1/29/2012
Work and Energy
Decoposition Reactions
• Energy - capacity to do work
– What is work?
• Potential energy- energy contained in an object
– chemical energy - potential energy in bonds of molecules
– free energy – potential energy available in a system to do useful work
• Kinetic energy - energy of motion; energy that is actively
doing work
– heat - kinetic energy of molecular motion
– electromagnetic energy – the kinetic energy of moving ‘packets’ of
radiation called photons
• Large molecule breaks
down into two or more
smaller ones
Starch molecule
AB  A + B
• Chemical reactions
Glucose molecules
2-1
(a) Decomposition reaction
Synthesis
Reactions
Exchange Reactions
• Two molecules exchange atoms or group of atoms
• AB+CD 
• Two or more small
molecules combine to
form a larger one
ABCD

AC + BD
Amino acids
AB + CD
A + B  AB
AC
C
A
D
B
C
A
D
B
C
A
D
B
+
Protein molecule
BD
(b) Synthesis reaction
Reversible Reactions
Reaction Rates
• Can be affected by:
– Concentration (more reactants = ?)
– Temperature (?)
• Can go in either direction under different
circumstances
• CO2 + H2O
H2CO3
2-4
(c) Exchange reaction
– catalysts - speed up reactions!
• Enzymes – most important biological catalysts
HCO3- + H+
• Law of mass action
– proceeds from the side of equation with greater quantity
of reactants to the side with the lesser quantity
• Equilibrium: when ratio of products to reactants is stable
reversible reax
2-5
2-6
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Oxidation-Reduction Reactions
Metabolism
• Oxidation
• All the chemical reactions of the body
– A molecule gives up electrons (or H+)
– The molecule is oxidized in this process
• Catabolism
– energy releasing (exergonic) decomposition reax
• produces smaller molecules
• Anabolism
• Reduction
– a molecule gains electrons (or H+)
– molecule is reduced when it accepts electrons
• oxidation-reduction (redox) reactions
– energy storing (endergonic) synthesis reax
– oxidation of one molecule is always accompanied by
the reduction of another
– Electrons are often transferred as H
• requires energy input
• production of protein or fat
• driven by energy that catabolism releases
2-7
2-8
Organic Molecules and
Carbon
Organic Compounds
• 4 valence electrons
– binds with other atoms that can provide it with four more
electrons to fill its valence shell
• 4 categories of carbon compounds
– carbohydrates
– lipids
– proteins
– Nucleotides & nucleic acids
• carbon atoms bind readily with each other –
carbon backbones
– forms long chains, branched molecules and rings
– forms covalent bonds with hydrogen, oxygen, nitrogen,
sulfur, and other elements
• carbon backbone carries a variety of functional
groups
2-9
2-10
Functional Groups
• small clusters of atoms
attached to carbon
backbone
Name and
Symbol
Hydroxyl
(—OH)
Structure
O
H
Sugars, alcohols
H
Fats, oils,
steroids,
amino acids
AKA ―condensation reaction‖
– A hydroxyl group is removed from one monomer
and a hydrogen from the next
H
Methyl
(—CH3)
C
H
• determines many of the
properties of organic
molecules
Dehydration Synthesis
Occurs in
O
Carboxyl
(—COOH)
Amino acids,
sugars, proteins
C
Dimer
O
H
Monomer 1
Monomer 2
H
Amino
(—NH2)
Amino acids,
proteins
N
H
OH
O
HO
H
H+ + OH–
O
Phosphate
(—H2PO4)
O
O
P
Nucleic acids, ATP
H2O
(a) Dehydration synthesis
O
H
Figure 2.15a
2-12
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Organic Molecules: Carbohydrates
Hydrolysis
• Splitting a polymer (lysis) by addition of a water molecule
– a covalent bond is broken
• All digestion reax consists of hydrolysis reactions
• hydrophilic organic molecule
• general formula
– (CH2O)n n = number of carbon atoms
– for glucose, n = 6, so formula is C6H12O6
Dimer
Monomer 1
Monomer 2
OH
O
H2O
HO
H+ + OH–
(b) Hydrolysis
Figure 2.15b
2-13
Monosaccharides
• Simplest carbohydrates
– simple sugars
Glucose
• composed of 2
monosaccharides
O
HO
• 3 important monosaccharides
– glucose, galactose and fructose
– same molecular formula - C6H12O6
• Isomers!
