Q1. When cells respond to external stimuli by receptors acting through second (and often third) messengers, this is called an ________________________ ______________________ .

Background

Topic: Cell Signaling Mechanisms

This question tests your understanding of how cells communicate and respond to external signals using receptors and intracellular signaling molecules (second messengers).

Key Terms:

• Receptor: A protein on the cell surface or inside the cell that binds to a specific ligand (signal molecule).

• Second Messenger: Small molecules that relay signals from receptors to target molecules inside the cell.

Step-by-Step Guidance

1. Recall the general process by which an external signal (like a hormone or neurotransmitter) binds to a receptor on the cell membrane.

2. Think about what happens after the receptor is activated—specifically, how the signal is transmitted inside the cell via second messengers.

3. Consider the term used to describe this entire process of signal transmission from outside to inside the cell, involving multiple messengers.

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Q2. There are five receptor types. a) Name each type, b) give a specific example, c) indicate a ligand for your example, d) indicate a 2nd messenger involved in its action, and e) describe the cellular response.

Background

Topic: Types of Cell Surface and Intracellular Receptors

This question assesses your knowledge of the main classes of receptors, their ligands, signaling pathways, and cellular effects.

Key Terms:

• Receptor Types: Includes G protein-coupled receptors, receptor tyrosine kinases, ligand-gated ion channels, nuclear receptors, and others.

• Ligand: A molecule that binds to a receptor to initiate a response.

• Second Messenger: Intracellular signaling molecules like cAMP, IP3, Ca2+, etc.

Step-by-Step Guidance

1. List the five major receptor types found in eukaryotic cells.

2. For each receptor type, think of a well-known example (e.g., a specific hormone receptor).

3. Identify a ligand that binds to each example receptor.

4. Determine the second messenger involved in the signaling pathway for each receptor.

5. Describe the typical cellular response triggered by activation of each receptor type.

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Q3. Give three reasons why glycolysis is considered a core metabolic pathway.

Background

Topic: Central Metabolism

This question tests your understanding of glycolysis and its importance in cellular metabolism.

Key Terms:

• Glycolysis: The metabolic pathway that converts glucose to pyruvate, generating ATP and NADH.

• Core Pathway: A pathway essential for energy production and metabolic integration.

Step-by-Step Guidance

1. Think about the universality of glycolysis across different organisms and cell types.

2. Consider the role of glycolysis in energy production (ATP generation) under both aerobic and anaerobic conditions.

3. Reflect on how glycolysis provides intermediates for other metabolic pathways (e.g., biosynthesis of amino acids, nucleotides).

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Q4. Why does it make sense that adenosine monophosphate (AMP) is a positive allosteric regulator of phosphofructokinase (PFK-1), while adenosine triphosphate (ATP) is a negative effector? What do high levels of these metabolites in the cell signal?

Background

Topic: Allosteric Regulation of Glycolysis

This question examines your understanding of enzyme regulation, specifically how energy status affects glycolytic flux via PFK-1.

Key Terms:

• Allosteric Regulation: Modulation of enzyme activity by binding of effectors at sites other than the active site.

• PFK-1: A key regulatory enzyme in glycolysis.

• AMP/ATP: Indicators of cellular energy status.

Step-by-Step Guidance

1. Recall the role of PFK-1 in glycolysis and why its regulation is important for cellular energy balance.

2. Think about what high levels of AMP and ATP indicate about the cell's energy state.

3. Explain why AMP would activate PFK-1 and why ATP would inhibit it, in terms of feedback regulation.

4. Connect these regulatory effects to the cell's need to produce or conserve ATP.

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Q5. A muscle biopsy from an individual who was incapable of prolonged, intense exercise indicated a severe deficiency of phosphoglycerate mutase, which converts 3-phosphoglycerate to 2-phosphoglycerate.

