You are not expected to read all of these articles - use "Ctrl+F" keyword searches to help you find what you are looking for.
This is a participation grade.
It is designed to help you become familiar with the reading material to the left.
Goal - do every-other question in each section.
The articles on the left will be the "notes" you will be able to use on the quiz (Thurs-Fri) - get familiar with what they say.
You are not expected to read all of these articles - use "Ctrl+F" keyword searches to help you find what you are looking for.
You are not expected to read all of these articles - use "Ctrl+F" keyword searches to help you find what you are looking for.
This is a participation grade.
It is designed to help you become familiar with the reading material to the left.
Goal - do every-other question in each section.
The articles on the left will be the "notes" you will be able to use on the quiz (Thurs-Fri) - get familiar with what they say.
You are not expected to read all of these articles - use "Ctrl+F" keyword searches to help you find what you are looking for.
a.) Glycolysis converts one molecule of glucose into two molecules of
b.) Glycolysis will form NADH in reaction number
c.) Glycolysis occurs within the
d.) Glycolysis will form a total of
e.)
f.) What will pyruvic acid eventually be converted into prior to entering into the main reactions of the Krebs cycle?
g.) How many times is glucose and its derivatives changed/transformed during glycolysis?
h.) What is used to begin the reactions of glycolysis?
i.) What is added to ADP to transform it into ATP?
Humans and other organisms use the energy stored in glucose, which is produced in photosynthesis, to create high energy molecules of ATP through the process of cellular respiration. ATP is an energy source that powers the catabolic and anabolic processes of living things.
Cellular respiration involves a number of major steps — glycolysis, which is discussed in this article, Krebs cycle, the electron transport chain, and chemiosmosis. Keep in mind that the overall object of cellular respiration is to transfer the energy within the bonds of glucose into ATP. Glycolysis, as we will see, has nine reactions that are used to convert the glucose into two molecules of pyruvic acid (pyruvate).
Glycolysis begins with a molecule of glucose, which is a six-carbon carbohydrate that contains carbon, hydrogen, and oxygen. The first reaction of glycolysis occurs after an ATP is used as the power source for this reaction, which transforms glucose into glucose-6-phosphate (G6P) through the transfer of one phosphate from ATP to glucose. The enzyme that is used to catalyze this first reaction is hexokinase, or HK.
In reaction two of glycolysis, another enzyme is used on G6P to convert it into fructose-6-phosphate (F6P). The F6P then moves to reaction three, in which an ATP is used to attach a second phosphate onto the molecule of F6P, which forms a new molecule called fructose 1, 6-bisphosphate. This molecule is named this because the base of the molecule is a type of fructose that has two phosphate groups (bisphosphate) attached to the first (1) and sixth (6) carbon on the fructose; hence, fructose 1, 6-bisphosphate (F1, 6-DP). This reaction is catalyzed by the enzyme phosphofructokinase (PFK).
In reaction four, the single molecule of fructose 1, 6-bisphosphate is split in two. The six-carbon fructose molecule becomes two three-carbon molecules.
In reaction five, the two three-carbon molecules are converted into 1, 2-diphosphoglyceric acid (1, 2-DPGA) by the addition of a phosphate group onto each molecule that is supplied from the cytoplasm of the cell. In this fifth reaction, a molecule of nicotinamide adenine dinucleotide (NAD+) forms a molecule of NADH, which is used in the electron transport chain. Two molecules of NADH are formed in this fifth reaction, because it occurs two times per one six-carbon glucose molecule that enters glycolysis.
In reaction six, energy is given off to form a molecule of ATP. Since this occurs two times in this sixth reaction, two molecules of ATP are formed in reaction six. The 1, 2-diphosphoglyceric acid is also converted into 3-phosphoglyceric acid (3-PGA).
In reaction seven, the phosphate group that was attached to the third carbon of 3-PGA is relocated onto the second carbon of the molecule which forms 2-phosphoglyceric acid (2-PGA). In reaction eight, a double bond is formed, and the result is phosphoenolpyruvic acid (PEP). No ATP is produced during these reactions, nor is any used.
In the final reaction, reaction nine, the phosphate group from PEP is transferred to ADP, and two molecules of ATP are formed. The net result of glycolysis is two pyruvic acid molecules and 4 ATP (2 net ATP, as two were used to initiate glycolysis). Pyruvic acid will be converted prior to entering Krebs cycle into acetyl CoA.
The Krebs (citric acid) cycle takes place immediately after glycolysis. However, while glycolysis occurs outside of the mitochondria — in the cytoplasm of the cell — Krebs is the first part of cellular respiration that occurs within the mitochondria. In the Krebs cycle, one molecule of pyruvic acid at a time will enter into it to be converted into carbon dioxide, several molecules of NADH, as well as ATP and FADH2.
