Carbohydrates Flashcards
Give 4 monosaccharide hexoses
Glucose
Fructose
Galactose
Mannise
Reduction of glucose yields______
Sorbitol
Oxidation of glucose yields______
Glucuronic acid
Hexose obtained from mammary glands
Galactose
Hexose that is constituent of glycolipids and glycoproteins
Galactose
Give 3 pentose
Ribose
Ribulose
Xylulose
Hexose intermediate in pentose phosphate pathways
Ribulose
Pentose excreted in urine in essential pentosuria
Xylulose
Non-reducing disaccharide
Sucrose
Give 2 reducing disaccharides
Lactose
Maltose
Intermediate disaccharide in the digestion of starch
Maltose
Storage polysaccharide in animals
Glycogen
Chief constituent polysaccharide of plant cell wall
Cellulose
Polysaccharide of fructose that is readily soluble in water and is used to determine GFR
Inulin
Example of ketose
Fructose
Examples of aldose
Glucose
Galactose
Mannose
Isomers/Epimers/Enantiomers/Anomers
Compounds that have the same chemical formula
Isomers
Isomers/Epimers/Enantiomers/Anomers Glucose Fructose Galactose Mannose
Isomers
Isomers/Epimers/Enantiomers/Anomers
Isomers that differ in configuration around only one specific carbon atom (except the carbonyl carbon)
Epimers
Isomers/Epimers/Enantiomers/Anomers
Glucose and galactose
Epimers
Differ only at OH position in C4
Isomers/Epimers/Enantiomers/Anomers
Glucose and mannose
Epimers
Differ only at OH at C2
Isomers/Epimers/Enantiomers/Anomers
Are optical isomers or stereoisomers
Enantiomers
Isomers/Epimers/Enantiomers/Anomers
Pairs of structures that are mirror images of each other
Enantiomers
Isomers/Epimers/Enantiomers/Anomers
D sugar and L sugar
Enantiomers
Monosaccharide stucture with a five membered ring
Furanose
Monosaccharide structure with six-membered ring
Pyranose
Isomers/Epimers/Enantiomers/Anomers
Rotation around the carbonyl carbon produces _____ which are labeled alpha and beta
Anomers
Unlike epimers, anomers can undergo interconversion (from alpha to beta, and vice versa) without energy expenditure or need for enzymes, in a process called _____
Mutarotation
2 body tissues that require insulin for glucose cellular transport
Adipose
Muscle
Glucose transporter
RBC
Brain, kindey colon, placenta
Glut 1
Glucose transporter
Liver, pancreas
Small intestine, kidney
GLUT 2
Glucose transporter
Brain
Kidney, Placenta
GLUT 3
Glucose transporter
Muscle
Adipose
Heart, skeletal muscle
GLUT 4
Glucose transporter
Small intestine
GLUT 5
Glucose transporter
Small intestine, kidney
SGLT 1
Glucose transporter
Insulin-stimulated glucose uptake
GLUT 4
Glucose transporter
Frucose absorption
Small intestine
Glucose transporter
Sodium-dependent active uptake of glucose against a concentration gradient
SGLT 1
Major pathway for glucose metabolism that converts glucose into 3 carbon compounds to provide energy
Glycolysis
Most common type og glycolysis
Embden-Maeyerhoff-Parnas Pathway
Site of glycolysis
Cytosol
Substrate for glycolysis
Glucose
What are the end-products of glycolysis
2 molecules of either pyruvate or lactate
Rate-limiting step in glycolysis
F6P—>F1,6BP
Enzyme: PFK 1
Rate-limiting enzyme in glycolysis
PFK1
Identify enzyme
Glucose—>G6P
Hexokinase
Hexokinase/Glucokinase
Present in most tissues
Hexokinase
Hexokinase/Glucokinase
Can phosphorylase glucose and other hexoses
Both
Hexokinase/Glucokinase
Present only liver parenchyma and islet cells of pancreas
Glukokinase
Hexokinase/Glucokinase
Inhibited by G6P
Hexokinase
Hexokinase/Glucokinase
Inhibited by F6P
Glucokinase
Hexokinase/Glucokinase
Low Km, high affinity
Hexokinase
Hexokinase/Glucokinase
High Km, low affinity
Glucokinase
Hexokinase/Glucokinase
Low Vmax
Hexokinase
Hexokinase/Glucokinase
High Vmax
Glucokinase
Hexokinase/Glucokinase
