Lehninger Principles of Biochemistry, authored by David L. Nelson and Michael M. Cox, is a comprehensive textbook that explores the biochemical principles underlying biological processes. This 7th edition delves into topics such as signal transduction, enzyme function, metabolism, and molecular genetics. The book is structured into chapters that cover fundamental concepts, detailed mechanisms, and applications in various biological contexts. Key features include in-depth explanations of G protein-coupled receptors, receptor tyrosine kinases, and the regulation of cellular responses. The text is designed for students and professionals in biochemistry, molecular biology, and related fields, providing a solid foundation for understanding the biochemical basis of life. Published by W.H. Freeman and Company, this edition includes updated content and online resources to enhance learning and comprehension.
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CHAPTER 12 Biosignaling
12.1 General Features of Signal Transduction
12.2 G Protein–Coupled Receptors and Second
Messengers
12.3 GPCRs in Vision, Olfaction, and Gustation
12.4 Receptor Tyrosine Kinases
12.5 Receptor Guanylyl Cyclases, cGMP, and Protein
Kinase G
12.6 Multivalent Adaptor Proteins and Membrane Rafts
12.7 Gated Ion Channels
12.8 Regulation of Transcription by Nuclear Hormone
Receptors
12.9 Signaling in Microorganisms and Plants
12.10 Regulation of the Cell Cycle by Protein Kinases
12.11 Oncogenes, Tumor Suppressor Genes, and
Programmed Cell Death
Self-study tools that will help you practice what you’ve learned and reinforce
this chapter’s concepts are available online. Go to
www.macmillanlearning.com/LehningerBiochemistry7e.
he ability of cells to receive and act on signals from beyond the
plasma membrane is fundamental to life. Bacterial cells receive
constant input from membrane proteins that act as information
receptors, sampling the surrounding medium for pH, osmotic strength, the
availability of food, oxygen, and light, and the presence of noxious
chemicals, predators, or competitors for food. These signals elicit
appropriate responses, such as motion toward food or away from toxic
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substances or the formation of dormant spores in a nutrient-depleted
medium. In multicellular organisms, cells with different functions
exchange a wide variety of signals. Plant cells respond to growth
hormones and to variations in sunlight. Animal cells exchange information
about the concentrations of ions and glucose in extracellular fluids, the
interdependent metabolic activities taking place in different tissues, and, in
an embryo, the correct placement of cells during development. In all these
cases, the signal represents information that is detected by specific
receptors and converted to a cellular response, which always involves a
chemical process. This conversion of information into a chemical change,
signal transduction, is a universal property of living cells.
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12.1 General Features of Signal Transduction
Signal transductions are remarkably specific and exquisitely sensitive.
Specificity is achieved by precise molecular complementarity between the
signal and receptor molecules (Fig. 12-1a), mediated by the same kinds of
weak (noncovalent) forces that mediate enzyme-substrate and antigen-
antibody interactions. Multicellular organisms have an additional level of
specificity, because the receptors for a given signal, or the intracellular
targets of a given signal pathway, are present only in certain cell types.
Thyrotropin-releasing hormone, for example, triggers responses in the
cells of the anterior pituitary but not in hepatocytes, which lack receptors
for this hormone. Epinephrine alters glycogen metabolism in hepatocytes
but not in adipocytes; in this case, both cell types have receptors for the
hormone, but whereas hepatocytes contain glycogen and the glycogen-
metabolizing enzyme that is stimulated by epinephrine, adipocytes contain
neither. Adipocytes respond to epinephrine by metabolizing
triacylglycerols to release fatty acids, which are then transported to other
tissues.
FIGURE 12-1 Six features of signal-transducing systems.
Three factors account for the extraordinary sensitivity of signal
transduction: the high affinity of receptors for signal molecules,
cooperativity (often but not always) in the ligand-receptor interaction, and
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