Chapter 2: The Chemical Context of Life - Exam Slides PDF

Chapter 2 The Chemical Context of Life Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc....

Chapter 2 The Chemical Context of Life Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc. Kathleen Fitzpatrick A Chemical Connection to Biology § Biology is the study of life § Organisms and their environments are subject to basic laws of physics and chemistry § One example is the use of formic acid by ants to protect themselves against predators and microbial parasites © 2017 Pearson Education, Inc. Figure 2.1 © 2017 Pearson Education, Inc. Concept 2.1: Matter consists of chemical elements in pure form and in combinations called compounds § Organisms are composed of matter § Matter is anything that takes up space and has mass © 2017 Pearson Education, Inc. Elements and Compounds § Matter is made up of elements § An element is a substance that cannot be broken down to other substances by chemical reactions § A compound is a substance consisting of two or more elements in a fixed ratio § A compound has characteristics different from those of its elements © 2017 Pearson Education, Inc. Figure 2.2 Na Cl NaCl Sodium Chlorine Sodium chloride © 2017 Pearson Education, Inc. The Elements of Life § About 20–25% of the 92 natural elements are required for life (essential elements) § Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter § Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur § Trace elements are required by an organism in only minute quantities © 2017 Pearson Education, Inc. Table 2.1 © 2017 Pearson Education, Inc. Concept 2.2: An element’s properties depend on the structure of its atoms § Each element consists of unique atoms § An atom is the smallest unit of matter that still retains the properties of an element © 2017 Pearson Education, Inc. Subatomic Particles § Atoms are composed of subatomic particles § Relevant subatomic particles include § Neutrons (no electrical charge) § Protons (positive charge) § Electrons (negative charge) © 2017 Pearson Education, Inc. § Neutrons and protons form the atomic nucleus § Electrons form a “cloud” of negative charge around the nucleus § Neutron mass and proton mass are almost identical and are measured in daltons © 2017 Pearson Education, Inc. Figure 2.4 Cloud of negative Electrons charge (2 electrons) Nucleus − − + + + + (a) (b) © 2017 Pearson Education, Inc. Atomic Number and Atomic Mass § Atoms of the various elements differ in number of subatomic particles § An element’s atomic number is the number of protons in its nucleus § An element’s mass number is the sum of protons plus neutrons in the nucleus § Atomic mass, the atom’s total mass, can be approximated by the mass number © 2017 Pearson Education, Inc. Isotopes § All atoms of an element have the same number of protons but may differ in number of neutrons § Isotopes are two atoms of an element that differ in number of neutrons § Radioactive isotopes decay spontaneously, giving off particles and energy © 2017 Pearson Education, Inc. Radioactive Tracers § Radioactive isotopes are often used as diagnostic tools in medicine § Radioactive tracers can be used to track atoms through metabolism § They can also be used in combination with sophisticated imaging instruments © 2017 Pearson Education, Inc. Figure 2.5 Cancerous throat tissue © 2017 Pearson Education, Inc. Radiometric Dating § A “parent” isotope decays into its “daughter” isotope at a fixed rate, expressed as the half-life § In radiometric dating, scientists measure the ratio of different isotopes and calculate how many half- lives have passed since the fossil or rock was formed § Half-life values vary from seconds or days to billions of years © 2017 Pearson Education, Inc. The Energy Levels of Electrons § Energy is the capacity to cause change § Potential energy is the energy that matter has because of its location or structure § The electrons of an atom differ in their amounts of potential energy § An electron’s state of potential energy is called its energy level, or electron shell © 2017 Pearson Education, Inc. Figure 2.6 (a) A ball bouncing down a flight of stairs can come to rest only on each step, not between steps. Third shell (highest energy level in this model) Second shell (higher Energy energy level) absorbed First shell (lowest energy level) Energy lost Atomic nucleus (b) © 2017 Pearson Education, Inc. Electron Distribution and Chemical Properties § The chemical behavior of an atom is determined by the distribution of electrons in electron shells § The periodic table of the elements shows the electron distribution for each element © 2017 Pearson Education, Inc. Figure 2.7 Hydrogen 2 Atomic number Helium 1H He 2He Atomic mass 4.003 Element symbol First shell Electron distribution diagram Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon 3Li 4Be 5B 6C 7N 8O 9F 10Ne Second shell Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon 11Na 12Mg 13AI 14SI 15P 16S 17CI 18Ar Third shell © 2017 Pearson Education, Inc. Figure 2.7a 2 Atomic number Helium He 2He 4.003 Element symbol Atomic mass Electron distribution diagram © 2017 Pearson Education, Inc. Figure 2.7b Hydrogen Helium 1H 2 He First shell © 2017 Pearson Education, Inc. Figure 2.7c Lithium Beryllium Boron Carbon 3 Li 4Be 5B 6C Second shell Sodium Magnesium Aluminum Silicon 11 Na 12Mg 13Al 14 Si Third shell © 2017 Pearson Education, Inc. Figure 2.7d Nitrogen Oxygen Fluorine Neon 7N 8O 9F 10Ne Second shell Phosphorus Sulfur Chlorine Argon 15P 16S 17Cl 18Ar Third shell © 2017 Pearson Education, Inc. § Valence electrons are those in the outermost shell, or valence shell § The chemical behavior of an atom is mostly determined by the valence electrons § Elements with a full valence shell are chemically inert © 2017 Pearson