Life Chemistry and Energy

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Life Chemistry and Energy
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Chapter 2 Life Chemistry and Energy

• Key Concepts
• 2.1 Atomic Structure Is the Basis for Lifes
  Chemistry
• 2.2 Atoms Interact and Form Molecules
• 2.3 Carbohydrates Consist of Sugar Molecules
• 2.4 Lipids Are Hydrophobic Molecules
• 2.5 Biochemical Changes Involve Energy

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Chapter 2 Opening Question
Why is the search for water important in the
search for life?
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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Living and nonliving matter is composed of atoms.

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Like charges repel different charges attract.
• Most atoms are neutral because the number of
  electrons equals the number of protons.
• Daltonmass of one proton or neutron
• (1.7 1024 grams)
• Mass of electrons is so tiny, it is usually
  ignored.

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Elementpure substance that contains only one
  kind of atom
• Living things are mostly composed of 6 elements
• Carbon (C) Hydrogen (H) Nitrogen
  (N)
• Oxygen (O) Phosphorus (P) Sulfur (S)

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• The number of protons identifies an element.
• Number of protons atomic number
• For electrical neutrality, protons
  electrons.
• Mass numbertotal number of protons and neutrons

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• A Bohr model for atomic structurethe atom is
  largely empty space, and the electrons occur in
  orbits, or electron shells.

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Behavior of electrons determines whether a
  chemical bond will form and what shape the bond
  will have.

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Figure 2.1 Electron Shells
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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Atoms with unfilled outer shells tend to undergo
  chemical reactions to fill their outer shells.
• They can attain stability by sharing electrons
  with other atoms or by losing or gaining
  electrons.
• The atoms are then bonded together into
  molecules.

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Concept 2.1 Atomic Structure Is the Basis for
Lifes Chemistry

• Octet ruleatoms with at least two electron
  shells form stable molecules so they have eight
  electrons in their outermost shells.

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Concept 2.2 Atoms Interact and Form Molecules

• Chemical bond is an attractive force that links
  atoms together to form molecules.
• There are several kinds of chemical bonds.

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Table 2.1 Chemical Bonds and Interactions
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Concept 2.2 Atoms Interact and Form Molecules

• Ionic bonds
• Ions are charged particle that form when an atom
  gains or loses one or more electrons.
• Cationspositively charged ions
• Anionsnegatively charged ions
• Ionic bonds result from the electrical attraction
  between ions with opposite charges.
• The resulting molecules are called salts.

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Figure 2.2 Ionic Bond between Sodium and Chlorine
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Concept 2.2 Atoms Interact and Form Molecules

• Ionic attractions are weak, so salts dissolve
  easily in water.

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Concept 2.2 Atoms Interact and Form Molecules

• Covalent bonds
• Covalent bonds form when two atoms share pairs of
  electrons.
• The atoms attain stability by having full outer
  shells.
• Each atom contributes one member of the electron
  pair.

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Figure 2.3 Electrons Are Shared in Covalent Bonds
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Concept 2.2 Atoms Interact and Form Molecules

• Carbon atoms have four electrons in the outer
  shellthey can form covalent bonds with four
  other atoms.

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Figure 2.4 Covalent Bonding (Part 1)
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Figure 2.4 Covalent Bonding (Part 2)
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Concept 2.2 Atoms Interact and Form Molecules

• Properties of molecules are influenced by
  characteristics of the covalent bonds
• Orientationlength, angle, and direction of bonds
  between any two elements are always the same.
• Example Methane always forms a tetrahedron.

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Concept 2.2 Atoms Interact and Form Molecules

• Strength and stabilitycovalent bonds are very
  strong it takes a lot of energy to break them.
• Multiple bonds
• Singlesharing 1 pair of electrons
• Doublesharing 2 pairs of electrons
• Triplesharing 3 pairs of electrons

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Concept 2.2 Atoms Interact and Form Molecules

• Degree of sharing electrons is not always equal.
• Electronegativitythe attractive force that an
  atomic nucleus exerts on electrons
• It depends on the number of protons and the
  distance between the nucleus and electrons.

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Table 2.2 Some Electronegativities
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Concept 2.2 Atoms Interact and Form Molecules

• If two atoms have similar electronegativities,
  they share electrons equally, in what is called a
  nonpolar covalent bond.
• If atoms have different electronegativities,
  electrons tend to be near the most attractive
  atom, in what is called a polar covalent bond

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Concept 2.2 Atoms Interact and Form Molecules

• Hydrogen bonds
• Attraction between the d end of one molecule and
  the d hydrogen end of another molecule forms
  hydrogen bonds.
• They form between water molecules.
• They are important in the structure of DNA and
  proteins.

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Figure 2.5 Hydrogen Bonds Can Form between or
within Molecules
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Concept 2.2 Atoms Interact and Form Molecules

• Water molecules form multiple hydrogen bonds with
  each otherthis contributes to high heat capacity.

