What is the name of the bond that holds carbohydrates together?
Twenty different amino acids are found in human protein in varying quantities and combinations. They are linked together by peptide bonds to form the primary structure of proteins. Peptide bonds in proteins are also specialized covalent bonds, like the glycosidic bonds in carbohydrates.
The lipids found in the membrane consist of two parts: hydrophilic (water soluble) and hydrophobic (water insoluble). The hydrophobic portion of the lipids is the non-polar long hydrocarbon chains of two fatty acids. The fatty acids are present as esters bonded to glycerol.
- Small, nonpolar molecules are hydrophobic, so they can easily cross the phospholipid bilayer of the plasma membrane. Polar molecules and ions are hydrophilic, so they cannot very easily cross the hydrophobic portion of the plasma membrane (formed by the phospholipid tails).
- The Water Race: Hydrophobic & Hydrophilic Surfaces. Nonpolar molecules that repel the water molecules are said to be hydrophobic; molecules forming ionic or a hydrogen bond with the water molecule are said to be hydrophilic.
- All of the lipid molecules in cell membranes are amphipathic (or amphiphilic)—that is, they have a hydrophilic (“water-loving”) or polar end and a hydrophobic (“water-fearing”) or nonpolar end. The most abundant membrane lipids are the phospholipids. These have a polar head group and two hydrophobic hydrocarbon tails.
Because of the chemical and structural nature of the phospholipid bilayer (hydrophobic core), only lipid-soluble molecules and some small molecules are able to freely pass through the lipid bilayer. Ions and large polar molecules cannot pass through the lipid bilayer.
- Permeability of phospholipid bilayers. Although ions and most polar molecules cannot diffuse across a lipid bilayer, many such molecules (such as glucose) are able to cross cell membranes. These molecules pass across membranes via the action of specific transmembrane proteins, which act as transporters.
- The most important property of the cell membrane is its selective permeability: some substances can pass through it freely, but others cannot. Small and nonpolar (hydrophobic) molecules can freely pass through the membrane, but charged ions and large molecules such as proteins and sugars are barred passage.
- Nonpolar and small polar molecules can pass through the cell membrane, so they diffuse across it in response to concentration gradients. Carbon dioxide and oxygen are two molecules that undergo this simple diffusion through the membrane. The simple diffusion of water is known as osmosis.
Unlike other biomolecule groups, fatty acid monomers are not directly bonded to each other in polymer chains. Dehydration synthesis reactions in lipids form an ester linkage between the carboxyl group of a fatty acid and the hydroxyl group of an alcohol monomer such as glycerol.
- The monomers of these organic groups are: Carbohydrates - monosaccharides. Lipids - glycerol and fatty acids. Nucleic acids - nucleotides.
- fats, lipids). However, there are categories of lipids that are both hydrophobic and hydrophilic. Thus, lipids are largely insoluble in polar solvents (water), and are soluble in nonpolar molecules. As such, the nonpolar regions are hydrophobic/lipophilic, and the polar regions are hydrophilic/lipophobic.
- In this structure the nonpolar fatty acid chains of the phospholipid are sequestered together away from contact with water, thereby maximizing hydrophobic interactions. Therefore, lipids, particularly phospholipids are of current interest in many fields such as biochemistry, chemistry, and polymer science.
Updated: 2nd October 2019