LESSON 5 - AMINO ACIDS PDF

Section 20.1 Characteristics of Proteins Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Chapter 20 Chapter Outline 20.1 Characteristics of proteins 20.2 Am...

Section 20.1 Characteristics of Proteins Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 1  Chapter 20 Chapter Outline 20.1 Characteristics of proteins 20.2 Amino acids: The building blocks for proteins 20.3 Essential amino acids 20.4 Chirality and amino acids 20.5 Acid–base properties of amino acids 20.6 Cysteine: A chemically unique amino acid 20.7 Peptides 20.8 Biochemically important small peptides 20.9 General structural characteristics of proteins 20.10 Primary structure of proteins Copyright ©2016 Cengage Learning. All Rights Reserved. 2  Chapter 20 Chapter Outline 20.11 Secondary structure of proteins 20.12 Tertiary structure of proteins 20.13 Quaternary structure of proteins 20.14 Protein hydrolysis 20.15 Protein denaturation 20.16 Protein classification based on shape 20.17 Protein classification based on function 20.18 Glycoproteins 20.19 Lipoproteins Copyright ©2016 Cengage Learning. All Rights Reserved. 3  Section 20.1 Characteristics of Proteins Protein: Naturally-occurring, unbranched polymer in which the monomer units are amino acids Most abundant substance in cells after water – Account for about 15% of a cell’s overall mass Elemental composition - Carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S) – Average nitrogen content is 15.4% by mass Contain iron (Fe), phosphorus (P), and other metals in certain specialized proteins Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 4  Section 20.1 Characteristics of Proteins Proteins are naturally occurring polymers in which the monomer units are _____. a.triacylglycerols b.amino acids c.carbohydrates d.nucleosides Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 5  Section 20.1 Characteristics of Proteins Proteins are naturally occurring polymers in which the monomer units are _____. a.triacylglycerols b.amino acids c.carbohydrates d.nucleosides Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 6  Section 20.2 Amino Acids: The Building Blocks for Proteins Amino Acids Contain both an amino (—NH2) and a carboxyl (—COOH) group – -amino acids: Amino acids in which the amino group and the carboxyl group are attached to the - carbon atom Side chains (R) - Vary in size, shape, charge, acidity, functional groups present, hydrogen-bonding ability, and chemical reactivity – >700 amino acids are known Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 7  Section 20.2 Amino Acids: The Building Blocks for Proteins Standard Amino Acids 20 -amino acids normally found in proteins Divided based on the properties of R-groups – Nonpolar amino acids: Contain one amino group, one carboxyl group, and a nonpolar side chain Hydrophobic - Not attracted to water molecules Found in the interior of proteins, where there is no polarity – Polar amino acids - Hydrophilic Types - Polar neutral, polar acidic, and polar basic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 8  Section 20.2 Amino Acids: The Building Blocks for Proteins Polar Amino Acids Polar neutral: Contain polar but neutral side chains – Six amino acids belong to this category Polar acidic: Contain a carboxyl group as part of the side chains – Two amino acids belong to this category Polar basic: Contain an amino group as part of the side chain – Three amino acids belong to this category Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 9  Section 20.2 Amino Acids: The Building Blocks for Proteins Nomenclature Three-letter abbreviations are used for naming standard amino acids – Abbreviations are the first three letters of the amino acid’s name Exceptions: Isoleucine (Ile), tryptophan (Trp), asparagine (Asn), and glutamine (Gln) – One-letter symbols - Used for comparing amino acid sequences of proteins Usually the first letter of the name When more than one amino acid has the same letter, the most abundant amino acid gets the 1st letter Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 10  Section 20.2 Amino Acids: The Building Blocks for Proteins Table 20.1 - 20 Standard Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 11  Section 20.2 Amino Acids: The Building Blocks for Proteins Table 20.1 - 20 Standard Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 12  Section 20.2 Amino Acids: The Building Blocks for Proteins Table 20.1 - 20 Standard Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 13  Section 20.2 Amino Acids: The Building Blocks for Proteins Practice Exercise Classify the following amino acids based on the polarity of their R-groups. O O d. H 2N CH C OH a. H 2N CH C OH CH2 CH3 O H 2N CH C OH CH2 b. O H 2N CH C OH e. CH2 OH CH2 CH2 O CH2 c. H 2N CH C OH NH2 CH2 C O OH Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 14  Section 20.2 Amino Acids: The Building Blocks for Proteins Practice Exercise Classify the following amino acids based on the polarity of their R-groups. O O d. H 2N CH C OH