Chapter 3:Why is carbon so important in biological molecules?- Organic/inorganic molecules and functional groupso Organic: consisting of a carbon skeleton bonded to hydrogen atomso Inorganic: carbon dioxide and all molecules without carbono The carbon atom is very versatileo Has 4 electrons in outermost shello CAN hold up to 8 electrons in outer shell Therefore, a carbon atom can become stable by forming up to four covalent bonds with up to 4 atoms So, organic molecules can assume complex shapes, including branchedchains, rings, sheets, and helices- Function groups: determine the characteristics and chemical reactivity of the moleculeso Less stable than the carbon backbone and more likely to participate in chemical reactionsoHow are organic molecules synthesized?- Small organic molecules (called monomers) are joined together to form longer molecules (called polymers)- Monomers are joined together through dehydration synthesis (or CONDENSATION RXN), resulting in the loss of a water molecules from the reacting molecule-- Polymers are broken apart through hydrolysis (“water cutting”)o Water is broken into H and OH and is used to break the bond between monomerso- All biological molecules fall into one of four categorieso Carbohydrateso Lipidso Proteinso Nucleotides/nucleic acidsWhat are carbohydrates?- Carbohydrate molecules are composed of C. H. and O in ratio of 1:2:1o If a carbohydrate consists of just one sugar molecule, it is a monosaccharideo Two linked monosaccharides form a disaccharideo A polymer of many monosaccharides is a polysaccharideo Important energy sources for most organismso Most small carbohydrates are water-soluble due to the polar OH functional group- There are several monosaccharides with slightly different structureso Example: monosaccharides Glucose (C6H12O6): the most common in living organisms-Sugar dissolving in waterFructose: “fruit sugar” found in fruits, corn syrup, and honeyGalactose: “milk sugar” found in lactoseRibose and deoxyribose (found in RNA and DNA)dehydrationsynthesis Fig. 3-1hydrolysis Fig. 3-2-Disaccharides consist of two monosaccharides linked by dehydration synthesiso Disaccharides are two-part sugarsThey are used for short-term energy storageWhen energy is required, they are broken apart into their monosaccharide subunits by hydrolysiso Examples of disaccharides:Sucrose (table sugar): glucose +fructoseLactose (milk sugar): glucose + GalactoseMaltose (malt sugar): glucose + glucose-Polysaccharides are chains of simple sugarso Starch: an energy-storage molecule in plants, formed in roots and seedso Glycogen: an energy-storage molecule in animals, found in liver & muscleso Both are polymers of glucose moleculesoo Many organisms use polysaccharides as a structural materialo Cellulose (a polymer of glucose) is one of the most important structural polysaccharidesFound in cell walls of plantsIndigestible for most animalsChemical formula for starch and cellulose is the same but they are very differentStarch (easily digested) vs. cellulose (indigestible for most animals)(b) A starch molecule(a) Potato cells(c) Detail of a starch moleculestarch grainsFig. 3-8oo Chitin: (a polymer of modified glucose units) is found in:Outer coverings of insects, crabs, and spidersCell wall of many fungiWhat are Lipids?- Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbono Large chains of nonpolar hydrocarbonso Hydrophobic and water insolubleo Used for energy storageo Waterproof coverings on plant and animal bodieso Primary component of cellular membranes- Lipids are classified into three major groups:o Oils, fats, and waxeso Phospholipidso Steroids containing rings of carbon, hydrogen, and oxygen- Oils, fats, and waxes (examples of triglycerides)o Made of one or more fatty acid subunitso 3 fatty acids + glycerol triglyceride o Saturated: fats that are solid at room temperatureFig. 3-10o Unsaturated: fats that are liquid at room temperature (linked to heart disease)o Waxes are highly saturated and solid at room temperature Form waterproof coatings on leaves/stems in plants, fur in mammals, and insects exoskeletons Used to build honeycomb structureso Phospholipids: main component of cell membranes Form plasma membranes around all cells They have hydrophobic and hydrophilic portions- Polar functional groups form the “head” and are water-soluble- ^head ^tail- Nonpolar fatty acids form the “tails” and are water insoluble o Steroids: composed of four carbon rings fused together with various functional groups protruding from them Cholesterol (found in the membranes of animal cells) Male and female sex hormonesWhat are proteins?- Proteins have a variety of functionso Enzymes are proteins that promote chemical reactionso Structural proteins (elastin) provide support- Proteins are formed from chains of amino acids joined by peptide bondso All amino acids (total of 20) have a similar structureo Contain amino, carboxyl, and a variable “R” groupo “R” group distinguishes each amino acidoo Amino acids are joined to form chains by dehydration synthesis (or CONDENSATION RXN) An amino group reacts with a carboxyl group, and water is lost The covalent bond resulting is a peptide bond, and the chain of two amino acids is called a dipeptide Long chains of amino acids are known as polypeptides, or proteins- Proteins exhibit up to four levels of structureo Primary structure (1◦) linear sequence of amino acids linked together in a proteino Secondary structure (2◦) is a helix, or a pleated sheetoo Tertiary structure (3◦) is the complex folding of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, etco Quaternary structure (4◦) occurs where multiple protein chains are linked togetheraminogrouphydrogenVariable “R” groupcarboxyl groupFig. 3-17oo Disruption of secondary, tertiary, and quaternary structure leads to denatured proteins and loss of function This can be due to a pH change, increase/decrease in temperature, or salt concentration changeWhat are nucleic acids?- Nucleotides act as energy carriers and intracellular messengerso Nucleotides are the monomers of nucleic acid chainso All nucleotides are made of three parts Phosphate group Five-carbon sugar Nitrogen-containing base- Deoxyribose Nucleotideo- Adenosine
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