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Mini biochem chapter 12 > Biochemistry Chapter 9 > Flashcards

Biochemistry Chapter 9 Flashcards

1
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front

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What are GLUT 2 & GLUT 4 ?

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  • Glut 2 is a solute carrier that’s a low-affinity transporter in hepatoycytes and pancreatic cells. After a meal, blood traveling through the hepatic portal vein from the intestine is rich in glucose. *
  • Glut 4 is in adipose tissue and muscle and responds to the glucose concentration in peripheral blood. The rate of glucose transport in these two tissues is increased by insulin, which stimulates the movement of additional GLUT 4 transporters to the membrane by a mechanism involving Exocytosis.
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What are GLUT 2 & GLUT 4 ?

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  • Glut 2 is a solute carrier that’s a low-affinity transporter in hepatoycytes and pancreatic cells. After a meal, blood traveling through the hepatic portal vein from the intestine is rich in glucose. *
    • Glut 4 is in adipose tissue and muscle and responds to the glucose concentration in peripheral blood. The rate of glucose transport in these two tissues is increased by insulin, which stimulates the movement of additional GLUT 4 transporters to the membrane by a mechanism involving Exocytosis.
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What is Glycolysis ?

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A cytoplasmic pathway that converts glucose into two pryruvates; releasing a modest amount of energy captured in two substrate-level phosphorylation and one oxidation reaction.

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Hexokinase ? Glucokinase ?

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Widely distributed in tissues and is inhibited by its product, glucose-6-phosphate * Found only in liver cells and pancreatic b islet cells; in the liver glucokinase is inhibited by insulin. Also because the GLUT transporters are specific for glucose( not phosphorylated glucose), the glucose gets trapped in the cell and can’t leak out.

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What is Phosphofructokinase-1 (PFK-1) ? (PFK-2) ?

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Rate-limiting enzyme and main control point in glycolysis. In this reaction, fructose 6-phosphate is phosphorylated to fructose 1,6-biphosphate using ATP.

  • Which converts a tiny amount of fructose 6-phosphate to fructose 2,6 biphosphate (F2,6-BP) and this in return activated PFK-1
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7
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Glyceraldehyde-3 Phosphate Dehydrogenase ?

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Catalyzes an oxidation and addition of inorganic phosphate (Pi) to its substrate Glyceraldehyde 3-phosphate. This results in the production of a high energy intermediate 1,3-biphosphoglycerate and the reduction of NAD+ to NADH

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3-phosphoglycerate Kinase ? Substrate-level phosphorylation ?

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Transfers the high energy phosphate from 1,3 biphosphoglycerate in ADP; forming ATP and 3-phosphoglycerate This type of reaction, in which ADP is directly phosphorylated to ATP using a high energy intermediate

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What is Pyruvate Kinase ? Feed-forward activation ?

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  • Activated by fructose 1,6 biphosphate from the PFK-1 reaction.
  • When the product of an earlier reaction of glycolysis ( fructose 1,6 -biphosphate ) stimulates or prepares, a later reaction in glycolysis (by activating private Kinase)
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10
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What is fermentation ?

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The absence of oxygen would occur.

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What is fermentation ? lactate dehydrogenase ?

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  • A metabolic process that converts sugar to acids, gases , and alcohol especially in the absence of oxygen.
  • The key fermentation enzyme in mammalian cells which oxidizes NADH to NAD+, replenishing the oxidized coenzyme for Glyceraldehyde-3-phosphate dehydrogenase. Without the mitochondria and oxygen, glycolysis would stop when all the available NAD+ had been reduced to NADH.
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12
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What are 1,3-Biphosphoglycerate(1,3-BG) & phosphoenolpyruvate (PEP) ?

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They are high energy intermediates used to generate ATP by substrate-level phosphorylation. This is the only ATP gained in anaerobic respiration.

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What is Dihydroxyacetone phosphate (DHAP) ?

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Intermediate in where its used in hepatic and adipose tissue for triacylglycerol synthesis. Its formed from fructose 1,6-biphosphate

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What are the irreversible enzymes ?

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  • Glucokinase or Hexokinase
  • PFK-1
  • Pyruvate Kinase
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biphosphoglycerate mutate ? 2,3-biphosphoglycerate (2,3-BPG)?

A
  • Red blood cells contain these
  • And they are produced by the red blood cells from 1,3-BPG in glycolysis.
  • Mutates are enzymes that move a functional group from one place in a molecule to another*
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What is the function and regulation of Hexokinase ? Is it reversible ?

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  • It phosphorylates glucose to form glucose-6-phosphate, “trapping “ glucose in the cell. Its regulation is to inhibit glucose-6-phosphate.
  • It is irreversible
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18
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What is the function of Glyceraldehyde-3-phosphate dehydrogenase ? Is it reversible ?

