Biochemistry : Peptide Hormone Pathways

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #1062 : Biochemistry

A researcher is analyzing a hormone. His results reveal that the hormone does not enter the cell. What can you conclude about this hormone?

Possible Answers:

It could have aspartic acid as one of its amino acids

It is negatively charged at physiological pH

It is positively charged at physiological pH

It forms clumps in an aqueous solution

Correct answer:

It could have aspartic acid as one of its amino acids

Explanation:

Steroid hormones are nonpolar molecules that can travel across the hydrophobic (or nonpolar) interior of the plasma membrane whereas peptide hormones are polar molecules that cannot travel across the hydrophobic interior. The question states that the hormone cannot enter the cell. This means that it cannot traverse the plasma membrane and, therefore, must be a peptide hormone. A peptide is made up of several amino acids. There are polar and nonpolar amino acids. Since they are polar, peptide hormones must have at least a few polar amino acids. These polar amino acids can be positively charged, negatively charged, or uncharged. There are twelve polar amino acids, five of which are charged (aspartic acid, glutamic acid, histidine, lysine, and arginine). Aspartic acid and glutamic acid are negatively charged at physiologic pH, whereas the other three are positively charged. A molecule that forms clumps in water is hydrophobic and nonpolar. Since we are dealing with a peptide hormone, the hormone will dissolve and not form clumps in water. A steroid hormone, on the other hand, is nonpolar and will form clumps in water.

Example Question #1 : Peptide Hormone Pathways

Which of the following hormones does not have its receptor in the cytoplasm?

Possible Answers:

Hormone containing phenylalanine, histidine, and methionine

Hormone containing isoleucine, glycine, and tryptophan

Hormone containing valine, leucine, and lysine

None of these hormones will have a cytoplasmic receptor

Correct answer:

Hormone containing phenylalanine, histidine, and methionine

Explanation:

A hormone is a signaling molecule that binds to a receptor and initiates a signaling cascade inside the cell. The receptor for a hormone can be found on the periphery of the cell (on plasma membrane) or inside the cell (cytoplasm or nucleoplasm). A steroid hormone is nonpolar and can traverse the hydrophobic interior of the plasma membrane whereas a peptide hormone is polar and cannot traverse the hydrophobic interior; therefore, a steroid hormone will have its receptor inside the cell whereas a peptide hormone will have its receptor on the plasma membrane. The question is asking us to find the polar, peptide hormone (because its receptor will be found on the plasma membrane, not in cytoplasm). To answer this question, we need to know which amino acids are polar. Recall that there are twelve polar amino acids. They are serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartic acid, glutamic acid, histidine, lysine, and arginine; therefore, the hormone containing phenylalanine, histidine, and methionine is most likely to be polar. The rest of the hormones have nonpolar amino acids only.

Example Question #1064 : Biochemistry

Which of the following molecules might be involved in a peptide hormone pathway? 

I. G protein coupled receptor

II. Receptor tyrosine kinase

III. Cyclic adenosine monophosphate

Possible Answers:

I and II

I and III

II and III

I, II and III

Correct answer:

I, II and III

Explanation:

Peptide hormones are polar molecules that cannot traverse the plasma membrane. Recall that plasma membranes have a hydrophobic interior. Since peptide hormones are polar, they cannot travel through this hydrophobic interior of the plasma membrane; therefore, peptide hormones signal cells by binding to receptors on the plasma membrane. There are several types of hormone receptors on the membrane, including G protein coupled receptors and receptor tyrosine kinases. Upon binding, the receptors activate themselves and other intracellular molecules called second messengers. This leads to a signaling cascade that ultimately results in upregulation or downregulation of processes inside the cell. Second messenger molecules facilitate the amplification and propagation of signal throughout the cell. Cyclic adenosine monophosphate, or cAMP, is one of the most common second messenger molecules; therefore, all three molecules listed in this question are involved in peptide hormone pathway.

Example Question #1065 : Biochemistry

How does insulin facilitate the entry of glucose into adipose and muscle tissue?

Possible Answers:

Increasing the translocation of GLUT-2 receptors to the cell surface

Increasing the permeability of the plasma membrane to all solutes

Inhibiting glucokinase in the liver

Increasing the translocation of GLUT-4 receptors to the cell surface

Binding with plasma glucose to form an absorbable complex

Correct answer:

Increasing the translocation of GLUT-4 receptors to the cell surface

Explanation:

Insulin promotes the translocation of GLUT-4 receptors to the cell surface through cell signaling triggered by its binding to cell surface insulin receptors. GLUT-2 transporters are insulin-independent and are found in tissues like the pancreas and liver where immediate glucose sensing is important for whole body function (The pancreas needs to sense glucose so it can secrete insulin for the rest of the body. Imagine if the pancreas itself needed insulin.)