a. H 2N CH C OH CH2 CH3 Non-polar O H 2N CH C OH Non-polar CH2 b. O H 2N CH C OH e. CH2 Polar Neutral OH CH2 CH2 O CH2 c. H 2N CH C OH NH2 CH2 Polar Basic Polar Acidic C O OH Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 15  Section 20.2 Amino Acids: The Building Blocks for Proteins Amino acids are organic compounds that contain a _____ group and a _____ group and are found in proteins as _____. a.hydroxy; carboxyl; -hydroxy amino acids b.amino; carboxyl; -amino acids c.amino; carboxyl; beta amino acids d.hydroxy; carboxyl; beta hydroxy amino acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 16  Section 20.2 Amino Acids: The Building Blocks for Proteins Amino acids are organic compounds that contain a _____ group and a _____ group and are found in proteins as _____. a.hydroxy; carboxyl; -hydroxy amino acids b.amino; carboxyl; -amino acids c.amino; carboxyl; beta amino acids d.hydroxy; carboxyl; beta hydroxy amino acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 17  Section 20.3 Essential Amino Acids Standard amino acids needed for protein synthesis and must be obtained from dietary sources – Types of dietary proteins - Complete, incomplete, and complementary Essential Amino Acids Arginine* Methionine Histidine Phenylalanine *Not essential for adults but is Isoleucine Threonine required for growth in children Leucine Tryptophan Lysine Valine Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 18  Section 20.3 Essential Amino Acids Incomplete dietary proteins contain inadequate amounts of: a.one or more essential amino acids. b.one or more nonessential amino acids. c.at least one essential and one nonessential amino acid. d.none of the above. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 19  Section 20.3 Essential Amino Acids Incomplete dietary proteins contain inadequate amounts of: a.one or more essential amino acids. b.one or more nonessential amino acids. c.at least one essential and one nonessential amino acid. d.none of the above. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 20  Section 20.4 Chirality and Amino Acids Four different groups are attached to the - carbon atom in all of the standard amino acids – Exception: In glycine, the R-group is hydrogen 19 of the 20 standard amino acids contain a chiral center – Molecules with chiral centers exhibit enantiomerism (left- and right-handed forms) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 21  Section 20.4 Chirality and Amino Acids Amino acids found in nature and in proteins are ʟ isomers – Exceptions: Some bacteria – Monosaccharides prefer ᴅ isomers Rules for drawing Fischer projection formulas for amino acid structures – —COOH group is placed at the top of the projection formula Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 22  Section 20.4 Chirality and Amino Acids – R group is placed at the bottom, positions the carbon chain vertically – —NH2 group is placed in a horizontal position – NH2 on the left - ʟ isomer – NH2 on the right - ᴅ isomer Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 23  Section 20.4 Chirality and Amino Acids Practice Exercise Name the following amino acids with correct designation for the enantiomer (chiral carbon is indicated by *). A B C COOH COOH COOH *C *C H 2N *C H H2N H H NH2 CH CH 3 CH 2 CH 2 CH 2 SH CH 3 OH Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 24  Section 20.4 Chirality and Amino Acids Practice Exercise Name the following amino acids with correct designation for the enantiomer (chiral carbon is indicated by *). A B C COOH COOH COOH *C *C H 2N *C H H2N H H NH2 CH CH 3 CH 2 CH 2 CH 2 SH CH 3 A = L-isoleucine OH B = D-cysteine C = L-tyrosine Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 25  Section 20.4 Chirality and Amino Acids With few exceptions, the amino acids found in nature and in proteins are _____ isomers. a.alpha b.beta c.ᴅ d.ʟ Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 26  Section 20.4 Chirality and Amino Acids With few exceptions, the amino acids found in nature and in proteins are _____ isomers. a.alpha b.beta c.ᴅ d.ʟ Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 27  Section 20.5 Acid–Base Properties of Amino Acids In pure form, amino acids are white crystalline solids – Decompose before they melt Not very soluble in water -amino acids exist as zwitterions in solution and in solid state – Zwitterions: Molecules with positive charge on one atom and negative charge on another, but have no net charge Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 28  Section 20.5 Acid–Base Properties of Amino Acids Carboxyl groups give up protons to produce a negatively charged species Amino groups accept protons to produce a positively charged species Amino acid forms in solution – Zwitterions, positive ion, and negative ion – Equilibrium shifts with change in pH Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 29  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 30  Section 20.5 Acid–Base Properties of Amino Acids Isoelectric Point (pI) pH at which