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56 Cards in this Set
- Front
- Back
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glucose to glycogen is called what?
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glycogenesis.
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Glycogen phosphorylase, which is involved in the breakdown of glycogen, catalyzes what?
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the attack on a glycosidic bond by inorganic bond.
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Glycogen phosphylase catalyzes the reaction in which an _________ glycosidic linkage between two glucose residues at the ____________ end of glycogen undergoes attack by _________ _________, removing the terminal glucose residue.
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alpha 1--> 4
nonreducing inorganic phosphate |
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why can't sk. mm not contribute glucose to the blood?
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because it lacks the enzmy glucose 6-phosphatase
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what does glucose 6-phosphatase do?
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it convertes glucose 6-phosphate to glucose. (and this is needed for glucose to go into the blood)
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where is glucose 6-phosphatase present?
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only in the liver and kidneys.
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so the glucose 6-phosphate formed from glycogen in sk. mm enters ________ and serves as an _____ source to support muscle contraction
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glycolysis
energy |
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The liver enzyme glucose 6-phosphatase is normally compartmentalized in the lumen of the ER because...
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glucose 6-phosphatae would remove an intermediate of glycolysis if it were localized in the cytosol.
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so glucose 6-phosphataes is compartmentalized in the ER to prevent it from doing what?
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aborting glycolysis by converting all of the glucose 6-phosphate in the cytosol to glucose.
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By compartmentalizing the enzyme glucose 6-phosphatase, hepatic cells can separate two processes that compete for what 2 processes?
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glycolysis and generation of glucose for release into the blood.
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How is a new glycogen molecule initiated?
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Glycogenin catalyzes the addition of several initial residues of glucose to itself.
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Glycogenin initiates a glycogen molecule by the autocatalytic transfer of a glucose residue from ___________ to the hydroxyl group if its Tyr 194 residue. Then, glycogenin's chain-extending activity adds _____ more glucose residues to this initial glucose residue. This short chain of glucose residues serves as a ________ for glycogen synthase, which catalyzes the remainder of the glycogen main chain.
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UD-glucose
7 primer |
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Which of the following is TRUE about the structure of glycogen?
A- Glycogen chains on the outer tier do NOT have branches B- Glcogen chains can have only one branch C- Each chain consists of hundreds of glucose residues D- Glycogen chains terminate with ( alpha 1--> 6) branches |
A
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Glycogen can have many tiers. The outer tier is _________
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unbranched.
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how many residues does each chain have on a glycogen molecule?
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12-14
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how many branches do inner chains have?
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they have 2 (alpha 1--> 6) branches each. (remember--chains on the outer tier have no branches!)
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what will the AMP-dependent protein kinase (ADPK) suppress?
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protein synthesis.
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The AMP-dependent protein kinase stimulates _______-_______processes such as glucose transport, glycolysis, and fatty acid oxidation and suppresses _________-______ processes such as the synthesis of fatty acids, cholesterol, and protein.
The ADPK meditates regulation by ______, which is a sensitive indicator if the cell's energetic state. When ATP levels become depleted, the rise in [AMP] causes the ADPK to do what? |
energy-generating
energy-requiring to phosphorylate key proteins, thereby regulating their activities. |
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which of the following is TRUE about isozymes?
A-- they have the same amino acid sequence B- They have the same kinetic properties C- They catalyze the same reaction D- they cannot be expressed in the same cell at the same time |
C
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so isozymes are different ____ of an enzyme that catalyze the same _____. The distribution of different isozymes often varies with tissue type, developmental stage, and different locations and metabolic roles in the same cell.
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forms
reaction |
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do isozymes have same kinetic and regulatory properties and same amino acid sequences?
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no.
They have different kinetic and regulatory properties because they have different, albeit usually similar, amino acid sequences. |
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can isozymes be expressed in the same cell at the same time?
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yes. Different isozymes may be needed in different locations and to carry out different metabolic roles in the same cell.
An example of this is the different isocitrate dehydrogenaes isozymes of the cytosol and the mitochondrion. |
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what is the maximum number of isozymes that can exist for a heterodimeric protein that consists of combiation of four different polypeptides?
