DNA Synthesis, Mitosis, and Meiosis Chapter 5 Cancer DNA Synthesis, Mitosis, and Meiosis Figure 5.2

5.1 Chapter 5 Section 1 What Is Cancer? Figure 5.2

Potentially cancerous cell 5.1 What Is Cancer? What Is Cancer? Unregulated cell division Tumor: mass of cells with no function Malignant if tumor invades surrounding tissue (cancerous) Tumor Metastatic if individual cells break away and start a new tumor elsewhere (cancerous) Normal cell Potentially cancerous cell Benign if tumor has no effect on surrounding tissue (noncancerous) Normal cell division Unregulated cell division Figure 5.2

Potentially cancerous cell 5.1 What Is Cancer? 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 Benign if tumor has no effect on surrounding tissue (noncancerous) Metastatic if individual cells break away and start a new tumor elsewhere (cancerous) Malignant if tumor invades surrounding tissue (cancerous) Normal cell division Unregulated cell division Tumor Potentially cancerous cell Normal cell Figure 5.2

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.

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

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

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

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

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

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

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).

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

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

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

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

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

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

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

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

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

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

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

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

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

5.3 The Cell Cycle and Mitosis PLAY Animation—Mitosis

5.3 The Cell Cycle and Mitosis - 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

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

5.3 The Cell Cycle and Mitosis

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

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

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

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?

5.4 Cell Cycle Control PLAY Animation—The Cell Cycle

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

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

5.4 Cell Cycle Control and Mutation Oncogenes When proto-oncogenes mutate, they become oncogenes Their proteins no longer properly regulate cell division They usually over stimulate cell division (a) Mutations to proto-oncogenes Functional protein stimulates cell division only when conditions are right. Mutated protein may overstimulate cell division by overriding checkpoint control. Mutation Protein DNA Proto-oncogene Mutated proto-oncogene (oncogene) Figure 5.12a

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

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

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

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

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

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

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

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

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)

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

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

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

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

5.6 Meiosis Homologous pairs of chromosomes carry the same genes. Alleles But each chromosomes may carry a different version of the gene, called alleles Alleles code for a different version of the same protein Figure 5.22

5.6 Meiosis Meiosis Specialized form of cell division in gonads to produce gametes Meiosis reduces number of chromosomes in each cell by one-half Gamete gets one of each pair Somatic cells are diploid (2n), but gametes are haploid (1n) Eggs and sperm fuse to form diploid Zygote

5.6 Meiosis Chromosome Replicaton Before meiosis can occur, DNA is duplicated DNA is duplicated in the S phase Creates 2 sister chromotids Held together by centromere Figure 5.22

Interphase and Meiosis Cell division that reduces diploid to haploid Meiosis takes place in two stages: meiosis I and meiosis II G1 S Cell growth and preparation for division End of previous mitotic event S and G phases similar to the S and G phases of mitosis Interphase and Meiosis Cell growth Interphase (G1, S, G2) DNA is copied G2 Figure 5.22

5.6 Meiosis Steps of Meiosis Meiosis I separates the members of a homologous pair from each other. After meiosis I, the resulting cells are haploid (n) Meiosis I is therefore called ‘reduction division’ Meiosis II is essentially like mitosis; it separates the sister chromatids

5.6 Meiosis Four Steps of Meiosis I Meiosis I separates the members of a homologous pair from each other. During prophase I there may be crossing over between members of homologous pairs

5.6 Meiosis Four Steps of Meiosis I Metaphase I homologous pairs line up at the equator of cell Microtubules attach to centromere

5.6 Meiosis Four Steps of Meiosis I Anaphase I Homologous pairs are separated by shortening microtubules Telophase I – nuclear envelop reforms

5.6 Meiosis Meiosis II Consists of Prophase II, Metaphase II, Anaphase II, and Telophase II Virtually identical to mitosis Sister chromatids are separated

5.6 Meiosis Two events create millions of different gametes from each parent Crossing over during prophase I Random alignment during metaphase I > Both increase the variation of next generation

5.6 Meiosis Crossing over during prophase I exchange of equivalent portions of chromosomes between members of a homologous pair Results in new assortment of genes in gametes

5.6 Meiosis Random Assortment during metaphase I Homologous pairs of chromosomes arrange arbitrarily at cell equator Results in new assortment of genes in gametes

5.6 Meiosis Meiosis

5.6 Meiosis - Mistakes in Meiosis Nondisjunction: failure of homologues to separate normally during meiosis Results in a gamete having one too many chromosomes (trisomy) or one too few chromosomes (monosomy)

5.6 Meiosis - Mistakes in Meiosis Human Nondisjunction of autosomes

5.6 Meiosis - Mistakes in Meiosis Human Nondisjunction of sex chromosomes

5.6 Meiosis Inheriting Cancer For cancer mutations to be passed on to offspring, they must occur in cells that give rise to gametes. Mutations in somatic cells (e.g., skin cancer) are not heritable.

Comparison of Mitosis & Meiosis – Fig 5.27

Meiosis – cell division for reproduction 5.6 End of Chapter 5 Section 6 Meiosis – cell division for reproduction Figure 5.2

5.6 End of Chapter 5 Figure 5.2