CH 3: Water and Life AP Biology

Transcription

1 CH 3: Water and Life AP Biology

2 Life requires ~25 chemical elements About 25 elements are essential for life Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N) Four elements make up most of remaining 4%: phosphorus (P) sulfur (S) calcium (Ca) potassium (K) AP Biology

3 Valence Electrons Valence electrons are found in the outermost shell of an atom Only valence electrons participate in chemical reactions.

4 Electronegativity Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons. Differences in electronegativity values can tell you which type of bond two atoms will form.

5 Covalent Bonds Covalent bonds can be divided in two groups based on equal and unequal sharing of electrons between atoms Non Polar Bonds Polar bonds

6 Non Polar Covalent Bond Equal sharing of electrons between two atoms. Both atoms have same electronegativity value.

7 Polar Covalent Bond Unequal sharing of electrons bet. two atoms Both atoms have diff. electronegativity value

8 Polar Covalent Bond Cl having higher electronegativity value pulls shared pair of electrons more towards itself than H higher electronegative atom - lower electronegative atom +

9 Ionic bond CaCO 3 One of the atom lose electron to the second atom due to very high electronegativity difference, example NaCl

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11 Van der Waals Interactions If electrons are distributed asymmetrically in molecules or atoms, they can result in hot spots of positive or negative charge called induced positive or negative dipoles Van der Waals interactions are weak attractions between molecules that are close together as a result of these charges 2011 Pearson Education, Inc.

12 Collectively, such interactions can be strong, as between molecules of a gecko s toe hairs and a wall surface 2011 Pearson Education, Inc.

13 2-1 The Nature of Matter Water Structure Hydrogen How many electrons are needed? Oxygen How many electrons are needed? Slide 13 of 40 Copyright Pearson Prentice Hall End Show

14 Properties of Water Polarity Universal Solvent Cohesion Leads to capillary action Adhesion

15 Oxygen has 8 electrons and hydrogen has 1 proton causing O to attract electrons more towards itself. Electrons of bonds spend more time around O atom than around H atoms.

16 O has slight negative charge and H has slight negative charge

17 Water molecules stick together because of Hydrogen bonding

18 Water is a universal solvent that can dissolve almost everything (ionic and polar compounds).

19 Do you dissolve in water? Hydrophilic substances have attraction to H 2 O polar or non-polar? AP Biology

20 Or don t you? Hydrophobic substances that don t have an attraction to H 2 O polar or non-polar? AP Biology fat (triglycerol)

21 How is it important to life? Many substances in cells must be in solution. Water makes it possible to dissolve them.

22 Cohesion and Adhesion cohesion = water attracted to other water molecules because of polar properties adhesion = water attracted to other materials

23 Adhesion Two types of water-conducting cells Direction of water movement 300 m Cohesion Adhesion cause water transport in plants.

24 As water evaporates from a leaf, hydrogen bonds cause water molecules leaving the veins to tug on molecules farther down, and the upward pull is transmitted through the water conducting cells all the way to the roots. Adhesion of water to cell walls by hydrogen bonds helps counter the downward pull of gravity. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.2

25 Cohesion How is it important to life? An example would be our blood being pumped through our body Cohesiveness of the cytoplasm in the cells

26 Water s High Specific Heat The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC The specific heat of water is 1 cal/g/ºc Water resists changing its temperature because of its high specific heat 2011 Pearson Education, Inc.

27 Water s high specific heat can be traced to hydrogen bonding Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form The high specific heat of water minimizes temperature fluctuations to within limits that permit life 2011 Pearson Education, Inc.

28 Floating of Ice on Liquid Water Ice floats in liquid water because hydrogen bonds in ice are more ordered, making ice less dense. As water begins to freeze, molecules are moving too slowly to break hydrogen bonds. If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth 2011 Pearson Education, Inc.

29 Ice floats AP Biology

30 Why is ice floats important? Oceans & lakes don t freeze solid surface ice insulates water below allowing life to survive the winter if ice sank ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw seasonal turnover of lakes cycling nutrients in autumn AP Biology

31 Heat of vaporization Evaporative cooling AP Biology Organisms rely on heat of vaporization to remove body heat

32 Ionization of water & ph Water ionizes H + splits off from H 2 O, leaving OH H 2 O H + + OH AP Biology

33 Ionization of water & ph if [H + ] = [ - OH], solution is neutral if [H + ] > [ - OH], solution is acidic if [H + ] < [ - OH], solution is basic ph scale how acid or basic solution is AP Biology H 2 O H + + OH