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6
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a heterodimeric protein consists of ___ different subunits. The number of different combinations of heterodimers is...
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2
AB, AC, AD, BC, BD, and CD |
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In hepatocytes, the enzyme hexokinase 4 (glucokinase), which catalyzes the conversion of glucose to glucose 6-phosphate, is regulated by a regulatory protein that
A- inhibits hexokinase 4 when blood glucose levels are high B- Irrevesibly inactivates hexokinase 4 C- phosphorylates hexokinase 4 D- sequesters hexokinase 4 inside the nucleus |
D
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the regulatory protein binds ____________ and transports it into the ______, where it is segregated from the other enzymes of glycolysis in the cytosol. This regulatory protein is in turn regulated by______, which binds an allosteric site and lowers the affinity of the regulatory protein for __________. Therefore, when glucose levels are high, the inhibition of the regulatory protein is relieved and hexokinase 4 enters the cytosol and begins to do what?
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hexokinase 4
nucleus glucose hexokinase 4 begins to phosphorylate glucose. |
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Which of the following is TRUE about the reactions described...
A- Only phosphofructokinase-1 catalyzes an exergonic reaction B- Phosphofructikinase-1 and fructose 1,6-bisphosphatase are inhibited by high levels of AMP. C-the fructose 1,6-bisphosphatase reaction favors gluconeogenesis D- The function of these two reactions is to act as a futile cycle |
C
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The fructose 1,6-bisphosphatase reaction favors what? This reaction is one of the reactions in the gluconeogenesis pathway that detours around an ________ glycolysis step
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gluconeogenesis.
irreversible |
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what is a futile cycle?
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it is one in which there is simultaneous operation of two opposing pathways in the same cell. When this happens, no work is accomplished and the energy of both reactions is dissipated as heat.
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how do we avoid a futile cycle?
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the two pathways are coordinately regualted to favor one direction at any given time.
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The glycolytic enzyme phosphofructokinase-1 reaction is stimulated by a high level of _____, which is an indicator of a low cellular energetic state.
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AMP
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Which of the following inhibits glycogen phosphorylase?
A- High levels of blood glucose B- High levels of Ca2+ C- epinephrine D- High levels of AMP |
A
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High levels of glucose _______ glycogen phosphorylase. Glucose binding to the allosteric site of the active, phosphorylated form induces a conformation change that exposes the phosphorylated _____ residues to the action of phosphorylase a phosphatase, which converts phosphorylase a to the less active phosphorlyase b form. This type of regulation ensures that glycogen is broken down into glucose 1-phosphate for glycolysis ONLY when there is a cellular demand for ______
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inhibit
ser |
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what 3 things activate glycogen phosporylase?
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high levels of Ca2+
epinephrine high levels of AMP |
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which of the following is TRUE about the flux control coefficient for each enzyme in a pathway?
A- it is intrinsic to each enzyme in a pathway B- It is a relative measure of reach enzyme's impact on the rate of metabolite flow in a pathway C- The sum of the flux control coefficients for any complete pathway is 0 D- It is an absolute measure of an enzyme's enhancement of the rate of metabolite flow in a pathway |
B
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The flux control coefficient expresses the relative contribution of each enzyme to setting the ______ at which metabolites flow through the pathway--that is, flux. The sum of the flux control coefficients for any complete pathay is _____. The flux control coefficient can have any value from ____ (for an enzyme with NO impact on the flux) to ____(for an enzyme that wholly determines the flux)
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rate
1 0 1 |
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is the flux control coefficient characteristic to each enzyme in a pathway?
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no--it is characteristic of the WHOLE system. --it is a function of the whole system of enzymes, and its value depends on the concentrations of substrates and effectors.
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What effect does glucagon have on carbohydrate metabolism?
A-It stimulates glycolysis B- It inhibits the breakdown of glycogen C- It decreases blood levels of glucose D- It stimulates gluconeogenesis |
D
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Glucagon, a hormone released by the pancreas to signal low blood sugar, stimulates the production of ______ by ________ in the liver, which then releases the glucose into the blood
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glucose
gluconeogenesis |
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does glucagon slow or quicken the comsumption of glucose by glycolysis in the liver?
