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Chapter 20Biochemistry: The Compounds of Life
© 2014 W. W. Norton Co., Inc.
Chapter Outline
• 20.1 The Composition of Proteins Amino Acids Chirality Zwitterions Peptides
• 20.2 Protein Structure and Function• 20.3 Carbohydrates• 20.4 Lipids• 20.5 Nucleotides and Nucleic Acids• 20.6 From Biomolecules to Living Cells
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Biomolecules
• Biomolecule – is an organic molecule present naturally in a living system.
• Amino acids – molecules that contain one amine group and one carboxylic acid group.
• Proteins – biological polymers made of amino acids.• masses ~ 105 g/mol or more
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Amino Acid Structure
• (a) amine group (NH3) + carboxylic acid (COOH) bonded to carbon
• (b) three-dimensional representation 20 - 4
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Amino Acids with Nonpolar R Groups
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AA with Nonpolar R Groups (cont.)
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Amino Acids with Polar R Groups
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Amino Acids with Acidic R Groups
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Amino Acids with Basic R Groups
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Chirality in Nature
• All amino acids except one are chiral.• D (dextro-, right) and L (levo-, left)• Refer to positions in space of substituents• All amino acids in proteins are L-enantiomers.
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Zwitterions
• Zwitterion – a molecule that has both positively- and negatively-charged groups in its structure.
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Zwitterion: pH Dependence
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Peptides
• Peptide bond – the result of a condensation reaction between the carboxylic acid group of one amino acid and the amine of another.
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Chapter Outline
• 20.1 The Composition of Proteins• 20.2 Protein Structure and Function
Primary StructureSecondary StructureTertiary and Quaternary StructureEnzymes: Proteins as Catalysts
• 20.3 Carbohydrates• 20.4 Lipids• 20.5 Nucleotides and Nucleic Acids• 20.6 From Biomolecules to Living Cells
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Protein Structure
• Primary (1) structure – the sequence in which the amino acids occur in the polymer.
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Amino acid residues
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Protein Structure (cont.)
• Secondary (2) structure – pattern of arrangement of segments of the protein chain.• helix , random coil, or -pleated sheets
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Tertiary Structure
• Tertiary (3) structure – three-dimensional, biologically active structure of the protein.• Arises because of interactions between R
groups.
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Quaternary Structure
• Quaternary (4) structure – the larger structure functioning as a single unit that results when two or more protein chains associate.
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hemoglobin
© 2014 W. W. Norton Co., Inc.
Proteins as Catalysts: Enzymes
• Active site – the location on an enzyme where a reactive substance binds.
• Substrate – the reactant that binds to the active site in an enzyme-catalyzed reaction.
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Enzymes as Catalysts
• Highly selective:• Efficient, selective for one optical isomer.• Products are optically pure.
• Models:• Lock-and-key; only substrate fits into active
site.• Induced-fit; substrate binds to active site and
changes 3D structure of transition state.• Also explains inhibitor activity
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Inhibitors• Inhibitor – a compound that diminishes or
destroys the ability of an enzyme to catalyze a reaction.• Blocks active site or changes substrate shape
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Chapter Outline
• 20.1 The Composition of Proteins• 20.2 Protein Structure and Function• 20.3 Carbohydrates
Molecular Structures of Glucose and Fructose
Dissacharides and PolysaccharidesGlycolysis Revisited
• 20.4 Lipids• 20.5 Nucleotides and Nucleic Acids• 20.6 From Biomolecules to Living Cells
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Carbohydrates
• General formula = Cx(H2O)y• Monosaccharides, disaccharides, or
polysaccharides.• Glucose = most abundant monosaccharide, in
nature and the human body• Examples:
• Starch; energy-storage polysaccharide in plants
• Cellulose; provides structural support in plants
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Glucose
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Fructose
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Disaccharides/Polysaccharides
• Glycosidic linkage – a C–O–C bond between sugar molecules
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Two Polymer Forms of Glucose
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Starch; -glucose with -1,4-glycosidic bonds
Cellulose; -glucose with -1,4-glycosidic bonds
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Biomass• Biomass – sum total of the mass of organic
matter in any given ecological system.• Typically used as fuel (wood, animal dung)
• Biofuels:• Ethanol = gas additive, substitute• From fermentation of food stock (cornstarch)• C6H12O6(aq) 2 CH3CH2OH(aq) + 2 CO2(g)
• Cellulose conversion?
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Glycolysis Revisited
• Living cells use glucose as a fuel in a series of reactions called glycolysis.• Pyruvate – converted into different products
depending on type of cell + enzymes present.
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Chapter Outline
• 20.1 The Composition of Proteins• 20.2 Protein Structure and Function• 20.3 Carbohydrates• 20.4 Lipids
Function and Metabolism of LipidsOther Types of Lipids
• 20.5 Nucleotides and Nucleic Acids• 20.6 From Biomolecules to Living Cells
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© 2014 W. W. Norton Co., Inc.
Lipids
• Lipids – class of water-insoluble compounds that are common structural materials in cells.• Glyceride – lipid consisting of esters
formed between fatty acids and the alcohol glycerol.
• Fats – solid triglycerides containing primarily saturated fatty acids.
• Oils – liquid triglycerides containing primarily unsaturated fatty acids.
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Triglycerides
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Table 20.3 (cont.)
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Structure of Fatty Acids
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Phospholipids• Phospholipid – molecule of glycerol + two fatty
acids + polar phosphate group.
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Cholesterol
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• Cholesterol:• Essential component
of cell walls and steroid hormones
• Important in biosynthesis of proteins
• Overaccumulation leads to plaque
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Chapter Outline
• 20.1 The Composition of Proteins• 20.2 Protein Structure and Function• 20.3 Carbohydrates• 20.4 Lipids• 20.5 Nucleotides and Nucleic Acids
From DNA to New Proteins• 20.6 From Biomolecules to Living Cells
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Nucleotides
• Nucleotides:• Monomer unit
from which nucleic acids are made contains:- Five-carbon sugar- Phosphate group- Nitrogen-containing base
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N-Containing Bases
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Nucleic Acid: Biopolymer
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• DNA, RNA• Anionic character keeps
them from passing through cell walls
• Structures written using single-letter labels for bases.
• H bonding between strands
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DNA
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Replication
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Replication: process by which one double-stranded DNA forms two new DNA molecules, each one containing one strand from the original molecule and one new strand.
© 2014 W. W. Norton Co., Inc.
From DNA to Protein
• Transcription – process of copying information of DNA to RNA.
• Messenger RNA (mRNA) – polynucleotide that carries the code for synthesizing a protein from DNA.
• Codon – three-base sequence that encodes for a specific amino acid.
• Translation – process of assembling proteins from information encoded in RNA.
• Transfer RNA (tRNA) – polynucleotide that delivers amino acids one at a time to polypeptide chains being assembled.
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Chapter Outline• 20.1 The Composition of Proteins• 20.2 Protein Structure and Function• 20.3 Carbohydrates• 20.4 Lipids• 20.5 Nucleotides and Nucleic Acids• 20.6 From Biomolecules to Living Cells
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Origins of Biomolecules
• How were they first formed on Earth?• How did they assemble into living cells?
• Some of extra-terrestrial origins• Strands of RNA may form spontaneously on
clay surfaces• Capable of self-replication• RNA world hypothesis
• Deep-ocean hydrothermal vents
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ChemTours: Chapter 20
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