Chemical level of organization

Wed, Jul 20, 2011

All about the chemical level of organization ..

THREE MAJOR TYPES OF CHEMICAL BONDS:

Ionic Bonds—an ionic bond is formed whenever two atoms bond together and one atom of the pair gains or loses electrons. One atom will become positive and the other will become negative. Compounds bonded together with ionic bonds are electrical conductors and tend to form crystals. Many ionic compounds are soluble in water because the water molecule is polar. Generally, if the valence shell is less than half-filled the atom will loose electrons (donate them) and become a cation. If the valence shell is more than half-filled, an atom will accept electrons and become an anion.

Ionic, covalent and hydrogen bonds

Covalent Bonds—when a covalent bond is formed between two atoms; both atoms share electrons in the valence shells equally. Atoms can share one – three electron pairs between them. Compounds with covalent bonds are not electrolytes. Carbon atoms which form the backbone of biological molecules are covalently bonded together. If one atom attracts the shared electrons more strongly than the other, a Polar Covalent Bond (water) is formed. Covalent bonds between identical atoms are Nonpolar Covalent Bonds.

Hydrogen Bonds—hydrogen bonds are the weakest of the three types. They are formed by weak attractions of hydrogen atoms between molecules. Large molecules may contain many hydrogen bonds (DNA, RNA), and they confer structural stability to these molecules.

ACIDS AND BASES:

An acid is a substance that donates hydrogen ions to a solution. A base is a substance that accepts hydrogen ions (or positively charged ions) from a solution.

Salts dissociate into cations and anions in water, but neither is H⁺ or OH^–. Solid forms of salts are found in bones and teeth. Confer strength to these tissues.

SOLVENTS, SOLUTIONS, AND SUSPENSIONS:

Water is the most abundant inorganic substance found in all living systems. In body fluids, the solvent is water.

Solvent–a liquid or gas in which some other material (the Solute) has been dissolved. (Sugars dissolved in water, for instance. Water is the solvent, sugars are the solutes). The solvent and solute combined make up the Solution. (Milk and tears are examples of solutions). Solutes such as calcium salts and proteins in milk do not settle out of solution, however, cells in blood will settle out of solution and the mixture is, hence, called a Suspension.

Concentrations of materials in solution are usually expressed in terms of Moles per Liter. A mole is equal to the number of molecules of a material in a given volume of solution. (Calculate one mole/liter NaCl using periodic table). This type of information is useful in making dilutions of materials.

solution equals

PROPERTIES OF WATER:

- Participates in many chemical reactions. Used to help break materials down in Hydrolysis reactions.

- Has a high heat capacity. Can absorb a great deal of heat before it changes its physical state. Also gives up a great deal of heat with only a small change in temperature.

- Serves as a lubricant and part of lubricating fluids. Major part of mucus and other lubricating fluids. (Important in the chest and abdomen because of organ-to-organ contact and a moveable joints (Diarthroses) of the body).

- Is an excellent solvent and suspending medium. Because water is polar, it can dissolve many materials and ionically bonded molecules.

BIOLOGICAL MACROMOLECULES:

There are 4 major classes of these “large” molecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids. Each group contains more than one type, but all are assembled by reactions called Dehydration synthesis (removing a molecule of water from two molecules) and broken down by Hydrolysis (to cut with water) reactions (add the water back to the molecules).

-Carbohydrates include sugars, starches, glycogen, and cellulose. They represent on about 2 to 3 percent of the total body weight, but have several funtions (energy sources, energy storage, a component of DNA and RNA for example). Can group into MONOSACCHARIDES (single sugars “monomers” of carbohydrates–structural part of DNA and RNA, used for energy by cells), DISACCHARIDES (two monosaccharides bonded together in a glycosidic bond–transport forms of carbohydrates, are not as readily absorbed by cells), and POLYSACCHARIDES (many monosaccharides joined together to form chains–energy storage form of carbohydrates called Glycogen. Plant cells store Starch. Cellulose is a polysaccharide found in plant cell walls that is non-digestable by humans).