Liver activity induced by iinsulin
Glucokinase
Identify enzyme
G6PF6P
Phosphohexose isomerase
Identify enzyme
F6P—>F1,6BP
PFK1
Rate-limiting enzyme of glycolysis
PFK1/PFK2
Product is F1,6BP
PFK1
PFK1/PFK2
Product is F2,6BP
PFK2
PFK1/PFK2
Activated by F2,6BP and AMP
PFK1
2 activators of PFK1
F2,6BP
AMP
PFK1/PFK2
Activated by well-fed state
Increased insulin
Decreased glucagon
PFK2
PFK1/PFK2
Inhibited by citrate and ATP
PFK1
PFK1/PFK2
Inhibited during fasting state
Decreased Insulin
Increased glucagon
PFK2
2 inhibitors of PFK1
Citrate
ATP
Inhibitors of PFK2
Fasting state
Dec insulin
Inc glucagon
Identify enzyme
F1,6BP—>DHAP and GA3P
Aldolase
Identify enzyme
DHAP—>GA3P
Triose phosphate isomeras
Identify enzyme
GA3P—>1,3BPG
Glyceraldehyde phosphate dehydrogenase
Identify enzyme
1,3BPG—> 3PG
Phosphoglycerate kinase
Identify enzyme
3PG—>2PG
Phosphoglycerate mutase
Identify enzyme
2PG—> PEP
Enolase
Identify enzyme
PEP—>Pyruvate
Pyruvate kinase
How many ATP per molecule of PEP is produced in substrate-level phosphorylation
1
What activates pyruvate formation
F1,6BP
Hormone that inhibits pyruvate formation
Glucagon
2 steps in glycolysis that produce ATP
1,3BPG—>3PG (enzyme: phosphoglycerate kinase)
PEP—>Pyruvate (enzyme: pyruvate kinase)
2 enzymes in involved in ATP-producing steps in glycolysis
Phosphoglycerate kinase
Pyruvate kinase
Step in glycolysis that produces NADH
GA3P—> 1,3BPG
enzyme: glyceraldehyde 3 phosphate dehydrogenase
Enzyme involved in NADH-producing step in Glycolysis
Glyceraldehyde 3 phosphate dehydrigenase
End product of aerobic glycolysis
Pyruvate
End product of anaerobic glycolysis
Lactate
Identify enzyme
Pyruvate—>lactate
Lactate DH
NADH used
Major fate of pyruvate in lens, cornea, kidney medulla, testes, RBC, WBC
Lactate
Glycerophosphate shuttle/Malate aspartate shuttle
ATP yield per NADH is 1.5
Glycerophosphate
Glycerophosphate shuttle/Malate aspartate shuttle
ATP yield per NADH is 2.5
Malate aspartate
Glycerophosphate shuttle/Malate aspartate shuttle
Tissues: Brain, white muscle
Glycerophosphate
Glycerophosphate shuttle/Malate aspartate shuttle
Tissue: heart and most tissues
Malate aspartate
Net ATP yield for aerobic glycolysis glycerophosphate shuttle
5
See page 9 of topnotch handout
Net ATP yield for aerobic glycolysis malate aspartate shuttle
7
Net ATP yield for anaerobic glycolysis
2
Fate of pyruvate and enzyme involved
Anaerobic glycolysis
Lactate, lactate DH
Fate of pyruvate and enzyme involved
Fermentation
Ethanol
Pyruvate decarboxylase
Fate of pyruvate and enzyme involved
Gluconeogenesis
OAA, pyruvate carboxylase
Fate of pyruvate and enzyme involved
Citric acid cycle
Acetyl CoA, pyruvate DH
Identify enzyme
Pyruvate—> Acetyl Coa
Pyruvate DH complex (E1 + E2 + E3)
Enumerate coenzymes of pyruvate DH complex
Thiamine pyrophosphate FAD NAD+ Coenzyme A (contains panthotenic acid) Lipoic acid
Most common enzyme defect in glycolysis and its presentation
Pyruvate dehydrogenase, hemolytic anemia
Identify enzyme
Provide lipids as alternative fuel
Deficiency presents as low exercise capacity, especially on high carbohydrate diets
Muscle phosphofructokinase
Identify enzyme
Its deficiency is the most common cause of congenital lactic acidosis
Pyruvate dehydrogenase
Clinical manifestation af ALDOLASE A deficiency
Hemolytics anemia
Treatment for pyruvate dehydrogenase deficiency
Ketogenic diet
In arsenic poisoning, arsenic competes with inorganic phosphate as a substrate of what glycolytic enzyme
Glyceraldehyde 3 phosphate dehydrogenase
Deficiency of this glycolytic enzyme leads to acumulation of lactate, decreased acetyl CoA, leading to psychomotor retardation and death
Pyruvate dehydrogenase
Final common pathway for the aerobic oxidationof carbohydrates, lipids and proteins
