The chemical building blocks of life

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Chapter 3

• The chemical building blocks of life

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Carbon The framework of biological molecules

• Biological molecules consist primarily of
• Carbon atoms bound to carbon atoms
• Carbon bound to other molecules
• Molecules consisting only of carbon and hydrogen
  are called hydrocarbons
• Hydrocarbons store energy-good fuels
• Gasoline is rich in hydrocarbons
• Carbon can form up to four covalent bonds
• Carbon can be bound to functional groups with
  specific properties

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Chemical vs. structural formulas

• Easy way to express the particular atoms that
  makeup an element
• Uses chemical symbol and number of atoms
• Propane-C3H8
• Butane-C4H10

• Graphical representation to show how atoms are
  arranged.
• Shows chemical bonding
• Propane
• Butane

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Primary functional chemical groups
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Biological Molecules

• Isomers are molecules with the same chemical
  formula
• Structural isomers-differ in carbon structure
• Example glucose and fructose
• Stereoisomer-differ in how the groups attached to
  the carbon skeleton are arranged (have same
  carbon skeleton)
• Subcategory Enantiomers mirror-images of each
  other
• A molecule that has mirror-image versions is
  called a chiral molecule
• When carbon is bound to 4 different molecules,
  symmetry exists
• Polarized light has single plane, chiral
  molecules rotate this plane either to the left or
  to the right
• Call 2 chiral forms D for dextrorotatory L for
  levorotatory
• In living systems, only single enantiomer
  (D-sugars L-amino acids

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Chiral molecules
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Four biological macromolecules

• Carbohydrates
• Nucleic Acids
• Proteins
• Lipids
• Table 3.1 pg. 35

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Biological Molecules

• Biological molecules are typically large
  molecules constructed from smaller subunits
• Monomer single subunit (mono-1 -mer-unit)
• Polymer many units (poly-many -mer-unit)
• Nature of a polymer is determined by the monomers
  used to build the polymer
• 1.) Dehydration reactions formation of large
  molecules by the removal of water
• ?Example monomers are joined to form polymers
• 2.) Hydrolysis reactions breakdown of large
  molecules by the addition of water
• ?Example polymers are broken down to monomers

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Making and breaking macromolecules
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Carbohydrates

• Molecules with a 121 ratio of C, H, O
• Empirical formula (CH2O) n
• Examples sugars, starch, glucose
• C-H covalent bondsenergy
• Carbs are good energy storage molecules

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Monosaccharides

• Mono single saccharum sugar
• Simplest of the carbohydrates
• Can contain as few as 3 carbon atoms
• Normally have 6
• Empirical formula C6H12O6 or (CH2O)6
• very important in energy storage
• -fructose is a structural isomer of glucose
• -galactose is a stereoisomer of glucose
• 6-carbon sugars can exist in a straight-chain
  form, but in water, they form rings

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Monosaccharides

• Example glucose
• Important in energy storage
• 7 C-H bonds
• 2 forms (a ß)
• Depends on orientation of carbonyl group
• Fructose is a structural isomer of glucose
• Galactose is a stereoisomer of glucose

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Structure of the glucose molecule
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Isomers and Stereoisomers
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Disaccharides

• di- 2
• 2 monosaccharides linked together by dehydration
  synthesis
• Used for sugar transport or energy storage
• Examples sucrose (sugarcane), lactose (milk
  sugar), maltose (storage)

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Polysaccharides

• Poly means many
• Long chains of sugars
• Used for energy storage
• Plants use starch animals use glycogen
• Used for structural support
• Plants use cellulose animals use chitin
• Examples
• Starches
• Amylose simplest starch
• Amylopectin branched, complex starch
• Glycogen

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Polymers of Glucose
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Polymers of glucose

• Cellulose

• Chitin

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Polymers of glucose

• Cellulose

• Chitin

• Polymer of ß-glucose
• Main component of plant cell walls
• Cows digest cellulose by means of bacteria and
  protists inside their digestive tracts

• Found in arthropods and many fungi
• Modified form of cellulose where N-acetyl group
  replaces a hydroxyl in each glucose unit
• Forms hard exoskeleton of insects and crustaceans

