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Chapter 3 Biological Molecules 3.1. Why Is Carbon So Important in Biological Molecules? • All contain carbon – Organic refers to molecules containing a carbon skeleton – Inorganic refers to carbon dioxide and all molecules without carbon 3.1. Why Is Carbon So Important in Biological Molecules? • Each carbon can form up to four bonds (single(2 electrons), double, or triple) and rings • Carbon makes bonds mostly with H, N, and O in living systems • Biomolecules are large and contain “functional groups” attached to the carbon backbone. • Functional groups in organic molecules confer chemical reactivity and other characteristics 3.2. Organic Molecule Synthesis • Biomolecules are polymers (chains) of subunits called monomers • Monomers are joined together through dehydration synthesis – An H and an OH are removed, resulting in the loss of a water molecule (H2O) 3.2. Organic Molecule Synthesis • Polymers are broken apart through hydrolysis (“water cutting”) – Water is broken into H and OH and used to break the bond between monomers 3.2. Organic Molecule Synthesis • All biological molecules fall into one of four categories – Carbohydrates – Lipids – Proteins – Nucleic Acids What Are Carbohydrates? • Composition – Made of C, H, and O in the ratio of 1:2:1 (CH2O)n • Types – Simple or single sugars are monosaccharides – Two linked monosaccharides are disaccharides – Long chains of monosaccharides are polysaccharides What Are Carbohydrates? • Function: – Energy source – Structure • Most are water- soluble due to the polar OH functional groups Monosaccharides • Basic Structure – Backbone of 3-7 carbon atoms – Many –OH and –H functional groups – Usually found in a ring form in cells • Examples: – – – – Glucose (C6H12O6): the most common Fructose (found in corn syrup and fruits) Galactose (found in lactose) Ribose and deoxyribose (found in RNA and DNA) Monosaccharides Monosaccharides • Fate inside a cell – Some broken down to free their chemical energy – Some are linked together by dehydration synthesis Disaccharides • Disaccharides are two-part sugars – Sucrose (table sugar) = glucose + fructose – Lactose (milk sugar) = glucose + galactose – Maltose (malt sugar)= glucose + glucose Polysaccharides • Monosaccharides are linked together to form chains (polysaccharides) • Storage polysaccharides: – Polymers of Glucose: • STARCH. Formed in roots and seeds • GLYCOGEN. Found in liver and muscles Polysaccharides • Structural polysaccharides – Cellulose (polymer of glucose) – Found in the cell walls of plants • Indigestible for most animals due to orientation of bonds between glucoses Polysaccharides • Structural polysaccharides continued – Chitin (polymer of modified glucose units) • Found in the outer coverings of insects, crabs, and spiders • Found in the cell walls of many fungi 3.4. What Are Lipids? • Oils, Fats, and Waxes • Function – Energy source ; storage – Water-proofing (membranes) – Hormones • Contain Only Carbon, Hydrogen, and Oxygen • Most are hydrophobic and water insoluble, due to long non-polar chains • Types: fatty acids, triglycerides, phospholipids, steroids • Main subunit: – Fatty acid Oils, Fats, and Waxes • Made of one or more fatty acid subunits • Formed by dehydration synthesis – 3 fatty acids + glycerol triglyceride (95% of all lipids in the body) Oils, Fats, and Waxes • Fats and oils used for long-term energy storage – high density of stored chemical energy Oils, Fats, and Waxes • Fat solidity is due to single or double carbon bonds – Fats that are solid at room temperature are saturated (carbon chain has as many hydrogen atoms as possible, and mostly or all C-C bonds), e.g. beef fat Oils, Fats, and Waxes • Fats that are liquid at room temperature are unsaturated (fewer hydrogen atoms, many C=C bonds), e.g. corn oil • Unsaturated trans fats have been linked to heart disease Oils, Fats, and Waxes • Waxes are composed of long hydrocarbon chains and are strongly hydrophobic • Waxes are highly saturated and solid at room temperature Oils, Fats, and Waxes • Waxes form waterproof coatings – Leaves and stems of plants – Fur in mammals – Insect exoskeletons • Used to build honeycomb structures Phospholipids • Phospholipids: form plasma membranes around all cells • Construction – 2 fatty acids + glycerol + a short polar functional group Phospholipids • Phospholipids have hydrophobic and hydrophilic portions – Polar functional groups are water soluble – Nonpolar fatty acid “tails” are water insoluble Steroids • Steroids are composed of four carbon rings fused together • Examples of steroids – Cholesterol • Found in membranes of animal cells – Male and female sex hormones 3.5. What Are Proteins? • Proteins are formed from chains of amino acids (monomers; 20 different) • The type, number and position of amino acids in a protein dictates its function Amino Acids • All amino acids have similar structure – All contain amino and carboxyl groups – All have a variable “R” group • • • Some R groups are hydrophobic Some are hydrophilic Cysteine R groups can form disulfide bridges Amino Acids Diversity (20) Protein Synthesis • Amino acids are joined to form chains by dehydration synthesis – An amino group reacts with a carboxyl group, and water is lost Dehydration Synthesis • Resultant covalent bond is a peptide bond • Long chains of amino acids are known as polypeptides or just proteins Four Levels of Structure • Proteins exhibit up to four levels of structure – Primary structure is the sequence of amino acids linked together in a protein – Secondary structures are helices and pleated sheets – Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds – Quaternary structure is found where multiple protein chains are linked together R R O C N C H R C C N N C C N C C O R H N C C C N N C C N C C O H R O N C O N C C N C C O R R C R O O R O C R O R O R Pleated sheet R O C N C N C C O H R C C N C O polypeptide R R O R C C N N C C C O R hydrogen bond s s s-s s-s s s s-s keratin s s Three Dimensional Structures – Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure – Disruption of these bonds leads to denatured proteins and loss of function 3.6 What Are Nucleic Acids? • Nucleotides are the monomers of nucleic acid chains • Each nucleotide has three parts – 5-carbon sugar (ribose or deoxyribose) – phosphate group – Nitrogen containing base Molecules of Heredity • A Phosphodiester bond between nucleotides to make a chain: • Two types of nucleotides – Ribonucleotides (A, G, C, and U) found in RNA – Deoxyribonucleotides (A, G, C, and T) found in DNA Molecules of Heredity • Two types of polymers of nucleic acids – DNA (deoxyribonucleic acid) found in chromosomes • Carries genetic information needed for protein construction – RNA (ribonucleic acid) • Copies of DNA used directly in protein construction Molecules of Heredity • Each DNA molecule consists of two chains of nucleotides that form a double helix Functions of Nucleic Acids • DNA and RNA, the Molecules of Heredity, Are Nucleic Acids • Other Nucleotides Act as : – Messengers: Intracellular Cyclic nucleotides (e.g. cyclic AMP) carry chemical signals between molecule – Energy carriers: • Adenosine triphosphate (ATP) carries energy stored in bonds between phosphate groups • NAD+ and FAD carry electrons – Enzyme assistants • Coenzymes help enzymes promote and guide chemical reactions Vitamin NH2 N C C NH2 N C C N N HC HC N C N CH O CH2 H H O P O OH O HO H P O H OH O P O P O HO N C N CH OH O O O CH2 H H N C C N P O HC O H H OH OH NH2 O HO O P O OH CH2 H H OH OH Cyclic adenosine monophosphate (cyclic AMP) (intracellular communication) Adenosine triphosphate (ATP) (energy carrier) A sampling of the diversity of nucleotides N C N CH O H H OH Coenzyme (active in cellular metabolism)