Carbohydrates Flashcards
0
Q
Functions of Carbohydrates
A
1) Energy source
2) Storage form of energy
3) Part of cell membranes
4) Structural components
1
Q
Most abundant organic molecules in nature
A
Carbohydrates
2
Q
Classification of Carbohydrates
A
1) Monosaccharide - 1 sugar unit
2) Disaccharide - 2 sugar unit
3) Oligosaccharide - 3-10 sugar unit
4) Polysaccharide - >10 sugar unit
3
Q
Simplest carbohydrates; Cannot be hydrolyzed further
A
Monosaccharide
4
Q
Condensation products of 2 monosaccharide units; Sugar units are linked by Glycosidic Bonds
A
Disaccharide
5
Q
Glucose + Glucose
A
Maltose
6
Q
Glucose + Galactose
A
Lactose
7
Q
Glucose + Fructose
A
Sucrose
8
Q
Condensation products of 3-10 monosaccharides; Most are not digested by human enzymes
A
Oligosaccharide
9
Q
Condensation product of >10 monosaccharide units; May be linear or branched polymers
A
Polysaccharide
10
Q
Homopolymer of glucose forming an alpha-glucosidic chain, called a Glucosan or Glucan; Most important dietary source of Carbohydrate in cereals, potatoes, legumes and other vegetables
A
Starch
11
Q
Storage polysaccharide in animals; More highly branched structure than amylopectin with chains of 12-14 alpha-D-glucopyranose residues with branching by means of alpha1-6 glucosidic bonds
A
Glycogen
12
Q
Polysaccharide of Fructose used to determine the glomerular filtration rate
A
Inulin
13
Q
Chief constituent of plant cell walls; Insoluble and consists of beta-D-glucopyranose units linked beta1-4 bonds to form long, straight chains strengthened by cross-linking hydrogen bonds; cannot be digested by mammals
A
Cellulose
14
Q
Structural polysaccharide in the exoskeleton of crustaceans and insects
A
Chitin
15
Q
Complex carbohydrates containing amino sugars and uronic acids; They may be attached to a protein molecule to form a proteoglycan
A
Glycosaminoglycans or Mucopolysaccharides
16
Q
Proteins containing branched or unbranched oligosaccharide chains; Occur in cell membranes and many other situations
A
Glycoproteins or Mucoproteins
17
Q
Compounds that have the same chemical formula but different structures
A
Isomers
18
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Compounds that differ in configuration around only one specific carbon atom, with the exception of the carbonyl carbon
A
Epimers
19
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Pairs of structures that are mirror images of each other
A
Enantiomers
20
Q
Sugars are convertible between a linear form and a ring form; Most are in the cyclic or ring form
A
Anomers
21
Q
Can spontaneously interconvert through a process called
A
Mutarotation
22
Q
Principal sites of Carbohydrate Digestion
A
Mouth
Intestinal lumen
23
Q
Physical Digestion; Carbohydrate digestion begins during
A
Mastication
24
Chemical digestion of Carbohydrates in mouth
Salivary amylase
25
Amylase can only digest ?