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Nucleic Acids

• 2 types
• DNA (deoxyribonucleic acid)
• RNA (ribonucleic acid)
• Functions
• specialized for the storage, transmission, and
  use of genetic information

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Nucleic Acids

• Nucleic acids are polymers of nucleotides
• Nucleotides sugar phosphate nitrogenous base
• Sugar deoxyribose in DNA or ribose in RNA
• Nitrogenous bases include
• Purines adenine and guanine
• Pyrimidines thymine, cytosine, uracil

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Structure of a nucleotide

• Made up of 3 elements
• Five-carbon sugar (ribose or deoxyribose)
• Organic nitrogenous base
• Phosphate group
• Sugar numbers are given as primes to
  distinguish between numbering on rings of bases

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Structure of Nucleic Acids Nitrogen-containing
bases
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DNA

• Nucleotides connected by phosphodiester bonds
• Double helix 2 polynucleotide strands connected
  by hydrogen bonds
• Polynucleotide strands are complementary
• Genetic information is carried in the sequence of
  nucleotides

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The structure of DNA
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RNA

• Contains ribose instead of deoxyribose
• Contains uracil instead of thymine
• Single polynucleotide strand
• Functions
• Read the genetic information in DNA
• Direct the synthesis of proteins

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DNA vs. RNA
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Other Nucleotides

• ATP adenosine triphosphate
• Primary energy currency of the cell
• NAD and FAD
• Electron carriers for many cellular reactions

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Proteins

• Seven functions
• enzyme catalysts
• defense
• transport
• support
• motion
• regulation
• storage

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Proteins

• Proteins are polymers of amino acids
• Amino acids
• Amino group (-NH2) carboxyl group (-COOH)
• 20 different
• Joined together by dehydration synthesis
• Amino acids are held together by peptide bonds
• Table 3.2 Functions of proteins

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Peptide Bond
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Amino Acid Structure

• Central carbon atom surrounded by
• Amino group
• Carboxyl group
• Single Hydrogen
• Variable R-group

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Proteins

• The structure of the R group dictates the
  chemical properties of the amino acid.
• Amino acids can be classified as
• Nonpolar
• Polar
• Charged
• Aromatic
• Special function

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Proteins

• The shape of a protein determines its function.
• Primary structure-sequence of amino acids
• Secondary structure-interaction of groups in the
  peptide backbone
• a-helix ß-sheet
• Tertiary structure-folded shape of the
  polypeptide chain
• Protein folding is aided by chaperone proteins.
• Quaternary structure-interactions between
  multiple polypeptide subunits

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Proteins
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Proteins
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Proteins

• Motifs are common elements of secondary structure
  seen in many polypeptides.
• Domains are functional regions of a polypeptide.

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Proteins

• Denaturation is a change in the shape of a
  protein, usually causing loss of function
• May involve complete unfolding
• Caused by changes in the proteins environment
• pH
• Temperature
• Salt Concentration

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Lipids

• Lipids are a group of molecules that are
  insoluble in water.
• A high proportion of nonpolar C-H bonds causes
  the molecule to be hydrophobic
• Two main categories
• Fats (triglycerides)
• Phospholipids

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Lipids

• Triglycerides (fats) are composed of 1 glycerol
  3 fatty acids
• Fatty acids are long hydrocarbon chains which may
  be
• Saturated
• Unsaturated
• Polyunsaturated

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Lipids
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Lipids

• Triglycerides are
• An excellent molecule for energy storage
• Store 2X as much energy as carbohydrates
• Animal fats are usually saturated fats and solid
  at room temperature
• lard
• Plant fats are usually unsaturated fats and
  liquid at room temperature
• Vegetable, canola, olive, peanut oils

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Lipids

• Phospholipids are composed of
• 1 glycerol
• 2 fatty acids
• A phosphate group

• Phospholipids contain polar heads and nonpolar
  tails

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Lipids
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Lipids

• Phospholipids spontaneously form micelles or
  lipid bilayers
• These structures cluster the hydrophobic regions
  of the phospholipid toward the inside and leave
  the hydrophilic regions exposed to the water
  environment.
• Lipid bilayers are the basis of biological
  membranes.
• Cell membranes

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Lipids