PEP High School Biology, Required, Book 1: The Catalytic Center of Life Activities – Cell Metabolism and the Discovery of Enzymes

Imagine each of your cells as a miniature factory running nonstop. Every chemical reaction happening within it, second by second, is collectively known ascellular metabolism. Without any intervention, these reactions would be so slow at normal temperature and pressure that they'd almost come to a halt. Yet life thrives because of a remarkable "biological catalyst" —enzymes, which accelerate reaction rates by millions of times.

Metabolic Boundaries and Logistics

Before metabolism can begin, substances must cross the cell membrane. Small molecules rely ontransport proteins(carrier proteins and channel proteins) for facilitated diffusion or active transport. Larger molecules such as proteins, on the other hand, enter and exit viaendocytosisandexocytosis, using the membrane's fluidity to form vesicles for "transmembrane delivery."

The Essence of Enzymes: Nature's Accelerators

Essence: Enzymes are organic catalysts produced by living cells. The vast majority are proteins, while a small minority are RNA.
Principle: By significantly lowering the "activation energy" required for chemical reactions, they ensure complex metabolism runs efficiently and stably even in environments with $H^+$ concentrations like $150\text{ mmol}\cdot\text{L}^{-1}$.

💡 Scientific Reflection

The debate between Pasteur and Liebig teaches us that the truth in science often lies at the intersection of opposing viewpoints. By breaking open cells, Büchner preserved Liebig's proposed "substance" while acknowledging the "cellular origin" championed by Pasteur's research.

QUESTION 1

In 1773, Spallanzani placed meat in a small metal cage and had an eagle swallow it. 1. Why was the meat placed in a metal cage? 2. What substance caused the meat to disappear? 3. How could you prove your hypothesis?

1. To prevent mechanical grinding by the stomach; 2. A chemical substance in gastric juice; 3. Collect gastric juice and test it outside the body.

1. To protect the eagle's digestive tract; 2. Decomposition by bacteria; 3. To increase the eagle's exercise.

QUESTION 2

Yogurt from a supermarket has bloated packaging. The yogurt contains lactic acid bacteria and yeast. Based on this, analyze the cause of the bloating. Is the following explanation reasonable? Lactic acid bacteria produce carbon dioxide under anaerobic conditions, causing the bloating.

Unreasonable. Lactic acid fermentation only produces lactic acid, not gas. The bloating is caused by $CO_2$ produced by yeast.

Reasonable. After the expiration date, lactic acid bacteria change their metabolic pathway and produce gas.

QUESTION 3

A yeast culture is processed into: A (supernatant after lysis — cytosol), B (pellet — organelles), and C (intact cells). After adding equal amounts of glucose under aerobic conditions, which one ultimately produces $CO_2$ and $H_2O$?

Tube C

Tubes A and B

QUESTION 4

Describe the types of cellular respiration in yeast and the differences in their products.

Facultative anaerobe: Produces $CO_2$ and $H_2O$ under aerobic conditions; produces alcohol and $CO_2$ under anaerobic conditions.

Aerobic respiration only: Produces $CO_2$ and $H_2O$; dies under anaerobic conditions.

QUESTION 5

Which enzyme can catalyze the hydrolysis of salivary amylase?

A. Amylase

B. Protease

C. Lipase

D. Maltase