Background

Topic: Glycolytic Enzyme Deficiencies and Exercise Physiology

This question tests your understanding of the glycolytic pathway and the consequences of enzyme deficiencies on muscle metabolism.

Key Terms:

• Phosphoglycerate Mutase: Enzyme that catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate in glycolysis.

• Metabolic Block: Accumulation of intermediates due to enzyme deficiency.

Step-by-Step Guidance (Part a)

1. Review the steps of glycolysis and locate where phosphoglycerate mutase acts.

2. Consider what happens to glycolytic flux if this step is blocked—what intermediates accumulate, and what products are not formed?

3. Think about how this block would affect ATP production during intense exercise.

4. Relate the enzyme deficiency to the inability to sustain ATP production needed for prolonged, intense muscle activity.

Step-by-Step Guidance (Part b)

1. Recall how lactic acid is produced during anaerobic glycolysis.

2. Consider whether the glycolytic block would increase or decrease pyruvate and lactate formation.

3. Think about whether lactic acid buildup is likely in this scenario, and why.

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Q6. Paper is made from cellulose fibers. Why does paper lose its shape and strength when soaked in water, but not when soaked in oil?

Background

Topic: Carbohydrate Structure and Solubility

This question tests your understanding of the chemical properties of cellulose and its interactions with polar and nonpolar solvents.

Key Terms:

• Cellulose: A polysaccharide composed of glucose units linked by β(1→4) glycosidic bonds.

• Hydrogen Bonding: Intermolecular forces important for cellulose fiber structure.

• Polarity: Water is polar; oil is nonpolar.

Step-by-Step Guidance

1. Recall the structure of cellulose and how its fibers are held together.

2. Think about how water interacts with cellulose via hydrogen bonding.

3. Consider why oil, being nonpolar, does not disrupt these interactions.

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Q7. What three metabolic states promote flux through the pentose phosphate pathway?

Background

Topic: Regulation of the Pentose Phosphate Pathway (PPP)

This question tests your understanding of when and why cells increase activity through the PPP.

Key Terms:

• Pentose Phosphate Pathway: A metabolic pathway parallel to glycolysis, generating NADPH and ribose-5-phosphate.

• Metabolic State: Cellular conditions that influence pathway activity.

Step-by-Step Guidance

1. Recall the main products of the PPP (NADPH, ribose-5-phosphate).

2. Think about cellular processes that require increased NADPH (e.g., fatty acid synthesis, antioxidant defense).

3. Consider when cells need more ribose-5-phosphate (e.g., rapid cell division, nucleotide synthesis).

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Q8. Individuals with glucose-phosphate dehydrogenase (G6PD) deficiency do not very well tolerate antimalarial drugs such as primaquine and yet are resistant to developing malaria even without primaquine therapy. (Primaquine generates reactive oxygen species.)

Background

Topic: Redox Biology and Enzyme Deficiencies

This question explores the role of G6PD in red blood cells, glutathione function, and the effects of oxidative stress.

Key Terms:

• G6PD: Enzyme that catalyzes the first step in the pentose phosphate pathway, producing NADPH.

• Glutathione: A tripeptide that protects cells from oxidative damage.

• Reactive Oxygen Species (ROS): Chemically reactive molecules that can damage cells.

Step-by-Step Guidance (Part a)

1. Recall the function of glutathione in red blood cells, especially in detoxifying ROS.

2. Think about how glutathione is maintained in its reduced form and why this is important for cell survival.

Step-by-Step Guidance (Part b)

1. Consider the role of G6PD in generating NADPH, which is required to regenerate reduced glutathione.

2. Explain how G6PD deficiency affects glutathione levels and the cell's ability to handle oxidative stress.

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Q9. Explain why 3 net ATP molecules are generated by glycolysis when glucose-1-phosphate from glycogen breakdown is the source, but dietary glucose produces only 2 net ATP by glycolysis.

Background

Topic: Glycogen Metabolism and Glycolytic ATP Yield

This question tests your understanding of the differences in ATP yield depending on the source of glucose entering glycolysis.

