Question 1

Which of the following is true during a typical cAMP-type signal transduction event?

Accepted Answer

During a typical cAMP-type signal transduction event, the hormone binds to its receptor on the cell surface, which activates adenylyl cyclase. Activated adenylyl cyclase then generates cAMP, the second messenger, which goes on to activate protein kinase A and ultimately phosphorylate downstream targets. Therefore, adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation occurs.

Question 2

In the cAMP pathway,a signalling molecule binds to and activates the cell surface receptor but the adenylyl cyclase remains inactivated.What is the most likely reason for this?

Accepted Answer

Adenylyl cyclase is activated by the G protein when GDP is replaced by GTP on the G protein. If this step does not occur, adenylyl cyclase remains inactive, despite the activation of the cell surface receptor.

Question 3

What condition would exist in a patient whose thyroid gland cannot sequester iodine?

Accepted Answer

If the thyroid gland cannot sequester iodine, it cannot produce enough thyroid hormones, leading to hypothyroidism and potentially causing goiter, which is an enlargement of the thyroid gland due to overstimulation by TSH.

Question 4

How can a single hormone can have multiple effects?

Accepted Answer

A single hormone can have multiple effects because there are different types of receptors in different target tissues, different second messengers in different target tissues, and different signaling cascades in different target tissues. All of these factors contribute to the hormone producing different effects in different tissues.

Question 5

Tadpoles must undergo a major metamorphosis to become frogs.This change includes reabsorption of the tail,growth of limbs,calcification of the skeleton,increase in rhodopsin in the eye,development of lungs,change in hemoglobin structure,and reformation of the gut from the long gut of an herbivore to the short gut of a carnivore.Amazingly,all of these changes are induced by thyroxine.What is the most likely explanation for such a wide array of effects of thyroxine?

Accepted Answer

The answer of Tadpoles must undergo a major metamorphosis to...

Question 6

The vast majority of obese individuals have high leptin levels (db),while only a few rare obese individuals (ob)do not produce leptin.Which of the following hypotheses explains why leptin can cure obese individuals who produce no leptin (ob)while having no effect on other obese individuals (db)?

Accepted Answer

The fact that leptin can cure obese individuals who produce no leptin (ob)while having no effect on other obese individuals (db) suggests that the issue is not with the production of leptin itself, but with the ability of the brain to respond to it. Therefore, choice C, stating that ob individuals have dysfunctional leptin receptors in the brain, best explains this observation. Choices A and B are inconsistent with the fact that leptin can cure ob individuals. Choice D is too broad and redundant with the other three choices.

Question 7

Why would most of the females in a college dormitory tend to have their menstrual cycles synchronized after living together for an extended period of time?

Accepted Answer

Studies have shown that pheromones, chemical signals released by one individual that can affect the physiology or behavior of another individual, play a role in menstrual synchrony. During the menstrual cycle, females release a group of pheromones called "copulins" that can affect the timing and duration of other females’ menstrual cycles through a mechanism called the “Lee-Boot effect” or the “Whitten effect”. While living in close quarters in a dormitory, exposure to these pheromones from the other females can lead to synchronization of menstrual cycles.

Question 8

Which of the following statements correctly describes the relationship between the hypothalamus (H)and the anterior (AP)and posterior (PP)lobes of the pituitary?

Accepted Answer

The hypothalamus communicates directly with the posterior pituitary through neural connections, and indirectly with the anterior pituitary through the circulatory system via the release of releasing hormones which stimulate or inhibit the anterior pituitary's secretion of hormones. Therefore, statement C is the best choice as it describes the correct relationship between the hypothalamus and both lobes of the pituitary.

Question 9

A weightlifter decides to try taking steroids to improve his performance level.Following a month of use,he notes that the steroids have had no effect on his performance.Which of the following is the most likely reason for this?

Accepted Answer

The answer of A weightlifter decides to try taking steroids...

Question 10

Of the following types of molecules,which can function as both neurotransmitters and hormones?

