Term
| Major metabolic roles of glycolysis |
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Definition
| Entry point of carbohydrates into metabolism; Generate energy (ATP) from carbohydrates; Supply precursors for amino acid, large lipids, and purine/pyrimidine biosynthesis; In times of energy excess, generate precursors for fat and glycogen biosynthesis (the energy storage molecules) |
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Term
| General difference in metabolism in liver and muscle |
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Definition
| Muscle uses energy from glycolysis to do work and generates energy in the absence of oxygen. The liver uses carbons and energy from carbohydrates to make fat, serum proteins, and other biosynthetic precursors. |
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Term
| What is required for anaerobic glycolysis? |
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Definition
| Regeneration of NAD+ by lactate dehydrogenase, which regenerates NAD+ and causes the buildup of lactic acid |
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Term
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Definition
| Converts Glucose and ATP to G6P and ADP. It is irreversible, activates glucose and traps it inside the cell |
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Term
| Why is glucose converted to G6P? |
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Definition
| This traps the glucose in the cell; glucose can pass through the plasma membrane |
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Term
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Definition
| Converts F6P and ATP to F1,6BP and ADP. This is a major regulated step of glycolysis, commits sugars to the glycolytic pathway |
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Term
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Definition
Bis refers to the same functional group on different atoms within the same molecule (F 1,6 BP).
Di refers to two of the same functional groups attached to the same atom of a molecule, or linked together and attached to just one atom of the molecule (ie ADP, has the two phosphates attached to each other, which are then linked to the 5’-carbon of ribose). |
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Term
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Definition
| The pathway in which 1 mole of glucose is oxidized and cleaved to form 2 moles of pyruvate. It can be carried out in every cell type and generates 2 moles of ATP and 2 moles of NADH per mole of glucose. |
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Term
| Basic mechanism of glycolysis |
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Definition
| Glucose is phosphorylated to glucose-6-phosphate (G6P) by hexokinase (HK). In subsequent steps, one G6P molecule is oxidized to two pyruvate molecules with the generation of two molecules of NADH. A net generation of two ATP molecules occurs due to substrate level phosphorylation of ADP from pathway intermediates. |
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Term
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Definition
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Term
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Definition
| Used for generation of ATP in absence of oxygen or mitochondria. Lactate dehydrogenase oxidizes the NADH generated from glycolysis by reducing pyruvate to lactate. The energy yield is 2 moles of ATP per mole of glucose, much lower than the yield from aerobic oxidation. The lactate is released into the blood as lactic acid. |
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Term
| general enzyme regulation in glycolysis |
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Definition
| Glycolysis is regulated to make sure that ATP homeostasis is maintained without using excess glucose. HK, the first enzyme of glycolysis, is inhibited by G6P, so that glucose is not taken up and phosphorylated by a cell unless G6P enters a metabolic pathway. The entry of G6P into glycolysis occurs at PFK-1, the rate-limiting enzyme of the pathway. It is allosterically inhibited by ATP and allosterically activated by AMP. |
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Term
| secondary functions of glycolysis |
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Definition
| It provides biosynthetic precursors. For example, in liver and adipose tissue the generated pyruvate is a precursor for fatty acid biosynthesis. Precursors for amino acids and ribose-5-phosphate, the precursor of nucleotides, are also made. |
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Term
| preparative phase of glycolysis |
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Definition
| Glucose is phosphorylated twice by ATP and cleaved into two triose phosphates. |
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Term
| ATP-generating phase of glycolysis |
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Definition
| G3P is oxidized by NAD+ and phosphorylated using inorganic phosphate. The phosphate is then transferred to ADP to form ATP. The remaining phosphate is also rearranged to form another phosphate bond that is transferred to ADP. Because there were 2 moles of triose phosphate formed, the yield from the ATP-generating phase is 4 ATP and 2 NADH. |
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Term
| Why is G6P a branchpoint in carbohydrate metabolism? |
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Definition
| B/c it is a precursor for almost every pathway involving glucose, including glycolysis, pentose phosphate pathway, and glycogen synthesis. It can also be generated from other pathways, such as glycogenolysis and gluconeogenesis. |
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Term
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Definition
| PFK-1 is the first committed step of glycolysis, as its reaction is kinetically and thermodynamically irreversible. It phosphorylates F6P to F1,6BP and requires ATP. |
