Question

Identify two chemical classes of hormones, how do these different hormone classes affect the way these hormones are transported and how they interact and affect change on their target cells

Answer 1

Ans :

Two chemical classes of hormones :

1. Lipid derived hormones

2. Amino acids derived hormones

Lipid derived : Most lipid hormones are derived from cholesterol and thus are structurally similar to it. The primary class of lipid hormones in humans is the steroid hormones. Examples of steroid hormones include estradiol, which is an estrogen, or female sex hormone, and testosterone, which is an androgen, or male sex hormone

Amino acids derived : The amino acid-derived hormones are relatively small molecules that are derived from the amino acids tyrosine and tryptophan, This class also includes small proteins, like growth hormones produced by the pituitary, and large glycoproteins such as follicle-stimulating hormone produced by the pituitary and adrenal hormones epinephrine

Pathways :

Peptide :  

For a peptide hormone to initiate a cellular response it must first bind to a specific receptor on the cell surface. Hormones are synthesized by specific tissues and released into the circulation. Once in the blood, the hormone will bind to specific receptors on the surface of appropriate target cells. Of prime importance for our discussion of glycogen metabolism are the hormones insulin and glucagon. These hormones are released by, and regulate, the level of glucose within the circulation. Specific cells within the pancreas can measure the level of glucose in the blood and release the appropriate hormone. When blood glucose levels are low, the pancreas releases glucagon, which activates glycogen degradation in the liver to raise blood glucose levels. When the blood glucose levels are high, the pancreas releases insulin so that both the muscle and the liver will now synthesize glycogen to store excess glucose.

Once a hormone binds to its specific receptor, the receptor alters its conformation and activates intracellular enzymes to signal the cell. In the case of glucagon secretion, indicating low blood glucose levels, hormone binding will activate the enzyme adenylate cyclase, which converts ATP to cyclic AMP . The increase in intracellular cAMP levels activates a cyclic AMP-dependent protein kinase, which will phosphorylate various enzymes Two of the enzymes that are phosphorylated are glycogen synthase and glycogen phosphorylase kinase. Phosphorylation of glycogen synthase inactivates the enzyme. Phosphorylation of glycogen phosphorylase kinase activates this second kinase. The primary substrate of glycogen phosphorylase kinase is glycogen phosphorylase, which upon phosphorylation will be activated. Thus, under conditions of glucagon release the enzyme that makes glycogen is inactivated, and the enzyme that degrades glycogen is activated. This will enable the liver to degrade its own glycogen, thereby producing glucose to raise blood glucose levels. The muscle does not respond to glucagon, because muscle does not express cell surface receptors for glucagon.

Lipid hormones : Two pathways

Genomic pathwaysEdit

The first identified mechanisms of steroid hormone action were the genomic effects. In this pathway, the free hormones first pass through the cell membrane because they are fat soluble.In the cytoplasm, the steroid may or may not undergo an enzyme-mediated alteration such as reduction, hydroxylation, or aromatization. Then the steroid binds to a specific steroid hormone receptor, also known as a nuclear receptor, which is a large metalloprotein. Upon steroid binding, many kinds of steroid receptors dimerize: two receptor subunits join together to form one functional DNA-binding unit that can enter the cell nucleus. Once in the nucleus, the steroid-receptor ligand complex binds to specific DNA sequences and induces transcription of its target genes.

Non-genomic pathwaysEdit

Because non-genomic pathways include any mechanism that is not a genomic effect, there are various non-genomic pathways. However, all of these pathways are mediated by some type of steroid hormone receptor found at the plasma membrane.Ion channels, transporters, G-protein coupled receptors (GPCR), and membrane fluidity have all been shown to be affected by steroid hormones.Of these, GPCR linked proteins are the most common.