BIOCHEMISTRY METABOLISM USMLE STEP 1 UPDATED
ACTUAL EXAM QUESTIONS AND CORRECT ANSWERS
Question 1.
Action of fructose 2,6bP?
ANSWER
PFK-2 and FBPase 2 control F6P levels. F26BP itself upregulates PFK-1, promoting glycolysis
that means that FBPase2 is upregulated by glucagon in starvation states to reduce glycolysis
Question 2.
PDH complex similar to what other complex? what are the 5 co factors needed to execute function?
ANSWER
AKGDH cofactors needed PPi B1, FAD B2, NAD B3 Coa B5, and lipoic acid
-
Question 3.
PDH deficiency (congenital vs acquired)
ANSWER
prevents aerobic respiration acquired = alcohol = b1 (thiamine deficiency) CP: neuro defects
and lactic acidosis, increase in serum alanine during infancy Tx: diets in leucine and lysine -->
enter TCA and bypass PDH leucine/lysine = purely ketogenic
Question 4.
Pathways for pyruvate (x4)
ANSWER
--> alanine (muscle to liver amino groups)
--> OAA (to replenish the TCA or gluconeogenesis)
--> AcetylCoA TCA
--> lactate DH (anaerobic metabolism; in kidneys, RBC, WBC, eye lens and cornea, testes)
, Question 5.
ETC inhibitors
ANSWER
Cyanide (IV) CO (IV)
Question 6.
Glugoneogenesis bypass enzymes (x4) how does fatty acids make glucose acetyl CoA allosteric
activator of what enzyme for gluconeogenesis?
ANSWER
Pyruvate carboxylase PEP carboxykinase (via GTP) F16BP G6Pase in liver even number cannot,
odd number can enter and eventually make OAA pyruvate carboxylase (to make OAA)
Question 7.
HMP shunt (PPP) role x2 G6PDHase deficiency
ANSWER
Convert G6P vua G6PDH to create anabolic substrates AND antioxidation (protective) MAINLY
NADPH from G6p-R5p VERY common XLR disease in black people... Remember that G6PDH
linked to glutathione reductase (GSSG --> 2GSH) and glutathione peroxidase --> ultimately to
accept free radicals via peroxide
Question 8.
Essential fructosuria pathophys and mode of inheritence?
ANSWER
AR, benign, fructokinase deficiency. Lots of fructose in urine, but glucose won't be elevated in
urine (duh) copper reduction test since fructose is a reducing sugar (~ to glucose and
galactose) hexokinase compensates for it
ACTUAL EXAM QUESTIONS AND CORRECT ANSWERS
Question 1.
Action of fructose 2,6bP?
ANSWER
PFK-2 and FBPase 2 control F6P levels. F26BP itself upregulates PFK-1, promoting glycolysis
that means that FBPase2 is upregulated by glucagon in starvation states to reduce glycolysis
Question 2.
PDH complex similar to what other complex? what are the 5 co factors needed to execute function?
ANSWER
AKGDH cofactors needed PPi B1, FAD B2, NAD B3 Coa B5, and lipoic acid
-
Question 3.
PDH deficiency (congenital vs acquired)
ANSWER
prevents aerobic respiration acquired = alcohol = b1 (thiamine deficiency) CP: neuro defects
and lactic acidosis, increase in serum alanine during infancy Tx: diets in leucine and lysine -->
enter TCA and bypass PDH leucine/lysine = purely ketogenic
Question 4.
Pathways for pyruvate (x4)
ANSWER
--> alanine (muscle to liver amino groups)
--> OAA (to replenish the TCA or gluconeogenesis)
--> AcetylCoA TCA
--> lactate DH (anaerobic metabolism; in kidneys, RBC, WBC, eye lens and cornea, testes)
, Question 5.
ETC inhibitors
ANSWER
Cyanide (IV) CO (IV)
Question 6.
Glugoneogenesis bypass enzymes (x4) how does fatty acids make glucose acetyl CoA allosteric
activator of what enzyme for gluconeogenesis?
ANSWER
Pyruvate carboxylase PEP carboxykinase (via GTP) F16BP G6Pase in liver even number cannot,
odd number can enter and eventually make OAA pyruvate carboxylase (to make OAA)
Question 7.
HMP shunt (PPP) role x2 G6PDHase deficiency
ANSWER
Convert G6P vua G6PDH to create anabolic substrates AND antioxidation (protective) MAINLY
NADPH from G6p-R5p VERY common XLR disease in black people... Remember that G6PDH
linked to glutathione reductase (GSSG --> 2GSH) and glutathione peroxidase --> ultimately to
accept free radicals via peroxide
Question 8.
Essential fructosuria pathophys and mode of inheritence?
ANSWER
AR, benign, fructokinase deficiency. Lots of fructose in urine, but glucose won't be elevated in
urine (duh) copper reduction test since fructose is a reducing sugar (~ to glucose and
galactose) hexokinase compensates for it