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Term
| important cations in glycolysis enzyme reactions |
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Definition
| Hexokinases, kinases, and other enzymes that hydrolyze ATP require Mg2+. Kinases also require K+. |
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Term
| Net reaction in glycolysis |
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Definition
| Glucose + 2 NAD+ + 2 P + 2 ADP ---- > 2 Pyruvate + 2 NADH + 4 H+ + 2 ATP + 2 H2O |
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Term
| Net reaction in anaerobic glycolysis |
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Definition
| Glucose + 2 ADP + 2 P ---- > 2 Lactate + 2 ATP + 2 H2O + 2 H+ |
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Term
| How does pyruvate enter TCA cycle |
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Definition
| Pyruvate enters the mitochondria. However, cytosolic NADH must be oxidized via a shuttle system, which can be either the G3P shuttle or the malate-aspartate shuttle. |
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Term
| ATP generation post-glycolysis in TCA cycle |
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Definition
| Oxidation of pyruvate generates 12.5 moles of ATP per mole of pyruvate. Using G3P shuttle, 1.5 moles of ATP are produced per mole of NADH; using the malate-aspartate shuttle 2.5 moles of ATP are produce per mole of NADH. Thus, two NADH molecules produced during glycolysis can lead to 3 to 5 molecules of being produced. |
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Term
| Relationship between ATP, ADP and AMP concentrations |
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Definition
| AMP levels within the cytosol provide a better indicator of the rate of ATP utilization than the ATP concentration itself. [AMP] is determined by the equilibrium position of the adenylate kinase reaction, in which 2 ADP are converted to 1 AMP and 1 ATP. Hydrolysis of ATP to ADP in energy-requiring reactions increases both ADP and AMP levels in the cytosol. However, ATP is present in much higher quantities than AMP or ADP, so that a small decrease of ATP concentration in the cytosol causes a much larger percentage increase in the small AMP pool. |
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Term
| How is hexokinase regulated |
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Definition
| HK’s exist as tissue-specific isozymes. In most tissues, HK is a low-Km enzyme with a high affinity for glucose. It is inhibited by G6P. In the liver, glucokinase is a high-Km enzyme that is not readily inhibited by G6P. This allows glycolysis to continue in liver even when energy levels are high so that anabolic pathways can occur. |
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Term
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Definition
| PFK-1 is an allosteric enzyme with 6 binding sites: two are for substrates (Mg-ATP and F6P) and four are allosteric regulatory sites. These regulatory sites occupy a different domain than the catalytic site. When an allosteric effector binds, it changes the conformation of the active site. The allosteric sites for PFK-1 include an inhibitory site for MgATP, an inhibitory site for citrate and other anions, an activation site for AMP, and an activation site for F2,6BP. |
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Term
| How does AMP regulate PFK-1 |
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Definition
| Binding of AMP increases affinity of the enzyme for F6P, shifting the kinetic curve to the left. Increases in Amp can greatly increase the rate of the enzyme, particularly when [F6P] is low. |
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Term
| How does F2,6BP regulate PFK-1 |
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Definition
| F2,6BP is an allosteric activator of PFK-1 that opposes the ATP inhibition. F2,6BP is not an intermediate of glycolysis but is synthesized from F1,6BP by PFK-2. |
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Term
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Definition
| It is a bifunctional enzyme with a kinase domain and a phosphatase domain. At the kinase domain, F6P is phosphorylated to F2,6BP; at the phosphatase domain the opposite reaction occurs. |
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Term
| How is pyruvate kinase regulated |
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Definition
| PK exists as tissue-specific isoenzymes. The liver isoenzyme can be inhibited through phosphorylation by c-AMP-dependent protein kinase and allosteric regulation. PK is activated by F1,6BP, which ties the rate of PK to that of PFK-1, and inhibited by ATP, which signifies high energy levels. |
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Term
| Active amino group required by aldolase is supplied by what aa? |
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Definition
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Term
| G3P dehydrogenase reaction |
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Definition
| G3P + NAD+ --> NADH + 1,3BPG. Carbon 1 of G3P oxidized from aldehyde to acid. NAD+ is reduced (gains a proton and two electrons). High energy phospho-anhydride bond is formed. The enzyme requires an active sulfhydryl group. |
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Term
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Definition
| Dinucleotide of adenine and a niacin derivative. It is found in degradative pathways. |
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Term
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Definition
| Similar to NAD+ but is used in biosynthetic pathways |
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Term
| Phosphoglycerate kinase (PG) reaction |
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Definition
1,3BPG + ADP --> ATP + 3PG.
