Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 8
8.1
1. Cell division produces new cells in tissues that are rapidly growing or where there is constant
environmental erosion of cells. Apoptosis produces the adult shape of an organism and
eliminates damaged cells.
2. Histones are proteins that are attached to DNA. Chromatin is a collective term for DNA and its
associated proteins.
3. An unreplicated chromosome is composed of chromatin (DNA and associated proteins). A
replicated, condensed chromosome has two sister chromatids joined at a centromere.
4. The only body cells that are haploid are sperm cells and egg cells. All other body cells are
diploid.
5. Somatic cells are different from germ cells in that they do not undergo meiosis.
8.2
1. During interphase, a cell grows and produces proteins so that its normal biochemical functions
proceed. DNA replicates during interphase as a cell prepares to divide.
2. The mitotic spindle is composed of microtubules associated with cytoskeleton proteins. The
spindle originates from centrosomes that are at opposite ends of the cell. Spindle fibers grow
across to join at the midline of the cell. The function of the mitotic spindle is to form “trackways”
for the movements of chromosomes as cells divide.
3. The events of mitosis include:
 Prophase: chromosomes condense and become visible; mitotic spindle forms
 Prometaphase: nuclear envelope breaks up; spindle fibers attach to kinetochores on
each chromosome
 Metaphase: chromosomes line up on equator of cell
 Anaphase: sister chromatids separate and move to opposite poles of the cell
 Telophase: nuclear membranes reassemble around the daughter nuclei; chromosomes
decondense; spindle disappears
4. Mitosis is the division of duplicated chromosomes into new daughter nuclei. Cytokinesis is the
division of cytoplasm and organelles into two new daughter cells and the separation of these
cells.
8.3
1. Growth factors are proteins that stimulate cell division.
2. At cell cycle checkpoints, the cell cycle is controlled, ensuring that each stage of the cycle is
completed before the next stage begins. A cell will only proceed into mitosis if the G 1, S, and G2
checkpoints have been successfully passed. If they have not, the cell may stop or suspend the
cell cycle, or may enter apoptosis and die.
3. With every round of cell division, telomeres lose some nucleotides and are shortened just a bit.
After 50 divisions, the telomeres are so short that the cell does not divide any more. So a cell with
chromosomes that have very short telomeres has undergone many rounds of cell division.
8.4
1. Benign tumors do not spread to other areas of the body and do not invade nearby tissues. A
malignant tumor does invade nearby tissues and may metastasize to colonize other areas of the
body.
2. Cancer cells are different from normal cells in that they have lost the normal controls on the cell
cycle. Cancer cells therefore divide in an unregulated fashion. Cancer cells look different from
normal cells and lose some of the special features of the parent cell. Cancer cells may have their
own growth factors that signal when they should divide. Cancer cells lack contact inhibition; in
addition, they are essentially immortal and lack apoptosis. Cancer cells can stimulate the growth
of new blood vessels that supply them with nourishment and remove wastes.
3. An oncogene is an abnormal variant of a gene that normally controls cell division. Oncogenes
increase the rate of the cell cycle and cause tumors. A tumor suppressor gene promotes
apoptosis or prevents cell division. If a tumor suppressor gene mutates, cell division proceeds
unchecked and a tumor develops.
4. Surgery is physical removal of a tumor. Radiation directs energy from radioactive isotopes at
cancer cells to kill them. Chemotherapy delivers intravenous drugs that stop cells anywhere in the
body from dividing. Gene therapy delivers into the body a healthy gene that replaces a cancercausing gene.
8.5
1. Apoptosis allows the sculpting of bodies to form the mature shape of various structures. Thus,
cell death is a normal part of development.
2. One example of the protective function of apoptosis is the death of sunburned skin cells that
have been damaged by UV radiation. If these cells did not die by apoptosis, they might become
cancerous. Instead apoptosis proceeds, the damaged cells die, and the dead skin peels off.
3. A cell undergoing apoptosis first receives a signal at a membrane protein called a death
receptor. The signal triggers the release of caspase enzymes that destroy the cell from within.
Eventually, immune system cells engulf the dying cell, degrading or recycling its components.
4. In human fetal development, too little apoptosis of white blood cells that react with the body’s
own molecules will result in autoimmune disorders such as lupus and rheumatoid arthritis. Too
much apoptosis, as in the death of brain cells following a stroke, extends the damage and many
brain cells die.