Education, Inc. Electron Orbitals § An orbital is the three-dimensional space where an electron is found 90% of the time § Each electron shell consists of a specific number of orbitals © 2017 Pearson Education, Inc. Figure 2.8 First shell Second shell x y Neon, First with two shell filled shells z (10 electrons) Second 1s orbital 2s orbital Three 2p orbitals shell (a) Electron distribution (b) Separate electron orbitals diagram 1s, 2s, and 2p orbitals (c) Superimposed electron orbitals © 2017 Pearson Education, Inc. Figure 2.8a Neon, First with two shell filled shells (10 electrons) Second shell (a) Electron distribution diagram © 2017 Pearson Education, Inc. Figure 2.8b First shell Second shell x y z 1s orbital 2s orbital Three 2p orbitals (b) Separate electron orbitals © 2017 Pearson Education, Inc. Concept 2.3: The formation and function of molecules depend on chemical bonding between atoms § Atoms with incomplete valence shells can share or transfer valence electrons with certain other atoms § These interactions usually result in atoms staying close together, held by attractions called chemical bonds © 2017 Pearson Education, Inc. Covalent Bonds § A covalent bond is the sharing of a pair of valence electrons by two atoms § In a covalent bond, the shared electrons count as part of each atom’s valence shell © 2017 Pearson Education, Inc. Figure 2.9_1 Hydrogen atoms (2 H) + + © 2017 Pearson Education, Inc. Figure 2.9_2 Hydrogen atoms (2 H) + + + + © 2017 Pearson Education, Inc. Figure 2.9_3 Hydrogen atoms (2 H) + + + + + + Hydrogen molecule (H2) © 2017 Pearson Education, Inc. § A molecule consists of two or more atoms held together by covalent bonds § A single covalent bond, or single bond, is the sharing of one pair of valence electrons § A double covalent bond, or double bond, is the sharing of two pairs of valence electrons © 2017 Pearson Education, Inc. § The notation used to represent atoms and bonding is called a structural formula § For example, H—H § This can be abbreviated further with a molecular formula § For example, H2 © 2017 Pearson Education, Inc. Figure 2.10 Name and Electron Lewis Dot Space- Molecular Distribution Structure and Filling Formula Diagram Structural Model Formula (a) Hydrogen (H2) H H (b) Oxygen (O2) O O (c) Water (H2O) O H H (d) Methane (CH4) H H C H H © 2017 Pearson Education, Inc. Figure 2.10a Name and Electron Lewis Dot Space- Molecular Distribution Structure and Filling Formula Diagram Structural Model Formula (a) Hydrogen (H2) H H © 2017 Pearson Education, Inc. Figure 2.10b Name and Electron Lewis Dot Space- Molecular Distribution Structure and Filling Formula Diagram Structural Model Formula (b) Oxygen (O2) O O © 2017 Pearson Education, Inc. Figure 2.10c Name and Electron Lewis Dot Space- Molecular Distribution Structure and Filling Formula Diagram Structural Model Formula (c) Water (H2O) O H H © 2017 Pearson Education, Inc. Figure 2.10d Name and Electron Lewis Dot Space- Molecular Distribution Structure and Filling Formula Diagram Structural Model Formula (d) Methane (CH4) H H C H H © 2017 Pearson Education, Inc. § Bonding capacity is called the atom’s valence § Covalent bonds can form between atoms of the same element or atoms of different elements § A compound is a combination of two or more different elements © 2017 Pearson Education, Inc. § Atoms in a molecule attract electrons to varying degrees § Electronegativity is an atom’s attraction for the electrons in a covalent bond § The more electronegative an atom is, the more strongly it pulls shared electrons toward itself © 2017 Pearson Education, Inc. § In a nonpolar covalent bond, the atoms share the electron equally § In a polar covalent bond, one atom is more electronegative, and the atoms do not share the electron equally § Unequal sharing of electrons causes a partial positive or negative charge for each atom or molecule © 2017 Pearson Education, Inc. Figure 2.11 δ− δ− O H H δ+ δ+ H2 O © 2017 Pearson Education, Inc. Ionic Bonds § Atoms sometimes strip electrons from their bonding partners § An example is the transfer of an electron from sodium to chlorine § After the transfer of an electron, both atoms have charges § A charged atom (or molecule) is called an ion © 2017 Pearson Education, Inc. Figure 2.12_1 Na Cl Na Cl Sodium atom Chlorine atom © 2017 Pearson Education, Inc. Figure 2.12_2 + − Na Cl Na Cl Na Cl Na+ Cl− Sodium atom Chlorine atom Sodium ion Chloride ion (a cation) (an anion) Sodium chloride (NaCl) © 2017 Pearson Education, Inc. Animation: Ionic Bonds © 2017 Pearson Education, Inc. § A cation is a positively charged ion § An anion is a negatively charged ion § An ionic bond is an attraction between an anion and a cation © 2017 Pearson Education, Inc. § Compounds formed by ionic bonds are called ionic compounds, or salts § Salts, such as sodium chloride (table salt), are often found in nature as crystals © 2017 Pearson Education, Inc. Figure 2.13 Na+ Cl− © 2017 Pearson Education, Inc. Weak Chemical Interactions § Most of the strongest bonds in organisms are covalent bonds that form a cell’s molecules § Many large biological molecules are held in their functional form by weak bonds § The reversibility of weak bonds can be an advantage © 2017 Pearson Education, Inc. Hydrogen Bonds § A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom § In living cells, the electronegative partners are usually oxygen or nitrogen atoms © 2017 Pearson Education, Inc. Figure 2.14 δ– δ+ Water (H2O) δ– δ+ Hydrogen bond δ– Ammonia (NH3) δ+ δ+ δ+ © 2017 Pearson Education, Inc. Van der Waals Interactions § If electrons are not evenly distributed, they may accumulate by chance in one part of a molecule § Van der Waals interactions are attractions between molecules that are close together as a result of these charges © 2017 Pearson Education, Inc. § Collectively, such interactions can be strong, as between molecules of a gecko’s toe hairs and a wall surface © 2017 Pearson Education, Inc. Molecular Shape and Function § A molecule’s size and shape are key to its function § A molecule’s shape is determined by the positions of its atoms’ orbitals § In a covalent bond, the s and p orbitals may hybridize, creating specific molecular shapes © 2017 Pearson Education, Inc. Figure 2.15b Space-Filling Ball-and-Stick Hybrid-Orbital Model Model Model (with ball-and-stick model superimposed) Unbonded O electron O H H pairs 104.5º H H Water (H2O) H H C C H H H H H H Methane (CH4) (b) Molecular-shape models © 2017 Pearson Education, Inc. § Molecular shape determines how biological molecules recognize and respond to one another § Opiates, such as morphine, and naturally produced endorphins have similar effects because their shapes are similar and they bind the same receptors in the brain © 2017 Pearson Education, Inc. Figure 2.16 Carbon Nitrogen Hydrogen Sulfur Natural Oxygen endorphin Morphine (a) Structures of endorphin and morphine Natural endorphin Morphine Endorphin Brain cell receptors (b) Binding to endorphin receptors © 2017 Pearson Education, Inc. Concept 2.4: Chemical reactions make and break chemical bonds § Chemical reactions are the making and breaking of chemical bonds § The starting molecules of a chemical reaction are called reactants § The final molecules of a chemical reaction are called products © 2017 Pearson Education, Inc. Figure 2.UN03 2 H2 O2 2 H2O Reactants Chemical Products reaction © 2017 Pearson Education, Inc. § Photosynthesis is an important chemical reaction § Sunlight powers the conversion of carbon dioxide and water to glucose and oxygen 6 CO2 + 6 H2O → C6H12O6 + 6 O2 © 2017 Pearson Education, Inc. Figure 2.17 Leaf Bubbles of O2 © 2017 Pearson Education, Inc. § All chemical reactions are reversible: Products of the forward reaction become reactants for the reverse reaction § The two opposite-headed arrows indicate that a reaction is reversible 3 H2 + N ⇌ 2 NH3 © 2017 Pearson Education, Inc. § Chemical equilibrium is reached when the forward and reverse reactions occur at the same rate § At equilibrium the relative concentrations of reactants and products do not change © 2017 Pearson Education, Inc. Figure 2.UN04 Reactants Products 6 CO2 6 H2O Sunlight C6H12O6 6 O2 Carbon dioxide Water Glucose Oxygen © 2017 Pearson Education, Inc. Figure 2.UN05 Nucleus Protons (+ charge) + − determine element + Electrons (− charge) − form negative cloud and determine Neutrons (no charge) chemical behavior determine isotope Atom © 2017 Pearson Education, Inc. Figure 2.UN06 Single Double covalent bond covalent bond © 2017 Pearson Education, Inc. Figure 2.UN07 Ionic bond + − Electron transfer forms ions Na Cl Na Cl Na Cl Na+ Cl− Sodium atom Chlorine atom Sodium ion Chloride ion (a cation) (an anion) © 2017 Pearson Education, Inc.  Chapter 3 Water and Life Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc. Kathleen Fitzpatrick The Molecule That Supports All of Life § Water makes life possible on Earth § Water is the only common substance to exist in the natural environment in all three physical states of matter § Water’s unique emergent properties help make Earth suitable for life § The structure of the water molecule allows it to interact with other molecules © 2017 Pearson Education, Inc. Figure 3.1 © 2017 Pearson Education, Inc. Concept 3.1: Polar covalent bonds in water molecules result in hydrogen bonding § In the water molecule, the electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen § The water molecule is thus a polar molecule: The overall charge is unevenly distributed § Polarity allows water molecules to form hydrogen bonds with each other © 2017 Pearson Education, Inc. Figure 3.2 δ+ δ+ Polar covalent bond δ– δ– Region of partial Hydrogen bond δ+ negative charge δ– δ+ δ– δ+ δ– δ+ © 2017 Pearson Education, Inc. Concept 3.2: Four emergent properties of water contribute to Earth’s suitability for life § Four of water’s properties that facilitate an environment for life are § Cohesive behavior § Ability to moderate temperature § Expansion upon freezing § Versatility as a solvent © 2017 Pearson Education, Inc. Cohesion of Water Molecules § Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion § Cohesion helps the transport of water against gravity in plants § Adhesion is an attraction between different substances, for example, between water and plant cell walls © 2017 Pearson Education, Inc. Figure 3.3 Evaporation pulls water upward. H2O Adhesion Two types of water-conducting cells Direction Cohesion of water 300 µm movement H2O H2O © 2017 Pearson Education, Inc. Figure 3.3a Two types of water-conducting cells 300 µm © 2017 Pearson Education, Inc. Animation: Water Transport in Plants © 2017 Pearson Education, Inc. § Surface tension is a measure of how difficult it is to break the surface of a liquid § Water has an unusually high surface tension due to hydrogen bonding between the molecules at the air- water interface and to the water below © 2017 Pearson Education, Inc. Figure 3.4 © 2017 Pearson Education, Inc. Moderation of Temperature by Water § Water absorbs heat from warmer air and releases stored heat to cooler air § Water can absorb or release a large amount of heat with only a slight change in its own temperature © 2017 Pearson Education, Inc. Temperature and Heat § Kinetic energy is the energy of motion § The kinetic energy associated with random motion of atoms or molecules is called thermal energy § Temperature represents the average kinetic energy of the molecules in a body of matter § Thermal energy in transfer from one body of matter to another is defined as heat © 2017 Pearson Education, Inc. § A calorie (cal) is the amount of heat required to raise the temperature of 1 g of water by 1ºC § It is also the amount of heat released when 1 g of water cools by 1ºC § The “Calories” on food packages are actually kilocalories (kcal); 1 kcal = 1,000 cal § The joule (J) is another unit of energy; 1 J = 0.239 cal, or 1 cal = 4.184 J © 2017 Pearson Education, Inc. 