CELLS ARE US
MEETING CELLS' ENERGY NEEDS
NAVIGATION TABLE
Cells Are Us: Meeting Cells' Energy Needs |
Meeting Cells' Energy Needs
Pre-Test
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Introduction
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
Introduction
Need a reason for that next candy bar? Well, that candy bar gives you energy. Your body cells have to have energy to do all the things that cells do. Of course, the body can get energy from all sorts of foods besides candy!
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Objectives
This unit explains how cells extract energy from food. After completing this lesson, students should be able to:
Diagram of a cell, showing the mitochondrion (plural is mitochondria), which is the “energy transformer” of the cell.
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Why It Matters
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HOW WOULD YOU DEFINE “ENERGY”? WHY DO YOU NEED ENERGY?
Why It Matters
Energy is defined as the capacity or ability to do work. Every day, you have work to do. From getting out of bed, to going to school, to participating in clubs, sports, or other activities, you have a lot to do each day!
Energy can exist as “stored” energy or the energy of position (potential energy), or as the energy of motion (kinetic energy). Energy can exist in many forms like chemical energy, sound energy, mechanical energy, thermal or heat energy, and nuclear energy. In this unit, we will mostly be discussing chemical energy and thermal or heat energy. Those are the forms of energy that are most important inside the cell.
Molecules are held together by chemical bonds with an energy force. Breaking the chemical bonds between atoms releases that chemical energy. Whether or not that bond energy does anything depends on whether it can be captured and "put to work." One of the body's jobs is to break food down so that cells can break down some of the chemical bonds. Then that energy can be used to do things, before any left-over energy is finally converted and released as heat.
But heat energy has its uses. Ever notice how frogs or fish are sluggish on a cold day, but people can be just as active as always? People make use of their heat energy to make chemical reactions run better and to make muscles contract faster and stronger, even on cold days.
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WHY DO LIVING SYSTEMS NEED ENERGY?
Why It Matters
Living things need energy:
This energy has to be delivered in small and controlled steps, so that processes happen in an orderly way.
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ENERGY-CONTAINING NUTRIENTS ARE TRANSPORTED INTO CELLS, WHERE THE NUTRIENTS ARE CONVERTED INTO AN ENERGY FORM READILY USED BY THE CELL
Why It Matters
Energy-bearing nutrients have to be brought to the cells by blood and other tissue fluids. These nutrients then pass into cells through the cell membrane. The most readily available form of energy is the carbohydrate glucose. Glucose, a 6-carbon sugar molecule, is the common breakdown product of table sugar, flour, potatoes, and other starches. Even proteins and fats can get broken down into glucoses. Once inside the cell, glucose can be picked up by mitochondria, tiny organelles inside the cell, where the energy in glucose is released and then captured in a form that the cells can use. This process is called cellular respiration. Because of the mitochondria’s role in releasing and capturing energy for the cell, they are sometimes called the “powerhouse” of the cell.
A mitochondrion inside the cell of a rat heart. Mitochondria have an inner membrane that folds in many places (and that appears here as stripes). This folding vastly increases the surface area for energy production. Nearly all our cells have mitochondria.
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Why It Matters
This is very simplified diagram of respiration:
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Why It Matters
One More Thing!
Recent research has revealed that not only do mitochondria act as the powerhouse of the cell, they also control death of cells. When cells die, it seems that the cause arises because the membranes of mitochondria lose their charge, and this in turn causes a release of certain proteins from mitochondria into the cytoplasm of the cell. These proteins trigger a series of chemical reactions that kill the cell.
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SELF QUIZ 1
Why It Matters
The organelle that breaks down glucose to release and capture its energy is? (Click on the answer you think is correct)
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What We Know
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WHY OUR BODIES NEED AIR
What We Know
Just as air is needed to burn fossil fuels and release their energy (such as coal and natural gas), our bodies need air to burn the fuel of foodstuffs to release energy. What is it in air that is needed? .... OXYGEN.
Why is it important for mitochondria?
Mitochondria are the cell components that use oxygen to liberate the chemical energy of foodstuffs and trap it in energy storage compounds that cells can use later.