34 Increasingly Basic [H + ] < [OH ] Increasingly Acidic [H + ] > [OH ] Figure 3.10 ph Scale 0 1 Battery acid H + H+ H + H + OH OH H + H + H + H + Acidic solution OH OH H + H + OH OH OH H + H + H+ Neutral solution OH OH OH H + OH OH OH H + OH Basic solution Neutral [H + ] = [OH ] Gastric juice, lemon juice Vinegar, wine, cola Tomato juice Beer Black coffee Rainwater Urine Saliva Pure water Human blood, tears Seawater Inside of small intestine Milk of magnesia Household ammonia Household bleach Oven cleaner

35 Figure 3.UN05 Acidic [H + ] > [OH ] 0 Acids donate H + in aqueous solutions. Neutral [H + ] = [OH ] 7 Basic [H + ] < [OH ] Bases donate OH or accept H + in aqueous solutions 14

36 ACIDS An acid is a substance that increases the hydrogen ion concentration in a solution. When hydrochloric acid is added to water, hydrogen ions dissociate from chloride ions: HCl H + + Cl - Addition of an acid makes a solution more acidic. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

37 BASES Any substance that reduces the hydrogen ion concentration in a solution is a base. Some bases reduce H + by dissociating to OH - that combines with H + to form water. NaOH Na + + OH - OH - + H + H 2 O Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38 BASES Some bases reduce H + directly by accepting hydrogen ions. Ammonia (NH 3 ) acts as a base when the nitrogen s unshared electron pair attracts a hydrogen ion from the solution, creating an ammonium in (NH 4+ ). NH 3 + H + <=> NH 4 + Solutions with more OH - than H + are basic solutions. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

39 Buffers & cellular regulation ph of cells must be kept ~7 ph affects shape of molecules shape of molecules affect function ph affects cellular function Most biological fluids have ph values in the range of 6 to 8. However, ph values in the human stomach can reach 2. We control ph by buffers AP Biology

40 Some acids and bases (HCl and NaOH) are strong acids or bases. These molecules dissociate completely in water. Other acids and bases (NH 3 ) are weak acids or bases. For these molecules, the binding and release of hydrogen ions are reversible. At equilibrium there will be a fixed ratio of products to reactants. Carbonic acid (H 2 CO 3 ) is a weak acid: H 2 CO 3 <=> HCO H + At equilibrium when rate of forward reaction is equal to backward reaction, 1% of the molecules will be dissociated. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

41 Buffers Most buffers consist of an acid-base pair that reversibly combines with H +, Example Carbonic acid and bicarbonate ion (base) Buffers accept hydrogen ions from the solution when they are in excess and donate hydrogen ions when they have been depleted Pearson Education, Inc.

42 Buffers typically consist of a weak acid and its corresponding base. One important buffer in human blood and other biological solutions is carbonic acid. The chemical equilibrium between carbonic acid and bicarbonate acts at a ph regulator. The equilibrium shifts left or right as other metabolic processes add or remove H + from the solution. Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

43 Figure 3.11 Ocean Acidification: A threat to water quality CO 2 CO 2 + H 2 O H 2 CO 3 1. Some CO 2 in the atmosphere dissolves in the ocean where it reacts with water to form Carbonic acid (H 2 CO 3 ) H 2 CO 3 H + + HCO 3 2. Carbonic acid dissociates into (H + ) and bicarbonate ions (HCO 3 ) H + + CO 3 2 CO Ca 2+ HCO 3 CaCO 3 3. The added H + combines with CO 3 2 forming more HCO 3 4. Less CO 3 2 is available for calcification - the formation of calcium carbonate (CaCO 3 ) by marine organisms such as corals.

44 LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 4 Carbon and the Molecular Diversity of Life Lectures by Erin Barley Kathleen Fitzpatrick 2011 Pearson Education, Inc.

45 Overview: Carbon: The Backbone of Life Living organisms consist mostly of carbon-based compounds Carbon is unparalleled in its ability to form large, complex, and diverse molecules Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds 2011 Pearson Education, Inc.

46 Complex molecules assembled like TinkerToys

47 The Chemical Elements of Life and diversity The versatility of carbon makes possible the great diversity of organic molecules Variation at the molecular level lies at the foundation of all biological diversity 2011 Pearson Education, Inc.

48 Hydrocarbons are non polar molecules made by combination of C and H AP Biology

49 Isomers Molecules with same molecular formula but different structures (shapes) different chemical properties different biological functions 6 carbons 6 carbons AP Biology 6 carbons

50 Glucose and Fructose are isomers of each other AP Biology

51 Structural Isomers. The two butanes are structural isomers, molecules with the same molecular formula C 4 H 18 but differ in the covalent arrangement of atoms. Fig. 4.6a Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

52 Geometric isomers are compounds with the same covalent partnerships that differ in their spatial arrangement around a carbon-carbon double bond. The double bond does not allow atoms to rotate freely around the bond axis. The biochemistry of vision involves a light-induced change in the structure of rhodopsin in the retina from one geometric isomer to another. Fig. 4.6b Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

