chapter 21 enzymes and vitamins. chapter 21 table of contents copyright © cengage learning. all...

Chapter 21 Enzymes and Vitamins

Chapter 21 Table of Contents Copyright Cengage Learning. All rights reserved 2 21.1 General Characteristics of Enzymes 21.2 Enzyme Structure 21.3 Nomenclature and Classification of Enzymes 21.4 Models of Enzyme Action 21.5 Enzyme Specificity 21.6 Factors That Affect Enzyme Activity 21.7 Enzyme Inhibition 21.8 Regulation of Enzyme Activity 21.9 Antibiotics That Inhibit Enzyme Activity 21.10 Medical Uses of Enzymes 21.11 General Characteristics of Vitamins 21.12 Water-Soluble Vitamins 21.13 Fat-Soluble Vitamins

General Characteristics of Enzymes Return to TOC Section 21.1 Copyright Cengage Learning. All rights reserved 3 Enzymes are catalysts and are not consumed in the reactions Enzymes are proteins that act as a catalyst for biochemical reactions The human body has 1000s of enzymes Enzymes are the most effective catalysts known Most enzymes are globular proteins A few enzymes are now known to be ribonucleic acids (RNA) Enzymes undergo all the reactions of proteins including denaturation Enzyme activity is dramatically affected by: Alterations in pH Temperature Other protein denaturants

Section 21.2 Enzyme Structure Return to TOC Copyright Cengage Learning. All rights reserved 4 Simple and Conjugated Enzymes Enzymes are of two types: simple enzymes and conjugated enzymes Simple enzyme: composed only of protein (amino acid chains) Conjugated enzyme: Has a nonprotein part in addition to a protein part. Apoenzyme: Protein part of a conjugated enzyme. A cofactor : Nonprotein part of a conjugated enzyme. A holoenzyme is the biochemically active conjugated enzyme Apoenzyme + cofactor = holoenzyme (conjugated enzyme)

Section 21.2 Enzyme Structure Return to TOC Copyright Cengage Learning. All rights reserved 5 Cofactors Cofactors are important for the chemically reactive enzymes Cofactors are small organic molecules or Inorganic ions Organic molecule cofactors: also called as co-enzymes or co- substrates Co-enzymes/co-substrates are derived from dietary vitamins Inorganic ion cofactors Typical metal ion cofactors - Zn 2+, Mg 2+, Mn 2+, and Fe 2+ Nonmetallic ion cofactor - Cl - Inorganic ion cofactors derived from dietary minerals

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 6 Nomenclature: Most commonly named with reference to their function Type of reaction catalyzed Identity of the substrate A substrate is the reactant in an enzyme-catalyzed reaction: The substrate is the substance upon which the enzyme acts. E. g., In the fermentation process sugar to be converted to CO 2, therefore in this reaction sugar is the substrate

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 7 Three Important Aspects of the Naming Process 1.Suffix -ase identifies it as an enzyme E.g., urease, sucrase, and lipase are all enzyme designations Exception: The suffix -in is still found in the names of some digestive enzymes, E.g., trypsin, chymotrypsin, and pepsin 2.Type of reaction catalyzed by an enzyme is often used as a prefix E.g., Oxidase - catalyzes an oxidation reaction, E.g., Hydrolase - catalyzes a hydrolysis reaction 3.Identity of substrate is often used in addition to the type of reaction E.g. Glucose oxidase, pyruvate carboxylase, and succinate dehydrogenase

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 8 Practice Exercise Predict the function of the following enzymes. a.Maltase b.Lactate dehydrogenase c.Fructose oxidase d.Maleate isomerase Answers: a. Hydrolysis of maltose; b. Removal of hydrogen from lactate ion; c. Oxidation of fructose; d. Rearrangement (isomerization) of maleate ion