an amino acid exists in its zwitterion form – Carries zero net charge Different amino acids have different isoelectric points Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 31  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 32  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 33  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 34  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 35  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 36  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 37  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 38  Section 20.5 Acid–Base Properties of Amino Acids Draw the following polypeptides and determine their pI – FINAL – LIVE – HEAD – RATFINK Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 39  Section 20.5 Acid–Base Properties of Amino Acids An amino acid with a positive charge on one atom and a negative charge on another atom with an overall charge of zero is known as a _____. a.zeroion b.zwitterion c.neutral ion d.neutron Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 40  Section 20.5 Acid–Base Properties of Amino Acids An amino acid with a positive charge on one atom and a negative charge on another atom with an overall charge of zero is known as a _____. a.zeroion b.zwitterion c.neutral ion d.neutron Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 41  Section 20.5 Acid–Base Properties of Amino Acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 42  Section 20.6 Cysteine: A Chemically Unique Amino Acid Standard amino acid that has a side chain that contains a sulfhydryl group (—SH group) – Sulfhydryl group imparts cysteine a unique chemical property Cysteine, in the presence of mild oxidizing agents, dimerizes to form a cystine molecule – Cystine contains two cysteine residues linked via a covalent disulfide bond Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 43  Section 20.6 Cysteine: A Chemically Unique Amino Acid What functional group in the amino acid cysteine gives it the ability to react with another cysteine to form a cystine molecule? a.Amino group b.Carboxyl group c.Sulfhydryl group d.Hydroxyl group Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 44  Section 20.6 Cysteine: A Chemically Unique Amino Acid What functional group in the amino acid cysteine gives it the ability to react with another cysteine to form a cystine molecule? a.Amino group b.Carboxyl group c.Sulfhydryl group d.Hydroxyl group Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 45  Section 20.7 Peptides Nature of the Peptide Bond Under proper conditions, amino acids can bond together to produce a peptide chain – Peptide: Unbranched chain of amino acids Dipeptide - Compound containing two amino acids Oligopeptide - Peptide with 10 to 20 amino acid residues Polypeptide: Long unbranched chain of amino acids – Reaction is between the amino group of one amino acid and the carboxyl group of another amino acid Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 46  Section 20.7 Peptides Nature of the Peptide Bond Length of the amino acid chain can vary from a few amino acids to hundreds of amino acids – Peptide bonds: Covalent bonds between amino acids in a peptide Every peptide has an N-terminal end and a C- terminal end Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 47  Section 20.7 Peptides Peptide Nomenclature C-terminal amino acid residue keeps its full amino acid name All of the other amino acid residues have names that end in -yl – -yl suffix replaces the -ine or -ic acid ending of the amino acid name, except for tryptophan, for which -yl is added to the name Amino acid naming sequence begins at the N- terminal amino acid residue Example: Ala-leu-gly has the IUPAC name of alanylleucylglycine Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 48  Section 20.7 Peptides Isomeric Peptides Peptides that contain the same amino acids but present in different order are different molecules (constitutional isomers) with different properties – For example, two different dipeptides can be formed from one molecule of alanine and glycine Number of possible isomeric peptides increases rapidly as the length of the peptide chain increases Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 49  Section 20.7 Peptides How many isomeric peptides are possible from a peptide of four different amino acids? a.8 b.12 c.16 d.24 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 50  Section 20.7 Peptides How many isomeric peptides are possible from a peptide of four different amino acids? a.8 b.12 c.16 d.24 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 51  Section 20.8 Biochemically Important Small Peptides Small Peptide Hormones Best-known peptide hormones - Oxytocin and vasopressin – Produced by the pituitary gland – Hormones are nonapeptides (nine amino acid residues) Have six of the residues held in the form of a loop by a disulfide bond formed from the interaction of two cysteine residues Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 52  Section 