Carbohydrate Metabolism Glucose Regulation and Formation Flashcards
Anabolism
energy-requiring synthesis of more complex products
Catabolism
energy-yielding degradation of complex precursors
Pancrease
cell: islet cells
metabolic function: releases insulin, glucagon, and numerous hormones
Liver
Cell: hepatocyte
Metabolic function: maintains metabolic homeostasis by normalizing blood glucose and synthesizing and degrading glycogen, glucose, FAs and NAs, proteins, and ketone bodies
Muscle
Cell: skeletal, smooth, and cardiac muscles
Metabolic function: utilizes glucose, FAs and AAs to fuel muscular activity
Adipose Tissue
Cell: adipocyte
Metabolic function: stores energy via lipids very static
Key regulators
insulin glucagon epinephrine (adrena medulla) glucose ATP/AMP
Major fates of glucose, four of them ***
source of ATP (pyruvate) energy storage (glycogen) molecular precursor (ECM and cell wall polysacchs. structural backbone (ribose 5-phosphate)
Major pathways of Carbohydrate metabolism
- respiration –> forms ATP
- Storage –> forms glycogen, glucose
- Regenerative–> forms glucose (in liver)
- Synthetic–> forms NAs, lipids and AAs
Some metabolic pathways are exclusive which ones are they?
glycolysis and gluconeogenesis (liver)
glycogenesis and glycogenolysis
if one is occurring then the other cannot happen at the same time
Aerobic catabolic pathways
Citric acid cycle, and ETC(oxidative phosphorylation)
also glycolysis
anaerobic pathways
glycolysis
Glycogen stores intracellular glucose
structures and where they are found
branched glucose homopolysaccharide
primary mechanism for intracellular energy storage
primarily found in the liver(10% dry weight) and muscle(2%)
necessary to maintain cellular osmolarity
forms large molecular complexes stored in granule organelles
What starts the formation of glycogen and how many glucose molecules per chain in glycogen?
glycogenin
12 to 14 glucose residues
Glycogen pathway
1.glucose-> glucose 6-phosphate
2.glucose 6-phosphate -> glucose 1- phosphate
3.glucose 1-phosphate -> uracil diphosphate glucose
4.uracil diphosphate glucose -> glycogen chain
5.glycogen chain -> glycogen particle
enzymes
1. hexokinase
2. phophoglucomutase
3. UDP-glucose pryphosphorylase
4. glycogen synthase (point of regulation)
5. glycogen branching enzyme
Glycogenolysis
- Glycogen is broken down via glycogen phosphorylase and releases glucose-1-phosphate molecules
- once about 4 residues are left a transferase activity of debranching enzyme takes 3 of the four glucose molecules and puts them on the end of the chain.
- the one remaining glucose is cut via (alpha 1-6 glucosidase activity of debranching enzyme) and a free glucose is released.
What are the two fates of the glucose 1-phosphate molecules from the glycogen?
- phosphoglucomutase converts it to glucose 6-phosphate and off the glycolysis
- ONLY in LIVER!! the Glucose 6-phosphate can enter the liver and go to the ER of the liver where the enzyme Glucose 6-phosphatase removes the phosphate and releases the free glucose to the blood.
Glycogen regulation at glycogen synthase
-regulated by GSK3
-When glycogen synthase is phosphorylated it is inactive and is in the glycogen synthase b form
-When insulin is present is inactivates GSK3 and activates PP1 where glycogen synthase is activated.
–it is also activated by glucose-6-phosphate and glucose
inactivated by glucagon and epinephrine
Glycogen phoshorylase regulation
phosphorylase b is inactivated and is not phosphorylated but glucagon and epinephrine activate phosphorylase and lead to it being phosphorylated and activated.
kind of the opposite of glycogen synthase regulation with being phosphorylated or not
insulin signaling
activates glycogenesis via
IRS-1 which activates PI3K to activate PIP2 to activate PIP3 which in turn activates PKB which activates GSK3 to activate glycogen synthase
insulin activates GLUTs, hexokinase, and glycogen synthase
Epinephrine and glucagon in the liver
increase glycogenolysis and gluconeogensis to increase blood glucose
glycolysis is decativated
**goal is to create more glucose 6-phosphate for the blood
epinephrine in the muscles
increases glycogenolysis and glycolysis so that the liver can get more glucose to the blood
phosphorylase allosteric regulators
glucose (slows glycogenolysis)
insulin ( increases glycogenolysis)
gluconeogensis where is occurs and the process
occurs in all cells but mostly in the liver
lactate or pyruvate is converted to glucose
**energetically costly 4 ATP 2 GTP 2 NADH + H
