BIO 311C Textbook Notes based on Handout 1
BIO 311C Textbook Notes based on Handout 1 Bio 311C
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This 7 page Class Notes was uploaded by Sena Sarikaya on Tuesday September 20, 2016. The Class Notes belongs to Bio 311C at University of Texas at Austin taught by Dr. Buskirk in Fall 2016. Since its upload, it has received 9 views. For similar materials see Introductory Biology I in Biology at University of Texas at Austin.
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Date Created: 09/20/16
Textbook Notes for Handout 1 Ch. 2 2.3 The Formation & Function of Molecules Depend on Chemical Bonding btwn Atoms A. Covalent Bonds covalent bond: sharing of a pair of valence e by 2 atoms molecule: 2 or more atoms held together by cov. bond ex. molecular formula H 2 Lewis Dot structure H:H ex. structural formula HH single bond: 1 pair of shared e, represented w/ “” double bond: 2 pair of shared e ex. O=O valence: bonding capacity; usually # of unpaired e ex. for oxygen its 2; hydrogen its 1; nitrogen its 3; carbon its 4 phosphorus can have 3 or 5 H 2 and O 2 are pure elements NOT compounds compounds are 2 or more dif. elements ex. H O 2 electronegativity: attraction of a particular atom for the e of a covalent bond nonpolar covalent bond: 2 atoms w/ same electronegativity; e shared equally polar covalent bond: e not shared equally; one atom ore electronegative B. Ionic Bonds ions: charged atoms cations: (+) anions: () ionic bond: 2 ions of opp. charge bond ionic compounds or salts: compounds formed by ionic bonds ion can also be a charged molecule ex. +¿ ¿ NH 4 ionic bonds strong when dry but diss. in H 2 arrange in 3D lattice not molecules; formula for ionic comp. is a ratio C. Weak Chemical Bonds a. Hydrogen Bonds hydrogen bonds: attraction btwn H & electronegative atom b. Van der Waals Interactions vdwi: ever changing regions of (+) and () charge enabling atoms & mol. to stick to one & another individually weak but occurring simultaneously > powerful D. Molecular Shape & Function determines how biological molecules organize & respond to one another w/ specificity match btwn structure & funct. Concept Check 2.3 1. Why does HC=CH fail chemically? C needs 8 e in valence shell so missing 2 e per C 2. What holds atoms together in MgCl 2 ? Ionic bonds 3. Why would you want to learn the 3D shapes of naturally occurring signal molecules? Clue to receptor shapes; synthesize molecules that mimic the shapes to treat individuals who can’t produce their own 2.4 Chemical Reactions Make & Break Chemical Bonds chemical reaction: making & breaking of chemical bonds leading ot changes chemical equilibrium: the point @ which rxns offset on another exactly dynamic equil. b/c rxn still going on but no net effect on conc. of react. / prod. Ch. 3 3.1 Polar Covalent Bonds in Water Molecules Result in Hydrogen Bonding polar molecule: unequal sharing of e ex. H O 2 Concept Check 3.1 1. What is electronegativity; how does it affect interactions between water molecules? Electronegativity= how much an e is attracted to the e of a covalent bond. Electronegativity affects interactions in water molecules by causing a polar molecule that forms hydrogen bonds. 2. Why is this unlikely? H H / \ O O \ / H H Because H is partially () so H’s will repel and be attracted to the O’s forming hydrogen bonds between molecules. 3. What would the effect on properties of the water if O and H had equal electronegativity? Hydrogen bonds could not form if the molecule was nonpolar. 