Enzimas - Aula 07 - Módulo 1 - Bioquímica - Prof. Guilherme

How is Lactose Removed from Milk?

Introduction to Lactose and Enzymes

• The speaker recounts a question from a student about how lactose is removed from lactose-free milk, leading to research on the topic.

• Lactose consists of glucose and galactose; when broken down by enzymes, it results in a sweeter taste due to the presence of these simpler sugars.

Understanding Enzymes as Catalysts

• Enzymes are introduced as biological catalysts that accelerate chemical reactions without being consumed in the process.

• A common definition states that enzymes are proteins that speed up reactions, but there are exceptions where not all enzymes are protein-based.

Ribozymes: Non-Protein Enzymes

• Some enzymes, known as ribozymes, are made of RNA rather than proteins. This challenges the traditional view of enzymes solely being protein-based.

• Ribozymes play a crucial role in theories regarding the origin of life, suggesting early cellular forms may have relied on RNA for both genetic information and catalytic functions.

Characteristics of Enzymes

• The speaker emphasizes that enzymes are highly specific; they only catalyze specific reactions based on their unique three-dimensional structure.

• An example is given with lactase, which specifically breaks down lactose but does not act on similar sugars like maltose or sucrose due to its specificity.

Mechanism of Action: Lock and Key Model

• The lock-and-key model illustrates enzyme specificity: each enzyme (key) fits only one substrate (lock), ensuring precise interactions during biochemical processes.

• As catalysts, enzymes can be reused multiple times without being consumed in reactions; however, they can undergo denaturation under certain conditions.

Energy Activation and Reaction Facilitation

• Enzymes lower the activation energy required for reactions, making them more efficient. They facilitate processes similarly to how tools assist physical tasks.

Understanding Enzymatic Reactions and Their Importance

The Role of Enzymes in Reducing Energy Expenditure

• The speaker discusses the physical effort involved in moving bricks without tools, illustrating how using a wheelbarrow (representing enzymes) conserves energy during labor.

• Emphasizes that carrying multiple bricks at once is more efficient than transporting them one by one, paralleling this to how enzymes facilitate chemical reactions by lowering activation energy.

• Highlights that reducing activation energy accelerates chemical reactions, which is crucial for understanding enzyme functionality in biological processes.

Understanding Activation Energy and Reaction Pathways

• Clarifies the misconception about time versus reaction pathways; the graph's axes represent energy levels rather than time intervals.

• Explains that without enzymes, significant energy is required to convert reactants into products, while enzymes allow for these reactions with much less energy expenditure.

• Stresses that enzymes increase reaction speed without altering the overall pathway or time taken for the reaction to occur.

Importance of Enzymes in Various Fields

• Notes that standardized tests often include questions on enzyme graphs; understanding axis labels is critical for accurate interpretation.

• Provides examples of specific enzymes like lactase and DNA polymerase, explaining their functions based on their names and roles in digestion and DNA synthesis respectively.

Industrial Applications of Enzymes

• Discusses the extensive use of enzymes in biotechnology, particularly within food production (e.g., cheese making, baking).

• Mentions pharmacological applications where inhibitors target bacterial enzymes to develop antibiotics, highlighting their significance in medicine.

Mechanism of Enzyme Action

• Introduces key terms such as substrate—substances upon which an enzyme acts—and emphasizes its importance in enzymatic reactions.

• Describes how substrates fit into active sites on enzymes; proper three-dimensional structure is essential for effective binding and catalysis.

• Illustrates the process where after a reaction occurs, active sites become available again for new substrates to bind.

Understanding Enzymes and Their Functionality

The Role of Cofactors and Coenzymes

• Enzymes require cofactors or coenzymes to achieve their ideal shape for reactions. Most vitamins (e.g., B1, B2, C, D) act as coenzymes.

• A distinction is made between cofactors (inorganic minerals) and coenzymes (organic compounds like vitamins).

• An example includes vitamin B12, which contains cobalt and is essential for synthesizing new red blood cells.

• Without the appropriate cofactors or coenzymes, enzymes cannot function effectively; they become inactive.

Factors Influencing Enzyme Activity

Temperature

• Temperature significantly affects enzyme functionality; each enzyme has an optimal temperature range for maximum activity.

• Fever can disrupt enzymatic functions by raising body temperature beyond the optimal level, leading to denaturation of proteins.

• Graphical representation shows that low temperatures yield minimal enzymatic action, while increasing temperatures enhance activity until reaching an optimum around 36°C.

• Beyond the optimal temperature (around 37°C), enzymes begin to denature, losing their functional shape.

pH Levels

• Each enzyme operates best at a specific pH level; deviations can hinder their effectiveness.

• Oxygen plays a crucial role in cellular respiration by maintaining mitochondrial pH balance through proton capture during ATP production.

Enzyme Functionality and Inhibition

Enzyme Activity and Temperature

• Most enzymes operate optimally at around 36 degrees Celsius, although some function better in acidic or basic environments. The comparison between stomach enzymes (like pepsin) and intestinal enzymes (like trypsin) is a classic example often featured in exams.

Substrate Concentration Impact

• The concentration of substrate significantly affects enzyme activity. As substrate concentration increases, enzyme activity also rises until it reaches a saturation point where all active sites are occupied.

Understanding Saturation Kinetics

• The substrate is the specific compound that an enzyme acts upon; for instance, both pepsin and trypsin act on proteins. Without any substrate, there can be no enzymatic action.

• Enzymes have a maximum capacity known as saturation; beyond this point, adding more substrate does not increase the reaction rate due to all active sites being filled.

Active Site Occupancy

• At saturation, all active sites of the enzyme are occupied by substrates. For example, if there are 20 enzymes available but an excess of protein is present, they will continuously work until no free active sites remain.

Types of Enzyme Inhibitors

• Enzyme inhibitors can be classified into two types: irreversible and reversible. Irreversible inhibitors permanently deactivate enzymes (common in poisons), while reversible inhibitors temporarily inhibit enzyme function.

Irreversible Inhibitors

• These compounds permanently alter the structure of enzymes, preventing them from returning to their normal state. Many insecticides work through this mechanism by affecting critical respiratory enzymes in insects.

Reversible Inhibitors

• Reversible inhibitors allow for temporary inhibition; for instance, medications like paracetamol inhibit certain enzymes but can detach after some time allowing normal function to resume.

Effects of Caffeine on Enzymatic Action

Understanding Neurotransmitters and Inhibitors

The Role of Adenine in Neuronal Function

• Multiple types of receptors exist for neurotransmitters, including adenine, which can signal neurons to deactivate.

• When we feel sleepy, adenine is released due to prolonged neuronal activity, leading to neuron deactivation.

• Caffeine competes with adenine by binding to its receptor, preventing adenine from signaling the neuron to turn off.

Competitive and Non-Competitive Inhibitors

• Caffeine acts as a reversible competitive inhibitor by occupying the receptor site meant for adenine.

• Competitive inhibitors bind directly to the active site of enzymes, blocking substrate access; this can be visualized graphically.

Enzyme Activity and Substrate Concentration

• An increase in substrate concentration can displace competitive inhibitors from the enzyme's active site.

• The presence of a competitive inhibitor slows down the rate at which maximum enzyme activity is reached but does not change the final outcome.

Non-Competitive Inhibition Explained

• Non-competitive inhibitors bind elsewhere on the enzyme (allosteric sites), altering its shape and function without competing for the active site.

• Allosteric inhibition can significantly reduce enzymatic activity even if substrate concentration increases.

Conclusion on Learning and Understanding