Which observation suggested to Sutherland the involvement of...

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? (A) Enzymaticactivity was proportional to the amount of calcium added to a cell-free extract. (B) Receptor studies indicated that epinephrine was a ligand. (C) Glycogen breakdown was observed only when epinephrine was administered to intact cells. (D) Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?
(A) Enzymaticactivity was proportional to the amount of calcium added to a cell-free extract.
(B) Receptor studies indicated that epinephrine was a ligand.
(C) Glycogen breakdown was observed only when epinephrine was administered to intact cells.
(D) Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.

Key Concepts

Cellular Integrity in Signaling

The requirement for intact cells in certain signaling processes highlights that some intracellular components necessary for generating second messengers are only present or functional within the intact cellular environment. This ensures the proper sequence of events leading to the amplified physiological response.

Second Messenger

A second messenger is an intracellular signaling molecule released in response to an extracellular signal (such as a hormone or neurotransmitter). Its role is to amplify and propagate the signal within the cell, ultimately resulting in a physiological response.

cAMP

Cyclic AMP (cAMP) is one of the most well-known second messengers. It is produced from ATP by the enzyme adenylyl cyclase and mediates various hormonal actions by activating protein kinases, leading to the regulation of metabolic processes.

Signal Transduction

Signal transduction refers to the process by which an extracellular signal is conveyed into a cellular response. This process often involves receptor activation at the cell surface and sequential intracellular events, including the generation of second messengers.

Transcript

00:01 Let's talk a little bit about epinephrine's effect on liver cells.

00:07 So just to review, earl sutherland did research on how the animal hormone epinephrine or adrenaline triggers the flight or fight response in animals.

00:20 He observed that one effect of epinephrine is to mobilize fuel reserves that can be used by the animal to either defend itself, the fight, or try to.

00:30 Escape flight.

00:33 So epinephrine stimulates the breakdown of the storage polysaccharide glycogen within liver cells.

00:40 The breakdown of that glycogen releases the sugar glucose 1 phosphate, and the cell converts to glucose 6 phosphate.

00:49 And the liver of the muscle cell can then use this compound for energy production.

00:57 So in researching sutherland's team discovered that the epinephrine outside the cell stimulates glycogen breakdown by activating an enzyme, glycogen phosphorylase, inside the cell.

01:11 However, when they added epinephrine to a solution containing the enzyme and its substrate, the glycogen, no breakdown occurred.

01:21 So glycogen phosphorylase could only be activated by epinephrine when the hormone was added to intact cells.

01:29 And this told sutherland two different things.

01:34 First, the epinephrine does not interact directly with the enzyme responsible for glycogen breakdown.

01:40 There must be an intermediate step or a series of steps that occur within the cell.

01:47 Secondly, an intact membrane -bound cell has to be present for transmission of the signal to take place.

01:55 So his work suggested that the process going on at the receiving end of a cellular communication can be basically broken down into three stages.

02:07 Reception, transduction, and response.

02:12 So if we were to draw that, here is our plasma membrane, and here is our receptor.

02:29 So the first thing that happens is signal reception.

02:34 So here's our signaling molecule or a ligand, it will bind to the receptor.

02:43 So reception is the target cells detection of a signaling molecule coming from outside the cell...

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