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STEP1 > Biochem > Flashcards

Biochem Flashcards

1
Q

Where do you find the malate aspartate shuttle? What is its yield?

A

found in heart, liver, kidneys

yields 32 ATP/1 glucose

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2
Q

Where do you find the glycerol -3 -phosphate shuttle? What is its yield?

A

found in brain, skeletal muscle

yields 30 ATP/1 glucose

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3
Q

Where do you find GLUT1? What is special about this?

A

RBCs
Endothelium BBB
Other tissues
**mediates basal glucose uptake regardless of insulin around

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4
Q

Where do you find GLUT 2?

A

hepatocytes

pancreatic beta cells

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5
Q

Where do you find GLUT3?

A

neurons

placenta

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6
Q

Where do you find GLUT 4?

A

skeletal muscle
adipose tissue
requires insulin!!

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7
Q

What does GLUT 5 do?

A

fructose uptake, especially in GI tract

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8
Q

Where do you find hexokinase? What is its Km and Vmax?

A 
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)
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9
Q

Where do you find glucokinase? What is its Km and vmax?

A

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

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10
Q

Is hexokinase induced by insulin, inhibited by glucose-6-p?

A

not induced by insulin.

does experience neg. feedback inhibition by glucose-6-p

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11
Q

Is glucokinase induced by insulin, inhibited by glucose-6-p?

A

induced by insulin

does NOT experience neg. feedback

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12
Q

Which type of enzyme (hexokinase/glucokinase) is associated with maturity-onset diabetes of the young (MODY) when its genes are mutated?

A

glucokinase

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13
Q

In a starving state, we have a lower insulin/glucagon ratio. What happens next that regulates glycolysis?

A

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).

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14
Q

Where does gluconeogenesis take place?

A

hepatocytes
kidney
intestinal epithelium
**places that share glucose

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15
Q

When does gluconeogenesis take place?

A

happens when blood glucose is low

convert other molecules to pyruvate to make glucose

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16
Q

What stimulates the conversion of pyruvate–>oxaloacetate–>PEP?

A

acetyl CoA

17
Q

What is the cofactor for pyruvate carboxylase?

A

biotin

18
Q

Which molecules can feed in to gluconeogenesis?

A

odd chain fatty acids–>propionyl CoA
TCA cycle molecules
Amino acids

19
Q

What is the rate limiting enzyme for glycogen synthesis? Glycogenolysis?

A

glycogen synthesis: glycogen synthase

glycogenolysis: glycogen phosphorylase

20
Q

What is the rate limiting enzyme for TCA? hexose monophosphate shunt?

A

TCA-isocitrate dehydrogenase

hexose-monophosphate shunt: glucose-6-p dehydrogenase

21
Q

What stimulates the action of fructose-1,6-bisphosphatase?

What inhibits it?

A

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)

22
Q

Describe glycogenesis.

A

Glucose–>(hexokinase, glucokinase)–>G-6-p–>G-1-P–>(UDP-glucose pyrophosphorylase)–>UDP-glucose–>(glycogen synthase, branching enzyme)–>glycogen

23
Q

Which bonds does glycogen synthase form? Branching enzyme?

A

glycogen synthase: alpha1,4 glycosidic linkages

branching enzyme: forms alpha 1,6 glycosidic linkages

24
Q

Describe glycogenolysis.

A

alpha 1,4 Glycogen–>(glycogen phosphorylase)–>glucose-1-P–>(phosphoglucomutase)–>glucose-6-P–>(glucose-6-phosphatase)–>glucose

alpha1,6 glycogen–>(alpha1,6,glucosidase)–>glucose

25
Q

Describe what glycogenolysis is like in the muscle.

A

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.

26
Q

Describe how the debranching enzyme (alpha 1, 6 glucosidase) works.

A

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.

27
Q

What does insulin do to glycogenolysis v. glycogen synthesis?

A

insulin favors glycogen synthesis
inhibits glycogen phosphorylase
stimulates glycogen synthase

28
Q

What does glucagon do to glycogenolysis v. glycogen synthesis?

A

glucagon and epi (both higher in stressful states) favor glycogenolysis
stimulate glycogen phosphorylase
Epi does it via Beta Gs receptors.

29
Q

Describe in detail how glucagon stimulates glycogenolysis.

A

glucagon binds receptors
stimulates adenylyl cyclase, increased cAMP, triggers PKA.
PKA phosphorylates and activates glycogen phosphorylase kinase.
This activates glycogen phosphorylase
get glycogenolysis

30
Q

What’s the deal with von Gierke dx?

A

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

31
Q

What is the treatment for von Gierke dx?

A

frequent oral glucose and cornstarch before bed to prevent the fasting hypoglycemia

32
Q

What’s the deal with Pompe dx?

A

Type II
deficiency of alpha 1,4 glucosidase in lysosomes (acid maltase)

Infantile form-severe
Adult form-less severe

33
Q

Describe the features of the infantile form of Pompe dx?

A

cardiomegaly, hypertrophic cardiomyopathy

exercise intolerance

34
Q

Describe the features of the adult form of Pompe dx?

A

no heart involvement
gradual onset skeletal muscle weakness
diaphragm weakness-respiratory failure

35
Q

What’s the deal with Cori disease?

A

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

36
Q

What’s the deal with McArdle dx?

A

Type V
deficiency of glycogen phosphorylase
buildup of glycogen in the muscle, bursts. Muscle cramps
Rhabdomyolysis and myoglobinuria–>renal failure

normal life expectancy

37
Q

What is the treatment for McArdle dx?

A

Vit B6

38
Q

What is the inheritance pattern for all of the glycogen storage diseases?

A

autosomal recessive

39
Q

How do you remember which Type # the glycogen storage diseases are?

A

Very Poor Carbohydrate Metabolism

1, 2, 3, 5

STEP1 (54 decks)

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