Just prior to the main reactions of Krebs, the pyruvic acids produced during glycolysis are converted into acetyl CoA. Since two pyruvic acids eventually enter Krebs, they will form two acetyl CoA. This conversion will also produce one carbon dioxide and one NADH (this will be referred to as reaction 1). At this point, the acetyl CoA will enter into the main reactions of Krebs cycle.
In reaction 2, one acetyl CoA enters Krebs in which an enzyme catalyzes a reaction between it and a four-carbon molecule of oxaloacetate. The result of this catalyzed reaction is citric acid, a six-carbon molecule.
In reaction 3, citric acid is converted into isocitrate, which, like citric acid, is a six-carbon molecule. However, when isocitrate enters reaction 4, a carbon is lost to form one molecule of carbon dioxide. Reaction 4 also produces one NADH and one α-ketogluterate, which has five carbons due to the loss of one carbon in the formation of carbon dioxide.
In reaction 5, another carbon dioxide is given off as the five-carbon α-ketogluterate is converted into a four-carbon molecule succinyl-CoA. During this reaction, another NADH is produced. In the next reaction, reaction 6, the succinyl-CoA is converted into succinate along with one molecule of ATP.
In reaction 7, the four-carbon succinate is converted into a four-carbon fumarate, and this process involves a substance called flavin adenine dinucleotide (FAD). This molecule is activated to form one high-energy molecule known as FADH2, which, along with NADH, is used in the electron transport chain.
In reaction 8, the fumarate converts into a four-carbon molecule of malic acid, and in the last reaction of the Krebs cycle, reaction 9, an enzyme is used to convert malic acid into oxaloacetate. During this enzymatic reaction, another molecule of NADH is formed.
The oxaloacetate that is formed in reaction 9 is used to react with the second acetyl CoA, that is formed from the second pyruvic acid of the original glucose that had entered glycolysis, in reaction 2 of the next Krebs cycle.
For every molecule of pyruvic acid that enters the Krebs cycle, four NADH molecules, one FADH2 molecule, and three carbon dioxide molecules are produced. The NADH and FADH2 molecules will move on to the electron transport chain, while the carbon dioxide molecules are released as a waste product and are expelled into the atmosphere as we exhale. Remember, though, that two molecules of pyruvic acid are produced from one glucose molecule, therefore these numbers must be doubled to get the total product of two cycles of Krebs.
a.) The molecule that will enter Krebs is
b.) What must be present in order for Krebs to occur?
c.) How many total reactions will form carbon dioxide during Krebs?
d.) How many total reactions will form NADH during Krebs?
e.) How many total final products are made during Krebs?
f.) How many total carbon dioxides are formed from one pyruvic acid
g.) How many total NADH are made from one pyruvic acid
Thus far, in the two prior reactions of cellular respiration, one molecule of glucose was converted into two molecules of pyruvic acid during glycolysis. These pyruvic acids are converted, one at a time, into NADH and FADH2, which are used in this last step of cellular respiration — the electron transport chain and chemiosmosis. The NADH and FADH2 will be used to produce massive amounts of ATP. Like the Krebs cycle, the electron transport chain and chemiosmosis occurs within the mitochondria; specifically in the inner mitochondrial membrane.
We begin the biochemistry of the electron transport chain (ETC) with NADH; it loses two electrons as well as one hydrogen ion. The electrons pass through an enzyme that is embedded in the inner mitochondrial membrane, called NADH dehydrogenase. Simultaneously, four hydrogen ions are pumped through this enzyme and into the intermembrane space (area between the inner and outer mitochondrial membranes). As a result of this, NADH is recycled back into NAD+ and can once again enter Krebs and glycolysis again. Each of the enzymes in the ETC are named for what they do — the NADH dehydrogenase gets its name for oxidizing the NADH into NAD+.
After moving through the NADH dehydrogenase, the electrons are transferred to another enzyme embedded in the inner mitochondrial membrane called coenzyme Q. At the same time, FADH2 releases electrons into this same enzyme and is oxidized back into FAD which is recycled back to the Krebs cycle.
Cytochrome C reductase receives the electrons from coenzyme Q, and as these electrons pass through, another four hydrogen ions are pumped into the intermembrane space. The electrons continue on their way, and are next taken up by cytochrome C, which is located on the outer surface of the inner mitochondrial membrane. Cytochrome C now passes the electrons to cytochrome C oxidase, and as this occurs, another two hydrogen ions are pumped into the intermembrane space. The electrons then leave the ETC and combine with an oxygen ion. Each ion of oxygen also accepts two hydrogen ions to form one molecule of water. Because of this role, oxygen is called the terminal electron acceptor (the final electron acceptor), and this important function is why we must breathe in oxygen with every breath we take and why our cells require oxygen. At this point, the ETC has come to an end and we must move to chemiosmosis.