Alpha1-4 glycosidic bonds
26
Hydrolyzes complex carbohydrates to disaccharides and trisaccharides, but not directly to monosaccharides
Pancreatic amylase
27
Disaccharides in the _______ complete the digestive process
Brush border
28
Facilitated diffusion; For all sugars
GLUT-1 Transporter
29
Facilitated diffusion; For glucose, galactose, and fructose
GLUT-5 Transporter
30
Secondary active transport; Na/hexose symporter; For glucose and galactose
SGLT-1 Transporter
31
Absorption of sugar requires passage through two membranes:
1) Between lumen and enterocyte
| 2) Between enterocyte and capillary
32
Increase in blood glucose after a test dose of a carbohydrate compared with that after an equivalent amount of glucose; Tells how fast a carbohydrate is absorbed references are glucose and galactose
Glycemic Index
33
Glycemic Index >1
Fast absorption
34
Glycemic Index <1
Slow absorption
35
Glycemic Index = 1
Normal absorption
36
Sum of ALL the chemical reactions in a cell, tissue, or the whole body; Can either be catabolic or anabolic
Metabolism
37
Synthesis of compounds from smaller raw materials; Endergonic and divergent process
Anabolic
38
Breakdown of larger molecules; Usually oxidative reactions; Exergonic and convergent process
Catabolic
39
Crossroads of metabolism, the link between anabolic and catabolic pathways
Amphibolic
40
Regulators of Metabolism: Signals from within the cell
Substrate availability
Product inhibition
Allosteric activators/inhibitors
41
Regulators of Metabolism: Communication between cells
```
Direct contact
Synaptic signaling
Endocrine signaling
Gap junctions
Neurotransmitters
Hormones
```
42
Regulators of Metabolism: Second messenger systems
Calcium/inositol triphosphate (ITP)
Adenylyl cyclase system (cAMP)
Guanylate cyclase system (cGMP)
43
Inositol Triphosphate System: G protein used
Gq
44
Inositol Triphosphate System: Substrate used
Phosphatidylinositol - found in the cell membrane acted on by phospholipase C
45
Inositol Triphosphate System: 2nd Messengers
```
Diacyl glycerol (DAG) - activate protein kinase C
Inositol triphosphate (ITP) - release intracellular Ca
```
46
Membrane-bound enzyme that converts ATP to cyclic AMP or cAMP; cAMP hydrolyzed to 5'-AMP by cAMP phosphodiesterase
Adenylyl Cyclase System
47
Adenylyl Cyclase System: G protein used
Gs - Stimulates adenylate cyclase, increase cAMP
| Gi - Inhibits adenylate cyclase, decrease cAMP
48
Adenylyl Cyclase System: Substrate used
ATP
49
Adenylyl Cyclase System: 2nd Messengers
cAMP - activate protein kinase A
50
GLUT Transporter: GLUT - 1
Found in: erythrocytes, brain, kidney, colon, placenta
| Function: uptake of Glucose
51
GLUT Transporter: GLUT - 2
Found in: liver, pancreatic B cell, small intestine, kidney
| Function: rapid uptake and release of Glucose
52
GLUT Transporter: GLUT - 3
Found in: brain, kidney, placenta
| Function: uptake of Glucose
53
GLUT Transporter: GLUT - 4
Found in: heart, skeletal muscle, adipose tissue
| Function: insulin-stimulated uptake of Glucose
54
GLUT Transporter: GLUT - 5
Found in: small intestine
| Function: absorption of Glucose
55
Glycolysis: What is it for?
Major pathway for Glucose Metabolism that converts glucose into 3 carbon compounds to provide energy
56
Glycolysis: Where does it occur?
In the cytoplasm, in ALL cells
57
Glycolysis: Substrate
Glucose
58
Glycolysis: End-product
Pyruvate or lactate, depending on the presence of mitochondria and availability of oxygen
59
Glycolysis: Rate limiting Step
Reaction: fructose-6-phosphate ➡️ fructose 1,6-biphosphate
Enzyme: phosphofructokimase (PFK-1)
60
Cells with mitochondria; Cells with adequate O2 supply; End product: Pyruvate
Aerobic Glycolysis
61
Cells without mitochondria; Cells without sufficient O2; End product: Lactate
Anaerobic Glycolysis
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ATP used up to produce phosphorylated intermediates
Energy Investment
