Download 3.3 What Are Carbohydrates?

Chapter 3
Biological Molecules
Lecture Outlines by Gregory Ahearn,
University of North Florida
Copyright © 2011 Pearson Education Inc.
Chapter 3 At a Glance
 3.1 Why Is Carbon So Important in Biological
Molecules?
 3.2 How Are Organic Molecules Synthesized?
 3.3 What Are Carbohydrates?
 3.4 What Are Lipids?
 3.5 What Are Proteins?
 3.6 What Are Nucleotides and Nucleic Acids?
Biology: Life on Earth, 9e
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3.1 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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3.1 Why Is Carbon So Important in Biological
Molecules?
 Organic/inorganic molecules and functional
groups (continued)
– The carbon atom is versatile because it has four
electrons in an outermost shell that can
accommodate eight electrons
– Therefore, a carbon atom can become stable by
forming up to four bonds (single, double, or
triple)
– As a result, organic molecules can assume
complex shapes, including branched chains,
rings, sheets, and helices
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3.1 Why Is Carbon So Important in Biological
Molecules?
 Functional groups in organic molecules
determine the characteristics and chemical
reactivity of the molecules
– Functional groups are less stable than the
carbon backbone and are more likely to
participate in chemical reactions
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Table 3-1
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3.2 How Are Organic Molecules Synthesized?
– Small organic molecules (called monomers) are
joined to form longer molecules (called
polymers)
– Biomolecules are joined or broken through
dehydration synthesis or hydrolysis
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3.2 How Are Organic Molecules Synthesized?
 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 (H2O)
 The openings in the outer electron shells of the
two subunits are filled when the two subunits
share electrons, creating a covalent bond
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Author Animation: Monomers and Polymers
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Dehydration Synthesis

dehydration
synthesis

Fig. 3-1
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3.2 How Are Organic Molecules Synthesized?
 Polymers are broken apart through hydrolysis
(“water cutting”)
– Water is broken into H and OH and is used to
break the bond between monomers
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Author Animation: Hydrolysis
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Hydrolysis
hydrolysis

