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Questions and Answers
What is the name given to the energy needed to start a chemical reaction?
What is the name given to the energy needed to start a chemical reaction?
Activation energy
What is the role of enzymes in chemical reactions?
What is the role of enzymes in chemical reactions?
Enzymes lower the activation energy of chemical reactions
Enzymes are consumed during the reactions they catalyze.
Enzymes are consumed during the reactions they catalyze.
False
Enzymes can catalyze both forward and reverse reactions.
Enzymes can catalyze both forward and reverse reactions.
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What is the term for the molecule that an enzyme acts upon?
What is the term for the molecule that an enzyme acts upon?
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What is the name of the specific part of an enzyme where the chemical reaction occurs?
What is the name of the specific part of an enzyme where the chemical reaction occurs?
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What are the common sources of enzymes?
What are the common sources of enzymes?
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Which of the following is NOT a guideline for selecting the right microorganism for enzyme production?
Which of the following is NOT a guideline for selecting the right microorganism for enzyme production?
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What are some advantages of using enzymes in food processing?
What are some advantages of using enzymes in food processing?
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What is a primary disadvantage of using enzymes?
What is a primary disadvantage of using enzymes?
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What are the two main components of a holoenzyme?
What are the two main components of a holoenzyme?
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What are the three types of cofactors?
What are the three types of cofactors?
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What is the study of enzymes called?
What is the study of enzymes called?
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What are isozymes?
What are isozymes?
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Which of the following statements is TRUE about the active site of an enzyme?
Which of the following statements is TRUE about the active site of an enzyme?
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What are allosteric factors?
What are allosteric factors?
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What is enzyme kinetics concerned with?
What is enzyme kinetics concerned with?
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What is the transition state in an enzyme-catalyzed reaction?
What is the transition state in an enzyme-catalyzed reaction?
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What is activation energy (Ea)?
What is activation energy (Ea)?
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What is catalysis?
What is catalysis?
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What does the Enzyme Commission (EC) number of an enzyme indicate?
What does the Enzyme Commission (EC) number of an enzyme indicate?
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Which class of enzymes catalyzes oxidation-reduction reactions?
Which class of enzymes catalyzes oxidation-reduction reactions?
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Which class of enzymes transfers functional groups between molecules?
Which class of enzymes transfers functional groups between molecules?
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Which class of enzymes breaks down molecules using water?
Which class of enzymes breaks down molecules using water?
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Which class of enzymes break down molecules without using water?
Which class of enzymes break down molecules without using water?
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Which class of enzymes catalyzes the rearrangement of atoms within a molecule?
Which class of enzymes catalyzes the rearrangement of atoms within a molecule?
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Which class of a enzyme joins two molecules together?
Which class of a enzyme joins two molecules together?
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What are the four levels of enzyme specificity?
What are the four levels of enzyme specificity?
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Study Notes
Enzymes
- Enzymes lower the activation energy of chemical reactions.
- Activation energy is the energy needed to start a reaction.
- Enzymes catalyze both forward and reverse reactions.
- They are not consumed in the reaction.
- Enzymes have a high degree of specificity for a certain substrate or group of substrates.
- This specificity allows for precise control over biochemical reactions.
Applications of Enzymes
- Enzymes are used to upgrade product quality, like clarifying juice.
- They are used in the preparation of synthetic foods.
- They improve food flavor.
- They improve processing techniques and procedures.
- They are used in the utilization of by-products.
Sources of Enzymes
- Plants
- Animals
- Microorganisms
- Microorganisms are versatile and produce large amounts of enzymes.
- Microorganisms are easily modified by genetic engineering.
- Extracellular enzymes from microorganisms are easily recovered.
Guidelines in Selecting Right MCG
- MCG should be non-pathogenic.
- MCG should be non-toxigenic.
- MCG should not produce antibiotics.
- MCG should be stable and consistent.
- MCG should have high yield and activity.
Advantages of Enzymes
- Natural and non-toxic.
- Non-toxic products.
- Minimal side reactions.
- Mild operating conditions.
- Controlled rate of reaction.
- Easily inactivated.