Citric acid cycle
Site of TCA
Mitochondria
All substrates of TCA are in mitochondrial matrix except
Succinate dehydrogenase (inner mitochondrial membrane)
Initial substrate for TCA
Acetyl CoA
Products of TCA
2 CO2
1 GTP
3 NADH
1 FADH2
Rate-limiting step in TCA
Isocitrate—>alpha kg
Enzyme: isocitrate dehydrogenase
Enzyme for rate-limiting step of TCA
Isocitrate dehydrogenase
Identify enzyme
Acetyl CoA + OAA —> Citrate
Citrate synthase
In TCA, Acetyl CoA + ______ —> citrate
OAA
Identify enzyme and inhibitor
Citrate —-> isocitrate
Aconitase,
Fluoroacetate
Identify enzyme and byproduct
Isocitrate—> alpha kg
Isocitrate dehydrogenase,
CO2, NADH
Identify enzyme, by-products and inhibitor
Alpha kg —> succinyl CoA
Alpha kg dehydrogenase
CO2, NADH
Arsenite and ammonia
Identify enzyme and by-product
Succinyl CoA—>Succinate
Succinate thiokinase,
GTP
Identify enzyme and by-product
Succinate—>Fumarate
Succinate dehydrogenase
FADH2
Identify enzyme
Fumarate—>malate
Fumarase hydratase
Identify enzyme and by-product
Malate—>OAA
Malate dehydrogenase
NADH
3 reactions in TCA that produce NADH as by-product
Isocitrate—>alpha kg
Alpha kg—>succinyl CoA
Malate—> OAA
Reaction in TCA that produces GTP
Succinyl CoA—>Succinate
Reaction in TCA that produces FADH2
Succinate —> fumarate
TCA intermediate that delivers acetyl CoA to the cytosol dor fatty acid synthesis via its shuttle
Citrate
TCA intermediate used for heme synthesis and activation of ketone bodies in extrahepatic tissues
Succinyl CoA
TCA intermediate used for gluconeogenesis
Malate
T/F TCA does not synthesize new OAA
T
T/F
TCA proceeds under hormonal control
F
T/F
Four B vitamins are essential for TCA
T
These are reactions that replenish intermediates of the TCA that have been used for biosynthesis
Anaplerotic reactions
Most important anaplerotic reaction that maintains adequate comcentration of OAA
Pyruvate carboxylase Other anaplerotic susbtrates: Glutamine Glutamate Aspartate Propionyl CoA
Total ATP yield for 1 cycle of TCA
10
NADH (2.5x3)
FADH2 (1.5x1)
GTP (1)
Total ATP yieald for complete oxidation of glucose
30 or 32
Glcose —> Pyruvate 5 or 7
2 pyruvate —> Acetyl CoA 2.5 from NADH x 2 = 5
2 acetyle CoA in TCA —> 10 x 2 = 20
Process of synthesizing glucose from non-carbohydrate sources
Gluconeogenesis
Organ site of gluconeogenesis
Liver 90%
Kidney 10%
Site of gluconeogenesis in the cell
Mitochondria and cyosol
Substrates of gluconeogenesis include: Intermediates of glycolysis and TCA \_\_\_\_\_ through the Cori cycle \_\_\_\_\_ and \_\_\_\_\_\_ from TAG Carbon skeletons of glucogenic AA
Lactate
Glycerol, propionyl CoA
Rate-limiting step in gluconeogenesis
F1,6BP—>Fructose 6 Phosphate
Enzyme: fructose 1,6 bisphophatase
Gluconeogenesis
Identify enzyme
Pyruvate—>OAA
Pyruvate carboxylase
2 Co-factors of pyruvate carboxylase in gluconeogenesis
ATP
Biotin (CARBOXYLASES attach carbon atom with CO2 as a substrate. All carboxylases require biotin as co-factor)
Pyruvate —> OAA (pyruvate carboxylase)
Acetyl CoA—> malonyl CoA (Acetyl CoA carboxylase)
Propionyl CoA —> methylmalonyl CoA ( propionyl CoA carboxylase)
Gluneogenesis
Pyruvate carboxylase is allosterically activated by______
Acetyl CoA
In gluconeogenesis, OAA is reduced to _______ and exported from the mitochondrion tonthe cytosol, where it is converted back to OAA
Malate
Identify the enzyme in gluconeogenesis
OAA—> PEP
PEP Carboxykinase
Key enzyme that catalyzes net transfer out of the citric acid cycle into gluconeogenesis
PEP carboxykinase
OAA—>PEP
Rate-limiting enzyme of gluconeogenesis
Fructose 1,6 bisphosphatase
Inhibited by fructose 2,6 bisphosphate and AMP
What inhibits the rate-limiting enzyme of gluconeogenesis?
