Introduction to Biochemistry PDF

INTRODUCTION TO BIOCHEMISTRY  WATER Water, pH, Acids and Bases, and Buffers The water molecule,  Biochemistry...

INTRODUCTION TO BIOCHEMISTRY  WATER Water, pH, Acids and Bases, and Buffers The water molecule,  Biochemistry H₂O, consists of two It is the study of chemical processes in living hydrogen atoms organisms, including, but not limited to, living covalently bonded to an matter. oxygen atom. Biochemistry governs all living organisms and living processes. o Biochemical processes or Biochemical pathways  Formation of Dipoles A molecule with electrical charge distributed asymmetrically about its structure is referred to as a dipole. Due to the difference in electronegativity between oxygen and hydrogen, the shared electrons tend to spend more time closer to the oxygen atom than to the hydrogen atoms. Much of biochemistry deals with the structures,  Formation of Hydrogen Bonds functions and interactions of biological The partial positive macromolecules, such as proteins, nucleic acids, charge on the hydrogen carbohydrates and lipids, which provide the atoms of one water structure of cells and perform many of the molecule can attract the functions associated with life. partial negative charge on the oxygen atom of another water molecule. This attraction forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with surrounding water molecules: two through its hydrogen atoms and two through its lone pairs of electrons on the oxygen atom.  Biochemistry Application Medicine Nutrition Agriculture Research  Water is an IDEAL BIOLOGICAL SOLVENT Water's polarity and ability to form hydrogen bonds make it an excellent solvent for biological systems.  Water's polarity allows  ACIDS it to dissolve ionic compounds and other The term acid comes from the polar molecules. The Latin word acidus, which means positive end of water “sour.” molecules can surround Swedish chemist Svante negative ions, and the Arrhenius was the first to describe negative end can surround acids as substances that produce positive ions, effectively hydrogen ions (H+) when they separating and dissolving dissolve in water. them. Water’s capacity to form hydrogen bonds allows it to interact with a variety of molecules, including For example, hydrogen chloride ionizes completely in proteins, nucleic acids, and water to give hydrogen ions (H+), and chloride ions (Cl-). other biomolecules, It is the hydrogen ions that give acids a sour taste, change stabilizing their structures blue litmus indicator to red, and corrode some metals. and facilitating  Strong Acids biochemical reactions. An acid is strong if it completely ionizes (100%) in water. Form strong electrolytes.  Importance of Water Solvent Properties Temperature Regulation Transport Medium Structural Support Hydration and Homeostasis   Bronsted-Lowry Acids and Bases In 1923, J. N. Brønsted in Denmark and T. M. Lowry in Great Britain expanded the definition of acids and bases. A free disassociated proton (H+) does not actually exist in water. It undergoes hydration just like other cations because it  BASES has a strong attraction to polar water Are ionic compounds that dissociate into a metal molecules. The hydrated H+ is written as ion and hydroxide ions when they dissolve in H30+ and called hydronium ion. water. Most Arrhenius bases are formed from Groups 1A (1) and 2A (2) metals, such as NaOH, KOH, LiOH, and Ca(OH)2. For example, sodium hydroxide is an Arrhenius base that dissociates in water to give sodium ions (Na+), We can write the formation of a hydrochloric and hydroxide ions (OH- acid solution as a transfer of a proton from ). A base turns litmus hydrogen chloride to water. By accepting a indicator blue and proton in the reaction, water is acting as a phenolphthalein base according to the Brønsted-Lowry indicator pink. concept.  Strong Bases A base is strong if it completely ionizes (100%) in water. Form strong electrolytes. Examples: LiOH, NaOH, Ca(𝑂𝐻)2, Mg(𝑂𝐻)2, KOH  Identify the conjugate acid-base pars of the reaction below: Correct Answer Identify the conjugate acid-base pairs in the following reaction:  Conjugate Acid-Base Pairs According to the Brønsted-Lowry theory, a conjugate acid-base pair consists of molecules or ions related by the loss or gain of one (H+). Every acid-base reaction contains two conjugate acid-base pairs because  THE pH SCALE protons are transferred in both the On the pH scale, a number between o and 14 forward and the reverse reactions. represents the [H30+] for most solutions. In the laboratory, a pH meter is commonly used to determine the pH of a solution.   