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THE MIGHTY MITOCHONDRIA
What We Know
Mitochondria are the powerhouses of the cells. Their job is to "burn" the fuel (which we get from food) and capture some of the energy in high-energy chemical bonds that can be used later for various cell functions. This process is called cellular respiration. Cellular respiration involves many biochemical reactions. However, the overall process can be summed up in a single chemical equation:
C6H12O6 + 6O2 🡪 6CO2 + 6H2O + energy (stored in ATP)
Cellular respiration uses oxygen in addition to glucose. It releases carbon dioxide and water as waste products. Cellular respiration actually "burns" glucose for energy. However, it doesn't produce light or intense heat like burning a candle or log. Instead, it releases the energy slowly, in many small steps. The energy is used to form dozens of molecules of ATP. It’s important to note that cellular respiration takes place in both animal cells and plant cells.
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THE MIGHTY MITOCHONDRIA CONT’D
What We Know
The diagram on the next slide shows the structure of mitochondria and the relationships of the parts on the left. On the right, the diagram shows that sugars (glucose) are burned in two ways. Glucose, a sugar with 6 carbon atoms, first gets broken down to a 3-carbon molecule (pyruvic acid) in a stage of chemical reactions called glycolysis. The word glycolysis means "glucose splitting." That's exactly what happens in this stage. Enzymes split a molecule of glucose into two smaller molecules called pyruvic acid. Glycolysis does not require oxygen. Anything that doesn't need oxygen is described as anaerobic. This releases a little energy. If oxygen is present (aerobic conditions), the pyruvic acid can then be metabolized in a series of chemical reactions called the Krebs' or Citric Acid Cycle." This cycle of reactions gives off carbon dioxide as a waste product, produces electron carrying compounds, and rebuilds the first molecule in the cycle. The electron carrying compounds produced in the Krebs Cycle power the last step of cellular respiration called the electron transport chain. This step uses the electrons captured by the Krebs Cycle to transform oxygen into water and produce lots of ATP as well as regenerate the electron carriers used in the Krebs Cycle.
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THE MIGHTY MITOCHONDRIA CONT’D
What We Know
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HOW IS GLUCOSE CONVERTED TO PYRUVIC ACID DURING GLYCOLYSIS?
What We Know
The first step of cellular respiration, glycolysis, involves a series of chemical reactions that convert glucose to pyruvic acid. In the process a small amount of energy is released and trapped for use by the cell. Glucose molecules are first broken in half, from six carbons to the three carbons that are present in pyruvic acid. No oxygen is used during glycolysis, so it is said to be anaerobic. Some bacteria and primitive organisms that depend highly on glycolysis can live in environments that do not have much oxygen. In higher animals, if oxygen is in short supply, the pyruvic acid may accumulate and convert into another three-carbon acid, called lactic acid. Lactic acid is what makes muscles sore when they are overworked.
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THE KREBS OR CITRIC ACID CYCLE
What We Know
In the Krebs Cycle, the second step of cellular respiration, pyruvic acid goes through a series of chemical reactions, giving off carbon dioxide and water until pyruvic acid is regenerated. This occurs through a cyclic chain of reactions, called the Krebs' or Citric Acid Cycle. At several steps in the cycle, hydrogen and oxygen combine to form water, which explains what happens to the oxygen that is used in the cycle. In steps where a carbon atom is released, it reacts with oxygen to form carbon dioxide. At several points in the chain of reactions free hydrogen atoms are released, and they are handed off to proteins that are anchored in the membranes inside the mitochondria.
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RELEASING FOOD ENERGY WITH THE KREBS’ CYCLE
What We Know
The chemical reactions that convert one acid to another compound take off carbon, hydrogen, and oxygen atoms to produce carbon dioxide, water and free hydrogen. It is the hydrogen atoms that are most interesting. Like the gas in a bottle of soda pop, once the lid is removed, the energy will all be lost unless there is some way to trap it. The electrons of hydrogen atoms have energy; they are flying around with a lot of energy until they get caught by some other molecule.