20.8 Biochemically Important Small Peptides Small Peptide Neurotransmitters Enkephalins are pentapeptide neurotransmitters produced by the brain – Bind receptor sites in the brain to reduce pain Best-known enkephalins – Met-enkephalin: Tyr–Gly–Gly–Phe–Met – Leu-enkephalin: Tyr–Gly–Gly–Phe–Leu Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 53  Section 20.8 Biochemically Important Small Peptides Small Peptide Antioxidant Glutathione (Glu–Cys–Gly) - Tripeptide present in high levels in most cells – Regulates oxidation–reduction reactions – Antioxidant that protects cellular contents from oxidizing agents such as peroxides and superoxides – Unusual structural feature - Glu is bonded to Cys through the side-chain carboxyl group Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 54  Section 20.8 Biochemically Important Small Peptides What small peptides are produced in the brain to reduce pain, and which play a role in the “high” reported by long-distance runners? a.Oxytocin b.Vasopressin c.Enkephalins d.Glutathione Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 55  Section 20.8 Biochemically Important Small Peptides What small peptides are produced in the brain to reduce pain, and which play a role in the “high” reported by long-distance runners? a.Oxytocin b.Vasopressin c.Enkephalins d.Glutathione Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 56  Section 20.9 General Structural Characteristics of Proteins Protein General definition - Naturally-occurring, unbranched polymer in which the monomer units are amino acids Specific definition - Peptide in which at least 40 amino acid residues are present – The terms polypeptide and protein are used interchangeably to describe a protein – Several proteins have >10,000 amino acid residues Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 57  Section 20.9 General Structural Characteristics of Proteins Protein – Common proteins contain 400–500 amino acid residues – Small proteins contain 40–100 amino acid residues More than one polypeptide chain may be present in a protein – Monomeric: Protein which contains one polypeptide chain – Multimeric: Protein which contains two or more polypeptide chains Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 58  Section 20.9 General Structural Characteristics of Proteins Protein Classification Based on Chemical Composition Simple protein: Protein in which only amino acid residues are present – More than one protein subunit may be present Conjugated protein: Protein that has one or more non-amino-acid entities (prosthetic groups) present in its structure – One or more polypeptide chains may be present – Non-amino-acid components may be organic or inorganic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 59  Section 20.9 General Structural Characteristics of Proteins Protein Classification Based on Chemical Composition – May be classified further based on the nature of prosthetic group(s) present Lipoprotein contains lipid prosthetic groups Glycoprotein contains carbohydrate groups Metalloprotein contains a specific metal as its prosthetic group Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 60  Section 20.9 General Structural Characteristics of Proteins A _____ protein contains only amino acid residues, and a _____ protein contains one or more non-amino acids in the structures. a.simple; conjugated b.simple; prosthetic c.conjugated; simple d.conjugated; prosthetic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 61  Section 20.9 General Structural Characteristics of Proteins A _____ protein contains only amino acid residues, and a _____ protein contains one or more non-amino acids in the structures. a.simple; conjugated b.simple; prosthetic c.conjugated; simple d.conjugated; prosthetic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 62  Section 20.10 Primary Structure of Proteins Types of structures - Primary, secondary, tertiary, and quaternary Primary structure: Order in which amino acids are linked together in a protein Every protein has its own unique amino acid sequence – Frederick Sanger sequenced and determined the primary structure for the first protein (insulin) in 1953 Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 63  Section 20.10 Primary Structure of Proteins Figure 20.4 - Primary Structure of a Human Myoglobin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 64  Section 20.10 Primary Structure of Proteins Primary structure of a specific protein is the same within the organism – Structures of certain proteins are similar among different species of animals Example: Insulin from pigs, cows, sheep, and humans are similar but not identical Amino acids are linked to each other by peptide linkages Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 65  Section 20.10 Primary Structure of Proteins The order in which amino acids are linked in a protein is known as the _____ structure. a.primary b.secondary c.tertiary d.quaternary Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 66  Section 