Praktikum enzim katalase
This practical demonstrates that the catalase enzyme in chicken liver breaks down toxic hydrogen peroxide into water and oxygen, and that the enzyme's activity is significantly affected by temperature and pH.
Understanding how catalase functions and what disables it provides a concrete foundation for grasping broader metabolic processes and the protein-based nature of enzymes.
Section summaries
Review of metabolism and enzyme theory
optionalDhani opens with a greeting and identifies the video as a practical for class 12 metabolism (KD 3.2). He reviews that metabolism consists of chemical reactions inside cells accelerated by enzymes as biocatalysts. He then recaps enzyme structure (protein and non-protein components), the lock-and-key and induced-fit theories of enzyme action, and enzyme properties: protein-based, catalytic, substrate-specific, reversible, and thermolabile. He also lists factors affecting enzyme activity — inhibitors, temperature, substrate concentration, and pH — before narrowing the focus to these factors for the practical.
- Enzymes are biocatalysts that speed up cellular chemical reactions without being consumed
- Enzymes are thermolabile, meaning they only function within a specific temperature range
- Two competing models explain enzyme-substrate interaction: lock-and-key and induced fit
The theory review is useful for students who need a refresher but is not the core content of the video.
Introducing catalase and the experiment's purpose
watchDhani introduces catalase as the specific enzyme being studied, explaining that it breaks down H2O2 (hydrogen peroxide) into water and oxygen. He states that catalase is found in the liver of humans, cows, and other animals, and explains that the liver produces it because H2O2 is a toxic substance that the liver must detoxify. He describes the detection methods: bubbles indicate the presence of water, and a flame test confirms oxygen production. He then outlines the practical objectives — proving catalase works and identifying the factors that influence it.
- Catalase is located in the liver because the liver must neutralize toxic hydrogen peroxide
- Oxygen from the reaction is detected by a flame test, while water is indicated by bubble formation
- The practical has two goals: proving catalase works and identifying factors that affect its activity
This section establishes the biological rationale and experimental goals that frame everything that follows.
Safety warnings and materials preparation
watchDhani lists the safety requirements before starting: wearing a lab coat and gloves, specifically because hydrogen peroxide can cause skin irritation and itching, and because acid and base solutions are also hazardous. He then enumerates the materials: chicken liver extract as the catalase source, NaOH solution, HCl solution, hydrogen peroxide as the substrate, eight labeled test tubes, tongs, wire brush, mortar and pestle, pipettes, a Bunsen burner setup, beakers, a lid for flame testing, and a measuring cup. He explains that the lid is used to capture gas and test for flame.
- H2O2, HCl, and NaOH all pose skin hazards requiring gloves and a lab coat
- Eight test tubes are needed to accommodate different treatment conditions
- A Bunsen burner and lid are used together to test for oxygen gas via flame
Safety instructions and a complete materials list are essential before beginning any lab work.
Preparing chicken liver extract
watchDhani demonstrates how to make the catalase source by placing chicken liver into a mortar, adding a few drops of aquades (distilled water), and grinding it with a pestle. The resulting liquid is the liver extract containing the catalase enzyme. He humorously notes the use of chicken liver rather than human liver. This extract is the enzyme solution that will be distributed into the test tubes for the various experimental conditions.
- Chicken liver is crushed with a small amount of water to release and dissolve the catalase enzyme
- The resulting slurry serves as the crude enzyme source for all test tubes
- Using a mortar and pestle is the mechanical method for breaking open liver cells to extract the enzyme
This is a necessary preparatory step that directly affects the quality and consistency of the enzyme source.
Setting up test tubes with different treatments
watchDhani distributes 2 ml of liver extract into separate test tubes and applies four different experimental treatments: one tube is placed in cold water with ice to create a low-temperature condition, another is placed in hot water for a high-temperature condition, a third has 4-5 drops of NaOH added to create a basic environment, and a fourth has 4-5 drops of HCl added to create an acidic environment. He emphasizes that each treatment targets a specific variable — temperature or pH — so that the effect of each factor can be isolated.
- Four distinct conditions are created: cold, hot, basic (NaOH), and acidic (HCl)
- Each condition isolates a single variable so its individual effect on the enzyme can be observed
- 4-5 drops of NaOH or HCl are sufficient to shift the pH of the extract
This is the critical experimental design step where the independent variables are established.
Adding H2O2 substrate and preparing for observation
watchDhani instructs that 2 ml of hydrogen peroxide must be added to each test tube using a pipette, and stresses that separate pipettes must be used for NaOH, HCl, and H2O2 to avoid cross-contamination. He then explains that a fifth test tube should be prepared with liver extract and H2O2 but no additional treatment, serving as the control. He notes that if H2O2 is added directly without separation from the enzyme, the reaction would begin immediately, making controlled observation impossible.