63
ATP produced through substrate-level phosphorylation
Energy Generation
64
Irreversible and Regulated steps in Glycolysis
Step 1: Phosphorylation of Glucose
Step 3: Phosphorylation of Fructose-6-phosphate
Step 10: Formation of Pyruvate
65
Glycolysis: Step 1
Glucose➡️Glucose-6-phosphate
| Enzyme: Hexokinase or Glucokinase
66
Has a high affinity (low Km) for glucose, and in the liver it is saturated under normal conditions, so acts at a constant rate to provide glucose-6-phosphate to meet the cell's need
Hexokinase
67
Has a Km very much higher than the normal intracellular concentration of glucose; Removes glucose from the blood following a meal, providing glucose 6-phosphate in excess of requirements for glycolysis, which is used for glycogen synthesis and lipogenesis
Glucokinase
68
Glycolysis: Step 3 - Rate limiting step of Glycolysis
Fructose-6-phosphate➡️Fructose-1,6-biphosphate
| Enzyme: Phosphofructokinase-1
69
Converts fructose-6-phosphate to fructose-1,6-biphosphate; Activator: fructose-2,6-biphosphate and AMP; Inhibitor: ATP and Citrate
Phosphofructokinase-1 (PFK-1)
70
Converts fructose-6-phosphate to fructose-2,6-biphosphate; Activator: well fed state - increase insulin, decrease glucagon Inhibitor: starved state - decrease insulin, increase glucagon
Phosphofructokinase-2 (PFK-2)
71
Glycolysis: Step 10 - Substrate level phosphorylation that yields 1 ATP per molecule of phosphoenolpyruvate
Phosphoenolpyruvate (PEP)➡️Pyruvate
| Enzyme: pyruvate kinase
72
Activator of pyruvate kinase
Fructose-1,6-biphosphate (feedforward mechanism)
73
Inhibitor of pyruvate kinase
Increase glucagon + Increase cAMP➡️phosphorylation
74
ATP Production in Glycolysis
1) 1,3-biphosphoglycerate➡️3-phosphoglycerate
Enzyme: phosphoglycerate kinase
2) phosphoenolpyruvate➡️pyruvate
Enzyme: pyruvate kinase
75
How many net molecules of ATP can be produced from 1 glucose molecule via substrate-level phosphorylation?
2 ATP molecules
76
Production of NADH
Step 1: glyceraldehyde-3-phosphate➡️1,3-biphosphoglycerate
| Enzyme: glyceraldehyde-3-phosphate dehydrogenase
77
What happens to pyruvate?
1) pyruvate enters the citric acid cycle (aerobic glycolysis)
2) pyruvate reduced to lactate (anaerobic)
78
In Aerobic Glycolysis: NADH
Proceeds to Electron Transport Chain
79
NADH CANNOT pass through mitochondrial membrane and so needs shuttles
1) Malate-Aspartate Shuttle
| 2) Glycerol Phosphate Shuttle
80
In liver, kidney and heart
| 1 NADH = 3 ATP
Malate-Aspartate Shuttle
81
In skeletal muscle and brain
| 1 NADH = 2 ATP
Glycerol Phosphate Shuttle
82
In what part of the cell can you find the electron transport chain?
Inner mitochondrial membrane
83
In Anaerobic Glycolysis, NADH used to
Reduce pyruvate to lactate
84
Strictly Glycolytic Organs
```
RBCs
Lens
Cornea of eye
Kidney medulla
Testes
WBCs
```
85
ATP yield of Glycolysis
Anaerobic: 2 ATP
Aerobic: 6 (or 8) ATP
86
Found in RBCs where phosphoglycerate kinase is bypassed; Reduces hemoglobin affinity for O2
2,3-Bisphosphoglycerate
87
Inhibits pyruvate dehydrogenase by binding to lipoic acid; Competes with inorganic phosphate as a substrate for glyceraldehyde-3-phosphate dehydrogenase
Arsenic poisoning (Pentavalent Arsenic)
88
Most common enzyme defect in glycolysis; Manifests as chronic hemolytic anemia
Pyruvate Kinase Deficiency
89
Low exercise capacity, particularly on high carbohydrate diets
Muscle Phosphofructokinase Deficiency
90
Pyruvate kinase deficiency and G6PD deficiency both present with intravascular hemolytic anemia. Important differences are:
1) G6PD has HEINZ BODIES in the peripheral smear
| 2) G6PD often has a precipitating history of oxidative stress
91
Alternate Fates of Pyruvate
Pyruvate➡️Acetyl CoA
| Enzyme: Pyruvate dehydrogenase complex
92
Co-enzymes of Pyruvate dehydrogenase complex
1) Lipoic Acid
2) NAD
3) FAD
4) Thiamine pyrophosphate
5) Coenzyme A
93
```
Pyruvate➡️Acetyl CoA
Substrate?
