BIO.B Describe the events that occur during the cell cycle: interphase, nuclear division (mitosis and meiosis) and cytokinesis. The Cell Cycle: The series of events that take place when a cell duplicates its contents and divides. The cell cycle is a series of distinct phases in which a EUKARYOTIC cell: Grows Reproduces/Divides Performs normal functions (protein synthesis, respiration, transport of materials) The Cell Cycle The cell cycle consists of three distinct stages: 1. Interphase the longest phase of the cell cycle in which a cell performs the majority of its functions, such as preparing for nuclear division and cytokinesis. Interphase consists of 3 phases: Gap 1 (G1) - Cell growth, normal functions, organelles duplicate Synthesis (S) - DNA replication (Synthesis of DNA = New DNA is made by copying pre-existing DNA) Gap 2 (G2) - Additional growth 2. Nuclear division division of the nucleus There are two types of nuclear division: Mitosis a nuclear division that results in 2 somatic (body) cells with identical DNA. Meiosis a two-phase nuclear division that results in the production of 4 gametes (sex cells) that are genetically different. 3. Cytokinesis - division of the cytoplasm Nuclear Division: Mitosis vs. Meiosis The Cell Cycle Cell division only occurs if the cell is large enough and the DNA is undamaged! The surface area of a cell must be large enough for the transport of materials into and out of the cell. Cells that are large tend to have different shapes to help them function properly. The rate of cell division varies depending upon the location and function of the cell. Some cells are unlikely to divide. These cells stay in a phase known as (G0). Mitosis Mitosis = Division of nucleus Forms 2 somatic cells Somatic cells = all body cells except sex cells/gametes What are some examples of somatic cells that undergo mitosis? Are somatic cells genetically identical? Do they have the same DNA? DNA double helix DNA and histones Chromatin Supercoiled DNA Chromosome Structure Chromosomes a single piece of coiled DNA and proteins found in eukaryotic cells and prokaryotic cells. Chromosomes contain genes that code for specific traits. Each organism has a specific number of chromosomes. Chromosomes Uncondensed (uncoiled)DNA plus proteins is called chromatin. One half of a duplicated chromosome is a chromatid. Sister chromatids are held together at the centromere. Condensed, duplicated chromosome chromatid centromere Interphase -Preparing a cell for division Parent cell centrioles spindle fibers centrosome nucleus with chromatin (contains DNA) Interphase prepares the cell to divide by growing and duplicating the DNA. Chromatin and a nuclear membrane are both visible. Prophase 1 st stage of mitosis During prophase, chromatin condenses to form chromosomes and spindle fibers form. The nuclear membrane begins to dissolve. Metaphase 2 nd stage of mitosis During metaphase, chromosomes line up in the middle of the cell attached to spindle fibers. Anaphase 3 rd phase of mitosis During anaphase, sister chromatids separate and travel to opposite sides of the cell. Telophase 4 th & final stage of mitosis During telophase, two new nuclei form and chromosomes begin to uncoil. Cytokinesis division of the cytoplasm Cytokinesis differs in plant and animal cells. In animal cells, the plasma membrane pinches closed. In plant cells, a cell plate forms. How do cells know when to divide? 1.)InjuryCells know when repair is necessary because they rely on cell to cell contact. If a cell is missing they will start to divide until they come into contact with other cells. 2.)Growth factorsGrowth factors are types of proteins present in organisms that stimulate a cell to divide. 3.) CyclinsCyclins are proteins found within cells that help to control the cell cycle. Cell Differentiation Although all somatic cells contain the same DNA they may perform different functions in an organism. This is due to a process called cell differentiation, in which a cell will develop into its mature form based on the DNA (genes) that is expressed (read). Cells that perform similar functions are called tissues. Tissues that work together to perform specific functions are called organs. Organs that work together to perform specific functions form an organ system. Stem Cells Stem cells are special cells that have the ability to: divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types Stem cell research has the potential to change medicine. Why? Uncontrolled Cell Division Uncontrolled cell division results in tumors. Tumors can be malignant OR benign. Malignant tumors are cancerous and can metastasize within an organism. Cancer cells do NOT carry out necessary functions. Cancer cells come from normal cells with damage to the genes that are involved in cell cycle regulation. Carcinogens are substances that cause these gene mutations. Asexual Reproduction Asexual reproduction is the creation of offspring from a single parent. It forms offspring