Example Question #1066 : Biochemistry

Glucagon and epinephrine are similar in that they induce __________.

Possible Answers:

Gluconeogenesis and protein synthesis

glycogenolysis and gluconeogenesis

Prostaglandin synthesis only

Glycogenesis only

Lipid synthesis only

Correct answer:

glycogenolysis and gluconeogenesis

Explanation:

Glucagon and epinephrine are typically thought of as having catabolic effects; however, their purpose is to increase the availability of fuel substrates to extra-hepatic tissues during the fasting state or during fight or flight situations, respectively. So, while many of their effects like glycogenolysis and lipolysis conform to this pattern, they also induce the anabolic process of gluconeogenesis in the liver to increase the availability of glucose to other tissues.

Example Question #1 : Hormones And Neurotransmitters

The peptide hormone adrenocorticotropic hormone (ACTH) is secreted from the pituitary gland and stimulates the production of the glucocorticoid cortisol in the adrenal cortex. Which of the following best describes the feedback pathway by which ACTH is regulated by cortisol? 

Possible Answers:

Cortisol stimulates the release of fibroblast growth factor hormone from the hypothalamus, which results in an increase in ACTH released from the pituitary gland. This is a positive feedback loop. 

Cortisol inhibits the release of fibroblast growth factor hormone from the hypothalamus, which results in a decrease in ACTH released from the pituitary gland. This is a negative feedback loop. 

Cortisol stimulates the release of corticotropin-releasing hormone from the hypothalamus, which results in a decrease in ACTH released from the pituitary gland. This is a positive feedback loop. 

Cortisol inhibits the release of corticotropin-releasing hormone from the hypothalamus, which results in a decrease in ACTH released from the pituitary gland. This is a negative feedback loop. 

Cortisol stimulates the release of corticotropin-releasing hormone from the hypothalamus, which results in an increase in ACTH released from the pituitary gland. This is a positive feedback loop. 

Correct answer:

Cortisol inhibits the release of corticotropin-releasing hormone from the hypothalamus, which results in a decrease in ACTH released from the pituitary gland. This is a negative feedback loop. 

Explanation:

ACTH is regulated by a negative feedback loop, in which ACTH secretion stimulates production of cortisol, but this feeds back on to the hypothalamus to inhibit the production of corticotropin-releasing hormone (CRH). CRH is a positive regulator of ACTH production, so a decrease in CRH ultimately results in a decrease in ACTH. 

Example Question #2 : Hormones And Neurotransmitters

Deactivation of phospholipase-C will cause which of the following? 

Possible Answers:

Increase in cytosolic calcium levels

Release of diacylglycerol (DAG) from the plasma membrane

Release of inositol 1,4,5-triphosphate (IP3) from the plasma membrane

Maintenance of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in the plasma membrane

Correct answer:

Maintenance of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in the plasma membrane

Explanation:

Phospholipase C normally breaks down phosphatidylinositol (3,4,5)-trisphosphate (PIP3) into diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP3). This cascade eventually increases cytosolic calcium levels through its release from the endoplasmic reticulum and from the extracellular fluid. Malfunction in this enzyme results in PIP3 not being broken down.

Example Question #3 : Hormones And Neurotransmitters

Insulin does all of the following except __________.

Possible Answers:

increase DNA replication

decrease lipolysis

promote glycogen synthesis

promote gluconeogenesis

increase protein synthesis

Correct answer:

promote gluconeogenesis

Explanation:

Insulin is a peptide hormone that is released in the fed state. Thus, it promotes glucose storage and DNA replication, but decreases glycogen breakdown and the release of glucose.

Example Question #4 : Hormones And Neurotransmitters

Which of the following is true about glucagon?

Possible Answers:

It is a steroid hormone

It promotes the release of glucose in the blood

It is secreted by the liver

It is released by beta cells in the pancreas

It increases in the blood after a high carbohydrate meal

Correct answer:

It promotes the release of glucose in the blood

Explanation:

Glucagon is a peptide hormone that is released in the fasted state. It stimulates macromolecule breakdown and the production and subsequent release of glucose into the blood stream. It is synthesized and released from the alpha-cells in the pancreatic islets.

Example Question #2 : Peptide Hormone Pathways

All of the following will induce insulin release into the blood except __________.

Possible Answers:

an increase in blood glucagon-like peptide-1 (GLP-1)

an increase in blood growth hormone

a high carbohydrate meal

an increase in incretins in the blood

All of these would stimulate insulin release.

Correct answer:

an increase in blood growth hormone

Explanation:

Insulin release is induced by incretins in the blood (ex. GLP-1), and a high carbohydrate meal. Incretins are metabolic hormones that stimulate a decrease in blood glucose. Growth hormone does not cause an increase in blood insulin.

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