define enzymes?
What are enzymes made of?
Are all enzymes made of proteins?
What is the structure of an enzyme made of?
Where is the catalytic activity of an enzyme located?
How does the substrate attach to the active site?
what is the active site?
How many amino acids typically make up an enzyme’s active site?
- biological polymers that catalyse biochemical reactions.
- Enzymes are globular proteins made of one or more polypeptide chains.
- A ribozyme consist of RNA found in ribosomes; an example is peptidyl transferase in ribosomes.
- The structure is a linear chain of amino acids folded into a three-dimensional shape.
- It is located in the enzyme’s active site.
- Through non-covalent interactions such as hydrogen bonds and hydrophobic forces.
- Typically 3 to 12 amino acids.
How are the amino acids in an active site arranged despite being scattered in the polypeptide?
What are the two main regions of an enzyme’s active site?
What is the function of the binding site in an enzyme?
What is the function of the catalytic site in an enzyme?
Why can only a specific substrate bind to an enzyme’s active site?
Can similar substrates bind to the active site of an enzyme?
Through the secondary and tertiary folding of the protein, bringing them close together.
The binding site and the catalytic site.
It binds to the substrate using specific amino acids.
It converts the substrate into the product during catalysis.
Because the shape of the active site is specific to the substrate.
Yes, sometimes closely related substrates can also bind.
What is a cofactor in relation to enzymes?
What role does a cofactor play in enzyme activity?
What is a holoenzyme?
What is an apoenzyme?
Can enzymes that do not require cofactors still have inactive and active states?
Which enzyme is secreted in an inactive form called pepsinogen?
Why is pepsinogen inactive when secreted?
What activates pepsinogen into pepsin?
What happens to pepsinogen when it is exposed to HCl in the stomach?
What happens to the shape of the active site when a cofactor attaches to the enzyme?
A non-protein part required by some enzymes for activity.
It helps the substrate attach to the active site and participates in the catalytic process.
An active enzyme formed when a cofactor combines with the enzyme.
The inactive protein part of an enzyme without its cofactor.
Yes, they can be in inactive or active states through other mechanisms.
Pepsin.
It has an extra polypeptide fragment blocking the active site.
Exposure to hydrochloric acid (HCl).
The extra fragment is removed, activating it into pepsin.
The final shape of the active site is established.
What are the three main types of cofactors?
What are some examples of inorganic ion cofactors?
When do inorganic ion cofactors attach to enzymes? is it detachable?
What are inorganic ion cofactors also called?
Give an example of a reaction where an inorganic ion acts as a cofactor.
What are coenzymes?
Give examples of organic molecule cofactors.
Are organic molecule cofactors detachable or permanently bound?
What is a prosthetic group?
Are prosthetic groups detachable from the enzyme after the reaction?
Give an example of a prosthetic group and the enzyme it is attached to.
What role does NAD⁺ play in the alcohol dehydrogenase reaction?
Inorganic ions, organic molecules (coenzymes), and prosthetic groups
Fe²⁺, Mg²⁺, Cu²⁺, Zn²⁺
Only when the substrate binds to the enzyme
Activators
Glucose + ATP → (Hexokinase + Mg²⁺) → Glucose-6-phosphate + ADP
Organic cofactors derived from vitamins
ATP, NAD⁺, FAD
Detachable (like inorganic ions)
A permanently attached non-protein part of an enzyme
No, they remain covalently bonded to the enzyme
Iron-containing porphyrin ring in cytochromes
It acts as a coenzyme and is reduced to NADH₂
What is the first step in the mechanism of enzyme action?
What complex is formed when the enzyme binds to the substrate?
What happens to the substrate after it binds to the enzyme?
What happens after the product is formed in the enzyme-substrate reaction?
What does the Lock and Key model explain?
Who proposed the Lock and Key model and when?
In the Lock and Key model, what does the enzyme represent?
What does the substrate represent in the Lock and Key model?
According to the Lock and Key model, what must be true for the substrate to bind to the enzyme?
Does the active site of the enzyme change shape during substrate binding in the Lock and Key model?
The substrate binds to the active site of the enzyme.
Enzyme-substrate (ES) complex.
The substrate is converted into product while attached to the enzyme (EP complex).
The product is released, and the enzyme becomes available for reuse.
The specificity of enzyme-substrate interaction.
Emil Fischer, in 1894.
The lock.
The key.
The shape of the substrate must match the shape of the active site.
