本期內(nèi)容是 新陳代謝：細(xì)胞的呼吸作用與發(fā)酵 的基礎(chǔ)理論部分，實(shí)驗(yàn)手冊與實(shí)驗(yàn)?zāi)M請看后兩期。本部分內(nèi)容來自 University of California, Berkeley - UC Berkeley Extension, 虛擬實(shí)驗(yàn)的內(nèi)容來自 Labster. 本部分內(nèi)容均不會標(biāo)記為為原創(chuàng)，但由于是UP主購買的課程，因此不接受非授權(quán)的轉(zhuǎn)載，謝謝您的理解。

每一個生物基礎(chǔ)實(shí)驗(yàn)均會分為三部分：第一部分為實(shí)驗(yàn)的生物理論；第二部分為實(shí)驗(yàn)的指導(dǎo)手冊；第三部分為 Labster 的虛擬實(shí)驗(yàn)?zāi)M。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的實(shí)驗(yàn)手冊來自 Labster, 第三部分的實(shí)驗(yàn)?zāi)M過程由UP主操作。

Lab 5 - Cellular Respiration and Fermentation

新陳代謝

- Most energy in ecosystem comes from the sun;

- Plants (producers) use photosynthesis to convert light energy to chemical energy;

- Animals (consumers) eat plants and extract energy from sugar;

- All the chemical reactions in the cell are its metabolisM.

MetabolisM

- Many chemical reactions in the cell can be organized into metabolic pathways;

- Catabolic pathways break down food into sMaller molecules;

- Anabolic (biosynthetic) pathways drive the synthesis of biological important molecules.

Energy in Cells

Free energy: energy that can be harnessed to do work or drive chemical reactions.

- If ΔG<0, energy is released and reaction is spontaneous (Exergonic);

- If ΔG>0, energy is required and reaction is non-spontaneous (Endergonic).

Enzymes

- Even energetically favorable reactions require activation energy to get them started;

- Enzymes are effective catalysts because they reduce the activation energy for reactions.

- Most enzymes are proteins;

- They increase the rate of chemical reactions without being consumed in the process.

- Enzyme-substrate binding: ‘lock and key model’;

- Induced fit model: binding induces a mild shift of enzyme structure;

- Enzymes reduce activation energy by: increase local concentration, contort chemical bonds, participate in the reactions, etc.

Redox Reactions

- Oxidation: loss of electrons (e-) and H+?

????When a compound loses electrons, it is oxidized (OIL)

- Reduction: gain of electrons (e-) and H+

????When a compound gains electrons, it is reduced (RIG)

Oxidation Reactions Produce Energy

- Oxidation, or controlled burning, is used to extract energy;

- Cellular respiration produces energy by oxidizing sugar;

- Energy released is captured by high-energy bonds in activated carriers.

ATP: Energy Currency

- ATP: Phosphate groups are bulky and carry negative charges, causing a strain between the last two phosphates;

- The removal of the terminal phosphate releases energy.

Activated Carriers

- Activated carriers: sMall organic molecules that contain one or more energy-rich covalent bonds;

- They act like molecule shuttles.

Electron Carriers

- NAD and FAD: carry high-energy electrons;

- They act as intermediates in the catabolic reactions that generate ATP through the oxidation of food molecules.

Glycolysis

- Occurs in the cytosol;

- Split glucose (6-C) to pyruvate (3-C);

- Generate 2 ATP and 2 NADH;

- The process requires an input of energy at the start (preparatory phase), later more energy is produced (payoff phase).

Energy investment: invests 2 ATPs to modify glucose so it can be split into 2 3-carbon molecules (G3P);

Energy payoff: extracts energy from oxidizing G3P, produces 4 ATPs & 2 NADH.

Substrate-Level Phosphorylation

- Substrate-level phosphorylation: a phosphate group is removed from an organic molecule and directly transferred to ADP;

- Example: last step of glycolysis.

Transition Reaction: Pyruvate Oxidation

Citric Acid Cycle

? The Krebs cycle (TCA cycle)? takes place in the cytoplasM of bacteria and in the mitochondrial matrix of eukaryotes:

- Transfers the energy stored in acetyl CoA to NAD+ and FAD by reducing them;

- NADH and FADH2 carry electrons to the ETC.

- Intermediates from the Krebs cycle are used for synthesizing amino acids, fatty acids, nucleotides, etc.

- Krebs cycle: a carbon and energy wheel.

Cellular Respiration

[Aerobic respiration]

- Utilizes glycolysis, the Krebs cycle, and the electron transport chain (ETC);

- Relies on free oxygen as the final electron and hydrogen acceptor;

- Characteristic of many bacteria, fungi, protozoa, and animals;

- Occurs in cytosol and mitochondria.

Electron Transport Chain (ETC)

- Energy bearing reduced activated carriers (NADH, FADH2) pass the electrons in a sequential and orderly fashion from one redox molecule to the next;

- The flow of electrons down this chain is highly energetic and allows the transport of H+ outside of the membrane.

Electron Transport Chain (ETC)

- Takes place on the inner membrane of mitochondria, or plasMa membrane of bacteria;

- In the final step, oxygen accepts electrons and hydrogen, forming water (aerobic respiration).

Proton Motive Force

- The pumping of H+ out of the membrane creates an electrochemical H+ gradient across the membrane;

- A charge difference (membrane potential) and a concentration gradient combine to generate the proton motive force.

Electron Transport Chain (ETC)

- Released energy from electron carriers in the ETC is channeled through ATP synthase;

- ATP synthase can harness the electrochemical H+ gradient to synthesize ATP (oxidative phosphorylation);

- 1 NADH that enters the ETC = 3 ATP.

- 1 FADH2 that enters the ETC = 2 ATP.

Fermentation

- In muscle cell undergoing vigorous contraction, pyruvate is converted to lactate in the cytosol, restoring the NAD+;

- After a few minutes, the accumulated lactic acid causes muscle fatigue?

In microorganisMs that can grow anaerobically, pyruvate is converted into CO2 and ethanol (alcoholic beverages, baking);

Other fermentation products include solvents (acetone, butanol), organic acids (acetic acid), vitamins, antibiotics and hormones.

Fermentation

- Lactic acid fermentation gives us yogurt, sourdough bread, buttermilk…?

- Ethanol gives us beer and wine;

- CO2 gives us carbonation (beverages, bread)…

本期內(nèi)容到此結(jié)束，感謝閱讀！下一期為實(shí)驗(yàn)手冊 & 下下期將進(jìn)行 Labster 實(shí)驗(yàn)！