The proteins on the many membranes inside of mitochondria help to whip electrons from one to another. In the process the energy of these moving electrons can be captured. The energy is captured in a compound called adenosine diphosphate (ADP). The name indicates that the compound adenosine includes two molecules of phosphate. Phosphate is a molecule made up of one atom of phosphorus and four of oxygen. ADP can bind another phosphate molecule to become adenosine triphosphate (ATP) if there is enough free energy available to attach that third phosphate molecule. The phosphate bonds hold a lot of energy in a storage form, acting like a battery. The trick is to capture the energy released by food breakdown. In other words, the chemical reactions in mitochondria convert some of the energy of glucose into energy storage bonds in ATP.
So, how do mitochondria capture energy?
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SELF QUIZ 2
What We Know
Can you think of reasons why so many chemical reactions are needed for glycolysis and the Krebs cycle? Now (and only after you have done your best) click to check your answer.
It is not easy to break chemical bonds. Each bond-breaking step may require a chemical reaction to accomplish the break. Such chemicals are often proteins (enzymes) that can break the bond. It can't be done all at once. That's a good thing too. If many bonds were broken all at once, so much bond energy might be released that it can't be captured all at once. Too much energy would be lost as heat.
Also, the chemicals that run the energy-extraction process have to be regenerated so that the process is self-sustaining. This also has to be done in small steps in a cyclic way, so that one chemical leads to another, and that to another, and so on, until the original compound is formed. These steps are accomplished by enzymes, each one of which is unique for a given action. For example, one enzyme removes carbon dioxide from a compound in the Krebs cycle and as a result a new compound is formed. The new compound is then acted on by another enzyme to produce yet another compound. Eventually, enzyme action on the last compound in the cycle regenerates the compound that started the cycle.
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SO HOW DO HYDROGEN ELECTRONS GET TRAPPED?
What We Know
The last step in the reactions that moves energy into ATP is called the electron transport chain. Electron transport is achieved by passing the electrons of hydrogen through four complexes of proteins.
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WHERE DO THE ELECTRONS COME FROM?
What We Know
The electrons of hydrogen formed in the Krebs cycle are pulled off and transported by a series of proteins that are anchored in the inner membranes of mitochondria. Electrons are attracted to these proteins by the highly positive-charged iron atoms that are in the proteins.
Think of it as if each protein attached to the membrane were a basketball player, passing the ball (electron) to the next player, and so on. Because the electron has electric charge, there is associated force or energy. There is a gradient in electric charge as the electron moves from one protein to another. Some of the energy of these gradients gets captured in ATP (adenosine triphosphate).
Another way that energy capture has been described is in terms of a waterfall that has several steps. At the top, the water (electrons) has the most energy, with less energy at each step toward the bottom. If a paddlewheel is placed at each step, the energy of the falling water could be stored in a battery for example (in cells, ATP is like a battery).
Oxygen is used in the process, because it reacts with hydrogen to form water. So, you can see that there is such a thing as metabolic water. Animals that live in the desert, such as camels, are especially good at taking advantage of metabolic water to stay alive.
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LESSON SUMMARY
What We Know
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How We Know
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How We Know
Mitochondria, plural for mitochondrion, are the organelles that cells use as their energy factories. Think of them as the cell's way of recharging its battery.
What is a structure of a mitochondria?
A mitochondrion is an oval bag that is filled with membranes. Mitochondria are so small that you can only see them with the high-power magnification of an electron micrograph.
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HOW DO WE KNOW THAT MITOCHONDRIA ARE MEMBRANE-FILLED BAGS?
How We Know
Look at the picture. The membranes are clear, but the space between membranes is fuzzy and without form. Much of this faint background material is made up of chemicals and water.
Think about this picture in three dimensions. Pictures like this are made from very thin slices of cells. If you made a series of thin slices and took their pictures at different depths and reconstructed all the pictures into one, what do you think the three-dimensional structure would be like? ... a membrane-filled bag, right?
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HOW DO WE KNOW THAT MITOCHONDRIA ARE MEMBRANE-FILLED BAGS?
How We Know
This illustration from the National Institutes of Health (NIH) shows the three-dimensional structure of the mitochondria. For an animated illustration, click here.
Why do you think mitochondria have all those membranes?
