Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
BIOLOGICAL MOLECULES Chapter 3
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Why Is Carbon So Important in Biological Molecules?
Organic/inorganic molecules and functional groups Organic refers to
molecules containing a carbon skeleton bonded to hydrogen atoms
Inorganic refers to carbon dioxide and all molecules without
carbon
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Why Is Carbon So Important in Biological Molecules? The carbon atom
is key Is versatile because it has four electrons in the outer
shell Is stable by forming up to four bonds single, double, or
triple covalent Result organic molecules can assume complex shapes:
branched chains, rings, sheets, and helices Functional groups in
organic molecules Are less stable than the carbon backbone and are
more likely to participate in chemical reactions Determine the
characteristics and chemical reactivity of organic molecules
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Table 3-1
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Dehydration Synthesis Small organic molecules (called monomers) are
joined to form longer molecules (called polymers) Monomers are
joined together through dehydration synthesis, at the site where an
H + and an OH - are removed, resulting in the loss of a water
molecule (H 2 O) The openings in the outer electron shells of the
two subunits are filled when the two subunits share electrons,
creating a covalent bond dehydration synthesis
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Hydrolysis Polymers are broken apart through hydrolysis (water
cutting) Water is broken into H + and OH - and is used to break the
bond between monomers Digestive enzymes use to break down food
hydrolysis
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Biological Molecules The important organic molecules found in
living things: CarbohydratesLipidsProteinsNucleic Acids Sugar
FatEnzymesDeoxyribonucleic Starch Structural ProteinsRibonucleic
Acid Cellulose All contain Carbon, Hydrogen, and generally
Oxygen.
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Carbohydrates Carbohydrate molecules are composed of C, H, and O in
the ratio of 1:2:1 Monosaccharide - consists of just one sugar
molecule Disaccharide - Two linked monosaccharides Polysaccharide -
polymer of many monosaccharides
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Carbohydrates Hydrophilic due to the polar OH - functional group
Only mono- and disaccharides Functions: Energy source Combine with
other molecules through dehydration synthesis (plasma membrane,
cell wall, exoskeletons)
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Carbohydrates hydrogen bond hydroxyl group water There are several
monosaccharides with slightly different structures The basic
monosaccharide structure is: A backbone of 37 carbon atoms Most of
the carbon atoms have both a hydrogen (-H) and an hydroxyl group
(-OH) attached to them Chemical formula (CH 2 O) n
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Monosaccharides When dissolved in the cytoplasmic fluid of a cell,
the carbon backbone usually forms a ring Glucose (C 6 H 12 O 6 ) is
the most common monosaccharide in living organisms Fructose (fruit
sugar found in fruits, corn syrup, and honey) Galactose (milk sugar
found in lactose) Ribose and deoxyribose (found in RNA and DNA)
galactosefructose ribosedeoxyribose Note missing oxygen atom
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Disaccharides glucosefructose sucrose dehydration synthesis
Functions: They are used for short-term energy storage When energy
is required, they are broken apart by hydrolysis Examples: Sucrose
(table sugar) = glucose + fructose Lactose (milk sugar) = glucose +
galactose Maltose (malt sugar) = glucose + glucose
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Polysaccharides Storage polysaccharides include: Starch, an
energy-storage molecule in plants, formed in roots and seeds
Glycogen, an energy-storage molecule in animals, found in the liver
and muscles (b) A starch molecule (a) Potato cells (c) Detail of a
starch molecule starch grains
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Polysaccharides Polysaccharides as a structural material Cellulose
(a polymer of glucose) It is found in the cell walls of plants Most
abundant organic molecule on Earth It is indigestible for most
animals due to the orientation of the bonds between glucose
molecules
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Polysaccharides Chitin (a polymer of modified glucose units)
Nitrogen-containing functional group The outer coverings
(exoskeletons) of insects, crabs, and spiders The cell walls of
many fungi
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Review 1.What are carbohydrates used for? 2.What are the major
classes of carbohydrates? 3.What are the types and functions of
polysaccharides?
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Lipids are a diverse group of molecules that contain regions
composed almost entirely of hydrogen and carbon All lipids contain
large chains of non-polar hydrocarbons hydrophobic
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Lipids are diverse in structure and serve a variety of
functions: energy storage waterproof coverings on plant and animal
bodies primary component of cellular membranes hormones Lipids are
classified into three major groups 1.Oils, fats, and waxes
2.Phospholipids 3.Steroids
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Oils, fats, and waxes Carbon, hydrogen, oxygen Made of one
or more fatty acid subunits Fats and oils Are used primarily as
energy-storage molecules, containing twice as many calories per
gram as carbyhydrates and proteins Are formed by dehydration
synthesis Three fatty acids + glycerol triglyceride
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glycerolfatty acids triglyceride Synthesis of a Triglyceride Fig.