Accepted Answer

Catecholamines, such as dopamine, norepinephrine, and epinephrine, can function as both neurotransmitters in the nervous system and hormones in the endocrine system. Glucocorticoids, such as cortisol, are hormones produced by the adrenal gland and do not act as neurotransmitters. Second messengers, such as cAMP and IP3, are not molecules that can function as neurotransmitters or hormones. Adipocytes are fat cells and do not produce neurotransmitters or hormones.

Question 11

What changes might you predict/expect if a mutation caused a change in the timing of juvenile hormone,such that it remained high throughout the lifetime of the organism?

Accepted Answer

Juvenile hormone is responsible for keeping an organism in its juvenile state and preventing it from maturing reproductively. If this hormone remained high throughout the lifetime of the organism, it would maintain its juvenile state for the remainder of its life. This would result in a failure to undergo metamorphosis and reach adulthood. The organism would likely exhibit characteristics such as smaller size, reduced fertility, and inability to form structures required for stress response.

Question 12

How can the body prevent a hormone with different effects on different tissues from acting on inappropriate cells at inappropriate times?

Accepted Answer

The body can prevent a hormone with different effects on different tissues from acting on inappropriate cells at inappropriate times by shunting blood supply to the desired tissues, internalizing receptors on nontargeted cells, and changing the conformation of receptors on nontargeted cells. Therefore, all of the above answers apply.

Question 13

You spend two months in the mountains of Peru at ~ 3500 m altitude.After returning to Toronto,you notice that you can run your regular 10 k route significantly more easily than before you left.What is the reason for this burst of fitness?

Accepted Answer

At higher altitudes, the decrease in oxygen concentrations stimulates the release of erythropoietin (EP), which in turn stimulates the production of red blood cells. This ultimately increases the oxygen carrying capacity of blood, resulting in greater endurance and better athletic performance even at lower altitudes.

Question 14

Which of the following is not considered a second messenger?

Accepted Answer

Norepinephrine is a neurotransmitter and not a second messenger. Second messengers are intracellular molecules that transmit signals from cell surface receptors to target molecules inside the cell. Examples include cAMP, IP3, and DAG.

Question 15

When an ant locates a food source,it leaves a trail that other ants can follow to locate the same food source.What type of chemical signalling is this an example of?

Accepted Answer

Pheromones are chemical signals released by an organism that can affect the behavior or physiology of other individuals of the same species. In the case of the ant, the pheromones it leaves on its trail serve as a guide for other ants to follow to the food source. Therefore, it is an example of chemical signalling through pheromones.

Question 16

Signal transduction occurs when a chemical message at the cell surface elicits a response inside the cell.Which one of the following events is not associated with signal transduction?

Accepted Answer

Internal receptor binding is actually an essential part of signal transduction, as it allows the chemical message to be transmitted from the cell surface to the inside of the cell. Protein phosphorylation, cell-surface receptor binding, and second messenger activation are all common events in signal transduction.

Question 17

Which of the following best describes the neuroendocrine-to-endocrine pathway of hormone action?

Accepted Answer

The neuroendocrine-to-endocrine pathway of hormone action involves a neural organ producing hormones which then regulate another gland through the release of those hormones into the circulation. This describes choice A. Choice B describes a direct interaction between neural organ and the gland it regulates, which is not part of this pathway. Choice C describes a different type of interaction between a gland and neural tissue, which is also not part of this pathway. Choice D mentions negative feedback on the nervous system, which may occur in some cases with hormone release, but does not describe the pathway of hormone action being asked about.

Question 18

The posterior pituitary is anatomically and developmentally an extension of the hypothalamus.Which of the following is a true statement about the posterior pituitary?

Accepted Answer

The statement that the posterior pituitary's hormones are actually produced in neurosecretory cells that originate in the hypothalamus is true, while the statement that it is called the master gland is false. Therefore, only option B is the correct choice.

Quiz 47: Chemical Signals in Animals