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ELECTRON MICROGRAPHS SHOW US THAT MITOCHONDRIA CONTAIN MANY MEMBRANES
How We Know
Electron microscope image of a mitochondrion shows the membrane folds.
Image: Tom Deerinck and Jeff Martell
Can you figure out why the mitochondria have so many membranes?
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WHAT’S CONTAINED BETWEEN THE MEMBRANE FOLDS?
How We Know
Remember from the previous electron micrograph images that the folded membranes are surrounded by a material that appears fuzzy. How can we know what is there? There is a way to find out.
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A TOXIC BY-PRODUCT
How We Know
Mitochondria convert a large amount of energy into forms the cells can use, and the chemical reactions also make a byproduct of free-radicals. These radicals are highly reactive and toxic chemicals that can poison cells, which is especially serious for RNA and DNA. The DNA inside the mitochondria is an easy target, because it is already inside the mitochondria where the free radicals are being generated. The DNA inside mitochondria are genes and they are inherited only from the mother. Free radical poisoning is a special problem in nerve cells. Because nerve cells survive so long, the damaging effects in them can accumulate over time. This toxic effect may cause such brain diseases as Parkinson's Disease and Huntington's Disease. Prevention of free radical damage can perhaps be reduced by eating antioxidant rich foods, such as kale, spinach, and blueberries. Taking antioxidant supplements has not been shown to be an effective means of neutralizing free radicals-it appears it is best to consume them by eating foods. Read more about antioxidants here.
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A ROLE IN CELL DEATH
How We Know
Certain proteins that are trapped inside these membranes can trigger cell death once they are released. During certain stages of development and during aging, mitochondrial membranes break down to release these deadly poisons. This process is called "programmed cell death." Does this suggest that life span is dictated by genes from the mother? We are not sure because scientists have not looked into this!
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SELF QUIZ 2
How We Know
How do the genes in mitochondria differ from the genes in the cell nucleus?
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HOW DID WE DISCOVER THE FUNCTIONS OF THE MITOCHONDRIA?
How We Know
We know that mitochondria are important in meeting the cell’s energy needs, but how did scientists figure that out? Some of the energy that mitochondria convert for the cell produces heat, much like how a burning match produces heat. Burning matches consume oxygen. The human body also consumes oxygen when it transforms energy. So, scientists measured oxygen consumption in pure preparations of mitochondria and found that they consume much more oxygen and produce more heat than other organelles.
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DO YOU KNOW WHY THE BODY NEEDS OXYGEN?
How We Know
In non-living systems, oxygen can release the trapped energy of chemical bonds (as in wood and paper, for example). Of course the energy released in burning wood is "lost" (transferred to the environment) as light and heat. In a living system, oxygen does a similar thing, helping to release the stored chemical bond energy of foods. Except a living system cannot afford to release too much of the energy as heat.
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SELF QUIZ 3
How We Know
Scientists first discovered that mitochondria were important in meeting the cell’s energy needs by measuring their oxygen consumption and ______.
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HOW DO SCIENTISTS FIND OUT HOW ORGANISMS CAPTURE ENERGY?
How We Know
Scientists knew that the energy released in mitochondria needed to be captured temporarily in some kind of molecule. By testing the chemicals in mitochondria, they found one that could take up or give up large amounts of energy. The molecule that traps and stores energy is known as adenosine triphosphate (ATP). Our body heat comes from the leftover food energy that is not captured in ATP.
When scientists measured oxygen consumption and the build-up of ATP inside of cells, they found two sets of reactions:
The first set of reactions breaks glucose into a series of three-carbon molecules. This first step is called glycolysis. The second set, where oxygen is consumed, releases water and carbon dioxide as waste products. This includes the "Krebs cycle,“ which our Story Time hero discovered, and the electron transport chain. The Krebs Cycle produces carbon dioxide and powers the electron transport chain’s transformation of oxygen into water as well as the production of ATP.
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SELF QUIZ 4
How We Know
Identify the pair that is correct:
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Story Time
Hans Krebs (1900-1981)
Hans Krebs was born in a medieval town in Northern Germany called Hildesheim, near Hanover (pictures are on the right). Hans lived comfortably as a child, in a large house with a nice backyard and garden. Like most little boys, Hans loved the outdoors, and he spent many hours hiking and cycling through the woods and hills of the beautiful countryside. But Hans also loved books. He even liked to read encyclopedias!
