Amylase and pH: define the endpoint before comparing rates
הוצג| English | משמעות |
|---|---|
| active site/ˈæktɪv saɪt/ | אתר פעיל |
| buffer/ˈbʌfə/ | מרכך |
What would explain this observation?
- An amylase sample can digest starch quickly at one pH and slowly at another. A fair comparison needs the same starting amounts and a common endpoint.
Build the model
- Enzymes are protein molecules catalysing specific reactions in living organisms.
- The active site 活性位点 has a shape suited to the substrate; the lock-and-key model is a simplified explanation.
- Temperature and pH affect activity.
- Excessive heat or unsuitable pH can change the active site, reducing binding and catalysis.
- active site: The region of an enzyme where its substrate binds.
- buffer 缓冲液: A solution used to maintain an approximately stable pH.
Why should iodine be placed in separate sampling spots?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Iodine in separate spots tests small removed samples, so the main reaction mixture keeps reacting undisturbed. Iodine in the mixture would interfere with the enzyme, and temperature control is the water bath's job.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Amylase breaks starch into sugars.
- In an iodine sampling method, the endpoint is reached when a sample no longer turns iodine blue-black.
- With a fixed starting amount and endpoint, 1/time gives a comparative rate proxy.
- This proxy is not an independently measured amount of product per second.
In the lab: For required practical 5, use buffers to set a range of pH values, equilibrate amylase and starch in a controlled water bath, and keep concentrations and volumes the same. After mixing, sample into fresh iodine spots every 30 s. Do not add iodine to the main reaction. Repeat and record the last positive and first negative sampling times.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: the last positive iodine observation is at 60 s and the first negative at 90 s.
- The endpoint lies between them, so using 90 s gives a rate proxy of 1/90=0.0111 per second with a sampling limitation.
- Sampling every 15 s could locate the endpoint more closely without pretending to remove all other uncertainty.
Your turn: A fixed endpoint is first recorded at 80 s. Calculate the inverse-time rate proxy.
A fixed endpoint is first recorded at 80 s. Calculate the inverse-time rate proxy.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 0.0125 1/s. Known: endpoint first recorded at 80 s. Use rate proxy = 1/time. Proxy = 1/80 = 0.0125 per second. The true endpoint lies between the last positive and first negative observation, so faster sampling would sharpen it.
Check the conclusion and its limits
- Low temperature usually slows activity rather than permanently denaturing the enzyme.
- A buffer controls pH, not temperature.
- An optimum observed with this amylase and setup cannot be assumed for every enzyme or every biological condition.
Not true: Every enzyme has the same optimum pH and temperature. Each enzyme has its own optimum set by its structure and its usual environment - stomach pepsin works best near pH 2, intestinal enzymes near pH 8. One optimum cannot be assumed for all.
- Enzymes are protein molecules catalysing specific reactions in living organisms.
- Amylase breaks starch into sugars.
- Watch for: low temperature usually slows activity rather than permanently denaturing the enzyme.
Every enzyme has the same optimum pH and temperature.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Each enzyme has its own optimum set by its structure and its usual environment - stomach pepsin works best near pH 2, intestinal enzymes near pH 8. One optimum cannot be assumed for all.
The region of an enzyme where its substrate binds: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
active site means The region of an enzyme where its substrate binds.