III - Carbohydrates Flashcards
(364 cards)
1
Q
Most abundant organic molecules in nature
A
Carbohydrates
2
Q
Empiric Formula: (CH2O)n - hydrates of carbon
A
Carbohydrates
3
Q
Functions of Carbohydrates
A
energy source, storage form of energy, part of cell membranes, structural components
4
Q
Polymers of repeating sugar units
A
Carbohydrates
5
Q
One sugar unit
A
monosaccharide
6
Q
Two sugar units
A
disaccharide
7
Q
3-10 sugar units
A
oligosaccharide
8
Q
> 10 sugar units
A
polysaccharide
9
Q
How many sugar units do monosaccharides have?
A
One
10
Q
How many sugar units do disaccharides have?
A
Two
11
Q
How many sugar units do oligosaccharides have?
A
3-10
12
Q
How many sugar units do polysaccharides have?
A
> 10
13
Q
The simplest and most basic form of carbohydrate hence cannot be hydrolyzed further
A
monosaccharide
14
Q
From fruit juices, hydrolysis of cane sugar, maltose and lactose
A
Glucose
15
Q
The “sugar of the body”, carried by the blood, principal sugar used by the tissues
A
Glucose
16
Q
Present in urine in DM owing to its high levels in the blood
A
Glucose
17
Q
Found in fruit juices, honey, hydrolysis of cane sugar and inulin (from the Jerusalem artichoke)
A
Fructose
18
Q
Can be changed to glucose in the liver and so used in the body
A
Fructose
19
Q
Hereditary _____ intolerance leads to _____ accumulation and hypoglycemia
A
Fructose
20
Q
From the hydrolysis of lactose
A
Galactose
21
Q
Can be changed to glucose in the liver and metabolized, synthesized in the mammary gland to make the lactose of milk, a constituent of glycolipids and glycoproteins
A
Galactose
22
Q
Failure to metabolize _____ leads to cataracts
A
Galactose
23
Q
from the hydrolysis of plant mannans and gums
A
Mannose
24
Q
A constituent of many glycoproteins
A
Mannose
25
Monosaccharide found in nucleic acids
Ribose
26
Monosaccharides found in glycoproteins
Xylose, Arabinose, Mannose
27
Monosaccharide found in proteoglycans
Neuraminic Acid
28
Monosaccharide found in cardiac tissue
Lyxose
29
Ribose is found in
nucleic acids
30
Xylose is found in
glycoproteins
31
Arabinose is found in
glycoproteins
32
Mannose is found in
glycoproteins
33
Neuraminic Acid is found in
proteoglycans
34
Lyxose is found in
cardiac tissue
35
Condensation product of two monosaccharide units, linked by glycosidic bonds
disaccharide
36
Glucose + Glucose
Maltose - α(1→4)
37
Glucose + Galactose
Lactose - β(1→4)
38
Glucose + Fructose
Sucrose - α1→β2
39
From germinating cereals, malt, digestion by amylase or hydrolysis of starch
Maltose
40
From milk, found in urine during pregnancy
Lactose
41
From sorghum, pineapples, carrots, cane and beet sugar
Sucrose
42
From fungi and yeasts, the major source of insect hemolymph
Trehalose
43
Condensation product of 3-10 monosaccharides, most are not digested by human enzymes, maltotriose
Oligosaccharide
44
Condensation product of >10 monosaccharides, may be linear or branched, easily digested
Polysaccharide
45
Homopolymer of glucose forming an α-glucosidic chain called glucosan or glucan
Starch
46
Most important dietary source of carbohydrate in cereals, potatoes, legumes and other vegetables
Starch
47
Storage polysaccharide in animals ("animal starch")
Glycogen
48
More highly branched structure than amylopectin with chains of 12-14 α-D-glucopyranose residues with α(1→4) glycosidic linkage with branching via α(1→6) glycosidic bonds
Glycogen
49
Polysaccharide of fructose used to determine the GFR
Inulin
50
Chief constituent of plant cell walls, fiber, cannot be digested
Cellulose
51
Insoluble and consists of β-D-glucopyranose units linked by β(1→4) bonds to form long, straight chains strengthened by cross-linking H-bonds
Cellulose
52
Also known as mucopolysaccharides
Glycosaminoglycans
53
Complex carbohydrates containing amino sugars and uronic acids
Glycosaminoglycans
54
May be attached to a protein molecule to form a proteoglycan
Glycosaminoglycans
55
Also known as mucoproteins, found in cell membranes
Glycoproteins
56
Proteins containing branched or unbranched oligosaccharide chains
Glycoproteins
57