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Story Time
His father was a respected physician - an eye, ear, nose and throat doctor. His father, who also wrote poetry, created a mentally stimulating environment, where reading a wide variety of books was valued. He was also active in German politics, although he opposed the anti-Jewish and anti-democratic policies of Hitler and the Nazis. Hans' father believed that the only hope for Jews in Germany was to abandon their faith and become totally German. Thus, Hans was never instructed in the Jewish teachings. But, in Germany at that time religious instruction was required by the government, and so Hans was exposed to Christian teachings.
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HANS’S BIOLOGICAL FAMILY
Story Time
Both parents were stern with Hans and his brother and sister. High standards were set in every area - behavior, personal discipline, and schoolwork. Life was emotionally cold. There were no spontaneous hugs or goodnight kisses. Maybe the lack of outward signs of love had something to do with his poor behavior. Hans was by no means a model boy. He was fussed at by his family and by his schoolteachers for being sloppy. He thought of himself as unattractive and unpopular.
The grammar school he attended was over seven hundred years old. (In Europe, there are many schools that have histories that are centuries long.) He did not learn much in school, partly perhaps because all the good teachers had been drafted into the army to fight in World War I. In Germany then, most of the teachers were male. Hans admitted that he was just an ordinary student. His favorite subjects were history and music, NOT science!
What led young Hans to science? It might have begun with the love of living things that he gained from his father. They often went on family outings in the nearby countryside. Hans especially liked to discover plants that he had never seen before. For reasons unknown, Hans had a special love for learning new things. By age nine he was reading books on a variety of subjects, just for entertainment.
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HANS’S BIOLOGICAL FAMILY
Story Time
Because he was impressed with the family-doctor lifestyle of his father, Hans wanted to become a physician also. Hans went to college after he was released from the army at the end of World War I. The country was in shambles, and life at the university was primitive and difficult. Food was rationed, public transport was unreliable, gas and electricity were so scarce that people could not have lights on in their houses past 10 PM. But the spirit of learning and inquiry that Hans found at the university was exhilarating. For a boy like Hans who loved to learn things, the university became the most important thing in his life. In those days, the main point of a university in Germany was to explore and learn, not necessarily to prepare for a profession or career. In that place of higher learning, it did not take long for Hans to realize that his first love was scientific discovery. But he did go on to follow his father's footsteps and become a physician.
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HANS’S BIOLOGICAL FAMILY
Story Time
Classes in medical school were overcrowded. Then, as in many schools in Germany today, anyone who qualified and could pay the fees must be admitted. Hans became interested in scientific research from listening to his professors talk about their own research. Quickly, he realized that he wanted to be a scientist instead of a physician, which disappointed his father. His father worried that Hans would never make a good income as a scientist. At that time in Germany, the beginning of the Great Depression, the economy had collapsed. In one year, 1923, the value of the U.S. dollar relative to the German mark had exploded some 4,000,000,000,000 times. And Hans did live in poverty. He went many years living on a modest income. His first paid job was at the age of 25. Fortunately, that job was as a lab assistant to Otto Warburg, who won the Nobel Prize in 1931.
In his early career, Hans performed experiments in many subject areas that were totally unrelated to the area for which he was to become famous. However, some of this research prepared Hans' mind for understanding the research for which he was to become famous. His first job after graduating from medical school was in the laboratory of a famous scientist, Otto Warburg.
Otto Warburg
Source: The Nobel Prize
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HANS’S NOBEL PRIZE FAMILY
Story Time
Many scientists believe that the way to learn how to do great science is to study under a great scientist. It is true that many Nobel Prize winners have been students of other Nobel Prize winners.
The "family tree" of scientists, who taught Hans Krebs, shows the following relationships of science teachers and mentors:
Berthollet (1748-1822)
Gay-Lussac (1778-1850)
Liebig (1803-1873)
Kekule (1829-1896)
von Baeyer (1835-1917)
Fischer (1852-1919)
Warburg (1883-1970)
Krebs (1900- 1981)
All of these men were famous scientists. Each of the last four received Nobel Prizes, which began in 1901. There was only one scientist in Hans' biological family tree, a distant cousin, who was a physical chemist.