Calculating the pH and pOH of Solutions Because pH is a log scale, a change of one pH unit corresponds to a tenfold change in [H3O+]. It is important to note that the pH decreases as the [H3O+] increases. Soln A has a [H30+] 10x higher than B and 100x  Calculating the pH and pOH of Solutions than C. The pH/pOH scale is a logarithmic scale that corresponds to the [H3O+]/[ OH ̄ ] of aqueous solutions. Mathematically, pH/pOH is the negative logarithm (base 10) of the [H3O+]/[OH ̄] pH + pOH = 14  Acid and Base Strength Can be expressed in the equilibrium, Ka   BUFFERS A buffer is a solution that maintains pH by neutralizing added acid or base. In a buffer, an acid must be present to react with any OH- that is added, and a  Henderson-Hasselbach Equation base must be available to react with any added  Used to calculate the pH of the buffer solution H30+. However, that acid and base must not be able to neutralize each other. Buffer = Combination of an Acid-Base Conjugate Pair Most buffer solutions consist of nearly equal concentrations of:  Buffers may also contain:  Buffers in the Blood The arterial blood has a normal pH of 7.35– 7.45. If changes in H30+ lower the pH below 6.8 or raise it above 8.0, cells cannot function properly and death may result. The CO2 in our body dissolves as carbonic acid, and this weak acid dissociates to give bicarbonate and H30+ In the body, the concentration of carbonic acid is closely associated with the partial pressure of CO2. BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah What is a PROTEIN? characteristics to each type of amino acid. For example, alanine has a methyl, −𝐶𝐻3, as its R  The word “protein” is derived from the Greek group. word proteios, meaning “first.”  Proteins are large complex molecules made of Ionization of Amino Acid amino acids joined by peptide bonds.  Although we have amino acids with uncharged  There are many kinds of proteins that perform amino (−𝑁𝐻2) and carboxylic acid (-COOH) different functions. groups, these groups are ionized for amino acids in most body fluids. At physiological pH, the −𝑵𝑯𝟐 group gains 𝑯+ to give its ionized form −𝑵𝑯𝟑+ and the –COOH group loses 𝑯+ to give its ionized form −𝑪𝑶𝑶−  An ionized amino acid, which has both a positive and a negative charge, is a dipolar ion called zwitterion. The ionized regions have charge balance, which means that the ionized amino acid has an overall zero charge. What is an AMINO ACID?  Proteins are composed of molecular building blocks called amino acids.  There are only 20 different amino acids present in human proteins. AMINO ACID STEREOISOMERS  All the α-amino acids except for glycine are chiral because the α-carbon is attached to four different atoms. Thus, amino acids can exist as D and L isomers. We can draw Fischer projections for α– amino by placing the carboxylate group at the  Every amino acid top and the R group at the bottom. consists of a central  In the L isomer, the −𝑁𝐻3+ is on the left, and carbon atom called right in D isomer. In biological systems, the the α-carbon only amino acids incorporated into proteins are bonded to two the L isomers. There are D amino acids found functional groups: in nature, but not in proteins. an amino group (−𝑵𝑯𝟐) and a CLASSIFICATION OF AMINO ACIDS carboxylic acid  Nonpolar Amino Acids group ( - COOH). The α-carbon is also bonded o Have hydrogen, alkyl, to a hydrogen atom and an R group. or aromatic R groups,  It is the R group, which differs in each of the 20 which make them amino acids, that provides unique hydrophobic BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah  Polar Amino Acids POLAR NEUTRAL AMINO ACIDS o Have R groups that interact with water, which makes them hydrophilic o Polar neutral - Contain hydroxyl (-OH), thiol (- SH), or amide (−𝐶𝑂𝑁𝐻2), groups POLAR ACIDIC AMINO ACIDS o Polar Acidic - R group contains a carboxylate group (−𝐶𝑂𝑂−). o Polar Basic - R group contains an amino group, which ionizes to give an ammonium ion ESSENTIAL AMINO ACIDS POLAR BASIC AMINO ACIDS NONPOLAR AMINO ACIDS IONIZED FORMS OF AMINO ACIDS  A zwitterion with positive and negative charges and thus an overall neutral charge forms only at a certain pH called the isoelectric point (pI). However, an amino acid can exist: BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah o as a positive ion if a solution is more IONIZED FORMS OF POLAR ACIDIC AND acidic (has a lower pH) than its pI POLAR BASIC AMINO ACIDS o as a negative ion if a solution is more basic (has a higher pH) than its pI.  