53 Enantiomers or Stereoisomers are molecules that are mirror images of each other Enantiomers are possible if there are four different atoms or groups of atoms bonded to a carbon. They are like left-handed and right-handed versions. Fig. 4.6c Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

54 Form affects function AP Biology Structural differences create important functional significance amino acid alanine L-alanine used in proteins but not D-alanine medicines L-version active but not D-version sometimes with tragic results stereoisomers

55 Form affects function Thalidomide prescribed to pregnant women in 50s & 60s reduced morning sickness, but stereoisomer caused severe birth defects AP Biology

56 Functional groups Parts of organic molecules that are involved in chemical reactions give organic molecules distinctive properties hydroxyl carbonyl carboxyl amino sulfhydryl phosphate methyl AP Biology

57 Figure 4.9-a CHEMICAL GROUP Hydroxyl Carbonyl Carboxyl STRUCTURE (may be written HO ) NAME OF COMPOUND Alcohols (Their specific names usually end in -ol.) Ketones if the carbonyl group is within a carbon skeleton Carboxylic acids, or organic acids Aldehydes if the carbonyl group is at the end of the carbon skeleton EXAMPLE Ethanol Acetone Acetic acid Propanal FUNCTIONAL PROPERTIES Is polar as a result of the electrons spending more time near the electronegative oxygen atom. Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars. A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups). Acts as an acid; can donate an H + because the covalent bond between oxygen and hydrogen is so polar: Nonionized Ionized Found in cells in the ionized form with a charge of 1 and called a carboxylate ion.

58 Figure 4.9-b Amino Sulfhydryl Phosphate Methyl (may be written HS ) Amines Thiols Organic phosphates Methylated compounds Glycine Cysteine Glycerol phosphate 5-Methyl cytidine Acts as a base; can pick up an H + from the surrounding solution (water, in living organisms): Nonionized Found in cells in the ionized form with a charge of 1+. Ionized Two sulfhydryl groups can react, forming a covalent bond. This cross-linking helps stabilize protein structure. Cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be permanently curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds. Contributes negative charge to the molecule of which it is a part (2 when at the end of a molecule, as above; 1 when located internally in a chain of phosphates). Molecules containing phosphate groups have the potential to react with water, releasing energy. Addition of a methyl group to DNA, or to molecules bound to DNA, affects the expression of genes. Arrangement of methyl groups in male and female sex hormones affects their shape and function.

59 Figure 4.9a Hydroxyl STRUCTURE (may be written HO ) Alcohols (Their specific names usually end in -ol.) NAME OF COMPOUND EXAMPLE Is polar as a result of the electrons spending more time near the electronegative oxygen atom. FUNCTIONAL PROPERTIES Ethanol Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars.

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62 Figure 4.9c Carboxyl STRUCTURE Carboxylic acids, or organic acids NAME OF COMPOUND EXAMPLE Acts as an acid; can donate an H + because the covalent bond between oxygen and hydrogen is so polar: FUNCTIONAL PROPERTIES Acetic acid Nonionized Ionized Found in cells in the ionized form with a charge of 1 and called a carboxylate ion.

63 Figure 4.9d Amino STRUCTURE Amines NAME OF COMPOUND EXAMPLE Acts as a base; can pick up an H + from the surrounding solution (water, in living organisms): FUNCTIONAL PROPERTIES Glycine Nonionized Ionized Found in cells in the ionized form with a charge of 1.

64 Figure 4.9e Sulfhydryl STRUCTURE Thiols NAME OF COMPOUND (may be written HS ) EXAMPLE Two sulfhydryl groups can react, forming a covalent bond. This cross-linking helps stabilize protein structure. FUNCTIONAL PROPERTIES Cysteine Cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be permanently curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds.

65 Figure 4.9f Phosphate STRUCTURE Organic phosphates NAME OF COMPOUND EXAMPLE Glycerol phosphate Contributes negative charge to the molecule of which it is a part (2 when at the end of a molecule, as at left; 1 when located internally in a chain of phosphates). Molecules containing phosphate groups have the potential to react with water, releasing energy. FUNCTIONAL PROPERTIES

66 Figure 4.9g Methyl STRUCTURE Methylated compounds NAME OF COMPOUND EXAMPLE Addition of a methyl group to DNA, or to molecules bound to DNA, affects the expression of genes. FUNCTIONAL PROPERTIES 5-Methyl cytidine Arrangement of methyl groups in male and female sex hormones affects their shape and function.

67 ATP: An Important Source of Energy for Cellular Processes One phosphate molecule, adenosine triphosphate (ATP), is the primary energytransferring molecule in the cell ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups 2011 Pearson Education, Inc.

68 Figure 4. UN04

69 Figure 4. UN05 Adenosine Reacts with H 2 O Adenosine Energy ATP Inorganic phosphate ADP

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