Glycolysis, Gluconeogenesis, Fate of pyruvate, Alcohol metabolism, PPP, Glycogen

Glycolysis oxidizes ________ into __________ and generates ______ through ________-______ _______________

Glycolysis oxidizes glucose into pyruvate and generates ATP through substrate-level phosphorylation

Glucose Transporters

• what do they do?

• What are the types and what tissue does it belong to?

• Which transporter is sensitive/dependent on insulin? (need insulin to work)

• Transport glucose across the membrane for glycolysis

• SGLT→ Renal tubules

• GLUT1→ Pancreatic beta cells and hepatocytes

• GLUT2→ Pancreatic cells, hepatocytes and kidney

• GLUT3→ CNS

• GLUT4→ skeletal muscle, cardiac muscle and adipose tissue

• Only GLUT4 (sket/card muscle + adipose) is sensitive to insulin

Is glycolysis anaerobic or aerobic?

Does it occur in the fed or fasting state?

Where does it occur

• Anaerobic

• Fed

• Cytosol

How is glycoslysis regulated?

• Allosteric regulation and hormonal regulation

Aside from ATP, what else does glycolysis generate?

• Precursors for fatty acid biosynthesis, amino acids and nucleotides

What are the phases of glycolysis?

What is the net yield?

• Preparative Phase: 2 ATP’s are invested

• ATP-Generative Phase: Generates 4 ATP and 2 NADHs

• Net yield: (4-2) ATP, 2 NADH, 2 Pyruvate

What steps of glycolysis are heavily regulated?

List the enzyme and how it is regulated allosterically vs hormonally

• 1, 3, 10

• Hexokinase: +Glucose, - G6P

  • Glucokinase: +Glucose, - F6P

• PFK: + ADP, AMP, F2,6-bsp; - ATP, citrate

• PEP kinase: +f1,6-bsp; - ATP, Acetyl CoA, LFCA, Alanine

Hexokinase vs Glucokinase

• Km

• Vmax

• Location

• Hexokinase has a lower Km and lower Vmax

  • Thus it binds glucose better at low concentration while Glucokinase binds better and more at higher concentrations

  • The liver only takes up glucose when there is a surplus

• Hexokinase is everywhere and Glucokinase is in the liver only

Fructose 2,6- bisphosphate feeding vs fasting

• What enzymes converts Fructose 6 phosphate into Fructose 1,6-bisphosphate

• PFK2

Fasting

• Insulin increases and activates PKA, which phosphorylates PFK2 and renders it inactive, thus F2,6-bsp activity decreases

Feeding

• Glucagon is active and activates PPP, which activates PFK2 and increases F2,6-bsp activity

Is there an alternative Fructose metabolism?

What enzymes can be deficient?

• yes

• fructokinase → benign deficiency as it can be easily replaced by the alternative pathway

• Aldolase B → severe effects because there is only this aldolase to perform the reaction

Nonclassical vs. Classical Galacticemia

Nonclassical → galactokinase deficiency causes galactose accumulation which in the eyes gets transformed into galacticitol which causes cataracts

Classical→ galactose 1-phosphate accumulates and causes the same but more serious and early symptoms

What are the fates of pyruvate

What is the main purpose?

aerobic → TCA → E transport chain

anaerobic → Lactate

Regenerating electron carriers (NAD+ from NADH) and creating ATP

Cori Cycle

• what other tissue can use lactate, what does it turn it into?

Tissues such as RBC’s create lactate because they lack mitochondria

They however cannot use this lactate

In the Cori Cycle, this lactate is shuttled to the liver, where it can be used for gluconeogenesis and turned back into glucose so the lactate generating tissues can use it again

• the heart, turns lactate into pyruvate

Gluconeogenesis

• What is the starting substrate?

• What are the precursors to the starting substrate?

• Where does it happen?

• What state does it happen in?

• How many steps are different from glycolysis?, which ones?

• Pyruvate

• Lactate, Amino acids such as alanine

• In the liver

• Fasting state

• 3 steps are different from glycolysis

• Pyruvate → Phosphoenol pyruvate; Fructose 1,6-bisphosphate → Fructose 6 phosphate; Glucose 6 phosphate → Glucose

What are the gluconeogenesis enzymes and their inhibitors

• Pyruvate carboxylase → (+) Acetyl coA (-) ADP

• Phosphoenol pyruvate carboxylase kinase (PECK) → (-) ADP

• Fructose 1-6 bisphosphatase → (-) Citrate and (-) AMP

• Glucose 6 phosphatase → (+) Glucose 6 phosphate

Alcohol and Hypoglycemia

• What reaction causes it

• What is the main presentation of alcoholic patients, why?

