molecule

(noun)

The smallest particle of a specific compound that retains the chemical properties of that compound; two or more atoms held together by chemical bonds.

Related Terms

Examples of molecule in the following topics:

  • Metabolic Pathways

    • An anabolic pathway requires energy and builds molecules while a catabolic pathway produces energy and breaks down molecules.
    • Another metabolic pathway might build glucose into large carbohydrate molecules for storage.
    • Catabolic pathways involve the degradation of complex molecules into simpler ones, releasing the chemical energy stored in the bonds of those molecules.
    • Anabolic pathways are those that require energy to synthesize larger molecules.
    • Catabolic pathways are those that generate energy by breaking down larger molecules.

  • Outcomes of Glycolysis

    • One glucose molecule produces four ATP, two NADH, and two pyruvate molecules during glycolysis.
    • Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH .
    • Two ATP molecules were used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and 2 NADH molecules for its use.
    • If the cell cannot catabolize the pyruvate molecules further (via the citric acid cycle or Krebs cycle), it will harvest only two ATP molecules from one molecule of glucose.
    • In this situation, the entire glycolysis pathway will continue to proceed, but only two ATP molecules will be made in the second half (instead of the usual four ATP molecules).

  • 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.
    • The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules.
    • Water is a poor solvent, however, for hydrophobic molecules such as lipids.
    • Nonpolar molecules experience hydrophobic interactions in water: the water changes its hydrogen bonding patterns around the hydrophobic molecules to produce a cage-like structure called a clathrate.

  • Molecules in Biological Membranes

  • More complex organic molecules and life

  • Functional Groups

    • Functional groups are groups of molecules attached to organic molecules and give them specific identities or functions.
    • Functional groups are groups of atoms that occur within organic molecules and confer specific chemical properties to those molecules.
    • When functional groups are shown, the organic molecule is sometimes denoted as "R."
    • An example of a hydrophobic group is the non-polar methane molecule.
    • The functional groups shown here are found in many different biological molecules, where "R" is the organic molecule.

  • 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.
    • This interactive shows the interaction of the hydrogen bonds among water molecules.

  • The Energy-Requiring Steps of Glycolysis

    • In the first half of glycolysis, energy in the form of two ATP molecules is required to transform glucose into two three-carbon molecules.
    • In the first half of glycolysis, two adenosine triphosphate (ATP) molecules are used in the phosphorylation of glucose, which is then split into two three-carbon molecules as described in the following steps.
    • Thus, the pathway will continue with two molecules of a single isomer.
    • At this point in the pathway, there is a net investment of energy from two ATP molecules in the breakdown of one glucose molecule.
    • The first half of glycolysis uses two ATP molecules in the phosphorylation of glucose, which is then split into two three-carbon molecules.

  • Hydrogen Bonding and Van der Waals Forces

    • Weaker bonds can also form between molecules.
    • When this happens, an interaction occurs between the δ+of the hydrogen from one molecule and the δ– charge on the more electronegative atoms of another molecule, usually oxygen or nitrogen, or within the same molecule.
    • This type of bond is common and occurs regularly between water molecules.
    • Hydrogen bonds occur in inorganic molecules, such as water, and organic molecules, such as DNA and proteins.
    • The slightly negative oxygen side of the water molecule and the slightly positive hydrogen side of the water molecule are attracted to each other and form a hydrogen bond.

  • The Energy-Releasing Steps of Glycolysis

    • In the second half of glycolysis, energy is released in the form of 4 ATP molecules and 2 NADH molecules.
    • So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules.
    • Both of these molecules will proceed through the second half of the pathway where sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment while also producing a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules .
    • Note that the second phosphate group does not require another ATP molecule.
    • The second half of glycolysis involves phosphorylation without ATP investment (step 6) and produces two NADH and four ATP molecules per glucose.