– produced by digestion of complex
carbohydrates
Disaccharides
CH2OH
H
Galactose
H
H
OH
H
H
OH
• 3 important disaccharides
– sucrose - table sugar
– lactose - sugar in milk
• glucose + galactose
– maltose - grain products
• glucose + glucose
CH2OH
H
H
H
OH
H
H
OH
OH
Fructose
O
HOCH2
H
OH
H
HO
OH
Figure 2.16
Sucrose
CH2OH
O
H
H
OH
H
H
H
HO
CH2OH
OH
OH
CH2OH
H
H
OH
O
HO
H
OH
OH
O
OH
H
H
H
H
H
H
OH
H
O
H
CH2OH
Maltose
CH2OH
CH2OH
O
H
H
OH
H
H
OH
O
H
O
HO
2-15
Polysaccharides
H
O
Lactose
H
CH2OH
CH2OH O
H
H
HO
OH
O
HO
2-14
H
OH
H
H
OH
OH
H
Figure 2.17
2-16
Carbohydrate Functions
• long chains of glucose
• quickly mobilized source of energy
• 3 polysaccharides of interest in humans
– Glycogen: energy storage in animals
• made in liver, muscles, brain, uterus, and vagina
– Starch: energy storage polysaccharide in plants
• only significant digestible polysaccharide in the
human diet
– all digested carbohydrates converted to glucose
– oxidized to make ATP
• Conjugated carbohydrate: bound to lipid or protein
– Glycolipids: cell membrane
– Glycoproteins: cell membrane
– proteoglycans (Carb. dominant & peptide/or protein)
• gels that hold cells and tissues together
– Cellulose: structural molecule of plant cell walls (fiber)
2-17
2-18
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Fatty Acids
Organic Molecules: Lipids
• Chain of 4 to 24 carbon atoms
• hydrophobic organic molecule
– composed of carbon, hydrogen and oxygen
– high ratio of hydrogen to oxygen
• More energy than carbs!
– carboxyl (acid) group on one end, methyl group on the other and
hydrogen bonded along the sides
• Classified
– saturated - carbon atoms saturated with hydrogen
– unsaturated - contains C=C bonds without hydrogen
– polyunsaturated – contains many C=C bonds
• Five primary types in humans
– fatty acids
– triglycerides
– phospholipids
– Eicosanoids (prostaglandins)
– steroids
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
O
C
H
HO
Palmitic acid (saturated)
CH3(CH2)14COOH
2-19
Lipids - Triglycerides
Figure 2.19
2-20
Phospholipids
• Formed by condensation of 1 glycerol and 3 fatty acids
Dehydration
Synthesis
• structural foundation
of cell membrane
– fatty acid ―tails‖
are hydrophobic
– phosphate ―head‖
is hydrophilic
CH3
N+
CH3
CH3
Nitrogencontaining
group
(choline)
CH2
CH2
O
–O
P
Phosphate
group
O
Hydrophilic region
(head)
O
CH2
O
O
C
(CH2)5
CH
CH
Glycerol
CH2
O
C
O
(CH2)12
Fatty acid
tails
CH3
Hydrophobic region
(tails)
CH
(CH2)5
CH3
(a)
(b)
2-36
Eicosanoids (prostaglandins)
• Chemical regulators
• produced in all tissues
– role in inflammation, blood clotting, hormone
action, labor contractions, blood vessel diameter
O
Steroids
• 3 6-C rings bonded to a 5-C ring
• Cholesterol –
• precurser from which other steroids are synthesized
– synthesized only by animals
• especially liver cells
– important component of cell membranes
– required for proper nervous system function
COOH
Figure 2.21
2-23
OH
2-24
OH
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1/29/2012
Organic Molecules: Proteins
Representative Amino Acids
Some nonpolar amino acids
Some polar amino acids
Methionine
• protein - a polymer of amino acids
H
Cysteine
H
H
N
• amino acid – central carbon with 3 attachments
C
H
– amino group (NH2), carboxyl group (COOH) and radical
group (R group)
CH2
CH2
S
C
H
CH3
OH
O
Tyrosine
H
SH
C
H
H
N
CH2
OH
H
C
O
OH
Arginine
H
H
N
• Essential A.A.s
CH2
C
C
O
• 20 amino acids differ only in functional (R) group
H
N
C
NH2+
(CH2)3
NH
O
OH
C
NH2
C
OH
(a)
• Note: they differ only in the R group
2-25
2-26
Structure of Proteins
Naming of Peptides
• peptide – molecule composed of two or more amino
acids joined by peptide bonds
Amino acids
– amino group of one A.A. bonds to carboxyl group of other A.A.