Compounds that have the same chemical formula but different structures
Isomers
58
Compounds that differ in configuration around only one specific carbon atom with the exception of the carbonyl atom
Epimers
59
Pairs of structures that are mirror images of each other
Enantiomers/Stereoisomers/Optical Isomers - Dextro- (R), Levo- (L)
60
More common configuration of sugars in the body (D vs. L)
Dextro- (R)
61
Compounds that differ in configuration (linear/ring)
Anomers
62
More common configuration of sugars in the body (linear vs. cyclic)
Cyclic
63
Linear form of sugars
Fischer Projection
64
Cyclic form of sugars
Haworth Projection
65
5C Ring
Furan
66
6C Ring
Pyran
67
α and β forms of sugar spontaneously interconvert through a process called
Mutarotation
68
Physical digestion in the mouth
Mastication
69
Amylase can only digest _____ glycosidic bonds
α(1→4) - glycogen
70
Facilitates diffusion for all sugars, found in the basement membrane
GLUT-2 Transporter
71
Facilitates diffusion for all sugars, found in the lumen of the SI
GLUT-5 Transporter
72
A secondary active transporter for glucose and galactose (needs Na-K-ATPase), Na/hexose symporter, for glucose and galactose
SGLT-1 Trasporter
73
Tells how fast a carbohydrate is absorbed compared to glucose and galactose
Glycemic Index
74
Fast Absorption: GI _ 1
GI > 1
75
Slow Absorption: GI _ 1
GI < 1
76
Food with ___ GI is beneficial for DM.
low GI
77
Disaccharidase deficiency found in Asians
Lactose Intolerance / Lactase Deficiency
78
Disaccharidase deficiency found in Greenland Eskimos
Isomaltase-Sucrase Deficiency
79
Acquired enzyme deficiency occurs during _____ where enzymes are removed in stool.
severe diarrhea
80
Sum of all the chemical reactions in a cell, tissue or the whole body
Metabolism
81
Synthesis of compounds from smaller raw materials
Anabolic Metabolism
82
An endergonic and divergent process
Anabolic Metabolism
83
Breakdown of larger molecules
Catabolic Metabolism
84
An exergonic and convergent process, usually oxidative
Catabolic Metabolism
85
Produces reducing equivalents and ATP mainly via the ETC
Catabolic Metabolism
86
Crossroads of metabolism, links anabolic and catabolic pathways
Amphibolic Metabolism
87
Regulators of Metabolism: signals from within the cell
substrate avaiability, product inhibition, allosteric activators/inhibitors
88
Regulators of Metabolism: communication between cells
gap junctions (direct contact), neurotransmitters (synaptic signaling), hormones (endocrine signaling)
89
Regulators of Metabolism: second messenger systems
calcium/inositol triphosphate (ITP), adenylyl cyclase system (cAMP), guanylate cyclase system (cGMP)
90
Inositol Triphosphate System: G Protein
Gq
91
Inositol Triphosphate System: Substrate
Phosphatidylinositol - found in the cell membrane, acted on by phospholipase C
92
Inositol Triphosphate System: 2nd Messengers
Diacyl glycerol (DAG) - activates protein kinase C, Inositol Triphosphate (ITP) - release intracellular Ca
93
Membrane-bound enzyme that converts ATP to cyclic AMP (cAMP) in response to hormones
Adenylyl cyclase
94
Hydrolyzes cAMP to 5'-AMP
cAMP phosphodiesterase
95
Adenylyl Cyclase System: G Protein
Gs - stimulates, increase cAMP, Gi - inhibits, decrease cAMP
96
Adenylyl Cyclase System: Substrate
ATP
97
Adenylyl Cyclase System: 2nd Messengers
cAMP - activates protein kinase A
98
GLUT-1 is found in
erythrocytes, brain, kidneys, colon, placenta
99
GLUT-2 is found in
liver, pancreatic β-cells, small intestines, kidneys
100
GLUT-3 is found in
brain, kidneys, placenta
101
GLUT-4 is found in
heart and skeletal muscle, adipose
102
GLUT-5 is found in
small intestines
103
GLUT Transporter in erythrocytes, brain, kidneys, colon, placenta
GLUT-1
104
GLUT Transporter in liver, pancreatic β-cells, small intestines, kidneys
GLUT-2
105
GLUT Transporter in brain, kidneys, placenta
GLUT-3
106
GLUT Transporter in heart and skeletal muscle, adipose
GLUT-4
107
GLUT Transporter in small intestines
GLUT-5
108
Function of GLUT-1
uptake of glucose
109
Function of GLUT-2
rapid uptake and release of glucose
110
Function of GLUT-3
uptake of glucose
