CARBOHYDRATES Flashcards
Rapoport-Luebering shunt pathway
- Found in RBCs where the reaction catalyzed by phosphoglycerate kinase is bypassed
-
1,3-BPG → 2,3-BPG
- Enzyme: Bisphosphoglycerate mutase
Lysosomal acid maltase deficiency
Pompe disease (Type II)
- ↑ Glycogen in lysosomes
- Juvenile onset: hypotonia, death from heart failure by age 2
- Adult onset: muscle dystrophy
Essential fructosuria
Fructokinase deficiency
• Fructose → Fructose-1-P
• Enzyme: Fructokinase or hexokinase
What is the substrate of PPP?
Glucose-6-phosphate
Liver phosphorylase deficiency
Hers disease (Type VI)
• Hepatomegaly, mild hypoglycemia
* No liver Glycogen Phosphorylase, so no liver glycogen breakdown = glycogen accumulates there = hepatomegaly
Discuss this graph
most common enzyme defect in glycolysis?
Pyruvate kinase
- converts PEP to pyruvate
- presents as hemolytic anemia
2 steps in glycolysis produce ATP via substrate-level phosphorylation
-
1,3-Bisphosphoglycerate → 3-Phosphoglycerate
- Enzyme: Phosphoglycerate kinase
-
Phosphoenolpyruvate → Pyruvate
- Enzyme: Pyruvate kinase
Differentiate PFK-1 and PFK 2
non-reducing sugar
Sucrose
Discuss the process of GLUCONEOGENESIS
Rate-limiting step of glycogenolysis
Shortening of glycogen chains
Enzyme: Glycogen phosphorylase
What type of glycolysis is utilized by:
- Cells with mitochondria
- Cells with adequate supply
AEROBIC GLYCOLYSIS AKA Embden-Meyerhof-Parnas Pathway
End product: Pyruvate
Heinz bodies and bite cells are found in what disorder?
G6PD deficiency
Second Phase of PPP
Nonoxidative and Reversible
- Enzymes:
- Transketolases (Cofactor: Thiamine)
- Transaldolases
- Products:
- Ribose-5 phosphate
- Fructose-6phosphate
- Glyceraldehyde-3phosphate
NADPH functions
o Reductive biosynthesis of fatty acids and steroids
o Glutathione reduction inside RBCs
o Cytochrome P450 monooxygenase system
o Oxygen-dependent bactericidal mechanism of WBCs
o Synthesis of nitric oxide
- Flatulence and diarrhea after ingestion of dairy products
- Seen in up to 90% of adults of African or Asian descent are lactase-deficient
Lactose intolerance
Lactase deficiency
GLUT 1 is found in ___
Brain, kidney, colon, placenta, RBC
Mono-saccharides
(Hexoses)
Glucose, Fructose, Galactose and mannose
- Isomers that differ in configuration around only one specific carbon atom (except the carbonyl carbon)
- Examples: glucose and galactose (differ only in position of –OH in C4), glucose and mannose (differ only in position of –OH in C2)
EPIMERS
Mono-saccharides
(Pentoses)
Ribose, Ribulose and Xylulose
What type of glycolysis is utilized by:
- Cells without mitochondria
- Cells without sufficient O2
ANAEROBIC GLYCOLYSIS
End product: Lactate
Muscle phosphorylase deficiency
McArdle syndrome (Type V)
Poor exercise tolerance, muscle cramps and myoglobinuria but no lactic acidosis, high muscle glycogen
* because muscle lacks the phosphorylase enzyme, it cannot retrive glucose residues from glycogen, leading to cramps.
* No GP in the muscle, (GP is the rate-limiting enzyme in
glycogenolysis), so no GP, no muscle glycogen breakdown
GLut 4 is found in ___
Heart and skeletal muscle, adipose tissue
“FHM” fat, heart, muscle
Purpose of PENTOSE PHOSPHATE PATHWAY Also known as the Hexose MonoPhosphate shunt
o Produces NADPH
o Produces ribose 5-phosphate required for biosynthesis of nucleotides
o Provides a mechanism for the metabolic use of 5-carbon sugars
o Take Note: Neither produces nor consumes ATP
- Characterized by Deficiency in NADPH oxidase
- Converts molecular oxygen into superoxide in leukocytes (especially neutrophils and macrophages) and used in the respiratory burst that kills bacteria
- Severe, persistent, and chronic pyogenic infections caused by catalase-positive bacteria
CHRONIC GRANULOMATOUS DISEASE
*In the absence of NADPH oxidase, neutrophils will not be able to convert oxygen to superoxide, which is used to kill bacteria that they’ve engulfed.
