{"id":114,"date":"2017-08-16T09:03:29","date_gmt":"2017-08-16T09:03:29","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/biology\/?page_id=114"},"modified":"2017-10-13T04:57:58","modified_gmt":"2017-10-13T04:57:58","slug":"biochemical-basis-of-life-2","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/biology\/biochemical-basis-of-life-2\/","title":{"rendered":"Biochemical Basis of Life"},"content":{"rendered":"
\n
Workshop Index<\/a>\u00a0Next Lesson \u27a1<\/a><\/div>\n

<\/p>\n

Biochemical Basis of Life<\/h1>\n

Objective<\/h4>\n

In this lesson, you will review organic molecules and their
\nfunctional groups. This lesson specifically discusses carbohydrates and their important functions within living things.<\/p>\n

\n

Organic Molecules<\/h3>\n

All matter is composed of atoms of elements. The electrons in atoms form bonds with those of other atoms to form molecules. Energy is stored in the bonds of molecules. Scientists think that living things might have evolved from complex molecules formed from chemical reactions occurring within the early oceans of earth. Living things are composed primarily of organic molecules and water.<\/p>\n

Organic molecules are those that have a carbon skeleton. In most living systems, the carbon skeleton has hydrogen and\/or other functional groups attaged to create a wide variety of compounds. Becuase carbon has four valence electrons, it tends to form covalent bonds with up to four atoms. The energy used by living things is stored in the covalent bonds of organic compounds.<\/p>\n

Hydrocarbons or alkyls are the simplest organic compounds, containing only carbon and hydrogen. Alkanes are saturated hydrocarbons, meaning there are no carbon double bonds present. Methane is an example of an alkane. Alkenes are characterized by having a double bond; they are unsaturated hydrocarbons. The degree of saturation of a hydrocarbon influences its reactivity and shape.<\/p>\n

\"Methane<\/center>The functional groups attached to carbon compounds determine the classification and reactivity of more complex organic molecules. Classes of organic compounds are often represented by the functional group bonded to a generic organic group that varies from amino acid to amino acid. These generic organic groups are sometimes represented with an R.<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Methyl Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Single carbon alkyl<\/li>\n
  • Component of fatty acid chains<\/li>\n
  • Insoluble in water<\/li>\n<\/ul>\n<\/td>\n
\"Methyl<\/td>\n<\/tr>\n
Ether Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Oxygen bonded to two alkyl groups<\/li>\n<\/ul>\n<\/td>\n
\"Ether<\/td>\n<\/tr>\n
Hydroxyl Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Present in alcohols, sugars, and amino acids<\/li>\n<\/ul>\n<\/td>\n
\"Hydroxyl<\/td>\n<\/tr>\n
Phenols<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Hydroxyl groups bound to a benzene ring<\/li>\n
  • Aromatic compounds<\/li>\n<\/ul>\n<\/td>\n
\"Phenol<\/td>\n<\/tr>\n
Sulfhydryl Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Sulfur analog of hydroxyl group<\/li>\n
  • Functionally similar to alcohols<\/li>\n
  • Form disulfide bonds in some amino acids<\/li>\n
  • Molecules with these are called thiols<\/li>\n<\/ul>\n<\/td>\n
\"Sulfhydryl<\/td>\n<\/tr>\n
Carbonyl Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Present in sugars, amino acids, and nucleotides<\/li>\n
  • Water soluble<\/li>\n<\/ul>\n<\/td>\n
\"Carbonyl<\/td>\n<\/tr>\n
Aldehydes<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Carbonyl group at end of a carbon backbone<\/li>\n
  • React to form more complex molecules<\/li>\n
  • Include odors of cinnamon, vanilla, and rancid butter<\/li>\n<\/ul>\n<\/td>\n
\"Aldehydes<\/td>\n<\/tr>\n
Ketones<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Carbonyl group attached in the middle of a carbon backbone<\/li>\n
  • Good solvents or polymers<\/li>\n<\/ul>\n<\/td>\n
\"Ketones<\/td>\n<\/tr>\n
Carboxyl Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Associated with organic acids<\/li>\n
  • Present in amino acids and fatty acids<\/li>\n
  • Very polar and water soluble<\/li>\n
  • Act as acids by ionizing by giving up H+ ions in solution<\/li>\n
  • Vinegar is a common example<\/li>\n<\/ul>\n<\/td>\n
\"Carboxyl<\/td>\n<\/tr>\n
Esters<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Formed by the reaction between an alcohol and an acid<\/li>\n
  • An alkyl group replaces an H on the organic acid and water is condensed<\/li>\n
  • Fruit odors and aspirin are examples<\/li>\n<\/ul>\n<\/td>\n
\"Esters<\/td>\n<\/tr>\n
Amine Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Nitrogen-based derivatives of ammonia<\/li>\n
  • Present in amino acids and nucleotides<\/li>\n
  • Water soluble<\/li>\n
  • Acts as a weak base in solution by attracting protons to produce an ionized form<\/li>\n<\/ul>\n<\/td>\n
\"Amine<\/td>\n<\/tr>\n
Phosphate Group<\/strong><\/td>\n<\/tr>\n
\n
    \n
  • Found in DNA, RNA, ATP, and many proteins and phospholipids<\/li>\n
  • Water soluble and acidic<\/li>\n
  • High-energy bonds<\/li>\n<\/ul>\n<\/td>\n
\"Phosphate<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Complex organic macromolecules called polymers<\/abbr> are formed from simple organic monomers<\/abbr>. Living things are composed primarily of only four kinds of organic polymers: carbohydrates, lipids, proteins, and nucleic acids. Each type of macromolecule is made of distinctive organic monomers. Organic monomers undergo dehydration synthesis<\/abbr> (also called condensation reactions) to produce complex polymers. In condensation reactions, one monomer loses an H atom and the other loses an OH atom when a new bond is formed, and water (H2O) is produced. In the opposite reaction, called hydrolysis<\/abbr>, polymers are broken down into monomer subunits by adding water.<\/p>\n