111
Function of GLUT-4
insulin-stimulated uptake of glucose
112
Function of GLUT-5
absorption of glucose
113
Major pathway for glucose metabolism that converts glucose into 3C compounds to provide energy
Glycolysis
114
Glycolysis: Location
Cytoplasm, all cells
115
Glycolysis: Substrate
Glucose
116
Glycolysis: End-Product
Pyruvate or Lactate - depends on the availability of oxygen or mitochondria
117
Glycolysis: Rate-Limiting Step
fructose 6-phosphate → fructose 1,6-bisphosphate
118
Glycolysis: Rate-Limiting Enzyme
Phosphofructokinase 1
119
Occurs in cells with mitochondria in the presence of oxygen to produce Pyruvate
Aerobic Glycolysis
120
Occurs in cells without mitochondria without oxygen to produce Lactate
Anaerobic Glycolysis
121
3 Irreversible Steps in Glycolysis
Step 1: phosphorylation of glucose, Step 3: phosphorylation of fructose 6-phosphate, Step 10: formation of pyruvate
122
Glycolysis: Step 1
glucose → glucose 6-P
123
Phosphorylates glucose in the first step of glycolysis
Hexokinase or Glucokinase
124
Phosphorylates glucose in most tissues with low Km (high affinity) and low Vmax, inhibited by glucose 6-P
Hexokinase
125
Phosphorylates glucose in liver parenchyma and pancreatic islets with high Km (low affinity) and high Vmax, inhibited by fructose 6-P, induced by insulin
Glucokinase
126
Glucose phosphorylator that is saturated in the liver and acts in a constant rate to provide glucose 6-P to meet the cell's need
Hexokinase
127
Glucose phosphorylator that removes glucose from the blood following a meal providing glucose 6-P in excess requirements for glycolysis which is used for glycogenesis and lipogenesis
Glucokinase
128
Glycolysis: Step 3
fructose 6-phosphate → fructose 1,6-bisphosphate
129
Phosphofructokinase 1 converts fructose 6-P to _____
fructose 1,6-BP
130
Converts fructose 6-P to fructose 1,6-BP
PFK1 - Phosphofructokinase 1
131
Phosphofructokinase 1 activators
fructose 2,6-BP, AMP
132
Phosphofructokinase 1 inhibitors
ATP, Citrate
133
Phosphofructokinase 2 converts fructose 6-P to _____
fructose 2,6-BP
134
Converts fructose 6-P to fructose 2,6-BP
Phosphofructokinase 2
135
Phosphofructokinase 2 activators
well-fed state - high insulin, low glucagon
136
Phosphofructokinase 2 inhibitors
fasting state - low insulin, high glucagon
137
Glycolysis: Step 10
phoshoenolpyruvate (PEP) → pyruvate
138
Forms pyruvate from PEP in glycolysis
Pyruvate kinase
139
Pyruvate kinase activator
fructose 1,6-BP - feedforward mechanism
140
Pyruvate kinase inhibitors
glucagon + cAMP = phosphorylation
141
ATP Consumption in Glycolysis
glucose → glucose 6-P (hoxokinase or glucokinase), fructose 6-phosphate → fructose 1,6-bisphosphate (phosphofructokinase 1)
142
ATP Production in Glycolysis
1,3-biphosphoglycerate → 3-phosphoglycerate (phosphoglycerate kinase), phosphoenolpyruvate → pyruvate (pyruvate kinase)
143
NADH Production in Glycolysis
glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate (glyceraldehyde 3-phosphate dehydrogenase)
144
Aerobic Glycolysis: Pyruvate
enters the Citric Acid Cycle
145
Aerobic Glycolysis: ATP Yield
6 or 8
146
Anaerobic Glycolysis: Pyruvate
reduced to lactate by NADH
147
Anaerobic Glycolysis: ATP Yield
2
148
NADH Shuttle found in liver, kidneys and brain
Malate-Aspartate Shuttle
149
Malate-Aspartate Shuttle is found in
liver, kidneys and brain
150
Malate-Aspartate Shuttle yields _ ATP
3 ATP
151
NADH Shuttle found in skeletal muscle and brain
Glycerol Phosphate Shuttle
152
Glycerol Phosphate Shuttle is found in
skeletal muscle and brain
153
Glycerol Phosphate Shuttle yields _ ATP
2 ATP
154
Strictly glycolytic organs
RBCs, testes, lens, cornea, kidney medulla, WBCs
155
Used to reduce pyruvate to lactate
NADH
156
Conversion to lactate is the major fate of pyruvate in
RBCs, testes, lens, cornea, kidney medulla, WBCs
157
Found in RBCs where phosphoglycerate kinase is bypassed
2,3-bisphosphoglycerate (2,3-BPG)
158
Catalyzes 1,3-BPG → 2,3-BPG
bisphosphoglycerate mutase
159
Catalyzed by bisphosphoglycerate mutase
1,3-BPG → 2,3-BPG
160
