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Sem 1: PATH20000 > Lecture 17: Glycogen Metabolism, Disaccharide Metabolism and the Pentose Phosphate Pathway > Flashcards

Lecture 17: Glycogen Metabolism, Disaccharide Metabolism and the Pentose Phosphate Pathway Flashcards

1
Q

___________:

• Major storage form of carbohydrate in

animals

• Branched polymer consisting of D-glucose

units

  • α1-4-linked glucose with α1-6-linked side branches
  • In the ______ helps maintain euglycemia during fasting periods
  • In ________ provides local energy but does not supply glucose for circulation
A

Glycogen

• Major storage form of carbohydrate in

animals

• Branched polymer consisting of D-glucose

units

  • α1-4-linked glucose with α1-6-linked side branches
  • In the Liver helps maintain euglycemia during fasting periods
  • In ________ provides local energy but does not supply glucose for circulation
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2
Q

Advantages to carbohydrate storage of Energy

A
  • Energy cannot be yielded from fat in the same space of time as from glycogen
  • Some organs such as the brain preferentially burn glucose – liver glycogen can provide this

during shorter stretches of fasting until depleted

• RBCs can only utilize glucose as their energy source through anaerobic glycolysis

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3
Q

Glycogen synthesis – regulated by _______

A

Glycogen synthesis – regulated by glycogen synthase

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4
Q
A
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5
Q

Linkage of the first few glucose units to form the minimal “primer” needed for glycogen synthase is catalyzed by ________, which attaches to the first glucose and catalyzes linkage of the first eight glucose by alpha(1,4) bonds

A

Linkage of the first few glucose units to form the minimal “primer” needed for glycogen synthase is catalyzed by Glycogenin, which attaches to the first glucose and catalyzes linkage of the first eight glucose by alpha(1,4) bonds

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6
Q

What does the formation of additional branches in Glycogen Synthesis do?

What Enzyme is responsible for this and by what mechanism?

A

Increases solubility and number of non-reducing ends upon which glucose units can be added (and in turn removed)

Enzyme = glucosyl 4:6 transferase (branching enzyme) breaks α1,4 bond to create α1,6 bonds

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7
Q

__________: breaking down of glycogen to yield glucose

  • Glycogen phosphorylase key enzyme
  • Acts until there are 4 glucose units left till branch point
  • Four units remaining are removed by ____________
A

Glycogenolysis: breaking down of glycogen to yield glucose

  • Glycogen phosphorylase key enzyme
  • Acts until there are 4 glucose units left till branch point
  • Four units remaining are removed by Debranching enzyme
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8
Q

______________ is used by both gluconeogenesis and glycogenolysis to release free glucose from glucose-6-phosphate.

A

Glucose-6-phosphatase is used by both gluconeogenesis and glycogenolysis to release free glucose from glucose-6-phosphate

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9
Q

Von Gierke’s Glycogen Storage Disease: Genetic deficiency of ____________ results in profound ________ as both gluconeogenic and glycogenolytic pathways are affected.

A

Von Gierke’s Glycogen Storage Disease: Genetic deficiency of glucose-6-phosphatase results in profound hypoglycemia as both gluconeogenic and glycogenolytic pathways are affected.

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10
Q

___________ and __________ are catabolic to release energy during periods of fasting/flight-fight response so they act to break down glycogen to glucose – use _____ as a second messenger and generally phosphorylate target enzymes.

A

Glucagon and epinephrine are catabolic to release energy during periods of fasting/flight-fight response so they act to break down glycogen to glucose – use cAMP as a second messenger and generally phosphorylate target enzymes

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11
Q

_________ turns on glycogen synthase and turns off glycogen phosphorylase to stimulate glycogen synthesis (via dephosphorylation)

A

Insulin turns on glycogen synthase and turns off glycogen phosphorylase to stimulate glycogen synthesis (via dephosphorylation)

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12
Q

_____________ turns off glycogen synthase and turns on glycogen phosphorylase to stimulate glycogen synthesis (via phosphorylation)

A

Glucagon/Epinephrine turns off glycogen synthase and turns on glycogen phosphorylase to stimulate glycogen synthesis (via phosphorylation)

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13
Q

As glycogen stores deplete ____________ takes over as the major source of glucose

A

As glycogen stores deplete gluconeogenesis takes over as the major source of glucose

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14
Q

Muscle does not contain _____________ so the glucose-1-P produced by glycogenolysis provides energy via glycolysis for contraction