Product?
Activator?
Inhibitor?
```
Substrate: Pyruvate
Product: Acetyl CoA, NADH, and CO2
Activator: NAD+, CoA and pyruvate
Inhibitor: NADH, acetyl CoA, ATP
94
Most common biochemical cause of congenital lactic acidosis; X-linked dominant condition; Increase lactate + Decreased acetyl CoA leads to deprivation of Acetyl CoA in the brain causing psychomotor retardation and death
Pyruvate Dehydrogenase Deficiency
95
Treatment of Pyruvate Dehydrogenase Deficiency
Ketogenic Diet
96
Alcohol + Nutritional deprivation = Thiamine Deficiency
| An acquired pyruvate dehydrogenase deficiency➡️fatal pyruvic and lactic acidosis
Chronic Alcoholism
97
Final common pathway for aerobic oxidation of ALL nutrients; Provides majority of ATP for energy
Tricarboxylic Acid Pathway (TCA) aka Kreb's Cycle or Citric Acid Cycle
98
TCA: Where does it occur?
In ALL cells with mitochondria
99
TCA: What is the substrate?
Acetyl Coa
100
TCA: What are the products?
CO2, GTP, NADH and FADH2
101
TCA: Rate limiting step
Reaction: isocitrate➡️alpha-ketoglutarate
Enzyme: isocitrate dehydrogenase
102
MNEMONIC: Officer Can I Keep Selling Sex For Money
```
Oxaloacetate
Citrate
Isocitrate
Ketoglutarate
Succinyl CoA
Succinate
Fumate
Malate
```
103
Acetyl CoA + Oxaloacetate ➡️Citrate
Enzyme: Citrate synthase
104
Citrate➡️Isocitrate (isomerization)
Enzyme: Aconitase
Inhibitor: Fluoroacetate (rat poison)
105
Isocitrate➡️alpha-ketoglutarate
Rate limiting step
Enzyme: Isocitrate dehydrogenase
Products: CO2 and NADH
106
Alpha-ketoglutarate➡️Succinyl-CoA
Enzyme: alpha-ketoglutarate dehydrogenase
Co-enzyme: similar to pyruvate dehydrogenase
Products: CO2 and NADH
Inhibitor: arsenite
107
Succinyl-CoA➡️Succinate
Enzyme: succinate thiokinase
Products: GTP by substrate level phosphorylation
108
Succinate➡️fumarate
Enzyme: succinate dehydrogenase
Products: FADH2
109
Fumarate➡️Malate
Enzyme: Fumarase (Fumarate hydratase)
110
Malate➡️Oxaloacetate
Enzyme: Malate dehydrogenase
Products: NADH
111
TCA Intermediates: Delivers acetyl CoA to the cytoplasm for fatty acid synthesis via citrate shuttle
Citrate
112
TCA Intermediates: Heme synthesis and activation of ketone bodies in extrahepatic tissues
Succinyl CoA
113
TCA Intermediates: May be used for gluconeogenesis
Malate
114
ATP yield for TCA
Acetyl CoA: 12 ATP
| Pyruvate: 15 ATP (extra 3 ATP - from NADH)
115
Production of New glucose
Gluconeogenesis
116
Gluconeogenesis from the following intermediates:
1) intermediates of glycolysis and the TCA
2) glycerol from triacylglycerols
3) lactate through the Cori Cycle
4) carbon skeletons (alpha-ketoacids) of glucogenic amino acids
117
Gluconeogenesis: Where does it occur?
Liver 90%
Kidney 10%
Prolonged fasting: Kidney 40%
(In both mitochondria and cytoplasm)
118
Gluconeogenesis: Substrate
Pyruvate
119
Gluconeogenesis: Product
Glucose
120
Gluconeogenesis: Rate limiting step
Reaction: Fructose-1,6-biphosphate➡️Fructose-6-phosphate
Enzyme: Fructose-1,6-biphosphatase
Activator: ATP
Inhibitor: Fructose-2,6-biphosphate and AMP
121
Conversion of lactate to glucose
Cori Cycle
122
Cori Cycle: Energy Expense
4 ATP molecules
123
True or False: Muscle cannot reconvert lactate to glucose. Lactate must first be transported to the liver for gluconeogenesis.
