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Chapter 5 Notes
The Structure and Function of Large
Biological Molecules
Objectives
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List the four major classes of macromolecules.
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Distinguish between monomers and polymers.
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Distinguish between a protein and a polypeptide
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Distinguish between a monosaccharide, disaccharide
and polysaccharide.
Distinguish between saturated and unsaturated fats.
Macromolecules
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The critically important large molecules of all living things fall into just four main
classes: carbohydrates, lipids, proteins and nucleic acids
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Members of three of these classes huge and called macromolecules:
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- carbohydrates
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-proteins
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-nucleic acids
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Macromolecules are large molecules composed of smaller molecules
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They complex in their structures
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The macromolecules in these classes are chain-like molecules called polymers
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A polymer is a long molecule consisting of many similar or identical building blocks
linked by covalent bonds
The repeating units that are the building blocks of a polymer are smaller molecules
called monomers
The Synthesis and breakdown of polymers
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The chemical mechanisms by which cells make and
break down polymers are facilitated by enzymes
Enzymes are specialized macromolecules that speed
up chemical reactions
Monomers are connected by a dehydration reactionloss of a water molecule
Polymers are disassembled to monomers by
hydrolysis-the reverse of the dehydration reaction
The Diversity of Polymers
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Each cell has thousands of different
macromolecules; the collection varies from one
type of cell to another even in the same
organism
The differences between human siblings reflect
small variations in polymers, particularly DNA
and proteins
The diversity of macromolecules in the living
world is vast, and the possible variety is
effectively limitless
Carbohydrates
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Carbohydrates include both sugars and
polymers of sugars
The simplest carbohydrates are the
monosaccharides, or simple sugars
Monosaccharides:
– Are the simplest sugars
– Can be used for fuel
– Can be converted into other organic molecules
– Can be combined into polymers
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Polysaccharides are macromolecules, polymers with a
few hundred to a few thousand monosaccharides joined by
glycosidic linkages
Some polysaccharides serve as storage material, others
serve as building material for structures that protect the
cell or the whole organism
Both plants and animals store sugars for later use in the
form of storage polysaccharides
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Plants store glucose as starch
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Animals store glucose as glycogen
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Cellulose is the major component of the tough walls that
enclose plant cells
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Chitin, another important structural
polysaccharide is found in the
exoskeleton of arthropods
– can be used as surgical thread
Lipids
•Lipids are a diverse group of hydrophobic molecules
•Lipids are the one class of large biological molecules
that do not consist of polymers
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Lipids are varied in form and function
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The most biologically important types of lipids:
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-fats-constructed from two kinds of smaller
molecules: glycerol and fatty acids
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-phospholipids
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-steroids
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Fatty acids vary in the length and number
and locations of double bonds they contain
– saturated fats have only C-C bonds in fatty acid
tails; solid at room temperature
– unsaturated fats have one or more double bond in
fatty acid tails; liquid at room temperature
Phospholipids
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Cells could not exist without another type of
lipid-phospholipids
Phospholipids are essential for cells because
they make up cell membranes
Phospholipids are diglycerides with a
phosphate group attached to glycerol backbone
– phosphate group is negatively charged
• polar and hydrophilic
– fatty acid tails are non-polar and hydrophobic
Bilateral structure formed by self-assembly of
phospholipids in an aqueous environment
Steroids
• Are lipids characterized by a carbon skeleton
consisting of four fused rings
- Found in cell membranes
- Is a precursor for some hormones
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Cholesterol is a component of animal cell
membranes and can be modified to form sex
hormones.
Proteins
• Proteins have many structures, resulting in a wide range of
functions inside the cell.
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Proteins account for more than 50% of the dry mass of most
cells, and they are instrumental in almost everything organisms
do
Protein functions:
– Structural support
– Speed up chemical reactions
– Storage
– Defense
– Transport
– Cellular communication
Polypeptides
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Diverse as proteins are, they are all unbranched
polymers constructed from the same set of 20
amino acids
Polymers of amino acids are called
polypeptides
A protein consists of one or more polypeptides
An amino acid is an organic molecule
possessing an amino group, a carboxyl group, a
hydrogen atom and a variable group
symbolized by R (side chain)
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The chemical properties of the “R” groups
determine the chemical properties of the
amino acids
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The “R” groups differs with each amino acid
Protein Structure and Function
•A protein’s specific conformation determines how it
functions
Four levels of Protein Structure
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All proteins share three superimposed levels of
structure, known as primary, secondary, and tertiary
structure
A fourth level, quaternary structure, arises when a
protein consists of two or more polypeptide chains
Primary Structure
Sickle Cell Anemia
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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
Nucleic Acids
• Store and transmit hereditary information
• Genes
– are the units of inheritance for the amino acid sequence
of polypeptides
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Genes consist of DNA which belongs to the class of
compounds called nucleic acids
Nucleic Acids are polymers made of monomers called
nucleotides
The two types of nucleic acids, deoxyribonucleic
acid(DNA) and ribonucleic acid (RNA)