BIOC 3022 Exam 4 Questions With Complete Solutions
Describe the 5 steps of the urea cycle in order Correct Answers
1) CPS-I: NH₄⁺ + HCO₃⁻ + 2ATP → carbamoyl phosphate
(mitochondria) 2) Ornithine transcarbamoylase: carbamoyl
phosphate + ornithine → citrulline (mitochondria) 3)
Argininosuccinate synthetase: citrulline + aspartate + ATP →
argininosuccinate (cytosol) 4) Argininosuccinate lyase:
argininosuccinate → arginine + fumarate (cytosol) 5) Arginase:
arginine + H₂O → urea + ornithine (cytosol)
Describe the catabolism/deamidation of asparagine Correct
Answers Asparaginase hydrolyzes asparagine → aspartate +
NH₄⁺; aspartate then undergoes transamination with α-
ketoglutarate → oxaloacetate + glutamate
Describe the deamidation of glutamine Correct Answers
Glutaminase cleaves glutamine + H₂O → glutamate + NH₄⁺
(releases ammonium directly)
Describe the Glucose-Alanine Cycle step by step Correct
Answers 1) In muscle, aminotransferase transfers amino group
from glutamate to pyruvate → alanine + α-ketoglutarate 2)
Alanine travels in blood to liver 3) In liver, alanine
aminotransferase reverses the reaction → pyruvate + glutamate
4) Pyruvate enters gluconeogenesis; glutamate releases NH₄⁺
via GDH → urea cycle
Describe the initial 3 steps of valine degradation Correct
Answers 1) Transamination removes α-amino group →
branched-chain α-keto acid 2) Branched-chain α-keto acid
,dehydrogenase complex catalyzes oxidative decarboxylation →
CoA-linked product 3) Acyl-CoA dehydrogenase (same as fatty
acid oxidation) introduces a double bond
Describe the pathway from purines to uric acid Correct
Answers Nucleic acids → purines → hypoxanthine/xanthine →
(xanthine oxidase) → uric acid → excreted in urine
Give examples of purely glucogenic amino acids Correct
Answers Alanine, Arginine, Asparagine, Aspartate, Cysteine,
Glutamate, Glutamine, Glycine, Histidine, Methionine, Proline,
Serine, Valine
How do brown, white, and beige adipocytes differ in UCP1
expression, mitochondrial density, and lipid droplet
morphology? Correct Answers Brown: UCP1+, high
mitochondria, multi-locular LD; White: UCP1-, low
mitochondria, uni-locular LD; Beige: UCP1+, medium
mitochondria, multi-locular LD
How do the three RNA polymerases differ? Correct Answers
They differ in template specificity, location within the nucleus,
and susceptibility to inhibitors.
How does a gated ion channel signal? Correct Answers Opens
or closes in response to signal ligand concentration or changes in
membrane potential, allowing specific ions to flow across the
membrane.
How does a nuclear receptor signal? Correct Answers A steroid
ligand binds the intracellular receptor, allowing it to enter the
,nucleus and directly regulate transcription of specific genes,
leading to mRNA and protein production.
How does a pathogen or inflammatory stimulus change cellular
metabolism? Correct Answers (a) Gene activation via
transcription factors as chromatin opens. (b) Increased metabolic
activity: more glycolysis, pyruvate → lactate, citrate diverted to
lipid/cholesterol synthesis, glutamine fuels TCA anaplerosis. (c)
Expression of inflammatory genes.
How does a receptor guanylyl cyclase signal? Correct Answers
Ligand binding to its extracellular domain stimulates formation
of the second messenger cyclic GMP (cGMP).
How does AMPK regulate fatty acid metabolism through ACC?
Correct Answers AMPK phosphorylates and inactivates ACC
(acetyl-CoA carboxylase), which normally converts acetyl-CoA
→ malonyl-CoA. Less malonyl-CoA means: less fatty acid
synthesis AND less inhibition of CPT-1 → increased β-
oxidation
How does an adhesion receptor (integrin) signal? Correct
Answers Binds molecules in the extracellular matrix, undergoes
a conformational change, and alters its interaction with the
cytoskeleton.
How does calcium activate calmodulin and what is the result?
Correct Answers 1) Ion channel opens (triggered by cAMP or
IP₃), 2) Ca²⁺ enters cytoplasm and binds calmodulin causing a
conformational change, 3) The conformational change enables
calmodulin to bind and activate other target proteins.
, How does cellular senescence connect aging to metabolic
disease? Correct Answers Senescent cells accumulate with age
AND in metabolic disease (obesity, insulin resistance). They
secrete inflammatory cytokines (SASP) that worsen insulin
resistance and tissue function, creating a vicious cycle linking
DNA damage → senescence → inflammation → worsened
metabolism → more ROS/damage
How does chain extension occur in FAS? Correct Answers
Malonyl-CoA is decarboxylated, and the resulting two-carbon
fragment is added to the growing chain
How does citrate cross the inner mitochondrial membrane?
Correct Answers Via the citrate transport protein (a specific
carrier)
How does citrate cross the outer mitochondrial membrane?
Correct Answers By free diffusion
How does DNA damage have systemic consequences beyond
the individual cell? Correct Answers DNA damage →
polymerase stalling (disrupts transcription/replication) and
genetic aberrations (aneuploidy, translocation, mutations,
deletions) → DNA damage signaling → cell fate alterations
(death, senescence, stem-cell loss) → tissue pathology → aging,
functional decline, atrophy, inflammation, and cancer
How does exercise intensity determine which fuel muscle uses?
