Turco 5 Flashcards
Glycogen bonds
Alpha 1,4 - most common
Alpha 1,6 - branch
All glycogen link to
Glycogenin protein
Why make a polymer vs free glucose?
Polymer will not draw as much water
Where is glycogen made?
Liver and muscle
Why branched vs linear glycogen?
Branched is more soluble because more terminal glucoses
Branched can make glycogen available more quickly…need to increase muscle contraction, need ATP, need to oxidize glucose, glucose needs to be available
Why not make more than 1 pound of glycogen?
Glycogen must have water so it would take up too much space
Glycogen problems often manifest as
___megalies
Advantage to TG storage
No water accompanies TGs
Glycogen synthesis process
Glucose enters via GLUT2/4
Made into G-6-P, then G-1-P then UDP-glc
Glycogen synthase forms alpha 1,4 bonds and branching enzyme forms alpha 1,6 bonds
Glucose-6-phosphate important
Can go to glycogen synthesis, pentose phosphate, or glycolysis
Glycogen syntahse regulation
Insulin will increase activity by dephosphorylating
Off by epinephrin and glucagon
Glycogen degradation
Glycogen phosphorylase uses INORGANIC PHOSPHATE to break alpha 1,4
Debranching enzyme hydrolyzes alpha 1,6
This forms glucose-1-P, then glucose-6-phosphate
G-6-P in liver ONLY, forms glucose via glucose-6-phosphatase
Muscle vs. liver with glycogen
Muscle will NOT release glucose back into bloodstream because no glucose-6-phosphatase…liver will
Glycogen phosphorylase mechnaism
Off by insulin via dephosphorylation
On by epinephrine and glucagon
In hard working muscle ONLY
AMP can allosterically activate glycogen phosphorylase
Allosteric effects of AMP in hardowrking muscle
Turn on glycogen phosphorylase
INcrease GLUT4 on muscle surface to increase glucose uptake
Turn on PFK1 to drive glycolysis
Type 1 name, enzyme, structural/clinical consquences
von Gierke’s
G-6-Pase
Severe postabsorptive hypoglycemia, lactic acidemia, hyperlipidemia, hepatomegaly***
Explanation for type 1 symptoms
Hypoglycemia because can’t mobilize glucose from liver
Hyperlipidemia because severe hypoglycemia so glucagon and cortisol secreted and turn on HSL which breaks down TGs and FAs released into blood
Type 2 name, enzyme, clinical
Pompes
Lysosomal alpha galactosidase (acid maltase)
Glycogen grnaules in lysosome and cardiomegaly
Explanation of Type 2
Alpha 1,4 glucosidase affected
Type 3 name, enzyme, clinical
Cori’s
Debranching enzyme
altered glycogen structure and hypoglycemia
Type 4 name, enzyme, clinical
Anderson’s
Branching enzyme
Altered glycogen structure
Type 3 vs. 4
4 - structure will be linear like starch
3 - single glucose stubs that can’t be removed
Type 5 name, enzyme, clinical
McArdle’s
Muscle phosphorylase
Excess muscle glycogen deposition, exercise induced cramps and fatigue
Type 6 name, enzyme, clinical
Hers
Liver phosphorylase
Hypoglycemia (not as severe as von Gierke’s) and hepatomegaly
Why is type 6 not as severe as type 1 hypoglycemia
Can make G-6-P from glycogen or gluconeogenesis
Type 6 interferes with just the glycogen degradation
Type 1 interferes with G-6-P conversion to glucose
Type 5 mech
Child running around, epinephrine released, muscle targeted, glycogen synthase off and phosphorylase on and can’t break down
Myopathic carnitine def vs. type 5
MC def - build up of TGs in muscle cytoplasm (Oil Red O or Sudan Black stain)
Type 5 - PAS stain will show glycogen in cytoplasm
Liver glycogen supply
12 hours sitting
1 hour exercising
RBCs cannot use
FAs or KBs
Methylmalonyl CoA mutase presnetation
Peripheral neuropathy with methylmalonyl acidemia and aciduria
MCAD presentation
Hypoglycemia and dicarboxylic acidemia
Energy of fuels
Carbs - 4
Fat - 9
Alcohol - 7
When does KB synthesis begin?
90 minutes after last meal
FA glucose
FA cannot be made into glucose but can be made from glucose
Where are KBs formed?
Liver
Acylcarnitines indicate
MCAD
Urea cycle and B-oxidation
B-oxidation powers urea cycle so if problem with B-oxidation then hyperammonia
