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Tutor profile: Joseph C.

Joseph C.
Science Coursework & Test Prep Tutor With 13 Years of Experience
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Subject: MCAT


During intense physical activity, such as sport exercise, glycogen phosphorylase is activated in muscle to increase glycogen breakdown. The possible mechanism of glycogen phosphorylase activation is most likely to involve which of the following? A.  A reduction in oxygen levels during intense cell respiration to produce more ATP. B.  An accumulation of lactic acid, which could serve as an allosteric regulator of glycogen phosphorylase. C.  An increase in cyclic AMP level, which could serve as an allosteric regulator of glycogen phosphorylase. D.  An elevation of CO2 levels during intense cell respiration to produce more ATP.

Joseph C.

During intense physical exercise, ATP in the muscles is consumed to produce energy. The energy provided by the ATP is stored in its phosphate bonds. When these bonds break down, the energy is released. The phosphate bonds break down in the process of hydrolysis and every time the phosphate is removed, the energy is released: 

ATP + H2O → ADP + Pi 

2ADP + H2O → 2AMP + 2Pi 

The final product of the ATP hydrolysis is cyclic AMP. From the passage, we already know that cyclic AMP serves as an allosteric regulator of glycogen phosphorylase, which suggests that it would be the most likely mechanism of glycogen phosphorylase activation during physical exercise.

Subject: Biochemistry


The following peptide is digested with both cyanogen bromide and trypsin: Ala-Phe-Ile-Met-Gln-Gln-Met-Arg-Val-Lys-Ser-Thr-Arg-Glu-Asn-Cys-Gly 

How many fragments will result? A.  4 B.  5 C.  6 D.  More than 6

Joseph C.

Cyanogen bromide cleaves at the C-terminal side of Met, while trypsin cleaves at the C-terminal side of Lys or Arg. Here are the 6 fragments:  

1) Ala-Phe-Ile-Met

 2) Gln-Gln-Met

 3) Arg

 4) Val-Lys

 5) Ser-Thr-Arg

 6) Glu-Asn-Cys-Gly

Subject: Biology


Drugs that stimulate multiple egg production probably contain, or increase the production of, which of the following hormones? 

 IV. Estrogen

Joseph C.

The hormonal cycle of women is relatively complex and involves all four hormones sex hormones (LH, FSH, estrogen and progesterone), at one point or another. Following the menses, caused by a low concentration of estrogen in the blood, the cycle continues in the follicular or proliferative phase in which FSH (= follicle stimulating hormone) stimulates the production of estrogen and the maturation of the follicles in the ovary. At midcycle, a surge of concentration stimulates ovulation (i.e. egg production).

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