identical to the parent. Environment determines what form of reproduction is most advantageous. For example: Asexual reproduction is an advantage because organisms d0 not need to waste time and energy looking for a mate. Asexual reproduction occurs more quickly than sexual reproduction. A disadvantage to asexual reproduction is that genetically identical organisms are produced; therefore during unfavorable conditions an entire population can be harmed. Asexual Reproduction in Prokaryotes All prokaryotes reproduce asexually by a process known as binary fission. Binary fission is the splitting of a parent cell into two genetically identical daughter cells. How is similar to mitosis? How is it different? (Look at the diagram.) Asexual Reproduction in Eukaryotes Some eukaryotes can reproduce asexually by mitosis. There are different types of mitotic reproduction which include: Budding Fragmentation/Regeneration Vegetative Propagation Budding Budding - forms a new organism from a small projection growing on the surface of the parent. bud Hydra Yeast Fragmentation OR Regeneration Fragmentation or (regeneration) is the splitting of the parent into pieces that each grow into a new organism. Can you think of any organisms that regenerate? Vegetative Propagation Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant. Do you know of any plants that use vegetative propagation to reproduce? Sexual Reproduction During sexual reproduction offspring are formed from two parents. Both parents produce sex cells called gametes. Male Gamete vs. Female Gamete SPERM EGG Fertilization must occur for sexual reproduction to be successful. Fertilization is the joining of a sperm and an egg. Types of Cells Body cells are also called somatic cells. They are formed by MITOSIS. Somatic cells are located throughout the body (heart, brain, stomach, lung, skin, etc) DNA in your somatic cells is NOT passed on to your children. Germ cells develop into gametes. They are formed by MEIOSIS. Germ cells are located in the ovaries and testes. DNA in your gametes IS passed on to your children. Haploid vs. Diploid Cells Somatic cells (body cells) are diploid cells. Diploid cells (2n) have two copies of every chromosome. One copy comes from your mother and one copy comes from your father. Gametes (sperm and eggs) are haploid cells. Haploid cells (n) have one copy of each chromosome. What is the human haploid number? (n = 23) Diploid number? (2n = 46) Mitosis makes diploid cells. Meiosis makes haploid cells. Types of Chromosomes All cells contain DNA located in chromosomes. Cells have two types of chromosomes: Autosomes: Non-sex chromosomes (Pairs 1-22) Sex Chromosomes: Chromosomes that contain genes related to your sex. (Pair 23) XX = female XY = male Homologous Chromosomes Homologous chromosomes: Chromosomes that have the same structure and contain the same genes in the same locations. In a homologous pair of chromosomes, one chromosome is inherited from mom and one chromosome is inherited from dad. Meiosis Meiosis = A type of nuclear division that divides a diploid cell into four haploid cells. Meiosis is the process that forms gametes (sperm and eggs); therefore it is necessary for sexual reproduction to occur. Meiosis Germ cells (46 chromosomes) undergo two rounds of cell division, which results in cells with a reduced number of chromosomes (23 chromosomes). Interphase occurs before Meiosis I (the first division) but DOES NOT occur before Meiosis II (the second division). Meiosis increases genetic variation and diversity. Stages of Meiosis I What is a tetrad? Homologous chromosomes line up together to form tetrads in a process called synapsis. Stages of Meiosis II Name That Phase! Crossing Over Crossing over: An exchange of genetic material between homologous chromosomes during prophase I of meiosis. Crossing over increases genetic variability in gametes. Mitosis Vs. Meiosis Mitosis has one cell division. Meiosis has two cell divisions. During meiosis homologous chromosomes pair up. During mitosis homologous chromosomes never pair up. Gametogenesis Where does MEIOSIS occur???? Meiosis occurs in organs called gonads. Female gonads are ovaries. Male gonads are testes. Inside the gonads are germ cells. Germ cells produce gametes by the process of meiosis. Female germ cells = oocytes Male germ cells = spermatocytes Oocytes are formed by a type of meiosis called oogenesis. Spermatocytes are formed by a type of meiosis called spermatogenesis. Oogenesis Vs. Spermatogenesis Reproductive Organs MALE FEMALE Fertilization and Beyond.. 1 st : Fertilization joining of sperm and egg 2 nd : Growth and Development occurs by the process of MITOSIS Zygote Embryo Fetus Infant Embryo Fetus Infant Pregnancy & Birth Advantages to Sexual Reproduction Advantages: Greater variety/diversity in organisms. Greater ability to adapt and evolve. Disadvantages: Requires more energy than asexual reproduction. Requires more time (finding a mate) than asexual reproduction.