• dehydration synthesis/condensation
H
H
• Peptides named number
of amino acids
H
– dipeptides have 2
– tripeptides have 3
– oligopeptides < 15
– polypeptides > 15
– proteins have > 50
N
H
O
C
+
C
N
OH
R1
H
OH
C
Amino acid 2
Beta
sheet
C
C
C
N
C
C
Secondary structure
C
C
H
Folding and coiling
due to interactions
among R groups and
between R groups
and surrounding water
C
Alpha
helix
A dipeptide
O
Tertiary structure
C
C
R2
H
Sequence of amino
acids joined by
peptide bonds
O
H
Amino acid 1
Primary structure
Peptide
bonds
H
N
C
H
R2
C
O
+
C
H2O
Alpha helix or beta
sheet formed by
hydrogen bonding
C
Beta chain
Alpha
chain
C
C
C
Chain 1
H
R1
OH
Chain 2
Alpha
chain
Denature
Beta
chain
2-28
Peptide bond
Protein Functions
Quaternary structure
Association of two
or more polypeptide
chains with each
other
Heme
groups
Enzymes
• Structure
• communication (hormones/receptors)
• Membrane Transport
– channels in cell membranes
– carrier proteins on cell membranes
• Muscle activity
• Catalysts (enzymes)
• Enzymes - function as biological catalysts
– permit reactions to occur rapidly
• Substrate: substance an enzyme acts upon
• Products: result of chemical reax
• Naming Convention – ends in ―ase‖
• Lipase = enzyme digests Lipids
• Protease = digests proteins
• Deoxyribonuclease = digests ??
• Immunity/Protection (recognition/antibodies/clotting proteins)
• Movement (motor proteins) • Cell adhesion
2-29
2-30
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Enzymes and Activation Energy
Enzyme Structure and Action
• Substrate approaches active site on enzyme molecule
Free energy content
Activation
energy
Activation
energy
Net
energy
released
by
reaction
Energy level
of reactants
Net
energy
released
by
reaction
• Substrate binds to active site forming enzyme-substrate
complex
– highly specific fit – enzyme-substrate specificity
• Reaction products released
• Enzyme remains unchanged and is ready to repeat the
process
Energy level
of products
Time
(a) Reaction occurring without a catalyst
Time
(b) Reaction occurring with a catalyst
2-31
2-32
Enzymatic Reaction Steps
Sucrose (substrate)
1 Enzyme and
substrate
O
Active site
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Sucrase (enzyme)
2 Enzyme–substrate
complex
O
Glucose
3 Enzyme
and reaction
products
Fructose
Figure 2.27
2-33
Enzymatic Action: Important Points!!
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• Reusability of enzymes
• Astonishing speed
– one enzyme molecule can consume millions of
substrate molecules per minute
• Factors that change enzyme shape
– pH and temperature
2-36
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Cofactors and Coenzymes
Coenzyme NAD+
• Cofactors: inorganic non-protein helper
Glycolysis
– (iron, copper, zinc, magnesium and calcium ions)
– binds to enzyme induces a change in shape, which
activates active site
Glucose
Aerobic respiration
Pyruvic acid
ADP + Pi
• Coenzymes
– organic cofactors derived from water-soluble vitamins
(niacin, riboflavin)
– accept electrons from an enzyme in one pathway and
transfer them to an enzyme in another
ATP
Pyruvic acid
•
2-37
CO2 + H2O
Figure 2.28
NAD+
transports electrons from one metabolic pathway to
another
2-38
Metabolic Pathways
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• Chain of reactions, with each step usually catalyzed by a
different enzyme
•



ABCD
• A is initial reactant, B+C are intermediates and D
is the end product
• Regulation of metabolic pathways
– activation or deactivation of enzymes
– cells can turn on or off pathways
2-40
Organic Molecules:
Nucleotides
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• 3 components of nucleotides
1. nitrogenous base
2. sugar (monosaccharide)
3. one or more phosphate groups
• ATP – best known nucleotide
– adenine (nitrogenous base)
– ribose (sugar)
– phosphate groups (3)
2-42
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ATP (Adenosine Triphosphate)
Adenine
NH2
C
– Phosphate group, sugar, nitrogenous base
C
N
N
C
N
N
C
CH
HC
CH
C
HC
C
N
N
Nucleic Acids
• polymers of nucleotides
Adenine
NH2
• DNA (deoxyribonucleic acid)
N
N
• body’s most
important
Ribose
energy-transfer molecule
Adenosine
Ribose
Triphosphate
O
–O
O
P O
–O
P O
–O
O
P
Monophosphate
O
CH2
O
O
–O
HO
H H
OH
(a) Adenosine triphosphate (ATP)
P
CH2
OH
O
O
H H
H
H
O
H
H
OH
(b) Cyclic adenosine monophosphate (cAMP)
ATP contains adenine, ribose and 3 phosphate groups
– constitutes genes
• instructions for synthesizing all of the body’s proteins
• transfers hereditary information from cell to cell and
generation to generation
2-43
• RNA (ribonucleic acid) – 3 types
– messenger RNA, ribosomal RNA, transfer RNA
2-44
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