Correct Answers At low intensities: primarily fatty acids
Describe the 5 steps of the urea cycle in order Correct Answers
1) CPS-I: NH₄⁺ + HCO₃⁻ + 2ATP → carbamoyl phosphate
(mitochondria) 2) Ornithine transcarbamoylase: carbamoyl
phosphate + ornithine → citrulline (mitochondria) 3)
Argininosuccinate synthetase: citrulline + aspartate + ATP →
argininosuccinate (cytosol) 4) Argininosuccinate lyase:
argininosuccinate → arginine + fumarate (cytosol) 5) Arginase:
arginine + H₂O → urea + ornithine (cytosol)
Describe the catabolism/deamidation of asparagine Correct
Answers Asparaginase hydrolyzes asparagine → aspartate +
NH₄⁺; aspartate then undergoes transamination with α-
ketoglutarate → oxaloacetate + glutamate
Describe the deamidation of glutamine Correct Answers
Glutaminase cleaves glutamine + H₂O → glutamate + NH₄⁺
(releases ammonium directly)
Describe the Glucose-Alanine Cycle step by step Correct
Answers 1) In muscle, aminotransferase transfers amino group
from glutamate to pyruvate → alanine + α-ketoglutarate 2)
Alanine travels in blood to liver 3) In liver, alanine
aminotransferase reverses the reaction → pyruvate + glutamate
4) Pyruvate enters gluconeogenesis; glutamate releases NH₄⁺
via GDH → urea cycle
Describe the initial 3 steps of valine degradation Correct
Answers 1) Transamination removes α-amino group →
branched-chain α-keto acid 2) Branched-chain α-keto acid
,dehydrogenase complex catalyzes oxidative decarboxylation →
CoA-linked product 3) Acyl-CoA dehydrogenase (same as fatty
acid oxidation) introduces a double bond
Describe the pathway from purines to uric acid Correct
Answers Nucleic acids → purines → hypoxanthine/xanthine →
(xanthine oxidase) → uric acid → excreted in urine
Give examples of purely glucogenic amino acids Correct
Answers Alanine, Arginine, Asparagine, Aspartate, Cysteine,
Glutamate, Glutamine, Glycine, Histidine, Methionine, Proline,
Serine, Valine
How do brown, white, and beige adipocytes differ in UCP1
expression, mitochondrial density, and lipid droplet
morphology? Correct Answers Brown: UCP1+, high
mitochondria, multi-locular LD; White: UCP1-, low
mitochondria, uni-locular LD; Beige: UCP1+, medium
mitochondria, multi-locular LD
How do the three RNA polymerases differ? Correct Answers
They differ in template specificity, location within the nucleus,
and susceptibility to inhibitors.
How does a gated ion channel signal? Correct Answers Opens
or closes in response to signal ligand concentration or changes in
membrane potential, allowing specific ions to flow across the
membrane.
How does a nuclear receptor signal? Correct Answers A steroid
ligand binds the intracellular receptor, allowing it to enter the
,nucleus and directly regulate transcription of specific genes,
leading to mRNA and protein production.
How does a pathogen or inflammatory stimulus change cellular
metabolism? Correct Answers (a) Gene activation via
transcription factors as chromatin opens. (b) Increased metabolic
activity: more glycolysis, pyruvate → lactate, citrate diverted to
lipid/cholesterol synthesis, glutamine fuels TCA anaplerosis. (c)
Expression of inflammatory genes.
How does a receptor guanylyl cyclase signal? Correct Answers
Ligand binding to its extracellular domain stimulates formation
of the second messenger cyclic GMP (cGMP).
How does AMPK regulate fatty acid metabolism through ACC?
Correct Answers AMPK phosphorylates and inactivates ACC
(acetyl-CoA carboxylase), which normally converts acetyl-CoA
→ malonyl-CoA. Less malonyl-CoA means: less fatty acid
synthesis AND less inhibition of CPT-1 → increased β-
oxidation
How does an adhesion receptor (integrin) signal? Correct
Answers Binds molecules in the extracellular matrix, undergoes
a conformational change, and alters its interaction with the
cytoskeleton.
How does calcium activate calmodulin and what is the result?
Correct Answers 1) Ion channel opens (triggered by cAMP or
IP₃), 2) Ca²⁺ enters cytoplasm and binds calmodulin causing a
conformational change, 3) The conformational change enables
calmodulin to bind and activate other target proteins.
, How does cellular senescence connect aging to metabolic
disease? Correct Answers Senescent cells accumulate with age
AND in metabolic disease (obesity, insulin resistance). They
secrete inflammatory cytokines (SASP) that worsen insulin
resistance and tissue function, creating a vicious cycle linking
DNA damage → senescence → inflammation → worsened
metabolism → more ROS/damage
How does chain extension occur in FAS? Correct Answers
Malonyl-CoA is decarboxylated, and the resulting two-carbon
fragment is added to the growing chain
How does citrate cross the inner mitochondrial membrane?
Correct Answers Via the citrate transport protein (a specific
carrier)
How does citrate cross the outer mitochondrial membrane?
Correct Answers By free diffusion
How does DNA damage have systemic consequences beyond
the individual cell? Correct Answers DNA damage →
polymerase stalling (disrupts transcription/replication) and
genetic aberrations (aneuploidy, translocation, mutations,
deletions) → DNA damage signaling → cell fate alterations
(death, senescence, stem-cell loss) → tissue pathology → aging,
functional decline, atrophy, inflammation, and cancer
How does exercise intensity determine which fuel muscle uses?
Correct Answers At low intensities: primarily fatty acids
