The Molecules of Life

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The Molecules of Life

• Chapter 3

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Polymers Are Built of Monomers

• Organic molecules are formed by living organisms.
• Carbon-based core
• The core has attached groups of atoms called
  functional groups.
• The functional groups confer specific chemical
  properties on the organic molecules.

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Five principal functional groups
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Macromolecules

• The building materials of the body are known as
  macromolecules because they can be very large.
• There are four types of macromolecules
• Proteins
• Nucleic acids
• Carbohydrates
• Lipids

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Macromolecules

• Large macromolecules are actually assembled from
  many similar small components, called monomers.
• The assembled chain of monomers is known as a
  polymer.

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Dehydration Synthesis

• All polymers are assembled the same way.
• A covalent bond is formed by removing a hydroxyl
  group (OH) from one subunit and a hydrogen (H)
  from another subunit.

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Dehydration Synthesis

• Because this amounts to the removal of a molecule
  of water (H2O), this process of linking together
  two subunits to form a polymer is called
  dehydration synthesis.

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Hydrolysis

• The process of disassembling polymers into
  component monomers is essentially the reverse of
  dehydration synthesis.
• A molecule of water is added to break the
  covalent bond between the monomers.
• This process is known as hydrolysis.

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Proteins

• Proteins are complex macromolecules that are
  polymers of many subunits called amino acids.

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Proteins

• The covalent bond linking two amino acids
  together is called a peptide bond.
• The assembled polymer is called a polypeptide.

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Proteins

• Amino acids are small molecules with a simple
  basic structure, a carbon atom to which three
  groups are added
• an amino group (NH2)
• a carboxyl group (COOH)
• a functional group (R)
• The functional group gives amino acids their
  chemical identity.
• There are 20 different types of amino acids.

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Proteins

• Protein structure is complex.
• The order of the amino acids that form the
  polypeptide is important.
• The sequence of the amino acids affects how the
  protein folds together.

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Proteins

• The way that a polypeptide folds to form the
  protein determines the proteins function.
• Some proteins are comprised of more than one
  polypeptide.

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Proteins

• There are four general levels of protein
  structure
• Primary
• Secondary
• Tertiary
• Quaternary

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Proteins

• Primary structurethe sequence of amino acids in
  the polypeptide chain.
• Determines all other levels of protein structure.

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Proteins

• Secondary structure forms because regions of the
  polypeptide that are nonpolar are forced
  together hydrogen bonds can form between
  different parts of the chain.
• The folded structure may resemble coils, helices,
  or sheets.

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Proteins

• Tertiary structurethe final 3-D shape of the
  protein.
• The final twists and folds that lead to this
  shape are the result of polarity differences in
  regions of the polypeptide.

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Proteins

• Quaternary structurethe spatial arrangement of
  proteins comprised of more than one polypeptide
  chain.

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Proteins

• The shape of a protein affects its function.
• Changes to the environment of the protein may
  cause it to unfold or denature.
• Increased temperature or lower pH affects
  hydrogen bonding, which is involved in the
  folding process.
• A denatured protein is inactive.

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Proteins

• Enzymes are globular proteins that have a special
  3-D shape that fits precisely with another
  chemical.
• They cause the chemical that they fit with to
  undergo a reaction.
• This process of enhancing a chemical reaction is
  called catalysis.

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Nucleic Acids

• Nucleic acids are very long polymers that store
  information.
• Comprised of monomers called nucleotides.
• Each nucleotide has 3 parts
• a five-carbon sugar
• a phosphate group
• an organic nitrogen-containing base

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Nucleic Acids

• There are five different types of nucleotides.
• Information is encoded in the nucleic acid by
  different sequences of these nucleotides.

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Nucleic Acids

• There are two types of nucleic acids
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)
• RNA is similar to DNA except that
• it uses uracil instead of thymine
• it is comprised of just one strand
• it has a ribose sugar

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Nucleic Acids

• The structure of DNA is a double helix because
• There are only two base pairs possible
• Adenine (A) pairs with thymine (T)
• Cytosine (C) pairs with Guanine (G)
• Properly aligned hydrogen bonds hold each base
  pair together.
• A sugar-phosphate backbone comprised of
  phosphodiester bonds gives support.

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Nucleic Acids

• The structure of DNA helps it to function.
• The hydrogen bonds of the base pairs can be
  broken to unzip the DNA so that information can
  be copied.
• Each strand of DNA is a mirror image so that the
  DNA contains two copies of the information.
• Having two copies means that the information can
  be accurately copied and passed to the next
  generation.

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Carbohydrates

• Carbohydrates are monomers that make up the
  structural framework of cells and play a critical
  role in energy storage.
• A carbohydrate is any molecule that contains the
  elements C, H, and O in a 121 ratio.

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Carbohydrates

• The sizes of carbohydrates varies
• Simple carbohydratesconsist of one or two
  monomers.
• Complex carbohydratesare long polymers.

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Carbohydrates

• Simple carbohydrates are small.
• Monosaccharides consist of only one monomer
  subunit.
• An example is the sugar glucose (C6H12O6).
• Disaccharides consist of two monosaccharides.
• An example is the sugar sucrose, which is formed
  by joining together glucose and fructose.

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Carbohydrates

• Complex carbohydrates are long polymer chains.
• Because they contain many C-H bonds, these
  carbohydrates are good for storing energy.
• These bond types are the ones most often broken
  by organisms to obtain energy.
• The long chains are called polysaccharides.

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Carbohydrates

• Plants and animals store energy in polysaccharide
  chains formed from glucose.
• Plants form starch.
• Animals form glycogen.
• Some polysaccharides are structural and resistant
  to digestion by enzymes.
• Plants form cellulose cell walls.
• Some animals form chitin for exoskeletons.

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Lipids

• Lipidsfats and other molecules that are not
  soluble in water.
• Lipids are nonpolar molecules.
• There are many different types of lipids.
• fats
• oils
• steroids
• rubber
• waxes
• pigments

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Lipids

• Fats are converted from glucose for long-term
  energy storage.
• Fats have two subunits
• 1. fatty acids
• 2. glycerol
• Fatty acids are chains of C and H atoms, known as
  hydrocarbons.
• The chain ends in a carboxyl (COOH) group.

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Saturated and unsaturated fats
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Lipids

• Fatty acids have different chemical properties
  due to the number of hydrogens that are attached
  to the non-carboxyl carbons
• If the maximum number of hydrogens are attached,
  then the fat is said to be saturated.
• If there are fewer than the maximum attached,
  then the fat is said to be unsaturated.

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Saturated and unsaturated fats
H
H
H
H
C
C
C
C
H
H
(c) Oil (unsaturated) Fatty acids that contain
double bonds between one or more pairs of
carbon atoms
(b) Hard fat (saturated) Fatty acids with
single bonds between all carbon pairs
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Phospholipids

• Biological membranes involve lipids.
• Phospholipids make up the two layers of the
  membrane.
• Cholesterol is embedded within the membrane.

Outside of cell
Carbohydrate chains
Cell membrane
Cholesterol
Phospholipid
Membrane proteins
Inside of cell