Biochemistry Practice Questions XII with Answers

Biochemistry Practice Questions XII with Answers
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  1. The above pathway is a metabolic process called gluconeogenesis. Which four enzymes are unique to gluconeogenesis?

 

  1. Which of the following statement is incorrect?
  • A. the conversion of pyruvate to oxaloacetate occurs in mitochondrial matrix
  • B. Oxaloacetate cannot freely move out of mitochondrial matrix
  • C. Oxaloacetate becomes phosphoenolpyruvate in cytoplasm
  • D. The conversion of phosphoenolpyruvate to fructose-1,6-bisphosphate is a reversible process.
  • E. Glucose-6-phosphate becomes hydrolyzed to glucose and inorganic phosphate in Mitochondria

 

  1. How is oxaloacetate used in gluconeogenesis transported from mitochondrial matrix to cytoplasm?
  • A. There is an oxaloacetate transporter in mitochondrial matrix that transport it to cytoplasm through a facilitated diffusion mechanism.
  • B. Oxaloacetate transporter actively transports oxaloacetate against gradient by hydrolyzing ATP.
  • C. Oxaloacetate is reduced to malate through a part of citric acid cycle and then transported to cytoplasm.
  • D. Oxaloacetate reacts with acetyl-coenzyme A, becomes citrate, and then transported to cytoplasm.
  • E. Oxaloacetate becomes α-ketoglutarate, then becomes glutamate, and then transported to cytoplasm.

 

  1. What are cofactors required to convert pyruvate to glucose through gluconeogenesis? Select all that relevant.
  • A. biotin
  • B. NADH
  • C. NAD+
  • D. Thiamine pyrophosphate (TPP)
  • E. Coenzyme A

 

  1. In liver, glycolysis and gluconeogenesis are reciprocally regulated. Mitochondrial acetyl CoA is a regulator of these processes. Will glycolysis or gluconeogenesis be stimulated if ATP citrate lyase is inhibited?

 

  1. The hydrolysis of glucose-6-phosphate to glucose and inorganic phosphate occurs in the lumen of endoplasmic reticulum. This particular step is regulated by the transport of glucose-6-phosphate, glucose, and inorganic phosphate instead of the actual chemical step. Imagine that there is a mutation in the glucose transporter responsible for the transport of glucose to blood. If this mutation lowers Km for glucose of the glucose transporter, what will happen to the overall gluconeogenesis?
  • A. stimulated.
  • B. suppressed.

 

  1. In addition to its role in gluconeogenesis, the reaction mediated by glucose-6-phosphatase is also involved in the breakdown of glycogen. If the transporter transporting inorganic phosphate from ER to cytoplasm is mutated and inhibited, what will happen?
  • A. glucose-6-phosphate hydrolysis is stimulated
  • B. Blood glucose concentration will be elevated
  • C. Glycogen will accumulate in cells
  • D. Gluconeogenesis will be stimulated
  • E. Glycolysis will be suppressed.

 

  1. Fill the blank. When there are two choices, circle the correct one.

When blood glucose concentration becomes low, pancreatic ____ cells will secret a

hormone called _______. This hormone than binds to a receptor on liver cell

surface called _________. This binding of the hormone to the receptor activates a

membrane embedded enzyme called _________, which synthesizes a

second messenger called ______________ from ATP. This second messenger

binds to an intracellular protein kinase called _________________. This binding of

the second messenger to the protein kinase (activates / inhibits; circle one) its protein

kinase activity. One of protein being regulated by this mechanism is glycogen

phosphorylase, which becomes phosphorylated when this signaling is activated. The

phosphorylation of glycogen phosphorylase induces conformation changes, shifting it

from (T/R-form) to (T/R-form). At the end, this signaling (promotes/inhibits) glycogen

breakdown.

 

  1. When cells are in oxygen rich environment, pyruvate produced from glycolysis is converted to acetyl coenzyme A in mitochondria by an enzyme complex called pyruvate dehydrogenase. Which of following cofactors are required for this process? Select all necessary.
  • A. Pyridoxal phosphate
  • B. NADH
  • C. Thiamine pyrophosphate
  • D. Lipoic acid
  • E. Biotin

 

  1. Overall, the citric acid cycle produces 3 molecules of NADH, 1 molecule of FADH2, and 1 ATP from 1 molecule of acetyl coenzyme A. If isocitrate dehydrogenase is mutated and thus converts all α-ketoglutarate to 2-hydroxyglutarate (oxaloacetate is assumed to be from other metabolic processes), how many NADH, FADH2, and ATP will be produced from a molecule of acetyl coenzyme A?

 

  1. Pyruvate dehydrogenase is regulated by phosphorylation. The enzyme phosphorylating pyruvate dehydrogenase becomes activated by AMP-activated protein kinase. What will happen to pyruvate dehydrogenase when cells are treated with metformin, a diabetes drug?

 

  1. In the glyoxalate shunt, isocitrate becomes glyoxalate (which then becomes malate upon reaction with acetyl CoA) and succinate. How many molecules of NADH, FADH2, and ATP will be generated from glyoxalate shunt?

 

  1. In glutaminolysis pathway shown above, glutamine, instead of glucose, is used as an energy source. Glutamine is converted to glutamate in mitochondria. Glutamate then reacts with oxaloacetate to produce α-ketoglutarate that enters the citric acid cycle. After converting α-ketoglutarate to succinate, fumarate, and then to malate, the malate is removed from mitochondria and becomes pyruvate in cytoplasm. How many molecules of NADH, FADH2, and ATP will be produced when glutamine is converted to malate through this process?

 

  1. NADH produced in mitochondria enters electron transport chain (ETC) through complex I (aka NADH Q reductase complex). FADH2 produced in mitochondria enters ETC through complex II (succinate dehydrogenase). Complex I pumps 4 protons to intermembrane space during this process while complex II does not pump protons. Assuming that 3 protons are equivalent to 1 ATP and 1 proton is needed to transport ADP into mitochondrial matrix, how many more ATP will be produced from NADH oxidation than from FADH2 oxidation?

 

  1. When NADH is oxidized by the complex I, ubiquinone becomes reduced. What will be the product of this step?

 

  1. In complex III, reduced ubiquinone is oxidized while transporting electrons to cytochrome c proteins. How many electrons are carried by ubiquinone and cytochrome C?

 

  1. How many protons will be pumped to the intermembrane space if 1 molecule of NADH is oxidized through ETC?

 

  1. How many protons will be pumped to the intermembrane space if 1 molecule of FADH2 is used through ETC?

 

  1. When 3 molecules of NADH and 1 molecule of FADH2 are consumed through ETC, how many molecules of oxygen will be converted to water?

 

  1. When NADH produced in cytoplasm is used for respiration through the glycerol-3-phosphate shuttle, how many molecules of proton will be pumped to the intermembrane space?