A

Muscle does not contain glucose-6-phosphatase so the glucose-1-P produced by glycogenolysis provides energy via glycolysis for contraction

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15
Q

__________ is often accompanied by high ketone levels and lactic acidosis as the body tries to restore glucose and provide alternative fuel sources for the body

A

Hypoglycemia is often accompanied by high ketone levels and lactic acidosis as the body tries to restore glucose and provide alternative fuel sources for the bod

problem with fatty acid oxidation, not enough energy being created to create the negative regulators of glycolysis and positive of gluconeogenesis

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16
Q

__________________________________:

  • Build-up of glycogen in the body’s cells
  • Hypoglycemia and lactic acidosis can occur
  • Mutation in Glucose-6- phosphatase
A

Type I - Glycogen STrogae Disease (aka Von Gierke disease)

  • Build-up of glycogen in the body’s cells
  • Hypoglycemia and lactic acidosis can occur
  • Mutation in Glucose-6- phosphatase
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17
Q

_______________________________\_:

  • Debranching enzyme mutation leading to deficiency
  • Characterized by storage of structurally abnormal glycogen
  • Poor muscle tone in children is often the first sign of this disease
  • Ketone/FA levels elevated as the body switches to other fuel sources other than glycogen
  • Indistinguishable clinically from Type 1
A

Type III Glycogen Storage Disease (aka. Cori’s Disease) :

  • Debranching enzyme mutation leading to deficiency
  • Characterized by storage of structurally abnormal glycogen
  • Poor muscle tone in children is often the first sign of this disease
  • Ketone/FA levels elevated as the body switches to other fuel sources other than glycogen
  • Indistinguishable clinically from Type 1
18
Q

________________________________\_:

  • Muscle glycogen phosphorylase absent = exercise intolerance.
  • The least severe form of the disease
A

Type V Glycogen Storage Disease (aka. McArdle’s):

  • Muscle glycogen phosphorylase absent = exercise intolerance.
  • The least severe form of the disease
19
Q

_________________________________:

  • Acid alpha-glucosidase (GAA) (acid maltase) mutation (also called α-1,4-glucosidase)
  • The classic form is an infantile-onset inherited and often fatal disorder that disables the heart and skeletal muscles.
  • Infants with this disorder typically experience muscle weakness (myopathy), poor muscle tone (hypotonia), an enlarged liver (hepatomegaly), and heart defects.
  • Lysosomal glycogen is not necessary for maintaining blood glucose so hypoglycemia is not observed
  • Enzyme replacement therapy
A

Type II Glycogen storage disease/lysosomal dysfunction (aka. Pompe Disease):

  • Acid alpha-glucosidase (GAA) (acid maltase) mutation (also called α-1,4-glucosidase)
  • The classic form is an infantile-onset inherited and often fatal disorder that disables the heart and skeletal muscles.
  • Infants with this disorder typically experience muscle weakness (myopathy), poor muscle tone (hypotonia), an enlarged liver (hepatomegaly), and heart defects.
  • Lysosomal glycogen is not necessary for maintaining blood glucose so hypoglycemia is not observed
  • Enzyme replacement therapy
20
Q

_________ +_________use the sodium-glucose co-transporter system for absorption into the enterocyte (active transport – required energy)

_______ uses the GLUT5 transporter for absorption into the enterocyte

All three sugars enter the portal circulation where they are readily taken up by ______ in the liver.

A

Glucose** and G_alactose_** use the sodium-glucose co-transporter system for absorption into the enterocyte (active transport)

Fructose uses the GLUT5 transporter for absorption into the enterocyte

All three sugars enter the portal circulation where they are readily taken up by GLUT2 in the liver.

21
Q

Absorption of fructose does not induce an insulin response (T/F)

A

True

22
Q

Sucrose does not undergo reactions that are typical of aldehydes and ketones. Therefore, sucrose is a __________ sugar.

A

Sucrose does not undergo reactions that are typical of aldehydes and ketones. Therefore, sucrose is a nonreducing sugar.

23
Q

Age upon weaning and when disorders of fructose metabolism usually present?

A

6 months

24
Q

In tissues other than the liver fructose is phosphorylated by ______ to form fructose-6-phosphate which enters glycolysis.

A

In tissues other than the liver fructose is phosphorylated by Hexokinase to form fructose-6-phosphate which enters glycolysis.

