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Nutrition and Metabolism > The Liver and Gluconeogenesis > Flashcards

The Liver and Gluconeogenesis Flashcards

1
Q

Definition of glycolysis

A

Process of breaking down of glucose in the cytoplasm with or without oxygen

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2
Q

Definition of glycogenolysis

A

Breakdown of glycogen to glucose 1 phosphate by the sequential removal of glucose monomers via glycogen phosphorylase

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3
Q

Definition of gluconeogenesis

A

Metabolic process by which organisms produce sugars for catabolic reactions from non carbohydrate precursors

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4
Q

Describe the glucose requirements

A

Continuous
Glucose is the preferred fuel source for all tissues
Some tissues have a continuous glucose dependence

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5
Q

Average blood glucose conc and what happens if its too high or too low

A

Physiological circulating [glucose] = 3.9-6.2mM
Average fasting 4.4-5mM for most adults

2.5> = coma/death
If it rises for an extended time, dehydration, body tissue wasting and eventually death occurs

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6
Q

Roles of glucose

A

Energy source

Glucose => Pyruvate => 2ATP
Glucose => CO2 + H2O => 31 ATP
NADPH source
Needed for synthetic reactions and drug metabolism
Pentose sugar source (nucleotides, DNA)
Source of C for other sugars and glycoconjugates (mannose, galactose, glucuronic acid)

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7
Q

Advantages of glucose as a metabolic fuel

A

Water soluble, does not need a carrier in circulation
Can cross the blood brain barrier
Can be oxidized anaerobically

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8
Q

Disadvantages of glucose as a metabolic fuel

A

Relatively low yield of ATP/mole compared to FA
Osmotically active
High concentrations can directly damage cells/lead to accumulation of toxic byproducts (fructose, sorbitol)

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9
Q

Pathways involving glucose

A

Predominant pathways involving glucose are different in different tissues
All tissues use glucose
Only the liver can provide glucose for other tissues

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10
Q

Role of glucose in skeletal muscle
Main pathways
Function of each pathway

A

Glycolysis, anaerobic muscle contraction
Glycolysis/TCA, energy
Glycogen synthesis and degradation , energy store for muscle contraction

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11
Q

Role of glucose in heart/brain
Main pathways
Function of each pathway

A

Glycolysis/TCA, ENERGY

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12
Q

Role of glucose in adipose
Main pathways
Function of each pathway

A

Glycolysis

Production of glycerol phosphate for TAGS

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13
Q

Role of glucose in eRBC
Main pathways
Function of each pathway

A

Glycolysis, Energy

Pentose phosphate pathway, NADPH generation

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14
Q

Role of glucose in the liver
Main pathways
Function of each pathway

A

Glycolysis/TCA in fed state, acetyl CoA production =>FA synthesis
Pentose phosphate pathway, NADPH generation, pentoses
Glycogen synthesis/glycogenolysis, glucose glorage for other tissues
Gluconeogenesis, glucose for other tissues

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15
Q

Sources of blood glucose

A 
Diet (does not last long)
Liver glycogen (lasts a while)
Liver gluconeogenesis (lasts the longest)
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16
Q

Gluconeogenesis

A 
Occurs in carbohydrate deprivation
Glucose synthesized from non carbohydrate sources in the liver
Lactate
Glycerol
Other monosaccharides
Glucogenic AA
17
Q

Gluconeogenesis is not the reversal of glycolysis

Describe the pathway from pyruvate to glucose

A

3 irreversible reactions in glycolysis must be bypassed

  • Pyruvate =(pyruvate carboxylase)=> oxaloacetate
  • Oxaloacetate =(malate dehydrogenase)=> malate (as oxaloacetate cant pass through the mitochondrial membrane)
  • Malate =(malate dehydrogenase)=> oxaloacetate
  • Oxaloacetate =(phosphoenolpyruvate carboxykinase)=> phosphoenol pyruvate
  • Fructose 1,6 biphosphate =(fructose 1,6 biphosphatase)=> fructose 6 phosphate
  • Glucose 6 phosphate =(glucose 6 phosphatase)=> glucose!
18
Q

2 mechanisms that are activated in gluconeogenesis

A

Metabolism of substrate

  • glycerol from fat breakdown
  • AA from muscle protein breakdown

Activation of enzymes

  • Glucose 6 phosphatase
  • fructose 1, 6 biphosphatase by citrate
  • PEPCK
  • pyruvate carboxylase by acetyl CoA
19
Q

The Cori cycle (lactate) and glucose alanine cycle
What is the function of the Cori cycle?
What is the function of the glucose alanine cycle

A

Glucose from the liver is transported to the muscle
Glucose => G6P => Pyruvate => Acetyl CoA
Pyruvate => Alanine and lactate

Alanine and lactate => pyruvate in the liver, used in the TCA cycle
G6P can be reformed into glucose (gluconeogenesis)

Cori used to process lactate after exercise
Alanine formed from muscle degradation for energy needs

20
Q

How is blood glucose maintained

Why does it need to be maintained

A

Insulin, glucagon, adrenaline, cortisol and glucose all signal and coordinate activity of
liver
adipose
muscle

Maintain physiological [blood glucose] needed to preserve brain function

21
Q

Insulin vs glucagon

What is their function

A

Insulin, anabolic hormone, promotes synthesis and storage

Glucagon, catabolic hormone, promotes degradation of stored fuel

22
Q

4 main metabolic effects of insulin on liver

A

Inhibition of gluconeogenesis
Activation of glycogen synthesis (active glycogen synthase)
Increase FA synthesis and lipid assembly
Increased AA uptake and protein synthesis

23
Q

3 main metabolic effects of insulin on muscle

A

Increased glucose uptake by increased no of GLUT4
Increased AA and protein synthesis
Activation of glycogen synthesis (glycogen synthase active)

24
Q

What are the 3 main effects of glucagon on the liver

A

Increased [blood glucose]
increased glycogenolysis and gluconeogenesis (in liver)

Increase in circulating fatty acids and ketone bodies
increase in adipose tissue lipolysis, increased FA oxidation in liver and ketone body formation

Decrease in plasma AA
increase in liver uptake for gluconeogenesis

25
Q

Metabolic pathway of RBC and brain

A

RBC
-glycolysis => lactate

Brain
-glycolysis => TCA => OX PHOS all the time

26
Q

WHERE DOES GLUCONEOGENESIS OCCUR

A

Only the liver

27
Q

Why are fatty acids unable to be glucogenic?

A

Pyruvate => Acetyl CoA is an irreversible reaction

28
Q

What is the main source of glucose in gluconeogenesis?

A

Lactate

Nutrition and Metabolism (14 decks)

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