20.10 Primary Structure of Proteins The order in which amino acids are linked in a protein is known as the _____ structure. a.primary b.secondary c.tertiary d.quaternary Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 67  Section 20.11 Secondary Structure of Proteins Arrangement in space adopted by the backbone portion of a protein Types - Alpha-helix ( helix) and the beta- pleated sheet ( pleated sheet) Alpha-helix structure: A single protein chain adopts a shape that resembles a coiled spring (helix) – Coil configuration maintained by hydrogen bonds – Twist of the helix forms a right-handed, or clockwise, spiral Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 68  Section 20.11 Secondary Structure of Proteins – Hydrogen bonds between C=O and N—H entities are orientated parallel to the axis of the helix – All of the amino acid R groups extend outward from the spiral There is not enough room within the spiral Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 69  Section 20.11 Secondary Structure of Proteins Beta-pleated sheet structure: Two fully extended protein chain segments in the same or different molecules – Held together by hydrogen bonds H-bonding between chains - Inter and/or intramolecular Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 70  Section 20.11 Secondary Structure of Proteins The two most common types of secondary structures of proteins are the _____ and the _____. a.alpha helix; alpha pleated sheet b.beta helix; alpha pleated sheet c.alpha helix; beta pleated sheet d.beta helix; beta pleated sheet Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 71  Section 20.11 Secondary Structure of Proteins The two most common types of secondary structures of proteins are the _____ and the _____. a.alpha helix; alpha pleated sheet b.beta helix; alpha pleated sheet c.alpha helix; beta pleated sheet d.beta helix; beta pleated sheet Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 72  Section 20.12 Tertiary Structure of Proteins Overall three-dimensional shape of a protein Results from the interactions between amino acid side chains (R groups) that are widely separated from each other Types of stabilizing interactions observed – Covalent disulfide bonds – Electrostatic attractions (salt bridges) – Hydrogen bonds – Hydrophobic attractions Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 73  Section 20.12 Tertiary Structure of Proteins Types of Stabilizing Interactions Disulfide bonds - Covalent, strong, and involve two cysteine units Electrostatic interactions (salt bridges) - Involve the interaction between charged side chains of acidic and basic amino acids Hydrogen bonds - Can occur between amino acids with polar R groups Hydrophobic interactions - Occur when two nonpolar side chains are close to each other Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 74  Section 20.12 Tertiary Structure of Proteins Figure 20.13 - Stabilizing Influences that Contribute to the Tertiary Structure Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 75  Section 20.12 Tertiary Structure of Proteins What type of attractive interaction, that contributes to the tertiary structure of a protein, would be found buried in a nonaqueous environment within the protein? a.Hydrogen bonds b.Salt bridges c.Hydrophilic interactions d.Hydrophobic interactions Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 76  Section 20.12 Tertiary Structure of Proteins What type of attractive interaction, that contributes to the tertiary structure of a protein, would be found buried in a nonaqueous environment within the protein? a.Hydrogen bonds b.Salt bridges c.Hydrophilic interactions d.Hydrophobic interactions Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 77  Section 20.13 Quaternary Structure of Proteins Organization among the various peptide subunits in a multimeric protein – Highest level of protein organization – Found in proteins that have two or more polypeptide chains (subunits) – Subunits are independent of each other and not covalently bonded to each other – Contain even number of subunits Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 78  Section 20.13 Quaternary Structure of Proteins The structure of hemoglobin, with organization of its alpha and beta subunits, is an example of what type of protein structure? a.Primary b.Secondary c.Tertiary d.Quaternary Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 79  Section 20.13 Quaternary Structure of Proteins The structure of hemoglobin, with organization of its alpha and beta subunits, is an example of what type of protein structure? a.Primary b.Secondary c.Tertiary d.Quaternary Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 80  Section 20.14 Protein Hydrolysis Reverse of peptide bond formation – Results in the regeneration of an amine and carboxylic acid functional groups – Protein digestion - Enzyme-catalyzed hydrolysis Free amino acids produced are absorbed into the bloodstream and transported to the liver for the synthesis of new proteins – Hydrolysis of cellular proteins to amino acids is an ongoing process, as the body resynthesizes needed molecules and tissue Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 81  Section 20.14 Protein Hydrolysis Which of the following best describes what happens to a small peptide when placed in an acid solution and heated? a.The small peptide combines to form a long-chain protein. b.The small peptide is resistant to acid and heat. c.The small peptide undergoes hydrolysis to produce free amino acids. d.The small peptide undergoes hydrolysis to produce free amino acids, which recombine upon cooling to form a different peptide. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 82  Section 20.14 Protein Hydrolysis Which of the following best describes what happens to a small peptide when placed in an acid solution and heated? a.The small peptide combines to form a long-chain protein. b.The small peptide is resistant to acid and heat. c.The small peptide undergoes hydrolysis to produce free amino acids. d.The small peptide undergoes hydrolysis to produce free amino acids, which recombine upon cooling to form a different peptide. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 83  Section 20.15 Protein Denaturation Partial or complete disorganization of a protein’s characteristic three-dimensional shape – Occurs due to disruption of its secondary, tertiary, and quaternary structural interactions Coagulation - Precipitation out of biochemical solution of denatured protein – Example: Egg white is a concentrated solution of protein albumin, which forms a jelly when heated Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 84  Section 20.15 Protein Denaturation Cooking denatures proteins – Makes it easy for enzymes in our body to hydrolyze/digest protein – Kills microorganisms by denaturation of proteins A fever of above 106°F is dangerous – Denatures and inactivates the body’s enzymes, which function as catalysts Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 85  Section 20.15 Protein Denaturation What is the consequence of protein denaturation? a.Partial or complete loss of a protein’s three-dimensional structure b.Loss of biochemical activity of the protein c.Disruption of the secondary, tertiary, and quaternary structural interactions d.All the above Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 86  Section 20.15 Protein Denaturation What is the consequence of protein denaturation? a.Partial or complete loss of a protein’s three-dimensional structure b.Loss of biochemical activity of the protein c.Disruption of the secondary, tertiary, and quaternary structural interactions d.All the above Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 87  Section 20.16 Protein Classification Based on Shape Fibrous proteins: Protein molecules with elongated shape – One dimension is much longer than the others – Generally insoluble in water – Have a single type of secondary structure – Tend to have simple, regular, and linear structures – Aggregate together to form macromolecular structures Example: Hair, nails, etc Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 88  Section 20.16 Protein Classification Based on Shape Globular proteins: Protein molecules with peptide chains folded into spherical or globular shapes – Water soluble substances - Hydrophobic amino acid residues are in the protein core Membrane proteins: Proteins associated with cell membranes – Insoluble in water - Hydrophobic amino acid residues are on the surface Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 89  Section 20.16 Protein Classification Based on Shape Fibrous Proteins: -Keratin Provide protective coating for organisms Major protein constituent of hair, feather, nails, horns, and turtle shells Mainly made of hydrophobic amino acid residues Individual molecules are almost wholly  helical – Pairs of these helices twine about one another to produce a coiled coil – Coiling at higher levels produces the strength associated with -keratin-containing proteins Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 90  Section 20.16 Protein Classification Based on Shape Fibrous Proteins: Collagen Most abundant protein in humans (30% of total body protein) Major structural material in tendons, ligaments, blood vessels, and skin Organic component of bones and teeth Predominant structure - Triple-helix – Glycine and proline help maintain the structure of the triple-helix Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 91  Section 20.16 Protein Classification Based on Shape Globular Proteins: Hemoglobin An oxygen-carrier molecule in blood – Transports oxygen from lungs to tissues Tetramer (four polypeptide chains) – Each subunit contains a heme group One molecule can transport up to four oxygen molecules at time Iron atom in heme interacts with oxygen Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 92  Section 20.16 Protein Classification Based on Shape Globular Proteins: Myoglobin Oxygen-storage molecule in muscles Monomer – Consists of a single peptide