25
Q

Fructose Metabolism in the Liver

Glucokinase does not recognize fructose meaning metabolism is different in the liver. Fructose is phosphorylated on C1 by ________ to form fructose-1-P which enters glycolysis

A

Fructose Metabolism in the Liver

Glucokinase does not recognize fructose meaning metabolism is different in the liver. Fructose is phosphorylated on C1 by fructokinase to form fructose-1-P which enters glycolysis

26
Q

_________________ Deficiency :

  • Infants are healthy until they ingest fructose
  • Fructose-1- phosphate accumulates causing hypoglycemia, nausea & vomiting, abdominal pain, sweating, tremors, confusion, lethargy, seizures, and coma
  • Fructose-1-phosphate is a _________ inhibitor of phosphorylase (glycogen degradation) and thus accumulation is linked to hypoglycemia.
  • Patients maintained on a diet free of both fructose and sucrose remain symptom-free
A

Aldose B Deficiency:

  • Infants are healthy until they ingest fructose
  • Fructose-1- phosphate accumulates causing hypoglycemia, nausea & vomiting, abdominal pain, sweating, tremors, confusion, lethargy, seizures, and coma
  • Fructose-1-phosphate is a competitive inhibitor of phosphorylase (glycogen degradation) and thus accumulation is linked to hypoglycemia.
  • Prolonged ingestion may cause cirrhosis (liver disease), mental deterioration, and proximal renal tubular acidosis with urinary loss of phosphate and glucose
  • Patients maintained on a diet free of both fructose and sucrose remain symptom-free
27
Q

__________________ Deficiency:

  • This deficiency causes benign elevation of blood and urine fructose levels (benign fructosuria).
  • The condition is asymptomatic and diagnosed accidentally when a non-glucose-reducing substance is detected in urine.
A

Fructokinase Deficiency:

  • This deficiency causes benign elevation of blood and urine fructose levels (benign fructosuria).
  • The condition is asymptomatic and diagnosed accidentally when a non-glucose-reducing substance is detected in urine.
28
Q

Galactose:

  • Found in milk/dairy products
  • Converted to intermediates of the ______ pathway
  • ___________ is also used for the synthesis of glycoproteins/glycolipids and proteoglycans
A

Galactose:

  • Found in milk/dairy products
  • Converted to intermediates of the glucose pathway
  • UDP galactose is also used for the synthesis of glycoproteins/glycolipids and proteoglycans
29
Q

The appearance of high concentrations of galactose in the blood after lactose intake may be due to either a ________ deficiency or a _______________ deficiency.

A

The appearance of high concentrations of galactose in the blood after lactose intake may be due to either a galactokinase deficiency** or a **uridylyl transferase deficiency

30
Q

________________________:

  • Results from deficiency of galactose-1-phosphate uridyl transferase
  • Is the most common cause of galactosemia
  • The clinical features of this illness include vomiting, lethargy, and failure to thrive soon after breastfeeding is begun.
A

Classic Galactosemia:

  • Results from deficiency of galactose-1-phosphate uridyl transferase
  • Is the most common cause of galactosemia
  • The clinical features of this illness include vomiting, lethargy, and failure to thrive soon after breastfeeding is begun.
31
Q

_____________________:

  • Results due to galactokinase deficiency
  • Galactose accumulates and is reduced to galactinol, which causes cataracts.
A

Non-classical Galactosemia:

  • Results due to galactokinase deficiency
  • Galactose accumulates and is reduced to galactinol, which causes cataracts.
32
Q

Which is more serious, Classical or Non-Classical Galactosemia?

Why?

A

Classical Galactosemia

Lack of uridylyltransferase is more serious as galactose-1-phosphate accumulates and interferes with glycogen synthesis and degradation.

33
Q

Accumulation of fructose-1-phosphate or galactose-1-phosphate is __________ to the cell than fructose or galactose. Enzymes that impair their metabolism, resulting in accumulation of the monophosphate-sugar, presents with ___________ disease.

A

Accumulation of fructose-1-phosphate or galactose-1-phosphate is more toxic** to the cell than fructose or galactose and thus enzymes that impair their metabolism, resulting in accumulation of the monophosphate-sugar, presents with **more severe disease.

