Macromolecules

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Macromolecules

• Large organic molecules of
• 100,000 Daltons or more

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Four Classes

• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids

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Construction

• Subunit of any macromolecule is called a monomer
• There are approximately 50 common monomers
• Two monomers combine to form a dimer
• Several monomers combine to form a polymer
• A polymer consists of many similar or identical
  subunits linked together, like beads on a
  string
• Monomers link together by a process called
  condensation synthesis (water is released)
• Polymers break apart by a process called
  hydrolysis (water is added)

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The synthesis and breakdown of polymers
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Carbohydrates

• Most abundant class of macromolecules
• Contain carbon, hydrogen, oxygen (C,H,O)

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Monosaccharides

• Monosaccharide single sugar
• Contain 3 to 6 carbon atoms
• Most common and arguably most important is
  glucose (C6H12O6), usually ringed, linear in
  solution

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Some monosaccharides
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Linear and ring forms of glucose
(b) Abbreviated ring structure. Each corner
represents a carbon. The rings
thicker edge indicates that you are
looking at the ring edge-on the components
attached to the ring lie above or
below the plane of the ring.
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Glucose Function

• Glucose is the major energy supply for cells
• In the process of respiration, glucose is broken
  down to allow for ATP production
• ATP (adenosine triphosphate) is the fuel for the
  cell
• Most of the process of respiration occurs in a
  cellular organelle called the mitochondrion
• Other examples of monosaccharides include ribose
  and fructose

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Disaccharides

• Disaccharide two sugars
• The bond that links two sugars together is called
  glycosidic
• Maltose - 2 glucose molecules linked together
  (malt sugar)
• Lactose - a glucose and galactose linked together
  (milk sugar)
• Sucrose - a glucose and fructose linked together
  (table sugar, cane sugar)

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Examples of disaccharide synthesis
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Polysaccharides

• Polysaccharide many sugar
• These have two main functions, storage and
  structure
• Storage molecules include starch and glycogen
• Starch (amylose) is a storage form of glucose
  that occurs in plants
• It is a mostly linear polymer of glucose and
  linkage is between the 1 and 4 carbons of
  neighboring a-glucose molecules
• Humans are able to digest starch (enzyme is
  amylase)
• Glycogen is a storage form of glucose that occurs
  in animal liver and muscle cells
• It is a branched polymer of glucose

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Structural Polysaccharides

• Chitin is a structural component of arthropod
  exoskeletons
• Cellulose is the major structural material of
  which plants are made
• Cellulose is probably the single most abundant
  organic molecule in the biosphere, comprising
  over 50 of the organic matter in the world
• Wood is largely cellulose while cotton and paper
  are almost pure cellulose
• It is a linear polymer of glucose, but this time
  the linkage is between the 1 and 4 carbons of
  b-glucose
• This single difference results in humans (and
  most organisms) being unable to digest cellulose
• Cows and termites rely on bacteria in their guts
  to break down the cellulose

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Starch vs. Cellulose

• The top molecule is starch, the bottom is
  cellulose
• Notice the orientation of the linkages (in red)
• This difference is due to the a and b
  designation for glucose

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Starch and cellulose structures
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Chitin, a structural polysaccharide
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Lipids

• Very diverse group
• Some members are not quite 100,000 Daltons in
  size
• All lipids are hydrophobic (i.e. little or no
  affinity for water)
• Hydrophobicity is the single common trait of the
  group

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Fats

• Fats are polymers of glycerol and 3 fatty acids,
  and are sometimes called triacylglycerides
• Main function is energy storage, storing 2X more
  energy per gram than carbohydrates
• Most fats from animal sources are saturated, (all
  the bonds are single), and solidify at room
  temperature (lard, butter)
• Fats from plant sources are generally unsaturated
  (contain at least one double or triple bond), and
  are liquid at room temperature (corn oil, canola
  oil)
• For health reasons, it is best to avoid saturated
  fats and hydrogenated fats (trans fats)
• Fats are hydrogenated for increased shelf life

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The synthesis and structure of a fat, or
triacylglycerol
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Phospholipids

• Phosphate group replaces one of the fatty acids,
  so glycerol connects to two fatty acids and one
  phosphate
• Phospholipids are amphipathic
• The fatty acid portion is hydrophobic and the
  phosphate portion is hydrophilic
• Phospholipids make up the cell membrane bilayer

