Fructose and Pentose Phosphate Pathway

Question 1

Galactose and fructose have the same chemical formula as ____.
The disaccharides , ____ and ____ are hydrolyzed two monosaccharides by enzymes at the brush border of intestinal epithelial cells

Answer 1

Glucose
Lactose
Sucrose

Question 2

Most fructose is ingested in the form of the disaccharide ___. It is converted into glycolytic intermediates which can be used for generating energy, or stored as glycogen or fatty acids.

Answer 2

Sucrose

Question 3

Fructose can be found in ____. Sucrose is found in ____.

Answer 3

Honey
Fruit

Question 4

We can synthesize fructose from glucose through the ____ pathway.

Answer 4

Polyol

Question 5

Fructose is an ____ of glucose.

Answer 5

Isomer

Question 6

The polyol pathways occurs normally in seminal vesicles to produce fructose as an ___ source for sperm

Answer 6

Energy

Question 7

Cataracts is caused by hyperglycemia, the polyol pathway can lead to elevated sorbitol and ___ levels in the eye, causing high pressure and glycated lens.

Answer 7

Fructose

Question 8

Polyol pathway:

Answer 8

Question 9

In the lumen of the gut, the ____/___ complex breaks down disaccharide sucrose into fructose and glucose.

Answer 9

Sucrase/isomaltase

Question 10

Dietary fructose is taken up from the lumen of the gut by ____ transporters.

Answer 10

GLUT5

Question 11

Transport of fructose across the apical membrane is through ____ transporter

Answer 11

GLUT2

Question 12

Fructose is metabolized primarily in the ____.

Answer 12

Liver

Question 13

Fructose metabolism first step:
Fructose is phosphorylated by _____ into fructose 1-phosphate

Answer 13

Fructokinase

Question 14

The 4th step of glycolysis:
The ___ enzyme cleaves fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate.

Liver cells express ____ _, which can also use fructose 1-phosphate as a substrate.

Answer 14

Aldolase
Aldolase B

Question 15

Glycolysis 4th step:

Question 16

Only Aldolase B in the liver can use _____ as a substrate. Aldolase B cleaves it into dihydroxyacetone phosphate and glyceraldehyde.

Answer 16

Fructose 1-phosphate

Question 17

The products of fructose metabolism can enter _____. Excess fructose can be stored either as glycogen or fat.

Answer 17

Glycolysis

Question 18

Which major regulatory step in glycolysis is bypassed in fructose 1-phosphate catabolism?

Answer 18

Phosphofructokinase-1 phosphorylates Fructose 6-P into fructose 1,6-bis-P

Question 19

In muscle, fructose can also be phosphorylated directly by _____, (although glucose is its preferred substrate), producing Fructose 6-phosphate

Answer 19

Hexokinase

Question 20

The disaccharide lactose is the principe source of ____ in our diet. ____ can be converted to glucose 1 phosphate for storage as glycogen or used in glycolysis.

Answer 20

Galactose
Galactose

Question 21

UDP-galactose is an important precursor for _____ of proteins and phospholipids

Answer 21

Glycosylation

Question 22

The sugar of uridine diphosphate glucose (UDP-glucose) can be epimerized to _____, which is a substrate for the synthesis of ____, the primary source of galactose in our diets.

Answer 22

UDP-galactose
Lactose

Question 23

Lactose synthesis:

Answer 23

Question 24

Lactose is digested in the lumen of the gut by the enzyme ____ which cleaves the disaccharide lactose into the monosaccharides galactose and glucose.

Answer 24

Lactase

Question 25

Galactose is transported through ____ and the ____ (secondary active transport system).

Answer 25

GLUT2 SGLT

Question 26

The first step in Intracellular galactose metabolism is its phosphorylation by ____ into galactose 1-phosphate.

Answer 26

Galactokinase

Question 27

____ ____ ____ transferase converts UDP-glucose and galactose 1-phosphate to UDP-galactose and glucose 1-phosphate

Answer 27

Galactose 1-phosphate uridyl

Question 28

Glucose 1-phosphate produced by transferase can be converted to _____ a substrate for glycolysis, pentose phosphate pathway, fatty acid synthesis, etc.

Answer 28

Glucose 6-phosphate

Question 29

_____ interconverts UDP-galactose and UDP-glucose. UDP-glucose can be used as a substrate for ____ synthesis or can be used to sustain ____ metabolism.

Answer 29

Epimerase Glycogen Galactose

Question 30

The end product of galactose metabolism is ___ ____, which can enter glycogenesis directly or be converted to glucose 6-phosphate for glycolysis or export

Answer 30

Glucose 1-phosphate

Question 31

About 10% of the glucose 6-phosphate in each cell is diverted to the ___ ___ pathway.

