Biochemistry Lecture No. 21: Metabolism – The Big Picture
Friday October 26 , 2012
-When blood glucose is high, the pancreas secretes insulin. Initially, the flux through glycolysis and citric
acid cycle is high due to the high concentration of substrate (glucose derivatives) and insulin present.
Eventually, the concentration of ATP and other energy indicators of the cell increase, inhibiting glycolysis
and the citric acid cycle. In this state, fatty acid synthesis, the pentose phosphate pathway and
biosynthesis are favoured.
Unfed State (Liver & Adipocytes):
-When blood glucose is low, the pancreas secretes glucagon. Glucose is produced from glycogen and
gluconeogenesis (from amino acids obtained from protein degradation). Adipocytes release fatty acids
from storage and eventually, the liver produces ketone bodies. All of these actions occur simultaneously
when the body is in the unfed state. Biosynthesis is not favoured as the focus of tissues is on energy
conservation. The liver will always pump out some glucose (packaged correctly) in order to sustain the
brain. Muscles on the other hand will not only take in energy of any form, but will also provide a source
of protein when gluconeogenesis.