True
124
Important steps in Gluconeogenesis
Step 10: Pyruvate➡️OAA➡️PEP
Step 3: Fructose-1,6-biphosphate➡️Fructose-6-phosphate
Step 1: Glucose-6-phosphate➡️Glucose
125
Requires biotin and ATP; Allosterically activated by Acetyl CoA
Pyruvate carboxylase
126
Requires GTP
PEP Carboxykinase
127
ALL Carboxylases require ____ as a Co-factor
Biotin
128
Promotes Glycolysis and Inhibits Gluconeogenesis
Fructose-2,6-biphosphate
Activates: Phosphofructokinase-1➡️favors Glycolysis
Inhibits: Fructose-1,6-biphosphatase➡️inhibits Gluconeogenesis
129
Final step of Gluconeogenesis which is shared with Glycogen degradation
Glucose-6-phosphate➡️Glucose
130
End goal of Glucose-6-phosphate➡️Glucose
Releases free Glucose into the circulation
131
Enzyme of Glucose-6-phosphate➡️Glucose
Glucose-6-phosphatase
132
Glucose-6-phosphate➡️Glucose: Where does it occur?
Liver and Kidneys only
133
Regulation of Gluconeogenesis
1) Circulating levels of Glucagon
2) Availability of Glucogenic substrates
3) Allosteric activation by Acetyl CoA
4) Allosteric inhibition by AMP
134
Energy expenditure of Gluconeogenesis
Use of 4 ATPs
Use of 2 GTPs
Oxidizes 2 NADH back to NAD+
135
In hyperglycemia, the glomerular filtrate may contain more glucose than can be reabsorbed; Occurs when the venous blood glucose concentration exceeds 9.5-10.0mmol/L (renal threshold)
Glucosuria
136
Alcoholism: High amounts of cytoplasmic NADH is formed by:
Alcohol dehydrogenase
| Acetaldehyde dehydrogenase
137
Hypoglycemia: High amounts of NADH favors the ff reactions:
Pyruvate➡️Lactate
OAA➡️Malate
DHAP➡️Glycerol-3-phosphate
138
High fetal glucose consumption; Risk of maternal and fetal hypoglycemia especially during fasting
Hypoglycemia during Pregnancy
139
Due to increase estrogen; Fasting Hypoglycemia
Hyperinsulinemia
140
Due to increase HPL; Post-prandial hyperglycemia
Insulin resistance
141
Premature and LBW babies have little adipose tissue; Enzymes of Gluconeogenesis are not yet completely functional
Hypoglycemia in the Neonate
142
Major storage carbohydrate in animals; Branched polymer of alpha-D-glucose
Glycogen
143
Glycogen: Where's it stored?
Liver and Muscle only
Liver: 100g = 6% of liver
Muscle: 400g = <1% of muscle
144
Synthesis of new glycogen molecules from alpha-D-glucose
Glycogenesis
145
Glycogenesis: Where does it occur?
Liver
Muscle
(Occurs in cytosol)
146
Glycogenesis: Substrates
UDP-glucose
ATP and UTP
Glycogenin - a core, primer protein
147
Glycogenesis: Product
Glycogen
148
Glycogenesis: Rate limiting step
Reaction: Elongation of glycogen
Enzyme: Glycogen synthase
149
Important Steps in Glycogenesis
Glucose-6-phosphate➡️Glucose-1-phosphate
Synthesis of UDP-Glucose
Elongation of Glycogen chains
Formation of branches in glycogen
150
Enzyme of Glucose-6-phosphate➡️Glucose-1-phosphate
Enzyme: Phosphoglucomutase
| Reversible - Not a rate limiting step
151
Synthesis of UDP-Glucose: Activated form
Glucose
152
Synthesis of UDP-Glucose: Enzyme
UDP-glucose phosphorylase
153
Synthesis of UDP-Glucose: Substrates
Glucose-1-phosphate
| UTP
154
Rate limiting step of Glycogenesis
Elongation of Glycogen chains
| Enzyme: Glycogen synthase
155
Formation of branches in glycogen: Enzyme
Branching enzyme composed of amylo alpha(1-4)➡️alpha(1-6) transglucosidase
156
Shortening of glycogen chains to produce molecules of a-D-glucose
Glycogenolysis
157
Glycogenolysis: Where does it occur?
