Exam 3 Flashcards
- Which of the following statements about gluconeogenesis is true?
A) It occurs in the kidney, but not the liver.
B) It synthesizes glucose from fatty acids.
C) It is especially important during fasting.
D) It does not consume ATP.
C) It is especially important during fasting.
Gluconeogenesis synthesizes glucose from non-carbohydrate precursors like pyruvate and occurs mainly in the liver. It is upregulated during fasting to maintain
blood glucose levels. The pathway requires energy input in the form of ATP.
How does gluconeogenesis get around the irreversible steps of glycolysis?
A) It runs the steps of glycolysis backward.
B) It uses different enzymes and reactions.
C) It activates the once-inactive glycolytic enzymes.
D) It inhibits the enzymes catalyzing irreversible steps.
B) It uses different enzymes and reactions.
Gluconeogenesis cannot simply run glycolysis in reverse because of three irreversible steps. Instead it uses different enzymes like pyruvate carboxylase and phosphoenolpyruvate carboxykinase to bypass these steps.
How is ATP formed in glycolysis?
A) By oxidative phosphorylation
B) By substrate-level phosphorylation
C) By photophosphorylation
D) By decarboxylation
B) By substrate-level phosphorylation
ATP formation in glycolysis occurs by substrate-level phosphorylation, where a phosphate group is transferred from a high-energy reactant (a substrate) to ADP
to form ATP.
Where does the reaction catalyzed by pyruvate carboxylase take place?
A) Mitochondrial matrix
B) Mitochondrial inner membrane
C) Cytoplasm
D) Endoplasmic reticulum
A) Mitochondrial matrix
Pyruvate carboxylase catalyzes the carboxylation of pyruvate to
oxaloacetate in the mitochondrial matrix.
During periods of prolonged fasting, which organ predominantly supplies glucose to
the rest of the body?
A) Pancreas
B) Liver
C) Stomach
D) Kidneys
B) Liver
During periods of prolonged fasting, the liver predominantly supplies glucose to the rest of the body. This is done through gluconeogenesis, the process of
synthesizing glucose from noncarbohydrate precursors.
In gluconeogenesis, which molecule can be converted directly into glucose?
A) Pyruvate
B) Lactate
C) Fructose-1,6-bisphosphate
D) Glucose-6-phosphate
D) Glucose-6-phosphate
In gluconeogenesis, the final step is the conversion of glucose-6-phosphate
into glucose. This reaction is catalyzed by the enzyme glucose-6-phosphatase.
Which of the following enzymes is NOT allosterically regulated in glycolysis?
A) Hexokinase
B) Phosphofructokinase
C) Aldolase
D) Pyruvate kinase
C) Aldolase
Hexokinase, phosphofructokinase, and pyruvate kinase are all regulated by
allosteric modulators. Aldolase catalyzes a reversible reaction and is not a regulated
enzyme.
Which of the following steps in the glycolysis pathway is irreversible?
A. Conversion of glucose to glucose-6-phosphate
B. Conversion of fructose 6-phosphate to fructose 1,6-bisphosphate
C. Conversion of 3-phosphoglycerate to 2-phosphoglycerate
D. Both A and B
E. Both B and C
D. Both A and B
In the glycolysis pathway, the conversion of glucose to
glucose-6-phosphate (catalyzed by hexokinase) and the conversion of fructose
6-phosphate to fructose 1,6-bisphosphate (catalyzed by phosphofructokinase-1) are
irreversible steps. This means that these reactions do not readily run in reverse under
physiological conditions. These are also important regulatory points in the glycolytic
pathway.
Which type of metabolic pathway breaks down complex molecules into simpler ones
to release energy?
A) Anabolic pathways
B) Catabolic pathways
C) Amphibolic pathways
D) Exergonic pathways
B) Catabolic pathways
Catabolic pathways are metabolic pathways that break down complex
molecules into simpler ones, releasing energy in the process. An example is the breakdown of glucose in the process of glycolysis.
