The Structure and Function of Macromolecules

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Chapter 5

• The Structure and Function of Macromolecules

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The Molecules of Life

• Overview
• Another level in the hierarchy of biological
  organization is reached when small organic
  molecules are joined together
• Atom ---gt molecule ---? compound

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Macromolecules

• Are large molecules composed of smaller molecules
• Are complex in their structures

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Macromolecules

• Most macromolecules are polymers, built from
  monomers
• Four classes of lifes organic molecules are
  polymers
• Carbohydrates
• Proteins
• Nucleic acids
• Lipids

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• A polymer
• Is a long molecule consisting of many similar
  building blocks called monomers
• Specific monomers make up each macromolecule
• E.g. amino acids are the monomers for proteins

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The Synthesis and Breakdown of Polymers

• Monomers form larger molecules by condensation
  reactions called dehydration synthesis

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The Synthesis and Breakdown of Polymers

• Polymers can disassemble by
• Hydrolysis (addition of water molecules)

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• Although organisms share the same limited number
  of monomer types, each organism is unique based
  on the arrangement of monomers into polymers
• An immense variety of polymers can be built from
  a small set of monomers

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Carbohydrates

• Serve as fuel and building material
• Include both sugars and their polymers (starch,
  cellulose, etc.)

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Sugars

• Monosaccharides
• Are the simplest sugars
• Contain a carbonyl group and a hydroxyl group.
• Can be used for fuel
• Can be converted into other organic molecules
• Can be combined into polymers

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• Examples of monosaccharides

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• Monosaccharides
• May be linear
• Can form rings

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• Disaccharides
• Consist of two monosaccharides
• Are joined by a glycosidic linkage

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Polysaccharides

• Polysaccharides
• Are polymers of sugars
• Serve many roles in organisms
• Source of energy

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Storage Polysaccharides

• Starch
• Is a polymer consisting entirely of aglucose
  monomers
• Is the major storage form of glucose in plants

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• Glycogen
• Consists of glucose monomers
• Is the major storage form of glucose in animals

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Structural Polysaccharides

• Cellulose
• Is a polymer of glucose
• Found in the cell walls of plant cells.
• Build up with ßglucose monomers.

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• Has different glycosidic linkages than starch

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• Is a major component of the tough walls that
  enclose plant cells

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• Cellulose is difficult to digest
• Cows have microbes in their stomachs to
  facilitate this process

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• Chitin, another important structural
  polysaccharide
• Is found in the exoskeleton of arthropods
• Can be used as surgical thread

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Lipids

• Lipids are a diverse group of hydrophobic
  molecules
• Lipids
• Are the one class of large biological molecules
  that do not consist of polymers
• Share the common trait of being hydrophobic

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Fats

• Are constructed from two types of smaller
  molecules, a single glycerol and usually three
  fatty acids
• Vary in the length and number and locations of
  double bonds they contain
• Store energy, cushion organs and insulate.

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• Saturated fatty acids (animal fat)
• Have the maximum number of hydrogen atoms
  possible
• Have no double bonds
• Solid at room temperature

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• Unsaturated fatty acids (fish, plant fat)
• Have one or more double bonds
• Liquid at room temperature

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• Phospholipids
• Have only two fatty acids
• Have a phosphate group instead of a third fatty
  acid

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• Phospholipid structure
• Consists of a hydrophilic head and hydrophobic
  tails

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• The structure of phospholipids
• Results in a bilayer arrangement found in cell
  membranes

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Steroids

• Steroids
• Are lipids characterized by a carbon skeleton
  consisting of four fused rings
• Differ in functional groups attached to rings

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• One steroid, cholesterol
• Is found in cell membranes
• Is a precursor for some hormones

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Proteins

• Proteins have many structures, resulting in a
  wide range of functions
• Proteins do most of the work in cells and act as
  enzymes
• Proteins are made of monomers called amino acids

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• An overview of protein functions