The monomers of carbohydrates are called monosaccharides<\/abbr>. They produce polymers by forming glycosidic bonds<\/abbr>. There are several classes of carbohydrates, which will be discussed in detail later.<\/p>\n

Lipids typically contain long fatty acid<\/abbr> chains and are non-polar and water insoluble. Fats like triglycerides and oils are lipids composed of glycerol bonded to fatty acid chains. Other lipids, such as steroids, contain distinctive ring structures.<\/p>\n

Proteins have several levels of structure, but all proteins are composed of amino acid<\/abbr> monomers joined by peptide bonds<\/abbr> in dehydration synthesis reactions. Proteins are very important in controlling metabolism in their action as enzymes.<\/p>\n

The monomers of the nucleic acids DNA and RNA are called nucleotides. Nucleotides form phosphodiester bonds<\/abbr> in dehydration synthesis reactions to form the DNA backbone. Another important nucleotide in all living things is called adenosine triphosphate<\/abbr> (ATP).<\/p>\n

ATP is a very important molecule in living things. It is often called the energy currency of the cell. It is composed of a pentose sugar called ribose, an amine called adenine, and three phosphate groups. The line of phosphates contains very high-energy bonds that are easily broken. Energy is transferred by dehydration synthesis reactions by making and breaking high-energy bonds in ATP.<\/p>\n

Examples of dehydration synthesis reactions for three of the four main classes of organic macromolecules are shown below.<\/p>\n

\"Carbohydrate<\/center>\"Lipid<\/p>\n

\"Nucleic<\/center><\/p>\n

Hydrolysis reactions for each type of macromolecule are the opposite process of that shown above. In hydrolysis, water is split by hydrolytic enzymes, breaking it into an H atom and an OH group. These react to form simple monomers when the molecular bonds of the polymer are broken.<\/p>\n

\n

Question<\/h4>\n

What is formed by the dehydration synthesis of sucrose?<\/p>\n

    \n
  1. Glucose and fructose<\/li>\n
  2. Monosaccharides<\/li>\n
  3. Water<\/li>\n
  4. Cellulose<\/li>\n<\/ol>\n

