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Chapters 2-4
Organic Molecules and Enzymes
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2.3: Chemical Constituents of CellsOrganic v. Inorganic Molecules
Organic molecules • Contain C and H• Usually larger than inorganic molecules• Dissolve in water and organic liquids• Carbohydrates, proteins, lipids, and nucleic acids
Inorganic molecules • Generally do not contain C and H• Usually smaller than organic molecules• Usually dissociate in water, forming ions • Water, oxygen, carbon dioxide, and inorganic salts
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Inorganic Substances
Water • Most abundant compound in living material• Two-thirds of the weight of an adult human• Major component of all body fluids• Medium for most metabolic reactions• Important role in transporting chemicals in the body• Absorbs and transports heat
Oxygen (O2) • Used by organelles to release energy from nutrients in
order to drive cell’s metabolic activities• Necessary for survival
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Inorganic Substances
Carbon dioxide (CO2)• Waste product released during metabolic reactions• Must be removed from the body
Inorganic salts• Abundant in body fluids• Sources of necessary ions (Na+, Cl-, K+, Ca2+, etc.)• Play important roles in metabolism
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Organic SubstancesCarbohydrates
• Provide energy to cells
• Supply materials to build cell structures
• Water-soluble
• Contain C, H, and O
• Ratio of H to O close to 2:1 (C6H12O6)
• Monosaccharides – glucose, fructose• Disaccharides – sucrose, lactose• Polysaccharides – glycogen, cellulose
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Organic SubstancesCarbohydrates
O
(a) Monosaccharide
O O
O
(b) Disaccharide
O
O
O
(c) Polysaccharide
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Organic SubstancesLipids• Soluble in organic solvents; insoluble in water• Fats (triglycerides)
• Used primarily for energy; most common lipid in the body
• Contain C, H, and O but less O than carbohydrates (C57H110O6)
• Building blocks are 1 glycerol and 3 fatty acids per molecule
• Saturated and unsaturated
Glycerolportion
Fatty acidportions
C
O
OH C C
H
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
C
O
OH C C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
C
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
C
H
H
H
C
O
OH C C
H
HH
C
H
H
C
H
H
C
H
H
C
H H
H
C
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+Neutral Fats
Triglycerides are formed from a fatty acid and glycerol (a sugar).
They are the most plentiful source of stored energy to our bodies. Two types:
Saturated- contain only single bonds Unsaturated- contains one(mono) or more(poly) double
bonds
Short, unsaturated fats are liquids (oils) and come from plants.
Long, saturated fats are solid (butter and meat fat) and come from animals.
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Organic SubstancesLipids
• Phospholipids
• Building blocks are 1 glycerol, 2 fatty acids, and 1 phosphate per molecule
• Hydrophilic and hydrophobic
• Major component of cell membranes
C
H
C
OH
CH
H
Glycerol portion
(a) A fat molecule
O
O
Fatty acid
Fatty acid
Fatty acid
H
C
H H
HH
C
H
H
N
O
O
Fatty acid
Fatty acid
O
POCH
O–
Phosphate portion
(b) A phospholipid molecule(the unshaded portion may vary)
H
CH
C
H
H
O
(c) Schematic representationof a phospholipid molecule
Water-insoluble (hydrophobic) “tail”
Water-soluble(hydrophilic)“head”
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Organic Substances Lipids• Steroids
• Four connected rings of carbon• Widely distributed in the body, various
functions• Component of cell membrane• Used to synthesize hormones• Cholesterol
(a) General structure of a steroid
CC
CH2C
H2C C
H
(b) Cholesterol
C
CH CH2
CH2
CH
CH3
CH2
HC
HC
H2
H2
CH2 CHCH2
CH3
CH3
CH2
CH
CH3
HO C
CH3
CH2
CHC
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+ Organic SubstancesProteins• Structural material• Energy source• Hormones• Receptors• Enzymes• Antibodies
• Protein building blocks are amino acids
• Amino acids held together with peptide bonds
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H N
H
C
H
C
O
OH
S
C
H
HH
H N
H
C
H
C
O
OH
C
C
C
H
H
C H
C H
H
CH
CH
H N
H
C
H
C
O
OH
R
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Organic SubstancesNucleic Acids
• Carry genes• Encode amino acid sequences of proteins
• Building blocks are nucleotides
• DNA (deoxyribonucleic acid) – double polynucleotide• RNA (ribonucleic acid) – single polynucleotide
S
P B
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4.3: Control of Metabolic Reactions• Enzymes
• Control rates of metabolic reactions
• Lower activation energy needed to start reactions
• Most are globular proteins with specific shapes
• Not consumed in chemical reactions
• Substrate specific
• Shape of active site determines substrate
Product molecule
Active site
(a) (b) (c)
Substrate molecules
Unalteredenzymemolecule
Enzyme-substratecomplex
Enzymemolecule
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Enzyme Action
• Metabolic pathways• Series of enzyme-controlled reactions leading to
formation of a product• Each new substrate is the product of the
previous reaction
• Enzyme names commonly:• Reflect the substrate• Have the suffix – ase• Examples: sucrase, lactase, protease,
lipase
Substrate1
Enzyme A Substrate2
Enzyme B Substrate3
Enzyme C Substrate4
Enzyme DProduct
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Factors That Alter Enzymes
• Factors that alter enzymes:• Heat• Radiation• Electricity• Chemicals• Changes in pH
+ 16Regulation of Metabolic Pathways
• Limited number of regulatory enzymes
• Negative feedback
Inhibition
Substrate1
Substrate2
Enzyme B Substrate3
Enzyme C Substrate4
Enzyme DProduct
Rate-limitingEnzyme A
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