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ลำดับตอนที่ #19 : [[R.S.]]Biology Test::Chapter9::28 or 29.1.09
The Summary of Biology for
Chapter 9 :: Cellular Respiration
Chapter.9 :: Cellular Respiration [[Page.220]]
9-1 Chemical Pathways [[Page.221]]
- Food provides living things with the chemical building block they need to grow and reproduce. They also serve as raw material and source of energy.
- A calorie is the amount of energy needed to raise the temperature of 1 gram of water 1 degree Celsius.
· One gram of sugar glucose [[C6H12O6]] when burned in the presence of oxygen, releases 3811 calories of heat energy.
- Cells gradually release the energy from glucose and other food compounds.
· This process begins with a pathway called glycolysis which releases only a small amount of energy.
- In the presence of oxygen, glycolysis is followed by the Krebs cycle and the electron transport chain.
· Glycolysis, the Krebs cycle, and the electron transport chain make up a process called cellular respiration.
- Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.
6O2 + C6H12O6 => 6CO2 + 6H2O + Energy
Oxygen + glucose === > carbon dioxide + water + energy
- If cellular respiration took place in just one step, all of the energy from glucose would be released at once and most of it would be lost in the form of light & heat
- The cell needs to find a way to trap those little bits of energy [[that it makes]] by using them to make ATP.
- In cellular respiration, glycolysis takes place in the cytoplasm while the Krebs cycle & electron transport take place inside the mitochondria.
· Each of the three stages captures some of the chemical energy in food molecules and uses it to produce ATP.
=cytosol means cytoplasm,, via means by,, pyruvate means pyruvic na =
- Glycolysis is the process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid, a 3-carbon compound.
- Even though glycolysis is an energy-releasing process, at its pathway’s beginning, it needs to put 2 molecules of ATP to get the process going.
· When the glycolysis is complete, 4 ATP molecules have been produced, giving the cell a net gain of 2 ATP molecules [[= get 2 ATP molecules additional]]
- One of the reactions of glycolysis removes 4 high-energy electrons and passes them to an electron carrier called NAD+, or nicotinamide adenine dinucleotide.
· NAD+, known as NADH, holds the high-energy electrons until they can be transferred to other molecules. [[before it holds any electrons, it’s called NADH]]
· Glycolysis can produce a lot of ATP in a very high speed and glycolysis itself doesn’t require oxygen.
· When cell generates large amounts of ATP from glycolysis, all of cell’s available NAD+ r filled up with electrons, so cell need to stop producing ATP
- Fermentation release energy from food molecules by producing ATP in the absence of oxygen
· It doesn’t require oxygen, so it is said to be anaerobic.
· The two main types of fermentation are alcoholic fermentation and lactic acid fermentation.
1. Alcoholic fermentation :: yeasts + microorganisms use this process to form ethyl alcohol and carbon dioxide as wastes.
Pyruvic acid + NADH => alcohol + CO2 + NAD+
:: it causes bread dough to rise because the small amount of alcohol produced by yeast in dough evaporates when the bread is baked.
2. Lactic acid fermentation :: produced by our muscles during rapid exercise when body can’t supply oxygen to the tissues. The buildup of lactic acid causes a painful, burning sensation to our muscles.
Pyruvic acid + NADH => lactic acid + NAD+
:: this process converts glucose into lactic acid.
:: unicellular organisms also produce lactic acid as a waste product.
= pyruvate is pyruvic acid,,
lactate is lactic acid=
~the first part [[glucose and pyruvate thingy]] is glycolysis na and the second part is the conversion of pyruvic acid to lactic acid.
คือ ตอนแรก glucose ถูกแปลงเป็น pyruvic acid แล้วปล่อยพลังงานออกมา ทำให้ NAD+ กลายเป็น NADH จากนั้นพลังงานใน NADH ตัวนี้ ก็ถูกเอาไปใช้ในการแปลง pyruvic acid เป็น lactic acid อีกรอบนึง ทำให้มันกลับเป็น NAD+ อีกหน ((เพราะถูกเอาพลังงานออก)) ละ NAD+ ตัวนี้ก็ย้อนกลับไปเอาพลังงานจาก glucose มาอีกรอบ กลายเป็นลูกศรฟ้าๆแดงๆในรูปนั่นแหละ ^_^
9-2 The Krebs Cycle and Electron Transport [[Page.226]]
- At the end of glycolysis, about 90 percent of the chemical energy that was available in glucose is still unused, locked in the pyruvic acid. To extract this energy, the cell turns to the final steps of cellular respiration that needs oxygen.
· Because the pathways of cellular respiration require oxygen, they are said to be aerobic.
- In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the Krebs cycle.
