Carbohydrate Metabolism Flashcards
Where does glycolysis occur?
In the Cytosol of all mammalian cells
What is the substrate in glycolysis?
Glucose
What are the end products in glycolysis?
2 molecules of either:
1. Pyruvate
2. Lactate
Name the rate limiting enzyme in glycolysis?
Phosphofructokinase-1
Metabolic Process that is promoted by insulin.
Glycogenesis
Metabolic pathway that is responsible for maintenance of a normal serum glucose concentration in a patient rescued from being trapped under rubble in a building for 4 days.
Gluconeogenesis
What is the reverse process of glycolysis?
Gluconeogenesis
The immediate donor of the phosphoryl group to ADP in the production of ATP during glucose metabolism in erythrocytes.
Phosphoenolpyruvate
Reaction that is unique to gluconeogenesis
Oxaloacetate phosphoenolpyruvate
What is the rate limiting enzyme of gluconeogenesis?
Fructose-1,6-biphosphatase
Differentiate Hexokinase vs Glucokinase
Hexokinase
1. Present in most tissues
2. Can phosphorylate glucose & other hexoses
3. Inhibited by glucose-6-P
4. Low km
5. Low Vmax
6. High affinity
Glucokinase
1. Present only in liver parenchymal cells, Islets cells of the pancreas
2. Can phosphorylate glucose & other hexoses
3. Inhibited by frucose-6-P
4. High Km
5. High Vmax
6. Low affinity
Identify the 2 steps in glycolysis which produce ATP via substrate level phosphorylation.
- 1,3-Biphosphoglycerate to 3-Phosphoglycerate
(Enzyme: Phosphoglycerate kinase) - Phosphoenolpyruvate to Pyruvate
(Enzyme: Pyruvate kinase)
What is the end product of anaerobic glycolysis?
Lactate
1 NADH = ____ ATP
2.5 ATPs
1 FADH2 = _______ ATP
1.5 ATP
Malate aspartate shuttle is primarily seen in which tissues?
Heart muscles & Most tissues
What enzyme joins monosaccharides to form a disaccharide?
Glycosyltransferase
How does the cell ensure that the glucose taken by GLUT remains inside rather than diffusing back out?
Hexokinases irreversibly catalyze the phosphorylation of intracellular glucose to glucose 6-P
How does insulin signaling effect the activity of PFK-1?
Insulin signaling activates PFK-1 activity
What is the significance of 2,3-BPG ?
- Important allosteric effector of Hb
- It decreases the affinity of Hb for Oxygen , thereby increasing O2 delivery to tissues
Why does a deficiency in PDHC activity cause lactic acidosis?
( Pyruvate Dehydrogenase Complex)
Deficiency results to:
1. Rise in pyruvate
2. Upregulate other reactions of pyruvate metabolism such as reduction to lactate by NADH-requiring LDH leading to lactic acidosis
Which Step in Citric Acid Cycle generates GTP?
Substrate -level phophorylation of GDP to GTP occuRs during the conversion of Succinyl coA to Succinate via cleavage of the high energy thioester bond in succinyl coA
What are the major TCA cycle regulation sites?
What are the effectors?
The major sites of cycle regulation:
1.Citrate Synthase - Inh by Citrate, its product.
2. Isocitrate dehydrogenase - Inh by NADH & ATP; Activated by ADP & Calcium
3. Alpha-KGD Complex - Inh by NADH & Succinyl CoA ; Activated by Calcium
What other substrates can be used in gluconeogenesis?
- Glycerol
- Pyruvate
- Alpha-keto acids generated by the degradation of glucogenic amino acids produced from muscle proteolysis
Is gluconeogenesis an endergonic or exergonic process?
Endergonic - uses energy from ATP and GTP hydrolysis
In what 2 tissues and in what subcellular locale is glycogen stored?
Glycogen a branched homopolymer of glucose is stored in the cytosol of liver and muscle cells primarily.
What is the role of glucose 6- phosphatase in glycogenolysis?
hydrolyzes glucose 6-p in the liver and the kidneys, generating free glucose that enter the blood stream
Is the rate of fructose metabolism faster or slower than of glucose?
Fructose metabolism is faster because it bypasses the key rate-limiting enzyme of glycolysis , PFK-1 .
What is the fate of the ribulose 5-P product of the oxidative reactions?
The ribulose-P can be reversibly isomerized to ribose 5-P and used in Purine and Pyrimidine nucleotide synthesis & xylulose 5-P that is used in sugar interconversions.
Andersen disease is a deficiency of which enzyme?
Branching enzyme
Hers disease is a deficiency of which enzyme?
Liver phosphorylase
Pompe Disease is deficiency of which enzyme?
Lysosomal acid maltase
Enzyme deficient in a infant presenting with vomiting, night sweats, tremors after ingesting fruit juices with positive reducing sugar in urine but negative for glucose.
Aldolase B deficiency- Hereditary Fructose Intolerance
Characteristics of this step in glycolysis catalyzedd by phosphofructokinase and gluconeogenesis by fructose-1,6-biphosphatase?
Phosphofructokinase is inhibited more or less completely by physiologic concentrations of ATP
This is the most common disease producing enzyme abnormality in humans
Glucose-6-Phosphate Dehydrogenase Deficiency
This transporter on the luminal side of enterocytes absorbs glucose or galactose.
SGLT1
Effects of insulin on GLUT4 transporter resulting in reduced serum glucose ?
It promotes GLUT 4 mobilization to the plasma membrane
Among the transporters, only which requires insulin?
GLUT-4
This type of glucose transporter is found within the small intestine and spermatocytes.
GLUT-5
Ability to produce lactose in breastmilk of a female with classic galactosemia due to GALT deficiency
Galactose can be produced from a glucose metabolite by EPIMERIZATION
NADPH produced from the HMP shunt is needed in the ff pathways? (5)
- Reductive reactions for FA and steroid synthesis
- Reduction of glutathione
- NO synthesis
- Respiratory burst
- CYP 450 reactions
Disease, cherry red spot on macula + (+) hepatosplenomegaly?
Nieman Pick - Sphingomyelinase deficiency
Disease cherry red spots ; (-) hepatosplenomegaly
Tay sach’s : Hexosaminidase A
Enzyme deficient in Gaucher’s ?
Glucocerebrosidase
Enzyme deficient in Krabbe’s?
Galactocerebrosidase