Fructose 2,6 bisphosphate
AMP
Final step shared by gluconeogenesis and glycogenolysis
Glucose-6-phosphate—>Glucose
Enzyme: glucose-6-phosphatase
The cycle through which lactate formed by glycolysis in skeletal muscle is transported to the liver where it is converted back to glucose through gluconeogenesis
Cori cycle
Gluconeogenesis from pyruvate requires
Cleavage of ______ bonds
Oxidation of ______
Gluconeogenesis from pyruvate requires
Cleavage of 6 high-enerfy phosphate bomds (4 ATP + 2 GTP)
Oxidation of 2 NADH
Energy for gluconeogenesis comes from _____
Oxidation of fatty acids
Glucosuria occurs when venous blood glucose concentration exceeds _____mmol/L (renal threshold)
10
Major storage of carbohydrate in animals
Glycogen
Approximately ____g of glycogen is stored in the liver
500
Glygogen is a branched polymer of alpha D glucose
With primary glycosidic bond at ______
And branch pointd after 8 to 10 residues at _____
a (1->4)
a (1->6)
Site of glycogenesis
Cytosol
Liver and muscle
Substrate for glycogenesis
a-D-glucose
Rate-limiting step for glycogenesis
Elongation of glycogen chains
ie, creation of a(1,4) glycosidic bonds by enzyme glycogen synthase
Each glycogen chain how how many glucose residues?
12-14
Protein that serves as primer for glycogen synthesis when glycogen is completely depleted
Glycogenin
Identify the 2 enzymes
G6P—>G1P
G1P + UTP —> UDP-Glucose
Phosphoglucomutase
UDP-glucose pyrophosphorylase
In glycogenesis, the rate limiting enzyme _____ forms _____ bonds between glucise residues. Hence, elongation of the chain
Glycogen synthase
a(1->4)
In glycogenesis, branch formation is facilitated by ____ enzyme, which forms a(1->6) bonds by transferring 5 to 8 glucosyl residues
Branching enzyme composed of amylo a(1->4) to a(1->6) transglucosidase
Alpha (1->4) glycogen bonds form at the (reducing/non-reducing end)
Non-reducing
ie, carbon 4
Site of glycogenolysis
Liver and muscle
Cytosol
Products of glycogenolysis
Glucose in liver
Glucose-6-phosphate in muscle
Rate-limiting step for glycogenolysis
Shortening of glycogen chains
Enzyme: glycogen phosphorylase
In glycogenolysis, shortening of chains proceeds with sequential cleavage of ____ bonds between glucosyl residues at the non-reducing end of the molecule
a(1->4)
Rate-limiting enzyme in glyconolysis and its coenzyme
Glycogen phosphorylase
Pyridoxal phosphate
In glycogenolysis, shortening of chains stops when
When only 4 glucosyl units remain
Limit dextran
Removal of branches in glycogenolysis is facilitated by what enzyme
Debranching enzyme composed of
a(1->4) glucantransferase
Amylo a(1->6) glucosidase
In glycogenolysis, cleavage of what bonds yield free glucose
a(1->6)
Enzyme for lysosomal degradation of glycogen and disease associated
Alpha (1->4) glucosidase aka acid maltase
Deficient in Pompe disease
A. Glycogen synthase/B. Glycogen phosphorylase
Activated by Glucose-6-phosphate
A
A. Glycogen synthase/B. Glycogen phosphorylase
Inhibited by ATP
B
A. Glycogen synthase/B. Glycogen phosphorylase
Activated by calcium (muscle)
B
A. Glycogen synthase/B. Glycogen phosphorylase
Activated by glucagon and epinephrine
B
A. Glycogen synthase/B. Glycogen phosphorylase
Inhibited by glucagon and epinephrine
A
A. Glycogen synthase/B. Glycogen phosphorylase
Activated by insulin
A
A. Glycogen synthase/B. Glycogen phosphorylase
Inhibited by insulin
B
A. Glycogen synthase/B. Glycogen phosphorylase
Active when phosphorylated
B
A. Glycogen synthase/B. Glycogen phosphorylase
Active when dephosphorylated
A
Phosphorylation of galactose into galactose 1 phosphate is facilitated by