Which organ can use lactate, a product of muscle anaerobic respiration, as a
precursor for gluconeogenesis?
A) Pancreas
B) Kidneys
C) Liver
D) Heart
E) A and B
C) Liver
The liver can take up lactate, a product of muscle anaerobic respiration, and
use it as a precursor for gluconeogenesis. This is part of the Cori cycle, where lactate
produced by the muscles is transported to the liver, converted to glucose, and then sent
back to the muscles.
Which of the following metabolic conversions occurs in the liver but not skeletal
muscle?
A) Glycogenolysis
B) Gluconeogenesis
C) Glycolysis
D) Oxidation of fatty acids
B) Gluconeogenesis
Gluconeogenesis occurs in the liver but not skeletal muscle. Skeletal muscle performs glycogenolysis, glycolysis, and fatty acid oxidation but not gluconeogenesis.
Reciprocal regulation of glycolysis and gluconeogenesis prevents:
A) ATP generation.
B) Glucose utilization.
C) Simultaneous operation.
D) Precursor availability.
C) Simultaneous operation.
Reciprocal regulation ensures that glycolysis and gluconeogenesis are not
highly active at the same time. This prevents a futile cycle in which substrates would be interconverted without net flux.
Which of the following best represents a recurring motif in metabolic pathways?
A) Every metabolic pathway is unique and does not share any common features with others
B) Metabolic pathways often involve the transfer of phosphate groups, redox reactions, or the coupling of endergonic and exergonic reactions
C) Metabolic pathways only take place in the mitochondria
D) Metabolic pathways rely on the destruction of ATP to release energy
B) Metabolic pathways often involve the transfer of phosphate groups, redox reactions, or the coupling of endergonic and exergonic reactions
Metabolic pathways frequently involve common motifs, such as the transfer
of phosphate groups (as in ATP), redox reactions (where one molecule is oxidized and another reduced), and the coupling of energetically unfavorable reactions (endergonic) with favorable ones (exergonic) to drive the overall process forward.
Chylomicrons are:
A) Formed in the liver from triglycerides and cholesterol synthesized in the hepatocytes.
B) Assembled in intestinal epithelial cells from dietary lipids.
C) The largest and least dense of the lipoprotein particles.
D) B and C are both correct.
E) A and C are both correct.
D) B and C are both correct.
Chylomicrons are assembled and secreted by intestinal epithelial cells using dietary lipids. They are the largest and least dense lipoprotein particle.
When considering the structural aspects of receptor tyrosine kinases (RTKs), which
statement accurately describes them?
A) They are devoid of kinase activity and reside primarily inside the cell.
B) They possess a singular transmembrane domain with both extracellular ligand-binding and intracellular kinase regions.
C) Their composition is entirely intracellular without any membrane-spanning segments.
D) Each RTK consists of two distinct polypeptide chains that operate independently.
E) none of the above
B) They possess a singular transmembrane domain with both extracellular ligand-binding and intracellular kinase regions.
Receptor tyrosine kinases are distinguished by a single transmembrane domain. This structural feature allows them to have an extracellular segment responsible
for ligand binding and an intracellular portion that houses the kinase domain.
Which of the following is true regarding G protein-coupled receptors?
A) They lack intracellular domains.
B) They interact with GTP-binding proteins inside the cell.
C) They have tyrosine kinase activity.
D) They directly catalyze the formation of second messengers.
B) They interact with GTP-binding proteins inside the cell.
G protein-coupled receptors interact with GTP-binding proteins (G proteins)
inside the cell to initiate signaling cascades that lead to second messenger formation.
Which molecule is NAD+?
C
Which molecule is Vitamin B2 (riboflavin)?
E
Which molecule is Acetyl CoA?
A
Which molecule Diacylglycerol?
D
Which molecule is Inositol-3 phosphate?
C
Which molecule is 1,3 Bisphosphoglycerate?
A
Which molecule is Biotin?
E
