Lecture 1 Metabolic pathways in the liver and fuel distribution to tissues Flashcards
What does the portal vein in the liver do with regards to metabolism?
It brings nutrients into the liver.
Do hepatocyte enzymes turn over quickly or slowly?
Quickly
What is the function of the GLUT2 transporter?
It allows passive diffusion of glucose through the hepatocyte membrane.
What does glucokinase (Hexokinase IV) do?
It facilitates phosphorylation of glucose to glucose-6-phosphate.
What effect does glucokinase’s high Km have?
It means that it needs high substrate concentrations to achieve maximum reaction velocities. This means that G-6-P isn’t made when glucose is in low concentration. This allows the glucose to go to other tissues where it is needed more.
Is glucose inhibited by G-6-P? What effect does this have?
It is not inhibited by G-6-P. This means that G-6-P can be made continually.
What is meant when G-6-P is referred to as the ‘transfer station’ in the liver?
It means that many sugars such as fructose, galactose and mannose are all converted to G-6-P in the liver which then has multiple fates depending on the needs of other tissues.
Name 5 fates available to G-6-P in the liver.
Dephosphorylation to yield free glucose to send to other tissues.
Made into liver glycogen.
Enter glycolysis to form acetyl-CoA then ATP for use by the hepatocytes.
Enter glycolysis to form acetyl-CoA to be made into fatty acids and later TAGs.
Enter the pentose phosphate pathway to yield NADPH and ribose-5-phosphate.
Name 3 fates available to amino acids in the liver.
Make into proteins for liver and other tissues.
Make into hormones, nucleotides.
Make into CAC intermediates or pyruvate for gluconeogenesis or convert to acetyl-CoA or liver cell energy or conversion to fatty acids then TAGs.
Name 5 fates available to fatty acids in the liver.
Use FAs to synthesise liver lipids.
Oxidise FAs to acetyl-CoA and NADH to then yield ATP, or ketone bodies, or cholesterol.
Convert FAs to phospholipids.
Convert FAs to TAGs for storage.
Carry FA to heart and muscle for oxidation.
What protein carries FAs in the bloodstream and why?
Albumin because FAs are hydrophobic and therefore insoluble in the blood. Albumin hides the FAs within itself and allows for transport.
What is simple diffusion?
Diffusion of a nonpolar compound through the membrane down its electrochemical gradient.
What is facilitated diffusion?
Diffusion through a channel down its electrochemical gradient.
What is primary active transport?
Transport against electrochemical gradient, powered by ATP.
What is secondary active transport?
Transport against electrochemical gradient driven by concurrent movement of ion down its electrochemical gradient.
