Biology Ch 15 Fifth Edition Brooker BRCC
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Figure 15.1 A missense mutation that causes red blood cells to sickle in sickle cell disease.
Scanning electron micrographs of (a) a normal red blood cell and (b) a sickled red blood cell. As
shown above the micrographs, a missense mutation in the β-globin gene (which codes for a
subunit of hemoglobin) changes the sixth amino acid in the β-globin polypeptide from glutamic
acid (Glu) to valine (Val). (c) This micrograph shows how this alteration to the structure of
β-globin causes the formation of abnormal fiber-like structures. In normal red blood cells,
hemoglobin proteins do not form fibers.
Concept Check: Based on the fiber-like structures seen in part (c) of this figure, what aspect of
hemoglobin structure does a glutamic acid at the sixth
position in normal β-globin prevent? Speculate as to how the charge of this amino acid may play
a role. - ANS Chapter 15 Concept Checks
Figure 15.1 At neutral pH, glutamic acid is negatively charged. Perhaps the negative
charges repel each other and prevent hemoglobin proteins from aggregating into
fiber-like structures
Figure 15.3 Example of a somatic mutation. This child has a streak of white hair. This is due to a
somatic mutation in a single cell during embryonic development. This cell continued to divide to
produce a streak of white hair.
Concept Check: Can this child with a streak of white hair transmit this
trait to his future offspring? - ANS Chapter 15 Concept Checks
Figure 15.3 This trait is due to a mutation that occurred in a somatic cell, so it cannot be
transmitted to the individual's offspring.
Figure 15.6 Formation and structure of a thymine dimer.
Concept Check: Why is a thymine dimer harmful? - ANS Chapter 15 Concept Checks
Figure 15.6 A thymine dimer is harmful because it can cause an error in DNA replication that
results in a mutation.
Figure 15.8 Nucleotide excision repair in E. coli.
, Concept Check: Which components of the NER system are responsible for removing the
damaged DNA? - ANS Chapter 15 Concept Checks
Figure 15.8 UvrC and UvrD are responsible for removing the damaged DNA. UvrC
makes cuts on both sides of the damage, and then UvrD removes the damaged region.
Figure 15.9 An individual affected by xeroderma pigmentosum.
Concept Check: Why is this person so sensitive to sunlight? - ANS Chapter 15 Concept Checks
Figure 15.9 The Sun produces UV light and other harmful radiation that can damage DNA. This
person has a defect in the nucleotide excision repair system. Therefore, her DNA is more likely
to suffer mutations, which can cause pigmentation changes and other effects on the skin.
Figure 15.11 General features of a signal transduction pathway involving a growth factor that
promotes cell division. A detailed description of this pathway is found in Chapter 9 (look back at
Figure 9.10).
Concept Check: How does the presence of a growth factor ultimately affect the function of a
cell? - ANS Chapter 15 Concept Checks
Figure 15.11 Growth factors turn on a signal transduction pathway that ultimately leads to cell
division.
Figure 15.14 The formation of a fused gene found in people with certain forms of leukemia. The
fusion of the bcr and abl genes creates a fused gene that encodes a fusion protein, leading to
leukemia. The blue regions are the promoters for the bcr and abl genes.
Concept Check: The bcr gene is normally expressed in white blood cells. Explain how this
observation is related to the type of cancer that the translocation between chromosomes 9 and
22 causes. - ANS Chapter 15 Concept Checks
Figure 15.14 The type of cancer associated with this translocation is leukemia, which is a
cancer of blood cells. The fused gene is expressed in white blood cells because it has the bcr
promoter. The abnormal fusion protein promotes cancer in these cells.
Figure 15.15 The cell cycle and checkpoints. As discussed in Chapter 16, eukaryotic cells
advance through a cell cycle composed of G1 , S, G2, and M phases (look ahead to Figure
16.2). The yellow bars indicate common checkpoints where the cell cycle is stopped if genetic
abnormalities are detected. The p53 protein stops a cell at the G1 checkpoint if it senses DNA
damage.
Concept Check: Why is it an advantage for an organism to have checkpoints where the cell
cycle can be stopped? - ANS Chapter 15 Concept Checks
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