Essentials of Anatomy and Physiology

• DNA →RNA →proteins (structural proteins
  and enzymes that catalyze reactions) →heredi-
  tary characteristics.


• A genetic disease is a “mistake” in the DNA,
  which is copied by mRNA and results in a mal-
  functioning protein.

Cell Division

1. Mitosis—one cell with the diploid number of chro-
   mosomes divides once to form two cells, each with
   the diploid number of chromosomes (46 for
   humans).

• DNA replication forms two sets of chromosomes
  during interphase.


• Stages of mitosis (see Fig. 3–5 and Table 3–4):
  prophase, metaphase, anaphase, and telophase.

Cytokinesis is the division of the cytoplasm fol-

lowing telophase.

• Mitosis is essential for growth and for repair and
  replacement of damaged cells.


• Most adult nerve and muscle cells seem unable to
  divide; their loss may involve permanent loss of
  function.

2. Meiosis—one cell with the diploid number of chro-
   mosomes divides twice to form four cells, each with
   the haploid number of chromosomes (23 for
   humans).

• Oogenesis in the ovaries forms egg cells.


• Spermatogenesis in the testes forms sperm cells.


• Fertilization of an egg by a sperm restores the
  diploid number in the fertilized egg.

Cells 65

REVIEW QUESTIONS

1. State the functions of the organic molecules of
   cell membranes: cholesterol, proteins, and phos-
   pholipids. (p. 48)


2. Describe the function of each of these cell
   organelles: mitochondria, lysosomes, Golgi appa-
   ratus, ribosomes, proteasomes, and endoplasmic
   reticulum. (p. 51)


3. Explain why the nucleus is the control center of
   the cell. (p. 49)


4. What part of the cell membrane is necessary for
   facilitated diffusion? Describe one way this
   process is important within the body. (p. 54)


5. What provides the energy for filtration? Describe
   one way this process is important within the body.
   (p. 54)


6. What provides the energy for diffusion? Describe
   one way this process is important within the body.
   (p. 52)


7. What provides the energy for active transport?
   Describe one way this process is important within
   the body. (p. 54)


8. Define osmosis, and describe one way this process
   is important within the body. (p. 52–53)


9. Explain the difference between hypertonic and
   hypotonic, using human cells as a reference point.
   (p. 53)


10. In what way are phagocytosis and pinocytosis sim-

ilar? Describe one way each process is important

within the body. (p. 56)

11. How many chromosomes does a human cell have?
    What are these chromosomes made of? (p. 56)


12. Name the stage of mitosis in which each of the
    following takes place: (p. 63)
    a. The two sets of chromosomes are pulled
    toward opposite poles of the cell
    b. The chromosomes become visible as short rods
    c. A nuclear membrane re-forms around each
    complete set of chromosomes
    d. The pairs of chromatids line up along the
    equator of the cell
    e. The centrioles organize the spindle fibers
    f. Cytokinesis takes place after this stage


13. Describe two specific ways mitosis is important
    within the body. Explain why meiosis is impor-
    tant. (pp. 60, 62)


14. Compare mitosis and meiosis in terms of: (pp.
    60–62)
    a. Number of divisions
    b. Number of cells formed
    c. Chromosome number of the cells formed


15. Explain the triplet code of DNA. Name the mol-
    ecule that copies the triplet code of DNA. Name
    the organelle that is the site of protein synthesis.
    What other function does this organelle have in
    protein formation? (pp. 56–58)