Chapter 9: The Cell Cycle & Cellular Reproduction - Biology PDF

Because learning changes everything. ® Biology Sylvia S. Mader...

Because learning changes everything. ® Biology Sylvia S. Mader Michael Windelspecht Chapter 9 The Cell cycle & Cellular Reproduction Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  Outline  9.1 The Cell Cycle  9.2 The Eukaryotic Chromosome  9.3 Mitosis & Cytokinesis  9.4 The Cell Cycle & Cancer  9.5 Prokaryotic Cell Division 2  9.1 The Cell Cycle Orderly set of stages from the first division of a eukaryotic cell to the time the resulting daughter cells divide. The two major stages of the cell cycle: Interphase (includes several stages). Mitotic stage (includes mitosis and cytokinesis Mammalian cell= 20 hrs.  Interphase The longest part of the cell cycle ( 90% of the cell cycle). Divided into 3 stages: 1. G1 Stage (Gap 1): -Cell grows in size. -Cell doubles its organelles ( mitochondria & ribosomes). -Accumulates materials needed for DNA synthesis. Nerve & muscle cell remain in Go 2. S Stage: -DNA replication occurs. - All proteins associated with DNA are synthesized. -Duplication of chromosomes. Every chromosome is made of 2 identical chromatids 3. G2 Stage (Gap 2): Cell synthesizes proteins necessary for division.(e.g. microtubule proteins). Sister Chromatids  Figure 9.2 5  Mitotic Stage -follows interphase. Mitosis: division of the nucleus. Cytokinesis: division of the cytoplasm. Result= two genetically identical daughter cells.  Control of the Cell Cycle -A signal is a molecule that influences the activities of a cell. -Cycle is controlled by internal and external signals. -External signals: Growth factors are signaling proteins received at the plasma membrane. -Internal signals: Family of proteins called Cyclins that increase and decrease as the cell cycle continues. -Specific cyclins must be present for the cell to proceed from one stage to the next. -Without cyclins, the cell cycle stops at G1, M, or G2 (checkpoints).  Cell Cycle Checkpoints  G1 checkpoint: p53 checks for DNA damage & initiates DNA repair. If repair is not possible, apoptosis results. RB, checks nutrient availability  G2 checkpoint: Checks if DNA replication was properly completed or if DNA is damaged.  M checkpoint: Checks for proper alignment of chromosomes & attachment to mitotic spindle.  The Cell Cycle G1 checkpoint is the primary check point of cell cycle: p53 stops cycle if DNA is damaged & initiates repair. RB ( retinoblastoma) checks nutrient availability Interphase S G1 checkpoint (growth and DNA Cell cycle main checkpoint. G1 replication) G2 checkpoint If DNA is damaged, apoptosis G2 will occur. Otherwise, the cell G1 Mitosis checkpoint. (growth and final Mitosis will occur is committed to divide when G0 (growth) preparations for G growth signals are present M 2 if DNA has s division) and nutrients are available. si replicated properly. e ne ase s e se se i as Apoptosis will ha ok ha h t op Anapha Metaph op Cy occur if the DNA is op r r ep P damaged and Tel at cannot be repaired. L M M checkpoint Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned. 9  Apoptosis - Programmed cell death caused by enzymes= Caspases. - Caspases are controlled by inhibitors, but can be unleashed by internal or external signals. - Cell division & apoptosis are opposing forces. - Cell division increases the number of somatic cells while apoptosis decreases it. - These opposing processes keep number of cells at an appropriate level. Loses contact with neighboring containcells Cell rounds Plasma membrane Cell fragments normal cells Chromatin up, and nucleus blisters, and blebs DNA condenses, and collapses. form. fragments. nucleus fragments. Engulphed up by WBC Apoptosis and Cell Division  9.2 The Eukaryotic Chromosome - A chromosome consist of a single DNA molecule condensed in the cell by histone proteins. - DNA+ histones= Chromatin - Nucleosome: DNA around 8 histone. - Nucleosomes are joined by “linker” DNA Euchromatin represents the active chromatin that can be transcribed by RNA polymerase & transcription factors. Heterochromatin, a more highly compacted form of the chromosome  Inactive chromatin.  Genes hardly ever transcribed.  Compact chromosomes are more easily moved than extended chromatin.  Most chromosomes have both compaction levels. 9.3 Mitosis and Cytokinesis  Eukaryotic cell division involves: 1- Mitosis (nuclear division) 2- Cytokinesis (division of cytoplasm).  Before mitosis begins: -Chromatin condenses (coils) into distinctly visible chromosomes. - Each species has a characteristic chromosome number. 13 14  Eukaryotic Chromosomes - Diploid (2n) number: in diploid cells there are 2 copies of each chromosomes. ( humans, 2n=46 chromosomes or 23 pairs) - Haploid (n) number: only gametes (sperm and eggs) have only one of each pair of chromosomes. ( n=23) - In the S phase each chromosome replicates; 2 genetically identical sister chromatids result attached at the centromere with a protein complex= Kinetochores. - Each chromatid (daughter chromosome) goes to one daughter cell.  