1. Phosphoryl group transfer, and the high energy of the phospho-anhydride bond is conserved as a high energy bond of ATP
2. Reversible reaction; substrate-level phosphorylation
3. Since 1 glucose gives rise to 2 molecules of 1,3 BPG, this step
generates 2 ATP molecules per glucose, but the overall yield of glycolysis is zero at this point (due to the two
activation steps). |
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Term
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Definition
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Term
| Pyruvate Kinase (PK) reaction |
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Definition
| PEP + ATP --> ADP + Pyruvate |
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Term
| Why is PEP a high energy phosphate donor |
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Definition
| B/c PEP cannot isomerize to form phosphopyruvate due to a lack of hydroxyl on C2 |
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Term
| What are the three irreversible steps of glycolysis |
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Definition
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Term
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Definition
| ATP (high energy available; it is also a substrate for the reaction. Allosteric inhibitor) and Citrate (from the Krebs tricarboxylic acid cycle, and signifies adequate carbon skeletons for biosynthesis) |
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Term
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Definition
F2,6BP (links the regulation of glycolysis to hormonal signals [in the liver only]. Major PFK-1 activator) and
AMP (indicating low energy levels) |
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Term
| Why is AMP indicator of low energy levels |
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Definition
B/c the ratio of [AMP]/[ATP] increases more rapidly than the [ADP]/[ATP] ratio.
The [AMP]/[ATP] ratio is proportional to the square of the [ADP]/[ATP] ratio. |
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Term
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Definition
| The rate at which product is formed |
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Term
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Definition
| Concentration of substrate required to reach half Vmax |
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Term
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Definition
| Maximal velocity that can be achieved at an infinite concentration of substrate |
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Term
| Difference btwn hexokinase and glucokinase |
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Definition
| Hexokinase has a high glucose affinity and works at low glucose levels. Glucokinase has low glucose affinity and only works at high glucose levels. Glucokinase is in the liver because when glucose blood levels are low, the enzyme should be secreting glucose, not having it undergo glycolysis. |
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Term
| What hormone is released when blood glucose levels are low |
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Definition
| Glucagon (mnemonic: Glucose R Gone) |
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Term
| What hormone is released when blood glucose levels are high |
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Definition
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Term
| Hormonal Regulation of PFK-2 |
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Definition
1. Activators of the cAMP system tend to signal a need for energy (hormones
epinephrine and glucagon)
2. Liver stops using glucose so glucose can be exported
3. To stop the liver from using glucose, glycolysis is slowed down by reducing F2,6BP levels, which reduces PFK-1 activity (liver specific in response to glucagon)
4. Muscle will still use glucose, as skeletal muscle PFK-2 is not phosphorylated (different isozyme – but heart is an exception) |
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Term
| Mechanism of hormone regulation of PFK-2 |
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Definition
| Hormone binding to receptor causes adenylate cyclase to convert ATP to cAMp. cAMp i/a's with cAMP-dependent protein kinase to phosphorylate PFK-2, activating its phosphatase activity. This lowers F2,6BP levels and PFK-1 activity |
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Term
| Difference in reaction velocity vs [S] curve for allosteric and Michaelis-Menten enzymes |
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Definition
| allosteric enzymes have sigmoid curve, MM enzymes have hyperbolic curve |
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Term
| Difference in reaction velocity vs [S] curve for allosteric and Michaelis-Menten enzymes |
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Definition
| allosteric enzymes have sigmoid curve, MM enzymes have hyperbolic curve |
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Term
| In Michaelis-Menten, what are the rate constants k1, k-1, and k2 |
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Definition
| k1 is E + S to ES, k-1 is ES to E + S, k2 is ES to E + P |
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Term
| Regulation of PFK-2 in the liver |
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Definition
| Job of the liver is to export glucose and begin gluconeogenesis when blood glucose levels drop; when blood glucose levels drop glucagon is released, the cAMP cascade is activated, PFK-2 is phosphorylated, PFK-1 less active, glycolysis is slowed, and glucose export and gluconeogenesis can occur |
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Term
