Chapter 5 The Structure and Function of Macromolecules Campbell and Reece. Biology 6th edition

Polymer Principles Most macromolecules are polymers –The large molecules in three of the four classes of life’s organic compounds- carbohydrates, proteins, and nucleic acids- are chainlike molecules called polymers A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds

Most macromolecules are polymers –The repeating units that serve as the building blocks of a polymer are small molecules called monomers –Monomers are connected by a reaction in which two molecules are covalently bonded to each other –Polymers can also be disassembled into their monomer parts

Carbohydrates-Fuel and Building Material Carbohydrates include both sugars and their polymers. –Sugars, the smallest carbohydrates, serve as the fuel and carbon sources Monosaccharides (single sugar) are simple sugars. Glucose is the most common monosaccharide, and key to the chemistry of life! Disaccharides consist of two monosaccharides joined by a covalent bond (maltose, lactose, sucrose)

Carbohydrates-Fuel and Building Material Polysaccharides, the polymers of sugars, have storage and structural roles –Polysaccharides are macromolecules, polymers with a few hundred to a few thousand monosaccharides. –Some polysaccharides serve as storage material, others as building material for structures that protect the cell

Storage Polysaccharides Starch is a storage polysaccharide of plants. –Consists solely of glucose monomers –Because glucose is a major cellular fuel, starch represents stored energy Glycogen is a storage polysaccharide of animals –Consists of glucose monomers that is more extensively branched than starch

Polysaccharide Structure Glycogen Structure Starch Structure

Structural Polysaccharides Cellulose is a polysaccharide which is a major component of tough cell walls of plants –Is a polymer of glucose like starch, but is a non branching structure –Strands of cellulose will hydrogen bond parallel to each other, creating a strong framework

Lipids- Diverse Hydrophobic Molecules Lipids are the one class of large biological molecules that does not include polymers –The compounds called lipids are grouped together because they share one important trait: they have little or no affinity for water –Their hydrophobic nature is based on their molecular structure made mostly of hydrocarbons

Fats store large amounts of energy Fats are large molecules, and are assembled from smaller molecules. –A fat is constructed from two kinds of smaller molecules: glycerol and fatty acids Glycerol is an alcohol with three carbons A fatty acid has a long carbon skeleton, usually carbons –Fats have fatty acid “tails”, and a glycerol “head” The tail is non-polar, the head is polar

Fat Structure Glycerol head Fatty acid tails

Fats store large amounts of energy Fatty acids very in length and in the number of locations of double bonds –A saturated fatty acid is saturated with hydrogen and therefore has no double bonds. Tend to be solid fats- lard, butter, etc

Fats store large amounts of energy –An unsaturated fatty acid has one or more double bonds, formed by the removal of hydrogen atoms from the carbon skeleton –A fatty acid will have a kink in its tail wherever the double bond occurs Tend to be more liquidy fats like oils

Phospholipids are major components of cell membranes Phospholipids are similar to fats, but they have only two tails rather than three. –Phospholipid tails are hydrophobic, and are excluded from water (water fearing) –Phospholipid heads are hydrophilic, and has an affinity for water (water loving)

Phospholipids are major components of cell membranes –At the surface of a cell, phospholipids are arranged in a bilayer (double layer). The hydrophilic heads are in contact with the aqueous solution inside and outside of the cell The hydrophobic tails point toward the interior of the membrane, away from the water.

Steroids include cholesterol and certain hormones Steroids are lipids characterized by a carbon skeleton consisting of four fused rings. –Cholesterol is a steroid that is found in the cell membranes of animal cells and is also the precursor from which other steroids are synthesized.

Proteins- Many Structures, Many Functions Proteins are used for structural support, storage, transport, signaling, movement, and defense inside a cell. As enzymes, proteins regulate metabolism by selectively accelerating chemical reactions in the cell. Consistent with their diverse functions, they vary in structure- each type of protein having its own conformation Proteins are constructed from amino acids. –Strings of amino acids are called polypeptides.

A polypeptide is a polymer of amino acids connected in a specific sequence There are 20 amino acids that come together in different combinations to form a polypeptide chain. –Amino acids bind together by covalent bonds called peptide bonds

A protein’s function depends on its specific conformation Polypeptide ≠ Protein –A functional protein is not just a polypeptide chain. It is a chain that has been twisted, folded, and coiled into a molecule with a specific shape

Four Levels of Protein Structure When a cell makes a polypeptide, the chain generally folds spontaneously to assume the functional conformation for that protein. –In the complex architecture of a protein, we can recognize three superimposed levels of structure, as well as a fourth structure made of multiple polypeptide chains

Four Levels of Protein Structure Primary Structure –The sequence of amino acids LysCysThrAsnAlaGlyPhe

Four Levels of Protein Structure Secondary Structure –Coiled or folded patterns that contribute to the protein’s overall conformation α helix –A delicate coil held together by hydrogen bonds between every four amino acids Β-pleated sheet –Two or more regions of the chain lie parallel to each other

Four Levels of Protein Structure Secondary Structure Β-pleated sheet Α helix

Four Levels of Protein Structure Tertiary Structure –Superimposed on the patterns of secondary structure is a protein’s tertiary structure, consisting of irregular contortions from interactions of the side chains of various amino acids

Four Levels of Protein Structure There are many interactions that aid in the conformation of the protein: –Hydrogen bond –Van der Waals interactions –Disulfide bridges Where two sulfhydryl groups come together –Ionic bonds

Four Levels of Protein Structure Quaternary Structure –Overall protein structure that results from multiple polypeptide subunits Ex. Collagen- long fibers coming together Ex. Hemoglobin- two polypeptide chains working together

Nucleic Acids-Informational Polymers The amino acid sequence of a polypeptide is programmed by a unit of inheritance known as a gene. Genes consist of DNA, which is a polymer belonging to the class of compounds known as nucleic acids

Nucleic Acids-Informational Polymers Nucleic acids store and transmit hereditary information –There are two types of nuclei acids: deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) –DNA provides directions for its own replication, we well as it directs RNA synthesis and, through RNA, controls protein synthesis.

A nucleic acid strand is a polymer of nucleotides Nucleic acids are polymers of monomers called nucleotides –Each nucleotide is made of three parts: a nitrogenous base, a phosphate, and a sugar

A nucleic acid strand is a polymer of nucleotides In a nucleic acid polymer, or polynucleotide, nucleotides are joined by covalent bonds between the sugar of one nucleotide and a phosphate of another nucleotide –This bonding results in a backbone with a repeating pattern (sugar, phosphate, sugar, phosphate…)

Inheritance is based on replication if the DNA double helix The RNA molecules if cells consist of a single polynucleotide chain, unlike DNA which is a double chain (a double helix) Only certain bases in the DNA double helix are compatible with each other –A (adenine) binds with T (thymine) –C (cytosine) binds with G (guanine)

Inheritance is based on replication if the DNA double helix If we were to read the sequence of bases along one strand of the double helix, we would know the sequence of the other side The two strands of the double helix are complimentary, each the predictable counterpart of the other –It is this feature of DNA that makes it possible to copy DNA so precisely

Inheritance is based on replication if the DNA double helix In preparation for cell division, each of the strands of a DNA molecule act as a template to order new nucleotides into a new complementary strand

In Conclusion That was a quick overview of macromolecules. We have briefly examined the architecture of molecules, but have not yet explored the interactions between those molecules that result in biochemical changes collectively called cellular metabolism