Mitosis in Animal Cells Centrosome: Microtubule organizing center of animal cell. (MTOC). -Each centrosome contains two barrel shaped centrioles and has an aster. - organizes the mitotic spindle. - The spindle contains many fibers. Each fiber is a cylindrical bundle of microtubules. Mitosis is divided into 5 stages: prophase, prometaphase, metaphase, anaphase telophase. Phases of Mitosis in Animal and Plant Cells Early Prophase Centrosomes have duplicated. Chromatin is condensing into chromosomes, and the nuclear envelope is fragmenting. Phases of Mitosis in Animal and Plant Cells Prophase Nucleolus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and spindle is in process of forming. Phases of Mitosis in Animal and Plant Cells Prometaphase The kinetochore of each chromatid is attached to a kinetochore spindle fiber. Polar spindle fibers stretch from each spindle pole and overlap. Phases of Mitosis in Animal and Plant Cells Metaphase Centromeres of duplicated chromosomes are aligned at the metaphase plate (center of fully formed spindle). Kinetochore spindle fibers attached to the sister chromatids come from opposite spindle poles. Phases of Mitosis in Animal and Plant Cells Anaphase Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell. Phases of Mitosis in Animal and Plant Cells Telophase Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin.  Cytokinesis in animal cell  Cleavage furrow  It deepens when a contractile ring of actin filaments forms a circular constriction between the 2 daughter nuclei. Contractile ring continues to separate until there are two independent daughter cells Mitosis in plant cell  Mitosis in plants is similar to mitosis in animals.  The plant cells lack centrioles lack asters. However, spindle still forms.  Cytokinesis in Plant Cells  Rigid cell wall of plant cells does not permit furrowing.  Small flattened disks produced from GA appear between the two daughter plant cells. They fuse to form Cell plate. Phases of Mitosis in Plant Cells Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. centrosome has centrioles Animal Cell aster 20 µm duplicated 20 µm spindle chromosomes at 20µm 9 µm 20µm daughter chromosome cleavage furrow 16µm at Interphase chromosome pole metaphase plate nuclear centromere envelope kinetochore fragments nucleolus MITOSIS chromatin condenses nucleolus kinetochore disappears spindle spindle fiber kinetochore fibers forming spindle fiber polar spindle fiber Metaphase Telophase Early Prophase Prophase Prophase Centromeres of duplicated chromosomes Anaphase Daughter cells are forming Centrosomes have duplicated. Nucleolus has disappeared, and Nucleolus has disappeared, and are aligned at the metaphase plate (center Sister chromatids part and become daughter Chromatin is condensing into duplicated chromosomes are visible. duplicated chromosomes are visible. of fully formed spindle). Kinetochore spindle chromosomes that move toward the spindle as nuclear envelopes and chromosomes, and the nuclear Centrosomes begin moving apart, Centrosomes begin moving apart, fibers attached to the sister chromatids poles. In this way, each pole receives the same nucleoli reappear. Chromosomes will centrosome envelope is fragmenting. and spindle is in process of forming. and spindle is in process of forming. come from opposite spindle poles. number and kinds of chromosomes as the parent cell. become indistinct chromatin. lacks centrioles Plant Cell at Interphase spindle pole lacks 25µm 6.2µm 6.2µm cell wall chromosomes centrioles and aster 20µm spindle fibers 6.2µm cell plate 6.6µm Animal cell(Early prophase, Prophase, Metaphase, Anaphase, Telophase): © Ed Reschke; Animal cell(Prometaphase): © Michael Abbey/Photo Researchers, Inc.; Plant cell(Early prophase, Prometaphse): © Ed Reschke; Plant cell(Prophase, Metaphase, Anaphase): © R. Calentine/Visuals Unlimited; Plant cell(Telophase): © Jack M. Bostrack/Visuals Unlimited; 26 Functions of Mitosis in Animal & Plant Cells  Permits growth and repair.  In flowering plants, meristematic tissue retains the ability to divide throughout the life of the plant  In mammals, mitosis is necessary when:  A fertilized egg becomes an embryo  An embryo becomes a fetus  A cut heals or a broken bone mends 27  Reproductive & Therapeutic Cloning  Stem Cells: Retain the ability to divide Ex: Red bone marrow stem cells divide to produce various types of blood cells  Reproductive cloning: to produce an individual that is genetically identical to the one that donated a nucleus.  Therapeutic cloning: to produce specialized human tissues, either by using adult stem cells or embryonic stem cells. 