
Concept explainers
A.
To explain: The size of rats can be increased by blocking apoptosis.
Concept introduction: Apoptosis in simple terms can be defined as programmed cell death. The cell is kept alive with the trophic factors that are produced under good nutritional conditions. In the absence of trophic factors, the cells activate a suicide program called as intrinsic pathway of apoptosis. Cells enter apoptosis when they do not receive any signal or when apoptosis is initiated with signals from the adjacent cells (paracrine signaling) called death signals in an extrinsic apoptotic pathway that occurs during development.
Case summary: Person L is charged with highly classified research where his task is to develop a strain of dog-sized rats to deploy behind enemy lines. He has been given four strategies to increase the size of rats.
B.
To explain: The size of rats can be increased by blocking p53 function.
Concept introduction: Radiation leads to double-stranded and single-stranded breaks in the DNA. In order to reverse the damage, cell cycle checkpoint mechanisms are activated. There are two proteins namely ATM and ATR that recognize the strand damages. ATM activates a kinase called Chk1/2, which gives inactivating phosphorylation to Cdc25C phosphatase, thus the cell gets arrested at the M phase. ATR activates a protein called p53, which in turn activates another protein called p21 that inhibits the G1 cyclin CDK. This inactivation helps the cell to perform DNA repair activity with the respective polymerases and excision enzymes.
Case summary: Person L is charged with highly classified research where his task is to develop a strain of dog-sized rats to deploy behind enemy lines. He has been given four strategies to increase the size of rats.
C.
To explain: The size of rats can be increased by overproducing growth factors, mitogen, or survival factors.
Concept introduction: Growth factors are typical cell signaling molecules that stimulate cell growth, cell division, and differentiation during development. Growth factors are usually hormones either protein hormones or steroid hormones. Mitogens are molecules in the cell that stimulates mitosis. Mitogens are usually proteins and are ligands in the MAP kinase pathway. Trophic factors are survival factors that signal the cell to keep performing its
Case summary: Person L is charged with highly classified research where his task is to develop a strain of dog-sized rats to deploy behind enemy lines. He has been given four strategies to increase the size of rats.
D.
To explain: The researcher obtaining a taxi driver license and switch careers.
Case summary: Person L is charged with highly classified research where his task is to develop a strain of dog-sized rats to deploy behind enemy lines. He has been given four strategies to increase the size of rats.

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Chapter 18 Solutions
Essential Cell Biology (Fourth Edition)
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