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 9 Six Major Classes Enzymes are grouped into six major classes based on the types of reactions they catalyze ClassReaction Catalyzed 1. OxidoreductasesOxidation-reductions 2. TransferasesFunctional group transfer reactions 3. HydrolasesHydrolysis reactions 4. Lyases Reactions involving addition or removal of groups form double bonds 5. IsomeraseIsomerisation reactions 6. Ligases Reactions involving bond formation coupled with ATP hydrolysis

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 10 Oxidoreductase An oxidoreductase enzyme catalyzes an oxidation reduction reaction: Oxidation and reduction reactions are always linked to one another An oxidoreductase requires a coenzyme that is either oxidized or reduced as the substrate in the reaction. E.g., Lactate dehydrogenase is an oxidoreductase and the reaction catalyzed is shown below

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 11 Transferase A transferase is an enzyme that catalyzes the transfer of a functional group from one molecule to another Two major subtypes: Transaminases - catalyze transfer of an amino group to a substrate Kinases - catalyze transfer of a phosphate group from adenosine triphosphate (ATP) to a substrate

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 12 Hydrolase A hydrolase is an enzyme that catalyzes a hydrolysis reaction The reaction involves addition of a water molecule to a bond to cause bond breakage Hydrolysis reactions are central to the process of digestion: Carbohydrases hydrolyze glycosidic bonds in oligo- and polysaccharides (see reaction below) Proteases effect the breaking of peptide linkages in proteins, Lipases effect the breaking of ester linkages in triacylglycerols

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 13 Lyase A lyase is an enzyme that catalyzes the addition of a group to a double bond or the removal of a group to form a double bond in a manner that does not involve hydrolysis or oxidation Dehydratase: effects the removal of the components of water from a double bond Hydratase: effects the addition of the components of water to a double bonds

Section 21.3 Nomenclature and Classification of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 14 Isomerase, and Ligase An isomerase is an enzyme that catalyzes the isomerization (rearrangement of atoms) reactions. A ligase is an enzyme that catalyzes the formation of a bond between two molecules involving ATP hydrolysis: ATP hydrolysis is required because such reactions are energetically unfavorable Require the simultaneous input of energy obtained by a hydrolysis of ATP to ADP

Section 21.4 Models of Enzyme Action Return to TOC Copyright Cengage Learning. All rights reserved 16 Enzyme Active Site The active site: Relatively small part of an enzymes structure that is actually involved in catalysis: Place where substrate binds to enzyme Formed due to folding and bending of the protein. Usually a crevice like location in the enzyme Some enzymes have more than one active site

Section 21.4 Models of Enzyme Action Return to TOC Copyright Cengage Learning. All rights reserved 17 Enzyme Substrate Complex Needed for the activity of enzyme Intermediate reaction species formed when substrate binds with the active site Orientation and proximity is favorable and reaction is fast

Section 21.4 Models of Enzyme Action Return to TOC Copyright Cengage Learning. All rights reserved 18 Two Models for Substrate Binding to Enzyme Lock-and-Key model: Enzyme has a pre-determined shape for the active site Only substrate of specific shape can bind with active site Induced Fit Model: Substrate contact with enzyme will change the shape of the active site Allows small change in space to accommodate substrate (e.g., how a hand fits into a glove)

Section 21.4 Models of Enzyme Action Return to TOC Copyright Cengage Learning. All rights reserved 19 Forces That Determine Substrate Binding H-bonding Hydrophobic interactions Electrostatic interactions

Section 21.5 Enzyme Specificity Return to TOC Copyright Cengage Learning. All rights reserved 20 Absolute Specificity: An enzyme will catalyze a particular reaction for only one substrate This is most restrictive of all specificities (not common) E.g., Urease is an enzyme with absolute specificity Stereochemical Specificity: An enzyme can distinguish between stereoisomers. Chirality is inherent in an active site (amino acids are chiral compounds) L-Amino-acid oxidase - catalyzes reactions of L-amino acids but not of D-amino acids.