- During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
· Because citric acid is the first compound formed, Krebs cycle is also known as the citric acid cycle.
A. As pyruvic acid enters the mitochondria, one of its carbon atom becomes carbon dioxide which is eventually released into the air, it releases energy, converting NAD+ to NADH. The other two carbon atoms are joined to coenzyme A to form acetyl-CoA [[acetyl part of acetyl-CoA made up of 2 carbon, 1 oxygen, 3 hydrogen]]. So, acetyl-CoA adds 2-carbon acetyl group to a 4-carbon compound [[at first it’s 2-carbon pyruvic acid chai pa but another 2-carbon molecules from the cycle ma join, making it 4-carbon]], forming a 6-carbon molecule [[4-carbon + another 2 from acetyl-CoA]] called citric acid.
B. As the cycle continues, citric acid is broken down into a 5-carbon molecule, more carbon dioxide is release, and electrons are transferred to energy carrier, NADH. Then, it is broken down into 4-carbon molecule, converting NAD+ to NADH along with ADP to ATP. Along the way after that, two more molecules of carbon dioxide from 4-carbon molecule are released, and electrons join NAD+ and FAD[[flavine adenine dinucleotide]], forming NADH and FADH2. Now that it becomes 2-carbon molecule, it goes back to the beginning of the cycle again, waiting for another 2-carbon of pyruvic acid that is going to join with Coenzyme A.
- The product from this Krebs cycle is 4 NADH, 1 FADH2 and 1 molecule of ATP.
- เรารู้ว่าตรง Krebs cycle นี่เราเขียนงงแล้วก็ยาวมากๆ ซึ่งเราเดาว่า เราอ่านแล้วเข้าใจ((มั้ง))อยู่คนเดียว .. ถ้าไม่เข้าใจก็มาถามละกัน นะ เราทำให้มันหายงงมากกว่านี้ไม่ได้แล้วอ่ะ TT^TT
- The electrons from Krebs cycle in the electron carrier, NADH and FADH2, are passed to the electron transport chain.
- The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.
A. High energy electrons from NADH and FADH2 are passed along one carrier protein of electron transport chain to the next. [[in eukaryotes, this carrier protein is located in inner membrane of mitochondria. In prokaryotes, this carrier is in cell membrane]]. At the end of this chain is an enzyme that combines these electrons with hydrogen ions to form water and oxygen serves as the final electron acceptor of electron transport chain.
B. Every time 2 high-energy electron transport down the chain, their energy transport hydrogen ions[[H+]] across the membrane. During electron transport, H+ build up in intermembrane, making it positively charge. The other side of membrane, from which H+ have been taken, is now negatively charged.
C. The inner membranes contain protein spheres called ATP synthases. As H+ escape through channels into these proteins, ATP synthases spin, grabbing ADP as each time it rotates and making it ATP. On average, each pair of high-energy electrons that moves down the chain provides enough energy to produce 3 moles of ATP from ADP.
- In total …
· Glycolysis produces 2 ATP
· Krebs cycle and electron transport produce 34 more ATP. [[the final wastes of cellular respiration are water and carbon dioxide]]
· So the overall ATP that cellular respiration produces are 36
· 36 ATP = only 38 percent of the total energy of glucose,, another 62 percent is released as heat.
- To obtain energy, the body uses ATP already in muscles and new ATP made by lactic acid fermentation and cellular respiration. But then, it can only supply energy for a limited time.
- In a running race, after the runners have passed the 50-meter mark, the store of ATP that produce by glycolysis and cellular respiration, is nearly gone. At this point, their muscle cells are producing most of their ATP by lactic acid fermentation which can last about 90 seconds.
- For exercise longer than about 90 seconds, cellular respiration is the only way to generate a continuing supply of ATP.
· Our bodies store energy in muscles and other tissues in the form of carbohydrate glycogen. These glycogen are usually enough to last for 15-20 min. of activity. After that, our bodies begin to break down other stored molecules, including fats, for energy.
- Photosynthesis is the process that ‘deposits’ energy but cellular respiration is the process that ‘withdraws’ energy.
- Also photosynthesis removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food.
Comparing Photosynthesis and Cellular Respiration* | ||
Photosynthesis | Cellular respiration | |
Function | Energy capture | Energy release |
Location | Chloroplasts | Mitochondria |
Reactants | CO2 and H2O | C6H12O6 and O2 |
Products | C6H12O6 and O2 | CO2 and H2O |
Equation | 6CO2 + 6H2O =energy=> C6H12O6 + 6O2 | 6O2 and C6H12O6 =energy=> 6CO2 + 6H2O |
Ps. Sry jing jing na ,, I have no time for proofreading lei TT^TT
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