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• Enzymes
• Are a type of protein that acts as a catalyst,
  speeding up chemical reactions

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Polypeptides

• Polypeptides
• Are polymers (chains) of amino acids
• A protein
• Consists of one or more polypeptides

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• Amino acids
• Are organic molecules possessing both carboxyl
  and amino groups
• Differ in their properties due to differing side
  chains, called R groups

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Twenty Amino Acids

• 20 different amino acids make up proteins

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Amino Acid Polymers

• Amino acids
• Are linked by peptide bonds

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Protein Conformation and Function

• A proteins specific conformation (shape)
  determines how it functions

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Four Levels of Protein Structure

• Primary structure
• Is the unique sequence of amino acids in a
  polypeptide

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• Secondary structure
• Is the folding or coiling of the polypeptide into
  a repeating configuration
• Includes the ? helix and the ? pleated sheet

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• Tertiary structure
• Is the overall three-dimensional shape of a
  polypeptide
• Results from interactions between amino acids and
  R groups

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• Quaternary structure
• Is the overall protein structure that results
  from the aggregation of two or more polypeptide
  subunits

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Review of Protein Structure
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Sickle-Cell Disease A Simple Change in Primary
Structure

• Sickle-cell disease
• Results from a single amino acid substitution in
  the protein hemoglobin

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Fibers of abnormalhemoglobin deform cell into
sickle shape.
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What Determines Protein Conformation?

• Protein conformation Depends on the physical and
  chemical conditions of the proteins environment
• Temperature, pH, etc. affect protein structure

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Denaturation is when a protein unravels and loses
its native conformation(shape)
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The Protein-Folding Problem

• Most proteins
• Probably go through several intermediate states
  on their way to a stable conformation
• Denaturated proteins no longer work in their
  unfolded condition
• Proteins may be denaturated by extreme changes in
  pH or temperature

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• Chaperonins
• Are protein molecules that assist in the proper
  folding of other proteins

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• X-ray crystallography
• Is used to determine a proteins
  three-dimensional structure

Figure 5.24
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Nucleic Acids

• Nucleic acids store and transmit hereditary
  information
• Genes
• Are the units of inheritance
• Program the amino acid sequence of polypeptides
• Are made of nucleotide sequences on DNA

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The Roles of Nucleic Acids

• There are two types of nucleic acids
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)

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Deoxyribonucleic Acid

• DNA
• Stores information for the synthesis of specific
  proteins
• Found in the nucleus of cells

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DNA Functions

• Directs RNA synthesis (transcription)
• Directs protein synthesis through RNA
  (translation)

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The Structure of Nucleic Acids

• Nucleic acids
• Exist as polymers called polynucleotides

(a) Polynucleotide, or nucleic acid
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• Each polynucleotide
• Consists of monomers called nucleotides
• Sugar phosphate nitrogen base

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Nucleotide Monomers

• Nucleotide monomers
• Are made up of nucleosides (sugar base) and
  phosphate groups

Figure 5.26
(c) Nucleoside components
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Nucleotide Polymers

• Nucleotide polymers
• Are made up of nucleotides linked by theOH
  group on the 3 carbon of one nucleotide and the
  phosphate on the 5 carbon on the next

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Gene

• The sequence of bases along a nucleotide polymer
• Is unique for each gene

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The DNA Double Helix

• Cellular DNA molecules
• Have two polynucleotides that spiral around an
  imaginary axis
• Form a double helix

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• The DNA double helix
• Consists of two antiparallel nucleotide strands

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A,T,C,G

• The nitrogenous bases in DNA
• Form hydrogen bonds in a complementary fashion (A
  with T only, and C with G only)

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DNA and Proteins as Tape Measures of Evolution

• Molecular comparisons
• Help biologists sort out the evolutionary
  connections among species

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The Theme of Emergent Properties in the Chemistry
of Life A Review

• Higher levels of organization
• Result in the emergence of new properties
• Organization
• Is the key to the chemistry of life

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