Lec 2 Biological Molecules.pdf

BIO 11 UNIFYING CONCEPTS OF BIOLOGY BIOLOGICAL MOLECULES LECTURE 2 OVERVIEW: The Molecules of BIO 11 UNIFYING CONCEPTS OF BIOLOGY Life All living things are made up of fou...

BIO 11 UNIFYING CONCEPTS OF BIOLOGY BIOLOGICAL MOLECULES LECTURE 2 OVERVIEW: The Molecules of BIO 11 UNIFYING CONCEPTS OF BIOLOGY Life All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids Macromolecules are large molecules composed of thousands of covalently connected atoms Molecular structure and function are inseparable I. Macromolecules are polymers, built from monomers A polymer is a long molecule consisting of many similar building blocks These small building-block molecules are called monomers Three of the four classes of life’s organic molecules are polymers Carbohydrates Proteins Nucleic acids The Synthesis and Breakdown of Polymers BIO 11 UNIFYING CONCEPTS OF BIOLOGY A dehydration reaction occurs when two monomers bond together through the loss of a water molecule Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction The Diversity of Polymers BIO 11 UNIFYING CONCEPTS OF BIOLOGY Each cell has thousands of different macromolecules Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species An immense variety of polymers can be built from a small set of monomers II. Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or single sugars Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks Sugars BIO 11 UNIFYING CONCEPTS OF BIOLOGY Monosaccharides have molecular formulas that are usually multiples of CH2O Glucose (C6H12O6) is the most common monosaccharide Monosaccharides are classified by The location of the carbonyl group (as aldose or ketose) The number of carbons in the carbon skeleton Though often drawn as linear skeletons, in aqueous solutions many sugars form rings Monosaccharides serve as a major fuel for cells and as raw material for building molecules BIO 11 UNIFYING CONCEPTS OF BIOLOGY A disaccharide is formed when a dehydration reaction joins two BIO 11 UNIFYING CONCEPTS OF BIOLOGY monosaccharides This covalent bond is called a glycosidic linkage Polysaccharides BIO 11 UNIFYING CONCEPTS OF BIOLOGY Polysaccharides, the polymers of sugars, have storage and structural roles The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages a. Storage Polysaccharides BIO 11 UNIFYING CONCEPTS OF BIOLOGY Starch, a storage polysaccharide of plants, consists entirely of glucose monomers Plants store surplus starch as granules within chloroplasts and other plastids The simplest form of starch is amylose  BIO 11 UNIFYING CONCEPTS OF BIOLOGY Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver and muscle cells b. Structural Polysaccharides BIO 11 UNIFYING CONCEPTS OF BIOLOGY The polysaccharide cellulose is a major component of the tough wall of plant cells Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ The difference is based on two ring forms for glucose: alpha (α) and beta (β) Polymers with α glucose are helical BIO 11 UNIFYING CONCEPTS OF BIOLOGY Polymers with β glucose are straight In straight structures, H atoms on one strand can bond with OH groups on other strands Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants  BIO 11 UNIFYING CONCEPTS OF BIOLOGY Enzymes that digest starch by hydrolyzing α linkages can’t hydrolyze β linkages in cellulose Cellulose in human food passes through the digestive tract as insoluble fiber Some microbes use enzymes to digest cellulose Many herbivores, from cows to termites, have symbiotic relationships with these microbes  BIO 11 UNIFYING CONCEPTS OF BIOLOGY Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi III. Lipids are a diverse group of hydrophobic molecules Lipids are the one class of large biological molecules that do not form polymers The unifying feature of lipids is having little or no affinity for water Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds The most biologically important lipids fats phospholipids steroids Fats BIO 11 UNIFYING CONCEPTS OF BIOLOGY Fats are constructed from two types of smaller molecules: glycerol and fatty acids Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon A fatty acid consists of a carboxyl group attached to a long carbon skeleton Fats separate from water because water molecules form BIO 11 UNIFYING CONCEPTS OF BIOLOGY hydrogen bonds with each other and exclude the fats In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride Fatty acids vary in length (number of carbons) and in the BIO 11 UNIFYING CONCEPTS OF BIOLOGY number and locations of double bonds Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Unsaturated fatty acids have one or more double bonds Hydrogenation is the process of converting unsaturated fats to BIO 11 UNIFYING CONCEPTS OF BIOLOGY saturated fats by adding hydrogen Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds These trans fats may contribute more than saturated fats to cardiovascular disease Phospholipids BIO 11 UNIFYING CONCEPTS OF BIOLOGY In a phospholipid, two fatty acids and a phosphate group are attached to glycerol The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head When phospholipids are added to water, they self-assemble BIO 11 UNIFYING CONCEPTS OF BIOLOGY into a bilayer, with the hydrophobic tails pointing toward the interior The structure of phospholipids results in a bilayer arrangement found in cell membranes Phospholipids are the major component of all cell membranes Steroids BIO 11 UNIFYING CONCEPTS OF BIOLOGY Steroids are lipids characterized by