ubiquitin

protein

Learn about this topic in these articles:

Ciechanover

  • In Aaron J. Ciechanover

    …first step a molecule called ubiquitin (from the Latin ubique, meaning “everywhere,” because it occurs in so many different cells and organisms) attaches to a protein targeted for destruction and accompanies it to a proteasome—essentially a sac of powerful enzymes that break the protein into its component amino acids. The…

    Read More

Hershko

  • In Avram Hershko

    …begins when a molecule called ubiquitin (from the Latin ubique, meaning “everywhere,” because it occurs in so many different cells and organisms) attaches itself to the protein targeted for destruction. It then accompanies the protein to a proteasome, which is essentially a structure of powerful enzymes that break the protein…

    Read More

Rose

  • In Irwin Rose

    …first step a molecule called ubiquitin (from the Latin ubique, meaning “everywhere,” because it occurs in so many different cells and organisms) attaches to the protein targeted for destruction and accompanies it to a proteasome—essentially a sac of powerful enzymes that divide the protein into its component amino acids. The…

    Read More
Also called:
biological molecule
Key People:
Jacques Dubochet

biomolecule, any of numerous substances that are produced by cells and living organisms. Biomolecules have a wide range of sizes and structures and perform a vast array of functions. The four major types of biomolecules are carbohydrates, lipids, nucleic acids, and proteins.

Among biomolecules, nucleic acids, namely DNA and RNA, have the unique function of storing an organism’s genetic code—the sequence of nucleotides that determines the amino acid sequence of proteins, which are of critical importance to life on Earth. There are 20 different amino acids that can occur within a protein; the order in which they occur plays a fundamental role in determining protein structure and function. Proteins themselves are major structural elements of cells. They also serve as transporters, moving nutrients and other molecules in and out of cells, and as enzymes and catalysts for the vast majority of chemical reactions that take place in living organisms. Proteins also form antibodies and hormones, and they influence gene activity.

Likewise, carbohydrates, which are made up primarily of molecules containing atoms of carbon, hydrogen, and oxygen, are essential energy sources and structural components of all life, and they are among the most abundant biomolecules on Earth. They are built from four types of sugar units—monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Lipids, another key biomolecule of living organisms, fulfill a variety of roles, including serving as a source of stored energy and acting as chemical messengers. They also form membranes, which separate cells from their environments and compartmentalize the cell interior, giving rise to organelles, such as the nucleus and the mitochondrion, in higher (more complex) organisms.

All biomolecules share in common a fundamental relationship between structure and function, which is influenced by factors such as the environment in which a given biomolecule occurs. Lipids, for example, are hydrophobic (“water-fearing”); in water, many spontaneously arrange themselves in such a way that the hydrophobic ends of the molecules are protected from the water, while the hydrophilic ends are exposed to the water. This arrangement gives rise to lipid bilayers, or two layers of phospholipid molecules, which form the membranes of cells and organelles. In another example, DNA, which is a very long molecule—in humans, the combined length of all the DNA molecules in a single cell stretched end to end would be about 1.8 metres (6 feet), whereas the cell nucleus is about 6 μm (6 10-6 metre) in diameter—has a highly flexible helical structure that allows the molecule to become tightly coiled and looped. This structural feature plays a key role in enabling DNA to fit in the cell nucleus, where it carries out its function in coding genetic traits.

Kara Rogers