No, the enzyme is considered rigid, and the shape of the active site does not change.
What part of a key is equivalent to the enzyme’s active site?
What does the key-lock analogy explain about enzyme action?
What are enzymes that follow the lock and key model called?
Name two enzymes that follow the lock and key model.
What is the most significant property of enzymes?
What is meant by absolute specificity in enzymes?
Give an example of an enzyme that shows absolute specificity.
What is the reaction catalyzed by urease?
draw digram for lock and key model
The notched portion of the key
That enzymes are highly specific in their action
Non-regulatory enzymes
Sucrase, Maltase
The ability of an enzyme to catalyze one specific reaction
When one enzyme can catalyze only one substrate and essentially no others
Urease
Urea + Water → (Urease) → Ammonia + Carbon dioxide
Who proposed the induced fit model and in which year?
What is the key feature of the active site in the induced fit model?
What happens to the shape of the enzyme’s active site when the substrate binds?
Why does the active site change shape during enzyme-substrate interaction?
What happens to the active site after the reaction is completed?
How does the flexibility of the active site benefit the enzyme’s function?
Give an example of an enzyme that can perform more than one related reaction.
What are enzymes that follow the induced fit model called?
Give an example of an allosteric or regulatory enzyme.
Write the two reactions catalyzed by carbonic anhydrase.
Daniel Koshland proposed the induced fit model in 1959.
The active site is flexible, not rigid.
It is molded into a precise shape to match the substrate.
This shape change allows the enzyme to perform its catalytic function more effectively.
The active site regains its original shape after the reaction ends.
The flexibility allows the enzyme to bind more than one type of related substrate and carry out multiple related reactions.
Carbonic anhydrase is an example; it adds O₂ to hemoglobin and controls formation of carbonic acid/bicarbonates.
Enzymes following this model are called regulatory or allosteric enzymes.
Hexokinase is an example of an allosteric enzyme.
Hb + 4O₂ → HbO₄ (Oxyhaemoglobin)
CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻ (all catalyzed by carbonic anhydrase)
Difference between induced fit and lock and key model
- In the induced fit model, active site of the enzyme does not completely fit to the substrate.
- In the lock and key model, the active site of the enzyme is the complement of the substrate. So, it precisely fits to the substrate.
- In the induced fit model, the active site of the enzyme has to undergo a conformational change to improve binding.
- The lock and key model describes the specificity of the active site of the enzyme to a particular substrate.
What is meant by energy of activation?
Why is heat used as energy of activation in non-living systems?
Why can’t heat be used as energy of activation in living systems?
Approximately how many chemical reactions occur in a living cell at any time?
How is the rate of enzymatic reaction measured?
What are external factors that influence the rate of enzymatic reactions?
the minimum amount of energy required for molecules to react.
To increase the no. of effective collisions between molecules.
Because living cells contain heat-sensitive proteins that would be damaged by high temperatures.
Around 1,000 reactions.
By the amount of substrate converted or product formed over time.
Temperature, pH, substrate concentration, enzyme concentration, inhibitors, and activators.
Under what condition does the living system operate?
How is the excited state of molecules achieved in a living system?
What is formed when enzyme (E) reacts with reactant (A)?
What does the AE complex react with to form the final product?
How does an enzyme lower the energy of activation?
What is meant by energy of activation in a biochemical reaction?
What does the enzyme change in order to reduce energy dependency?
Isothermal condition (constant temperature).
Through biochemical processes.
AE transitional complex.
Reactant B, to form AB and release enzyme.
By converting energy-dependent steps into energy-independent ones.
It is the energy needed to break existing bonds and initiate a reaction.
The energy requirement of the reaction pathway.
How does heating affect enzyme and substrate movement?
What is the effect of a 10°C temperature increase on reaction rate?
What is the optimum temperature for enzyme activity?
Why does enzyme activity decrease beyond the optimum temperature?
What happens to an enzyme when it is denatured?
Which bonds in enzymes are most sensitive to temperature changes?
What is the optimum temperature for most human enzymes?
What is the optimum temperature for thermophilic bacteria?
Why are thermophilic bacterial enzymes used in biological washing powders?
What happens to enzymes at freezing temperatures?
Can enzymes recover activity after freezing?
What is the minimum temperature for enzyme activity?
Heating increases molecular motion, making enzymes and substrates move faster, increasing collision chances.
A 10°C increase typically doubles the reaction rate (Q₁₀ rule).
The optimum temperature is the temperature at which enzyme activity is highest.