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Concept 2.2 Atoms Interact and Form Molecules

• A lot of heat is required to raise the
  temperature of waterthe heat energy breaks the
  hydrogen bonds.
• In organisms, presence of water shields them from
  fluctuations in environmental temperature.

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Concept 2.2 Atoms Interact and Form Molecules

• Water has a high heat of vaporizationa lot of
  heat is required to change water from liquid to
  gaseous state.
• Thus, evaporation has a cooling effect on the
  environment.
• Sweating cools the bodyas sweat evaporates from
  the skin, it transforms some of the adjacent body
  heat.

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Concept 2.2 Atoms Interact and Form Molecules

• Hydrogen bonds also give water cohesive strength,
  or cohesionwater molecules resist coming apart
  when placed under tension.
• This permits narrow columns of water to move from
  roots to leaves of plants.

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Concept 2.2 Atoms Interact and Form Molecules

• Any polar molecule can interact with any other
  polar molecule through hydrogen bonds.
• Hydrophilic (water-loving)in aqueous
  solutions, polar molecules become separated and
  surrounded by water molecules
• Nonpolar molecules are called hydrophobic
  (water-hating) the interactions between them
  are hydrophobic interactions.

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Figure 2.6 Hydrophilic and Hydrophobic
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Concept 2.2 Atoms Interact and Form Molecules

• Functional groupssmall groups of atoms with
  specific chemical properties
• Functional groups confer these properties to
  larger molecules, e.g., polarity.
• One biological molecule may contain many
  functional groups.

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Figure 2.7 Functional Groups Important to Living
Systems (Part 1)
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Figure 2.7 Functional Groups Important to Living
Systems (Part 2)
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Concept 2.2 Atoms Interact and Form Molecules

• Macromolecules
• Most biological molecules are polymers (poly,
  many mer, unit), made by covalent bonding of
  smaller molecules called monomers.

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Concept 2.2 Atoms Interact and Form Molecules

• Proteins Formed from different combinations of
  20 amino acids
• Carbohydratesformed by linking similar sugar
  monomers (monosaccharides) to form
  polysaccharides
• Nucleic acidsformed from four kinds of
  nucleotide monomers
• Lipidsnoncovalent forces maintain the
  interactions between the lipid monomers

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Concept 2.2 Atoms Interact and Form Molecules

• Polymers are formed and broken apart in reactions
  involving water.
• Condensationremoval of water links monomers
  together
• Hydrolysisaddition of water breaks a polymer
  into monomers

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Figure 2.8 Condensation and Hydrolysis of
Polymers (Part 1)
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Figure 2.8 Condensation and Hydrolysis of
Polymers (Part 2)
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Concept 2.3 Carbohydrates Consist of Sugar
Molecules

• Carbohydrates
• Source of stored energy
• Transport stored energy within complex
  organisms
• Structural molecules that give many organisms
  their shapes
• Recognition or signaling molecules that can
  trigger specific biological responses

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Concept 2.3 Carbohydrates Consist of Sugar
Molecules

• Monosaccharides are simple sugars.
• Pentoses are 5-carbon sugars
• Ribose and deoxyribose are the backbones of RNA
  and DNA.
• Hexoses (C6H12O6) include glucose, fructose,
  mannose, and galactose.

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Figure 2.9 Monosaccharides (Part 1)
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Figure 2.9 Monosaccharides (Part 2)
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Concept 2.3 Carbohydrates Consist of Sugar
Molecules

• Monosaccharides are covalently bonded by
  condensation reactions that form glycosidic
  linkages.
• Sucrose is a disaccharide.

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Concept 2.3 Carbohydrates Consist of Sugar
Molecules

• Oligosaccharides contain several monosaccharides.
• Many have additional functional groups.
• They are often bonded to proteins and lipids on
  cell surfaces, where they serve as recognition
  signals.

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Concept 2.3 Carbohydrates Consist of Sugar
Molecules

• Polysaccharides are large polymers of
  monosaccharides the chains can be branching.
• Starchesa family of polysaccharides of glucose
• Glycogenhighly branched polymer of glucose main
  energy storage molecule in mammals
• Cellulosethe most abundant carbon-containing
  (organic) biological compound on Earth stable
  good structural material

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Figure 2.10 Polysaccharides (Part 1)
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Figure 2.10 Polysaccharides (Part 2)
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Figure 2.10 Polysaccharides (Part 3)
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Concept 2.4 Lipids Are Hydrophobic Molecules

• Lipids are hydrocarbons (composed of C and H
  atoms) they are insoluble in water because of
  many nonpolar covalent bonds.
• When close together, weak but additive van der
  Waals interactions hold them together.

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Concept 2.4 Lipids Are Hydrophobic Molecules

• Lipids
• Store energy in CC and CH bonds
• Play structural role in cell membranes
• Fat in animal bodies serves as thermal
  insulation

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Concept 2.4 Lipids Are Hydrophobic Molecules

• Triglycerides (simple lipids)
• Fatssolid at room temperature
• Oilsliquid at room temperature
• They have very little polarity and are extremely
  hydrophobic.