The pI values of the polar acidic amino acids (aspartic acid, glutamic acid) are about pH 3. At IONIZED FORMS OF NONPOLAR AND POLAR pH values of 3, the carboxylic acid group in the NEUTRAL AMINO ACIDS R groups of their zwitterions is not ionized. However, at physiological pH values, which are  The pI values for nonpolar and polar neutral greater than 3, the carboxylic acid in the R amino acids are from pH 5.1 to 6.3. Alanine group loses 𝐻+ to form a negatively charged forms its zwitterion in a solution with a pH of 6.0, which is also its pI value. In the zwitterion −𝑪𝑶𝑶− form, alanine contains carboxylate anion  The pI values of basic amino acids are typically higher than physiological pH value, ranging (−𝑪𝑶𝑶− ) and an ammonium cation (−𝑵𝑯𝟑+), from pH 7.6 to 10.8. Thus, at physiological pH which give an overall charge of zero. values, the amines in the R groups of the basic  In a solution with a pH lower than its pI amino acids (lysine, arginine, and histidine) gain (pH6.0), the −𝑵𝑯𝟑+ loses 𝐻+ to form an amino group (−𝑁𝐻2). Because the −𝑪𝑶𝑶− remains ionized, alanine has an overall negative charge (1-). BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah FORMATION OF PEPTIDES PEPTIDES  A peptide bond is an amide bond that forms when the −𝑪𝑶𝑶− of one amino acid reacts with the −𝑵𝑯𝟑+ of the next amino acid. The linking of two or more amino acids by peptide bonds forms a peptide.  Amidation reaction between the zwitterions of glycine and alanine The AA glycine on the left with a free −𝑵𝑯𝟑+ is called the N terminal AA. The AA alanine on the right with a free −𝑪𝑶𝑶− is called the C terminal AA. NAMING PEPTIDES  With the exception of the C terminal amino acid, the names of all the other amino acids in a peptide end with yl. For example, a tripeptide consisting of alanine at the N terminal, glycine, and serine at the C terminal is named as one word: alanylglycylserine. For convenience, the order of amino acids in the peptide is often written as the sequence of three-letter abbreviations. BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah DRAWING PEPTIDES Draw the structure and give the name for the tripeptide Gly-Ser-Met  STEP 1: Draw the structure for each amino acid in the peptide, starting with the N- terminus.  STEP 2: Remove the O atom from the carboxylate group of the N-terminal amino acid and two H atoms from the ammonium group in the adjacent amino acid. Repeat this process until the C-terminus is reached.  STEP 3: Use peptide bonds to connect the amino acids. BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah o POLYPEPTIDES IN THE BODY - Enkephalins and endorphins are natural painkillers produced in the body. They are polypeptides that bind to receptors in the brain to give relief from pain. LEVELS OF PROTEIN STRUCTURE  Primary Structure o The primary structure of a protein is the particular sequence of amino acids held together by peptide bonds. o For example, a hormone that stimulates the thyroid to release thyroxin is a - Two hormones produced by the tripeptide with the amino acid sequence pituitary gland are the Glu–His–Pro. nonapeptides (nine-amino-acid peptides) oxytocin and vasopressin. o The first protein to have its primary structure determined was insulin, which is a hormone that regulates the glucose level in the blood.  Secondary Structure o The secondary structure of a protein describes the type of structure that forms when amino acids o In the primary structure of human form hydrogen bonds within a insulin, there are two polypeptide polypeptide or between polypeptides. chains. In chain A, there are 21 o The three most common types of amino acids, and chain B has 30 secondary structure are the alpha helix, amino acids. the beta-pleated sheet, and the triple helix. o Alpha Helix (α-helix) - In an alpha helix (α-helix), hydrogen bonds form between the oxygen of the C=O groups and BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah the hydrogen of N-H groups of inability to handle daily tasks. the amide bonds in the next turn Alzheimer's patients have of the α-helix distinctly different brain tissue from people who do not have the disease. - In the brain of a normal person, small beta-amyloid proteins, made up of 42 amino acids, exist in the alpha-helical form. In the brain of a person with Alzheimer's, the o Beta-pleated Sheet (β-pleated sheet) beta-amyloid proteins change - In β-pleated sheet, hydrogen shape from the normal alpha bonds form between the oxygen helices that are soluble, to sticky atoms in the carbonyl groups of beta-pleated sheets, forming one polypeptide chain and the clusters of insoluble protein hydrogen atoms in the N-H fragments called plaques groups of the amide bonds in adjacent polypeptide chains. o Triple Helix  Tertiary Structure - Collagen, which is the most o The tertiary structure of a protein abundant protein in the body, involves attractions and repulsions makes up from 25% to 35% of all between the R groups of the amino protein in vertebrates. The strong acids in the polypeptide chain. structure of collagen is a result of three α helical polypeptides woven together like a braid to form a triple helix. o As interactions occur between different parts