polarity

Examples of polarity in the following topics:

• Water’s Polarity

  • Water's polarity is responsible for many of its properties including its attractiveness to other molecules.
  • One of water's important properties is that it is composed of polar molecules.
  • The two hydrogen atoms and one oxygen atom within water molecules (H2O) form polar covalent bonds.
  • As a result of water's polarity, each water molecule attracts other water molecules because of the opposite charges between them, forming hydrogen bonds.
  • A polar substance that interacts readily with or dissolves in water is referred to as hydrophilic (hydro- = "water"; -philic = "loving").

• Water’s Solvent Properties

  • Water's polarity makes it an excellent solvent for other polar molecules and ions.
  • A polar molecule with partially-positive and negative charges, it readily dissolves ions and polar molecules.
  • Water is therefore referred to as a solvent: a substance capable of dissolving other polar molecules and ionic compounds.
  • When ionic compounds are added to water, individual ions interact with the polar regions of the water molecules during the dissociation process, disrupting their ionic bonds.
  • Since many biomolecules are either polar or charged, water readily dissolves these hydrophilic compounds.

• Climate Change and Biodiversity

  • One such unexpected species contact is between polar bears and grizzly bears .
  • The rate of warming appears to be accelerated in the arctic, which is recognized as a serious threat to polar bear populations that require sea ice to hunt seals during the winter months; seals are the only source of protein available to polar bears.
  • As a result, grizzly bear habitat now overlaps polar bear (Ursus maritimus) habitat.
  • However, in 2006 a hunter shot a wild grizzly-polar bear hybrid known as a grolar bear, the first wild hybrid ever found.

• Fluid Mosaic Model

  • Hydrophobic, or water-hating molecules, tend to be non-polar.
  • This arrangement gives the overall molecule an area described as its head (the phosphate-containing group), which has a polar character or negative charge, and an area called the tail (the fatty acids), which has no charge .
  • They interact with other non-polar molecules in chemical reactions, but generally do not interact with polar molecules.
  • The hydrophilic regions of the phospholipids tend to form hydrogen bonds with water and other polar molecules on both the exterior and interior of the cell.
  • In an aqueous solution, phospholipids tend to arrange themselves with their polar heads facing outward and their hydrophobic tails facing inward.

• Covalent Bonds and Other Bonds and Interactions

  • There are two types of covalent bonds: polar and nonpolar.
  • In a polar covalent bond, the electrons are unequally shared by the atoms because they are more attracted to one nucleus than the other .
  • When polar covalent bonds containing hydrogen are formed, the hydrogen atom in that bond has a slightly positive charge (δ+) because the shared electrons are pulled more strongly toward the other element and away from the hydrogen atom.
  • Whether a molecule is polar or nonpolar depends both on bond type and molecular shape.
  • Both water and carbon dioxide have polar covalent bonds, but carbon dioxide is linear, so the partial charges on the molecule cancel each other out.

• The Plasma Membrane and the Cytoplasm

  • A single phospholipid molecule consists of a polar phosphate "head," which is hydrophilic, and a non-polar lipid "tail," which is hydrophobic.
  • The polar heads contact the fluid inside and outside of the cell .
  • In the case of the plasma membrane, only relatively small, non-polar materials can move through the lipid bilayer (remember, the lipid tails of the membrane are nonpolar).
  • The polar heads contact the fluid inside and outside of the cell.

• Virus Classification

  • Viruses can contain double-stranded DNA (dsDNA), single-stranded DNA (ssDNA), double-stranded RNA (dsRNA), single-stranded RNA with a positive polarity (ssRNA), ssRNA with a negative polarity, diploid (two copies) ssRNA, and partial dsDNA genomes.
  • Positive polarity means that the genomic RNA can serve directly as mRNA and a negative polarity means that their sequence is complementary to the mRNA .

• Phospholipids

  • A single phospholipid molecule has a phosphate group on one end, called the "head," and two side-by-side chains of fatty acids that make up the lipid "tails. " The phosphate group is negatively charged, making the head polar and hydrophilic, or "water loving."
  • As the phosphate groups are polar and hydrophilic, they are attracted to water in the intracellular fluid.
  • The polar heads contact the fluid inside and outside of the cell.
  • The phosphate may be modified by the addition of charged or polar chemical groups.

• Selective Permeability

  • Polar substances present problems for the membrane.
  • While some polar molecules connect easily with the outside of a cell, they cannot readily pass through the lipid core of the plasma membrane.

• Functional Groups

  • Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity.
  • An example of a hydrophobic group is the non-polar methane molecule.