Liver
Muscle
(In the cytosol)
158
Glycogenolysis: Substrate
Glycogen
159
Leaves about 4 glucose residues before a branch point
Limit dextrin
160
Glycogenolysis: Products
Glucose-1-phosphate
Free glucose - produced during the debranching process
Liver: can release free glucose to circulation
Muscle: limited to glucose-6-phosphate within muscle only
161
Glycogenolysis: Rate limiting step
Reaction: Removal of glucose
Enzyme: glycogen phosphorylase
162
Glycogenolysis: Removal of branches
Enzyme: debranching enzyme
Bonds cleave: alpha(1-4) and alpha(1-6)
Products: Free Glucose
163
Conversion of Glucose-1-phosphate to Glucose-6-phosphate
Enzyme: phosphoglucomutase
Liver: Glucose-6-phosphate further converted to glucose
Muscle: Glucose-6-phosphate is the final product
164
Lysosomal degradation of Glycogen
Enzyme: alpha(1-4) glucosidase aka Acid maltase - an enzyme that is different from glycogen phosphorylase
165
Glycogen Storage Disease: Type I
Von Gierke's
Glucose-6-phosphatase deficiency
Hypoglycemia + Lactic Acidosis/Ketosis
166
Glycogen Storage Disease: Type II
Pompe's
Acid maltase deficiency
Cardiomegaly and heart failure
167
Glycogen Storage Disease: Type III
Cori's
Debranching enzyme deficiency
Milder form of Type I
168
Glycogen Storage Disease: Type IV
Andersen's
Branching enzyme deficiency
Severe form of Type I (early death from heart and liver failure)
169
Glycogen Storage Disease: Type V
McArdle's
Skeletal Muscle glycogen phosphorylase deficiency
Glycogen in muscle: Muscle cramps + myoglobinuria but NO lactic acidosis
170
Glycogen Storage Disease: Type VI
Hers'
Hepatic Glycogen phosphorylase deficiency
Glycogen in liver cells: hypoglycemia
171
Glycogen Storage Disease: Type VII
Tarui's
PFK deficiency
Like Type V + hemolytic anemia
172
Glycogen Storage Disease: Type VIII
Hepatic phosphylase kinase deficiency
| Like Type VI
173
Important source of Galactose
Disaccharide lactose in milk
174
Phosphorylation of galactose
Galactose➡️Galactose-1-phosphate
| Enzyme: Galactokinase or Hexokinase
175
Formation of UDP-galactose
Galactose-1-phosphate + UDP-glucose➡️UDP-galactose + glucose-1-phosphate
Enzyme: galactose -1-phosphate uridyl transferase
176
Use of galactose as carbon source
UDP-galactose➡️UDP-glucose
| Enzyme: UDP-hexose-4-epimerase
177
Causes Galactosemia and Galactosuria
Galactokinase Deficiency
178
Absence of galactose-1-phosphate uridyltransferase; Autosomal recessive; Galactitol accumulation - causes Cataracts + Hepatosplenomegaly + mental retardation; Absolute contraindication to breastfeeding
Classic Galactosemia
179
Galactosemia, Galactosuria, cataracts within a few days of birth, vomiting and diarrhea after milk ingestion, hypoglycemia, liver disease and cirrhosis, lethargy and hypotonia, mental retardation; eliminate sources of galactose from the diet
Gal-1-Phosphate Uridyltransferase Deficiency
180
Important source of fructose
Disaccharide sucrose found in honey and fruits
181
Phosphorylation of fructose
Fructose➡️Fructose-1-phosphate
| Enzyme: Fructokinase or hexokinase
182
Formation of DHAP an Glyceraldehyde
Fructose-1- phosphate➡️dihydroxyacetone phosphate (DHAP) + Glyceraldehyde
