Biology, 28.11.2019 02:31, GarettNguyen1166

A. the signal molecules that bind to gpcrs all have a similar structure. b. signaling cascades associated with gpcrs always operate at the same speed, regardless of the initiating signal. c. the cyclic amp pathway can activate gene transcription, whereas the inositol phospholipid pathway cannot. d. some g proteins inhibit the production of cyclic amp. all second messenger molecules diffuse rapidly through the cytosol, thereby amplifying and spreading the signal.

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answered: jshu1998

The true option is D: some G proteins inhibit the production of cyclic AMP.

Explanation:

A. False. GPCRs have evolved to recognize a diversity of extracellular physical and chemical signals, such as nucleotides, peptides, amines, Ca²⁺, and photons.

B. False. the cAMP is a second messenger present in different signaling cascades and provokes very different responses depending on the type of cell which it acts on, the substance that induces this cell and the receptor activated. Glucogen degradation and the stop of its synthesis in stressful situations are two examples of immediate responses mediated by the catalytic subunits of protein kinase A. Inhibition of glucogenesis and gastrin secretion by islets of Langerhans are two examples of late responses mediated by PKA.

C. False. The inositol phospholipid pathway (PIP₂), by hydrolysis, produces 2 second messengers: DAG and IP₃. These molecules activate different cascades. IP₃, for example, unites to receptors in the SER, which are ligand-regulated Ca²⁺ channels. This union allows the flow of Ca²⁺ to the cytosol. It forms an active complex with the protein calmodulin, and this complex binds to different proteins, including CaM kinases. These CaM kinases regulate gene expression phosphorylating transcription factors, like CREB.

D. True. Some hormones inhibit adenylate cyclase and diminish the levels of cAMP and suppress protein phosphorylation. For example, the union of somatostatin to its receptor activates an inhibitory G protein (Gi), which inhibits adenylate cyclase and lowers the concentration of cAMP.

E. False. The activity of the second messenger Ca²⁺, as well as the cAMP, can be restricted in space; after the response provoked by its liberation, Ca²⁺ is eliminated before it can diffuse to distant parts of the cell.

answered: Guest

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )

answered: Guest

Environmental science studies the interactions between the physical, chemical, and biological components of the environment, including their effects on all types of organisms. earth science (also known as geoscience), is an inclusive term for all sciences related to earth (geology, meteorology, oceanogr maphy, etc). although environmental and earth science cover essentially the same material, environmental science places greater emphasis on the biological realm, while earth science places greater emphasis on the physical realm. environmental and earth science study the interactions of four major systems or “spheres” (figure 8.6). the geosphere consists of the core, mantle and crust of the earth.the atmosphere contains all of the earth’s air and is divided into troposphere, stratosphere, mesosphere, thermosphere and ionosphere.the hydrosphere contains all of the solid, liquid and gaseous water on earth, extending from the depths of the sea to the upper reaches of the troposphere where water is found. ninety-seven percent of the hydrosphere is found in salty oceans, and the remainder is found as vapor or droplets in the atmosphere and as liquid in ground water, lakes, rivers, glaciers and snowfields. the biosphere is the collection of all earth’s life forms, distributed in major life zones known as biomes: tundra, boreal forest, temperate deciduous forest, temperate grassland, desert, savannah, tropical rainforest, chaparral, freshwater, and marine.although the four systems have their unique identities, there is substantial interaction between them. environmental scientists study the effects of events in one sphere on the other spheres. for example, a volcanic eruption in the geosphere may cause profound direct and indirect effects on the hydrosphere, atmosphere and biosphere as follows: example 1 (volcano) on may 18, 1980, mount saint helens, in the state of washington, erupted. this event altered the surrounding environment, and provided scientists with an opportunity to study the effects of volcanic eruptions on the geosphere, hydrosphere, atmosphere and biosphere. such studies are vital because volcanic eruptions will continue to occur, and will have increasing impact on humans as people continue to settle lands closer to dormant volcanoes. the following are but a few of the myriad of interactions resulting from a volcanic