Life and Chemistry: Large Molecules

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Life and ChemistryLarge Molecules
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Macromolecules Giant Polymers

• There are four major types of biological
  macromolecules
• Proteins
• Carbohydrates
• Lipids
• Nucleic acids

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Macromolecules Giant Polymers

• Macromolecules are giant polymers.
• Polymers are formed by covalent linkages of
  smaller units called monomers.

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Condensation and Hydrolysis Reactions

• Macromolecules are made from smaller monomers by
  means of a condensation or dehydration reaction
  in which an OH from one monomer is linked to an H
  from another monomer.
• The reverse reaction, in which polymers are
  broken back into monomers, is a called a
  hydrolysis reaction.

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Figure 3.3 Condensation and Hydrolysis of
Polymers (Part 1)
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Figure 3.3 Condensation and Hydrolysis of
Polymers (Part 2)
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Proteins Polymers of Amino Acids

• Proteins are polymers of amino acids. They are
  molecules with diverse structures and functions.

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Proteins Polymers of Amino Acids

• An amino acid has four groups attached to a
  central carbon atom
• A hydrogen atom
• An amino group (NH3)
• The acid is a carboxyl group (COO).
• Differences in amino acids come from the side
  chains, or the R groups.

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Table 3.2 The Twenty Amino Acids Found in
Proteins (Part 1)
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Table 3.2 The Twenty Amino Acids Found in
Proteins (Part 2)
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Table 3.2 The Twenty Amino Acids Found in
Proteins (Part 3)
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Proteins Polymers of Amino Acids

• Proteins are synthesized by condensation
  reactions between the amino group of one amino
  acid and the carboxyl group of another. This
  forms a peptide linkage.
• Forms a polypeptide.

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Figure 3.5 Formation of Peptide Linkages
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Proteins Polymers of Amino Acids

• There are four levels of protein structure
  primary, secondary, tertiary, and quaternary.
• The precise sequence of amino acids is called its
  primary structure.
• The peptide backbone consists of repeating units
  of atoms NCCNCC.
• Enormous numbers of different proteins are
  possible.

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Figure 3.6 The Four Levels of Protein Structure
(Part 1)
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Proteins Polymers of Amino Acids

• A proteins secondary structure consists of
  regular, repeated patterns in different regions
  in the polypeptide chain.
• This shape is influenced primarily by hydrogen
  bonds arising from the amino acid sequence (the
  primary structure).
• The two common secondary structures are the a
  helix and the b pleated sheet.

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Proteins Polymers of Amino Acids

• The a helix is a right-handed coil.
• The R groups point away from the peptide backbone.

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Figure 3.6 The Four Levels of Protein Structure
(Part 2)
ß pleated sheets form from peptide regions that
lie parallel to each other.
Stabilized by hydrogen bonds between N-H groups
on one chain with the CO group on the other.
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Proteins Polymers of Amino Acids

• Tertiary structure is the three-dimensional shape
  of the completed polypeptide.
• Interaction between R groups.
• Includes the location of disulfide bridges, which
  form between cysteine residues.

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Figure 3.4 A Disulfide Bridge
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Proteins Polymers of Amino Acids

• Other factors determining tertiary structure
• The nature and location of secondary structures
• Hydrophobic side-chain aggregation and van der
  Waals forces, which help stabilize them
• The ionic interactions between the positive and
  negative charges deep in the protein, away from
  water

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Proteins Polymers of Amino Acids

• It is now possible to determine the complete
  description of a proteins tertiary structure.
• The location of every atom in the molecule is
  specified in three-dimensional space.

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Proteins Polymers of Amino Acids

• Quaternary structure results from the ways in
  which multiple polypeptide subunits bind together
  and interact.
• This level of structure adds to the
  three-dimensional shape of the finished protein.

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Figure 3.8 Quaternary Structure of a Protein
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Proteins Polymers of Amino Acids

• Shape is crucial to the functioning of some
  proteins.
• The combination of attractions, repulsions, and
  interactions determines the right fit.

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Figure 3.9 Noncovalent Interactions between
Proteins and Other Molecules
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Proteins Polymers of Amino Acids

• Changes in temperature, pH, salt concentrations,
  and oxidation or reduction conditions can change
  the shape of proteins.
• This loss of a proteins normal three-dimensional
  structure is called denaturation.

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Figure 3.11 Denaturation Is the Loss of Tertiary
Protein Structure and Function
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Figure 3.12 Chaperonins Protect Proteins from
Inappropriate Folding
Chaperonins are specialized proteins that help
keep other proteins from interacting
inappropriately with one another.
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Carbohydrates Sugars and Sugar Polymers

• Carbohydrates are carbon molecules with hydrogen
  and hydroxyl groups.
• They act as energy storage and transport
  molecules.
• They also serve as structural components.

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Carbohydrates Sugars and Sugar Polymers

• There are four major categories of carbohydrates
  
• Monosaccharides
• Disaccharides, which consist of two
  monosaccharides
• Oligosaccharides, which consist of between 3 and
  20 monosaccharides
• Polysaccharides, which are composed of hundreds
  to hundreds of thousands of monosaccharides

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Carbohydrates Sugars and Sugar Polymers

• The general formula for a carbohydrate monomer is
  multiples of CH2O, maintaining a ratio of 1
  carbon to 2 hydrogens to 1 oxygen.
• During the polymerization, which is a
  condensation reaction, water is removed.
• Carbohydrate polymers have ratios of carbon,
  hydrogen, and oxygen that differ somewhat from
  the 121 ratios of the monomers.