Disadvantages of Enzymes
- Limited substrate range.
- Enzymes can only act on only one substrate or a family of structurally similar substrates.
Holoenzyme, Apoenzyme, Cofactor
- Holoenzyme = apoenzyme + cofactor
- Cofactor:
- Metal ion
- Ligands
- Coenzymes
- Prosthetic group
- Co-substrate
- Cofactor:
- Apoenzyme = protein portion of an enzyme.
- Cofactor = non-protein portion of an enzyme.
- Cofactors help in catalyzing biochemical reactions.
Types of Cofactors
- Co-enzymes - vitamin derivative (vitamin itself or derived from it)
- Usually, water-soluble.
- Metal ions - metals (Na, Fe, Mn, Mg, Cu, K, Zn).
- Ligands - forms complexes with biomolecules.
Enzymology
- Study of enzymes.
- Isozymes - multiple forms of enzymes that catalyze the same reaction but differ in protein structure.
- Examples: Hexokinase and glucokinase.
- Active site (AS) - part of the enzyme where the chemical reaction occurs.
Allosteric Factors (AF) and Regulatory Site (RS)
- Allosteric Factors (AF) are activators or inhibitors of enzymatic activity that alter kinetic properties of the enzyme.
- Regulatory site (RS) is the part where an allosteric factor binds.
- Binding of AF at the RS can modulate the enzyme's activity.
Enzyme Kinetics
- Study of reaction of enzyme catalysis.
- Deals with the rate/ speed of catalyzed reaction.
- Transition State - an activated complex formed between enzyme and substrate.
- The substrate can either return to the original state or form new Products.
Activation Energy (Ea) and Catalysis
- Activation energy - catalysis of reaction.
- Amount of energy to bring 1 mole of reactant or substrate to transition state.
- Catalysis - process by which enzymes facilitate chemical reactions.
Enzyme Mechanism
- https://www.youtube.com/watch?v=ZQzzBCf5wck
- https://www.youtube.com/watch?v=qgVFkRn8f10
Enzyme Classification & Nomenclature (by IUBMB)
- E.C. 1. 2. 3. 4.
- EC - Enzyme Commission
- Type of reaction
- Subclass (nature of donor)
- Sub-subclass(nature of acceptor)
- Serial no. of enzyme within the subclass
Enzyme Classification - Oxidoreductase
- Oxidize or reduce substrates by transfer of hydrogens or electrons or by use of oxygen.
- Systematic name is formed as "donor : acceptor + oxidoreductase".
- Example: H2O2 + H2O2 → O2 + 2H2O
- Catalase, EC 1.11.1.6
Enzyme Classification - Transferase
- Remove groups (not including H) from substrates and transfer them to acceptor molecules (not including water).
- Systematic name is formed as "donor : acceptor + group transferred + transferase".
- Example: ATP + D-glucose →ADP + D-glucose 6-phosphate
- Glucokinase, EC 2.7.1.2
Enzyme Classification - Hydrolase
- Hydrolytic or cleavage reaction.
- Water participates in the breakage of covalent bonds of the substrate.
- Systematic name is formed as "substrate hydrolase".
- Example: Triacylglycerol + H2O →diacylglycerol + a fatty acid anion
- Triacylglycerol acylhydrolase (triacylglycerol lipase, EC 3.1.1.3)
Enzyme Classification - Lyases
- Remove groups from their substrates (not by hydrolysis) to leave a double bond or conversely add groups to double bonds.
- Systematic name is formed as "substrate prefix-lyase"
- Example: Malate → fumarate + H2O
- Malate hydro-lyase (fumarate hydratase, EC 4.2.1.2; formerly known as fumarase)
Enzyme Classification - Isomerase
- Isomerization reaction or intramolecular rearrangement.
- Systematic name is formed as "substrate prefix- isomerase".
- Prefix indicates the types of isomerization involved.
- Example: L-alanine →D-alanine
- Alanine racemase (alanine recemase, EC 5.1.1.1)
Enzyme Classification - Ligases/Synthetase
- Catalyze the covalent linking of two molecules, coupled with the breaking of a pyrophosphate bond as in ATP.