Key Terms:

• Glycogenolysis: Breakdown of glycogen to glucose-1-phosphate.

• ATP Investment: Steps in glycolysis that consume ATP.

Step-by-Step Guidance

1. Recall the steps of glycolysis and where ATP is consumed and produced.

2. Compare the entry points of glucose-1-phosphate (from glycogen) and free glucose (from diet) into glycolysis.

3. Identify which ATP-consuming step is bypassed when starting from glucose-1-phosphate.

4. Calculate the net ATP yield for each scenario, stopping before the final calculation.

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Q10. Consuming large amounts of alcohol when blood glucose levels are low can lead to hypoglycemia (low blood sugar) due to low rates of gluconeogenesis. Considering that ethanol is oxidized to acetaldehyde by alcohol dehydrogenase (ADH) along with the reduction of NAD+ to NADH + H+, how do you explain the connection between alcohol consumption and hypoglycemia?

Background

Topic: Alcohol Metabolism and Gluconeogenesis

This question tests your understanding of how alcohol metabolism affects the NAD+/NADH ratio and the consequences for gluconeogenesis.

Key Terms:

• Alcohol Dehydrogenase (ADH): Enzyme that converts ethanol to acetaldehyde, producing NADH.

• NAD+/NADH Ratio: Important for redox balance and metabolic pathways.

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate precursors.

Step-by-Step Guidance

1. Recall the reaction catalyzed by ADH and its effect on the NAD+/NADH ratio.

2. Think about how increased NADH affects key gluconeogenic reactions (e.g., conversion of lactate to pyruvate, malate to oxaloacetate).

3. Explain why gluconeogenesis is inhibited under these conditions, leading to hypoglycemia.

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Q11. List the three enzymes in glycolysis that are bypassed in gluconeogenesis and match them with the enzymes in gluconeogenesis that replace them.

Background

Topic: Glycolysis vs. Gluconeogenesis

This question tests your knowledge of the irreversible steps in glycolysis and how they are circumvented in gluconeogenesis.

Key Terms:

• Irreversible Steps: Steps in glycolysis that cannot be reversed by the same enzymes.

• Bypass Enzymes: Enzymes in gluconeogenesis that catalyze the reverse reactions.

Step-by-Step Guidance

1. Identify the three irreversible enzymes in glycolysis.

2. For each, recall the corresponding bypass enzyme(s) in gluconeogenesis.

3. Match each glycolytic enzyme with its gluconeogenic counterpart(s).

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Q12. The intracellular signaling enzyme protein kinase A (PKA) is activated by cyclic adenosine monophosphate (cAMP) binding, after upstream receptor activation by glucagon and epinephrine.

Background

Topic: Hormonal Regulation of Glycogen Metabolism

This question tests your understanding of how hormonal signals regulate glycogen synthesis and breakdown via PKA.

Key Terms:

• Protein Kinase A (PKA): A kinase activated by cAMP, which phosphorylates target proteins.

• Glycogen Synthase: Enzyme that synthesizes glycogen.

• Glycogen Phosphorylase: Enzyme that breaks down glycogen.

• cAMP Phosphodiesterase: Enzyme that degrades cAMP, turning off PKA signaling.

Step-by-Step Guidance (Part a)

1. Recall how PKA activation affects the phosphorylation state of glycogen synthase and glycogen phosphorylase.

2. Think about how phosphorylation alters the activity of these enzymes (activation or inhibition).

Step-by-Step Guidance (Part b)

1. Based on the effects in part (a), determine whether glycogen storage increases or decreases.

Step-by-Step Guidance (Part c)

1. Recall the role of cAMP phosphodiesterase in terminating cAMP signaling.

2. Consider how inhibition of this enzyme by caffeine would affect cAMP levels and PKA activity.

3. Explain how this would influence the effects of glucagon and epinephrine signaling.

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