In the years (1926-1930) that Hans studied with Otto Warburg, he learned important techniques for testing ideas about energy transformation in living tissue. But Hans also learned the value of inventing new tools and approaches for conducting experiments. Maybe the most important lesson was the value of hard work. Warburg worked long and hard hours all his life; he was working in his lab eight days before he died, at the age of 81.
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HANS’S NOBEL PRIZE FAMILY
Story Time
Another role model for Hans was Otto Myeroff, who worked in the same institute and who received the Nobel Prize in 1922. In those early years, the pay for young researchers was very low (remember, the German economy had collapsed). Hans and his colleagues continued to be supported by their parents, many of whom had lost their life savings in the economic crash in Germany.
After four years in Warburg's lab, Hans was told that he should leave, because Warburg wanted a steady stream of novices that he could train. Krebs felt that his abilities were not appreciated by Warburg. Only years later did Hans learn that Warburg considered him to be his favorite pupil. Warburg also worked behind the scenes for many years to help get Hans invited to give papers at important meetings and institutes.
So Hans left and got on the medical faculty at Freiburg University in 1931. There he was in charge of a 40-bed hospital and had a research laboratory. Although he had many physician duties in the school's hospital, Hans was free for the first time to pursue his own research ideas. Here, he and a medical student assistant studied nitrogen metabolism in the liver and made a major discovery, the ornithine cycle. This discovery was important, and it also prepared Hans' mind to accept the idea that a chemical compound could go through a series of transformations that finally led to a re-making of the original compound. The ornithine cycle was the first such cycle ever discovered. Now we know of about 100 such cycles, including the one that Hans discovered to make him famous, the citric acid cycle (Krebs cycle).
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HANS’S NOBEL PRIZE FAMILY
Story Time
In 1933, Adolph Hitler seized power. Hans knew that as a Jew he must leave his homeland because Adolph Hitler had taken over the country and was persecuting Jews. Indeed, despite his growing fame from the ornithine cycle work, Hans was literally fired from his university job. All Jews in Germany who were in government positions were fired in 1933. But Hans had influential fans outside of Germany. Hans believed that his sense of urgency to complete work, rather than put it off, saved his life. Had he pursued the ornithine research leisurely, he would not have become famous in time to save him from the Nazis. When he realized that he must flee Germany, he quickly landed a Rockefeller Fellowship and an invitation to work at the prestigious University of Cambridge in England. But the only position he could get, despite the fact that he was world famous, was at the lowest rank on the academic ladder. He took it anyway so that he could continue his work.
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THE LATER YEARS
Story Time
Hans arrived in England with "virtually nothing but a sigh of relief." But Hans was happy in England. There was much less prejudice against Jews than in Germany and also fewer social barriers, such as those in Germany due to politics, religion, exclusive student fraternities, and class consciousness. The people in Great Britain were generous and friendly. Hans had found a new home and would never turn back to the old.
In Britain, Hans completed his work on the now famous Krebs cycle, for which he later won the Nobel Prize in 1953. He hypothesized the existence of certain chemical compounds and reactions that might explain the observed waste products of carbon dioxide and water. He and his first graduate student, William Johnson, tested the hypotheses in a series of biochemical studies in the very active breast muscle of pigeons. Hans sent the manuscript to the prestigious journal, Nature, only to learn that they did not want to publish it. William Johnson had to leave science, because he could not secure a suitable position. The last Hans heard of Johnson, he was managing a turtle farm on Cayman Island. (The turtle farm is still there, and it is quite a tourist attraction.) Hans eventually published this classic paper, the one that won him the Nobel prize, in a Dutch journal (Enzymologia, vol. 4, pp. 148-156, 1937). His place in the history of great science had been secured.