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Concept 2.4 Lipids Are Hydrophobic Molecules

• Triglycerides consist of
• Three fatty acidsnonpolar hydrocarbon chain
  attached to a polar carboxyl group (COOH)
  (carboxylic acid)
• One glycerolan alcohol with 3 hydroxyl
  (OH) groups
• Synthesis of a triglyceride involves three
  condensation reactions.

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Figure 2.11 Synthesis of a Triglyceride
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Concept 2.4 Lipids Are Hydrophobic Molecules

• Fatty acid chains can vary in length and
  structure.
• In saturated fatty acids, all bonds between
  carbon atoms are single they are saturated with
  hydrogens.
• In unsaturated fatty acids, hydrocarbon chains
  contain one or more double bonds. These acids
  cause kinks in the chain and prevent molecules
  from packing together tightly.

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Figure 2.12 Saturated and Unsaturated Fatty
Acids (Part 1)
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Figure 2.12 Saturated and Unsaturated Fatty
Acids (Part 2)
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Concept 2.4 Lipids Are Hydrophobic Molecules

• Fatty acids are amphipathic they have a
  hydrophilic end and a hydrophobic tail.
• Phospholipidtwo fatty acids and a phosphate
  compound bound to glycerol
• The phosphate group has a negative charge, making
  that part of the molecule hydrophilic.

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Figure 2.13 A Phospholipids
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Concept 2.4 Lipids Are Hydrophobic Molecules

• In an aqueous environment, phospholipids form a
  bilayer.
• The nonpolar, hydrophobic tails pack together
  and the phosphate-containing heads face
  outward, where they interact with water.
• Biological membranes have this kind of
  phospholipid bilayer structure.

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Figure 2.13 B Phospholipids
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Concept 2.5 Biochemical Changes Involve Energy

• Chemical reactions occur when atoms have enough
  energy to combine, or change, bonding partners.
• sucrose H2O glucose fructose
• (C12H22O11) (C6H12O6)
  (C6H12O6)
• reactants
  products

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Concept 2.5 Biochemical Changes Involve Energy

• Metabolismthe sum total of all chemical
  reactions occurring in a biological system at a
  given time
• Metabolic reactions involve energy changes.

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Concept 2.5 Biochemical Changes Involve Energy

• All forms of energy can be considered as either
• Potentialthe energy of state or position, or
  stored energy
• Kineticthe energy of movement (the type of
  energy that does work) that makes things change
• Energy can be converted from one form to another.

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Concept 2.5 Biochemical Changes Involve Energy

• Two basic types of metabolism
• Anabolic reactions link simple molecules to form
  complex ones.
• They require energy inputs energy is captured in
  the chemical bonds that form.
• Catabolic reactions break down complex molecules
  into simpler ones.
• Energy stored in the chemical bonds is released.

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Figure 2.14 Energy Changes in Reactions (Part 1)
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Figure 2.14 Energy Changes in Reactions (Part 2)
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Concept 2.5 Biochemical Changes Involve Energy

• The laws of thermodynamics apply to all matter
  and energy transformations in the universe.
• First law Energy is neither created nor
  destroyed.
• Second law Disorder (entropy) tends to increase.
  
• When energy is converted from one form to
  another, some of that energy becomes unavailable
  for doing work.

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Figure 2.15 The Laws of Thermodynamics (Part 1)
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Figure 2.15 The Laws of Thermodynamics (Part 2)
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Figure 2.15 The Laws of Thermodynamics (Part 3)
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Concept 2.5 Biochemical Changes Involve Energy

• If a chemical reaction increases entropy, its
  products are more disordered or random than its
  reactants.
• If there are fewer products than reactants, the
  disorder is reduced this requires energy to
  achieve.

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Concept 2.5 Biochemical Changes Involve Energy

• As a result of energy transformations, disorder
  tends to increase.
• Some energy is always lost to random thermal
  motion (entropy).

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Concept 2.5 Biochemical Changes Involve Energy

• Metabolism creates more disorder (more energy is
  lost to entropy) than the amount of order that is
  stored.
• Example
• The anabolic reactions needed to construct 1 kg
  of animal body require the catabolism of about 10
  kg of food.
• Life requires a constant input of energy to
  maintain order.

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Answer to Opening Question

• One way to investigate the possibility of life on
  other planets is to study how life may have
  originated on Earth.
• An experiment in the 1950s combined gases thought
  to be present in Earths early atmosphere,
  including water vapor. An electric spark provided
  energy.
• Complex molecules were formed, such as amino
  acids. Water was essential in this experiment.

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Figure 2.16 Synthesis of Prebiotic Molecules in
an Experimental Atmosphere (Part 1)
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Figure 2.16 Synthesis of Prebiotic Molecules in
an Experimental Atmosphere (Part 2)