BHS 150.2 Biochemistry
Notetaker: Laurel Hammang
Date: 01/25/13, 1st hour
Page1
Overview
Integration of metabolism occurs in the liver
Final 2 pathways:
gluconeogenesis
glycogen metabolism
One function of liver: supply body with glucose
Brain needs glucose constantly, works under insulin-independent mechanism
>3-4 days, brain can use other fuel sources of glucose (starvation)
RBCs need glucose supply for protection/ prevent damage
After ingesting a meal, BG levels rise
stored in liver as glycogen for short term energy
broken down and released as needed when BS levels drop
stored as fat tissue for longer term energy storage
Glucagon increases when insulin levels decrease, vice versa
Insulin works via a receptor tyrosine kinase mechanism
Glucagon works via a metabotropic receptor mechanism
Our bodies can store enough glycogen for 12 hours, after that, our bodies undergo gluconeogenesis:
using other sources such as amino acids and carbs to produce new glucose if glucose levels fall too low
Glycogen Metabolism
Glycogen: storage form of glucose
Made in muscle for muscle use only for quick energy; made in liver for remainder of body
Made with primer: glycogenin
Glucose molecules are linked together via alpha 1,4 glycosidic bonds
When chain gets too long, an alpha 1,4 glycosidic bond is broken and a alpha 1,6 glycosidic bond
so that the chain can be packed tightly and not increase osmotic pressure
Glycogenesis: glycogen synthesis
1. Glucose is phosphorylated with hexokinase (muscle) or glucokinase (liver)
Phosphate group traps the glucose inside the cell (glucose-6-phosphate)
2. Phosphoglucomutase is activated when high levels of G6P
glycolysis pathway is moving too fast to keep up when there is so much G6P present, so this
enzyme (a glycogen synthesis enzyme) is activated
3. Phosphoglucomutase converts G6PGlucose-1-P
4. UDP-Glucose Phosphorylase adds 2 phosphates and a uridine base to glucose to create high energy
phosphate bond
committed step**
adds potential energy to glucose to make another bond
5. Glycogen synthetase transfers glucose from UDP and adds it to glycogen chain with an alpha 1,4 bond
6. Branching enzyme breaks an alpha 1,4 bond and creates an alpha 1,6 to create a new branch on long
glycogen chain.
This compacts the storage structure and decreases osmolarity
Glycogenolysis: break down of glycogen
1. Glycogen phosphorylase breaks an alpha 1,4 bond and adds a phosphate to the glucose
2. Glucose at end becomes glucose 1-phosphate
3. Phosphoglucomutase converts G1P to G6P, which feeds into glycolysis
*this would be the end of the pathway if this were in a muscle cell
*If this were in the liver, the pathway would continue:
4. Glucose-6-phosphatase removes the phosphate from the glucose molecule
when phosphate is attached, glucose is trapped inside the cell
5. Transferase breaks the alpha 1,4 bond of the branched chain and makes a new alpha 1,4 bond at the
end of the long chain, leaving one single glucose where the branch was previously via alpha 1,6 bond
This step must be done because the enzyme is too big to reach the last few bonds between the
branched molecules
6. Debranching enzyme removes the last single-branched glucose from the chain by breaking the alpha
1,6 bond
this frees the glucose molecule so it can be released into the bloodstream for energy
Regulation
Insulin levels are high when glucose levels are high
Activates storage of glucose
Activates a phosphatase (synthetase)
Phosphatase: removes a phosphate group
Glycogen synthetase stimulates glycogen synthesis when a phosphate group is added
Glycogen phosphorylase is inactive when dephosphorylated
*Adding a phosphate doesn’t always activate something
Insulin levels are low when glucose levels are low
Break down of glycogen is stimulated
Activates a kinase (which adds a phosphate)
Glycogen synthetase is inactive when phosphorylated
Glycogen phosphorylase is activated when phophorylated
Clicker Question:
In human cells, glycogen is: Easily broken down to provide glucose residues and is the main storage
form of glucose.