Galactokinas
Formation of UDP galactose is facilitaed by what enzyme
Galactose 1 P uridyl transferase (GALT)
Identify enzyme that facilitates use of galactose as carbon source
UDP hexose 4 epimerase
Reaction: UDP galactose —> UDP glucose
Identify enzyme deficiency
Cataracts in early childhood
Galactosemia, galactosuria
Autosomal recessive
Galactokinase deficiency
Identify enzyme deficiency
Severe symptoms of galactosemia, galactosuria, cataracts, diarrhea, vomiting, jaundice
Poor growth in children, severe mental retardarion, liver damage
Premature ovarian failure in children
Galactose 1 phosphate uridyl transferase deficiency
Enxyme for phosphorylation of fructose
Fructokinase or hexokinase
Identify enzyme
Fructose 1 P —> DHAP + glyceraldehyde
Aldolase B
Clinical manifestation of essential fructosuria (fructokinase deficiency)
Asymtomatic
Identify enzyme deficiency
Profound hypoglycemia and vomiting
Jaundice, hemorrhage, hepatomegaly, renal dysfunction, hyperuricemia, lactic acidosis, death
Symptoms appear after waening from milk
Aldolase B deficiency
Hereditary fructose intolerance
What pathway
Glucose—> Sorbitol —> Fructose
Polyol pathway
In polyol pathway, what enzyme catalyzes this rxn
Glucose—> Sorbitol
Aldolase reductase
Aldolase reductase used in polyol pathway is found in what tissues
Lens Retina Schwann cells Liver Kidney Placenta RBC Ovaries Seminal vesicles
Identify enzyme
Sorbitol—>fructose
Sorbitol dehydrogenase
Give 3 tissues that contain enzyme sorbitol dehydrogenase
Liver
Ovaries
Seminal vesicles
T/F
Uronic acid pathway does not produce glucose
T
Alternative pathway for oxidation of glucose
And ascorbic acid in plants and animals
Uronic acid pathway
Absence of this enzyme in guinea pigs and primates renders them incapable of synthesis of ascorbic acid
L gulonolactone oxidase
Essential component of GAGs
Required in detox of insoluble compounds such as
Bilirubin, steroids, morphine and other drugs
Glucuronic acid
Clinical manifestation of essential pentosuria
Increased xylulose in the urine
Xylulose reductase deficiency
T/F Pentose phosphate pathway produces 10 ATP and consumes 2 ATP overall
F
PPP does not produce nor consume ATP
2 products of PPP
NADPH
Ribose 5 phosphate for synthesis of nucleotides
Where does PPP occur?
Cytosol
RBC
Tissues that produce lipids ( liver, adipose, adrenals, thyroid, testes, lactating mamaries
Substrate for PPP
Glucose-6-phosphate
Rate-limiting step for PPP and enzyme
Glucose 6 P—> 6 phosphogluconate
Enzyme: Glucose 6 phosphate dehydrogenase
2 phase of PPP
Oxidative (irreversible)
Non-oxidative (reversible)
Key enzyme and products of oxidative phase if PPP
G6P dehydrogenase
2 NADPH
Ribulose 5 phosphate
Key enzyme and products of non-oxidative phase of PPP
Transketolases( cofactors: thiamine
Transaldolases
Ribose 5 P
F6P
Glyceraldehyde 3 phosphate
Substrate for reductive biosynthesis of fatty acid synthesis and steroids
Glutathione reduction inside RBCs
NADPH
Most common disease producing enzyme in humans
G6PD
Precipitating factors for G6PD
Infection (most common)
Drugs (sulfonamides, primaquine, chloramphenicol)
Fava beans
Altered hemoglobin that precipitates within RBCs
Heinz bodies
Abnormally shaped RBCs due to phagocytic removal of Heinz bodies in spleen
Bite cells
Chronic granulomatous disease is caused by deficiency of what enzyme
NADPH oxidase
Enzyme that converts molecular oxygen into superoxide in leukocytes (especially netrophils and macrophages) used in the respiratory burst that kills bacteria
NDPH oxidase