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  • Its function is to generate NADH while phosphorylating Glyceraldehyde-3- phosphate to 1,3-biphosphoglycerate.
  • It is reversible so yes
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19
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What is the function of 3-phosphoglycerate Kinase ? Is it reversible ?

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  • Its function is to perform a substrate-level phosphorylation, transferring a phosphate from 1,3-biphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate.
  • It is reversible so yes
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20
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How does insulin promote glucose entry into cells ?

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GLUT 4 is saturated when glucose levels are only slightly above 5 mM so glucose entry can only be increased by increasing the number of transporters. Insulin promotes the fusion vesicles containing preformed GLUT 4 with the cell membrane.

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Why does pyruvate undergo fermentation for glycolysis to continue ? What are pyruvate ?

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  • Fermentation must occur to regenerate NAD+, which is limited supply in cells. Fermentation generates no ATP or energy carriers; it merely regenerates the coenzymes needed in glycolysis. *
  • End product of glycolysis
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Why is it necessary that fetal hemoglobin does not bind 2,3-BPG ?

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The binding of 2,3-BPG decreases hemoglobins affinity for oxygen. Fetal Hemoglobin must be able to “steal” oxygen from maternal hemoglobin at the paternal interface; therefore, it would be disadvantageous to lower its affinity for oygen.

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Which enzyme is responsible for trapping a galactose in the cell? What enzyme in galactose metabolism results in a product that can feed directly into glycolysis, linking the two pathways ?

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Galactose is phosphorylated by galactokinase, trapping it in the cell. Galactose 1-phosphate uridyltransferase produces glucose 1-phosphate, a glycolytic intermediate, thus linking the pathways

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Which enzyme is responsible for trapping fructose in the cell ? What enzyme in fructose metabolism results in a product that can feed directly into glycolysis, linking the two pathways ?

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  • Fructose is phosphorylated by fructokinase, trapping it in the cell(with a small contribution from Hexokinase).
  • Aldolase B produces dihydroyacetone phosphate (DHAP) and Glyceraldehyde(which can be phosphorylates to form Glyceraldehyde 3-phosphate), which are glycolysis intermediates, thus linking the pathways.
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What is pyruvate dehydrogenase complex (PDH) ?

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Complex of enzymes that is irreversible and can’t be used to convert acetyl-CoA to pyruvate or to glucose. In the liver is activated by the insulin whereas in the nervous system, the enzyme is not responsive to hormones.

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What are the reactants of the pyruvate dehydrogenase complex? What are the products ?

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  1. Reactants : Pyruvate, NAD+, and CoA are the reactants
  2. Products: Acetyl-CoA, NADH, and CO2
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How does acetyl-CoA affect PDH complex activity ?

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It inhibits the PDH complex. As a product of the enzyme complex, a buildup of acetyl-CoA from either the citric acid or fatty acid oxidation signals that the cell is energetically satisfied and that the production of acetyl-CoA should be slow or stopped. Pyruvate can then be used to form other products, such as oxaloacetate for use in glucogenesis

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What is glycogen ?

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A branched polymer or glucose, represents a storage form of glucose. Glycogen synthesis and degradation occur primarily in liver and skeletal muscle, although other tissues store smaller quantities.

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What is starch ?

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Plants store excess glucose in long a- linked chains of glucose

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What is Glycogenesis ?

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Synthesis of glycogen granules, which beings with a core protein called glycogenin.

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What is glycogen synthases ?

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Is a rate limiting enzyme of glycogen synthesis and forms the a- 1,4 glycosidic bond found in the linear glucose chains of the granule.

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What is glycogenolysis ?

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The rate-limiting enzyme, the process of breaking down glycogen, is glycogen phosphorylase . In contrast to hydrolases, a phosphorylase breaks bonds using an inorganic phosphate instead of water.

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What is glycogen phosphorylase ?

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Breaks a a-1,4 glycosidic bond, releasing glucose 1-phosphate from the periphery of the granule. It can’t break a-1,6 bonds, and therefore stops when it nears the outermost branch points.

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What are isoforms ? Glycogen storage diseases ?

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  • Slightly different versions of the same protein ; in the case of glycogen enzymes, there are often different isoforms of the enzymes in the liver and muscle.
  • Defiencies of these are the diseases because all are characterized by accumulation of glycogen in one or more tissues.
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What is the structure of glycogen ? What type of glycosidic links exist in a glycogen granule ?

A
  • Glycogen is made up of a core protein of glycogenin with linear chains of glucose emanating(proceed or issue forth) out from the center. *
  • This is connected by a-1,4 glycosidic links. Some of these chains are branched, which requires a-1,6 glycosidic bonds
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What are the two main enzymes of Glycogenesis and what does each accomplish ?