Section 21.5 Enzyme Specificity Return to TOC Copyright Cengage Learning. All rights reserved 21 Group Specificity: Involves structurally similar compounds that have the same functional groups. E.g., Carboxypeptidase: Cleaves amino acids one at a time from the carboxyl end of the peptide chain Linkage Specificity: Involves a particular type of bond irrespective of the structural features in the vicinity of the bond Considered most general of enzyme specificities E.g., Phosphatases: Hydrolyze phosphateester bonds in all types of phosphate esters

Section 21.6 Factors That Affect Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 22 Temperature Higher temperature results in higher kinetic energy which causes an increase in number of reactant collisions, therefore there is higher activity. Optimum temperature: Temperature at which the rate of enzyme catalyzed reaction is maximum Optimum temperature for human enzymes is 37C (body temperature) Increased temperature (high fever) leads to decreased enzyme activity

Section 21.6 Factors That Affect Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 23 pH pH changes affect enzyme activity Drastic changes in pH can result in denaturation of proteins Optimum pH: pH at which enzyme has maximum activity Most enzymes have optimal activity in the pH range of 7.0 - 7.5 Exception: Digestive enzymes Pepsin: Optimum pH = 2.0 Trypsin: Optimum pH = 8.0

Section 21.6 Factors That Affect Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 24 Substrate Concentration Substrate Concentration: At a constant enzyme concentration, the enzyme activity increases with increased substrate concentration. Substrate saturation: the concentration at which it reaches its maximum rate and all of the active sites are full Turnover Number: Number of substrate molecules converted to product per second per enzyme molecule under conditions of optimum temperature and pH

Section 21.6 Factors That Affect Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 25 Enzyme Concentration Enzyme Concentration: Enzymes are not consumed in the reactions they catalyze At a constant substrate concentration, enzyme activity increases with increase in enzyme concentration The greater the enzyme concentration, the greater the reaction rate.

Section 21.6 Factors That Affect Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 26 Practice Exercise Describe the effect that each of the following changes would have on the rate of a reaction that involves the substrate sucrose and the intestinal enzyme sucrase. a.Decreasing the sucrase concentration b.Increasing the sucrose concentration c.Lowering the temperature to 10 C d.Raising the pH from 6.0 to 8.0 when the optimum pH is 6.2 Answers: a. Decrease rate b. Increase rate c. Decrease rate d. Decrease rate

Section 21.7 Enzyme Inhibition Return to TOC Copyright Cengage Learning. All rights reserved 27 Enzyme Inhibitor: a substance that slows down or stops the normal catalytic function of an enzyme by binding to it. Competitive Inhibitors: Compete with the substrate for the same active site Will have similar charge & shape Noncompetitive Inhibitors: Do not compete with the substrate for the same active site Binds to the enzyme at a location other than active site

Section 21.7 Enzyme Inhibition Return to TOC Copyright Cengage Learning. All rights reserved 28 Reversible Competitive Inhibition A competitive enzyme inhibitor: resembles an enzyme substrate in shape and charge Binds reversibly to an enzyme active site and the inhibitor remains unchanged (no reaction occurs) The enzyme - inhibitor complex formation is via weak interactions (hydrogen bonds, etc.). Competitive inhibition can be reduced by simply increasing the concentration of the substrate.

Section 21.7 Enzyme Inhibition Return to TOC Copyright Cengage Learning. All rights reserved 29 Reversible Noncompetitive Inhibition A noncompetitive enzyme inhibitor decreases enzyme activity by binding to a site on an enzyme other than the active site. Causes a change in the structure of the enzyme and prevents enzyme activity. Increasing the concentration of substrate does not completely overcome inhibition. Examples: Heavy metal ions Pb 2+, Ag +, and Hg 2+.

