Glycoprotein hormones are a group of hormones that are biochemically characterized by long chains of sugars attached to their protein backbones. The addition of these sugar molecules, a process known as glycosylation, affects the stability, secretion, and signal transduction of these hormones.

There are four major glycoprotein hormones in mammals:

1. Follicle-stimulating hormone (FSH): FSH is produced by the pituitary gland and plays a critical role in reproduction. In females, FSH stimulates the growth of ovarian follicles and the production of estradiol during the first half of the menstrual cycle. In males, FSH stimulates the production of sperm.

2. Luteinizing hormone (LH): LH is also produced by the pituitary gland and is involved in reproduction. In females, LH triggers ovulation and stimulates the corpus luteum to produce progesterone during the second half of the menstrual cycle. In males, LH stimulates the production of testosterone.

3. Thyroid-stimulating hormone (TSH): TSH, produced by the pituitary gland, stimulates the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3), hormones that regulate the body's metabolism.

4. Human chorionic gonadotropin (hCG): hCG is produced by the placenta during pregnancy. It maintains the production of progesterone by the corpus luteum, thus sustaining the pregnancy in its early stages.

These hormones are made up of two subunits: an alpha subunit, which is similar for all four hormones, and a beta subunit, which is unique for each hormone and determines its specific biological action.

Each of these hormones acts by binding to specific glycoprotein hormone receptors on the surface of target cells, leading to the activation of intracellular signaling pathways. Dysregulation of glycoprotein hormone production or signaling can lead to various diseases, including infertility, thyroid disorders, and certain types of cancer.