3-12 Dehydration synthesis
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Oils, fats, and waxes Fats are solid at room temperature are
saturated (the carbon chain has as many hydrogen atoms as possible,
and mostly or all C-C bonds); for example, beef fat Produced in
animals
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Oils, fats, and waxes Oils are liquid at room temperature
are unsaturated (with fewer hydrogen atoms, and many C=C bonds);
for example, corn oil Produced by plants Unsaturated trans fats
have been linked to heart disease
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Oils, fats, and waxes Waxes are similar to fats Most animals
dont have the enzymes to break them down. Functions: form
waterproof coatings such as on: Leaves and stems of land plants Fur
in mammals Insect exoskeletons used to build honeycomb
structures
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Phospholipids These form plasma membranes around all cells
Phospholipids consist of two fatty acids + glycerol + a short polar
functional group containing nitrogen Hydrophilic polar functional
groups form the head Hydrophobic non-polar fatty acids form the
tails polar head glycerol backbone phosphate group variable
functional group (hydrophilic) (hydrophobic) fatty acid tails
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Lipids Steroids Composed of four carbon rings fused together with
various functional groups protruding from them Examples:
Cholesterol (animal cell membranes) Male and female sex
hormones
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins Functions Enzymes are proteins that promote chemical
reactions Structural proteins (e.g., elastin, keratin) provide
support Hormones Antibodies Toxins
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins Polymers of amino acids joined by peptide bonds All amino
acids have a similar structure All contain amino and carboxyl
groups All have a variable R group Some R groups are hydrophobic
Some are hydrophilic Cysteine R groups can form disulfide bridges
amino group hydrogen variable group carboxylic acid group
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins The sequence of amino acids in a protein dictates its
function Amino acids are joined to form chains by dehydration
synthesis An amino group reacts with a carboxyl group, and water is
lost amino acid amino group amino group carboxylic acid group amino
acidpeptide water peptide bond dehydration synthesis
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins Amino acids are joined to form chains by dehydration
synthesis The covalent bond resulting after the water is lost is a
peptide bond, and the resulting chain of two amino acids is called
a peptide Long chains of amino acids are known as polypeptides
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins Proteins exhibit up to four levels of structure Primary
structure is the sequence of amino acids Secondary structure is a
helix, or a pleated sheet Repeating structure with hydrogen bonds
Tertiary structure refers to complex foldings of the protein chain
held together by disulfide bridges, hydrophobic/hydrophilic
interactions, and other bonds Quaternary structure occurs where
multiple polypeptides are linked together
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
The Four Levels of Protein Structure Fig. 3-21 (a) Primary
structure: The sequence of amino acids linked by peptide bonds (c)
Tertiary structure: Folding of the helix results from hydrogen
bonds with surrounding water molecules and disulfide bridges
between cysteine amino acids (d) Quaternary structure: Individual
polypeptides are linked to one another by hydrogen bonds or
disulfide bridges (b) Secondary structure: Usually maintained by
hydrogen bonds, which shape this helix helix hydrogen bond heme
group leu val lys gly his ala lys val lys pro
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Proteins The functions of proteins are linked to their three-
dimensional structures Precise positioning of amino acid R groups
leads to bonds that determine secondary and tertiary structure
Disruption of secondary and tertiary bonds leads to denatured
proteins and loss of function Extreme heat Extreme changes in pH UV
radiation
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
sugar phosphate base Nucleotides and Nucleic Acids Nucleotides act
as energy carriers and intracellular messengers Nucleotides are the
monomers of nucleic acid chains Three parts: Phosphate group
Five-carbon sugar Nitrogen-containing base Deoxyribose
Nucleotide
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Nucleotides and Nucleic Acids Nucleotides act as energy carriers
Adenosine triphosphate (ATP) is a ribose nucleotide with three
phosphate functional groups ADP and cAMP NAD and FAD: electron
carriers
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
Nucleic Acids DNA and RNA, the molecules of heredity Polymers of
nucleotides DNA (deoxyribonucleic acid) is found in chromosomes and
carries genetic information needed for protein construction RNA
(ribonucleic acid) makes copies of DNA and is used directly in the
synthesis of proteins
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hydrogen bond Nucleic Acids Each DNA molecule consists of two
chains of millions of nucleotides that form a double helix linked
by hydrogen bonds
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Copyright 2011 Pearson Education Inc.Biology: Life on Earth, 9e
The Pleated Sheet: An Example of Secondary Structure Fig. 3-21
pleated sheet hydrogen bond