Inhibits pyruvate dehydrogenase by binding to lipoic acid, competes with inorganic phosphate as a substrate for glyceraldehyde 3-P dehydrogenase
Arsenic (Pentavalent)
161
Most common enzyme deficiency in glycolysis, manifests as intravascular hemolytic anemia
Pyruvate Kinase Deficiency
162
Glycolytic enzyme deficiency which manifests as low exercise capacity particularly on high carbohydrate diets
Muscle Phosphofructokinase Deficiency
163
Fate of Pyruvate: Citric Acid Cycle
Acetyl CoA (pyruvate dehydrogenase)
164
Fate of Pyruvate: Anaerobic Glycolysis
Lactate (lactate dehydrogenase)
165
Fate of Pyruvate: Fermentation
Ethanol (pyruvate decarboxylase)
166
Fate of Pyruvate: Gluconeogenesis
Oxaloacetate (pyruvate carboxylase)
167
Pyruvate dehydrogenase coenzymes
Lipoic Acid, NAD, FAD, Thiamine pyrophosphate (B1 derivative), Coenzyme A
168
Pyruvate dehydrogenase substrate
Pyruvate
169
Pyruvate dehydrogenase products
Acetyl CoA, NADH, CO2
170
Pyruvate dehydrogenase activators
NAD, CoA, Pyruvate
171
Pyruvate dehydrogenase inhibitors
NADH, Acetyl CoA, ATP
172
Most common cause of congenital lactic acidosis, x-linked dominant, dec. acetyl CoA deprives brain causing psychomotor retardation and death, treated with ketogenic diet
Pyruvate Dehydrogenase Deficiency
173
An acquired pyruvte dehydrogenase deficiency aggravated by thiamine deficiency leading to fatal pyruvic and lactic acidosis
Chronic Alcoholism
174
Final common pathway for the aerobic oxidation of all nutrients
Tricarboxylic Acid Pathway/Krebs Cycle/Citric Acid Cycle
175
Provides majority of ATP for energy, gluconeogenesis from AA skeletons, building blocks for AA and heme (succinyl CoA)
TCA Pathway
176
TCA Pathway: Functions
provides majority of ATP for energy, gluconeogenesis from AA skeletons, building blocks for AA and heme (succinyl CoA)
177
TCA Pathway: Location
Mitochondrial matrix (except succinyl dehydrogenase - inner mitochondrial membrane), all cells with mitochondria
178
TCA Pathway: Substrate
Acetyl CoA
179
TCA Pathway: Products
3 CO2, GTP, 4 NADH, FADH
180
TCA Pathway: Rate-Limiting Step
isocitrate → α-ketoglutarate
181
TCA Pathway: Rate-Limiting Enzyme
isocitrate dehydrogenase
182
TCA Pathway: ATP Yield from Acetyl CoA
12
183
TCA Pathway: ATP Yield from Pyruvate
15
184
TCA Pathway Sequence
Citrate 6C, Isocitrate 6C, α-Ketoglutarate 5C, Succinyl CoA 4C, Succinate 4C, Fumarate 4C, Malate 4C, Oxaloacetate 4C
185
Acetyl CoA + Oxaloacetate → Citrate
Citrate Synthase
186
Catalyzed by citrate synthase
Acetyl CoA + Oxaloacetate → Citrate
187
Citrate → Isocitrate (isomerization)
Aconitase
188
Catalyzed by aconitase
Citrate → Isocitrate (isomerization)
189
Inhibits aconitase
Fluooroacetate (rat poison)
190
Isocitrate → α-Ketoglutarate
Isocitrate dehydrogenase (rate-limiting enzyme)
191
Catalyzed by isocitrate dehydrogenase
Isocitrate → α-Ketoglutarate (rate-limiting step)
192
Products from Isocitrate → α-Ketoglutarate (isocitrate dehydrogenase)
CO2, NADH
193
α-Ketoglutarate → Succinyl CoA
α-Ketoglutarate dehydrogenase
194
Catalyzed by α-ketoglutarate dehydrogenase
α-Ketoglutarate → Succinyl CoA
195
Coenzymes for α-ketoglutarate dehydrogenase
Thiamine Pyrophosphate (B1 derivative), Lipoic Acid, FAD
196
Products from α-Ketoglutarate → Succinyl CoA (α-ketoglutarate dehydrogenase)
CO2, NADH
197
Inhibits α-ketoglutarate dehydrogenase
Arsenite
198
Succinyl CoA → Succinate
Succinate thiokinase
199
Catalyzed by succinate thiokinase
Succinyl CoA → Succinate
200
Product from Succinyl CoA → Succinate (succinate thiokinase)
GTP (ATP equivalent)
201
Succinate → Fumarate
Succinate dehydrogenase
202
Catalyzed by succinate dehydrogenase
Succinate → Fumarate
203
Product from Succinate → Fumarate (succinate dehydrogenase)
FADH2
204
Fumarate → Malate
Fumarase (fumarate hydratase)
205
Catalyzed by fumarase (fumarate hydratase)
Fumarate → Malate
206
Malate → Oxaloacetate
Malate dehydrogenase
207
Catalyzed by malate dehydrogenase
Malate → Oxaloacetate
208
Product of Malate → Oxaloacetate (malate dehydrogenase)
NADH
209
TCA Intermediates: _____ delivers acetyl CoA to the cytoplasm for fatty acid synthesis via _____ shuttle.
