Understanding Signal Transduction: Extracellular vs
School
Sahuaro High School**We aren't endorsed by this school
Course
BIOLOGY 12
Subject
Biology
Date
Dec 11, 2024
Pages
3
Uploaded by lisamooney
118 Key Question: How do the properties of signal molecules determine the nature of the signal transduction pathway? Cell receptors fall into two broad classes. Extracellular receptors bind hydrophilic signal molecules outside of the cell. The signal molecule does not have to pass across the Hydrophilic signal molecules are received by extracellular receptors _ Hydrophilic signal molecules such as epinephrine are water soluble and cannot cross the plasma membrane. The epinephrine receptor is an example of a G-coupled receptor. Epinephrine accelerates heart rate and is involved in the fight or flight response. Extracellular The first messenger fluid (signal molecule) binds to the receptor protein. Receptor protein G-protein subunit Intracellular from the receptor domain of the protein activates =~ receptor protein ‘the enzyme. - changes shape. Active enzyme produces a second messenger. The second messenger triggers a cascade of phosphorylation events leading to a cellular response. \/ Cell response Cytoplasm Hydrophilic signal molecules cannot cross the plasma membrane and must exert their effect by interacting with an extracellular receptor. Hydrophilic signals include water soluble hormones such as epinephrine and insulin. The signal molecule is the first messenger. When it binds, the extracellular receptor changes shape, triggering a sequence of biochemical reactions, including activation of a second messenger. As a consequence, the original signal is amplified, bringing about a cellular response. This pathway is given in more detail in the next activity. Types of Signal Transduction plasma membrane to cause a cellular response. Most cell receptors are extracellular receptors. Intracellular receptors bind hydrophobic signal molecules that pass into the cell directly across the plasma membrane. Intracellular receptors may be located in the cytoplasm or on the nucleus. Hydrophobic signal molecules are received by intracellular receptors Estrogen is the primary female sex hormone. It is involved in the development and maintenance of female characteristics. Estrogen is a steroid (as is the male sex hormone testosterone). Extracellular fluid Signal molecule Lipid soluble signal molecule passes = cross the plasma ¥ receptor/signal Receptor/signal complex acts as a transcription factor, binding to DNA to begin transciption. Nucleus The protein product roduced alters the cell’s activity. Cell response Cytoplasm Hydrophobic hormones, such as steroids (e.g. estrogen), diffuse freely across the plasma membrane and into the cytoplasm of target cells. Once inside the cell, they bind to intracellular receptors in the cytoplasm to form a receptor- signal complex. The complex moves to the cell nucleus where it binds directly to the DNA and acts as a transcription factor, resulting in the transcription of a one or more specific genes. Concentrations of the different gene products (proteins) change as a result (a phenotypic change).
o @ 5. . Describe the differences between an intracellular receptor and an extracellular receptor: . What must a signal molecule do in order to activate a receptor? . In terms of their ability to cross the plasma membrane, describe the difference between a hydrophobic signal molecule and a hydrophilic signal molecule: (a) Describe the process of signal transduction via an extracellular receptor: . (b) Describe the differences between a first messenger and a second messenger: Describe the process of signal transduction via an intracellular receptor: The diagram on the right represents a cell signaling process. (a) Does this diagram represent an extracellular or intracellular «— Plasma membrane signaling process? Explain your answer: (b) What type of receptor is B? (c) What does A represent? (d) Would A be hydrophobic or hydrophilic? Explain your answer: 119
Quorum sensing and bioluminescence in bacteria 4 Quorum sensing is a process of cell to cell communication between bacterial cells. It involves extracellular signaling molecules called autoinducers. Bacteria share information about cell density in their environment and then alter their cellular response through changes in gene expression. Quorum sensing allows the bacterial population to act together in a coordinated way. A critical number (quorum) is required for the action to be beneficial. Quorum sensing helps to ensure that energy and resources are not expended unnecessarily. It regulates many activities in bacteria, including symbiosis, virulence, motility, antibiotic production, and biofilm formation. Explain the significance of signal amplification in signal transduction pathways: 121 Autoinducer Luminescence is controlled by an autoinducer, which acts as a local regulator. As bacterial density increases, more and more Inactive LuxR autoinducer is produced. When the level of autoinducer is high enough, it activates the protein LuxR, which then stimulates the expression of the genes encoding the proteins involved in luminescence. Genes for luminescence Proteins involved in luminescence The Hawaiian bobtail squid (left) lives in a mutually beneficial symbiotic relationship with the bacterium Aliivibrio fischeri, which luminesces when the bacterial population reaches a certain density. Hatchling squid capture bacteria from the environment and house them at high densities in a light organ. The bacteria receive sugars and amino acids and the squid uses the luminescing bacterial to provide camouflage through counter-illumination (producing light on their bellies to match the light coming down from above). Luminescent bacteria produce light as the result of a chemical reaction that converts chemical energy to light energy. Explain why each molecule in the cCAMP signal cascade is phosphorylated: How does the bobtail squid make use of the quorum sensing abilities of Aliivibrio fischerr? Use the information presented above and opposite to justify the claim that signal transduction patnways influence how cells respond to their environment: