The Structure and Function of Macromolecules

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The Structure and Function of Macromolecules
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II. Classes of Organic Molecules

• What are the four classes of organic molecules?
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

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A. Carbohydrates

• Sugars
• Carbo carbon, hydrate water carbohydrates
  have the molecular formula (CH2O)n
• Functions
• Store energy in chemical bonds
• Glucose is the most common monosaccharide
• Glucose is produced by photosynthetic autotrophs

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1. Structure of Monosaccharides

• An OH group is attached to each carbon except
  one, which is double bonded to an oxygen
  (carbonyl).

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• Classified according to the size of their carbon
  chains, varies from 3 to 7 carbons.

Triose 3 carbons
Pentose 5 carbons
Hexose 6 carbons
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• In aqueous solutions many monosaccharides form
  rings

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2. Structure of Disaccharides

• Double sugar that consists of 2 monosaccharides,
  joined by a glycosidic linkage.
• What reaction forms the glycosidic linkage?
• Condensation synthesis

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Examples of Disaccharides

• Lactose glucose galactose

Sucrose glucose fructose
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3. Polysaccharides

• Structure Polymers of a few hundred or a few
  thousand monosaccharides.
• Functions energy storage molecules or for
  structural support

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• Starch is a plant storage from of energy, easily
  hydrolyzed to glucose units
• Cellulose is a fiber-like structural material -
  tough and insoluble - used in plant cell walls
• Glycogen is a highly branched chain used by
  animals to store energy in muscles and the liver.
• Chitin is a polysaccharide used as a structural
  material in arthropod exoskeleton and fungal cell
  walls.

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B. Lipids

• Structure Greasy or oily nonpolar compounds
• Functions
• Energy storage
• membrane structure
• Protecting against desiccation (drying out)
• Insulating against cold
• Absorbing shocks
• Regulating cell activities by hormone actions

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1. Structure of Fatty Acids

• Long chains of mostly carbon and hydrogen atoms
  with a -COOH group at one end.
• When they are part of lipids, the fatty acids
  resemble long flexible tails.

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Saturated and Unsaturated Fats

• Unsaturated fats
• liquid at room temp
• one or more double bonds between carbons in the
  fatty acids allows for kinks in the tails
• most plant fats
• Saturated fats
• have only single C-C bonds in fatty acid tails
• solid at room temp
• most animal fats

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Saturated fatty acid
Unsaturated fatty acid
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2. Structure of Triglycerides

• Glycerol 3 fatty acids
• 3 ester linkages are formed between a hydroxyl
  group of the glycerol and a carboxyl group of the
  fatty acid.

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3. Phospholipids

• Structure Glycerol 2 fatty acids phosphate
  group.
• Function Main structural component of
  membranes, where they arrange in bilayers.

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Phospholipids in Water
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4. Waxes

• Function
• Lipids that serve as coatings for plant parts and
  as animal coverings.

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5. Steroids

• Structure Four carbon rings with no fatty acid
  tails
• Functions
• Component of animal cell membranes
• Modified to form sex hormones

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C. Proteins

• Structure
• Polypeptide chains
• Consist of peptide bonds between 20 possible
  amino acid monomers
• Have a 3 dimensional globular shape

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1. Functions of Proteins

• Enzymes which accelerate specific chemical
  reactions up to 10 billion times faster than they
  would spontaneously occur.
• Structural materials, including keratin (the
  protein found in hair and nails) and collagen
  (the protein found in connective tissue).

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• Specific binding, such as antibodies that bind
  specifically to foreign substances to identify
  them to the body's immune system.
• Specific carriers, including membrane transport
  proteins that move substances across cell
  membranes, and blood proteins, such as
  hemoglobin, that carry oxygen, iron, and other
  substances through the body.

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• Contraction, such as actin and myosin fibers that
  interact in muscle tissue.
• Signaling, including hormones such as insulin
  that regulate sugar levels in blood.

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2. Structure of Amino Acid Monomers

• Consist of an asymetric carbon covalently bonded
  to
• Hydrogen
• Amino group
• Carboxyl (acid) group
• Variable R group specific to each amino acid

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Properties of Amino Acids

• Grouped by polarity
• Variable R groups (side chains) confer different
  properties to each amino acid
• polar, water soluble.
• non-polar, water insoluble
• positively charged
• negatively charged.

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3. Primary Structure

• Unique sequence of amino acids in a protein
• Slight change in primary structure can alter
  function
• Determined by genes
• Condensation synthesis reactions form the peptide
  bonds between amino acids

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4. Secondary Structure

• Repeated folding of proteins polypeptide
  backbone
• stabilized by H bonds between peptide linkages in
  the proteins backbone
• 2 types, alpha helix, beta pleated sheets

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5. Tertiary Structure

• Irregular contortions of a protein due to bonding
  between R groups
• Weak bonds
• H bonding between polar side chains
• ionic bonding between charged side chains
• hydrophobic and van der Waals interactions
• Strong bonds
• disulfide bridges form strong covalent linkages

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5. Quaternary Structure

• Results from interactions among 2 or more
  polypeptides

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Factors That Determine Protein Conformation

• Occurs during protein synthesis within cell
• Depends on physical conditions of environment
• pH, temperature, salinity, etc.
• Change in environment may lead to denaturation of
  protein
• Denatured protein is biologically inactive
• Can renature if primary structure is not lost

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D. Nucleic Acids

• Two kinds
• DNA
• double stranded
• can self replicate
• makes up genes which code for proteins
• is passed from one generation to another
• RNA
• single stranded
• functions in actual synthesis of proteins coded
  for by DNA
• is made from the DNA template molecule

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1. Nucleotide Monomer Structure

• Both DNA and RNA are composed of nucleotide
  monomers.
• Nucleotide 5 carbon sugar, phosphate, and
  nitrogenous base

Deoxyribose in DNA
Ribose in RNA
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2. Building the Polymer

• Phosphate group of one nucleotide forms strong
  covalent bond with the 3 carbon of the sugar of
  the other nucleotide.

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3. Functions of Nucleotides

• Monomers for Nucleic Acids
• Transfer chemical energy from one molecule to
  another (e.g. ATP)

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• DNA
• Double helix
• 2 polynucleotide chains wound into the double
  helix
• Base pairing between chains with H bonds
• A - T
• C - G

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Summary of the Organic Molecules