CHAPTER 12 (Pictures)

CHAPTER 12 (Pictures) - 1 Lehninger Principles of...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Lehninger Principles of Biochemistry Fourth Edition Chapter 12: Biosignaling Copyright 2004 by W. H. Freeman & Company David L. Nelson and Michael M. Cox 2 Biosignaling The fundamental of life start with the ability of cells to receive act on signals Bacteria cells : Receive constant signals that samples medium pH, osmotic strength, availability of food, oxygen and light, presence of noxious chemicals, predators and competitors for food The signals elicit appropriate responses such as a motion toward food or away from toxic substance or formation of dormant spores in a nutrient-depleted medium In Multicellular organism : Plants cell response to growth hormones and to variations in sunlight Animal cells exchange information on: Stage of embryonic development Concentration of ions and glucose in extracellular fluids Interdependent metabolic activities taking place in different tissues Signals in animals may be ( Table 12-1 ) Autocrine acting on the cell that produce them Paracrine acting on a near neighbor Endocrine carried in the bloodstream for the produce cells to a distant target cell 3 4 Molecular Mechanisms of Signal Transduction Specificity : Achieved because of precise molecular complementarity between signals and receptor molecule ( Figure 12-1a ). In multicellular organism receptors for a given signal or the intacellular target of a given signal pathway are present only in certain cell types. Examples Thyrotropin releasing hormone triggers responses in the cells of anterior pituitary but not in hepatocytes (lacking receptors) Epinephrine alters glycogen metabolism in hepatocytes but not erythrocytes although both cell types have receptor. WHY? Hepatocytes have glycogen-metabolizing enzyme that is stimulated by epinephrine, but erythrocytes do not. 5 6 Molecular Mechanisms of Signal Transduction Sensitivity : Factors accounting for extraordinary sensitivity are: High affinity of receptors for signal molecules. The affinity btw signal (ligand) and receptor can be expressed as dissociation constant Kd ~ 10-10 M or less, meaning receptor can detect picomolar concentration of ligand. Coorporativity in receptor-ligand interaction results in large changes in receptor activation of small changes in ligand concentration. Amplification by enzyme cascade ( Figure 12-1b ) Signal Enzyme 1 >many molecules E2 >many molecules E3 >and so on. 7 8 9 Molecular Mechanisms of Signal Transduction Sensitivity Modification Desensitization ( Figure 12-1c ). When stimulus falls below a certain threshold, the system again becomes sensitive (e.g, Eyes reaction when moving from light to dark or verse versa) Integration ( Figure 12-1d ) Ability of the system to receive multiple signals and produce a unified response appropriate to the needs of the cell or organism....
View Full Document

Page1 / 35

CHAPTER 12 (Pictures) - 1 Lehninger Principles of...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online