Insulin is needed in ___
GLUT 4 transporter (“FHM” - fat, heart, muscle)
Important products of PPP
NADPH and Ribose-5-phosphate
Most common cause of congenital lactic acidosis
Pyruvate dehydrogenase deficiency
- X-linked dominant
- ↑ lactate (anaerobic glycolysis) + ↓ acetyl CoA (citric acid cycle) leads to brain deprived of acetyl CoA leading to psychomotor
- retardation and death
- Treat with ketogenic diet
Where does TCA occur?
- In all cells with mitochondria
- Mitochondrial matrix
- Except: succinate dehydrogenase (inner mitochondrial membrane)
What are the fates of Pyruvate?
Glucose 6 phosphatase is present in ___
The liver but not in the muscle.
The end product of glycogenolysis in the muscle is Glucose - 6 - Phosphate
GLUT 5 is found in ___
Small intestine (lumen)
for the Absorption of fructose
ATP yield of Glycolysis
This final step is shared by gluconeogenesis and glycogenolysis, because both pathways yield glucose.
GLUCOSE-6-PHOSPHATE → GLUCOSE
Enzyme: Glucose 6-phosphatase
Classic galactosemia
(Galactose-1-phosphateuridyltransferase deficiency)
Galactose-1P + UDP-glucose → UDP-galactose + Glucose-1P
Enzyme: Galactose-1-P uridyl transferase (GALT)
- Autosomal recessive
- More severe symptoms
- Galactosemia, galactosuria, cataracts, diarrhea, vomiting, jaundice
- Poor growth in children, severe mental retardation, and liver damage
- Premature ovarian failure in females
Hexokinase and glucokinase are ____
Isozymes
Which step is rate-limiting step of glycolysis?
Fructose-6-phosphate → Fructose-1,6-bisphosphate
Enzyme: Phosphofructokinase-1
Differentiate hexokinase from Glucokinase.
- Functional group is a ketone
- Carbonyl carbon at any other position
- Example: fructose
Ketose
What is the rate-limiting step of Glycogenesis?
Elongation of glycogen chains i.e., creation of α-(1,4) glycosidic bonds Enzyme: Glycogen synthase
- Optical isomers or stereoisomers
- Pairs of structures that are mirror images of each other
- The enantiomers are designated as a D-sugar (Dextrorotatory) and an L-sugar (Levorotatory)
- D-sugars are more common
ENANTIOMERS
What are the substrates for gluconeogenesis?
o Intermediates of glycolysis and the TCA
o Lactate through the Cori Cycle
o Glycerol and propionyl CoA from triacylglycerols
o Carbon skeletons of glucogenic amino acids
In this cycle, Lactate formed by glycolysis in skeletal muscle is transported to the liver where it is converted back to glucose through gluconeogenesis
Cori cycle
Branching enzyme deficiency
Andersen disease (Type IV)
Hepatosplenomegaly,↑ polysaccharide with few branch points, death from heart or liver failure before age 5
What are the 5 coenzymes of Pyruvate dehydrogenase (pyruvate to Acetyl CoA)?
o Thiamine pyrophosphate (from vitamin B 1 )
o FAD (from vitamin B 2 )
o NAD+ (from vitamin B 3 )
o Coenzyme A (contains pantothenic acid) (from vitamin B 5 )
o Lipoic acid (antioxidant)
Carbohydrates that can act as reducing agents because they have an aldehyde group or a free ketose group
REDUCING SUGARS
Insulin is not needed in ____
RBc, intestinal mucosa, liver, brain
How may ATPs will be produced for every molecule of ACetyl CoA from tha TCA cycle?
Galactokinase deficiency
Galactose → Galactose-1-P
Enzyme: Galactokinase
- Autosomal recessive
- Relatively mild symptoms
- Galactosemia and galactosuria
• Cataracts in early childhood
Where does PPP occur?
o RBCs and tissues that produce lipids (liver, adipose tissue, adrenals, thyroid, testes, lactating mammaries)
o In the cytosol
- Intolerance of ingested sucrose
- Seen in about 10% of the Inuit people of Greenland and Canada
Sucrase isomaltase complex deficiency
Glucose + Galactose
lactose
Disaccharides
Which step is rate-limiting in TCA cycle?
