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Biology 102

Biology 102. Lecture 4: Biological Molecules. Lecture outline. Organic molecules: Overview Carbohydrates Functions Structure Lipids. 1. Living organisms are composed of organic molecules. Organic: Have a carbon “skeleton” Carbon-carbon bonds

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Biology 102

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  1. Biology 102 Lecture 4: Biological Molecules

  2. Lecture outline • Organic molecules: Overview • Carbohydrates • Functions • Structure • Lipids

  3. 1. Living organisms are composed of organic molecules • Organic: Have a carbon “skeleton” • Carbon-carbon bonds • Each C atom can form as many as 4 bonds with other atoms • What other molecule is similar? • Functional groups • Specific arrangements of atoms that give each type of organic molecule their unique characteristics

  4. All organisms are composed of similar organic molecules • Carbohydrates • Lipids • Proteins • Nucleic acids • Complex biological molecules (polymers) are synthesized from more simple molecules (monomers) • So, monomers are basically subunits of polymers.

  5. Audesirk, p. 39 • Biological molecules are joined together by removing water: Dehydration synthesis • Biological molecules are split apart by adding water: Hydrolysis • “hydro”=water, “lysis”=to cut Audesirk, p. 39

  6. 2. Carbohydrates • Key functions: • Serve as a source of energy • Energy is “stored” within the bonds of all organic molecules, but carbohydrates are the most easily broken down to release energy • Starch, glycogen and glucose are all examples of carbohydrates that provide energy • Provide structure • Cellulose forms the cell walls of plants • Chitin forms the cell walls of fungi and the exoskeleton of arthropods (insects, crabs, etc…)

  7. Structure of carbohydrate monomers • Composition • Contain Carbon, Hydrogen and Oxygen at ratios of 1:2:1 • So, literally is Carbon plus water! • Monosaccharides: sugar monomer, or “single sugar” • When dissolved in water, usually forms a ring • Here, ring is 5 carbons and one o the oxgyens • Carbohydrates are polar • Where are the negative and positive charges? C6H12O6

  8. Fructose: sugar found in corn syrup and orange juice Galactose: sugar found in milk Ribose: sugar that forms part of RNA backbone Deoxyribose: sugar that forms part of DNA backbone Several other monosaccharides with slightly different structures from glucose

  9. Carbohydrate polymers • Disaccharides: “di” means “two” • Two monosaccharides linked by dehydration synthesis • Note how an “H” of one monosaccharide combines with the “OH” of the other. Audesirk,Fig. 3-1

  10. Polysaccharides are chains of monosaccharides • Starch: energy storage • Enzyme in our saliva breaks down starch into sugar monomers • Cellulose: structure • Forms plant cell walls • We cannot break down cellulose, so it passes undigested through us • Chitin: structure • Cell walls of fungi • Contains nitrogen atoms!

  11. 3. Lipids • Key functions • Energy storage molecules (i.e. fat); long-term • Fats and oils have over 2X the amount of energy for a given unit of weight compared to carbohydrates: • 9.3 Calories/g compared to 4.1 Calories/g • Waterproof coverings on plants and animals • Essential components of cell membranes • Hormones (i.e. testosterone and estrogen) • Contain large non-polar regions • Specifically, the long hydrocarbon chains are non-polar

  12. Oils and fats (triglycerides) • Contain only Carbon, Hydrogen and Oxygen (just like carbohydrates!) • Formed when three fatty acid subunits join to a single glycerol molecule • Synthesized with a dehydration synthesis reaction

  13. The difference between oils and fats • Fats: solid at room temperature • They are “saturated” with Hydrogens: NO DOUBLE BONDS BETWEEN CARBONS • Resulting hydrocarbon chain is straight • Allows chains to fit together in solid clumps H H H H H H -C-C-C-C-C-C-H H H H H H H

  14. The difference between oils and fats (cont.) • Oils: liquid at room temperature • They are “unsaturated” : HAVE SOME BONDS BETWEEN CARBONS • Resulting hydrocarbon chain is kinked • Do not fit together as well, and so remain fluid H H H H H -C-C=C-C-C-C-H H H H H H Note the double bond and lower number of Hydrogens: “unsaturated”

  15. Phospholipids • Key component of membranes, including the plasma (cell) membrane • Phosphate-containing head region (polar!) • Note where the charges would be… • Two fatty acid tails (non-polar) • Why not polar?

  16. Steroids • Composed of four rings of carbon • Various functional groups protrude from the rings • Cholesterol: • Key component of membranes • Used to synthesize other steroids • Testosterone and estradiol • Sex hormones • Note similarity in structure

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