a carbon skeleton consisting of four fused rings Cholesterol, an important steroid, is a component in animal cell membranes Although cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease IV. Proteins include a diversity of structures, resulting in a wide range of functions Proteins account for more than 50% of the dry mass of most cells Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances BIO 11 UNIFYING CONCEPTS OF BIOLOGY BIO 11 UNIFYING CONCEPTS OF BIOLOGY Polypeptide BIO 11 UNIFYING CONCEPTS OF BIOLOGY Polypeptides are unbranched polymers built from the same set of 20 amino acids A protein is a biologically functional molecule that consists of one or more polypeptides Amino Acid Monomers BIO 11 UNIFYING CONCEPTS OF BIOLOGY Amino acids are organic molecules with carboxyl and amino groups Amino acids differ in their properties due to differing side chains, called R groups BIO 11 UNIFYING CONCEPTS OF BIOLOGY Amino Acid Polymers BIO 11 UNIFYING CONCEPTS OF BIOLOGY Amino acids are linked by peptide bonds A polypeptide is a polymer of amino acids Polypeptides range in length from a few to more than a thousand monomers Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus) Protein Structure and Function BIO 11 UNIFYING CONCEPTS OF BIOLOGY A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape The sequence of amino acids determines a protein’s three- dimensional structure A protein’s structure determines its function Four Levels of Protein Structure BIO 11 UNIFYING CONCEPTS OF BIOLOGY The primary structure of a protein is its unique sequence of amino acids Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain Tertiary structure is determined by interactions among various side chains (R groups) Quaternary structure results when a protein consists of multiple polypeptide chains Primary Structure BIO 11 UNIFYING CONCEPTS OF BIOLOGY Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word Primary structure is determined by inherited genetic information Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin Sickle-Cell Disease: A Change in Primary Structure Secondary Structure BIO 11 UNIFYING CONCEPTS OF BIOLOGY The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone Typical secondary structures are a coil called an α helix and a folded structure called a β pleated sheet Tertiary Structure BIO 11 UNIFYING CONCEPTS OF BIOLOGY Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents These interactions between R groups include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions Strong covalent bonds called disulfide bridges may reinforce the protein’s structure Quaternary Structure BIO 11 UNIFYING CONCEPTS OF BIOLOGY Quaternary structure results when two or more polypeptide chains form one macromolecule Collagen is a fibrous protein consisting of three polypeptides coiled like a rope Hemoglobin is a globular protein consisting of four polypeptides: two alpha and two beta chains  Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel This loss of a protein’s native structure is called What determines denaturation A denatured protein is biologically inactive protein structure? Protein Folding in the Cell BIO 11 UNIFYING CONCEPTS OF BIOLOGY Chaperonins are protein molecules that assist the proper folding of other proteins Diseases such as Alzheimer’s, Parkinson’s, and mad cow disease are associated with misfolded proteins  BIO 11 UNIFYING CONCEPTS OF BIOLOGY Scientists use X-ray crystallography to determine a protein’s structure Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization Bioinformatics uses computer programs to predict protein structure from amino acid sequences V. Nucleic acids store, transmit, and help express hereditary information The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene Genes are made of DNA, a nucleic acid made of monomers called nucleotides The Roles of Nucleic Acids BIO 11 UNIFYING CONCEPTS OF BIOLOGY There are two types of nucleic acids Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA provides directions for its own replication DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis Protein synthesis occurs on ribosomes The Components of Nucleic Acids BIO 11 UNIFYING CONCEPTS OF BIOLOGY Nucleic acids are polymers called polynucleotides Each polynucleotide is made of monomers called nucleotides Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups The portion of a nucleotide without the phosphate group is called a nucleoside BIO 11 UNIFYING CONCEPTS OF BIOLOGY Nucleotide Polymers BIO 11 UNIFYING CONCEPTS OF BIOLOGY Nucleotide polymers are linked together to build a polynucleotide Adjacent nucleotides are joined by covalent bonds that form between the —OH group on the 3' carbon of one nucleotide and the phosphate on the 5' carbon on the next These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages The sequence of bases along a DNA or mRNA polymer is unique for each gene The Structures of DNA and RNA Molecules BIO 11 UNIFYING CONCEPTS OF BIOLOGY In the DNA double helix, the two backbones run in opposite 5'→ 3' directions from each other, an arrangement referred to as antiparallel  BIO 11 UNIFYING CONCEPTS OF BIOLOGY Complementary Base Pairing DNA and Proteins as Tape Measures of BIO 11 UNIFYING CONCEPTS OF BIOLOGY Evolution The linear sequences of nucleotides in DNA molecules are passed from parents to offspring Two closely related species are more similar in DNA than are more distantly related species Molecular biology can be used to assess evolutionary kinship