Hans Krebs Source: The Nobel Prize
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REFERENCES
Story Time
Krebs, Hans. Reminiscences and Reflections. Clarendon Press Oxford. 1981.
https://www.nobelprize.org/prizes/medicine/1953/krebs/biographical/
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Common Hazards
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TOXINS THAT AFFECT THE MITOCHONDRIA
Common Hazards
How might mitochondria be affected by toxic chemicals? Mitochondrial toxins fall into three categories. They can:
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ELECTRON TRANSPORT INHIBITORS
Common Hazards
Environmental toxins such as herbicides, insecticides, and fungicides can prevent the passing of electrons by binding to one or more of the proteins that carry electrons. Examples:
Electron Transport Inhibitors
Cyanide is a well-known poison that prevents the addition of high energy phosphate groups to make the energy storage compound, ATP. Other well-known compounds that act this way include the pesticides pentachlorophenl (PCP) and 2,4-dinitrophenol (DNP).
Uncouplers
Mixed Action Toxins
Certain herbicides inhibit electron transport at high concentration and promote uncoupling at low concentrations. Some insecticides, such as DDT and cyclodiene, are also in this group.
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WE WILL LEAVE YOU WITH SOMETHING TO THINK ABOUT
Common Hazards
Part of the way that these toxins act comes from their ability to penetrate and stick in membranes. When any compound gets incorporated in a membrane, it can disturb the position of the other compounds that are normally found there. In the membranes that make up the folds inside of mitochondria, such disturbance interferes with the passing of electrons that is needed to couple energy to ATP synthesis.
Here is a question to think about: Could herbicides and insecticides affect processes in other membranes, such as those in the nuclear membrane or membranes where proteins are made (endoplasmic reticulum), or even the cell membranes of excitable cells such as nerve cells?
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Activities
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Activities
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Self-Study Game
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Self-Study Game
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Post-Test
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A-D
Glossary
Adenosine triphosphate (ATP) - the "energy molecule" of the cell. Cells use ATP and derivatives of ATP to perform metabolic functions. The energy comes from the high energy bonds between the phosphate molecules. Return to How We Know
Aerobic - description for a process that requires oxygen. Return to What We Know
Anaerobic - description of a process that does not require oxygen. Return to What We Know
Cellular respiration - A series of metabolic reactions that take place within a cell to convert chemical energy from foodstuffs like glucose into usable energy (ATP), water, and carbon dioxide. Return to Why It Matters | Return to What We Know
Citric acid cycle - a series of chemical reactions that occur in the mitochondria used in aerobic organisms in which water is added and carbon dioxide and the original molecule are produced. Return to What We Know
DNA - abbreviation for deoxyribonucleic acid; nucleic acid that stores genetic information. Return to How We Know
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
E-GL
Glossary
Electron micrograph - A picture taken by a very high-powered microscope that magnifies enough to see large molecules. In both light and electron microscopes, illumination is provided by a source (lamp, filament in the electron gun) which is focused by a condenser lens onto the specimen. A first magnified image is formed by the objective lens. This image is further magnified by the projector lens onto a ground glass screen (light) or fluorescent screen (electrons). Return to How We Know
Electron transport chain - a series of protein complexes that transfers electrons between complexes coupled with the transfer of protons across the inner mitochondrial membrane to produce ATP and convert oxygen into water. Return to What We Know | Return to How We Know
Free-Radicals - an unstable atom, molecule, or ion that has an unpaired valence (outer) electron. Return to How We Know
Glycolysis - a series of metabolic reactions in the cytoplasm that does not require oxygen and breaks glucose down into pyruvic acid. This process occurs quickly and produces 2 ATP and 2 NADH. Return to What We Know | Return to How We Know
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GR-R
Glossary
Gradient - a measure of change in a physical quantity, such as concentration or temperature, over a specified range or distance. Return to What We Know
Kinetic energy - energy associated with motion. A rock rolling down a hill has kinetic energy. Also see potential energy. Return to Why It Matters
Krebs cycle - a series of chemical reactions that occur in the mitochondria used in aerobic organisms in which water is consumed, carbon dioxide is released, and the original molecule is regenerated. Return to What We Know | Return to How We Know
Organelle - specialized structures in cells that perform various jobs. Example: ribosomes produce proteins. Return to How We Know
Potential energy - energy that an object (or piece of matter) has because of its position or an arrangement of its parts (for example chemical bonds.) A rock at the top of a hill has potential energy. Also see kinetic energy. Return to Why It Matters
RNA - abbreviation for ribonucleic acid; a nucleic acid present in all cells that is necessary for transcribing/translating the information coded in DNA into protein products. Return to How We Know
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Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 1
Why It Matters
The organelle that breaks down glucose to release and capture its energy is?