chain and one heme unit – One molecule carries one O2 molecule Has a higher affinity for oxygen than hemoglobin Oxygen stored in myoglobin molecules serves as a reserve source for working muscles when oxygen demand exceeds its supply Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 93  Section 20.16 Protein Classification Based on Shape Aqueous soluble proteins fold into a spherical or globular shape. Which of the following contains only soluble proteins? a.Fibrin, insulin, hemoglobin b.Myoglobin, myosin, keratin c.Hemoglobin, insulin, immunoglobulin d.Elastin, myosin, keratin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 94  Section 20.16 Protein Classification Based on Shape Aqueous soluble proteins fold into a spherical or globular shape. Which of the following contains only soluble proteins? a.Fibrin, insulin, hemoglobin b.Myoglobin, myosin, keratin c.Hemoglobin, insulin, immunoglobulin d.Elastin, myosin, keratin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 95  Section 20.17 Protein Classification Based on Function Proteins play crucial roles in biochemical processes Diversity of functions exhibited by proteins exceeds the role of other biochemical molecules Functional versatility of proteins stems from their ability to: – Bind small molecules specifically and strongly – Bind other proteins and form fiber-like structures – Integrate into cell membranes Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 96  Section 20.17 Protein Classification Based on Function Catalytic proteins are known for their role as catalysts – Almost every chemical reaction in the body is driven by an enzyme Defense proteins are central to functioning of the body’s immune system – Known as immunoglobulins or antibodies Transport proteins bind to small biomolecules, transport them to other locations in the body, and release them as needed Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 97  Section 20.17 Protein Classification Based on Function Messenger proteins transmit signals to coordinate biochemical processes between different cells, tissues, and organs – Examples: Insulin, glucagon, and human growth hormone Contractile proteins are necessary for all forms of movement – Examples: Actin and myosin – Human reproduction depends on the movement of sperm, which is possible because of contractile proteins Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 98  Section 20.17 Protein Classification Based on Function Structural proteins confer stiffness and rigidity – Collagen is a component of cartilage – -keratin gives mechanical strength and protective covering to hair, nails, feathers, and hooves Transmembrane proteins control the movement of small molecules and ions through the cell membrane – Have channels to help molecules enter and exit the cell – Selective, allow passage of only one type of molecule or ion Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 99  Section 20.17 Protein Classification Based on Function Storage proteins bind (and store) small molecules – Ferritin - Iron-storage protein which saves iron for use in the biosynthesis of new hemoglobin molecules – Myoglobin - Oxygen-storage protein present in muscle Regulatory proteins are found embedded in the exterior surface of cell membranes – Act as sites for receptor molecules – Bind to enzymes (catalytic proteins) and control enzymatic action Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 100  Section 20.17 Protein Classification Based on Function Nutrient proteins are important in the early stages of life, from embryo to infant – Examples: Casein (found in milk) and ovalbumin (found in egg white) Milk provides immunological protection for mammalian young Buffer proteins are part of the system by which the acid–base balance within body fluids is maintained Fluid-balance proteins maintain fluid balance between blood and surrounding tissue Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 101  Section 20.17 Protein Classification Based on Function Which of the following proteins plays the role of biochemical catalysts in the human body? a.Hormones b.Enzymes c.Transferrin d.Antibodies Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 102  Section 20.17 Protein Classification Based on Function Which of the following proteins plays the role of biochemical catalysts in the human body? a.Hormones b.Enzymes c.Transferrin d.Antibodies Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 103  Section 20.18 Glycoproteins Contain carbohydrates or carbohydrate derivatives in addition to amino acids – Examples: Proteins in cell membrane and blood group markers of the ABO system Collagen – Structural feature - 4-hydroxyproline (5%) and 5- hydroxylysine (1%) – Carbohydrate units are attached by glycosidic linkages to collagen at its 5-hydroxylysine residues Direct the assembly of collagen triple helices into collagen fibrils Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 104  Section 20.18 Glycoproteins Immunoglobulins Produced as a protective response to the