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 © 2017 Pearson Education, Inc. § 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 © 2017 Pearson Education, Inc. Figure 3.5 Burbank San Bernardino Santa Barbara 73º 90º 100º Los Angeles Riverside 96º (Airport) 75º Santa Ana Palm Springs 70s (ºF) 84º 106º 80s Pacific Ocean 68º 90s 100s San Diego 72º 40 miles © 2017 Pearson Education, Inc. Evaporative Cooling § Evaporation (or vaporization) is transformation of a substance from liquid to gas § Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas § As a liquid evaporates, its remaining surface cools, a process called evaporative cooling § Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water © 2017 Pearson Education, Inc. Floating of Ice on Liquid Water § Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense than water § Water reaches its greatest density at 4ºC § If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth © 2017 Pearson Education, Inc. Figure 3.6 Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Hydrogen bonds are stable © 2017 Pearson Education, Inc. Figure 3.6a © 2017 Pearson Education, Inc. § Many scientists are worried that global warming is having a profound effect on icy environments around the globe § The rate at which glaciers and Arctic sea ice are disappearing poses an extreme challenge to animals that depend on ice for their survival © 2017 Pearson Education, Inc. Figure 3.7 Benefiting from loss of ice: Phyto- Bowhead plankton whales Capelin Harmed by loss of ice: Russia Arctic ocean Extent of sea ice in Sept. 2014 Extent of sea ice in Sept. 1979 Polar bears Bering Strait North Pole Greenland Pacific walrus Alaska Black Canada guillemots Sea ice in Sept. 2014 Ice lost from Sept. 1979 to Sept. 2014 © 2017 Pearson Education, Inc. Water: The Solvent of Life § A solution is a liquid that is a completely homogeneous mixture of substances § The solvent is the dissolving agent of a solution § The solute is the substance that is dissolved § An aqueous solution is one in which water is the solvent © 2017 Pearson Education, Inc. Figure 3.8 – Na+ + + – – + – – Na+ – + + CI– CI– + – – + – + – – © 2017 Pearson Education, Inc. § Water is a versatile solvent due to its polarity § When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell © 2017 Pearson Education, Inc. § Water can also dissolve compounds made of nonionic polar molecules § Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions © 2017 Pearson Education, Inc. Figure 3.9 δ+ δ– δ– δ+ © 2017 Pearson Education, Inc. Hydrophilic and Hydrophobic Substances § A hydrophilic substance is one that has an affinity for water § A hydrophobic substance is one that does not have an affinity for water § Oil molecules are hydrophobic because they have relatively nonpolar bonds § Hydrophobic molecules related to oils are the major ingredients of cell membranes © 2017 Pearson Education, Inc. Solute Concentration in Aqueous Solutions § Most chemical reactions in organisms involve solutes dissolved in water § When carrying out experiments, we use mass to calculate the number of solute molecules in an aqueous solution © 2017 Pearson Education, Inc. § Molecular mass is the sum of all masses of all atoms in a molecule § Numbers of molecules are usually measured in moles, where 1 mole (mol) = 6.02 ´ 1023 molecules § Avogadro’s number and the unit dalton were defined such that 6.02 ´ 1023 daltons = 1 g § Molarity (M) is the number of moles of solute per liter of solution © 2017 Pearson Education, Inc. Possible Evolution of Life on Other Planets § Biologists seeking life on other planets have concentrated their search on planets that might have water § More than 800 planets have been found outside our solar system; there is evidence that a few of them have water vapor § In our solar system, Mars has been found to have water © 2017 Pearson Education, Inc. Figure 3.10 Dark streaks © 2017 Pearson Education, Inc. Concept 3.3: Acidic and basic conditions affect living organisms § A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other § The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+) § The molecule that lost the proton is now a hydroxide ion (OH–) § The molecule with the extra proton is now a hydronium ion (H3O+), though it is often represented as H+ © 2017 Pearson Education, Inc. § Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed © 2017 Pearson Education, Inc. Figure 3.UN01 + – H H O H O O H O H H H H 2 H2O Hydronium Hydroxide ion (H3O+) ion (OH–) © 2017 Pearson Education, Inc. § Though statistically rare, the dissociation of water molecules has a great effect on organisms § Changes in concentrations of H+ and OH– can drastically affect the chemistry of a cell © 2017 Pearson Education, Inc. § Concentrations of H+ and OH– are equal in pure water § Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH– § Biologists use the pH scale to describe whether a solution is acidic or basic (the opposite of acidic) © 2017 Pearson Education, Inc. Acids and Bases § An acid is a substance that increases the H+ concentration of a solution § A base is a substance that reduces the H+ concentration of a solution § Strong acids and bases dissociate completely in water § Weak acids and bases reversibly release and accept back hydrogen ions, but can still shift the balance of H+ and OH– away from neutrality © 2017 Pearson Education, Inc. The pH Scale § In any aqueous solution