Chapter 5 Friday September 12 2014 10 03 AM The seven functional groups that are most important in the chemistry of life Hydroxyl group OH Carbonyl group C O O Carboxyl group COOH C O COO Amino group NH2 NH3 Sulfhydryl group SH Phosphate group Sugars Methyl group CH3 The synthesis and breakdown of polymers 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 VARIETY Why hydrolysis Water is the solvent of living systems Easy reaction mild conditions shift in pH acid pH of stomach Enzyme catalyzed enzymes work in water Carbohydrates 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 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 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 Figure 5 6 Storage polysaccharides of plants and animals Biology Page 5 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 Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver and muscle cells Figure 5 7 Starch and cellulose structures 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 and beta Figure 5 8 The arrangement of cellulose in plant cell walls Polymers with glucose are helical Polymers with 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 Enzymes that digest starch by hydrolyzing linkages can t hydrolyze 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 Biology Page 6 Chitin Fats Chitin another structural polysaccharide is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi Figure 5 10 The synthesis and structure of a fat or triacylglycerol 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 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 Figure 5 11 Saturated and unsaturated fats and fatty acids Fatty acids vary in length number of carbons and in the 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 Fats made from saturated fatty acids are called saturated fats and are solid at room temperature Fats made from unsaturated fatty acids are called unsaturated fats or oils and are liquid at room temperature Most animal fats are saturated Plant fats and fish fats are usually unsaturated A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits Hydrogenation is the process of converting unsaturated fats to 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 Certain unsaturated fatty acids are not synthesized in the human body These must be supplied in the diet These essential fatty acids include the omega 3 fatty acids required for normal growth and thought to provide protection against cardiovascular disease The major function of fats is energy storage Humans and other mammals store their fat in adipose cells Biology Page 7 Humans and other mammals store their fat in adipose cells Adipose tissue also cushions vital organs and insulates the body Phospholipids Figure 5 12 The structure of a phospholipid 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 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 Cholesterol is a steroid Steroids are lipids characterized by a carbon skeleton consisting of four fused rings Steroids found in the human body Estradiol and Testosterone Biology Page 8 Chapter 6 Friday September 12 2014 10 03 AM Microscopy Microscopes Magnification the ratio of an object s image size to its real size Resolution the measure of the clarity of the image or the minimum distance of two distinguishable points Contrast visible differences in parts of the sample Two basic types of electron microscopes EMs are used to study subcellular structures 1 Scanning electron microscopes SEMs focus a beam of electrons onto the surface of a specimen providing images that look 3 D 2 Transmission electron microscopes TEMs focus a beam of electrons through a specimen TEMs are used mainly to study the internal structure of cells Surface Volume Metabolic requirements set upper limits on the size of cells The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2 the volume increases by a factor of n3 Small cells have a greater surface area relative to
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