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Carbohydrates Sugars and Sugar Polymers

• All living cells contain the monosaccharide
  glucose (C6H12O6).
• Glucose exists as a straight chain and a ring,
  with the ring form predominant.
• The two forms of the ring, a-glucose and
  b-glucose, exist in equilibrium when dissolved in
  water.

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Figure 3.13 Glucose From One Form to the Other
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Figure 3.14 Monosaccharides Are Simple Sugars
(Part 1)
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Figure 3.14 Monosaccharides Are Simple Sugars
(Part 2)
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Carbohydrates Sugars and Sugar Polymers

• Monosaccharides are bonded together covalently by
  condensation reactions. The bonds are called
  glycosidic linkages.

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Figure 3.15 Disaccharides Are Formed by
Glycosidic Linkages
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Carbohydrates Sugars and Sugar Polymers

• Oligosaccharides contain more than two
  monosaccharides.
• Many proteins found on the outer surface of cells
  have oligosaccharides attached to the R group of
  certain amino acids, or to lipids.

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Carbohydrates Sugars and Sugar Polymers

• Polysaccharides are giant polymers of
  monosaccharides connected by glycosidic linkages.
  
• Cellulose is a giant polymer of glucose joined by
  b-1,4 linkages.
• Starch is a polysaccharide of glucose with a-1,4
  linkages.

Structure of cellulose as it occurs in a plant
cell wall.
Cellulose Fibers from Print Paper (SEM x1,080).
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Figure 3.16 Representative Polysaccharides (Part
1)
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Carbohydrates Sugars and Sugar Polymers

• Starches vary by amount of branching.

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Carbohydrates Sugars and Sugar Polymers

• Carbohydrates are modified by the addition of
  functional groups.

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Figure 3.17 Chemically Modified Carbohydrates
(Part 1)
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Figure 3.17 Chemically Modified Carbohydrates
(Part 2)
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Nucleic acids, composed of many nucleotides, are
  polymers that are specialized for storage and
  transmission of information.
• Two types of nucleic acid are DNA
  (deoxyribonucleic acid) and RNA (ribonucleic
  acid).

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Nucleic acids are polymers of nucleotides.
• A nucleotide consists of a pentose sugar, a
  phosphate group, and a nitrogen-containing base.
• In DNA, the pentose sugar is deoxyribose in RNA
  it is ribose.

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Figure 3.24 Nucleotides Have Three Components
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• DNA typically is double-stranded.
• The two separate polymer chains are held together
  by hydrogen bonding between their nitrogenous
  bases.
• The base pairing is complementary.
• Purines have a double-ring structure Adenine
  and Guanine.
• Pyrimidines have one ring Cytosine and Thymine.
• A pairs with T, G pairs with C.

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Figure 3.25 Distinguishing Characteristics of
DNA and RNA
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• The linkages that hold the nucleotides in RNA and
  DNA are called phosphodiester linkages.
• These linkages are formed between carbon 3 of the
  sugar and a phosphate group that is associated
  with carbon 5 of the sugar.
• The backbone consists of alternating sugars and
  phosphates.
• In DNA, the two strands are antiparallel.
• The DNA strands form a double helix, a molecule
  with a right-hand twist.

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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• Most RNA molecules consist of only a single
  polynucleotide chain.
• Instead of the base thymine, RNA uses the base
  uracil DNA has deoxyribose sugar, RNA has
  ribose.

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Figure 3.26 Hydrogen Bonding in RNA
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Nucleic Acids Informational MacromoleculesThat
Can Be Catalytic

• DNA is an information molecule. The information
  is stored in the order of the four different
  bases.
• This order is transferred to RNA molecules, which
  are used to direct the order of the amino acids
  in proteins.
• DNA RNA PROTEIN

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Lipids Water-Insoluble Molecules

• Lipids are insoluble in water.
• This insolubility results from the many nonpolar
  covalent bonds of hydrogen and carbon in lipids.

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Lipids Water-Insoluble Molecules

• Roles for lipids in organisms include
• Energy storage (fats and oils)
• Cell membranes (phospholipids)
• Capture of light energy (carotinoids)
• Hormones and vitamins (steroids and modified
  fatty acids)
• Thermal insulation
• Electrical insulation of nerves
• Water repellency (waxes and oils)

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Lipids Water-Insoluble Molecules

• Fats and oils store energy.
• Fats and oils are triglycerides, composed of
  three fatty acid molecules and one glycerol
  molecule.

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Figure 3.18 Synthesis of a Triglyceride
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Lipids Water-Insoluble Molecules

• Saturated fatty acids have only single
  carbon-to-carbon bonds and are said to be
  saturated with hydrogens.

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Lipids Water-Insoluble Molecules

• Unsaturated fatty acids have at least one
  double-bonded carbon in one of the chains the
  chain is not completely saturated with hydrogen
  atoms.

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Figure 3.19 Saturated and Unsaturated Fatty Acids
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Lipids Water-Insoluble Molecules

• Phospholipids have two hydrophobic fatty acid
  tails and one hydrophilic phosphate group
  attached to the glycerol.

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Figure 3.20 Phospholipid Structure
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Figure 3.21 Phospholipids Form a Bilayer
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Lipids Water-Insoluble Molecules

• Carotenoids are light-absorbing pigments found in
  plants and animals.

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Figure 3.22 b Carotene is the Source of Vitamin
A
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Lipids Water-Insoluble Molecules

• Steroids are signaling molecules.
• Steroids are organic compounds with a series of
  fused rings.

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Figure 3.23 All Steroids Have the Same Ring
Structure
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Lipids Water-Insoluble Molecules

• Waxes are highly nonpolar molecules consisting of
  saturated long fatty acids bonded to long fatty
  alcohols.
• A fatty alcohol is similar to a fatty acid,
  except for the last carbon, which has an OH
  group instead of a COOH group.