Answer 31

Pentose phosphate

Question 32

The products of the pentose phosphate pathway are reduced ____ and ____ ____ (used in nucleotide biosynthesis).

Answer 32

NADPH 5carbon sugars

Question 33

About 10% of ____ is metabolized through the pentose phosphate pathway.

Answer 33

Glucose

Question 34

Pentose phosphate pathway has two purposes: Generation of ____ and ____.

Answer 34

NADPH Five carbon sugars

Question 35

Five carbon sugars are used primarily for synthesizing ____.

Answer 35

Nucleotides

Question 36

The reducing power of NADPH is used for ___ ___, ___, and ____ synthesis. Also used for oxidation of toxins by ____ ____ enzymes. Also used for generation of reduced ____.

Answer 36

Fatty acid Cholesterol Nucleotide Cytochrome P450 Glutathione

Question 37

The pentose phosphate pathway is very active in the ____, ___, ____ mammary gland, ___ ___, and ___ ___ cells.

Answer 37

Liver Adipose Lactating Adrenal cortex Red blood

Question 38

The Pentose phosphate pathway is divided into the ____ phase and the ____ phase.

Answer 38

Oxidative Regenerative

Question 39

The oxidative phase of the pentose phosphate pathway converts glucose to _____. It generates ____ in the process. The key enzyme is ___ ___. These reactions are not reversible

Answer 39

Ribulose 5-phosphate NADPH 6-phosphate dehydrogenase

Question 40

The regenerative phase of the pentose phosphate pathway converts ribulose 5-phosphate to ____ ____ and glycolysis intermediates. It is reversible. The key enzymes are _____ and ____. These glycolysis intermediates can be used to generate five carbon sugars for ____ ___.

Answer 40

Ribose 5-phosphate Transketolase Transaldolase Nucleotide synthesis

Question 41

The first oxidation is catalyzed by ___ ____ ____. Glucose 6-phosphate is oxidized to 6-phosphoglucano-lactone. NADP+ is reduced to ____.

Answer 41

Glucose 6-phosphate dehydrogenase NADPH

Question 42

One of the most important functions of the NADPH, produced by the pentose phosphate pathway is to maintain _____ in the reduced state.

Answer 42

Glutathione

Question 43

Glutathione is a tripeptide: ___ ___, ___, ___. Glutathiones role is to neutralize ___ ___ so it does not damage the cell.

Answer 43

Glutamic acid, cysteine, glycine Oxidative stress

Question 44

The sulfide on glutathione can be oxidized by forming a ____ ___ with another glutathione.

Answer 44

Disulfide bond

Question 45

The rescuing power of NADPH is used to maintain _____ in reduced state so that it can remove ___ ____ from the cell.

Answer 45

Glutathione Hydrogen peroxide

Question 46

Diagram of glutathione function:

Answer 46

Question 47

Regenerative phase: Ribulose 5-phosphate is isomerized into ___ ____ or epimerized into ___ ____. These two molecules feed into the regenerative phase of PPP.

Answer 47

Ribose 5-phosphate Xylulose 5-phosphate

Question 48

____ ____ can exit the PPP and be used for nucleotide synthesis. ____ ___ is a transcriptional regulator.

Answer 48

Ribose 5-phosphate Xylulose 5-phosphate

Question 49

Regenerative phase key enzymes: 1. Transketolase transfers ___ ___ groups and uses ____ __ derived from thiamine pyrophosphate as a cofactor. 2. Transaldolase transfers ___ ___ groups

Answer 49

Two carbon Vitamin B1 Three carbon

Question 50

The goal of the regenerative phase is to allow the five carbon sugar to be turned into ___ ___ in situations when nucleotide synthesis is not required.

Answer 50

Glycolysis intermediates

Question 51

Glycolytic intermediates all have either ___ carbons or ___ carbons.

Answer 51

6 3

Question 52

When nucleotide synthesis is required, the reverse reactions of the PPP convert glycolysis intermediates into ___ ___ ____.

Answer 52

5 carbon sugars

Question 53

Regenerative phase: Transketolase reactions transfer two carbon groups

Answer 53

Question 54

Regenerative phase: Transaldolase reactions transfer three carbon groups

Answer 54

Question 55

PPP summary:

Answer 55

Question 56

When carbohydrates are abundant, the liver converts them to fatty acids and exports them as ____ for storage.

Answer 56

VLDL

Question 57

The carbohydrate response element binding protein ( _____) is a transcription factor. It is inhibited by phosphorylation by ___ ___ __ and adenosine monophosphate activated kinase (_____).