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slows
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When blood glucose levels are low, glucagon activates _________ __________, which converts glycogen to glucose 1-phosphate. Glucagon accomplishes this by activating phosphorylase b kinase, which convertes inactive phosphorylae b to its active a form, initiating the release if glucose into the blood.
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glycogen phosphorylase
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A metabolically active cell is in a steady state only if
A- The rate of metabolite flow in unchanged B- Intermediates are formed and comsumed at equal rates C- There is no flux D- It is at equilibrium with its surroundings |
B
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which of the following is true about fructose 2,6-bisphosphate in the liver?
A- It inhibits glycolysis B- It is inhibited by insulin C- It mediates the hormonal regulation of glucagon D- It stimulats fructose 1,6-bisphasphatase-1 |
C
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Glucagon reciprocally regulates glycolysis and gluconeogenesis by lowering cellular levels of _____________________. Fructose 2,6-bisphosphate allosterically _____________ PFK-1 and ________ FBPase-1. Therefore, by lowering the level of fructose 2,6-bisphosphate, glucagon ________ glycolysis and _______ gluconeogenesis. Fructose 2,6-bisphsphate also mediates the effects of insulin on glycoylsis and gluconeogenesis. By raising the level of fructose 2,6-bisphosphate, insulin ______ glycolysis and ________ gluconeogenesis.
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fructose 2,6-bisphosphate
stimulates inhibits inhibits stimulates stimulates inhibits |
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in myocytes (muscle cell), insulin inhibits
A- glycogen synthase kinase 3 (GSK3) B- GLUT 4 C- phosphorlyae a phosphatase (PP1) D- Glycogen synthase |
A
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Insulin activates ______ ______ __ (_____), which in turn phosphorylates and inactivates _____. This leads to the dephosphorylation and activation of _____ _________, which converts UDP-glucose into _________. By activation glycogen synthase through the inhibition of GSK3, insulin increases the storage of ________
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protein kinase B (PKB)
GSK3 glycogen synthase glycogen glucose |
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Insulin activates the glucose transporter ______ by triggering their movement from intracellular vesicles to the _________ ________ where it can uptake glucose from the blood into the myoctes
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GLUT 4
plasma membrane |
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insulin activates _____, which dephosphorylates glycogen phosphorylae (phosphorylase a), making it _____ active. By activating PP1, insulin stops the breakdown of __________
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PP1
less glycogen |
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Insulin activates _______ ______, which synthesizes glycogen from _____________.
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glycogen synthase
UDP-glucose |
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When the energetic needs of hepatocytes are being met, which of the following occurs?
A-Acetyl-CoA inhibits pyruvate carboxylase B- ATP inhibits phosphofructokinase-1 (PFK-1_ C- ATP inhibits fructose 2,6-bisphosphatase-1 D- Acetyl-COA stimulats pyruvate kinase |
B
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When the cell's energetic needs are being met, _____ accumulates. The increased concentration of ATP inhibits _______, slowing glycolysis and favoring gluconeogenesis.
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ATP
PFK-1 |
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when the cell's energetic needs are being met, acetyl-COA ________. The increased concentration of acetyl-CoA stimulates gluconeogenesis by activatin ________ __________, allowing ecess pyruvate to be converted to glucose.
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accumulates
pyruvate carboxylase |
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AMP _________ FBPase-1.
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inhibits
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To control the flux through a pathway, it is best to regulate
A- reversible reactions B- The fastest reactions C- Substrate-limited reactions D- Enzyme-limited reactions |
D
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Enzyme-limited reactions are far from ____________ due to low enzyme activity and are thus the rate-limiting steps in a pathway. These recations, which are often very exergonic are _______, are usually the primary target of regulation. Examples include the irreversible reactions catalyzed by PFK-1 and glycogen phosphorylase
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equilbirum
irreversible |
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Reversible reactions are _________ limiting. They are essentially in equilbirum because the substrate is consumed as fast as it is supplied. Enzyme-limited reactions are usually the primary target of regulation because they are the rate-limiting steps in a pathway
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substrate
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