AP Biology Chapter 5: The Structure and Function of Macromolecules

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AP Biology Chapter 5 The Structure and
Function of Macromolecules
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Macromolecules

• Large, complex molecules
• Four main classes of large biological molecules
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

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Polymers v. Monomers

• Polymers Long molecule made of many similar or
  identical building blocks linked by covalent
  bonds
• Monomers the small molecules put together in
  repeating units that are the building blocks of a
  polymer. May have their own functions

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Making Polymers

• Monomers are connected by a reactions in which
  two molecules are covalently bonded together
  through the loss of a water molecule
• This reaction is called a condensation reaction
  or a dehydration reaction

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Breaking Down a Polymer

• Polymers are disassembled by a reaction that is
  the reverse of dehydration
• Hydrolysis (from Greek break with water) Bonds
  between monomers are broken by the addition of
  water molecules, a hydrogen attaching to one
  monomer and a hydroxyl attaching to the other.

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Variety of Polymers

• Every cell has thousands of varieties of
  macromolecules
• These molecules are constructed from only 40 to
  50 common monomers
• Analogy 26 letters of the alphabet can be
  combined to form millions of words
• Shortcoming macromolecules are much longer than
  the average word and they can be branched or 3D.

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Carbohydrates

• Sugars and their polymers
• Simplest monosaccharides (simple/single sugars)
  have the empirical molecular formula of CH2O
• Glucose C6H12O6 is the most common
  monosaccharide
• Can exist in linear or ring form

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Carbohydrate Polymers

• Disaccharides or double sugars consist of 2
  monosaccharides covalently bonded together by a
  glycosidic linkage which forms by dehydration
  synthesis

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Polysaccharides

• Polysaccharides are macromolecules, polymers with
  a few hundred to a few thousand monomers
• Functions
• storage, hydrolyzed to provide sugar for the cell
• Building materials for structures within the cell
• Function is determined by its sugar monomers and
  the position of the glycosidic linkages

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Storage Polysaccharides

• Starch found in plants (organelle plastids),
  made of entirely glucose monomers joined by a 1-4
  glycosidic linkage. Bond angles make the
  molecule helical
• Amylose simplest unbranched form
• Amylopectin more complex, branched form

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Storage Polysaccharides

• Glycogen found in animals, stored in liver and
  muscle cells. Extensively branched
• In humans, glycogen banks do not last longer than
  a day

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Structure Polysaccharides

• Cellulose major component of plant cell walls
• Plants produce 1011 ton of cellulose per year
• Cellulose is a polymer of glucose, however it
  uses the ß form, which gives it a different 3D
  shape
• Forms straight unbranched chains

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Cellulose

• Because of the different structure, very few
  organisms have the enzymes necessary to break
  down cellulose
• Makes it a very strong and resistantinsoluble
  fiber

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Chitin

• Carbohydrate used by arthropods (insects,
  spiders, crustaceans, and related animals) to
  build their exoskeletons
• Also used for cell walls in fungi
• Feels leathery and can become hardened when
  encrusted with calcium carbonate (shells)
• Similar to cellulose molecules except the
  glucose has a nitrogen-containing side group

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Lipids

• Not polymers
• Hydrophobic-- have little to no affinity to water
• Consist mostly of hydrocarbons
• Include waxes, certain pigments, oils, fats,
  phospholipids, and steroids

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Fats

• Not polymers, but they are large molecules
  assembled from smaller molecules by dehydration
  synthesis
• Fats or triacylglycerides (TAGs) are made from a
  glycerol (a small 3C alcohol) and 3 fatty acids
  (a long carbon skeleton usually 16-18C long
  with a carboxyl end) joined by ester bonds.
  Fatty acids can be the same, or they can all be
  different

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Types of Fats

• Fatty acids differ in length and the number and
  location of double bonds
• Saturated contains all single bonded fatty acids
  (saturated with Hs) . Found in animal fats.
  Solid at room temperature
• Unsaturated contains one or more double bond
  which creates kinks in the tails. Found in
  plant and fish oils. Liquid at room temperature.
  

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Functions of Fats

• Energy is stored in the C-H bonds? the less C-H
  bonds, the less energy stored in the molecule
• A gram of fat stores twice as much energy as a
  gram of polysaccharide
• Fats also work as insulators and cushions for
  organs

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Phospholipids

• Similar to fats except they only have 2 fatty
  acids. The third space is filled with a
  phosphate group.
• Phospholipids are ampipathetic because they have
  a negative head portion which is hydrophilic
  and nonpolar tail portion which is hydrophobic

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Phospholipids in Water

• When phospholipids are dropped into water, they
  form micelles or circles hiding their hydrophobic
  tails in the inside and their hydrophilic heads
  facing outward into the water.
• In cells, membranes of phospholipids form as a
  bilayer having the heads pointing out and into
  the cell (aqueous environments)