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The structure of a phospholipid
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Phospholipid bilayer
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Proteins

• This class of macromolecules makes up more than
  50 of the dry weight of most cells
• Proteins are important in nearly ALL cellular
  processes
• Contain carbon, hydrogen, oxygen, nitrogen,
  sulfur (C,H,O,N,S)
• Functions include support, transport,
  coordination of cell and body activities, cell
  recognition, stimulus receptors, muscle
  contraction, acceleration of chemical reactions
  (enzymes)
• Subunits are the 20 amino acids

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Amino Acids

• The general amino acid
• Notice the two functional groups, amine and
  carboxylic acid
• Amino acids link by peptide bonds that occur
  between amino group of one aa and the carboxylic
  acid of the next
• Dipeptide two aa linked
• Polypeptide many aa linked together

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Four Levels of Protein Organization

• Primary Structure the sequence of amino acids
• Secondary Structure the uniform, predictable
  folding or coiling due to hydrogen bonding,
  shapes include a-helix and b-sheet
• Tertiary Structure the irregular, unpredictable
  folding due to the bonding between R groups
  and/or between sulfide groups
• The activity (effectiveness) of a protein is due
  in large part to the tertiary structure
• When a protein is denatured, the tertiary
  structure is disrupted permanently and biological
  activity is lost
• Quaternary Structure combination of 2 or more
  polypeptide subunits (e.g., hemoglobin), not all
  proteins have quaternary structure

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Levels of protein structure
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Primary structure
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Secondary structure
? pleated sheet
H
O
H
H
Amino acidsubunits
C
C
N
N
N
C
C
C
R
O
H
C
C
R
R
H
H
C
C
H
C
R
O
C
C
O
O
C
N
H
N
H
C
C
R
H
R
H
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Abdominal glands of the spider secrete silk
fibers that form the web
The radiating strands, made of dry silk fibers
maintained the shape of the web
The spiral strands (capture strands) are elastic,
stretching in response to wind, rain, and the
touch of insects
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Tertiary structure
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Quaternary Structure
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Making a polypeptide
Carboxyl end(C-terminus)
(b)
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An Overview of Protein Functions
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A chaperonin in action
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Enzymes

• Essentially all reactions in living systems
  require enzymes
• All enzymes are proteins
• Enzymes are biological catalysts, meaning they
  provide the conditions that allow for reactions
  to occur much faster than they normally would
• The enzyme itself is not used up in the reaction
• Enzymes are substrate-specific, meaning they only
  act on certain molecules (e.g., amylase acts on
  starch but not cellulose)
• When the substrate binds to the enzyme at the
  active site of the enzyme, the substrate becomes
  more reactive
• The activation energy is lowered, making the
  reaction occur more quickly

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The catalytic cycle of an enzyme
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Proteins Nucleic Acids

• The amino acid sequence determines the folding
  and therefore the activity of a protein
• Proteins are responsible for nearly ALL cell
  processes (e.g., enzymes catalyze all chemical
  reactions)
• What determines the amino acid sequence?
• Genetic material, genes, DNA

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Nucleic Acids

• DNA is deoxyribonucleic acid
• RNA is ribonucleic acid
• DNA is the primary component of chromosomes
• DNA is found in the nucleus, mitochondria and
  chloroplasts
• RNA is located in the nucleus and at the
  ribosomes
• Relationship between proteins and nucleic acids
• DNA gt mRNA gt tRNA rRNA ribosome gt protein
• Some DNA functions to provide the blueprint for
  protein structure
• Much genomic DNA has still unknown function

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Nucleic Acid Structure

• Nucleoside pentose nitrogenous base
• Pentose 5 carbon sugar, deoxyribose in DNA and
  ribose in RNA
• Nitrogenous bases adenine, thymine, guanine,
  cytosine (A,T,G,C)
• Nucleotide pentose base phosphate
• Nucleic Acid many nucleotides linked together
  by phosphodiester bonds
• DNA is a double helix
• RNA is a single helix

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The components of nucleic acids
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DNA ? RNA ? protein
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Sickle-cell disease
Exposed hydrophobic region