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  • Glycogen syntheses attaches the glucose molecule from UDP glucose to the growing glycogen chain, forming an a-1,4 link in the process.
  • Branching enzyme creates a branch by breaking an a-1,4 link in the growing chain and moving a block of olgioglucose to another location in the glycogen granule. The oligoglucose is then attached with an a-1,6 link.
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What are the two main enzymes of glycogenolysis, and what does each accomplish ?

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* Glycogen phosphorylase removes a glucose molecule from glycogen using a phosphate, breaking the a-1,4 link and creating glucose 1-phosphate.

  • Debranching enzyme moves all of the glucose from a branch to a longer glycogen chain by breaking an a-1,4 link and forming a new a-1,4 link and to the longer chain. The branch point is left behind; this is removed by breaking the a-1,6 link to form a free molecule of glucose.
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What is gluconeogenesis ?

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The liver maintains glucose levels in the blood during fasting through either glycogenolysis or that…..

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What are Glucogenic amino acids ? What are ketogenic amino acids ?

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  • (All except leucine and lysine) can be converted into intermediates that feed into Glycogenesis.
  • While that happens ketogenic amino acids ( degraded directly into acetyl-CoA which is precursor for ketone bodies) which can be used as an alternative fuel particularly during periods of prolonged starvation.
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What is Pyruvate carboxylase ?

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A mitochondrial enzyme that is activated by acetyl CoA(from B- oxidation) . The product, oxaloacetate (OAA), is a citric acid cycle intermediate and cannot leave the mitochondria.

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What is Phosphoenolpyruvate carboxykinase (PEPCK) ?

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Cytoplasm is induced by glucagon and cortisol, which generally act to raise blood sugar raise levels. It converts OAA to phosphoenolpyruvate (PEP) in a reaction that requires GTP.

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What is glucose-6-phosphatase ?

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Found only in the lumen of the ER in liver cells. Glucose-6-phosphatase is transported into the ER, and free glucose is transported back into the cytoplasm, where it can diffuse out of the cell using GLUT transporters.

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Under what physiological conditions should the body carry out gluconeogenesis ?

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It occurs when an individual has been fasting for >12 hours. To carry out gluconeogenesis, hepatic (and renal) cells have enough energy to drive the process of glucose creation, which requires sufficient fat stores to undergo B-oxidation.

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What are the four enzymes unique to gluconeogenesis ? Which irreversible glycolytic enzymes do they replace ?

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  • Pyruvate Carboxylase and it replaces Pyruvate Kinase *
  • phosphoenolpyruvate carboxykinase (PEPCK) replaces Pyruvate Kinase *
  • Fructose 2,6- biphosphotase replaces Phosphofructokinase-1 *
  • Glucose-6-phosphatase replaces Glucokinase
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How does acetyl-CoA shift the metabolism of Pyruvate ?

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Inhibits Pyruvate dehydrogenase complex while activating Pyruvate carboxylase. The net effect is to shift from burning Pyruvate in the citric acid cycle to creating new glucose molecules for the rest of the body. The acetyl-CoA for this regulation comes predominantly from B-oxidation, not glycolysis

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The Pentose phosphate pathway (PPP) ?

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Also known as hexose monophosphate (HMP) shunt, occurs in the cytoplasm of all cells, where it serves two major functions: * Production of NADPH (a reducing agent in anabolic reactions, such as fat and DNA synthesis. It also generates free radicals in immune cells) Serving as a source of ribose 5-phosphate for nucleotide synthesis

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What is glucose-6-phosphate dehydrogenase (G6PD) ?

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First part of PPP begins with glucose-6-phosphate, ends with ribulose 5-phosphate and is irreversible. This part produces NADPH and involves the important rate limiting step

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What are reasons cells require NADPH?

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  • * Biosynthesis, mainly fatty acids and cholesterol
  • Assisting in cellular bleach production in certain white blood cells, thereby contributing to bactericidal activity Maintenance of a supply of reduced glutathione to protect against reactive oxygen species(acting as bodys natural antioxidant)
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What is Glutathione ?

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A reducing agent that can help reverse radical formation before damage is done to the cell

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What is Fructose-1,6 Biphosphate ?

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Cytoplasm is a key control point of gluconeogenesis and represents the rate limiting step of the process. It reverses the action of Phosphofructokinase-1, the rate limiting step of glycolysis.

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What is the function and regulation of Pyruvate Kinase ? Is it reversible ?

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  • Its function is to perform another substrate-level phosphorylation, transferring a phosphate from phosphoenolpyruvate (PEP) to ADP, forming ATP and pyruvate. Its regulation is to be activated by fructose 1,6-biphosphate.
  • It is irreversible so no
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What is debranching enzyme ? What are isoforms?

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Its a two enzyme complex that deconstructs the branches in glycogen that have been exposed by glycogen phosphorylase. * Its an ambiguous term describing either several different forms of protein coded from the same gene or proteins with amino acid sequence and function similarities even when they are from a different gene.

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Mini biochem chapter 12 (12 decks)

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