Up to this point, a large amount of hydrogen ions have been accumulating in the intermembrane space of the mitochondria, creating a high concentration of these ions. As you may recall from prior discussions on diffusion and osmosis, things tend to move from high to low concentration, meaning this high concentration of hydrogen ions will “want” to diffuse through the inner mitochondrial membrane, but they are unable to cross through it due to their positive charge. ATP synthase, another enzyme embedded through the entire inner mitochondrial membrane will permit these hydrogen ions to diffuse from high to low concentration.
As four hydrogen ions diffuse through the ATP synthase, the energy they transfer into the enzyme (ATP synthase) is used to combine a molecule of ADP with one phosphate group to form a molecule of ATP. In total, the process that occurs through the oxidation of all NADH and FADH2 produced from one molecule of glucose will result in the formation of approximately 30-34 molecules of ATP via the ETC and chemiosmosis. When this figure is combined with the four that are formed in glycolysis and Krebs, this brings the total ATP formed from one molecule of glucose, via aerobic cellular respiration (glycolysis + Krebs + ETC/Chemiosmosis) to 34-38 ATP.
a.) The electron transport chain and chemiosmosis occur in the
b.) NADH loses
c.) The electrons from NADH pass through an
d.) The electrons that had been released by the NADH, after moving through NADH dehydrogenase, they are transferred to another enzyme embedded in the inner mitochondrial membrane called
e.)
f.) Cytochrome C passes the electrons to
g.) The accumulated hydrogen ions in the intermembrane space diffuse back through the enzyme
h.) Oxidation of all NADH and FADH2 produced from one molecule of glucose results in the formation of approximately
Today, most living things use oxygen to make ATP from glucose. However, many living things can also make ATP without oxygen. This is true of some plants and fungi and also of many bacteria. These organisms use aerobic respiration when oxygen is present, but when oxygen is in short supply, they use anaerobic respiration instead. Certain bacteria can only use anaerobic respiration. In fact, they may not be able to survive at all in the presence of oxygen.
An important way of making ATP without oxygen is called fermentation. It involves glycolysis, but not the other two stages of aerobic respiration. Many bacteria and yeasts carry out fermentation. People use these organisms to make yogurt, bread, wine, and biofuels. Human muscle cells also use fermentation. This occurs when muscle cells cannot get oxygen fast enough to meet their energy needs through aerobic respiration.
There are two types of fermentation: lactic acid fermentation and alcoholic fermentation. Both types of fermentation are described below.
In lactic acid fermentation, pyruvate (also known as pyruvic acid) from glycolysis changes to lactic acid. This is shown in the Figure below. In the process, NAD+ forms from NADH. NAD+, in turn, lets glycolysis continue. This results in additional molecules of ATP. This type of fermentation is carried out by the bacteria in yogurt. It is also used by your own muscle cells when you work them hard and fast.
Did you ever run a race and notice that your muscles feel tired and sore afterward? This is because your muscle cells use lactic acid fermentation for energy. This causes lactic acid to build up in the muscles. It is the buildup of lactic acid that makes the muscles feel tired and sore.
In alcoholic fermentation, pyruvate changes to alcohol, NAD+, and carbon dioxide. This type of fermentation also explains why bread dough rises. Yeasts in bread dough use alcoholic fermentation and produce carbon dioxide gas. The gas forms bubbles in the dough, which cause the dough to expand. The bubbles also leave small holes in the bread after it bakes, making the bread light and fluffy.
While both forms of fermentation are used by different organisms and will produce different products, their purpose is the same — to recycle NADH into NAD+ to permit glycolysis to continue. If glycolysis is permitted to continue, even in anaerobic conditions, the cell is able to produce two net molecules of ATP from one molecule of glucose. While this is a considerably smaller quantity of ATP when compared to the total produced from one molecule of glucose in aerobic respiration, it is enough to keep the cell alive.
a.) Many organisms use
b.) An important way of making ATP without oxygen is called
c.) Fermentation involves
d.) Human
e.) In lactic acid fermentation, pyruvate (pyruvic acid) from glycolysis changes to
f.) The buildup of
g.) In alcoholic fermentation, pyruvate changes to
h.) Yeasts in bread dough produce
i.) The primary purpose of both forms of fermentation is to recycle
j.) When fermentation permits glycolysis to continue under anaerobic conditions, the cell produces a net of