Enzimas y metabolismo
Diploma del Bachillerato Internacional · IB Diploma · Biology · HL Tema 20 3:52 Narración en inglés · Subtítulos en inglés + 中文 quemados en pantalla
Capítulos
Transcripción
An enzyme 酶 works quickly at one temperature and slowly at another.
酶在某一温度下反应迅速，而在另一温度下反应缓慢。
Heating can increase successful collisions, but excessive heat can change the active site.
加热可增加有效碰撞次数，但过热会改变活性位点。
An enzyme is a biological catalyst.
酶是一种生物催化剂。
The substrate binds at an active site whose shape and chemical properties support the reaction.
底物结合在活性位点上，该位点的形状和化学性质支持反应进行。
A catalyst increases rate without being used up overall.
催化剂能加快反应速率，且自身在总体上不消耗。
Enzyme: A biological catalyst.
酶：一种生物催化剂。
Denaturation: A structural change that disrupts function.
变性：一种破坏功能的结构变化。
Measure rate using product formed per unit time, or a fixed endpoint.
使用单位时间内产物的生成量或固定终点来测量反应速率。
For an endpoint test, one over time is a rate proxy if the same amount of product or substrate change defines the endpoint each time.
对于终点法测试，若每次达到终点时产物或底物的变化量相同，则时间的倒数可作为速率的代理指标。
In the lab: For starch digestion, equilibrate enzyme and starch in a water bath, control pH with buffer, mix measured volumes, and test samples with iodine at fixed intervals.
在实验室中，进行淀粉消化实验时，将酶和淀粉在水浴中平衡，用缓冲液控制pH值，混合定量的体积，并在固定时间间隔用碘液检测样品。
Use a clean spot for each test.
每次测试使用干净的斑点。
Do not put iodine into the reaction mixture.
切勿将碘液加入反应混合物中。
Known: the endpoint is reached in 40 seconds.
已知：终点在40秒时到达。
Use rate proxy equals one divided by time.
使用速率代理等于1除以时间。
Rate proxy equals one divided by 40, which is 0.025 per second.
速率代理等于1除以40，即0.025每秒。
At 20 seconds, the proxy is 0.050 per second, twice as large.
在20秒时，该代理值为0.050每秒，是前者的两倍。
This comparison is valid only if the same endpoint and starting concentrations are used.
此比较仅在终点和起始浓度相同的情况下有效。
Your turn: A fixed endpoint takes 50 s.
轮到你了。 固定终点耗时50秒。
Calculate the rate proxy 1/time.
计算速率代理，即1除以时间。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 1 divided by 50 seconds gives a rate of 0.020 per second.
核对：1 ÷ 50 秒，速率为每秒 0.020。
An optimum is specific to the enzyme and conditions.
最适条件具有酶特异性和条件依赖性。
Low temperature usually slows the reaction, but it does not necessarily denature the enzyme.
低温通常会减缓反应速率，但不一定会使酶变性。
Endpoint intervals limit precision.
终点间隔会限制测量精度。
Not true: A low temperature always permanently denatures an enzyme.
不正确。 低温并不总是导致酶永久变性。
Low temperature usually only slows an enzyme because molecules collide less often; the active site is unchanged and warming restores activity.
低温通常只是减缓酶的活性，因为分子碰撞频率降低。 活性位点未发生改变，升温即可恢复活性。
Denaturation is a structural change from excessive heat or extreme pH, not a guaranteed result of cooling.
变性是由过热或极端pH引起的结构变化，而非降温的必然结果。
An enzyme is a biological catalyst.
酶是一种生物催化剂。
Measure rate using product formed per unit time, or a fixed endpoint.
可用单位时间内产物的生成量或固定终点来测量反应速率。
Watch for: an optimum is specific to the enzyme and conditions.
请注意：最适条件具有酶特异性和条件依赖性。
A fixed endpoint takes 80 seconds.
固定终点耗时80秒。
Find the rate proxy, one over time.
求速率代理，即1除以时间。
The same endpoint must define every trial.
同一终点必须定义每一次实验。
The result is a rate proxy of 0.0125 per second.
结果是速率指标为每秒0.0125。
The rate is estimated as one over the time to reach the endpoint.
速率用到达终点所需时间的倒数来估计。
A reaction that takes 50 seconds is slower than one that takes 20.
用时50秒的反应比用时20秒的反应慢。
One trial reaches a fixed endpoint in 20 s; another reaches twice as much product in 30 s.
一个实验在二十秒时达到固定终点。 另一个实验在三十秒时生成两倍产物。
Can their rates be ranked by 1/time?
能否用一除以时间来比较它们的速率？
Explain using product/time.
请用产物除以时间进行解释。
No: the endpoints differ.
不能：两次试验的终点不同。
Relative product per time is 1 over 20 and 2 over 30; under comparable conditions the second average is four thirds of the first.
单位时间的相对产物量分别是 1/20 和 2/30；在条件可比时，第二次的平均速率是第一次的三分之四。
Reciprocal-time comparison requires the same endpoint.
用时间倒数来比较，必须以相同的终点为前提。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。