glycoprotein

Examples of glycoprotein in the following topics:

• Fertilization

  • In mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida.
  • In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane .
  • (b) Acrosomal reactions help the sperm degrade the glycoprotein matrix protecting the egg and allow the sperm to transfer its nucleus.

• Protists as Human Pathogens

  • Trypanosoma brucei, the parasite that is responsible for African sleeping sickness, confounds the human immune system by changing its thick layer of surface glycoproteins with each infectious cycle .
  • The glycoproteins are identified by the immune system as foreign antigens and a specific antibody defense is mounted against the parasite.
  • However, T. brucei has thousands of possible antigens; with each subsequent generation, the protist switches to a glycoprotein coating of a different molecular structure.

• Thyroid Gland

  • These follicles contain a viscous fluid, called colloid, which stores the glycoprotein thyroglobulin.
  • This glycoprotein is the precursor to the thyroid hormones.

• Fluid Mosaic Model

  • They are always found on the exterior surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids).
  • Similar types of glycoproteins and glycolipids are found on the surfaces of viruses and may change frequently, preventing immune cells from recognizing and attacking them.
  • These carbohydrates on the exterior surface of the cell—the carbohydrate components of both glycoproteins and glycolipids—are collectively referred to as the glycocalyx (meaning "sugar coating").
  • Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

• Viral Morphology

  • Many viruses use some sort of glycoprotein to attach to their host cells via molecules on the cell called viral receptors .
  • Adenovirus, a non-enveloped animal virus that causes respiratory illnesses in humans, uses glycoprotein spikes protruding from its capsomeres to attach to host cells .
  • Glycoproteins embedded in the viral envelope are used to attach to host cells.
  • This figure shows three relatively-complex virions: the bacteriophage T4, with its DNA-containing head group and tail fibers that attach to host cells; adenovirus, which uses spikes from its capsid to bind to host cells; and HIV, which uses glycoproteins embedded in its envelope to bind to host cells.

• Red Blood Cells

  • A characteristic of red blood cells is their glycolipid and glycoprotein coating; these are lipids and proteins that have carbohydrate molecules attached.
  • In humans, the surface glycoproteins and glycolipids on red blood cells vary between individuals, producing the different blood types, such as A, B, and O.

• Steps of Virus Infections

  • A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope.
  • In influenza virus infection, glycoproteins attach to a host epithelial cell.

• Lipid-Derived, Amino Acid-Derived, and Peptide Hormones

  • This class also includes small proteins, such as growth hormones produced by the pituitary, and large glycoproteins, such as follicle-stimulating hormone produced by the pituitary .

• Membrane Fluidity

  • Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.

• Cell Signaling and Cell Death

  • For example, most normal animal cells have receptors that interact with the extracellular matrix, a network of glycoproteins that provides structural support for cells in an organism.