28 Reproductive and Therapeutic Cloning remove and discard egg Donor cells are egg nucleus starved to enter G0 remove Implant fuse egg embryo Go nucleus with Go into Go cells from nucleus culture surrogate animal to be mother cloned embryonic stem cells Clone is born a. Reproductive cloning remove and discard egg egg nucleus Subjected to nervous different treatments remove fuse egg Go nucleus with Go blood Go somatic cells nucleus culture embryonic stem cells muscle b. Therapeutic cloning 29  9.4 The Cell Cycle and Cancer  Abnormal growth of cells is called a tumor  Benign tumors are not cancerous  Encapsulated  Do not invade neighboring tissue or spread  Malignant tumors are cancerous  Not encapsulated  Readily invade neighboring tissues  May also detach and lodge in distant places (metastasis)  Results from mutation of genes regulating the cell cycle.  Carcinogenesis: Development of cancer  Tends to be gradual  May take years before a cell is obviously cancerous 30  Characteristics of cancer cells -Lack differentiation, nonspecialized & immortal so they enter the cycle repeatedly. -Abnormal nuclei & # chromosomes with extra copies of genes. - Do not undergo apoptosis. - Form tumors, no contact inhibition. - Undergo metastasis & angiogenesis (formation of new blood vessels). Cancer Cells vs. Normal Cells 32  Progression of Cancer As tumors grow rapidly, Blood vessels supplying Nutrients & oxygen become insufficient New mutations arise, and one cell (brown) has the ability to start a tumor. primary tumor lymphatic blood vessel vessel Cancer in situ. The tumor is at its place of origin. One cell (purple) mutates further. lymphatic blood vessel vessel Cancer cells now have the ability to invade lymphatic and blood vessels and travel throughout the body. New metastatic tumors are found some distance from the primary tumor. 33  The Origin of Cancer  Normal growth and tissue maintenance depends on a balance between signals that promote and signals that inhibit cell division.  Two types of genes if mutated may cause cancer in various ways.  Proto-oncogenes Oncogenes.  Proto-oncogene are normal genes that code for proteins which promote the cell cycle. If mutated, it may become an oncogene.  Tumor suppressor genes: code for proteins which inhibit the cell cycle and promote apoptosis in various ways.  If a tumor suppressor gene becomes inactive, it may promote cancer development. 34  Proto-oncogenes Become Oncogenes  Proto-oncogenes are part of a stimulatory pathway.  They promote progression through the cell cycle.  They include receptors and signaling molecules.  100 Oncogenes: which can lead to tumors, either by: 1. specify an abnormal protein product 2. produce abnormally high levels of a normal product. - Leads to uncontrolled cell division results. Ex: BRCA1, mutations which can cause breast and ovarian cancer. 35  Tumor Suppressor Genes Become Inactive  A mutation in a tumor suppressor causes the cell cycle to accelerate.  Examples are the RB and p53 genes which code for proteins with the same names.  Retinoblastoma is an inherited condition that results from a mutation in the RB gene.  The p53 gene turns on the expression of other cell cycle inhibitory genes.  Half of human cancers involve an abnormal or deleted p53 gene. 36  Causes of Cancer Heredity Radiation sources growth factor growth Activates signaling factor proteins in a stimulatory pathway that extends Viruses to the nucleus. Pesticides receptor activated &herbicides protein oncogene signaling protein a. Influences that cause mutated proto- P oncogenes P (called oncogenes) and mutated tumor suppressor genes signaling phosphate Stimulatory gene product protein P pathway promotes cell cycle b. Effect of growth factor Inhibitory pathway gene product inhibits proto-oncogene cell cycle Codes for a growth factor, a receptor protein, or a signaling protein in a stimulatory pathway. If a proto-oncogene becomes an oncogene, the end result can be active cell division. Stimulatory pathway & tumor suppressor gene Codes for a signaling inhibitory pathway 1,100X protein in an inhibitory pathway. If a tumor suppressor gene mutates, 37 the end result can be active cell division.  The Cell Cycle and Cancer  Chromosomes normally have special material at each end called telomeres  Telomeres get shorter after each cell division  When they get very short, the cell will no longer divide  Telomerase is an enzyme that maintains the length of telomeres  Mutations in telomerase gene:  Cause telomeres to continue to lengthen, which allows cancer cells to continuously divide. 38  9.5 Prokaryotic Cell Division  The prokaryotic (bacteria and archaea) chromosome is a ring of DNA and a few associated proteins.  Folded up in an area called the nucleoid  Replicated into two rings prior to cell division & the rings attach to the plasma membrane.  Binary fission  Splitting in two  Two replicate chromosomes are distributed to two daughter cells.  Produces two daughter cells identical to original cell—asexual reproduction 39 Binary Fission 40 41 42 43 44  Comparing Prokaryotes & Eukaryotes  Binary fission in prokaryotes and mitosis in cellular eukaryotes  ensure that new cells are identical to parent cell.  Mitosis in multicellular eukaryotes  Growth and repair of tissues. 46