Chapter 20 Biochemistry: The Compounds of Life. © 2014 W. W. Norton Co., Inc. Chapter Outline 20.1 The Composition of Proteins Amino Acids Chirality.

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


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


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


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


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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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.)


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


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


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.


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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Chapter 20 Biochemistry: The Compounds of Life. © 2014 W. W. Norton Co., Inc. Chapter Outline 20.1 The Composition of Proteins Amino Acids Chirality.

Documents

amino acid structure

hemoglobin slide

active structure

structure threedimensional

protein structure primary

amino acids molecules

tertiary structure tertiary

compounds of life slide