invasion of microorganisms or foreign molecules Serve as antibodies to combat invasion of the body by antigens – Antigen: Foreign substance, such as a bacterium or virus, that invades the human body – Antibody: Biochemical molecule that counteracts a specific antigen Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 105  Section 20.18 Glycoproteins Immunoglobulins Bonding of an antigen to variable regions of immunoglobulins occurs through hydrophobic interactions, dipole–dipole interactions, and hydrogen bonds Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 106  Section 20.18 Glycoproteins An _____ is a glycoprotein produced by an organism in response to an invasion of a foreign substance known as a _____. a.antibody; antigen b.antigen, immunoglobulin c.antigen; antibody d.antibody; immunoglobulin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 107  Section 20.18 Glycoproteins An _____ is a glycoprotein produced by an organism in response to an invasion of a foreign substance known as a _____. a.antibody; antigen b.antigen, immunoglobulin c.antigen; antibody d.antibody; immunoglobulin Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 108  Section 20.19 Lipoproteins Conjugated proteins that contain lipids and amino acids Help suspend lipids and transport them through the bloodstream Classes of plasma lipoproteins – Chylomicrons - Transport dietary triacylglycerols from intestine to the liver and to adipose tissue Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 109  Section 20.19 Lipoproteins – Very-low-density lipoproteins (VLDL) - Transport triacylglycerols synthesized in the liver to adipose tissue – Low-density lipoproteins (LDL) - Transport cholesterol synthesized in the liver to cells throughout the body – High-density lipoproteins (HDL) - Collect excess cholesterol from body tissues and transport it back to the liver for degradation to bile acids Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 110  Section 20.19 Lipoproteins Which class of plasma lipoproteins is responsible for transporting cholesterol synthesized in the liver to cells throughout the body? a.Chylomicrons b.Very-low-density lipoproteins (VLDLs) c.Low-density lipoproteins (LDLs) d.High-density lipoproteins (HDLs) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 111  Section 20.19 Lipoproteins Which class of plasma lipoproteins is responsible for transporting cholesterol synthesized in the liver to cells throughout the body? a.Chylomicrons b.Very-low-density lipoproteins (VLDLs) c.Low-density lipoproteins (LDLs) d.High-density lipoproteins (HDLs) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 112  Chapter 20 Concept Question 1 The peptide met-gly-phe-ser-ala is known as a _____. The N-terminal amino acid is _____, and the C- terminal amino acid is _____. The IUPAC name of this peptide is _____. a.pentapeptide; alanine; methionine; methionineglycinephenylalanineserinealanine b.hexapeptide; methionine; alanine; methionineglycinephenylalanineserinealanine c.hexapeptide; alanine; methionine; methionylglycylphenylalanylserylalanine d.pentapeptide; methionine; alanine; methionylglycylphenylalanylserylalanine Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 113  Chapter 20 Concept Question 1 The peptide met-gly-phe-ser-ala is known as a _____. The N-terminal amino acid is _____, and the C- terminal amino acid is _____. The IUPAC name of this peptide is _____. a.pentapeptide; alanine; methionine; methionineglycinephenylalanineserinealanine b.hexapeptide; methionine; alanine; methionineglycinephenylalanineserinealanine c.hexapeptide; alanine; methionine; methionylglycylphenylalanylserylalanine d.pentapeptide; methionine; alanine; methionylglycylphenylalanylserylalanine Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 114  Chapter 20 Concept Question 2 Egg whites are made up of albumin, a single-chain protein. Why does the albumin solidify when placed in a hot skillet? a.Heat causes denaturation of albumin destroying its primary, secondary, tertiary, and quaternary structures. b.Heat causes denaturation of albumin destroying its secondary, tertiary, and quaternary structures. c.Heat causes denaturation of albumin destroying its secondary and tertiary structures. d.Heat causes albumin chains to fuse together through the formation of new covalent bonds between the chains. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 115  Chapter 20 Concept Question 2 Egg whites are made up of albumin, a single-chain protein. Why does the albumin solidify when placed in a hot skillet? a.Heat causes denaturation of albumin destroying its primary, secondary, tertiary, and quaternary structures. b.Heat causes denaturation of albumin destroying its secondary, tertiary, and quaternary structures. c.Heat causes denaturation of albumin destroying its secondary and tertiary structures. d.Heat causes albumin chains to fuse together through the formation of new covalent bonds between the chains. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 116