- Separate pipettes prevent chemical cross-contamination between the acid, base, and substrate solutions
- A fifth control tube with no pH or temperature treatment provides the baseline for comparison
- Adding H2O2 last, after all other treatments are in place, ensures the reaction only starts when observation begins
Proper addition order and contamination prevention are essential for valid experimental results.
Observation procedure and alkaline condition results
watchDhani walks through the observation process: adding H2O2 to a tube, sealing it with a lid, and looking for bubbles as evidence of water production. He then opens the tube, inserts a glowing splint (lidi), and checks for flame as evidence of oxygen. For the alkaline condition (liver extract + NaOH + H2O2), he observes that many bubbles appeared but the flame was only small or weak, indicating the enzyme still worked but not optimally in a basic environment.
- Bubbles indicate water production; a glowing splint test confirms oxygen gas release
- The alkaline condition produced abundant bubbles but only a weak flame, meaning partial enzyme activity
- Sealing the tube before the flame test prevents oxygen from escaping and ensures a detectable result
This section demonstrates the first experimental result and the method for interpreting it.
Acidic and high-temperature condition results
watchDhani presents results for two conditions. In the acidic condition (liver extract + HCl + H2O2), very few bubbles appeared and no flame was detected at all, indicating the enzyme was essentially non-functional in acid. In the high-temperature condition (liver extract heated in boiling water + H2O2), no bubbles appeared and no flame was produced, and the water in the beaker was observed boiling, confirming the extreme heat. Dhani concludes that both conditions destroyed or severely inhibited catalase activity.
- Acidic conditions completely inhibit catalase — no bubbles and no flame were observed
- Boiling temperature denatures the enzyme, producing zero reaction as confirmed by no bubbles and no flame
- The boiling water in the beaker serves as visible confirmation that the extract was exposed to destructive heat
These results provide the clearest contrast with the control and demonstrate the destructive effects of extreme pH and temperature.
Cold condition and control results
watchDhani shows that the cold condition (liver extract in ice water + H2O2) produced very abundant bubbles and a bright, strong flame, indicating the enzyme remained functional at low temperatures though possibly at a reduced rate compared to normal conditions. The control tube (liver extract + H2O2 with no treatment) produced the most abundant bubbles and the brightest flame, confirming that catalase works optimally at normal or body temperature. This establishes the baseline maximum reaction for comparison with all other conditions.
- Cold-preserved enzyme remained fully functional, producing abundant bubbles and a bright flame
- The control condition showed the strongest reaction, confirming optimal activity at normal body temperature
- The control serves as the reference point against which all other conditions are measured
The control and cold-condition results complete the experimental data set needed for the analysis section.
Data analysis, conclusions, and closing
watchDhani compiles the observation results into a summary table and draws conclusions. He states that catalase successfully breaks H2O2 into water and oxygen, evidenced by bubbles and flame across conditions. He concludes that enzyme activity is influenced by both temperature and pH: boiling heat denatures the enzyme completely, acidic conditions inhibit it, basic conditions allow partial activity, cold conditions preserve function, and the untreated control shows optimal performance at normal body temperature. He closes with a reminder to ask questions in the comments and to subscribe.
- The data consistently show that catalase activity depends on maintaining proper temperature and pH
- Denaturation from heat is irreversible, while cold merely slows the enzyme without damaging it
- The practical successfully validates that enzymes are sensitive to their environmental conditions
This is the synthesis section where all observations are interpreted and the learning objectives are met.
Key points
- Catalase detoxifies hydrogen peroxide in living organisms — Catalase is an enzyme found in the liver that converts H2O2, a toxic byproduct of metabolism, into harmless water and oxygen gas. The liver produces this enzyme specifically because its metabolic role generates this dangerous substance that must be neutralized.
- High heat denatures catalase and abolishes its function entirely — When the liver extract was placed in boiling water, no bubbles or flame were observed after adding H2O2, because the heat destroyed the enzyme's protein structure through denaturation, rendering it permanently inactive.
- Extreme pH shifts inhibit catalase activity — In acidic conditions (HCl), the enzyme produced almost no bubbles and no flame, while in basic conditions (NaOH) it produced bubbles but only a weak flame, showing that both highly acidic and highly alkaline environments impair the enzyme's catalytic efficiency.
- Cold temperatures preserve enzyme structure but slow its rate — The liver extract stored in ice water still produced abundant bubbles and a bright flame when H2O2 was added, indicating the enzyme remained functional, though the reaction rate was lower than at normal body temperature.
- A control setup is necessary to establish baseline enzyme performance — A fifth test tube containing only liver extract and H2O2 with no additional treatment (no acid, base, or temperature shift) served as the reference point, showing the maximum expected reaction and confirming that observed reductions in other conditions were caused by the specific treatments.
“enzim katalase ini adalah Om suatu enzim yang dia Kerjanya mengubah H2O 2 atau hidrogen peroksida menjadi air dan oksigen” — Dhani
“protein dimana Kalau suatu protein dipanaskan maka protein tersebut akan rusak atau terdenaturasi” — Dhani
AI-generated from the transcript. May contain errors.
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