3.2 Four Emergent Properties of Water Contribute to Earth’s Suitability for life A. Cohesion of Water Molecules cohesion: H bonds holding the subst. together transport of water & dissolved nutrients against gravity of plants adhesion: clinging of one substance to another surface tension: how difficult it is to break the surface of a liquid related to cohesion B. Moderation of Temperature by Water a. Temperature & Heat kinetic energy: the energy of motion thermal energy: K.E. associated w/ random movement of atoms temperature: measurement of nrg of avg K.E. of molecules in matter doesn’t depend on volume like thermal nrg thermal nrg passes from hotter to cooler object heat: thermal nrg in transfer from one body of matter to another calorie (cal): unit of heat; the amount of heat it takes to raise the temp. of 1g of water 1C kilocalorie (kcal) : 1,000 cal; the amount of heat it takes to raise 1 kg of water 1C joule (J) : energy unit; 1 J = 0.239 cal b. Water’s High Specific Heat specific heat: amount of heat absorbed or lost for 1g of substance to change temp. by 1C water’s specific heat is 1cal/g * C high compared to other sub. ex. ethyl alcohol = 0.6 cal/g * C resist in changing temp. when absorbing or losing heat b/c of hydrogen bonding benefits: @ winter cooling water will warm air @ coastal areas it moderates temp. large body of water can absorb lots of heat w/o warming up a lot stabilize ocean temp. organisms are made up of a lot of water so better able to resist own temp. change c. Evaporative Cooling liquid to gas = vaporization/ evaporation heat of vaporization: how much heat liquid needs to absorb for 1g of it to go from liq. to gas water has high heat of vaporization b/c of hydrogen bonds effects of high heat of vap. of water… moderate Earth’s climate steam burns evaporative cooling: the surface of liquid that remains, as liquid evaporates, cools down hottest molecules w/ high K.E. leave as gas so cooler mol. left effect of evap. cooling… stabile lake & pond water keeps organisms from overheating B. Floating of Ice on Liquid Water water is less dense as solid than liquid hydrogen bonding C. Water: The Solvent of Life solution: liquid that is homogenous mix of 2 or more substances solvent: the dissolving agent solute: substance that is dissolved aqueous solution: solute is diss. in water; water = solvent water is good solvent b/c hydrogen bonding hydration shell: sphere of water mol. around each dissolved ion a. Hydrophilic & Hydrophobic Substances hydrophilic: substance w/ affinity for water doesn’t always dissolve ex. cellulose hydrophobic: substance that seems to repel water; nonpolar; can’t H bond b. Solute Concentration in Aqueous Solutions molecular mass: sum of masses of all atoms in a mol ex. C 12O 22 11 (sucrose) mol. mass = (12*12)+(22*1)+(11*16)=342 mole (mol): 6.02 x 10^23 or Avogadro’s number molarity: # of moles of solute per liter of solution D. Possible Evolution of Life on Other Planets seasonal streams on mars? b/c of H O rather than water 2 drilling into Mars could be next step if lifeforms are found… evolution gains new perspective Concept Check 3.2 1. Describe how properties of water affect upward movement of water in trees. Cohesion of water molecules cause water to stick to itself and adhesion of water causes water to slowly crawl up the interior side of the tree 2. Explain “It’s not the heat; it’s the humidity.” Humidity has water and water can absorb heat 3. How can freezing water crack boulders? Solid water is denser b/c hydrogen bonds cause water molecules to spread out 4. What is the benefit of water striders’ hydrophobic substance coated legs? What if the substance was hydrophilic? The substance allows the insect to walk on surface w/ water molecules b/c the nonpolar substance repels water; the insect would not be able to walk b/c the substance would interact w/ water and pull the legs and the insect in water 5. Concentration of ghrelin is 1.3 x 10^10M. How many molecules of ghrelin are in 1 L of blood? 1.3 x 10^10 3.3 Acidic & Basic Conditions Affect Living Organisms hydrogen ion (H+): single proton w/ +1 charge hydroxide ion (OH): water molecule w/ lost proton; has charge of 1 H O hydronium ion ( 3 +): water molecule w/ proton bound A. Acids & Bases acid: substance that increase H ion conc. of a sol. ex. HCl base: substance that reduces H ion conc. of sol. ex. NaOH B. The pH Scale pH: negative log (base 10) of H ion conc. pH = log[H+] C. Buffers buffers: substance that minimizes/ resists changes in H+ and OH concent. in sol. D. Acidification: A Threat to Water Quality ocean acidification: when carbon dioxide dissolves in seawater & reacts w/ water to make carbonic acid; pH is lowered in ocean
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