at 25ºC, the product of H+ and OH– is constant and can be written as [H+][OH–] = 10–14 § The pH of a solution is defined by the negative logarithm of H+ concentration, written as pH = –log [H+] § For a neutral aqueous solution, [H+] is 10–7, so pH = –(–7) = 7 © 2017 Pearson Education, Inc. § Acidic solutions have pH values less than 7 § Basic solutions have pH values greater than 7 § Most biological fluids have pH values in the range of 6 to 8 © 2017 Pearson Education, Inc. Figure 3.11 pH Scale 0 1 Battery acid Increasingly Acidic 2 Gastric juice (in stomach), lemon juice [H+] > [OH–] 3 Vinegar, wine, cola Acidic 4 Tomato juice solution Beer 5 Black coffee Rainwater 6 Urine Saliva Neutral 7 Pure water [H+] = [OH–] Human blood, tears 8 Seawater Neutral Inside small intestine solution Increasingly Basic 9 [H+] < [OH–] 10 Milk of magnesia 11 Household ammonia 12 Basic solution Household 13 bleach Oven cleaner 14 © 2017 Pearson Education, Inc. Buffers § The internal pH of most living cells is close to 7 § Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution § Most buffer solutions contain a weak acid and its corresponding base, which combine reversibly with H+ ions © 2017 Pearson Education, Inc. Acidification: A Threat to Our Oceans § Human activities such as burning fossil fuels threaten water quality § CO2 is the main product of fossil fuel combustion § About 25% of human-generated CO2 is absorbed by the oceans § CO2 dissolved in seawater forms carbonic acid; this process is called ocean acidification © 2017 Pearson Education, Inc. Figure 3.12 CO2 CO2 + H2O H2CO3 H2CO3 H+ + HCO3– H+ + CO32– HCO3– CO32– + Ca2+ CaCO3 © 2017 Pearson Education, Inc. § As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate § Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals § We have made progress in learning about the delicate chemical balances in oceans, lakes, and rivers © 2017 Pearson Education, Inc. Figure 3.UN02a [mmol CaCO3/(m2 day)] Calcification rate 20 10 0 220 240 260 280 [CO32–] (µmol/kg of seawater) Data from C. Langdon et al., Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef, Global Biogeochemical Cycles 14:639–654 (2000). © 2017 Pearson Education, Inc. Figure 3.UN04 0 Acidic – + [H ] > [OH ] + Acids donate H in aqueous solutions. Neutral – + [H ] = [OH ] 7 – Bases donate OH + or accept H in Basic – aqueous solutions. + [H ] < [OH ] © 2017 Pearson Education, Inc. 14  Chapter 4 Carbon and the Molecular Diversity of Life Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc. Kathleen Fitzpatrick Carbon: The Backbone of Life § Living organisms consist mostly of carbon-based compounds § Carbon is unparalleled in its ability to form large, complex, and varied molecules § Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds © 2017 Pearson Education, Inc. Figure 4.1 © 2017 Pearson Education, Inc. Figure 4.1a © 2017 Pearson Education, Inc. Concept 4.1: Organic chemistry is the study of carbon compounds § Organic chemistry is the study of compounds that contain carbon, regardless of origin § Organic compounds range from simple molecules to colossal ones © 2017 Pearson Education, Inc. Organic Molecules and the Origin of Life on Earth § Stanley Miller’s classic experiment demonstrated the abiotic synthesis of organic compounds § Experiments support the idea that abiotic synthesis of organic compounds, perhaps near volcanoes, could have been a stage in the origin of life © 2017 Pearson Education, Inc. Figure 4.2 “Atmosphere” CH4 Water vapor Electrode NH 3 H2 Condenser Cooled “rain” containing Cold organic water molecules H2O “sea” Sample for chemical analysis © 2017 Pearson Education, Inc. § The overall percentages of the major elements of life—C, H, O, N, S, and P—are quite uniform from one organism to another § Because of carbon’s ability to form four bonds, these building blocks can be used to make an inexhaustible variety of organic molecules § The great diversity of organisms on the planet is due to the versatility of carbon © 2017 Pearson Education, Inc. Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms § Electron configuration is the key to an atom’s characteristics § Electron configuration determines the kinds and number of bonds an atom will form with other atoms © 2017 Pearson Education, Inc. The Formation of Bonds with Carbon § With four valence electrons, carbon can form four covalent bonds with a variety of atoms § This makes large, complex molecules possible § In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape § However, when two carbon atoms are joined by a double bond, the atoms joined to the carbons are in the same plane as the carbons © 2017 Pearson Education, Inc. Figure 4.3 Molecule Molecular Structural Ball-and-Stick Model Space-Filling Formula Formula Model (a) Methane CH4 (b) Ethane C2H6 (c) Ethene (ethylene) C2H4 © 2017 Pearson Education, Inc. § The number of unpaired electrons in the valence shell of an atom is generally equal to its valence, the number of covalent bonds it can form © 2017 Pearson Education, Inc. Figure 4.4 Hydrogen Oxygen Nitrogen Carbon (valence = 1) (valence = 2) (valence = 3) (valence = 4) H O N C © 2017 Pearson Education, Inc. § The electron configuration of carbon gives it covalent compatibility with many different elements § The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the building code for the architecture of living molecules © 2017 Pearson Education, Inc. § Carbon atoms can partner with atoms other than hydrogen, such as the following: § Carbon dioxide: CO2 © 2017 Pearson Education, Inc.  § Urea: CO(NH2)2 © 2017 Pearson Education, Inc. Molecular Diversity Arising from Variation in Carbon Skeletons § Carbon chains form the skeletons of most organic molecules § Carbon chains vary in length and shape © 2017 Pearson Education, Inc. Figure 4.5 (a) Length (c) Double bond position Ethane Propane 1-Butene 2-Butene (b) Branching (d) Presence of rings Butane 2-Methylpropane Cyclohexane Benzene (isobutane) © 2017 Pearson Education, Inc. Figure 4.5a (a) Length Ethane Propane © 2017 Pearson Education, Inc. Figure 4.5b (b) Branching Butane 2-Methylpropane (isobutane) © 2017 Pearson Education, Inc. Figure 4.5c (c) Double bond position 1-Butene 2-Butene © 2017 Pearson Education, Inc. Figure 4.5d (d) Presence of rings Cyclohexane Benzene © 2017 Pearson Education, Inc. Animation: Carbon Skeletons © 2017 Pearson Education, Inc. Hydrocarbons § Hydrocarbons are organic molecules consisting of only carbon and hydrogen § Many organic molecules, such as fats, have hydrocarbon components § Hydrocarbons can undergo reactions that release a large amount of energy © 2017 Pearson Education, Inc. Figure 4.6 Nucleus Fat droplets 10 µm (a) Part of a human adipose cell (b) A fat molecule © 2017 Pearson Education, Inc. Figure 4.6a Nucleus Fat droplets 10 µm (a) Part of a human adipose cell © 2017 Pearson Education, Inc. Isomers § Isomers are compounds with the same molecular formula but different structures and properties § Structural isomers have different covalent arrangements of their atoms § Cis-trans isomers have the same covalent bonds but differ in their spatial arrangements § Enantiomers are isomers that are mirror images of each other © 2017 Pearson Education, Inc. Figure 4.7 (a) Structural isomers (c) Enantiomers Pentane 2-Methylbutane L isomer D isomer (b) Cis-trans isomers cis isomer: trans isomer: The two Xs are on The two Xs are the same side. on opposite sides. © 2017 Pearson Education, Inc. Figure 4.7a (a) Structural isomers Pentane 2-Methylbutane © 2017 Pearson Education, Inc. Figure 4.7b (b) Cis-trans isomers cis isomer: The two Xs trans isomer: The two Xs are on the same side. are on opposite sides. © 2017 Pearson Education, Inc. Figure 4.7c (c) Enantiomers CO2H CO2H C C H NH2 NH2 H CH3 CH3 L isomer D isomer © 2017 Pearson Education, Inc. Animation: Isomers © 2017 Pearson Education, Inc. § Enantiomers are important in the pharmaceutical industry § Two enantiomers of a drug may have different effects § Usually, only one isomer is biologically active § Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules © 2017 Pearson Education, Inc. Figure 4.8 Effective Ineffective Drug Effects Enantiomer Enantiomer Reduces Ibuprofen inflammation and pain S-Ibuprofen R-Ibuprofen Relaxes bronchial (airway) muscles, Albuterol improving airflow in asthma patients R-Albuterol S-Albuterol © 2017 Pearson Education, Inc. Animation: L-Dopa © 2017 Pearson Education, Inc. Concept 4.3: A few chemical groups are key to molecular function § Distinctive properties of organic molecules depend on the carbon skeleton and on the chemical groups attached to it § A number of characteristic groups can replace the hydrogens attached to skeletons of organic molecules © 2017 Pearson Education, Inc. The Chemical Groups Most Important in the Processes of Life § Estradiol and testosterone are both steroids with a common carbon skeleton, in the form of four fused rings § These sex hormones differ only in the chemical groups attached to the rings of the carbon skeleton © 2017 Pearson Education, Inc. Figure 4.UN04 Estradiol Testosterone © 2017 Pearson Education, Inc. § Functional groups are the components of organic molecules that are most commonly involved in chemical reactions § The number and arrangement of functional groups give each molecule its unique properties © 2017 Pearson Education, Inc. § The seven functional groups that are most important in the chemistry of life are the following: § Hydroxyl group § Carbonyl group § Carboxyl group § Amino group § Sulfhydryl group § Phosphate group § Methyl group © 2017 Pearson Education, Inc. Figure 4.9 Chemical Group Group Properties Examples Hydroxyl group (—OH) Alcohol Ethanol Carbonyl group ( C ═ O) Ketone Aldehyde Acetone Propanal Carboxyl group (—COOH) Carboxylic acid or organic acid Acetic acid Amino group (—NH2) Amine Glycine Sulfhydryl group (—SH) Thiol Cysteine Phosphate group (—OPO32−) Organic phosphate Glycerol phosphate Methyl group (—CH3) Methylated compound 5-Methylcytosine © 2017 Pearson Education, Inc. Figure 4.9a Chemical Group Compound Name Examples Hydroxyl group (—OH) Alcohol Ethanol Carbonyl group ( C ═ O) Ketone Aldehyde Acetone Propanal Carboxyl group (—COOH) Carboxylic acid or organic acid Acetic acid Amino group (—NH2) Amine Glycine © 2017 Pearson Education, Inc. Figure 4.9aa Hydroxyl group (—OH) Ethanol, the alcohol present in alcoholic beverages (may be written HO—) Polar due to electronegative oxygen. Forms hydrogen bonds with water. Compound name: Alcohol © 2017 Pearson Education, Inc. Figure 4.9ab Carbonyl group ( C ═ O) Acetone, Propanal, the simplest ketone an aldehyde Sugars with ketone groups are called ketoses; those with aldehydes are called aldoses. Compound name: Ketone or aldehyde © 2017 Pearson Education, Inc. Figure 4.9ac Carboxyl group (—COOH) Acetic acid, which Ionized form of —COOH gives vinegar its (carboxylate ion), sour taste found in cells Acts as an acid. Compound name: Carboxylic acid, or organic acid © 2017 Pearson Education, Inc. Figure 4.9ad Amino group (—NH2) Glycine, an amino acid Ionized form (note its carboxyl group) of —NH2, found in cells Acts as a base. Compound name: Amine © 2017 Pearson Education, Inc. Figure 4.9b Chemical Group Compound Name Examples Sulfhydryl group (—SH) Thiol Cysteine Phosphate group Organic (—OPO32−) phosphate Glycerol phosphate Methyl group (—CH3) Methylated compound 5-Methylcytosine © 2017 Pearson Education, Inc. Figure 4.9ba Sulfhydryl group (—SH) Cysteine, a sulfur- containing amino acid (may be written HS—) Two —SH groups can react, forming a “cross-link” that helps stabilize protein structure. Compound name: Thiol © 2017 Pearson Education, Inc. Figure 4.9bb Phosphate group (—OPO32−) Glycerol phosphate, which takes part in many important chemical reactions in cells Contributes negative charge. When attached, confers on a molecule the ability to react with water, releasing energy. Compound name: Organic phosphate © 2017 Pearson Education, Inc. Figure 4.9bc Methyl group (—CH3) 5-Methylcytosine, a component of DNA that has been modified by addition of a methyl group Affects the expression of genes. Affects the shape and function of sex hormones. Compound name: Methylated compound © 2017 Pearson Education, Inc. ATP: An Important Source of Energy for Cellular Processes § An important organic phosphate is adenosine triphosphate (ATP) § ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups § ATP stores the potential to react with water § This reaction releases energy that can be used by the cell © 2017 Pearson Education, Inc. Figure 4.UN05 Adenosine © 2017 Pearson Education, Inc. Figure 4.UN06 Reacts with H2O P P P Adenosine P P Adenosine Pi Energy ATP ADP Inorganic phosphate © 2017 Pearson Education, Inc. The Chemical Elements of Life: A Review § 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 © 2017 Pearson Education, Inc. Figure 4.UN01a © 2017 Pearson Education, Inc. Figure 4.UN01b © 2017 Pearson Education, Inc. Figure 4.UN01c © 2017 Pearson Education, Inc. Figure 4.UN08 © 2017 Pearson Education, Inc. Figure 4.UN09 © 2017 Pearson Education, Inc. Figure 4.UN10 a b c d e © 2017 Pearson Education, Inc. Figure 4.UN11 L-dopa D-dopa © 2017 Pearson Education, Inc. Figure 4.UN12 © 2017 Pearson Education, Inc.  Chapter 5 The Structure and Function of Large Biological Molecules Lecture Presentations by Nicole Tunbridge and © 2017 Pearson Education, Inc. Kathleen Fitzpatrick The Molecules of Life § All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids § Macromolecules are large molecules and are complex § Large biological molecules have unique properties that arise from the orderly arrangement of their atoms © 2017 Pearson Education, Inc. Figure 5.1 © 2017 Pearson Education, Inc. Figure 5.1a The scientist in the foreground is using 3-D glasses to help her visualize the structure of the protein displayed on her screen. © 2017 Pearson Education, Inc. Concept 5.1: Macromolecules are polymers, built from monomers § A polymer is a long molecule consisting of many similar building blocks § The repeating units that serve as building blocks are called monomers § Carbohydrates, proteins, and nucleic acids are polymers © 2017 Pearson Education, Inc. The Synthesis and Breakdown of Polymers § Enzymes are specialized macromolecules that speed up chemical reactions such as those that make or break down polymers § A dehydration reaction occurs when two monomers bond together through the loss of a water molecule § Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction © 2017 Pearson Education, Inc. Figure 5.2 (a) Dehydration reaction: synthesizing a polymer 1 2 3 Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond. H2O 1 2 3 4 Longer polymer (b) Hydrolysis: breaking down a polymer 1 2 3 4 Hydrolysis adds a water H2O molecule, breaking a bond. 1 2 3 H © 2017 Pearson Education, Inc. Animation: Polymers © 2017 Pearson Education, Inc. The Diversity of Polymers § A cell has thousands of different macromolecules § Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species § A huge variety of polymers can be built from a small set of monomers © 2017 Pearson Education, Inc. Concept 5.2: Carbohydrates serve as fuel and building material § Carbohydrates include sugars and the polymers of sugars § The simplest carbohydrates are monosaccharides, or simple sugars § Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks © 2017 Pearson Education, Inc. Sugars § 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 © 2017 Pearson Education, Inc. Figure 5.3 Aldoses Ketoses (Aldehyde Sugars) (Ketone Sugars) Trioses: three-carbon sugars (C3H6O3) Glyceraldehyde Dihydroxyacetone Pentoses: five-carbon sugars (C5H10O5) Ribose Ribulose Hexoses: six-carbon sugars (C6H12O6) Glucose Galactose Fructose © 2017 Pearson Education, Inc. Figure 5.3a Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Trioses: three-carbon sugars (C3H6O3) Glyceraldehyde Dihydroxyacetone © 2017 Pearson Education, Inc. Figure 5.3b Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Pentoses: five-carbon sugars (C5H10O5) Ribose Ribulose © 2017 Pearson Education, Inc. Figure 5.3c Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Hexoses: six-carbon sugars (C6H12O6) Glucose Galactose Fructose © 2017 Pearson Education, Inc. § Though often drawn as linear skeletons, in aqueous solutions many sugars form rings § Monosaccharides serve as a major fuel for cells and as raw material for building molecules © 2017 Pearson Education, Inc. Figure 5.4 (a) Linear and ring forms (b) Abbreviated ring structure © 2017 Pearson Education, Inc. § A disaccharide is formed when a dehydration reaction joins two monosaccharides § This covalent bond is called a glycosidic linkage © 2017 Pearson Education, Inc. Figure 5.5 (a) Dehydration reaction in the synthesis of maltose 1–4 glycosidic linkage H2 O Glucose Glucose Maltose (b) Dehydration reaction in the synthesis of sucrose 1–2 glycosidic linkage H2 O Glucose Fructose Sucrose © 2017 Pearson Education, Inc. Animation: Disaccharides © 2017 Pearson Education, Inc. Polysaccharides § Polysaccharides, the polymers of sugars, have storage and structural roles § The architecture and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages © 2017 Pearson Education, Inc. Storage Polysaccharides § Starch, a storage polysaccharide of plants, consists of glucose monomers § Plants store