Citrate
210
TCA Intermediates: Used for heme synthesis and activation of ketone bodies in extrahepatic tissues
Succinyl CoA
211
TCA Intermediates: May be used for gluconeogenesis
Malate
212
Production of new glucose
Gluconeogenesis
213
Gluconeogenesis can produce glucose from these intermediates
intermediates of glycolysis and the TCA cycle, glycerol from TGs, lactate through the Cori Cycle, carbon skeletons (α-ketoacids) of glucogenic AAs
214
Gluconeogenesis: Location
liver (90%), kidney (10%, 40% during fasting), both in the mitochondria and cytoplasm
215
Gluconeogenesis: Substrate
Pyruvate
216
Gluconeogenesis: Product
Glucose
217
Gluconeogenesis: Rate-Limiting Step
fructose 1,6-bisphosphate → fructose 6-phosphate
218
Gluconeogenesis: Rate-Limiting Enzyme
Fructose 1,6-bisphosphatase
219
Lactate generated during anaerobic metabolism is brought to the liver the be converted to glucose via hepatic gluconeogenesis.
Cori Cycle
220
The Cori Cycle uses _ ATP to produce glucose.
4 ATP
221
Important Steps in Gluconeogenesis
Step 10: pyruvate → OAA → PEP, Step 3: fructose 1,6-BP → fructose 6-P, Step 1: glucose 6-P → glucose
222
Gluconeogenesis: Step 10
pyruvate → OAA (pyruvate carboxylase), OAA → PEP (PEP carboxykinase)
223
Pyruvate → OAA
Pyruvate carboxylase
224
Pyruvate carboxylase requires
Biotin
225
Function of Carboxylases
Attaches a carbon atom using CO2 as a substrate
226
3 Carboxylase Reactions
pyruvate → OAA (pyruvate carboxylase), acetyl CoA → malonyl CoA (acetyl CoA carboxylase), propionyl CoA → succinyl CoA (propionyl CoA carboxylase)
227
Catalyzed by pyruvate carboxylase
Pyruvate → OAA
228
OAA → PEP
PEP carboxykinase
229
PEP carboxykinase requires
GTP
230
Catalyzed by PEP carboxykinase
OAA → PEP
231
Gluconeogenesis: Step 3
fructose 1,6-BP → fructose 6-P (fructose 1,6-bishosphatase) - rate-limiting step
232
Fructose 1,6-BP → Fructose 6-P
Fructose 1,6-bishosphatase
233
Catalyzed by fructose 1,6-bishosphatase
Fructose 1,6-BP → Fructose 6-P
234
Fructose 1,6-bishosphatase activator
ATP
235
Fructose 1,6-bishosphatase inhibitors
Fructose 2,6-BP, AMP
236
Performs dual functions: promote glycolysis and inhibit gluconeogenesis
Fructose 2,6-BP
237
Functions of Fructose 2,6-BP
activates phophofructokinase 1 (glycolysis), inhibits fructose 1,6-bishosphatase (gluconeogenesis
238
Gluconeogenesis: Step 1
glucose 6-P → glucose (glucose 6-phosphatase) - final step, shared with glycogen degradation
239
Glucose 6-P → Glucose occurs in
liver and kidneys only (muscle lacks glucose 6-phosphatase hence muscle glycogen can only be used by muscle itself)
240
Gluconeogenesis: Regulation
circulating levels of glucagon, availability of glucognic substrates, allosteric activation by acetyl CoA, allosteric inhibition by AMP
241
Gluconeogenesis: Energy Expenditure
4 ATP, 2 GTP, 2 NADH
242
In hyperglycemia, the glomerular filtrate may contain more glucose that can be reabsorbed. This occurs when the venous blood glucose concentration exceeds 9.5-10 mmol/L (renal threshold).
