Cabohydrate Metabolism

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Section 1

Question Answer
Digestionis the biochemical process by which food molecules, through hydrolysis, are broken down into simpler chemical units that can be used by cells for their metabolic needs.
Salivary alpha-amylaseis a constituent of saliva, the fluid secreted by the salivary glands.
Pyruvate is the carboxylate ion produced when pyruvic acid (a three-carbon keto acid) loses its acidic hydrogen atom.
Glycolysisis the metabolic pathway by which glucose( C6 molecule) is converted into two molecules of pyruvate( a C3 molecule), chemical energy in the form of ATP is produced, and NADH-reduced coenzymes are produced.
The conversion of glucose to pyruvate is an oxidation process in which no molecular oxygen is utilized.
What is the oxidizing agent in the conversion of glucose to pyruvate?is the NAD+.
Anaerobic pathwaysis the metabolic pathways in which molecular oxygen is not a participant
Aerobic pathwaysis the pathways that requires molecular oxygen
Glycolysis is anaerobic or aerobic pathways?it is an anaerobic pathway.
How many steps of glycolysis? and How many steps of Citric acid cycle?Glycolysis is a ten-steps process, which every step is enzyme-catalyzed.. Citric acid cycle is a eight-steps process.
Glycolysis stepsThere are two stages in the overall process, a six-carbon stage(steps 1-3) and a three-carbon stage (steps 4-10)

Section 2

Question Answer
Six-carbon stage of glycolysis Step1Formation of Glucose 6-phosphate.
Explain glycolysis Step1Glycolysis begins with the phosphorylation of glucose to yield glucose 6-phosphate, a glucose molecule with a phosphate group attached to the hydroxyl oxygen on carbon 6) the carbon atom outside the ring). The phosphate group is form an ATP molecule.
What's enzyme used in glycolysis Step1?hexokinase, an enzyme that requires Mg2+ ion for its activity, catalyzes the reaction.
Is glycolysis Step1 require energy?Yes, this reaction requires energy, which is provided by the breakdown of an ATP molecule.
Can glucose cross cell membrane?yes, it can.
Can glucose 6-phosphate cross cell membrane?no, it can't.
Six-carbon stage of glycolysis Step2Formation of Fructose 6-phosphate
Explain glycolysis Step2Glucose 6-phosphate is isomerized to fructose 6-phosphate by phosphoglucoisomerase. The net result of this change is the carbon 1 of glucose is no longer part of the ring structure.[Glucose, an aldose, forms a six-membered ring, and fructose, a ketose, forms a five-membered ring; both sugar however contain 6 carbon atoms.]
Six-carbon stage of glycolysis Step3Formation of Fructose 1,6-bisphosphate
Explain glycolysis Step3Ths step, like step 1, is a phosphorylation reaction and therefore requires the expenditure of energy. ATP is the source of the phosphat and energy.the fructose molecule now contains two phosphat groups.
What's enzyme used in glycolysis Step3?Phosphofructokinase
Three-carbon stage of glycolysis Step4Formation of Triose Phosphates
Explain glycolysis Step4The reacting C6 species is plit into two C3(triose)species. Because fructose 1,6-bisphosphate, the molecule being split, is unsymmetrical, the two triose produced are not identical. One product is dihydroxyacetone phosphate, and the other is glyceraldehyde 3-phosphate.
What's enzyme used in glycolysis Step4?Aldolase
Three-carbon stage of glycolysis Step5Isomerization of Triose Phosphates.
Explain glycolysis Step5Only one of the two triose produced in Step4, glyceraldehyde 3-phosphate, is a glycolysis intermediate. Dihydroxyacetone phosphate, the other triose, can, however, be readily converted into glyceraldehyde 3-phosphate(an aldose) are isomers, and the isomerization process from ketose to aldose is catalzed by the enzyme triosephosphate isomerase.
Three-carbon stage of glycolysis Step6Formation of 1,3-Bisphosphateglycerate
Explain glycolysis Step6In a reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase, a phosphate group is added to glyceraldehyde 3-phosphate to produce 1,3-bisphosphoglycerate.The hydrogen of the aldehyde group becomes part of NADH. The newly added phosphate group in 1,3-bisphosphoglycerate is a high-energy phosphate group. A high-energy phosphate group is produced when a phosphate group is attached to a carbon atom that is also participating in a C-C or C-O double bond.
Three-carbon stage of glycolysis Step7Formation of 3-phosphoglycerate
Explain glycolysis Step7In this step, the diphosphate species just formed is converted back to a monophosphate species. This is an ATP-producing step in which the C-1 phosphate group of 1,3-bisphosphoglycerate(the high-energy phosphate) is transferred to an ADP molecule to form the ATP. The enzyme involved is Phosphoglycerokinase.Remember that two ATP molecules are produced for each original glucose molecule because both C3 molecules produced from the glucose react. ATP production in this step involves substrate-level phosphorylation.
Substrates level phosphorylationis the biochemical process by which a high-energy phosphate group from an intermediate compound(substrate) is directly transferred to ADP to produce ATP. Substrate-level phosphorylation differs from oxidative phosphorylation in that the latter process involves the transfer of free phosphate ions in solution(Pi) to ADP molecules to form ATP.
Three-carbom stage of glycolysis Step8Formation of 2-Phosphoglycerate.
Explain glycolysis Step8In this isomerization step, the phosphate group of 3-phosphoglycerate is moved from carbon 3 to carbon2. The enzyme phosphoglyceromutase catalyzes the exchange of the phosphate group between the two carbons.
Three-carbon stage of glycolysis Step9Formation of Phosphoenolpyruvate
Explain glycolysis Step9This is an alcohol dehydration reaction that proceeds with the enzyme Enolase, another Mg2+ -requiring enzyme. The result is another compound containing a high-energy phosphate group; the phosphate group is attached to a carbon atom that is involved in a carbon-carbon double bound.
Three-carbon stage of glycolysis Step10Formation of Pyruvate
Explain glycolysis Step10In this step, substrate-level phosphorylation again occurs. Phosphoenolpyruvate transfers its high-energy phosphate group to an ADP molecule to produce ATP and pyruvate. The enzyme involved, Pyruvate kinase, requires both Mg2+ and K+ ions for its activity. Again, because two C3 molecules are reacting, Two ATP molecules are produced.

