Mod+10+Reading+Guide


 * __Module 10 Summary__**: Module 10, metabolic pathways for carbohydrates, describes how chemical reactions are catalyzed in a series to produce energy and other cellular compounds including glycolysis glycogenesis, glycogenolysis, gluconeogenesis, and other cellular processes.

Summary: **Catabolic reactions** break down complex molecules to release energy, and **anabolic reactions** use energy to build large molecules from simpler ones. A cell's **cytosol** is the fluid part of the cytoplasm which includes water, electrolytes and enzymes. Inside the mitochondria is a fluid section surrounded by an inner membrane called the matrix. The matrix of a mitochondrion holds enzymes that catalyze the oxidation of carbohydrates, fats, and amino acids.
 * __22.1 Metabolism and Cell Structure__**

Struggling Topic 1: Is there a non-memorizing way to help students learn the cell parts and organelles? We do this with my junior high students hoping that they will remember some when they get to high school sciences, but it seems to be memorization at a basic level.

Struggling Topic 2: How does the structure of a mitochondrion allow it to do such a variety of chemical reactions? Will the transamination of amino acids, the oxidation of fatty acids, the synthesis of ATP, and the electron transport chain all happen in the same location, or are there different sections of the mitochondrion for each of these reactions?

Summary: **ATP**, adenosine triphosphate, is a molecule composed of the nitrogen base adenine, a ribose sugar, and three phosphate groups. ATP is the most important variety of "high-energy" compounds and generates 7.3 kcal or 31kJ per mole when it loses a phophate group and becomes ADP. **ADP**, adenosine diphosphate, is produced when ATP expends energy by cleaving a phosphate group. ADP can lose a phosphate group to expend energy (becoming AMP) or receive a phosphate group to store energy as ATP. Many reactions in the cell, such as adding a phosphate group to glucose so it can be broken down, do not occur spontaneously because they have relatively high activation energies. When coupled with the hydrolysis of ATP, the reaction takes place because of the energy that is released as ATP is hydrolyzed to become ADP. A similar process drives many important cellular actions.
 * __22.2 ATP and Energy__**

Struggling Topic 1: The diagram in the book suggested that ADP could be hydrolyzed for energy to AMP. Is this commonly done in cells, or is ADP usually converted back to ATP before it is hydrolyzed further?

Struggling Topic 2: Last chapter we discussed how other nitrogen bases could form phosphates. Are other -sines used to make triphosphates for energy storage in the cell such as cytosine triphosphate, thymine triphosphate, or guanine triphosphate?

Summary: Review **oxidation** (involves the loss of hydrogen and electrons by a substance or an increase in oxygen) and **reduction** (a gain of hydrogen and electrons or a decrease in oxygen). When an enzyme catalyzes an oxidation, H+ and e- are removed from a substrate and taken by the coenzyme which is reduced. **NAD+**, nicotinamide adenine dinucleotide, is a coenzyme that bonds to ADP to produce a C=O in the oxidation of alcohols to aldehydes and ketones. The NAD+ is reduced to NADH and a H+ ion is released. **FAD**, flavin adenine dinucleotide, (has ribitol) is a coenzyme that accepts hydrogen atoms when it catalyzes an oxidation reaction and becomes FADH2. FAD typically bonds in oxidation reactions that produce C=C bonds. **Coenzyme A** is made of several components (vitamin b3, pantothenic acid; ADP; and aminoethanethiol), and it activates acyl groups - hence the A in CoA. When the free thiol -SH group of CoA bonds to an acetyl group the products are energy-rich thioesters such as Acetyl CoA.
 * __22.3 Important Coenzymes in Metabolic Pathways__**

Struggling Topic 1: NAD+ and FAD both accept H+. What makes NAD+ form C=O bonds and FAD form C=C bonds?

Struggling Topic: Students are often confused by the seemingly inconsistent definitions for oxidation and reduction. Do you have suggestions for introducing oxidation and reduction in a way that would allow students to easily assimilate the many different ways reactants can be oxidized and reduced?

__**22.4 Digestion of Carbohydrates**__ Summary: **Digestion** is the process that converts large molecules into small ones that can be absorbed easily by the body. Amylase and other enzymes break down large polysaccharides into **dextrins**, molecules that contain 3 to 8 glucose units. In the small intestine, the rest of the polysaccharides are hydrolyzed to glucose, lactose, and sucrose. The three common disaccharides hydrolyze as follows: lactase breaks lactose into galactose and glucose, sucrase breaks sucrose into fructose and glucose, and maltase breaks maltose into 2 glucose monosaccharides. Fructose and galactose are converted to glucose in the liver.