Glucosuria
243
In _____ high amounts of NADH is produced resulting in _____.
alcoholism, hypoglycemia
244
When alcohol is consumed, high amounts of cytoplasmic NADH is produced by
alcohol dehydrogenase, acetaldehyde dehydrogenase
245
High amounts of NADH favors
pyruvate → lactate, OAA → malate, DHAP → glycerol 3-phosphate
246
NADH diverts pyruvate to lactate and OAA to malate resulting in
decreased gluconeogenesis → hypoglycemia
247
High fetal glucose consumption results in
hypoglycemia in pregnancy
248
Hyperinsulinemia in pregnancy is due to _____ and causes _____.
high estrogen, fasting hypoglycemia
249
Insulin resistance in pregnancy is due to _____ and causes _____.
high human placental lactogen (HPL), post-prandial hyperglycemia
250
Causes of Hypoglycemia in the Neonate
premature and LBW babies have little adipose, enzymes for gluconeogenesis are not yet completely functional
251
Major storage carbohydrate in animals
Glycogen
252
A branched polymer f D-glucose, uses α(1→4) glycosidic bonds for elongation and α(1→6) glycosidic bonds for branching
Glycogen
253
Glycogen: Storage
liver - 100g, 6% of liver, muscle - 400g, < 1% of muscle
254
Glycogen: Primary Bond
α(1→4) - 8-10 glucosyl residues
255
Glycogen: Branching Bond
α(1→6)
256
Synthesis of new glycogen molecules from α-D-glucose
Glycogenesis
257
Glycogenesis: Location
Cytosol, liver and muscle
258
Glycogenesis: Substrates
UDP-glucose, ATP, UTP, glycogenin (core, primer protein)
259
Glycogenesis: Product
Glycogen
260
Glycogenesis: Rate-Limiting Step
addition of α(1→4) bonds
261
Glycogenesis: Rate-Limiting Enzyme
Glycogen synthase
262
Important Steps in Glycogenesis
glucose 6-P → glucose 1-P, synthesis of UDP-glucose, elongation of glycogen chain, formation of branches
263
Glucose 6-P → Glucose 1-P
Phosphoglucomutase
264
Catalyzed by phosphoglucomutase
Glucose 6-P → Glucose 1-P
265
Synthesis of UDP-glucose: Enzyme
UDP-glucose phosphorylase
266
Catalyzed by UDP-glucose phosphorylase
Synthesis of UDP-glucose
267
Synthesis of UDP-glucose: Substrates
glucose 1-P, UTP
268
Elongation of glycogen chain
Glycogen synthase forms α(1→4) glycosidic bonds between glucose residues at the non-reducing end (carbon 4) - rate-limiting step
269
Catalyzed by glycogen synthase
Elongation of glycogen chain - forms α(1→4) glycosidic bonds between glucose residues at the non-reducing end (carbon 4) - rate-limiting step
270
Formation of branches in glycogen
Branching enzyme composed of amylo-α(1→4) → α(1→6) transglucosidase forms new α(1→6) bonds by transferring 5-8 glucosyl residues
271
Catalyzed by branching enzyme - amylo-α(1→4) → α(1→6) transglucosidase
Formation of branches in glycogen - forms new α(1→6) bonds by transferring 5-8 glucosyl residues
272
1-4 residues remaining on a branch after glycogen phosphorylase has already shortened it
Limit Dextrin
273
Shortening of glycogen chains to produce molecules of α-D-glucose
Glycogenolysis
274
Glycogenolysis: Location
Cytosol, liver and muscle
275
Glycogenolysis: Substrate
Glycogen
276
Glycogenolysis: Products
free glucose, glucose 1-P, glucose 6-P in muscle
277
Glycogenolysis: Rate-Limiting Step
Removal of glucose - breaks α(1→4) bonds
278
Glycogenolysis: Rate-Limiting Enzyme
Glycogen phosphorylase
279
1-4 residues remaining on a branch after glycogen phosphorylase has already shortened it
Limit Dextrin
280
Important Steps in Glycogenolysis
removal of glucose, removal of branches, glucose 1-P → glucose 6-P, lysosomal degradation of glycogen
281
Removal of branches
Debranching enzyme composed of α(1→4) → α(1→4) glucantransferase (transfers limit dextrin) and amylo-α(1→6) glucosidase (removes free glucose)
282
Catalyzed by α(1→4) → α(1→4) glucantransferase