- Systematic name is formed as "X:Y ligase (Z)", Where X and Y are the two molecules to be joined together and Z is the product formed.
- Example: ATP + L-aspartate + NH3 →AMP + pyrophosphate + L-asparagine
- L-aspartate ammonia ligase (AMP-forming) (aspartate-ammonia ligase, EC 6.3.1.1).
Degree of Specificity
- Most enzymes relatively catalyze a small number of reactions.
-
Stereochemical specificity - enzyme specific to a single type of isomer (eg. D or L form)
- Sugars- D form, amino acids- L-form
- Example: Lactic acid dehydrogenase is specific for L- lactic acid to pyruvic acid.
-
Low specificity - enzyme has specificity to a type of linkage or bond to be split.
- Example: Lipase - specific to a linkage between an alcohol and an acid (glycerol and FA).
-
Group specificity - enzyme acts upon a substrate with a specific chemical linkage and a specific group on one side of the linkage.
- Example: Chymotrypsin- peptide bond cleavage of aromatic AA; Trypsin- basic AA in peptide bond.
-
Absolute specificity - most abundant and exclusive, for one substrate and one reaction only.
- Example: Urease- urea to CO2 and NH3; Maltase- maltose to 2 glucose.
Catalysis Models
- Lock & Key Hypothesis - proposed by E. Fischer.
- Substrate is the key & Enzyme is the lock.
- Substrate should be in complement.
- Induced Fit Model - proposed by D. Koshland.
- Initial Substrate is not completely complementary.
- Conformation of Enzyme is changed by the binding of the substrate.
- Active form of the enzyme is induced by substrate only.
Factors Affecting Enzyme Activity
-
pH
- Extreme pH inactivates enzymes.
- Protein unfolding of apoenzyme.
- Optimum pH for enzymes: pH 4.5–8.0
- Exceptions: Pepsin (1.5–2.0), arginase (pH 10).
-
Temperature
- Optimum at 30-40°C
- DNA polymerase: opt. at 72°C, stable up 94–95 °C
- Inactivates at 45°C
- Some enzymes show minimal activity at subfreezing temp, but most remain significantly active.
-
Substrate concentration
- As substrate concentration increases, Rate of enzyme-catalyzed reactions also increases.
- At saturation point, enzyme is working at its maximum capacity.
-
Enzyme concentration
- As enzyme concentration increases, Rate of enzyme-catalyzed reactions also increases.
- More active sites available for substrate binding, leading to more product formation.
-
Water activity
- Enzyme activities in aqueous media.
- Low water activity reduces enzyme activity.
- Decreased mobility & interactions.
- High water activity can lead to dilution effects.
- Decreases reactant concentration, and thus negatively affects enzyme activity.
Enzymes in Food Modification
- Enzymes modify food products.
- Pectin esterase - reacts with pectin and cleaves pectin.
- Amylases – hydrolyze starch.
- α-amylase – hydrolyzes starch randomly, reducing viscosity.
- β-amylase – attacks end units of starch chains, increasing sweetness.
- Lipase – hydrolyzes ester linkage TAG, affecting flavor.
- Phenolase – causes oxidative browning.
- Peroxidase – destroys Vitamin C, bleaches carotenoids, and leads to FA peroxidation.
- Indicator of heat treatment effectiveness.
- Ascorbic acid oxidase – oxidizes ascorbic acid, lowering vitamin C content.
Immobilized Enzymes
- Immobilized Enzymes: Enzymes fixed to a carrier.
- Movement of enzymes is restricted by physical/chemical means.
- Can be used repeatedly in batch operations.
- Advantages: High bio-catalytic activity, high yield, continuous process, reusability, economical, product purity.
- Disadvantages: Enzymes are sensitive to external factors (pH, temperature, contaminants).
- Ways of Immobilizing: Adsorption, Covalent bond binding, Cross-linking.
- Adsorption: Biophysical force, Electrostatic interaction, etc.
- Covalent bond binding.
- Cross-linking: Cross linking, Co-cross linking,
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