Answer 57

ChREBP Protein kinase A (PKA) AMPK

Question 58

Xylulose 5-phosphate (X5P) acts as an ____ ____ of protein phosphatase-2 (PP2A) which removed inhibitory phosphates from ChREBP, causing it’s translocation to the nucleus

Answer 58

Allosteric activator

Question 59

Xylulose 5-phosphate _____ carbohydrate response elements (ChoRE) in gene promoters, while ____ enhances transcription through sterol response elements and E-boxes. ____ ____ expression is thus coordinated by metabolic and endocrine signals.

Answer 59

Activates Insulin Lipogenic gene

Question 60

Lipogenic genes upregulated by ChREBP:

Answer 60

Pyruvate kinase Malic enzyme Citrate Lyase Acetyl CoA Carboxylase Fatty acid synthase

Question 61

Review

Answer 61

Question 62

Xylulose 5-phosphate promotes transcription of genes that convert ____ to ___.

Answer 62

Carbohydrates Fat

Question 63

Inborn errors of fructose metabolism: essential fructosuria is caused by inherited loss of function mutations in ____. It is benign. The only significant clinical finding is ___ ___ in the urine, which may be confused for diabetes.

Answer 63

Fructokinase Reducing sugars

Question 64

Without fructokinase, fructose is metabolized through ____ or eliminated in the urine.

Answer 64

Hexokinase

Question 65

Inborn errors of fructose metabolism: ____ ___ ____ is caused by inherited mutations in aldolase B. This condition is much more serious than essential fructosuria. This disease is silent until fructose is ingested.

Answer 65

Hereditary fructose intolerance

Question 66

Hereditary fructose intolerance: When patients ingest fructose, all intracellular phosphate gets trapped in ____ ___ because it cannot be metabolized. When a cells phosphate pool is trapped, ____ synthesis is impaired.

Answer 66

Fructose 1-phosphate ATP

Question 67

Clinical signs of hereditary fructose intolerance:

Answer 67

Vomiting, lethargy, aversion to fruit, recurrent hypoglycemic episodes, failure to thrive, hepatic failure

Question 68

Disorders of galactose metabolism: In ___ ___, dietary lactose is not broken down two monosaccharides in the small intestine. Gut bacteria Ferment lactose to lactic acid and water enters the lumen of the gut to offset the increased lactate.

Answer 68

Lactase deficiency

Question 69

Lactase deficiency aka ___ ___ results in diarrhea when dairy sugars are consumed.

Answer 69

Lactose intolerant

Question 70

_____ lactase deficiency is an autosomal recessive condition in which lactase activity declines over many years

Answer 70

Primary

Question 71

____ lactase deficiency is due to damage of brush border of intestinal enterocytes due to intestinal disease

Answer 71

Secondary

Question 72

____ lactase deficiency is a very rare genetic condition. It is the complete absence of lactase.

Answer 72

Congenital

Question 73

Disorders of galactose metabolism: _____ can result from inborn error of metabolism involving galactokinase, transferase, and epimerase

Answer 73

Galactosemia

Question 74

______ ____: nonclassical, galactose, accumulates, and is converted to galactitol through polyol pathway in the eyes leading to Cataracts

Answer 74

Galactokinase deficiency

Question 75

____ ____ ___ _____ deficiency: classical galactosemia. It is an autosomal recessive and very serious. It presents with jaundice, hepatomegaly, hypoglycemia, lethargy, and FTT

Answer 75

Galactose 1-phosphate uridyl transferase

Question 76

____ ___: the symptoms and prognosis are similar to transferase deficiency. The treatment is to restrict, but not to eliminate galactose from the diet.

Answer 76

Epimerase deficiency

Question 77

In transferase deficiency, the treatment is: Im Epimerase deficiency, the treatment is:

Answer 77

Galactose free diet Galactose restricted diet, very low amounts of galactose

Question 78

Why different treatments?

Answer 78

We need UDP galactose as a substrate for glycosylation reactions. With transferase deficiency, we can make UDP galactose from glucose. With a epimerase deficiency, the only way to make UDP galactose is from dietary galactose.

Question 79

_____ ____ ____ deficiency: is a common inborn error of metabolism as an X-linked trait where the enzyme is not completely inactive. It can provide enough flux through the pentose phosphate, oxidative Fais to provide reducing power for glutathione. Affected people are asymptomatic until they are exposed to elevated oxidative stress.

Answer 79

Glucose 6-phosphate dehydrogenase

Question 80

In people with glucose 6 phosphate, dehydrogenase deficiency, when they are exposed to oxidative stress their capacity to regenerate ____ is limited. Red blood cells are particularly affected by oxidative stress, causing ____ ___.

Answer 80

NAPDH Hemolytic anemia

Question 81

Substances that can cause hemolytic anemia in deficient individuals:

Answer 81

Question 82

Answer 82

Review

Question 83

Question 84