Biochem Flashcards
Where do you find the malate aspartate shuttle? What is its yield?
found in heart, liver, kidneys
yields 32 ATP/1 glucose
Where do you find the glycerol -3 -phosphate shuttle? What is its yield?
found in brain, skeletal muscle
yields 30 ATP/1 glucose
Where do you find GLUT1? What is special about this?
RBCs
Endothelium BBB
Other tissues
**mediates basal glucose uptake regardless of insulin around
Where do you find GLUT 2?
hepatocytes
pancreatic beta cells
Where do you find GLUT3?
neurons
placenta
Where do you find GLUT 4?
skeletal muscle
adipose tissue
requires insulin!!
What does GLUT 5 do?
fructose uptake, especially in GI tract
Where do you find hexokinase? What is its Km and Vmax?
all tissues except liver and pancreatic beta cells Km low (high affinity). Means that it works in the presence of low glucose. Vmax low (low capacity)
Where do you find glucokinase? What is its Km and vmax?
liver, beta cells of pancreas
Km is high (low affinity). Only works in the presence of high amounts of glucose.
Vmax is high (high capacity). Works very efficiently once activated
Is hexokinase induced by insulin, inhibited by glucose-6-p?
not induced by insulin.
does experience neg. feedback inhibition by glucose-6-p
Is glucokinase induced by insulin, inhibited by glucose-6-p?
induced by insulin
does NOT experience neg. feedback
Which type of enzyme (hexokinase/glucokinase) is associated with maturity-onset diabetes of the young (MODY) when its genes are mutated?
glucokinase
In a starving state, we have a lower insulin/glucagon ratio. What happens next that regulates glycolysis?
this high glucagon stimulates the glucagon receptor and activates adenylate cyclase. Increased cAMP. PKA activated. This phosphorylates PFK2-FBP-2 complex and favors the active FBP-2 and inactive PFK-2. This decreases glycolysis (don’t have the energy to spare).
Where does gluconeogenesis take place?
hepatocytes
kidney
intestinal epithelium
**places that share glucose
When does gluconeogenesis take place?
happens when blood glucose is low
convert other molecules to pyruvate to make glucose
What stimulates the conversion of pyruvate–>oxaloacetate–>PEP?
acetyl CoA
What is the cofactor for pyruvate carboxylase?
biotin
Which molecules can feed in to gluconeogenesis?
odd chain fatty acids–>propionyl CoA
TCA cycle molecules
Amino acids
What is the rate limiting enzyme for glycogen synthesis? Glycogenolysis?
glycogen synthesis: glycogen synthase
glycogenolysis: glycogen phosphorylase
What is the rate limiting enzyme for TCA? hexose monophosphate shunt?
TCA-isocitrate dehydrogenase
hexose-monophosphate shunt: glucose-6-p dehydrogenase
What stimulates the action of fructose-1,6-bisphosphatase?
What inhibits it?
stimulated byATP
inhibited by AMP, Fructose-2,6-BP (dude don’t release more glucose into the blood, insulin told me we are already flooded w/ the stuff, do some glycolysis, bro)
Describe glycogenesis.
Glucose–>(hexokinase, glucokinase)–>G-6-p–>G-1-P–>(UDP-glucose pyrophosphorylase)–>UDP-glucose–>(glycogen synthase, branching enzyme)–>glycogen
Which bonds does glycogen synthase form? Branching enzyme?
glycogen synthase: alpha1,4 glycosidic linkages
branching enzyme: forms alpha 1,6 glycosidic linkages
Describe glycogenolysis.
alpha 1,4 Glycogen–>(glycogen phosphorylase)–>glucose-1-P–>(phosphoglucomutase)–>glucose-6-P–>(glucose-6-phosphatase)–>glucose
alpha1,6 glycogen–>(alpha1,6,glucosidase)–>glucose
Describe what glycogenolysis is like in the muscle.
muscle doesn’t have glucose-6-phosphatase
so when it gets to g-6-p during glycogenolysis it uses it for glycolysis and energy. Doesn’t form glucose to share. That’s what the liver etc do.
Describe how the debranching enzyme (alpha 1, 6 glucosidase) works.
4 before a branch point glycogen phosphorylase stops working.
Then the transferase 4-alpha-D-glucanotransferase works and takes 3 of the glucoses and tacs them to the end of the chain.
Then the alpha 1, 6, glucosidase takes away the last glucose of the branch.
What does insulin do to glycogenolysis v. glycogen synthesis?
insulin favors glycogen synthesis
inhibits glycogen phosphorylase
stimulates glycogen synthase
What does glucagon do to glycogenolysis v. glycogen synthesis?
glucagon and epi (both higher in stressful states) favor glycogenolysis
stimulate glycogen phosphorylase
Epi does it via Beta Gs receptors.
Describe in detail how glucagon stimulates glycogenolysis.
glucagon binds receptors
stimulates adenylyl cyclase, increased cAMP, triggers PKA.
PKA phosphorylates and activates glycogen phosphorylase kinase.
This activates glycogen phosphorylase
get glycogenolysis
What’s the deal with von Gierke dx?
Type I
deficiency of glucose-6-phosphatase
compromised glycogenolysis and gluconeogenesis
**causes severe fasting hypoglycemia
increased glycogen in liver-hepatomegaly
increased blood lactate, triglycerides, and uric acid
What is the treatment for von Gierke dx?
frequent oral glucose and cornstarch before bed to prevent the fasting hypoglycemia
What’s the deal with Pompe dx?
Type II
deficiency of alpha 1,4 glucosidase in lysosomes (acid maltase)
Infantile form-severe
Adult form-less severe
Describe the features of the infantile form of Pompe dx?
cardiomegaly, hypertrophic cardiomyopathy
exercise intolerance
Describe the features of the adult form of Pompe dx?
no heart involvement
gradual onset skeletal muscle weakness
diaphragm weakness-respiratory failure
What’s the deal with Cori disease?
Type III
deficiency of alpha 1,6, glucosidase
presents as milder form of von Gierke. Glycogenolysis is messed up, but not gluconeogenesis
hepatomegaly, hypoglycemia, hyperlipidemia
BUT normal kidneys, lactate, and uric acid
What’s the deal with McArdle dx?
Type V
deficiency of glycogen phosphorylase
buildup of glycogen in the muscle, bursts. Muscle cramps
Rhabdomyolysis and myoglobinuria–>renal failure
normal life expectancy
What is the treatment for McArdle dx?
Vit B6
What is the inheritance pattern for all of the glycogen storage diseases?
autosomal recessive
How do you remember which Type # the glycogen storage diseases are?
Very Poor Carbohydrate Metabolism
1, 2, 3, 5