Beyond optimum, enzymes denature (lose structure), reducing activity despite more collisions.
A denatured enzyme unfolds, losing its active site shape and catalytic function.
Hydrogen bonds (which stabilize enzyme structure) are most heat-sensitive.
Most human enzymes work best at 37–38°C (body temperature).
Thermophilic bacteria have enzymes optimized for 70°C or higher (e.g., hot springs).
Their heat-resistant enzymes work in high-temperature washes (e.g., laundry detergents).
At freezing temps, enzymes become inactive but not denatured.
Yes, they regain function when warmed (reversible inactivation).
The minimum temperature is the lowest temp at which enzymes become active again.
What is the optimum pH for an enzyme?
Why is enzyme function sensitive to pH changes?
What happens when the pH slightly deviates from the optimum?
Can temporary pH changes permanently damage enzymes?
What happens to enzyme activity at very low (acidic) or high (basic) pH?
Do all enzymes have the same optimum pH?
The optimum pH is the specific pH at which an enzyme works most effectively.
pH affects ionization of amino acids, which are crucial for enzyme structure and function.
pH changes alter the charges on amino acid side chains, affecting enzyme shape and binding.
No, temporary pH shifts cause reversible inactivation, but extreme pH causes irreversible denaturation.
At very low/high pH, enzymes denature and lose function permanently.
No, different enzymes have different optimum pH
What is the general optimum pH range for most enzymes?
At what pH is pepsin most active?
Is trypsin active at pH 2?
At what pH does trypsin show maximum activity?
Which enzyme from green papaya acts in both acidic and alkaline media?
What is papain’s optimal temperature?
What is papain’s active pH range?
From where is papain obtained?
What is papain used for in plants?
what is it?
pH 6–8.
pH 2 (acidic medium).
No, it is inactive at pH 2.
pH 8 (alkaline medium).
Papain.
65°C.
pH 5–8.
From the latex of the papaya plant.
Protecting plants against insects.
cysteine protease
What happens to the rate of reaction if enzyme concentration increases while substrate is unlimited?
Why does the reaction rate increase with enzyme concentration?
What is the role of active sites in increasing reaction rate?
When does increasing enzyme concentration stop affecting reaction rate?
What is the state called when enzyme and substrate concentrations become equal?
- The rate of reaction increases proportionally.
- More enzymes mean more available active sites for the substrate.
- Active sites allow more substrate molecules to be converted into products faster.
- When enzyme and substrate concentrations reach equilibrium.
- Equilibrium state.
What is enzyme inhibition?
16. What are enzyme inhibitors?
17. Is enzyme inhibition always harmful? Explain.
18. Name some molecules that can act as enzyme inhibitors.
19. What are the two main types of enzyme inhibition?
- The failure of an enzyme to catalyze a reaction.
- Molecules that react with enzymes but are not converted into the desired products.
- No, it is normally part of regulating enzyme activity, but external causes can be harmful.
- Poisons, cyanides, antibodies, anti-metabolites, penicillin, sulpha drugs.
- Competitive and noncompetitive inhibition.
What is competitive inhibition?
How does a competitive inhibitor block enzyme activity?
What structural feature do competitive inhibitors share with the substrate?
Why can’t a competitive inhibitor be catalyzed like the normal substrate?
Is competitive inhibition permanent or temporary? What is it also called?
How does substrate concentration affect competitive inhibition?
Give an example of a competitive inhibitor and the enzyme it inhibits.
What reaction is catalyzed by succinate dehydrogenase?
A type of enzyme inhibition where a chemical competes with the substrate for the active site.
By binding to the active site, preventing the substrate from binding.
They are structurally similar to the normal substrate.
Because they are not similar enough chemically to undergo the reaction.
Temporary; also called reversible inhibition.
Increasing substrate concentration decreases the effect of inhibition, as the substrate outcompetes the inhibitor.
Malonate inhibits succinate dehydrogenase.
Conversion of succinate to fumarate.
importance of competitive inhibitors?
How does competitive inhibition support the lock and key hypothesis?
10. What does competitive inhibition show about substances similar to the substrate?
11. How are competitive inhibitors used in medicine?
12. Give an example of a drug that works as a competitive inhibitor to combat bacterial infection.
- Shows that enzymes have specific active sites for substrates (supports lock and key).
- Substances similar to the substrate are not always acted upon by enzymes.
- Used as drugs to control bacterial pathogens.
- Sulphonamides.