Fig. 3-2
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3.2 How Are Organic Molecules Synthesized?
 All biological molecules fall into one of four
categories
– Carbohydrates
– Lipids
– Proteins
– Nucleotides/nucleic acids
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Table 3-2 (1 of 2)
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Table 3-2 (2 of 2)
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3.3 What Are Carbohydrates?
 Carbohydrate molecules are composed of C,
H, and O in the ratio of 1:2:1
– If a carbohydrate consists of just one sugar
molecule, it is a monosaccharide
– Two linked monosaccharides form a
disaccharide
– A polymer of many monosaccharides is a
polysaccharide
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3.3 What Are Carbohydrates?
 Carbohydrates are important energy sources for
most organisms
 Most small carbohydrates are water-soluble due
to the polar OH functional group
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3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures
– The basic monosaccharide structure is:
– A backbone of 3–7 carbon atoms
– Most of the carbon atoms have both a hydrogen (-H)
and an hydroxyl group (-OH) attached to them
– Most carbohydrates have the approximate chemical
formula (CH2O)n where “n” is the number of carbons in
the backbone
– When dissolved in the cytoplasmic fluid of a cell, the
carbon backbone usually forms a ring
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3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures (continued)
– Example monosaccharides
–Glucose (C6H12O6): the most common
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3.3 What Are Carbohydrates?
 Glucose (C6H12O6) is the most common
monosaccharide in living organisms
– Sugar dissolving in water
water
hydrogen
bond
hydroxyl
group
Fig. 3-3
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3.3 What Are Carbohydrates?
 Additional monosaccharides are:
– Fructose (“fruit sugar” found in fruits, corn syrup,
and honey)
– Galactose (“milk sugar” found in lactose)
– Ribose and deoxyribose (found in RNA and
DNA, respectively)
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Monosaccharides
6
6
5
2
5
4
3 1
fructose
4
1
3
2
galactose
Fig. 3-5
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Ribose Sugars
5
5
4
1
3
2
ribose
4
1
3
2
Note “missing”
oxygen atom
deoxyribose
Fig. 3-6
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3.3 What Are Carbohydrates?
 There are several monosaccharides with slightly
different structures (continued)
– The fate of monosaccharides inside a cell is:
–Some are broken down to free their chemical
energy
–Some are linked together by dehydration
synthesis
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3.3 What Are Carbohydrates?
 Disaccharides consist of two monosaccharides
linked by dehydration synthesis
– Disaccharides are two-part sugars
–They are used for short-term energy storage
–When energy is required, they are broken
apart into their monosaccharide subunits by
hydroysis
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Synthesis of a Disaccharide
glucose
sucrose
fructose
•
dehydration
synthesis
•
Fig. 3-7
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3.3 What Are Carbohydrates?
 Examples of disaccharides include:
– Sucrose (table sugar) = glucose + fructose
– Lactose (milk sugar) = glucose + galactose
– Maltose (malt sugar) = glucose + glucose
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3.3 What Are Carbohydrates?
 Polysaccharides are chains of simple sugars
– 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
– Both starch and glycogen are polymers of
glucose molecules
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Starch is an Energy-Storing Plant Polysaccharide
starch grains
(a) Potato cells
(b) A starch molecule
(c) Detail of a starch molecule
Fig. 3-8
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3.3 What Are Carbohydrates?
 Polysaccharides are chains of simple sugars
(continued)
– Many organisms use polysaccharides as a
structural material
– Cellulose (a polymer of glucose) is one of the
most important structural polysaccharides
–It is found in the cell walls of plants
–It is indigestible for most animals due to the
orientation of the bonds between glucose
molecules
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Author Animation: Carbohydrate Structure and
Function
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Cellulose Structure and Function
Fig. 3-9
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3.3 What Are Carbohydrates?
 Polysaccharides are chains of simple sugars
(continued)
– Chitin (a polymer of modified glucose units) is
found in:
–The outer coverings of insects, crabs, and
spiders
–The cell walls of many fungi
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Chitin: A Unique Polysaccharide
Fig. 3-10
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3.4 What Are Lipids?
 Lipids are a diverse group of molecules that
contain regions composed almost entirely of
hydrogen and carbon
– All lipids contain large chains of nonpolar
hydrocarbons
– Most lipids are therefore hydrophobic and water
insoluble
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Author Animation: Lipids
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3.4 What Are Lipids?
 Lipids are diverse in structure and serve a
variety of functions
– They are used for energy storage
– They form waterproof coverings on plant and
animal bodies
– They serve as the primary component of cellular
membranes
– Still others are hormones
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Lipids in Nature: Fat
Fig. 3-11a
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3.4 What Are Lipids?
 Lipids are classified into three major groups
– Oils, fats, and waxes
– Phospholipids
– Steroids containing rings of carbon, hydrogen,
and oxygen
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3.4 What Are Lipids?
 Oils, fats, and waxes
– Oils, fats, and waxes are 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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Synthesis of a Triglyceride