Transfer of limit dextrin
283
Catalyzed by amylo-α(1→6) glucosidase
Removal of free glucose - breaks α(1→6) bonds
284
Glucose 1-P → Glucose 6-P
Phosphoglucomutase: liver - further converts glucose 6-P to glucose, muscles - glucose 6-P is the final product
285
Catalyzed by phosphoglucomutase
Glucose 1-P → Glucose 6-P: liver - further converts glucose 6-P to glucose, muscles - glucose 6-P is the final product
286
Lysosomal degradation of glycogen
α(1→4) glucosidase (acid maltase)
287
Catalyzed by α(1→4) glucosidase (acid maltase)
Lysosomal degradation of glycogen
288
Glycogen synthase activators
glucose 6-P, insulin, dephosphorylation, well-fed state
289
Glycogen synthase inhibitors
glucagon, epinephrine, phosphorylation, fasting state
290
Glycogen phosphorylase activators
Ca in muscle, glucagon, epinephrine, phosphorylation, fasting state
291
Glycogen phosphorylase inhibitors
glucose 6-P, ATP, insulin, dephosphorylation, well-fed state
292
Inherited disorders characterized by deposition of an abnormal type or quantity of glycogen in tissues, 12 types in total
Glycogen Storage Diseases
293
Glycogen Storage Disease Type I
Von Gierke's
294
Von Gierke's: Deficiency
glucose 6-phospatase
295
Von Gierke's: Findings
glycogen in liver and renal cells, hypoglycemia + lactic acidosis/ketosis
296
Glycogen in liver and renal cells, hypoglycemia + lactic acidosis/ketosis
Von Gierke's, GSD Type I
297
Glycogen Storage Disease Type II
Pompe's
298
Pompe's: Deficiency
acid maltase (α(1→4) glucosidase)
299
Pompe's: Findings
glycogen in lysosomes, cardiomegaly, heart failure
300
Glycogen in lysosomes, cardiomegaly, heart failure
Pompe's, GSD Type II
301
Glycogen Storage Disease Type III
Cori's
302
Cori's: Deficiency
debranching enzyme
303
Cori's: Findings
glycogen in liver and renal cells, MILD hypoglycemia + lactic acidosis/ketosis
304
Glycogen in liver and renal cells, MILD hypoglycemia + lactic acidosis/ketosis
Cori's, GSD Type III
305
Glycogen Storage Disease Type V
McArdle's
306
McArdle's: Deficiency
skeletal muscle glycogen phosphorylase
307
McArdle's: Findings
glycogen in muscle, muscle cramps + myoglobinuria without lactic acidosis
308
Glycogen in muscle, muscle cramps + myoglobinuria without lactic acidosis
McArdle's, GSD Type V
309
Important source of galactose, found in milk
Lactose
310
Lactose is hydrolyzed by lactase in the _____.
intestinal brush border
311
All disaccharidases and trisaccharidases are found in the _____.
brush border of the intestinal epithelium
312
Important Steps in Galactose Metabolism
phosphorylation of galactose, formation of UDP-galactose, use of galactose as a carbon source
313
Phosphorylation of galactose
galactose → galactose 1-P (hexokinase or glucokinase)
314
Formation of UDP-galactose (activated form of galactose)
galactose 1-P + UDP-glucose → UDP-galactose + glucose 1-P (galactose 1-P uridyltransferase)
315
Use of galactose as a carbon source
UDP-galactose → UDP-glucose (UDP-hexose 4-epimerase)
316
Galactokinase deficiency causes _____ and _____.
galactosemia, galactosuria
317
Causes cataracts in early childhood
Galactokinase Deficiency
318
Enzyme deficient in classic galactosemia
Galactose 1-P uridyltransferase
319
Galactitol accumulates causing cataracts within a few days after birth, hepatosplenomegaly and mental retardation
Classic Galactosemia
320
Vomiting and diarrhea after milk ingestion, hypoglycemia, liver disease and cirrhosis, lethargy and hypotonia, mental retardation
Classic Galactosemia
321
Classic galactosemia is a _____ to breastfeeding.
absolute contraindication
322
Important source of fructose, found in honey and fruits
Sucrose
323
Sucrose is hydrolyzed by sucrase in the _____.
