Glycogen and Carb metaolism Flashcards
Glycogenin, Glycogen Synthase, Branching Enzyme
polymerization of glucose (glycogen synthesis)
First step of glycogen synthesis
activate glucose
Primer protein for glycogen synthesis
Glycogenin
Transfers glucose from UDP-glucose to non-reducing ends forming alpha(1,4) glycosidic bonds
Glycogen Synthase (glycogen synthesis)
Cleaves off short fragments from alpha (1,4) chains and connects to make alpha (1,6) linkages
Branching Enzyme (glycogen synthesis)
Location of glycogen synthesis
cytosol
Releases glucose-1-phosphate from glycogen
glycogen phosphorylase (glycogen degradation)
Transfers branches and releases glucose
debranching enzyme (glycogen degradation)
Beta cells of pancreas
insulin
Alpha cells of pancreas
glucagon
Hormone released from adrenal medulla
epinephrine
Phosphorylation of glycogen phosphorylase
becomes active (glycogen degradation)
Phosphorylation of glycogen synthesis
becomes inactive
What organ synthesizes glycogen but do not respond to glucagon? They lack what enzyme that releases glucose to bloodstream?
muscles, lack glucose-6-phosphatase (G6P»Glucose)
Main source of blood glucose before breakfast.
glucoNEOgenesis
Main source of blood glucose during well-fed state.
glycogen degradation
muscle weakness/ exercise intolerance
enlarged liver
general symptoms of glycogen storage disease
defect in glucose-6-phosphatase
Type I GSD- van Gierke disease
inability to convert G6P to glucose for release to bloodstream
acid maltase deficiency
Type II GSK - Pompe disease
glycogen accumulation due to deficiency in the enzyme that catalyzes glycogen breakdown in lysosomes
defective glycogen debranching enzyme
Type III GSD - Cori disease
defective glycogen phosphorylase in muscles
Type IV GSD - McArdle disease
unable to use stored glycogen
buildup of NADH, CAC is inhibited, gluconeogenesis is inhibited (no pyruvate and OAA from CAC). NADH gets used up by lactate dehydrogenase and malate dehydrogenase
alcohol metabolism makes NADH
- causes lactic acidosis and hypoglycemia (inhibition of gluconeogenesis)
gel-like component of ECM comes from what?
proteoglycans (acidic and basic)
large molecules that consist mainly of acidic modified sugars
proteoglycans
where does glycosylation of proteins occur?
ER and Golgi
facilitate the excretion of poorly water-soluble metabolites
acidic carbohydrates are abundant in ECM
N-acetylglucosamine added
Heparan Sulfate
Keratin Sulfate
N-acetylgalactosamine added
Chondroitin Sulfate
Both sugars added
Dermatan Sulfate
Heparin
no sugar added
hyaluronic acid
degradation of proteoglycans
in lysosomes
proteins linked to long polymers of C-6 acids and aminosugars which are sulfated in the Golgi after synthsis
proteoglycans
mannose, galactose, and fucose
required for glycosylation of proteins
made by fructose-6-phosphate
mannose and fucose
- heavy regulation of PFK1 in glycolysis
genetic disease
- defective proteoglycan-degrading hydrolases leading to skeletal deformation and intellectual disability
Mucopolysaccharidosis (MPS)
Accumulation of dermatan sulfate and heparan sulfate caused by defective enzyme iduronate sulfatase
- X-linked recessive
Hunter
accumulation of dermatan sulfate and heparan sulfate caused by defective enzyme alpha-iduronase
- auto-recessive
Hurler-Scheie
accumulation of heparan sulfate caused by different defects of heparan sulfate degradation (A,B,C,D roots)
Sanfilippos’s (A, B, C, D)
occurs in the liver and require production of UDP-glucuronic acid to serve as a substrate
glycosylation
increases water solubility and is a common path for the body to excrete poorly water-soluble molecules such as hemoglobin
glycosylation
- glucuronate linked to a glucosamine and is the backbone of ECM
- also allow newly synthesized proteoglycans to be integrated into the meshwork of ECM
hyaluronic acid
- lack mitochondria thus do not undergo CAC or oxidative phosphorylation
- depends on glycolysis for energy
- can perform anaerobic reactions to produce lactate
- utilizes Cori cycle
- utilizes PPP for NADPH and/or ribose synthesis
RBCs
- can perform glycogen synthesis and degradation
- can fully metabolize glucose via glycolysis, CAC and ox. phos
- perform PPP when needed
- can perform anaerobic reactions to produce lactate
skeletal muscles
- can perform glycogen synthesis and degradation
- can fully metabolize glucose via glycolysis, CAC and ox. phos
- perform PPP when needed
- cannot perform anaerobic reactions to produce lactate
cardiac muscles
- fully metabolize glucose
- makes and degrades glycogen
- performs Cori cycle
- performs PPP if needed
- does not perform anaerobic reactions
hepatocytes
