Liver and gluconeogenesis Flashcards
Why is glucose used?
The requirement for glucose is continuous
* Glc is the preferred fuel source for all tissues
* some tissues have a continuous dependence on glucose
What is the blood glucose concentration in the human body?
- physiological circulating glc concentration 3.9-6.2 mM
- average fasting 4.4-5 mM for most adults
- if it drops to 2.5 or less coma and death can result
- if it rises for an extended time, dehydration, wasting of body tissue and eventually death will result
What is the roles of glucose?
- It is a source of energy
glucose → pyruvate gives 2 ATP
glucose → CO2 + H2O gives 31 ATP - it is a source of NADP
- needed for synthetic reactions (fatty acids, steroids) and drug metabolism
- it is a source of pentose sugars for for synthetic reactions (nucleotides, DNA )
- it is a source of carbon for other sugars and glycoconjugates (mannose,galactose, glucuronic acid
What are advantages of glucose as a metabolic fuel?
- Water soluble , so does NOT require a carrier in the circulation
- can cross the blood-brain barrier
- can be oxidised anaerobically
What are disadvantages of glucose as a metabolic fuel?
- relatively low yield of ATP/mole compared to fatty acids
- osmotically active
- In high concentrations can directly damage cells or lead to accumulation of toxic by-products (fructose, sorbitol)
What are Pathways involving glucose
- all tissues use glucose
- the liver can provide glc for other tissues
What is the role of glucose in skeletal muscle?
glycolysis - Anaerobic muscle contraction
Glycolysis/TCA cycle - energy
Glycogen synthesis and degradation - Energy store for
muscle contraction
What is the role of glucose in heart/brain muscle?
Heart/brain
Main Pathway - Glycolysis/TCA
Function - ENERGY
What is the role of glucose in Adipose tissue?
Adipose tissue
Main pathway - glycolysis
Function - Production of glycerol P’ for TAGS
What is the role of glucose in Erythrocyte?
Tissue - Erythrocyte
Main pathway - glycolysis
Pentose phosphate pathway
(shunt)
Energy - NADPH
What is a role of glucose in the liver?
Function of the pathways?
What are the sources of blood glc?
- Diet
- Liver Glycogen
- Liver gluconeogenesis
What is Gluconeogenesis?
In conditions of carbohydrate deprivation glc is synthesised from non-carbohydrate sources in the liver
* Lactate
* glycerol
* other monosaccharides
* glucogenic amino acids (all except leu, lys)
* NOT FROM FATTY ACIDS
What is the irreversible reaction of gluconeogenesis?
gluconeogenesis is not simply the reversal of glycolysis
There are 3 irreversible reactions in glycolysis that must be bypassed.
They are catalysed by:
* hexokinase/ glucokinase
* phosphofructokinase
* pyruvate kinase
- all in the cytosol
Role of Pruvate Kinase?
pyruvate kinase catalyses the conversion of PEP to pyruvate
pyruvate carboxylase and PEP carboxykinase are needed for the conversion of pyruvate to PEP in gluconeogenesis