surplus starch as granules within chloroplasts and other plastids § The simplest form of starch is amylose © 2017 Pearson Education, Inc. Figure 5.6 Storage structures (plastids) containing starch granules Amylose (unbranched) in a potato tuber cell Glucose Amylopectin monomer (somewhat branched) 50 µm (a) Starch Muscle tissue Glycogen granules Glycogen (extensively stored in muscle branched) tissue Cell wall 1 µm (b) Glycogen Plant cell, surrounded Cellulose microfibrils Cellulose molecule by cell wall in a plant cell wall (unbranched) 10 µm Hydrogen bonds Microfibril 0.5 µm (c) Cellulose © 2017 Pearson Education, Inc. Figure 5.6a Storage structures (plastids) Amylose Glucose containing starch granules (unbranched) monomer in a potato tuber cell Amylopectin (somewhat branched) 50 µm (a) Starch © 2017 Pearson Education, Inc. Figure 5.6aa Storage structures (plastids) containing starch granules in a potato tuber cell 50 µm © 2017 Pearson Education, Inc. Figure 5.6b Glycogen granules Glycogen stored in muscle (extensively branched) tissue 1 µm (b) Glycogen © 2017 Pearson Education, Inc. Figure 5.6ba Glycogen granules stored in muscle tissue 1 µm © 2017 Pearson Education, Inc. Figure 5.6c Cellulose microfibrils in a plant cell wall Cellulose molecule (unbranched) Hydrogen bonds Microfibril 0.5 µm (c) Cellulose © 2017 Pearson Education, Inc. Figure 5.6ca Cellulose microfibrils in a plant cell wall 0.5 µm © 2017 Pearson Education, Inc. Figure 5.6d Cell wall Plant cell, surrounded 10 µm by cell wall © 2017 Pearson Education, Inc. Animation: Polysaccharides © 2017 Pearson Education, Inc. § Glycogen is a storage polysaccharide in animals § Glycogen is stored mainly in liver and muscle cells § Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases © 2017 Pearson Education, Inc. Structural Polysaccharides § 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 (α) and beta (β) © 2017 Pearson Education, Inc. Figure 5.7 α Glucose β Glucose (a) α and β glucose ring structures (b) Starch: 1–4 linkage of α glucose monomers (c) Cellulose: 1–4 linkage of β glucose monomers © 2017 Pearson Education, Inc. Figure 5.7a α Glucose β Glucose (a) α and β glucose ring structures © 2017 Pearson Education, Inc. Figure 5.7b (b) Starch: 1–4 linkage of α glucose monomers (c) Cellulose: 1–4 linkage of β glucose monomers © 2017 Pearson Education, Inc. § Starch (α configuration) is largely helical § Cellulose molecules (β configuration) are straight and unbranched § Some hydroxyl groups on the monomers of cellulose can hydrogen-bond with hydroxyls of parallel cellulose molecules © 2017 Pearson Education, Inc. § Enzymes that digest starch by hydrolyzing α linkages can’t hydrolyze β linkages in cellulose § The 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 © 2017 Pearson Education, Inc. § Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods § Chitin also provides structural support for the cell walls of many fungi © 2017 Pearson Education, Inc. Figure 5.8 The structure of the chitin monomer Chitin, embedded in proteins, forms the exoskeleton of arthropods. © 2017 Pearson Education, Inc. Figure 5.8a Chitin, embedded in proteins, forms the exoskeleton of arthropods. © 2017 Pearson Education, Inc. Concept 5.3: Lipids are a diverse group of hydrophobic molecules § Lipids are the one class of large biological molecules that does not include true polymers § The unifying feature of lipids is that they mix poorly, if at all, with water § Lipids consist mostly of hydrocarbon regions § The most biologically important lipids are fats, phospholipids, and steroids © 2017 Pearson Education, Inc. Fats § 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 © 2017 Pearson Education, Inc. Figure 5.9 H2O Fatty acid (in this case, palmitic acid) Glycerol (a) One of three dehydration reactions in the synthesis of a fat Ester linkage (b) Fat molecule (triacylglycerol) © 2017 Pearson Education, Inc. Figure 5.9a H H2O Fatty acid (in this case, palmitic acid) Glycerol (a) One of three dehydration reactions in the synthesis of a fat © 2017 Pearson Education, Inc. Figure 5.9b Ester linkage (b) Fat molecule (triacylglycerol) © 2017 Pearson Education, Inc. Animation: Fats © 2017 Pearson Education, Inc. § Fats separate from water because water molecules hydrogen-bond to 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 § The fatty acids in a fat can be all the same or of two or three different kinds © 2017 Pearson Education, Inc. § 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 © 2017 Pearson Education, Inc. Figure 5.10 (a) Saturated fat (b) Unsaturated fat Structural formula of a saturated fat molecule Structural formula of an unsaturated Space-filling model fat molecule of stearic acid, a saturated fatty acid Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending. © 2017 Pearson Education, Inc. Figure 5.10a (a) Saturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid © 2017 Pearson Education, Inc. Figure 5.10aa © 2017 Pearson Education, Inc. Figure 5.10b (b) Unsaturated fat Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending. © 2017 Pearson Education, Inc. Figure 5.10ba © 2017 Pearson Education, Inc. § Fats made from saturated fatty acids are called saturated fats and are solid at room temperature § Most animal fats are saturated § Fats made from unsaturated fatty acids are called unsaturated fats or oils and are liquid at room temperature § Plant fats and fish fats are usually unsaturated © 2017 Pearson Education, Inc. § 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 © 2017 Pearson Education, Inc. § The major function of fats is energy storage § Humans and other mammals store their long-term food reserves in adipose cells § Adipose tissue also cushions vital organs and insulates the body © 2017 Pearson Education, Inc.