Biochem

Front 1

A patient with type 1 diabetes mellitus takes an insulin injection before eating dinner but then gets distracted and does not eat. Approximately 3 hours later, the patient becomes shaky, sweaty, and confused. These symptoms have occurred because of which of the following?

Back 1

Low blood glucose levels

Hint 1

Once insulin is injected, glucose transport into the peripheral tissues is improved. If the patient does not eat, the normal, fasting level of glucose will drop even further due to the injection of insulin, increasing the movement of glucose into muscle and fat cells. The patient becomes hypoglycemic, as a result epinephrine is released from the adrenal medulla. This leads to the signs and symptoms associated with high levels of epinephrine.

Front 2

Caffeine is a potent inhibitor of the enzyme cAMP phosphodiesterase. Which of the following consequences would you expect to occur in the liver after drinking two cups of strong espresso coffee?

Back 2

A prolonged response to glucagon

Hint 2

When glucagon binds to its receptor, the enzyme adenylate cyclase is eventually activated (through the action of G-proteins), which raises cAMP levels in the cell. The cAMP phosphodiesterase opposes this rise in cAMP, and hydrolyzes cAMP to 5′-AMP. If the phosphodiesterase is inhibited by caffeine, cAMP levels would stay elevated for an extended period of time, enhancing the glucagon response. The glucagon response in liver is to export glucose and to inhibit glycolysis.

Front 3

Assume that an increase in blood glucose concentration from 5 to 10 mM would result in insulin release by the pancreas. A mutation in pancreatic glucokinase can lead to maturity-onset diabetes of the young (MODY) because of which of the following within the pancreatic β-cell?

Back 3

A reduced ability to raise ATP levels

Hint 3

Insulin release is dependent on an increase in the [ATP]/[ADP] ratio within the pancreatic β-cell. The mutation in glucokinase results in a less active glucokinase at glucose concentrations that normally stimulate insulin release. Thus, higher concentrations of glucose are required to stimulate glycolysis and the TCA cycle to effectively raise the ratio of ATP to ADP.

Front 4

one of the following organs has the highest demand for glucose as a fuel?

Back 4

Brain

Hint 4

The brain requires glucose because fatty acids cannot readily cross the blood–brain barrier to enter neuronal cells. Thus, glucose production is maintained at an adequate level to allow the brain to continue to burn glucose for its energy needs.

Front 5

Glucagon release does not alter muscle metabolism because of which of the following?

Back 5

Muscle cells lack the glucagon receptor

Hint 5

Muscle does not express glucagon receptors, so they are nonreactive to glucagon.