glycerol

fatty acids
triglyceride
Fig. 3-12
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3.4 What Are Lipids?
 Oils, fats, and waxes (continued)
– Fats that are solid at room temperature are
saturated (the carbon chain has as many
hydrogen atoms as possible, and mostly or all CC bonds); for example, beef fat
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A Fat
Fig. 3-13a
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3.4 What Are Lipids?
 Oils, fats, and waxes (continued)
– Fats that are liquid at room temperature are
unsaturated (with fewer hydrogen atoms, and
many C=C bonds); for example, corn oil
–Unsaturated trans fats have been linked to
heart disease
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Author Animation: Triglycerides
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An Oil
Fig. 3-13b
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3.4 What Are Lipids?
 Oils, fats, and waxes (continued)
– Waxes are highly saturated and solid at room
temperature
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3.4 What Are Lipids?
 Oils, fats, and waxes (continued)
– Waxes form waterproof coatings such as on:
–Leaves and stems in plants
–Fur in mammals
–Insect exoskeletons
– Waxes are also used to build honeycomb
structures
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Lipids in Nature: Wax
Fig. 3-11b
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3.4 What Are Lipids?
 Phospholipids
– These form plasma membranes around all cells
– Phospholipids consist of two fatty acids +
glycerol + a short polar functional group
– They have hydrophobic and hydrophilic portions
–The polar functional groups form the “head”
and are water-soluble
–The nonpolar fatty acids form the “tails” and
are water insoluble
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Author Animation: Phospholipids
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Phospholipids
variable
functional phosphate
group
group
polar head
(hydrophilic)
glycerol
backbone
fatty acid tails
(hydrophobic)
Fig. 3-14
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3.4 What Are Lipids?
 Steroids
– Steroids are composed of four carbon rings
fused together with various functional groups
protruding from them
– Examples of steroids include:
–Cholesterol
–Found in the membranes of animal cells
–Male and female sex hormones
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Author Animation: Steroids
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Steroids
Fig. 3-15
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3.5 What Are Proteins?
 Functions of proteins
– Proteins have a variety of functions
–Enzymes are proteins that promote chemical
reactions
–Structural proteins (e.g., elastin) provide
support
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Structural Proteins
Fig. 3-16
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3.5 What Are Proteins?
 Proteins are formed from chains 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
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Amino Acid Structure
variable
group
amino
group
carboxylic
acid group
hydrogen
Fig. 3-17
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Amino Acid Diversity
glutamic acid (glu)
aspartic acid (asp)
(a) Hydrophilic functional groups
phenylalanine (phe)
leucine (leu)
(b) Hydrophobic functional groups
cysteine (cys)
(c) Sulfur-containing
functional group
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Fig. 3-18
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3.5 What Are Proteins?
 The sequence of amino acids in a protein
dictates its function
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3.5 What Are Proteins?
 Amino acids are joined to form chains by
dehydration synthesis
– An amino group reacts with a carboxyl group,
and water is lost
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Protein Synthesis
amino acid
amino acid
dehydration
synthesis

•
amino
group
carboxylic acid
group
water
peptide
amino
group
peptide
bond
Fig. 3-19
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3.5 What Are Proteins?
 Amino acids are joined to form chains by
dehydration synthesis (continued)
– 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, or just proteins
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3.5 What Are Proteins?
 Proteins exhibit up to four levels of structure
– Primary structure is the sequence of amino
acids linked together in a protein
– Secondary structure is a helix, or a pleated
sheet
– 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
protein chains are linked together
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Author Animation: Protein Structure
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The Four Levels of Protein Structure
(b) Secondary structure:
Usually maintained by
hydrogen bonds, which
shape this helix
(a) Primary structure:
The sequence of amino acids
linked by peptide bonds
leu
val
heme group
lys
lys
gly
his
hydrogen
ala bond
lys
val
lys
helix
pro
(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
Fig. 3-20
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The Pleated Sheet: An Example of Secondary
Structure
hydrogen
bond
pleated sheet
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Fig. 3-21
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3.5 What Are 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
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3.6 What Are Nucleic Acids?
 Nucleotides act as energy carriers and
intracellular messengers
– Nucleotides are the monomers of nucleic acid
chains
– All nucleotides are made of three parts:
–Phosphate group
–Five-carbon sugar
–Nitrogen-containing base
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Deoxyribose Nucleotide
phosphate
base
sugar
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Fig. 3-22
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3.6 What Are Nucleic Acids?
 Nucleotides act as energy carriers and
intracellular messengers (continued)
– Adenosine triphosphate (ATP) is a
deoxyribose nucleotide with three phosphate
functional groups
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The Energy-Carrier Molecule Adenosine
Triphosphate (ATP)
Fig. 3-23
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3.6 What Are Nucleic Acids?
 DNA and RNA, the molecules of heredity, are
nucleic acids
– There are two types of polymers of nucleic
acids
–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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3.6 What Are Nucleic Acids?
 Each DNA molecule consists of two chains of
nucleotides that form a double helix linked by
hydrogen bonds
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Deoxyribonucleic Acid
hydrogen
bond
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Fig. 3-24
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