mutation Mutation DNA Functional proteinstimulates celldivision only whenconditions are right. Mutated proteinmay overstimulatecell division byoverridingcheckpointcontrol. Protein Oncogenes • When proto-oncogenes mutate, they become oncogenes • Their proteins no longer properly regulate cell division • They usually over stimulate cell division Figure 5.12a

  38. 5.4 Cell Cycle Control and Mutation (b) Mutations to tumor-suppressor genes Mutated tumorsuppressor Tumor suppressor Mutation Mutation DNA Tumor-suppressorprotein stops tumorformation by suppressingcell division. Mutated tumor-suppressorprotein fails to stoptumor growth. Protein Tumor suppressor genes: genes for proteins that stop cell division if conditions are not favorable • When mutated, can allow cells to override checkpoints Figure 5.12b

  39. 5.4 Cell Cycle Control and Mutation – Many Mutations Are Required for Cancer to Develop • Angiogenesis: tumor gets its own blood supply • Loss of contact inhibition: cells will now pile up on each other

  40. 5.4 Cell Cycle Control and Mutation – Many Mutations Are Required for Cancer to Develop • Loss of anchorage dependence: enables a cancer cell to move to another location • Immortalized: cells no longer have a fixed number of cell divisions

  41. 5.4 Cell Cycle Control and Mutation – Many Mutations Are Required for Cancer to Develop • Multiple hit model: process of cancer development requires multiple mutations • Some mutations may be inherited (familial risk) • Most are probably acquired during a person’s lifetime

  42. 5.4 End of Chapter 5 Section 4 Cell Cycle Control and Mutation Figure 5.2

  43. 5.5 Chapter 5 Section 5 Cancer Detection and Treatment Figure 5.2

  44. 5.5 Cancer Detection and Treatment Cancer Detection • Early detection and treatment is best • Different detection methods for different cancers • Some cancers produce increased amount of a characteristic protein • Biopsies

  45. 5.5 Cancer Detection and Treatment • Biopsy: surgical removal of cells or fluid for analysis • Needle biopsy: removal is made using a needle • Laparoscope: surgical instrument with a light, camera, and small scalpel

  46. 5.5 Cancer Detection and Treatment - Treatment Methods • Chemotherapy: drugs that selectively kill dividing cells • Combination of different drugs used (“cocktail”) • Interrupt cell division in different ways • Helps prevent resistance to the drugs from arising • Normal dividing cells are also killed (hair follicles, bone marrow, stomach lining)

  47. 5.5 Cancer Detection and Treatment - Treatment Methods • Radiation therapy: use of high-energy particles to destroy cancer cells • Damages their DNA so they can’t continue to divide or grow • Usually used on cancers close to the surface • Typically performed after surgical removal of tumor

  48. 5.5 End of Chapter 5 Section 5 Cancer Detection and Treatment Figure 5.2

  49. 5.6 Chapter 5 Section 6 Meiosis – cell division for reproduction Figure 5.2

  50. 5.6 Meiosis Chromosomes of Somatic Cells • Humans have 46 chromosomes • Chromosomes come in homologous pairs • Diploid – cells have a pair of each chromosome • 22 pairs of autosomes • 1 pair of sex chromosomes

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