Struggling Topic 1: What happens in the stomach? Kids are taught to believe that digestion happens primarily in the stomach, but it sounds like carbohydrates do almost nothing in the stomach.

Struggling Topic 2: Is there any significant nutritional benefit to whether the polysaccharides in the carbohydrates we eat contain mostly maltose disaccharides? Does the process of converting galactose (assuming galactase is present in a non-lactose intolerant person) or fructose into glucose delay or complicate the digestion process? Would we be healthier if we didn't have as much fructose or galactose to change into glucose?

Summary: **Glycolysis** is an **anaerobic** process where no oxygen is required that happens in the cytoplasm of a cell when a six-carbon glucose molecule is broken down to yield two three-carbon pyruvate molecules. 2 ATP are needed to begin glycolysis, and these bind phosphates to each side of glucose to break it in half. Then the 4 ADP are converted to ATP as the two three-carbon sugar phosphate molecules are hydrolyzed. Glycolysis has 10 steps that are summarized on p. 803-805. 1 - Phosphorylation: first ATP invested, 2 - Isomerization, 3 - Phosphorylation: 2nd ATP invested, 4 - Cleavage - two trioses form, 5 - Isomerization of a triose, 6 - First energy-rich compound, 7 - Formation of 1st ATP, 8 - formation of 2-phosphoglycerate, 9 - second energy-rich compound, 10 - formation of second ATP and pyruvate. Overall, glycolysis costs 2 ATP and 1 glucose molecule to yield 4 ATP, 2 NADH, and 2 pyruvate. Fructose and galactose are converted to an intermediary of glycolysis so that that they can be used with a very similar process. 3 enzymes, hexokinase (feedback inhibition if there is too much glucose-6-phosphate in the cell), phosphofructokinase (increases rate when ADP and AMP are too plentiful but decreases rate when ATP is too plentiful in the cell), and pyruvate kinase (high levels of ATP and acetyl CoA inhibit the production of pyruvate), respond to the levels of ATP and continually sepped up or slow does the flow of glucose into gylocolysis.
 * __22.5 Glycolysis: Oxidation of Glucose__**

Struggling Topic 1: It sounded like fructose and galactose did not become glucose exactly before beginning glycolysis, but that they rather became an intermediate product of glycoysis first and the simply continued along the steps of glycolysis. Is this correct?

Struggling Topic 2: If fructose and galactose don't begin at step 1 of glycolysis, is ATP used in the formation of the intermediary that begins glycolysis at a later step than glucose would?

__**22.6 - Pathways for Pyruvate - QUIZ QUESTIONS ON THIS ONE!!!!**__ Summary: In **aeorbic** conditions, when oxygen is present, pyruvate is converted to acetyl coenzyme A (CoA), but when oxygen levels are low, pyruvate is reduced to lactate. In anaerobic yeast, pyruvate is converted to ethanol. More energy is obtained from glucose when oxygen levels are higher. In the matrix of the mitochondrion, pyruvate is oxidized to CO2 with the help of NAD+ to produce **acetyl CoA. Acetyl CoA** is an important intermediate compound in many metabolic processes. In anaerobic conditions, pyruvate is reduced to lactate to produce NAD+ which is then used to produce a small amount of ATP. When this lactate builds up, muscles quickly tire. In these anaerobic conditions, only 2 ATP molecules are produced per glucose molecule. Bacteria convert pyruvate to lactate under anaerobic conditions, and this can be used to prepare sauerkraut, sour cream, and yogurt. **Fermentation** is the process where some microorganisms, like yeast, convert sugar to ethanol in anaerobic conditions. **Decarboxylation** is the process where a carbon atom, in CO2, is removed from pyruvate so that the NAD+ is regenerated when the acetaldehyde is reduced to ethanol. This process is used to make alcoholic beverages and can produce solutions up to about 15% alcohol by volume. At this point the alcohol kills the yeast and fermentation stops.

Struggling Topic 1: Our muscles can function in anaerobic conditions for a given amount of time. What determines this amount of time?

Struggling Topic 2: What determines whether pyruvate will be fermented or reduced in an anaerobic environment? It seemed like it was determined by the cell that was in the anaerobic environment.

