BIO101: Introduction to Molecular and Cellular Biology

Unit 7: Cellular Reproduction: Mitosis

• Upon successful completion of this unit, you will be able to:

  • differentiate DNA from RNA;
  • describe how different organisms reproduce;
  • recognize the phases of mitosis;
  • describe the stages of the cell cycle;
  • describe what occurs in each of the phases of mitosis; and
  • explain the purpose of mitosis.

• 7.1: DNA and RNA

  Molecular biology is the study of subcellular structures, their interactions, and how they function in the biological processes of the cell. In particular, nucleic acids are important molecules that carry information that leads to the production of proteins. Proteins are the physical expression of genetic information in cells.

  The nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important molecules that carry genetic information throughout cells. Like an architect’s blueprint, nucleic acids have a set of rules that lead to the synthesis of the major building blocks of living things.

  • DNA and RNA Page

    As their names indicate, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are both nucleic acids. Any nucleic acid is a polymer made up of monomers called nucleotides.

    Any nucleotide consists of three components:

    1. A pentose (five-carbon sugar)
    2. A nitrogenous base attached to the pentose
    3. A phosphate group also attached to the pentose

    For DNA, the specific pentose in each of its nucleotides is deoxyribose, whereas RNA features ribose as the pentose in each of its nucleotides. There are normally four kinds of DNA nucleotides because there are four normal nitrogenous bases used in DNA: adenine, guanine, cytosine, and thymine.

    RNA also features four kinds of nucleotides, and the nitrogenous bases are nearly the same as for DNA, except that RNA uses uracil instead of thymine. DNA functions for self-replication (before a cell divides into two cells) and for transcription, a process that produces RNA. There are different functional categories of RNA including mRNA, tRNA, rRNA, and others.

    Watch this overview of DNA and RNA that explains how these important nucleic acids form the blueprint for life's structures. After you watch, you should be able to explain the difference between RNA and DNA, identify the three types of RNA, and discuss the central dogma of how information flows from gene to protein.

• 7.2: Cell Division

  All living things are made up of cells. All cells come from other cells through the process of cell division. Some cells divide for reproduction purposes, while others divide for growth, development, or repair.

  • The cell cycle includes all parts of the normal lifetime of a single, eukaryotic cell. It starts when a cell is created through the division of a previous cell, and it ends when that cell undergoes its own cell division to produce two new cells.

    A single cell cycle consists of four major phases of unequal length:

    1. The G₁ phase includes most of the normal lifetime of the cell. During G1, the cell goes about using its DNA as instructions for building proteins that allow the cell to metabolize and function for its specific purpose. During this time, the DNA has not yet replicated.
    2. The S phase is the first step in a cell's preparation for cell division. During the S phase, the DNA is replicated, yielding two identical copies of the DNA (one for each of two cells that will be created when this cell divides).
    3. The G₂ phase follows the S phase. Like the G1 phase, the G2 phase features much protein synthesis and metabolism, but most of this activity is concentrated on preparing for cell division.
    4. The M phase includes mitosis (the division of the nucleus) and cytokinesis (the division of the cytoplasm). By the end of the M phase, two separate cells have been created from the original cell, and each of these two cells enters its own cell cycle. 
  • The Cell Cycle Page

    Read this section to learn about the phases of the cell cycle. This includes interphase, mitosis, and cytokinesis. As you review the cell cycle, pay particular attention to the diagram in Figure 1. After you read, you should be able to list the phases of the cell cycle, describe the events that occur during each phase, and describe the roles of checkpoints in the cell cycle control system.

  • Mitosis is the division of a eukaryotic cell's nucleus. One of the hallmarks of mitosis is that when the original nucleus divides, two genetically identical nuclei are produced. That is, the chromosomes in one nucleus are exactly the same as the chromosomes in the other nucleus. Each nucleus is genetically identical to the nucleus in the original cell (before mitosis). Therefore, mitosis creates two nuclei from one, and each of those nuclei can serve as the nucleus of a new cell. When cytokinesis accompanies mitosis, the cytoplasm divides, forming two distinct cells. Each cell contains its own nucleus (created by mitosis). Cell division that features mitosis allows one parent cell to divide into two, genetically identical daughter cells.

    Creating new cells is important for several reasons. Mitosis allows for cell proliferation for the purpose of developing a unicellular zygote into a multicellular organism. Mitosis also allows for cell proliferation for the purpose of growing a multicellular organism. It also allows for the creation of new cells to replace cells that have been damaged by injury or infection in a multicellular organism. Mitosis is a means for a unicellular, eukaryotic organism to reproduce.

    As you review mitosis, think about how mitosis (as part of the M phase) fits into the cell cycle. Mitosis occurs in five phases.

    1. Prophase: During this first phase of mitosis, the microtubules that make up the mitotic spindle begin forming on the two centrioles, and those centrioles start to move to opposite poles.
    2. Prometaphase: Construction of the mitotic spindle is completed, and the nuclear envelope disintegrates, allowing microtubules of the mitotic spindle to connect to replicated chromosomes.
    3. Metaphase: Replicated chromosomes (each consisting of two identical sister chromatids) move along the spindle tubules until all replicated chromosomes are aligned at the metaphase plate, midway between the poles.
    4. Anaphase: Each pair of sister chromatids (one pair for each replicated chromosome) separate and move toward opposite poles. At this point, they are no longer called chromatids; rather each is an unreplicated chromosome.
    5. Telophase: The unreplicated chromosomes reach opposite poles. Each pole becomes a new nucleus, as each pole becomes enclosed by a new nuclear envelope. In most cases, cytokinesis (the division of the cytoplasm) occurs near the end of telophase, in which case the original cell is separated into two distinct cells, each with its own nucleus.
  • Mitosis Page

    Watch this video to review the particular events of each mitotic phase. Make sure you can illustrate the phases and describe the events that characterize each phase.

  • What is Plant Cell Mitosis? Page

    Watch this video, which discusses the cell cycle. Make sure you can recognize the phases of mitosis from the diagrams.
    

  • A Tour of Mitosis Page

    Watch this video for a guided tour of mitosis as seen on a microscopy slide of an onion root tip. The video gives examples of cells in four stages of mitosis: prophase, metaphase, anaphase, and telophase.
    

  • Prokaryotic Cell Division Page

    Prokaryotic cells typically reproduce by binary fission, which is much simpler than eukaryotic cell reproduction. Read this section and notice the differences observed in prokaryotic cell reproduction.
    

• Unit 7 Assessment

  • Unit 7 Assessment Quiz

    Take this assessment to see how well you understood this unit.

    • This assessment does not count towards your grade. It is just for practice!
    • You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
    • You can take this assessment as many times as you want, whenever you want.