Section 21.7 Enzyme Inhibition Return to TOC Copyright Cengage Learning. All rights reserved 30 Irreversible Inhibition An irreversible enzyme inhibitor inactivates enzymes by forming a strong covalent bond with the enzymes active site. The structure is not similar to enzymes normal substrate The inhibitor bonds strongly and increasing substrate concentration does not reverse the inhibition process Enzyme is permanently inactivated. E.g., Chemical warfare agents (nerve gases) and organophosphate insecticides

Section 21.8 Regulation of Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 31 Cellular processes continually produces large amounts of an enzyme and plentiful amounts of products if the processes are not regulated. General mechanisms involved in regulation: Proteolytic enzymes and zymogenscovalent modification of enzymes Feedback control Regulation of enzyme activity by various substances produced within a cell The enzymes regulated are allosteric enzymes

Section 21.8 Regulation of Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 32 Properties of Allosteric Enzymes All allosteric enzymes have quarternary structure: Composed of two or more protein chains Have at least two of binding sites: Substrate and regulator binding site Active and regulatory binding sites are distinct from each other: Located independent of each other Shapes of the sites (electronic geometry) are different Binding of molecules at the regulatory site causes changes in the overall three dimensional structure of the enzyme: Change in three dimensional structure of the enzyme leads to change in enzyme activity Some regulators increase enzyme activity activators Some regulators decrease enzyme activity - inhibitors

Section 21.8 Regulation of Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 33 Feedback Control Feedback Control: A process in which activation or inhibition of the first reaction in a reaction sequence is controlled by a product of the reaction sequence. Regulators of a particular allosteric enzyme may be: Products of entirely different pathways of reaction within the cell compounds produced outside the cell (hormones)

Section 21.8 Regulation of Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 34 Proteolytic Enzymes and Zymogens 2nd mechanism of regulating enzyme activity: Production of enzymes in an inactive forms (zymogens) Zymogens are turned on at the appropriate time and place Example: proteolytic enzymes: Most digestive and blood-clotting enzymes are proteolytic enzymes Hydrolyze peptide bonds in proteins Proteolytic enzymes are generated in an inactive form and then converted to their active form

Section 21.8 Regulation of Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 35 Covalent Modification of Enzymes 3rd Mechanism for regulation of enzyme activity Covalent modification: A process in which enzyme activity is altered by covalently modifying the structure of the enzyme: Involves adding or removing a group from an enzyme Most common covalent modification: addition and removal of phosphate group: Phosphate group is often derived from an ATP molecule. Addition of the phosphate (phosphorylation) catalyzed by a Kinase enzyme Removal of the phosphate group (dephosphorylation) catalyzed by a phosphatase enzyme. Phosphate group is added to (or removed from) the R group of a serine, tyrosine, or threonine amino acid residue in the enzyme regulated.

Section 21.9 Antibiotics That Inhibit Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 36 An anitibiotic is a substance that kills bacteria or inhibits their growth Antibiotics usually inhibit specific enzymes essential to life processes of bacteria Two families of antibiotics considered in this discussion are sulfa drugs and penicillins

Section 21.9 Antibiotics That Inhibit Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 37 Sulfa Drugs Many derivatives of sulfanilamide collectively called sulfa drugs exhibit antibiotic activities Sulfanilamide is structurally similar to PABA (p- aminobenzoic acid) Many bacteria need PABA to produce coenzyme, folic acid Sulfanilamide is a competitive inhibitor of enzymes responsible for converting PABA to folic acid in bacteria Folic acid deficiency retards bacterial growth and that eventually kills them Sulfa drugs dont affect humans because we absorb folic acid from our diet

Section 21.9 Antibiotics That Inhibit Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 38 Penicillins Accidently discovered by Alexander Fleming in 1928 Several naturally occurring penicillins and numerous synthetic derivatives have been produced All have structures containing a four-membered Beta- lactam ring fused with a five-membered thiazolidine ring Selectively inhibits transpeptidase by covalent modification of serine residue Transpeptidase catalyzes the formation of peptide cross links between polysaccharides strands in bacterial cell walls

Section 21.9 Antibiotics That Inhibit Enzyme Activity Return to TOC Copyright Cengage Learning. All rights reserved 39 Cipro The antibiotic ciprofloxacin hydrochloride (Cipro for short) Considered the best broad-spectrum antibiotics because it is effective against skin and bone infections as well as against infections involving the urinary, gastrointestinal, and respiratory systems It is the drug of choice for treatment of travelers diarrhea Bacteria are slow to acquire resistance to Cipro. Biochemical threats associated with terrorism has thrust Cipro into the spotlight because it is effective against anthrax.