    Reveal Answer<\/a><\/p>\n

    The correct answer is C. Dehydration synthesis builds complex molecules from simple ones, and water is produced as a by-product.<\/p>\n<\/section>\n

    Organic Molecules<\/h3>\n

    Carbohydrates are important sources of quick energy. The energy used by cells is released from the bonds of simple carbohydrates such as glucose. Carbohydrates also function in energy storage as starch and glycogen, and as important structural elements, particularly in plants, fungi, and arthropods.<\/p>\n

    \"Glucose<\/center>The simplest carbohydrates, monosaccharides, are classified based on the number of carbons present. For example, a triose<\/abbr> contains three carbons; a pentose<\/abbr> contains five, and a hexose<\/abbr>, such as glucose, contains six carbons. Sugars may also be classified based on functional groups present. An aldose<\/abbr> contains an aldehyde group; a ketose<\/abbr> contains a ketone group. Glucose is an aldohexose; it is a six carbon sugar with an aldehyde attached.<\/p>\n

    Monosaccharides often exist as isomers<\/abbr>. Isomers are molecules with the same chemical formula and often the same kinds of bonds between atoms, but in which the atoms are arranged differently. Glucose, for example, can have as many as sixteen different configurations of atoms. Various isomers of glucose are named according to location of functional groups. Unique isomers of simple carbohydrates are involved in many important metabolic pathways.<\/p>\n

    \"Glucose<\/center>Monosaccharides may also exist as straight chains or as ring forms. When there are five or more carbons in a chain, very stable ring structures called hemiacetals<\/abbr> may form. This occurs when the carbon on one end of a chain reacts with the hydroxyl on the opposite end. Several combinations are possible in pentose and hexose sugars. In living things, most five and six carbon monosaccharides most often occur in ring forms.<\/p>\n

    An oligosaccharide<\/abbr> is a more complex carbohydrate composed of two to ten monosaccharide subunits. A disaccharide<\/abbr> is an oligosaccharide composed of two monosaccharides, such as the sucrose molecule shown in the dehydration synthesis reaction for carbohydrates. Polysaccharides are very complex, composed of more than 10 monosaccharides. Cellulose, starch, glycogen, and chitin are all biologically important polysaccharides.<\/p>\n

    Cellulose<\/em> is the most abundant polymer on earth. If you are wearing cotton, you are wearing cellulose. The fruits and vegetables you eat are rich in cellulose. If you are sitting on a wooden chair, you are sitting on cellulose, and if you are taking notes, you are writing on cellulose. Cellulose is the primary structural component of plant cell walls. Cellulose monomers are linked together through 1,4 glycosidic bonds in a straight chain. In cellulose microfibrils, hydroxide groups in the monomers hydrogen bond with each other, holding the chains firmly together creating a lattice structure. This gives cellulose fibers high tensile strength. In plant cell walls, cellulose forms a matrix with hemicellulose and lignin to give plants support.<\/p>\n

    \"Cellulose\"<\/center>Starch<\/em> and glycogen<\/em> are storage carbohydrates. Starch is the primary form of energy storage in plants, while glycogen is the form of carbohydrate energy storage in animals. Starch and glycogen are polymers of alpha glucose. Amylose, a form of starch, has alpha 1-4 glycosidic bonds; while the starches amylopectin and glycogen have alpha 1-4 glycosidic bonds and alpha 1-6 glycosidic bonds. Starch polymers occur as unbranched or simply branched helices. Glycogen occurs as highly branched helices.<\/p>\n

    \"Starches\"<\/center>
    \"Glycogen\"<\/center>Chitin<\/em> is a complex carbohydrate common to fungi and arthropods. It is a primary component of fungal cell walls and of the hard exoskeleton of insects and crustaceans. Chitin is structurally similar to cellulose. It is made out of monomers of acetylglucosamine linked together in the same way as the glucose units that make up cellulose. Chitin differs from cellulose in that one hydroxyl group on each monomer is replaced by an acetylamino group. This allows for increased hydrogen bonding between adjacent polymers and increased strength.<\/p>\n

    \"Chitin\"<\/center><\/p>\n

    Summary<\/h3>\n