-Lipids include fats and oils, phospholipids, steroids, eicosanoids, and some parts of vitamines such a vitamins E and K (these are lipoproteins). Lipids (with the exception of phospholipids) are nonpolar and do not readily dissolve in water. For transport in the blood, lipids are often combined with proteins to form lipoproteins. Fats and oils may be grouped as Saturated (single carbon bonds between the fatty acid carbon atoms) or Unsaturated (at least one double bond between two carbon atoms of the fatty acid). TRIGLYCERIDES (fats and oils) are the most common lipids in the body. They store twice as much energy per volume than carbohydrates or proteins. Triglycerides protect organs such as the kidneys and serve as insulation for the body. PHOSPHOLIPIDS are found in the plasma membranes of all cells. A phosphate group is bonded on the third position of the glycerol molecule, making phospholipids polar molecules. Phospholipids are found in relatively high concentrations in the nervous system. STEROIDS (such as cholesterol, sex hormones, cortisol, bile salts, and Vitamin D) are 4-ringed, complex molecules, but they are soluble in lipids. Cholesterol serves as a part of cell membranes (makes them more flexible) and is a precursor for the synthesis of other types of steroids such as vitamin D, and bile salts. EISANOIDS are derived from a fatty acid names Arachidonic Acid and are divided into Prostaglandins and Leukotrienes. Prostaglandins contribute to inflammatory responses, prevent stomach ulcers, enlarge airways in the lungs, and influence blood clotting. Leukotrienes are involved in allergic and inflammatory responses.

-Proteins are the most diverse class of macromolecules. They are composed of monomer units called amino acids and participate as hormones, structural proteins, contractile proteins, antibodies, transport proteins, and as enzymes, to list a few of their functions. Proteins exhibit four levels of structural organization: Primary structure (the sequence of amino acids bonded together), Secondary structure (folding of the primary structure caused by hydrogen bonds along the polypeptide backbone [bonds between amino acids are called Peptide bonds]), Tertiary structure (further folding of the protein due to bonds between the variable regions (R-groups) of the amino acids. Ionic bonds, hydrogen bonds, disulfide bonds and covalent bonds may be formed at this point), and Quaternary structure (this level occurs when more than one polypeptide chain (Subunit) bond together to form the final, functional protein).

Folding patterns of proteins due to their sequence of amino acids give the molecules a very specific shape. This shape, in turn, helps them to function properly. If proteins are subjected to extremes in heat or pH, bonds will be broken between the amino acids and the protein will loose its shape. This is called Denaturation. Enzymes are proteins that aid in chemical reactions (they are Catalysts). They bind to specific molecules (Substrates) at a location called the Active Site. This forms an Enzyme-Substrate complex. The names of enzymes usually end with the suffix –ase (as in amylase, and catalase).

-Nucleic Acids are composed of monomers called nucleotides. They are the building blocks of DNA and RNA. DNA contains Deoxyribose, whereas RNA contains Ribose sugar. DNA molecules are double-stranded molecules found inside the cell’s nucleus and within mitochondria. DNA forms the genetic material of our cells.

RNA molecules are single-stranded and are formed from a DNA template molecule. RNA makes up part of ribosome organelles, and serves as a blueprint for synthesis of proteins within the cell.

Five basic molecules combine in different arrangements to make up these molecules. DNA contains Adenine, Cytosine, Guanine, and Thymine. RNA contains Adenine, Cytosine, Guanine, and Uracil. Adenine and Guanine are called Purines, whereas Cytosine, Thymine, and Uracil are Pyrimadines. In bonding pattern, a Purine always bonds with a pyrimadine molecule (A-T, C-G in DNA and A-U, C-G in RNA).

ATP (adenosine triphosphate) is another nucleotide that is used as the energy currency of body cells. It temporarily stores and transfers energy used in chemical reactions within cells. Muscle contractions, chromosome movements during division, and transport of materials across cell membranes are some of the functions of ATP.