A. No, sorry, but that is wrong. Membrane-like structures inside an organelle are necessary to capture energy released from breaking chemical bonds, but this occurs in another organelle.
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Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 1
Why It Matters
The organelle that breaks down glucose to release and capture its energy is?
B. No, sorry, but that is wrong. The Golgi apparatus adds certain sugar-like molecules to proteins, serving to put them in their final, functional form.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 1
Why It Matters
The organelle that breaks down glucose to release and capture its energy is?
C. Good for you. Although many organelles have membrane-like structures, only mitochondria have molecules inserted into t heir membranes that permit the trapping of energy.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 1
Why It Matters
The organelle that breaks down glucose to release and capture its energy is?
D. No, sorry, that is wrong. The cell membrane regulates what chemicals move into or out of cells. It cannot generate energy.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 2
How We Know
How do the genes in mitochondria differ from the genes in the cell nucleus?
A. Yes. The father's genes inside of sperm are chemically tagged and destroyed after an egg is fertilized. Only the mitochondria in the egg survive. In the developing embryo, the mitochondria get incorporated into each cell, where they divide like bacteria.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 2
How We Know
How do the genes in mitochondria differ from the genes in the cell nucleus?
B. No, genes inside mitochondria are made up of DNA, just like genes in the nucleus.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 2
How We Know
How do the genes in mitochondria differ from the genes in the cell nucleus?
C. Sorry, but this answer is wrong. We don't know much about gene regulation (turning on/off of specific genes) in mitochondria genes. This is the hot area of genetics research, but most of the effort is focused on the main genes in the nucleus. Even so, it is a good bet that mitochondrial genes are regulated differently. They are in a quite different chemical (and energy) environment than nuclear genes.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 2
How We Know
How do the genes in mitochondria differ from the genes in the cell nucleus?
D. No, that is wrong. The genes in the mitochondria come exclusively from the mother and mainly control mitochondrial functions. Genes in the nucleus control functions in the rest of the cell.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 3
How We Know
Scientists first discovered that mitochondria were important in meeting the cell’s energy needs by measuring their oxygen consumption and ______.
A. No, sorry, but this is wrong. Glucose is the chemical that mitochondria work on, but it does not prove what mitochondria do.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 3
How We Know
Scientists first discovered that mitochondria were important in meeting the cell’s energy needs by measuring their oxygen consumption and ______.
B. No, sorry, but this is wrong. The large surface area of the plates of membranes inside of mitochondria improve the efficiency of what mitochondria do, but they don't prove what it is they do.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 3
How We Know
Scientists first discovered that mitochondria were important in meeting the cell’s energy needs by measuring their oxygen consumption and ______.
C. No, sorry, but this is wrong. Mitochondria come in slightly different sizes, but size does not indicate the function.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 3
How We Know
Scientists first discovered that mitochondria were important in meeting the cell’s energy needs by measuring their oxygen consumption and ______.
D. Good for you! The fact that mitochondria give off heat is strong evidence that they are releasing energy (and perhaps saving some of it in some kind of storage form).
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 4
How We Know
Identify the pair that is correct:
A. Excellent. This is the correct answer. The initial stage of energy production produces only a little energy because oxygen is not consumed in the chemical reactions that begin the breakdown of glucose.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 4
How We Know
Identify the pair that is correct:
B. No, this is not right. The Krebs cycle produces many more molecules of ATP than does glycolysis.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 4
How We Know
Identify the pair that is correct:
C. No, this is not right. Since the glycolysis does not generate many ATP molecules, compared with the Krebs cycle of reactions, we know it must not be producing much energy.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |
SELF QUIZ 4
How We Know
Identify the pair that is correct:
D. No, this is not right. The Krebs cycle produces many more molecules of ATP than does glycolysis.
Meeting Cells' Energy Needs
Cells Are Us: Meeting Cells' Energy Needs |