SCT II - Carbohydrate Metabolism II Flashcards
Glycogen
POLYSACCHARIDE
1. Polymer of Glucose
2. α-1,4-glycosidic bonds
Blood-glucose level (mM)
5 mM
What enzyme catalyzes glycogenolysis?
GLYCOGEN PHOSPHORYLASE
Cleaves α-1,4-glycosidic bonds
What does glycogen phosphorylase need?
- Does NOT need ATP = REVERSIBLE
- Uses Inorganic Phosphate
What enzyme catalyzes the conversion of G-1-P to G-6-P?
Glucose-1-Phosphate
to | Phosphoglucomutase
Glucose-6-Phosphate
REVERSIBLE
Which enzyme catalyzes the conversion of G-6-P to Glucose?
Glucose-6-Phosphate
to | Glucose-6-Phosphatase
Glucose
Found in Endoplasmic Reticulum
Name the two debranching enzymes and their funciton
4-α-D-Glucanotransferase
Linearizes branched molecule
Amylo-α-1,6-Glycosidase
Breaks α-1,6-Glycosidic bond
Why do we store glycogen instead of glucose?
Glycogen is not as osmotically active
Why don’t we store excess glucose as fat instead of glycogen?
Glycogen is easier to breakdown than fat, which requires oxygen
Does insulin activate glycogenolysis or glycogenesis?
Glycogenesis, as it dephosphorylates (uses kinases)
Does glucagon activate glycogenolysis or glycogenesis
Glycogenolysis, as it phosphorylates (uses phosphatases)
What is cross regulation in glycogenolysis or glycogenesis
Cross-regulation ensures that both processes don’t take place at the same time
What is the allosteric regulation of phosphorylase in muscle and liver?
LIVER
Mediated by the AMP/ATP ratio
- High AMP = Glycogenolysis
- High ATP = Glycogenesis
MUSCLE
Mediated by glucose
- Glucose inhibits Glycogen Phosphorylase (inhibits Glycogenolysis)
What is the difference when Epinephrine binds to its β-adrenergic receptor or α-adrenergic receptor?
β-adrenergic
1. Increases [cAMP]i
2. cAMP activates glycogenolysis
α-adrenergic
1. Splits PIP2 to IP3 & DAG
2. IP3 & DAG release Ca2+ from ER
3. Ca2+ activates glycogenolysis via activation of glycogen phosphorylase
What is the bifunctional function of epinephrine?
Muscle: induces glycogenolysis & glycolysis
Liver: inhibits glycolysis in liver
How much NADPH is released through pentose phosphate pathway?
2
Name the phases and their products of the pentose phosphate pathway?
Non-Oxidative Phase
2x NADPH
Oxidative Phase
Pentoses & C3 C4 C6 C7 compounds
What is the rate limiting step of the pentose phosphate pathway?
Glucose-6-Phosphate
to | Glucose-6-Phosphate Dehydrogenase
Pentose-Phosphate
NADP+ to NADPH+H
CO2 OUT
What is the difference between NAD and NADP?
NAD
Used for catabolic pathways
NADP
Used for anabolic pathways
In the oxidative stage of the pentose phosphate pathway, how are isomerases and epimerases utilized?
Ribose-5-Phosphate
to | Phosphopentose Isomerase
Ribulose-5-Phosphate
to | Phosphopentose Epimerase
Xylulose-5-Phosphate
What are the uses of NADPH from the pentose phosphate pathway?
RBC & Brain
Reduce glutathione
Fatty Acid Synthesis
Reducing agent
What are the uses of CO2 from the pentose phosphate pathway?
Liver
Uses 20-30% CO2 for metabolic pathways
What are the uses of the pentose phosphate pathway for the muscle?
Muscle
Receive glycolytic intermediates (for glycolysis)
Utilize TCA cycle
How can glucose be converted to fructose?
Glucose
+
NADPH+H+
to | Reduction
to | Aldose Reductase
Sorbitol
+
NADP+
Sorbitol
+
NAD+
to | Oxidation
to | Sorbitol Dehydrogenase
Fructose
+
NADH+H+
Which enzyme is responsible for the formation of lactate? And what are its two subunits?
Lactose Synthase:
1. Galactosyl transferase
2. α-Lactalbumin
Which substance activates lactose synthase?
Prolactin hormone
What substance do we add in order to make an insoluble substance soluble to urea?
UDP-Glucouronic Acid
Which enzyme is used in the oxidation of UDP-glucose to UDP-glucuronic acid?
UDP-Glucose
to | **UDP-Glucose Dehydrogenase*
UDP-Glucuronic Acid
Which enzyme do humans lack in order to form Vitamin C (L-Ascorbic Acid)?
Gulonolacton Oxidase