Enzyme: Aldolase B
183
For Glycolysis; Fructose-1,6-biphosphate➡️DHAP+glycerol-3-phosphate
Aldolase A
184
For Fructose metabolism; Fructose-1-phosphate➡️DHAP+glyceraldehyde
Aldolase B
185
Defect in Fructokinase; Benign and asymptomatic whose only symptom is the appearance of fructose in blood and urine
Essential Fructosuria
186
Deficiency of Aldolase B; Autosomal recessive; Fructose-1-phosphate accumulates leading to decrease phosphate, decrease glycogenolysis, decrease gluconeogenesis; hypoglycemia, jaindice, cirrhosis, vomiting
Fructose Intolerance
187
Important component of Glycoprotein
Mannose Metabolism
188
Isomerization between mannose and fructose
Mannose-6-phosphate➡️fructose-6-phosphate
| Enzyme: phosphomannose isomerase
189
Glucose➡️Sorbitol
Enzyme: Aldose reductase
| Found in lens, retina, Schwann cells, liver, kidney, placenta, RBC, ovaries, seminal vesicles
190
Sorbitol➡️Fructose
Enzyme: Sorbitol dehydrogenase
| Found in the seminal vesicles only since Fructose is the fuel of sperm
191
Pentose Phosphate Pathway: What is it for?
```
1) Produces NADPH
FA and Steroid biosynthesis
Reduction of Glutathione
Cytochrome p450
WBC respiratory burst
Nitric oxide synthesis
2) Produces Ribose-5-phosphate for nucleotide synthesis
3) Metabolic use of 5-carbon sugars
```
192
Pentose Phosphate Pathway: Where does it occur?
In the cytoplasm
Active in: Liver, Adipose tissue, Adrenals, Thyroid, Testes, RBC, Lactating membranes
Low in: skeletal muscle, non-lactating mammaries
193
Pentose Phosphate Pathway: Substrate
Glucose-6-phosphate
| No consumption or production of ATP
194
Pentose Phosphate Pathway: Products
Ribose-5-phosphate
Fructose-6-phosphate
Glyceraldehyde-3-phosphate
NADPH
195
Pentose Phosphate Pathway: Rate limiting step
Reaction: glucose-6-phosphate➡️6-phosphogluconate
Enzyme: glucose-6-phosphate dehydrogenase
196
Pentose Phosphate Pathway: Phase 1
Oxidative
Irreversible
Enzyme: glucose-6-phosphate dehydrogenase
Product: NADPH ribulose-5-phosphate
197
Pentose Phosphate Pathway: Phase 2
Non-oxidative
Reversible
Enzyme: Transketolase (requires Thiamine)
Product: ribose-5-phosphate, glyceraldehyde-3-phosphate, fructose-6-phosphate
198
Removes H2O2 in reaction catalyzed by glutathione peroxidase; very important in RBCs
Glutathione
199
Reduced glutathione sequester harmful H2O2
Enzyme: glutathione peroxidase
200
Reduced glutathione recreated using NADPH
Enzyme: glutathione reductase
201
Most common disease producing enzyme abnormality in humans; Involves decrease NADPH in RBCs and decrease activity of glutathione reductase causing free radicals and peroxides to accumulate
Glucose-6-phosphate Dehydrogenase Deficiency
202
Precipitating factors of Glucose-6-phosphate Dehydrogenase Deficiency
Infection - most common
Drugs - antibiotics (sulfonamides, chloramphenicol), antimalarials (primaquine), antipyretics (except ASA and paracetamol)
Fava beans
203
Altered RBCs due to phagocytic removal of Heinz bodies in spleen
Bite cells in Heinz Bodies
204
Deficiency in NADPH oxidase; severe, persistent and chronic pyogenic infections
Chronic Granulomatous Disease