Summary: Glycogen stores excess glucose in limited amounts in skeletal, muscle, and liver cells. If glycogen stores are full and more glucose is present, then glucose is stored as triglycerols, but if glycogen stores are full and no glucose is present in the blood, glycogen will be broken down to replenish blood glucose levels. **Glycogenesis** is the synthesis of glycogen from glucose molecules that happens when the blood glucose level is high. Glycogenesis begins with the same first reaction as glycolysis - ATP is used to add a phosphate to carbon 6 of the glucose molecule. Next the phosphate is transferred to carbon 1. Then UTP (uridine triphosphate) is used to yield UDP-glucose. Then the the UDP-glucose attaches to the end of a glycogen chain to release UDP. UDP can react with ATP to form UTP and ADP so that the reaction may continue. **Glycogenolysis** is a process that breaks down glycogen into glucose. Free glucose (without the phosphate) can only be synthesized in the liver and kidneys with a glucose-6-phosphatase that removes the phosphate so that glucose can dissociate through a cell membrane. **Glucagon** is a hormone produced in the pancreas that accelerates the rate of glycogenolysis to raise blood glucose levels and inhibits the synthesis of glycogen. **Insulin** is a hormone produced in the pancreas to accelerate glycogen synthesis as well as degradation reactions such as glycolysis and inhibition of glucose synthesis.
 * __22.7 Glycogen Metabolism__**

Struggling Topic 1: Diabetes patients often take insulin. Does the inhibition of gluconeogenesis help them maintain a proper blood sugar level?

Struggling Topic 2: Approximately how much glucose is stored as glycogen compared to the amount that is used/needed by the body? It seems like this amount could change based upon the body's history and environmental factors. Never mind. I just found this answer in 22.8 = about 1 day worth of glucose can be stored as glycogen.

Summary: **Gluconeogenesis** is a process that synthesizes glucose from carbon atoms obtained from noncarbohydrate compounds that usually happens in the cytosol of liver cells. Most of gluconeogenesis is caused by the same enzymes that work in glycolysis only this time they work backwards. However, glycolysis reactions 1 (hexokinase), 3 (phosphofructokinase), and 10 (pyruvate kinase) are not reversible, so different enzymes are used to reverse these reactions. Reaction 10 is reversed by converting pyruvate to oxaloacetate and then hydrolyzing ATP and GTP to convert oxaloacetate to phosphoenolpyruvate. Reaction 3 is reversed by cleaving a phosphate from fructose-1,6-biophosphate by hydrolysis with water and releasing the energy that drives the reaction. Reaction 1 is reversed by simply using a different enzyme, glucose-6-phosphatease, that catalyzes the hydrolysis of glucose-6-phosphate with water. Gluconeogenesis requires 4 ATP, 2 GTP, and 2 NADH in energy. Lactate, produced from the anaerobic processing of pyruvate, provides a source of carbon for gluconeogensis in the liver to synthesize more glucose. The **Cori cycle** is the flow of lactate and glucose between the muscle and liver and is very active when someone has just finished vigorous exercise. See table on page 819 for enzymes that regulate glycolysis and gluconeogenesis.
 * __22.8 Gluconeogenesis: Glucose Synthesis__**

Struggling Topic 1: Does the Cori cycle allow a person to continually aerobically process pyruvate into lactate and then convert the lactate back into glucose using glyconeogenesis? It sounds like this would not yield a product of ATP over time since glycolysis only produces 2 ATP and gluconeogenesis requires 4 ATP. Is that why this cannot be continued indefinitely?

Struggling Topic 2: Do the enzymes that regulate glycolysis and gluconeogenesis correspond to the steps that are not reversible in each series of reactions? It seems like they would have to do so to insure that the reactions did not constantly flow in the direction of the equilibrium shifts.

__**Critique**__ A. specifics about how clearly the author communicated individual topics -22.5- the author's diagrams describing the 10 steps of glycolysis were much more helpful than the paragraph's words (p.803-805)

B. specifics about the amount of content and whether it was sufficient to help learn the material (did you need more examples?) -22.5 - the section describing glycolysis was overly detailed for me to understand the whole process the first two times through the material. Perhaps I could have benefited from more examples or a rewording of some of the material. Maybe a chart that described each step, its enzyme, and its reactant and product would have been more beneficial to me than the pictures the book did provide.

C. why did the author place this chapter where she did in the overall text? not later or earlier, transitions with previous chapter, with subsequent chapter(s), did this chapter seem out of place? -22.5 and 22.8 - section 22.5 on glycolysis seemed much more detailed than 22.8 on glyconeogenesis although both used the same (or very similar 10 steps). Although it might have been repetitive, it might have been good to walk through the 10 steps again when discussing glyconeogenesis in section 22.8.