Isocitrate → α-ketoglutarate
Enzyme: Isocitrate dehydrogenase
Glucose-6-phosphatase deficiency
Von Gierke disease (Type Ia)
↑ Glycogen in liver and renal tubule cells, hypoglycemia, lactic acidosis, ketosis, hyperlipemia
*because you do not have glucose-6-phosphatase, you cannot produce glucose, resulting to hypoglycemia.
Most common type of glycolysis.
Embden-Meyerhof-Parnas pathway
Glucose → Sorbitol
Enzyme?
Sorbitol → Fructose
Enzyme?
Aldose reductase
Sorbitol dehydrogenase
Discuss the pathway for glycolysis
What is the substrate and the end-products of glycolysis?
Glucose to 2 molecules of either pyruvate or lactate
3 to 10 sugar units
Where does glycogenesis occur?
o Liver and muscle
o Cytosol
Complete oxidation of Glucose will yield how many ATPs?
- Functional group is an aldehyde
- Carbonyl carbon at the end
- Examples: glucose, galactose, mannose
What are the products of GLYCOGENOLYSIS?
o Glucose in liver
o Glucose-6-phosphate in muscle
Discuss TCA/Kreb’s/ Citric Acid Cycle
Reactions catalyzed by carboxylase and requires BIOTIN as a cofactor.
Pyruvate → Oxaloacetate (Pyruvate carboxylase)
Acetyl CoA → Malonyl CoA (Acetyl CoA carboxylase)
Propionyl CoA → Methylmalonyl CoA (Propionyl CoA carboxylase)
GLUT 3 is found in ____
Brain, placenta, kidney
What is the rate limiting step in Gluconeogenesis?
Fructose 1,6-bisphosphate → Fructose 6-phosphate
Enzyme: Fructose 1,6-bisphosphatase
SGLT 1 is found in ___
Small intestine and kidneys
Which step is rate-limiting in PPP?
Glucose-6-phosphate → 6-phosphogluconate
Enzyme: Glucose-6-phosphate dehydrogenase (G6PD)
Protein that serves as a primer for glycogen synthesis when glycogen is completely depleted
GLYCOGENIN
What are the products of TCA?
- 2 CO2
- 1 GTP
- 3 NADH
- 1 FADH2
Debranching enzyme deficiency
Cori disease (Type IIIa)
Fasting hypoglycemia, hepatomegaly in infancy, ↑ limit dextrin, muscle weakness
Where does Gluconeogenesis occur?
o Occurs in the liver (90%) and the kidney (10%)
o Occurs in both mitochondria and cytosol
Anaerobic Glycolysis
First Phase of PPP
Oxidative and Irreversible
- Glucose-6-phosphate dehydrogenase
- Products: 2 NADPH and Ribulose-5 phosphate
Glucode and Galactose are ___ epimers
C4 epimers
Glucose + Glucose
Maltose
can undergo interconversion (from α to β, and vice versa) without energy expenditure or the need for enzymes, in a process called mutarotation
ANOMERS
- Compounds that have the same chemical formula
- Glucose, fructose, galactose, and mannose are all isomers of one another because they have the same formula C 6 H 12 O 6
ISOMERS
The sugar units are linked together by ____
glycosidic bonds
Glucose and Mannose are ___ epimers
C2
What are the 2 shuttles for transport of NADH in the ETC?
- 1 step in glycolysis produces NADH
- This is an oxidation reaction that passes electrons to NAD+ to make NADH
Glyceraldehyde-3-Phosphate → 1,3-Bisphosphoglycerate
Enzyme: Glyceraldehyde-3-phosphate dehydrogenase
What is the substrate for TCA?
Acety CoA
GLUT 2 is found in ___
Liver, pancreas, small intestine (basement membrane), kidney
Hereditary fructose intolerance
Aldolase B deficiency
• Fructose-1-P → DHAP + Glyceraldehyde
• Enzyme: Aldolase B
- Profound hypoglycemia and vomiting after consumption of fructose or sucrose
- Jaundice, hemorrhage, hepatomegaly and liver failure, renal dysfunction, hyperuricemia, lactic acidosis, and death
- Symptoms appear after weaning from milk
Polysaccharides
> 10 sugar units
Glycogen, Starch, Cellulose, Inulin
where does glycolysis occur?
In the cytosol of all mammalian cells
Glucose + Fructose
sucrose