intestinal brush border
324
Has the fastest metabolism and greatest yield of energy among sugars
Fructose
325
Important Steps in Fructose Metabolism
phosphorylation of fructose, formation of DHAP and glyceraldehyde
326
Phosphorylation of fructose
fructose → fructose 1-P (fructokinase or hexokinase)
327
Formation of DHAP and glyceraldehyde
fructose 1-P → dihydroxyacetone phosphate (DHAP) + glyceraldehyde (aldolase B)
328
Catalyzed by aldolase A
fructose 1,6-BP → DHAP + glycerol 3-P (glycolysis)
329
Catalyzed by aldolase B
fructose 1-P → DHAP + glyceraldehyde (fructose metabolism
330
Defective fructokinase, benugn and asymptomatic, only presents as fructosemia and fructosuria
Essential Fructosuria
331
Deficiency of aldolase B, autosomal recessive, fructose 1-P accumulates decreasing phosphate, glycogenolysis and gluconeogenesis
Fructose Intolerance
332
Severe hypoglycemia and lactic acidosis after fructose ingestion, vomiting, apathy, diarrhea, liver damage, jaundice, proximal renal tubule disorder resembling Fanconi syndrome
Fructose Intolerance
333
Important component of glycoproteins, very little contribution to diet
Mannose
334
Isomerization between mannose and fructose
mannose 6-P → fructose 6-P (phosphomannose isomerase)
335
Sorbitol metabolism in lens, retina, Schwann cells, liver, kidney, placenta, RBCs, ovaries, seminal vesicles
glucose → sorbitol (aldose reductase)
336
Sorbitol metabolism only found in the seminal vesicles
sorbitol → fructose (sorbitol dehydrogenase) - fructose is the fuel of sperm
337
In DM, there is excess glucose which is converted into sorbitol.The lens and nerves lack sorbitol dehydrogenase. Sorbitol accumulates and causes
cataract formation and peripheral neuropathy
338
Produces NADPH and ribose 5-P, metabolic use of 5-carbon sugars
Pentose Phosphate Pathway/Hexose Monophosphate Shunt
339
NADPH provides electrons for
FA and steroid biosynthesis, reduction of glutathione, cytochrome P450, WBC respiratory burst, nitric oxide synthesis
340
Pentose Phosphate Pathway: Location
Cytoplasm, liver, adipose, adrenals, thyroid, testes, RBC, lactating mammaries (high in tissue that produces lipids, low in skeletal muscle and non-lactating mammaries)
341
Pentose Phosphate Pathway: Substrates
glucose 6-P
342
Pentose Phosphate Pathway: Products
ribose 5-P, fructose 6-P, glyceraldehyde 3-P, NADPH
343
Pentose Phosphate Pathway: Rate-Limiting Step
glucose 6-P → 6-phosphogluconate
344
Pentose Phosphate Pathway: Rate-Limiting Enzyme
glucose 6-P dehydrogenase
345
Catalyzed by glucose 6-P dehydrogenase
glucose 6-P → 6-phosphogluconate
346
Pentose Phosphate Pathway: Phase 1
oxidative, irreversible
347
Pentose Phosphate Pathway: Phase 2
non-oxidative, reversible
348
Pentose Phosphate Pathway: Phase 1 Enzyme
glucose 6-P dehydrogenase
349
Pentose Phosphate Pathway: Phase 2 Enzyme
transketolases (requires thiamine)
350
Pentose Phosphate Pathway: Phase 1 Products
NADPH, ribulose 5-P
351
Pentose Phosphate Pathway: Phase 2 Products
ribose 5-P, glyceraldehyde 3-P, fructose 6-P
352
RBC transketolase activity can be used to diagnose
thiamine deficiency
353
Reduced _____ removes H2O2 in a reaction catalyzed by _____.
reduced glutathione (G-SH), glutathione peroxidase
354
Reacting with H2O2 oxidizes _____ but only reduced _____ can remove H2O2.
oxidized glutathione (G-S-S-G), glutathione
355
Reduced glutathione sequesters harmful H2O2
glutathione peroxidase
356
Glutathione peroxidase cofactor
Se - selenium
357
Reduced glutathione is recreated using NADPH
glutathione reductase
358
Most common disease producing enzyme abnormality in humans
Glucose 6-Phosphate Deficiency (G6PD)
359
Decreased NADPH in RBCs and decreased activity of glutathione reductase causing hemolytic anemia due to poor RBC defense against free radicals and peroxides, neonatal jaundice 1-2 days after birth
Glucose 6-Phosphate Deficiency (G6PD)
360
Precipitating factors for G6PD
Oxidative Stressors: infection (most common), drugs (AAA) - antibiotics (sulfonamides, chloramphenicol), antimalarials (primaquine), anti-pyretics (except ASA and paracetamol, fava beans
361
Altered hemoglobin precipitates within RBCs found in G6PD
Heinz BOdies
362
Altered RBcs due to phagocytic removal of Heinz bodies in the spleen
Bite cells
363
Converts molecular oxygen into superoxide in leukocytes (especially neutrophils and macrophages) and used in the respiratory burst that kills bacteria
NADPH oxidase
364
Deficiency in NADPH oxidase leading to severe, persistent and chronic pyogenic infections caused by catalase (+) bacteria
Chronic Granulomatous Disease