Section 3

Question Answer
Glycolysisa series of ten reactions that occur in the cytosol, is a process in which one glucose molecule is converted into two molecules of pyruvate. A net gain of two molecules of ATP and Two molecules of NADH results from the metabolizing of glucose to pyruvate
Fates of pyruvateWith respect to energy-yielding metabolism, the pyruvate produced by glycolysis can be converted to acetyl CoA under aerobic conditions or to lactate under anaerobic conditions. Some microorganisms convert pyruvate to ethanol, an anaerobic process.
Glycogenesisis the process whereby excess glucose is converted into glycogen. The glycogen is stored in the liver and in muscle tissue.
Glycogenolysisis the breakdown of glycogen into glucose. this process occurs when muscles need energy and when the liver is restoring a low blood-sugar level to normal.
Gluconeogenesisis the formation of glucose from lactate and certain other substraces. This process takes place in the liver when glycogen supplies are being depleted and when carbohydrate intake is low.
Cori cycleis the cyclic process involving the transport of lactate from muscle tissue to the liver, the resynthesis of glucose by gluconeogenesis, and the return of glucose to muscle tissue.
Pentose phosphate pathwayit metabolizes glucose to produce ribose( a pentose), NADH, and other sugars needed for biosynthesis.
Carbohydrate metabolism and hormoneInsulin decreases blood-glucose levels by promoting the uptake of glucose by cells. Glucagon increases blood-glucose levels by promoting the conversion of glycogen to glucose. Epinephrine stimulates the release of glucose from glycogen in muscle cells.

Section 4

Question Answer
Where dose starch digestion begin in the body, and what is the name of the enzyme involved in this initial digestive process?Mouth, Salivary alpha-amylase
Very little digestion of starch occurs in the stomach. Why?Salivary alpha-amylase is inactivated by the acidic environment of the stomach, and the stomach's own secretions do not contain any carbohydrate-digesting enzyme.
What is the primary site for carbohydrate digestion, and what organ produces the enzymes that are active at this location?Small intestine, Pancreas
Where dose the final step in carbohydrate digestion take place, and in what form are carbohydrates as they enter this final step?On the outer membranes of intestinal mucosal cells, where the enzymes that convert disaccharides to monosaccharides are located.
Where does the digestion of sucrose begin, and what is the reaction that occurs?Outer membranes of intestinal mucosal cells, Sucrose hydrolysis.
where dose the digestion of lactose begin, and what is the reaction that occurs?Outer membrane of intestinal mucosal cells, lactose hydrolysis.
Identify the three major monosaccharides produced by digestion of carbohydrates.Glucose, Galactose, Fructose
The various stages of carbohydrate digestion all involve the same general type of reaction. What is this reaction type?Hydrolysis of disaccharides
What is the starting material for glycolysis?Glucose
What is the end product from glycolysis?Pyruvate
What coenzyme functions as the oxidizing agent in glycolysis?NAD+
What is meant by the statement that glycolysis is an anaerobic pathway?The pathways in which molecular oxygen is not a participant
What is the first step of glycolysis pathway, and why is it important in retaining glucose inside the cell?Formation of glucose 6-phosphate, a species that cannot cross cell membrane
Step3 of glycolysis is the commitment step. ExplainStep3 of glycolysis commits the original glucose molecule to the glycolysis pathway. Glucose 6-phosphat(step1) and fructose 6-phosphat(step2) can enter other metabolic pathways, but fructose 1,6-biphosphate can enter only glycolysis
What twoC3 fragments are formed by the spiltting of a fructose 1,6-biphosphate molecule?Dihydroxyacetone phosphate, Glyceraldehyde 3-phosphate
In one step of the glycolysis pathway, a C6 chain is broken into C3 fragments, only one of which can be further degrade. What happens to the other C3 fragment?Be readily converted into glyceraldehyde 3-phosphate
How many pyruvate molecules are produced per glucose molecule during glycolysis?Two
How many molecules of ATP and NADH are produced per glucose molecule during glycolysis?2 ATP molecules and 2 NADH molecules
How many Steps in the glycolysis pathway produce ATP?Two
How many steps in the glycolysis pathway consume ATP?
Of the 10 steps of glycolysis, which one involve phosphorylation?Step 1 , 3 and 6
Of the 10 Steps of glycolysis, which one involve oxidation?
Where in a cell does glycolysis occur?cytosol