Where does a non-competitive inhibitor bind on an enzyme?
What is the other binding site (other than the active site) called?
Does a non-competitive inhibitor block the active site directly?
Can non-competitive inhibition be reversible?
Can non-competitive inhibition be irreversible?
To a site other than the active site.
Allosteric site.
No, it changes the enzyme’s shape so the active site can’t function properly.
Yes, if it inactivates the enzyme temporarily (reversible inhibition).
Yes, if it denatures the enzyme permanently (irreversible inhibition).
How do reversible non competitive enzyme inhibitors work?
Which type of enzyme inhibition is feedback inhibition an example of?
How does an irreversible non-competitive enzyme inhibitor affect an enzyme?
Give examples of irreversible non-competitive enzyme inhibitors.
Why are cyanides potent poisons?
Which heavy metal ions act as irreversible non-competitive enzyme inhibitors?
How do heavy metal ions inactivate enzymes?
What is the role of disulphide bridges in enzymes?
Prevent formation of enzyme-product complexes; stop substrate from being converted into product.
Reversible non-competitive enzyme inhibition.
Alters enzyme shape so substrate cannot bind to active site; permanently inactivates the enzyme.
Cyanides; salts of heavy metals.
Inhibit cytochrome oxidase essential for cellular respiration; combine with iron in prosthetic group.
Mercury (Hg²⁺), silver (Ag⁺), copper (Cu²⁺).
Combine with thiol (-SH) groups in enzyme; break disulphide bridges; cause denaturation.
Maintain enzyme’s tertiary structure.
What is feedback inhibition?
Which type of inhibition is feedback inhibition?
Is feedback inhibition reversible or irreversible?
In feedback inhibition, what binds to the enzyme to inhibit it?
Where does the product bind in feedback inhibition?
What happens to the active site when the product binds to the allosteric site?
Give an example of feedback inhibition involving aspartate and threonine.
What happens to the pathway when the product is consumed?
The inhibition of an enzyme by its own product.
Non-competitive inhibition.
Reversible.
The product of the enzyme’s pathway.
Allosteric site of the enzyme.
Active site can no longer bind the substrate.
Aspartate → (5 enzymatic reactions) → Threonine; excess threonine inhibits enzyme 1.
Product detaches from allosteric site; pathway resumes activity.
Give examples of competitive enzyme inhibitors.
Give examples of non-competitive enzyme inhibitors.
On what two bases can enzymes be classified?
Who gave the systematic nomenclature and classification of enzymes based on reaction types and mechanisms?
How many main classes of enzymes are there according to reaction type?
Name the six main classes of enzymes.
What do oxidoreductases do? Give an example.
What do transferases do? Give an example.
Antibodies, antimetabolites, penicillin, iodoacetate, malonate, CoA (high concentration).
Acetaldehyde, di-isopropyl fluorophosphate (DFP – nerve gas), mercury, silver, copper, cyanide.
Based on reaction type catalyzed; based on substrate acted upon.
International Union of Biochemistry.
Six.
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
Catalyze oxidation/reduction by removing or adding electrons or H⁺ ions; example: cytochrome oxidase oxidizes cytochrome.
Transfer a specific functional group (other than hydrogen) from one substrate to another without the group being free; example: hexokinase transfers phosphate from ATP to glucose.
What do hydrolases do?
Give examples of hydrolases.
Where do many hydrolases work in the body?
What do lyases do?
Give an example of a lyase and its action.
Break down large complex organic molecules into smaller ones by adding water (hydrolysis) and breaking specific covalent bonds.
Proteolytic enzymes such as pepsin, renin, and trypsin.
In the digestive tract.
Break specific covalent bonds and remove groups without hydrolysis.
Histidine decarboxylase breaks bonds between carbon atoms in histidine, producing carbon dioxide and histamine.
What do isomerases do?
Give one example of an isomerase.
What do ligases do and what is their energy source?
Give one example of a ligase.
On what basis, other than reaction type, can enzymes be classified?
What do lipases do? Give one example.
What do nucleases do? Give one example.
Which enzyme hydrolyzes ATP in muscles?
Rearrange atoms within a molecule.
Phosphohexose isomerase.
Join two molecules using ATP hydrolysis.
Polymerases.
By the substrate they act on.
Break down lipids into fatty acids + glycerol; example: pancreatic lipase.
Break down DNA or RNA; example: RNAases.
ATPases.
what enzymes cause breakdown of carbs?
