The Chemical Building Blocks of Life CHAPTER 3

Molecules and atoms from the environment are necessary to build new molecules Carbon moves from the environment to organisms where it is used to build carbohydrates, proteins, lipids or nucleic acids. Carbon is used in storage compounds and cell formation in all organisms. Nitrogen moves from the environment to organisms where it is used in building proteins and nucleic acids. Phosphorus moves from the environment to organisms where it is used in nucleic acids and certain lipids.

Carbon is the framework of organic molecules Carbon forms 4 covalent bonds Carbon-based molecules form a variety of structures: Linear chains Rings Branches Hydrocarbons (carbon and hydrogen chains) are relatively stable at body tempoeratures

Carbon Functional Groups Functional groups contain other atoms with different electronegativities Functional groups can be polar, non-polar, acidic, basic, and charged The chemical properties of functional groups determine the structure and function of biological molecules

Carbon Functional Groups Amino

Carbohydrates, proteins, lipids, and nucleic acids form polymers The subcomponents of biological molecules and their sequence determine the properties of that molecule. The structure and function of polymers are derived from the way their monomers are assembled. Polymers are long molecules built by linking smaller similar subunits (monomers) Carbohydrates, proteins, lipids, and nucleic acids form polymers All macromolecules can be formed by the process of dehydration synthesis Water is removed from two monomers as they form a polymer All macromolecules can be digested by the process of hydrolysis Water is added and a polymer disassemble into monomers

Dehydration Synthesis

Hydrolysis – molecules are hydrolyzed by hydrolytic enzymes

Carbohydrates Carbohydrates are composed of sugar monomers whose structures and bonding with each other by dehydration synthesis determine the properties and functions of the molecules. Glucose is the most common carbohydrate monomer Other monomers: Ribose Deoxyribose Fructose Glyceraldehyde Monomer carbohydrates functions: Energy release Subunits of larger polymers such as RNA, DNA, starch, cellulose, and glycogen

Carbohydrates Polymers Disaccharides – contain two carbohydrate monomers Maltose Sucrose Lactose Polysaccharides – contain three or more carbohydrate monomers Structural Polysaccharides Cellulose – forms cell walls of plants Chitin – forms cell walls of fungi and insect exoskeletons Storage Polysaccharides Starch – stores energy in plants Glycogen – stores energy in animal tissues (liver and muscles)

Carbohydrate Polymers Note the individual monomers Cellulose has a slightly different bonding pattern which forms rigid fibers Glycogen is branched Starch and glycogen are more flexible

Lipids Generally non-polar molecules with hydrocarbon chains Most lipids are hydrophobic Contain fatty acid chains Exist as saturated or unsaturated fatty acids Form solids fats Form soft fats and oils

Lipids Saturated and unsaturated fatty acids

Lipids Non-polar lipids Polar Lipids Triglycerides – energy storage Waxes – waterproofing; cuticles on plants and insects Oils – protection; prevent water loss Steroids – form hormones and vitamins Polar Lipids Phospholipids Contain polar and non-polar regions Form membranes – separate two aqueous solutions

Lipids Triglycerides

Lipids Phospholipid Structure

Lipids Steroids Aromatic rings with short fatty acid chains

Nucleic Acids Nucleic acids biological information is encoded in sequences of nucleotide monomers. Each nucleotide has 3 structural components: five-carbon sugar (deoxyribose or ribose), phosphate nitrogen base (adenine, thymine, guanine, cytosine or uracil). DNA and RNA differ in function and differ slightly in structure, and these structural differences account for the differing functions.

Nucleic Acids DNA Structure Double helix – two polymer chains linked by hydrogen bonds between nitrogenous bases Adenine links with Thymine (or Uracil in RNA) Cytosine links with Guanine Phosphates form strong covalent bonds with the deoxyribose sugar Forms a sugar-phosphate backbone Phosphodiester bonds hold backbone in place Benefits of DNA structure permits easy replication Provides a stable structure to maintain genetic sequences

Nucleic Acids DNA Structure in Detail

Nucleic Acids RNA Structure Single stranded polymer of nucleotides Five types of RNA with different functions mRNA – complementary copy of a DNA base sequence rRNA – forms ribosome tRNA – carries amino acids snRNA – processes RNA in eukaryotes only preRNA – newly formed RNA in eukaryotes only Limited base-pairing Present in some forms of RNA Ribose is the 5-carbon sugar Uracil replaces Thymine as a nitrogenous base

Nucleic Acids RNA Structure

Proteins Polymers comprised of amino acid sequences The specific order of amino acids in a polypeptide (primary structure) interacts with the environment to determine the overall shape of the protein Proteins structure involves secondary, tertiary and quaternary structure and function. The R group of an amino acid can be categorized by chemical properties (hydrophobic, hydrophilic, and ionic) R group interactions determine the structure and function of that region of the protein.

Proteins Proteins have an amino (NH2) end and a carboxyl (COOH) end and consist of a linear sequence of amino acids

Proteins Amino acids are connected by the formation of peptide bonds by dehydration synthesis between the amino and carboxyl groups of adjacent monomers

Proteins Proteins form several different structures as a result of R group interactions

Proteins

Proteins Tertiary Structure

Proteins Quaternary proteins contain 2 or more polypeptide chains

Protein Denaturing Excessive heat or pH can alter protein structure Why do proteins denature? Hydrogen bond interactions are disrupted and the protein changes shape