Alcohol is converted to acetaldehyde and produces NADH, which tricks the body into thinking they have enough energy and thus stopping TCA and gluconeogenesis

Although there is plenty of NADH, there is no metabolic fuel → glucose → thus the alcoholic patient becomes hypoglycemic (not enough sugar)

Because gluconeogenesis is inhibited, lactic acid builds up and the main presentation of alcoholic patients is lactic acidosis

• What are the other two names for PPP?

• What does the PPP bypass?

• What is the starting substrate?

• Where does the PPP happen in the cell?

• Hexose Monophosphate Shunt and HMP Shunt

• It bypasses the first stage of glycolysis

• The starting substrate is glucose 6 phosphate (G6P)

• In the cytosol

• What does the PPP generate?

• What is it used for?

• Generates NADHP, glycolysis intermediates and nucleic acid precursors

• NADHP is used for nucleotide synthesis, as a glutathione reductase (peroxidase) cofactor, for superoxide mutase reactions, for lysosome phagocytic activities, for nitric oxide synthesis, for fatty acid synthesis (steroid hormones from cholesterol), and for liver detoxification

Explain glucose 6 phosphate dehydrogenase deficiency

What other chemicals can help against oxidative stress?

If this enzyme is deficient, the oxidative phase of PPP cannot happen thus there is insufficient NADPH in the cell, which in turn results in glutathione reductase activity decreasing which means there wont be enough glutathione to prevent peroxide/oxidization damage from happening to RBCs

This causes hemolytic anemia, which means RBC’s are lysed due to oxidization

Ascorbate (Vitamin C), Vitamin E and Beta carotene

Regulation of PPP

• Determine the direction of the pathway depending on the following cell needs

  • NADPH only

  • NADPH and ribose 5 phosphate

  • Ribose 5 phosphate only

  • NADPH and pyruvate

• NADPH only → oxidative to produce NADPH and non-oxidative to go back to oxidative to make more NADPH

• NADPH and ribose 5 phosphate→ both as NADPH requires both and ribose5p requires non-oxidative

• Ribose 5 phosphate only → only non-oxidative because we can start from a glycolysis intermediate since the pathway is reversible

• NADPH and pyruvate → both because NADPH requires both and pyruvate requires non-oxidative as it creates glycolysis intermediates

Glycogen

• What type of glycogen does not get degraded during fasting?

• How are glucosyl units joined?

• How are they branched?

• What does branching allow?

• What are the two types of end, what are their purposes?

• Skeletal muscle glycogen

• Joined by alpha 1,4 glycosidic bonds

• Branched every 8-10 residues by alpha 1,6 glycosidic bonds

• Branching allows fast degradation at multiple points

• Reducing end has the glycogenin which creates the primer for synthesis, Non-reducing end is where UDP glucose is added or G1P is removed

• What are the enzymes of glycogenesis?

• What about glycogenolysis?

• The enzymes of glycogenesis are glycogenin for the primer, glycogen synthase and branching enzyme (transferase)

• The enzymes for glycogenolysis are glycogen phosphorylase and branching enzyme (transferase activity and alpha 1,6 glucosidase activity)

Glycogen Storage Diseases

Type O → glycogen synthase deficiency

Type I → glucose 6 phosphatase deficiency → Von Gierke Disease

Type II → lysosomal alpha amylase deficiency → Pompe Disease

Type III →amylase 1,6 glucosidase deficiency (debranching enzyme)

Type IV → amylase 4,6 glucosidase deficiency (branching enzyme → Andersen’s Disease

Type V → muscle phopshorylase deficiency → McArdle Disease

Type VI → liver phosphorylase → HERs disease

Type VII → PFK1 deficiency → Tarui’s Syndrome

Type XI → GLUT 2 deficiency → Fontani' and Bickel Syndrome

Hormonal Regulation of Glycogen

Glucagon + cAMP + PKA + which inactivates glycogen synthase (by phosphorylation) and activates glycogen phosphorylase (by dephosphorylation)

Insulin + PPP + which inactivates glycogen phosphorylase (by phosphorylation) and activates glycogen synthase (by dephosphorylation)

Allosteric regulation of glycogen

Glycogen synthase → +Glucose 6 phosphate

Glycogen synthase → +AMP or Ca+ and - by ATP, G6P or glucose