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What types of linkages does glycogen phosphorylase cleave?

alpha 1,4-glycosidic linkages in glycogen
(glycogen -> glucose 1-phosphate)

1

What three enzymes are required to break down glycogen?

1) glycogen phosphorylase
2) a debranching enzyme
3) phosphoglucomutase (converts glucose-1P into glucose-6P)

2

What organ is responsible for maintaining glucose levels?

Liver (contains glucose-6-phosphatase, which muscle does not have)
can take glucose-6P to glucose

3

What is type 5 glycogen storage disease? Enzyme deficiency? Inheritance? Presentation?

McArdle's syndrome - deficiency in skeletal muscle glycogen phosphorylase (myophosphorylase)

Autosomal recessive

increased glycogen in muscle but cannot break it down:
decreased exercise tolerance
painful muscle cramps
myoglobinuria (red urine) with strenuous exercise
arrhythmia from electrolyte abnormalities

4

What are the purely ketogenic amino acids?

Leucine and lysine
would not lead to increased formation of lactate in pts with PDH deficiency

5

Presentation of PDH deficiency?

multiple possible presentations ranging from neonatal death to mild episodic symptoms in adulthood

neurologic defects
lactic acidosis
increased serum alanine starting in infancy

6

What is essential fructosuria?

defect in fructokinase; autosomal recessive

benign and asymptomatic since fructose not trapped in cells
fructose in blood and urine
hexokinase takes over fructokinase function - turns into F6P (glycolysis or turned into G6P)

7

What is fructose intolerance?

deficiency of aldolase B; autosomal recessive
hereditary fructose intolerance - onset of vomiting and hypoglycemia

fructose 1-P accumulates, causes a decrease in available phosphate
phosphate loss results in inhibition of glycogenolysis and gluconeogenesis.

signs after consuming fruit, juice, honey
negative dipstick test (only glucose tested)
treatment to decrease fructose and sucrose intake

8

What type of cells make up a pheochromocytoma? What MEN syndromes is this associated with?

Chromaffin cells (derived form neural crest cells)

MEN 2A and 2B

9

What tissue is the adrenal cortex derived from? The adrenal medulla?

cortex derived from mesothelial cells
medulla derived from neural crest cells

10

What do high levels of fructose 2,6-bisphosphate promote? What enzymes does it regulate?

promotes glycolysis and inhibits gluconeogenesis
also decreases the gluconeogenic conversion of alanine to glucose

F2,6BP allosterically activates PFK1, the main regulatory step in glycolysis, which converts F6P to F1,6BP.

F2,6BP allosterically inhibits fructose 1,6-bisphosphatase, which converts F1,6BP to F6P.

11

What does inhibition of gluconeogenesis do to alanine conversion to glucose?

decreases the conversion of alanine to glucose
(alanine transaminated to pyruvate and then converted to glucose)

processes that inhibit gluconeogenesis also downregulate the production of gluconeogenic substrates (like pyruvate)

12

What is fructose 2,6-bisphosphate concentration regulated by?

bifunctional enzyme composed of:
phosphofructokinase-2
fructose 2,6-bisphosphatase

13

What is the function of smooth ER? In what cells is smooth ER abundant?

contains enzymes for steroid and phospholipid biosynthesis

steroid-producing cells in the adrenals, gonads, and liver all contain well-developed smooth ER

cholesterol-derived steroid hormones in the adrenals
detox of numerous drugs in hepatocytes
specialized SER is the sarcoplasmic reticulum in striated muscle cells

14

What is Keq if standard free energy change (deltaGo) is positive? Negative? Zero?

positive deltaGo: Keq is less than 1
negative deltaGo: Keq is more than 1
zero deltaGo: Keq equals 1

15

What is negative predictive value? Does pretest probability matter?

the probability of being free of a disease if the test result is negative

the NPV will vary with the pretest probability of a disease!!
pt with high pretest prob. will have low NPV with a negative test
pt with low pretest prob. will have high NPV with a negative test

16

TSH, LH, and FSH activate what type of receptors? Describe the transmembrane domain.

GPCRs

segments of the 7-tm alpha helices containing approximately 20 hydrophobic amino acids

17

Where does the thyroid migrate from? The GnRH-secreting neurons of the hypothalamus? The testes?
What does failure of each of these migrations lead to?

Thyroid migrates from tongue to lower anterior neck - failure leads to lingual thyroid or thyroid mass at any point along thyroglossal duct

GnRH-secreting neurons migrate from olfactory lobes to hypothalamus - failure is Kallman syndrome

Testes migrate from intra-abdominal location to scrotum - failure is called cryptorchidism

18

Where is epinephrine sythesized? Where is dopamine and NE synthesized?

Epinephrine - adrenal medulla
Dopamine and NE - CNS and PNS

19

What are cortisol's effects on Epinephrine production?

Cortisol increases activity of phenylethanolamine-N-methyltransferase (PNMT) which converts NE to epinephrine.

High levels of cortisol in the adrenal medulla because venous drainage from the adrenal cortex runs through the medulla. Catecholamine contents of the adrenal medulla are 80% epinephrine, 20% NE.

20

What type of signaling pathway does insulin work by? Glucagon? Cortisol? Catecholamines? Growth hormone receptors?

Insulin and growth hormone receptors - act via an intrinsic tyrosine kinase (cell surface receptor with resultant activation of tyrosine kinase)
THINK GROWTH FACTORS = intrinsic cell surface RTK

Glucagon and catecholamines - acts via cAMP through binding/activation of GPCRs

Cortisol - acts as a steroid receptor

21

What are the signaling pathways of endocrine hormones that act as vasdilators? What are these hormones?

ANP, NO (EDRF) - vasodilators

Act through cGMP via GPCR binding/activation

22

Which endocrine hormones work through a receptor-associated tyrosine kinase? Name an example of this kind of pathway.

Prolactin, immunomodulators (cytokines), and GH
PIG

JAK/STAT pathway

think acidophiles and cytokines!!

23

Is the nucleolus membrane-bound/does it have a membrane?

Nope.

24

How do you identify euchromatin in the nucleus on electron microscopy?

lighter "electron lucent" regions
DNA is unpackaged and is actively being transcribed

25

What is AFP and where is it synthesized? How does it change with gestational age?

alpha-fetoprotein
synthesized by fetal liver, GI tract, and yolk sac (in early gestation only)

Maternal serum AFP levels increase with gestational age.

26

What is the most common cause of elevated AFP levels in maternal serum? What is associated with decreased AFP levels?

Dating error (underestimation of gestational age)

Increased AFP also associated with:
- neural tube defects
- anterior abdominal wall defects
- multiple gestation

Down syndrome associated with decreased AFP levels.

27

What is hCG and what is it synthesized by? What conditions are associated with elevated hCG?

human chorionic gonadatropin (hCG) is synthesized by trophoblastic tissue

increased levels associated with:
- multiple gestation
- hyatidiform mole
- choriocarcinoma

28

What are estriol level reflective of in pregnancy? What do decreased levels suggest?

placental and fetal function - both are necessary for its synthesis

decreased levels suggestive of placental insufficiency

29

Mechanism of insulin activity?

insulin binds cell surface RTK
phosphorylation of a number of proteins (insulin receptor substrates)
leads to activation of protein phosphatase
protein phosphatase dephosphorylates glycogen syntase
glycogen synthase activated by dephosphorylation - promotes synth.