Hy Review Usmle Step 1: Biochemistry (D12)

Front 1

What is the rate-determining enzyme in Glycolysis?

Back 1

Phosphofructokinase-1 (PFK-1)

Front 2

What is the rate-determining enzyme in Gluconeogenesis?

Back 2

Fructose-1,6-bisphosphatase

Front 3

What is the rate-determining enzyme in TCA cycle?

Back 3

Isocitrate dehydrogenase

Front 4

What is the rate-determining enzyme in Glycogen synthesis?

Back 4

Glycogen synthase

Front 5

What is the rate-determining enzyme in HMP shunt?

Back 5

Glucose-6-phosphate degydrogenase (G6PD)

Front 6

What is the rate-determining enzyme in Glyccogenolysis?

Back 6

Glycogen phosphorylase

Front 7

In von Gierke's Disease, you are deficient in which enzyme? Which pathway does this effect?

Back 7

Glucose-6-Phosphatase.
Effects Gluconeogenesis.

Front 8

What do you find in Von Gierke's Disease?

Back 8

Severe fasting hypoglycemia
Increased glycogen in the liver
Hepatomegaly
Increased blood lactate (due to muscle anaerobic metabolism)

Front 9

What are the glycogen storage diseases?
What enzyme is deficient?

Back 9

"Very Poor Carbohydrate Metabolism"
V: Von Gierke's disease (Glucose-6-phosphatase, the last enzyme/step req in gluconeogenesis).
P: Pompe's Disease (lysosomal alpha-1,4-glucosdase)
C: Cori's Disease (debranching enzyme, aka alpha-1,6-glucosidase)
M: McArdle's Disease (Glycogen phosphorylase in the skeletal mm)

Front 10

What are the finding's in Pompe's Disease?

Back 10

Cardiomegaly and system findings leading to early death by age 3.
"Pompe's trashes the Pump (heart, liver, and muscle)

Front 11

Cori's disease is a milder form of which of the other glycogen storage diseases?
What is normal in Cori's that is increased in the worse form?

Back 11

Von Gierke's (type I)
Normal lactate levles

Front 12

What are the findings in McArdle's Disease?

Back 12

There is an increase in glycogen in the muscles, but since this disease lacks glycogen phosphorylase, glycogen can't be broken down--> painful muscle cramps, myoglobinuria w/strenous exercise.
Think M= McArdle=Muscle

Front 13

What are the cofactors required for the Pyruvate Dehydrogenase Complex?

Back 13

"TLC For No one"
Thiamine (B1;TPP; pyrophosphate)
Lipoic Acid
CoA (B5)
FAD (B2, riboflavin)
NAD (B5, pantothenate)

Front 14

A deficiency in Pyruvate Dehydrogenase would result in what?
Tx?

Back 14

Substrate backup, such as pyruvate and alanine, and lactate (-->lactic acidosis).
Can be congenital or acquired i.e. B1 deficiency seen in alcoholics.
Findings: Neurologic defects
Tx: increase intake of ketogenic nutrients (fatty food or those w/lysine, leucine)

Front 15

Amytal, Rotenone, and MPP will inhibit which complex of the electron transport chain?

Back 15

Complex I

Front 16

Antimycin A will inhibit which complex of the electron transport chain?

Back 16

Complex III

Front 17

What compounds or molecules will inhibit Complex IV of the electron transport chain?

Back 17

Hydrogen Sulfide (H2S), Carbon Monoxide (CO), Cyanide (CN-), and Azide (N3-)

Front 18

What is the purpose of the HMP shunt (pentose phosphate pathway)?

Back 18

To provide a source of NADPH from abundantly available glucose-6-phosphate.
Note: also yields Ribose for nucleotide synthesis, and glycolytic intermediates

Front 19

What is NADPH for?

Back 19

For reductive reactions, such as the glutathione reduction inside RBCs that protects from oxidative insult/attack (so glutathione= antioxidant).

Front 20

What is the rate-limiting step in the Oxidative phase of the HMP shunt?

Back 20

Glucose-6-P Dehydrogenase conversion of Glucose-6-P.
*note: oxidative phase is irreversible

Front 21

What are the products in the HMP shunt?

Back 21

CO2, Ribulose-5-P, 2NADPH

Front 22

What is/are the enzymes used in the Nonoxidative (reversible) phase of the HMP shunt?
What are the end products?

Back 22

Transketolases (start with Ribulose-5-P) which require B1 (thiamine).
Ribose-5-P, G3P, F6P

Front 23

What drugs do you not want to give to patients with a G6PD deficiency?
Why?

Back 23

Sulfonamides, Primaquine, anti-TB drugs, fava beans.
These drugs produce oxidizing agents, which will cause hemolytic anemia in a patient w/o G6PD (see FAp.102)

Front 24

What is the most common enzyme deficiency?

Back 24

Glucose-6-phosphate Dehydrogenase (G6PD) Deficiency, X-linked.

Front 25

What are Heinz bodies?

Back 25

Oxidized Hemoglobin precipitated within RBCs, which occurs in G6PD deficiency.

Front 26

Fructose intolerance is due to hereditary deficiency of what enzyme?
What results?
S/S?

Back 26

Aldolase B deficiency.
Fructose-1-P accumulation--> decreases available phosphate--> can't undergo glycogenolysis and gluconeogensis.
S/S: hypoglycemia, jaundice, cirrhosis, vomiting.

Front 27

How do you treat Fructose intolerance?

Back 27

Decrease fructose and sucrose (which has fructose).

Front 28

What enzyme is absent in classic galactosemia?
Result?

Back 28

Galactose-1-phosphate uridyltransderase (GALT)
Accumulates toxic substances like galactitol, which accumulates in the lens of the eye

Front 29

What are the Sx of classic galactosemia?
Tx?

Back 29

FTT, Jaundice, hepatomegaly, infantile cataracts, mental retardation
tx: exclude galactose and lactose (Galactose + glucose)

Front 30

What is the drug of choice for inhibiting alcohol dehydrogenase and tx methanol or ethylene glycol poisoning?
What drug inhibits acetaldehyde dehydrogenase?

Back 30

Fomepizole.
Disulfiram (antabuse): accumulates acetaldehyde, contributing or promoting hangover sx.

Front 31

What enzyme converts Ethanol to Acetaldehyde? Acetaldehyde to Acetate?

Back 31

Ethanol to acetaldehyde: Alcohol dehydrogenase
Acetaldehyde to Acetate: Acetaldehyde dehydrogenase (ASIANS have a variability of Acetaldehyde dehydrogenase, such that it may not be effective, so acetaldehyde builds up--> flushing)

Front 32

How much energy is produced from Proteins? Carbohydrates? Fat?

Back 32

Protein and Carbs: 4kcal
Fat: 1kcal

Front 33

Ketone bodies are formed from the metabolism of what?
What are the ketone bodies?

Back 33

Fatty acids.
Acetoacetate and beta-Hydroxybutyrate.