| Regulation of PFK-2 in skeletal muscle |
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Definition
| Job of skeletal muscle is to do work, using glucose or fat for energy; when blood glucose levels drop, muscle takes glucose from blood (special conditions) or uses its own glucose. PFK-2 in muscle not phosphorylated, so activity not altered under these conditions |
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Term
| Regulation of heart PFK-2 |
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Definition
| PFK-2 will be phosphorylated by insulin-stimulated protein kinase (protein kinase B), or an AMP-activated protein kinase. When phosphorylated its kinase acitivty is active (opposite of liver PFK-2). This allows for glycolysis to be activated under low energy conditions (high AMP) and when glucose levels are high (insulin release) |
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Term
| Regulation of HK (in muscle) |
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Definition
As PFK-1 is inhibited (by either
ATP, or lack of F 2,6 BP), the
levels of F6P increase. This
increases the levels of G6P, which
will feedback and inhibit the
activity of HK (not liver). |
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Term
| Regulation of glucokinase (liver) |
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Definition
| Glucokinase is not inhibited by G6P; under conditions of high blood glucose levels GK will be active, and can force liver glycolysis to proceed in order to store energy as fat. |
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Term
| How many forms of pyruvate kinase are there? |
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Definition
| 3. L (liver), M (muscle), A (other) |
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Term
| Regulation of L form of Pyruvate kinase |
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Definition
Activated by compounds which indicate a high level of glycolytic intermediates (PEP,F1,6BP)
Inhibited by compounds indicating high energy or adequate carbon skeleton precursors (ATP, alanine)
Also regulated by COVALENT MODIFICATION by the cAMP dependant protein kinase (phosphorylation inhibits activity) |
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Term
| How regulation of M form of pyruvate kinase differs from L form |
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Definition
| M form is not subject to covalent modification, so only allosteric controls apply (ie muscle glycolysis is not inhibited by the cAMP dependent protein kinase) |
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Term
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Definition
| metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is converted back to lactate. |
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Term
| Major equations of Michaelis-Menton enzyme kinetics |
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Definition
Et = [E] + [ES]
V = k3 [ES] = d [P] / dt
(Vmax = k3 Et)
d [ES] / dt = k1 [E] [S] - k2 [ES] - k3 [ES] |
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Term
| major assumptions of michaelis-menton enzyme kinetics |
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Definition
Reaction is not reversible under initial
conditions, and the reaction rapidly reaches a steady state,
such that d [ES] / dt = 0. |
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Term
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Definition
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Term
| Michaelis-Menton equation |
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Definition
| v = Vmax / (1 + (Km/[S])) |
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Term
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Definition
| Converts Michaelis-Menton eqn into a straight line by taking its reciprocal and setting it up in the form of y = mx + b |
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Term
| In Lineweaver-Burk, what are y, m, x,and b |
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Definition
| y is 1/V; m is (Km/Vmax); x is 1/[S]; b is 1/Vmax |
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Term
| On Lineweaver-Burk Plot, what are the X and Y intercepts |
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Definition
| LB plots 1/[S] vs 1/V. X intercept is (-1/Km); Y intercept is (1/Vmax) |
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Term
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Definition
| compete with substrate for binding to the active site. Increase Km but not Vmax. |
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Term
| non-competitive inhibitors |
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Definition
| bind to a site distinct from the substrate binding site. They induce a conformational change, which reduces enzyme activity. Km is not altered, but Vmax is reduced. |
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Term
| Effect of competitive inhibitor on Lineweaver-Burk plot |
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Definition
| presence of inhibitor shifts to the right, indicating lower affinity |
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Term
| Effect of non-competitive inhibitor on Lineweaver-Burk plot |
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Definition
| in presence of inhibitor, shifts upwards, indicating a lower Vmax |
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Term
| Effect of inhibitors on slope of line in Lineweaver-Burk plot |
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Definition
| Slope altered by (1 + [I]/Ki), where Ki is the dissocation constant of the inhibitor |
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