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Steroids

• Lipids characterized by a carbon skeleton made
  of 4 fused rings
• Steroids vary in the groups attached to these
  rings
• Cholesterol is a steroid which is a common
  component of animal cell membranes keeping them
  fluid
• Many hormones including human sex hormones, are
  made of steroids

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Proteins

• More than 50 of the dry weight of a cell is
  protein
• Used for structural support, storage, transport
  of other substances, signaling from one part of
  the org to another, movement, defense against
  foreign substances, and enzymes
• Humans have tens of thousands of different
  proteins
• Most structurally sophisticated moleculeshas a
  unique 3D shape or conformation
• All made from 20 amino acids
• Polymers of amino acids are polypeptides, A
  protein consists of one or more polypeptides
  folded and coiled into specific conformations

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Protein Functions
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Polypeptides

• Amino acids have carboxyl and amino groups
• R groups or side chains make each of the 20 amino
  acids different
• Physical and chemical properties of the R group
  will determine the unique characteristics of a
  particlar amino acid (hydrophilic, hydrophobic,
  etc)
• Amino acids are bonded together by the
  dehydration synthesis to form a peptide bond

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Amino Acids
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Protein Structure/Conformation

• A proteins specific conformation determines its
  function
• Four Levels of Structure Overview
• Primary Order of amino acids in a polypeptide
  chain
• Secondary Interactions between the amino acid
  backbones
• Tertiary Interactions between the R groups
• Quaternary Interactions between 2 or more folded
  polypeptide chains
• Proteins fold spontaneous

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Primary Structure

• A unique sequence of amino acids in a long
  polypeptide chain
• Any changes in primary structure can affect a
  proteins conformation and its ability to
  function
• Example Sickle cell anemia

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Secondary Structure

• Segments of the polypeptide strand repeatedly
  coil or fold in a pattern which contributes to
  the overall conformation
• Made by hydrogen bonds between the backbone of
  the amino acids (amino group and carboxyl
  groups)
• Structures formed include
• a-helices area with a helical or spiral shape.
  Held together by H bonds between every 4th amino
  acid
• ß-pleated sheets area where 2 or more regions of
  the polypeptide chain lay parallel

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Tertiary Structure

• Made of irregular contortions from interactions
  between side chains (R groups)
• Hydrogen Bonds between polar side groups
• Ionic Bonds between positively and negatively
  charged side chains
• Hydrophobic Interactions nonpolar side chains
  end up on the inside of a protein, away from
  watercaused by water excluding these side
  chains from H bond interactions. Once together,
  held in place by van der Waals
• Disulfide Bridges strong covalent bonds between
  cytosines sulfhydryl (-SH) groups

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Quaternary Structure

• The overall protein structure that results from
  the aggregation of 2 or more polypeptide subunits

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Denaturation

• Protein conformation depends on the physical and
  chemical conditions of the proteins environment
• pH, salt concentraion, temperature, and other
  aspects of the environment (aqueous or organic
  solvent) can unravel or change the conformation
  of the protein.
• Change in protein shape, causes it to lose its
  function
• Some proteins can Renature and reform their
  conformation, other cannot.

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Chaperonins

• Proteins go through intermediate states before
  they are in a stable conformation.
• This is assisted by Chaperonins, protein
  molecules that assist in the proper folding of
  other proteins.
• They work by keeping folding proteins away from
  bad influences in the cytoplasm while they fold

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Review The Four Levels of Protein Folding
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Nucleic Acids

• 2 Types
• Deoxyribonucleic Acid (DNA)
• Ribonucleic Acid (RNA)
• Function store and transmit inheritance
  information
• Info flows from DNA?RNA?Proteins
• Polymer of nucleotides or polynucleotide joined
  by phosphodiester bonds (phosphate to sugar)

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Nucleotides

• Monomers of Nucleic Acids
• Made of 3 parts
• 5 Carbon Sugar (Pentose)
• Ribose or Deoxyribose
• Phosphate group
• Nitrogenous Base
• Purines (A and G) (6 membered ring of C and N
  fused to a 5 membered ring)
• Pyrimidines (C, T, and U) (6 membered ring)
• Sequence of bases is unique to each gene

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DNA

• Genetic material inherited from parents
• Very long
• Consists of hundreds-thousands of genes
• Contains the information that programs all the
  cells activities.
• DNA is read by proteins and translated into
  proteins.
• Double stranded helix
• Only certain bases are compatible for bonding
  together, Adenine with Thymine (A-T) and Cytosine
  with Guanine (C-G)
• Has the ability to copy itself

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RNA

• Messenger RNA (mRNA) conveys the DNA code out of
  the nucleus to the cytoplasm (ribosome)
• Single stranded

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Molecular Clocks

• Linear sequences of nucleotides in DNA are passed
  from parent to offspring. DNA determines the
  amino acid sequences in proteins
• Siblings have DNA that is more alike than an
  unrelated person
• 2 species should have similar DNA if they are
  closely related based on fossil and anatomical
  evidence
• The more differences in the DNA codes, the longer
  the time the two species have evolved separately.