Other Hormone Pathways - Biochemistry

Insulin is secreted in response to high blood glucose levels, which increases cell uptake of glucose. Glycogen has the opposite effect - it stimulates glycogenolysis and lipolysis to release glucose into the bloodstream during times of fasting/starvation.

Epinephrine and glucagon are examples of hormones that affect G protein-coupled receptors like adenylate cyclase and increase levels of cAMP. The other hormones listed affect receptor tyrosine kinases and non-receptor tyrosine kinases.

Elevated arginine leads to an increase in secretion of insulin, not decreased. GIP, CCK and closing of the voltage gated potassium channels lead to an increase in secretion of insulin.

Ketone bodies, which include acetoacetate, beta-hydroxybutyrate, and acetone, are produced by the liver in the fasting state by beta-oxidation of fatty acids. They are then released into the blood stream, where they can be used as alternative energy sources for other organs, such as muscle, kidney, and brain. Apoprotein B is one of the proteins that hold lipoproteins together. Beta-carotene is a vitamin with antioxidant properties.

Epinephrine first binds to an adrenergic receptor. The activated receptor works via a G protein, and so GDP is exchanged for GTP and the protein is activated. This then causes activation of adenylate cyclase and subsequent conversion of ATP to cAMP. cAMP acts upon protein kinase A and several other effector molecules. Diacylglycerol and IP3 are second messengers that are uninvolved in this process.

Erythropoietin is a glycoprotein hormone produced in the kidney that stimulates the production of red blood cells in the bone marrow.

Glucagon is a short peptide hormone involved in triggering signal cascades in response to low blood glucose. Biotin, also known as vitamin B7, is a cofactor in fatty acid synthesis. Pyridoxal phosphate, the activated form of vitamin B6, is a cofactor in transamination reactions, among others. Epinephrine is a steroid hormone involved in the fight or flight response.

This question is asking us to identify a hormone that passes through the target cell's plasma membrane in order to affect that cell.

When looking at hormones, there are three general types: amine, peptide, and steroid. Out of these, steroid hormones are all capable of crossing the plasma membrane. In fact, the receptors for steroid hormones are often found in the cytoplasm or nucleus of the target cell. Generally, amine and peptide hormones act by binding to a receptor on the outer surface of the target cell's plasma membrane. However, thyroxine is an exception. Thyroxine is an amine hormone based off of the amino acid tyrosine. Normally, amine-derived hormones do not cross the plasma membrane, but the largely hydrophobic nature of thyroxine allows it to cross the plasma membrane and bind with its intracellular receptor.

Of the other answer choices shown, none of them cross the cell membrane. Epinephrine is an amine-derived hormone, utilizing tyrptophan as the starting material. Insulin, glucagon, and growth hormones are all peptide hormones.