of the peptide chain, segments of o Alzheimer’s Disease the chain twist and bend until the protein acquires a specific three- dimensional shape. o The tertiary structure of a protein is stabilized by interactions between the R groups of the amino acids in one region of the polypeptide chain and the R groups of amino acids in other regions of the protein - Alzheimer's disease is a form of dementia in which a person has increasing memory loss and BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah bridge (ionic bond) with the R group in aspartic acid, which has a negative charge. o HYDROGEN BONDS (Polar neutral and polar neutral – OH and – NH – or – NH2 ) - Form between H of a polar R group and the O or N of another o HYDROPHOBIC INTERACTIONS amino acid. For example, a (Nonpolar and nonpolar) hydrogen bond can form between - Are interactions between two the –OH groups of two serines or nonpolar R groups. Within a between the –OH of serine and the protein, the amino acids with nonpolar R groups move away −𝑁𝐻2 in the R group of from the aqueous environment to glutamine. form a hydrophobic center at the interior of the protein molecule. o DISULFIDE BONDS (- SH and – SH) o HYDROPHILIC INTERACTIONS - (-S-S-) are covalent bonds that (Polar neutral and water) form between the –SH groups of - Are attractions between the cysteines in a polypeptide chain. external aqueous environment and the R groups of polar amino acids moving the polar amino acids toward the outer surface of globular proteins where they form hydrogen bonds with water. o SALT BRIDGES (Polar basic – NH3+ and polar acidic – COO-) - Are ionic bonds between ionized R groups of basic and acidic amino acids. For example, the ionized R group of arginine, which has a positive charge, can form a salt BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah o Globular Proteins subunits are held together by the same - A group of interactions that stabilize tertiary proteins known structures as globular. proteins have compact, o Hemoglobin spherical shapes because sections - Hemoglobin, a globular protein of the polypeptide chain fold over that transports oxygen in blood, on top of each other due to the consists of four polypeptide chains various interactions between R or subunits: two α chains, and two groups. β chains. In the adult hemoglobin molecule, all four subunits (𝜶𝟐𝜷𝟐) - Myoglobin is a globular protein must be combined for hemoglobin that stores oxygen in skeletal to properly function as an oxygen muscle. It contains 153 amino carrier. acids in a single polypeptide chain with about ¾ of the chain in the α- helix secondary structure. Summary of Structural Levels in Proteins: o Fibrous Proteins - The fibrous proteins are proteins that consist of long, thin, fiber-like shapes. They are typically involved in the structure of cells and tissues. Two types of fibrous protein are the α- and β-keratins. - α-keratins: hair, wool, skin, and nails - β-keratins: feathers of birds and scales of reptiles  Quaternary Structure o When a biologically active protein consists of two or more polypeptide chains or subunits, the structural level is referred to as a quaternary structure. In the quaternary structure, the BBIO 109 LECTURE NOTES MODULE 2: PROTEINS AND ACIDS Magbanua, Keilah DENATURATION OF PROTEINS  Denaturation of a protein occurs when there is a change that disrupts the interactions between R groups that stabilize the secondary, tertiary, or quaternary structure. However, the covalent amide bonds of the primary structure are not affected.  The loss of secondary and tertiary structures occurs when conditions change, such as increasing the temperature or making the pH very acidic or basic. Examples of Protein Denaturation:  Sickle-Cell Anemia o Sickle-cell anemia is a disease caused by an abnormality in the shape of one of the subunits of the hemoglobin protein. In the β-chain, the sixth amino acid, glutamic acid, which is polar acidic, is replaced by valine, a nonpolar amino acid. MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH ENZYME molecules, which are called substrates.  The tertiary structure of an enzyme plays an  Biological catalysts known as enzymes are important role in how that enzyme catalyzes needed for most chemical reactions that take reactions. place in the body.  A catalyst increases the reaction rate by ACTIVE SITE changing the way a reaction takes place but  In a catalyzed reaction, an enzyme must first is itself not changed at the end of the bind to a substrate in a way that favors catalysis. reaction.  Within an enzyme's large tertiary structure is a  The chemical reactions in our cells must region called the active site, where the enzyme occur at incredibly fast rates under the mild binds one or more substrates & catalyzes the conditions of pH 7.4 and a body temperature reaction. of 37 °C.  