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BIO101 Study Guide

Unit 7: Cellular Reproduction: Mitosis

7a. Differentiate DNA from RNA in terms of structure and function

  • How are DNA and RNA chemically different?
  • How are DNA and RNA functionally different?
  • How are DNA and RNA different in terms of their roles in protein synthesis?
  • What organisms have both DNA and RNA?

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 usually four kinds of DNA nucleotides because there are four normal nitrogenous bases used in DNA:

  • Adenine
  • Guanine
  • Cytosine
  • 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. RNA has different functional categories, including mRNA, tRNA, rRNA, and others.

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7b. Describe the different methods of cell division among organisms

  • What are the different ways that organisms reproduce?
  • Why do organisms go through cell division?
  • What is the advantage of cloning versus genetic variation?
  • Why is genetic variation an advantage in more complex organisms?

To survive, organisms must pass their traits on to reproduce offspring. Prokaryotic organisms reproduce by binary fission. These unicellular organisms divide to continue the species' existence. Multicellular organisms divide for growth, development, and repair. Eukaryotic organisms reproduce asexually and sexually.

Asexual reproduction involves transferring 100 percent of DNA to their offspring (essentially cloning). For sexual reproduction, the offspring share DNA from two different parents and produce new genetic combinations.

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7c. Describe the phases of the cell cycle and mitosis

  • What is mitosis, and what are the phases of mitosis?
  • What types of cells undergo mitosis?
  • What are the phases of the cell cycle?
  • What occurs between periods of division?
  • What are the major events occurring in each phase of the cell cycle?

The Cell Cycle

The cell cycle includes all parts of the normal lifetime of a single eukaryotic cell. The cell cycle begins when a cell is created via the division of a previous cell and ends when the 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 cell's normal lifetime. During G1, the cell uses 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 been 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 the two cells that will be created when the 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 in multicellular organisms consists of the interphase and the mitotic phase.

Figure 10.5 The cell cycle in multicellular organisms consists of the interphase and the mitotic phase. During interphase, the cell grows, and the nuclear DNA is duplicated. Interphase is followed by the mitotic phase. During the mitotic phase, the duplicated chromosomes (thread-shaped structures in the nucleus that carry genes) are segregated and distributed into daughter nuclei. Following mitosis, the cytoplasm is usually divided as well by cytokinesis, resulting in two genetically identical daughter cells.


Mitosis

Mitosis is the division of a cell nucleus. Since only eukaryotic cells feature a nucleus, only eukaryotic cells undergo mitosis (recall that prokaryotic cells undergo a rudimentary cell division, or "binary fission). Mitosis is part of eukaryotic cell division (the other part is cytokinesis, which is the division of the cytoplasm).

Mitosis (the division of a eukaryotic cell's nucleus) occurs in five phases:

  1. Prophase: The first phase of mitosis. The microtubules that make up the mitotic spindle begin forming on the two centrioles, and these centrioles start to move to opposite poles.

  2. Prometaphase: Construction of the mitotic spindle is completed, and the nuclear envelope disintegrates, allowing the 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 (division of the cytoplasm) occurs near the end of telophase, when the original cell separates into two distinct cells, each with its own nucleus.

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7d. Explain the purpose of mitosis and the relationship between parent and daughter cells

  • What cells undergo mitosis in the human body?
  • When is mitosis initiated in the body?
  • Why is mitosis important?
  • Under what conditions does a cell undergo mitosis?

Recall that mitosis is the division of a eukaryotic cell's nucleus. One of the hallmarks of mitosis is that two genetically identical nuclei are produced when the original nucleus divides. The chromosomes in one nucleus are exactly the same as the chromosomes in the other nucleus. Moreover, each nucleus is genetically identical to the nucleus in the original cell (before mitosis). Mitosis creates two nuclei from one, and each of these 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 promotes cell proliferation so a unicellular zygote can develop into a multicellular organism.
  • Mitosis promotes cell proliferation to support the growth of a multicellular organism.
  • Mitosis creates new cells to replace damaged cells due to injury or infection in a multicellular organism.
  • Mitosis is a way for unicellular, eukaryotic organisms to reproduce.

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Unit 7 Vocabulary

This vocabulary list includes terms you will need to know to successfully complete the final exam.

  • adenine
  • anaphase
  • asexual reproduction
  • cell cycle
  • cell division
  • chromosome
  • cytokinesis
  • cytosine
  • G1 phase
  • G2 phase
  • guanine
  • metaphase
  • mitosis
  • M phase
  • nitrogenous bases
  • prometaphase
  • prophase
  • sexual reproduction
  • S phase
  • telophase
  • thymine
  • uracil