34
Q
A
35
Q

Pentose Phosphate Pathway (the hexose monophosphate shunt)

  • Main pathway for the generation of _______ and ____________ _(_synthesis of nucleotides)
  • Occurs in the ____________
  • Branches from glycolysis at the level of glucose-6-phosphate
  • Is it energy-yielding?
  • NADPH produced is an important reduction reagent required for __________ as well as glutathione reduction (protects against oxidative damage)
A

Pentose Phosphate Pathway (the hexose monophosphate shunt)

  • Main pathway for generation of NADPH and ribulose-5-phosphate (synthesis of nucleotides)
  • Occurs in the cytoplasm
  • Branches from glycolysis at the level of glucose-6-phosphate
  • Not a direct energy-yielding pathway
  • NADPH produced is an important reduction reagent required for Fatty Acid Synthesis as well as glutathione reduction (protects against oxidative damage)
36
Q

___________ Pathway:

  • Part of the pentose phosphate pathway which generates NADPH and ribulose-5-phosphate
  • _______________is responsible for the decarboxylation of 6- phosphogluconate to yield the 5C sugar ribulose-5- phosphate
  • is an ____________ reaction
  • When NADPH levels are low the oxidative reactions of the pathway are used to generate ribose-5- phosphate for nucleotide synthesis
A

Oxidative Pathway:

  • Part of the pentose phosphate pathway which generates NADPH and ribulose-5-phosphate
  • 6-phosphogluconate dehydrogenase is responsible for the decarboxylation of 6- phosphogluconate to yield the 5C sugar ribulose-5- phosphate
  • is an Irreversible reaction
  • When NADPH levels are low this pathway is used to generate ribose-5- phosphate for nucleotide synthesis
37
Q

NADPH is a ________ agent

NADPH is required for the redox reactions in tissues with _____________ (cholesterol, bile salts, steroid hormones, triglycerides)

The liver also uses NADPH for detoxification of and excretion of drugs

NADPH is also used for the reduction of the important __________ glutathione

A

NADPH is a reducing agent

NADPH is required for the redox reactions in tissues with active lipid synthesis (cholesterol, bile salts, steroid hormones, triglycerides)

The liver also uses NADPH for detoxification of and excretion of drugs

NADPH is also used for the reduction of the important antioxidant glutathione

38
Q

__________ pathway

  • Pentose-phosphates produced can be used for the generation of glycolytic intermediates
  • Glycolytic intermediates can be used to generate ribose-5- phosphate for nucleotide synthesis via this pathway
  • This reaction is _________
  • When NADPH levels are high this pathway can be used to generate ribose-5- phosphate
A

Non-Oxidative pathway

  • Pentose-phosphates produced can be used for the generation of glycolytic intermediates
  • Glycolytic intermediates can be used to generate ribose-5- phosphate for nucleotide synthesis via this pathway
  • This reaction is Reversible
  • When NADPH levels are high this pathway can be used to generate ribose-5- phosphate
39
Q

In non-dividing cells where requirements for nucleotides are ______, Ribose-5-Phosphate is reconverted back to glycolytic pathway

A

In non-dividing cells where requirements for nucleotides are Low, Ribose-5-Phosphate is reconverted back to glycolytic pathway

40
Q

Glucose-6-phosphate _____________ Deficiency:

  • _______ chromosomal disorder
  • Mainly affects red blood cells (RBC)
  • Hemolytic anemia in response to a trigger (anti-malarial drugs)
  • Insufficient production of ______ in affected persons causes excessive oxidative damage to RBC and lysis occurs
  • Natural protection against _______
A

Glucose-6-phosphate Dehydrogenase Deficiency:

  • X-linked chromosomal disorder
  • Mainly affects red blood cells (RBC)
  • Hemolytic anemia in response to a trigger (anti-malarial drugs)
  • Insufficient production of NADPH in affected persons causes excessive oxidative damage to RBC and lysis occurs
  • Natural protection against malaria
41
Q

Aldolase B and galactose-1-phosphate uridyl transferase result in severe forms of ________ and ________, due to the accumulation of fructose-1-phosphate and galactose-1-phosphate respectively

A

Aldolase B and galactose-1-phosphate uridyl transferase result in severe forms of Fructosemia** and **Galactosemia, due to the accumulation of fructose-1-phosphate and galactose-1-phosphate respectively

42
Q

The pentose phosphate pathway is a critical pathway for the synthesis of ________ and for the generation of ________ which is essential for cellular redox reactions

A

The pentose phosphate pathway is a critical pathway for the synthesis of nucleotides** and for the generation of **NADPH which is essential for cellular redox reactions

Sem 1: PATH20000 (22 decks)

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