This active site is often a small pocket that closely fits the shape of the substrate.  Within the active site, the R groups of amino NAME & CLASSIFICATION OF ENZYMES acids interact with the functional groups of the substrate to form hydrogen bonds, salt  The names of enzymes describe the bridges, or hydrophobic interactions. compound or the reaction that is catalyzed.  The actual names of enzymes are derived by TAKE NOTE! replacing the end of the name of the reaction The active site of a particular enzyme fits the shape of only a few types of substrates, which makes an or reacting compound with the suffix ase. enzyme very specific about the type of substrate it  For example, the compound sucrose is binds. hydrolyzed by the enzyme sucrase, and a lipid is hydrolyzed by a lipase. ENZYME-CATALYZED REACTION  An oxidase catalyzes an oxidation reaction, and a dehydrogenase removes hydrogen  The proper atoms. alignment of a substrate within the active-site forms an enzyme- substrate (ES) complex.  Within the active site, the amino acid R groups take part in catalyzing the chemical reaction. ENZYME ACTION  For example, acidic and basic R groups remove protons from or provide protons for the  Nearly all enzymes substrate. are globular  As soon as the catalyzed reaction is complete, the proteins. products are released from the enzyme so it can  Each has a unique bind to another substrate molecule. three-dimensional shape that recognizes and binds a small group of reacting MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH  We can write the catalyzed reaction of an enzyme (E) with a substrate (S) to form product (P) as follows:  In the induced-fit model, a substrate and enzymes work together to acquire a geometrical arrangement that lowers the activation energy.  A different substrate could not induce these  Let's consider the hydrolysis of sucrose by changes, and no catalysis would occur. sucrase. When a molecule of sucrose binds to the active site of sucrase, its glycosidic bond is placed in a position favorable for reaction.  The amino acid R groups catalyze the hydrolysis of sucrose with water to give the products glucose and fructose. The products in the active site are released, and the sucrase binds another sucrose substrate. LOCK-AND-KEY & INDUCED-FIT MODELS  The lock-and-key model describes the active site as having a rigid, nonflexible shape.  Only those substrates with shapes that fit exactly into the active site are able to bind with that enzyme. FACTORS AFFECTING ENZYME ACTIVITY  The shape of the active site is analogous to a lock, and the proper substrate is the key that fits into  Temperature the lock. o Low temp -> Little activity o High temp -> Increased activity o Enzymes are most active at optimum temperature, which for most  In induced-fit model, the active site adjusts to enzymes is 37 °C or body temperature fit the shape of the substrate more closely. o At temperatures above 50 °C, the  At the same time, the substrate adjusts its shape tertiary structure-and thus the shape of to better adapt to the geometry of the active sit. most proteins-is destroyed, causing a loss in enzyme activity.  As a result, the reacting section of the substrate o Certain organisms known as becomes properly aligned with the groups in thermophiles live in environments the active site that catalyze the reaction. where temperatures range from 50 °C to 80 °C. MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH o Thermophiles have enzymes that TAKE NOTE! contain more arginine and tyrosine In most enzyme-catalyzed reactions, the than the ordinary one. concentration of the substrate is much greater than the o These slight changes allow the enzymes concentration of the enzyme. in thermophiles to form more hydrogen bonds and salt bridges that stabilize the When enzyme concentration is kept constant, tertiary structures at high temperatures increasing the substrate concentration increases the and resist unfolding and the loss of rate of the catalyzed reaction until the substrate enzymatic activity. saturates the enzyme.  pH o Enzymes are most active at their optimum pH, the pH that maintains the proper tertiary structure of the protein. o If a pH value is above or below the optimum pH, the R group interactions are disrupted, which destroys the tertiary structure and the active site. o Small changes in pH are reversible, which allows an enzyme to regain its structure and activity. o However, large variations from optimum pH permanently destroy the structure of the enzyme. Enzymes in most cells have optimum pH ENZYME INHIBITION values around 7.4.  Many kinds of molecules called inhibitors cause enzymes to lose catalytic activity.  