Biochemistry and Metabolism
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MCAT Biology › Biochemistry and Metabolism
Acetyl-CoA is a react in the citric acid cycle, while 
Four
Twelve
Twenty-four
Two
Explanation
Each turn of the citric acid cycle is powered by one molecule of acetyl-CoA, resulting in three 
Since twelve 
Acetyl-CoA is a react in the citric acid cycle, while
Four
Twelve
Twenty-four
Two
Explanation
Each turn of the citric acid cycle is powered by one molecule of acetyl-CoA, resulting in three
Since twelve
What is the purpose of the formation of lactic acid during anaerobic respiration?
It allows NAD+ to reform
It allows NADH to reform
It allows FAD to reform
It allows FADH2 to reform
It allows glucose to reform
Explanation
Cells need a constant supply of NAD+ to accept electrons during glycolysis in order to produce pyruvate from glucose.
The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves. The supply of glycogen is limited, and eventually the body must break down free fatty acids (FFAs) through a process called beta-oxidation.
Which organ in the body cannot perform beta-oxidation, thus requiring the use of ketone bodies when stores of glucose are depleted?
Brain
Liver
Heart
Muscle
Explanation
The brain is unable to perform beta-oxidation of free fatty acids in the event of a prolonged fasting state. It is important to know this aspect of metabolism. In a fasting state, the liver beta-oxidizes free fatty acids into ketone bodies for the brain to use. Additionally, when energy demands are high, muscles can break down fat for additional ATP.
Unlike other organs in the body, the heart relies almost entirely on beta-oxidation for its energy needs.
What is the purpose of the formation of lactic acid during anaerobic respiration?
It allows NAD+ to reform
It allows NADH to reform
It allows FAD to reform
It allows FADH2 to reform
It allows glucose to reform
Explanation
Cells need a constant supply of NAD+ to accept electrons during glycolysis in order to produce pyruvate from glucose.
The process of glycolysis is used by all cells of the body to turn glucose into ATP for cellular energy. When stores of glucose are low, however, the body can break down a form of stored glucose in the liver to increase glucose reserves. The supply of glycogen is limited, and eventually the body must break down free fatty acids (FFAs) through a process called beta-oxidation.
Which organ in the body cannot perform beta-oxidation, thus requiring the use of ketone bodies when stores of glucose are depleted?
Brain
Liver
Heart
Muscle
Explanation
The brain is unable to perform beta-oxidation of free fatty acids in the event of a prolonged fasting state. It is important to know this aspect of metabolism. In a fasting state, the liver beta-oxidizes free fatty acids into ketone bodies for the brain to use. Additionally, when energy demands are high, muscles can break down fat for additional ATP.
Unlike other organs in the body, the heart relies almost entirely on beta-oxidation for its energy needs.
Most scientists subscribe to the theory of endosymbiosis to explain the presence of mitochondria in eukaryotic cells. According to the theory of endosymbiosis, early pre-eukaryotic cells phagocytosed free living prokaryotes, but failed to digest them. As a result, these prokaryotes remained in residence in the pre-eukaryotes, and continued to generate energy. The host cells were able to use this energy to gain a selective advantage over their competitors, and eventually the energy-producing prokaryotes became mitochondria.
In many ways, mitochondria are different from other cellular organelles, and these differences puzzled scientists for many years. The theory of endosymbiosis concisely explains a number of these observations about mitochondria. Perhaps most of all, the theory explains why aerobic metabolism is entirely limited to this one organelle, while other kinds of metabolism are more distributed in the cellular cytosol.
The primary purpose of the electron transport chain of mitochondria described in the passage is __________.
the generation of energy to sequester protons in the intermembrane space
to directly phosphorylate ADP
to directly phosphorylate AMP
to synthesize ATP synthase
to carry ADP into the mitochondrial matrix
Explanation
The electron transport chain serves to pump protons into the intermembrane space. The result is the buildup of the electrochemical gradient, and the passage of protons through ATP synthase. Essentially, the electron transport chain establishes the conditions for oxidative phosphorylation to occur.
During cellular respiration, where is NADH produced?
The cytosol and mitochondrial matrix
The nucleus
The endoplasmic reticulum
The cytosol
The mitochondrial intermembrane space
Explanation
NADH is produced during glycolysis, which occurs in the cytoplasm. NADH is also produced during the Krebs cycle, which occurs in the mitochondrial matrix. The protons generated in the production of NADH are later used in the intermembrane space to power ATP synthase during oxidative phosphorylation.
If the Krebs cycle is overstimulated, the body will produce too much of which of the following molecules?
Carbon dioxide
Oxygen
Glucose
Acetyl CoA
Pyruvate
Explanation
Of the answer choices, only carbon dioxide is a product of the Krebs cycle. If the cycle is overstimulated, too much of the products will be formed and the body will have too much carbon dioxide.
Glucose is the reactant that fuels glycolysis to produce pyruvate, which is then converted to acetyl CoA for the Krebs cycle. As such, each of these would be depleted as reactants fueling an overstimulation of the Krebs cycle.
Within the Krebs cycle, L-malate and NAD+ come together to form oxaloacetate, NADH, and H+. What type of chemical reaction is responsible for this step in the cycle?
Oxidation
Hydration
Decarboxylation
Dehydration
Explanation
In order for oxaloacetate to be formed, malate must lose electrons, which is the definition of an oxidation reaction. Alternately, NAD+ is reduced (gains electrons) to form NADH and H+.