Section 21.10 Medical Uses of Enzymes Return to TOC Copyright Cengage Learning. All rights reserved 40 Diagnose certain diseases: Enzymes produced in certain organ/tissues if found in blood may indicate certain damage to that organ/tissue

Section 21.11 General Characteristics of Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 41 Organic compounds Must be obtained from dietary sources Human body cant synthesize in enough amounts Essential for proper functioning of the body Needed in micro and milligram quantities 1 Gram of vitamin B is sufficient for 500,000 people Enough vitamin can be obtained from balanced diet Supplemental vitamins may be needed after illness Many enzymes contain vitamins as part of their structures - conjugated enzymes Two Classes Water Soluble and Fat Soluable Synthetic and natural vitamins are same 13 Known vitamins

Section 21.12 Water-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 42 Vitamin C Humans, monkeys, apes and guinea pigs need dietary vitamins Co-substrate in the formation of structural protein collagen Involved in metabolism of certain amino acids 100 mg/day saturates all body tissues - Excess vitamin is excreted RDA (mg/day): Great Britain: 30 United States and Canada: 60 Germany: 75

Section 21.12 Water-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 43 Vitamin B The preferred and alternative names for the B vitamins Thiamin (vitamin B 1 ) Riboflavin (vitamin B 2 ) Niacin (nicotinic acid, nicotinamide, vitamin B 3 ) Vitamin B 6 (pyridoxine, pyridoxal, pyridoxamine) Folate (folic acid) Vitamin B 12 (cobalamin) Pantothenic acid (vitamin B 5 ) Biotin Exhibit structural diversity Major function: B Vitamins are components of coenzymes

Section 21.13 Fat-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 44 Vitamins A, D, E, K Involved in plasma membrane processes More hydrocarbon like with fewer functional groups Vitamin A Has role in vision - only 1/1000 of vitamin A is in retina 3 Forms of vitamin A are active in the body Derived from b-carotine

Section 21.13 Fat-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 45 Functions of Vitamin A Vision: In the eye- vitamin A combines with opsin protein to form the visual pigment rhodopsin which further converts light energy into nerve impulses that are sent to the brain. Regulating Cell Differentiation - process in which immature cells change to specialized cells with function. Examples: Differentiation of bone marrow cells white blood cells and red blood cells. Maintenance of the healthy of epithelial tissues via epithelial tissue differentiation. Lack of vitamin A causes such surfaces to become drier and harder than normal. Reproduction and Growth: In men, vitamin A participates in sperm development. In women, normal fetal development during pregnancy requires vitamin A.

Section 21.13 Fat-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 46 Vitamin D Two forms active in the body: Vitamin D 2 and D 3 Sunshine Vitamin: Synthesized by UV light from sun It controls correct ratio of Ca and P for bone mineralization (hardening) As a hormone it promotes Ca and P absorption in intestine

Section 21.13 Fat-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 47 Vitamin E Four forms of Vitamin Es: a-, b-, g- and d-Vitamin E Alpha-tocopherol is the most active biological active form of Vitamin E Peanut oils, green and leafy vegetables and whole grain products are the sources of vitamin E Primary function: Antioxidant protects against oxidation of other compounds

Section 21.13 Fat-Soluble Vitamins Return to TOC Copyright Cengage Learning. All rights reserved 48 Vitamin K Two major forms; K 1 and K 2 K 1 found in dark green, leafy vegetables K 2 is synthesized by bacteria that grow in colon Dietary need supply: ~1/2 synthesized by bacteria and 1/2 obtained from diet Active in the formation of proteins involved in regulating blood clotting

chapter 21 enzymes and vitamins. chapter 21 table of contents copyright © cengage learning. all...

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