M2c L19 Flashcards
Explain why glucose is stored as glycogen
When the body doesn’t need to use the glucose for energy, it stores it in the liver and muscles. This stored form of glucose is made up of many connected glucose molecules.
produced in liver and skeletal muscle
Explain the metabolic importance of glycogen stores
to save space in the cell, if there is lots of glucose it requires a lot of energy to transport glucose
Explain why the fate of the end product of glycogen breakdown is different in muscle and in liver
glucose-6-phosphate goes to the muscle to then be used for glycolysis
glucose-6-phosphate goes to the liver, glucose-6-phosphatase changes it to glucose, then the glucose formed can be put into the bloodstream
Outline glycogen synthesis and glycogen breakdown
Occur at different times in the cell
Effectors that activate glycogen synthesis, inhibit glycogen breakdown
Effectors that inhibit glycogen synthesis, activate glycogen breakdown
Several levels of control
Reciprocal regulation
Briefly outline the a regulation of glycogen synthesis and glycogen breakdown
both happen in cytosol
Covalent modification
Phosphorylation, AMP, low blood glucose, activates glycogen phosphorylase
Dephosphorylation, ATP, glucose inactivates glycogen phosphorylase
Phosphorylation inactivates glycogen synthase
Dephosphorylation, high blood, glucose activates glycogen synthase
Briefly describe why glycogen synthesis and glycogen breakdown do not occur at the same time
what activates one deactivates another, they are regulated by hormones, which appear at different times
Outline the metabolic deficiency underlying some glycogen storage diseases
McArdle disease
Absence of muscle glycogen phosphorylase, Exercise intolerance, glycogen cannot be broken down to get glucose
von Gierke disease
In the absence of liver and kidney glucose-6-phosphatase, the liver is unable to put glucose back in the bloodstream, Accumulation of glycogen
why is excess glucose not stored as fat?
Fatty acids take longer to be released from fat, Fatty acid oxidation must have O2, glycolysis can happen with or without O2, Fat cannot be converted to glucose to maintain the blood glucose levels required by the brain
how is glucose activated to be turned into glycogen?
Requires energy from hydrolysis of UTP, UDP-glucose is formed
Glucose has been put in a higher energetic state, now it is ready to be attached to already existing glycogen
(UDP + ATP ←→ UTP + ADP)
When there is a long branch, the tip is being taken off and transferred to a glucose molecule within the branch 1,6 glycosidic bond, 1,4 & 1,6 linkages are joined
explain the glycogen stores in the muscle and in the liver
Muscle glycogen
Fuel reserved for production of ATP in muscle, Exercise mobilizes glycogen (glycogenolysis) cell knows energy will be needed, Muscle lacks glucose-6-phosphatase so glycogen cannot be used to provide blood glucose, important for clearance of glucose from blood after eating for storage, Once glycogen enters the muscle it will stay there until it is metabolized
Liver glycogen
Fuel reserved for maintenance of blood glucose levels, Lasts 12-24 hours on fasting
Liver glycogenesis is important for provision of blood glucose in the early stages of fasting
describe muscle fibers
Red muscle fibers
Rich blood flow, Has myoglobin and lots of mitochondria, Glycogen→ glucose, glycolysis→ pyruvate, then TCA cycle, anaerobic glycolysis
White muscle fibers
Less myoglobin, Fewer mitochondria, Glycogen → lactate, glycolysis only to turn in into lactate
why do animals store glycogen?
Good fuel source that can be quickly mobilized, it is glucose molecules joined by covalent bonds, easy for glycolysis, just need to be hydrolyzed
What is meant by ‘reciprocal’ regulation?
This is the type of regulation that prevents futile cycles. It works to speed up one pathway (or reaction) while preventing the opposite step or pathway from occurring. Frequently the same compound will activate the enzyme of one reaction and inhibit the reverse bypass reaction. Because allosteric regulation responds to the concentration of allosteric effectors, an increase in the amounts of effectors will determine which pathway is active.