Although inhibitors act differently, they all prevent the active site from binding with a substrate.  An enzyme with a reversible inhibitor can regain enzymatic activity, but an enzyme attached to an irreversible inhibitor loses  Enzyme and Substrate Concentration enzymatic activity permanently. o At higher enzyme concentrations, more molecules are available to bind and catalyze the reaction. o As long as the substrate concentration is greater than the enzyme concentration, there is a direct relationship between the enzyme concentration and enzyme activity MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH  Competitive Inhibitor o When the noncompetitive inhibitor is o A competitive bonded to the enzyme, the shape of the inhibitor has a enzyme is distorted. structure that is so o Examples of noncompetitive inhibitors similar to the are the heavy metal ions Pb2+, Ag+, and substrate it can bond Hg2+ that bond with amino acid side to the enzymes just groups such as -COO or -OH. like the substrate. o Catalytic activity is restored when o Thus, a competitive chemical reagents remove the inhibitors. inhibitor competes  Irreversible Inhibition for the active site on o In irreversible inhibition, a molecule the enzyme. causes an enzyme to lose all enzymatic o As long as the activity. inhibitor occupies o Most irreversible inhibitors are toxic the active site, the substrate cannot bind substances that to the enzyme and no reaction takes place o destroy enzymes. o Usually an irreversible inhibitor forms a As long as the concentration of the inhibitor is covalent bond with an amino acid side substantial, there is a loss of enzyme activity. group within the active site, which However, adding more substrate displaces the prevents the substrate from binding to competitive inhibitor. As more enzyme molecules the active site or prevents catalytic bind to substrate (ES), enzyme activity is regained. activity. o Insecticides and nerve gases act as irreversible inhibitors of acetylcholinesterase, an enzyme needed for nerve o conduction. o When acetylcholinesterase is inhibited, the transmission of nerve impulses is blocked, and paralysis occurs.  Noncompetitive Inhibitor o The structure of a noncompetitive inhibitor does not resemble the substrate and does not compete for the active site. o Antibiotics produced by bacteria, mold, or yeast are inhibitors used to stop bacterial growth. o Penicillin inhibits an enzyme needed for the formation of cell walls in bacteria, but not human cell membranes. o However, some bacteria are resistant to penicillin because they produce penicillinase, an enzyme that breaks down penicillin. o Instead, a noncompetitive inhibitor binds to a site on the enzyme that is not the active site. MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH ENZYME COFACTORS  Vitamins are classified into two groups by solubility: water-soluble and fat-soluble.  Enzymes  Water-soluble vitamins have polar groups known as such as -OH and -COOH, which make them simple soluble in the aqueous environment of the cells. enzymes consist only of  The fat-soluble vitamins are nonpolar proteins. compounds that are soluble in the fat (lipid) components of the body such as fat deposits and  Many cell membranes. enzymes require small  The water-soluble vitamins are required by molecules or many enzymes as cofactors to carry out certain metal ions called cofactors to catalyze reactions aspects of catalytic action. The coenzymes do not properly. remain bonded to a particular enzyme but are used over and over again by different enzymes to  When the cofactor is a small organic molecule, it facilitate an enzyme-catalyzed reaction is known as a coenzyme.  Thus, only small amounts of coenzymes are  If an enzyme requires a cofactor, neither the required in the cells. protein structure nor the cofactor alone has catalytic activity.  Many enzymes must contain a metal ion to carry out their catalytic activity.  The metal ions are bonded to one or more of the amino  acid R groups.  The metal ions from the minerals that we obtain from foods in our diet have various functions in catalysis. VITAMINS AND COENZYMES  The fat-soluble vitamins A, D, E, and K are  Vitamins are organic not involved as coenzymes, but they are molecules that are important in processes such as vision, formation essential for normal of bone, protection from oxidation, and proper health and growth. blood clotting.  They are required in  Because the fat-soluble vitamins are stored in trace amounts and the body and not eliminated, it is possible to must be take too much, which could be toxic. obtained from the diet because they are not synthesized in the body. MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH MODULE 3: ENZYYMES BBIO109 LECTURE NOTES MAGBANUA, KEILAH