Biology Chapter on ATP Functions

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Questions and Answers

What structural feature is characteristic of GPCRs?

Seven membrane-spanning helical segments (correct)

Single membrane layer

Two membrane-spanning segments

Five membrane-spanning segments

What happens to G alpha upon the stimulation of a GPCR by an agonist?

G alpha dissociates from the receptor and exchanges GDP for GTP (correct)

G alpha activates G beta-gamma

G alpha is inactivated permanently

G alpha remains bound to GDP

Where is the amino terminus located in a GPCR?

Cytosolic side

Membrane core

Extracellular face (correct)

Intra-cellular environment

What is the role of the G beta-gamma complex in relation to GPCRs?

It remains unchanged during receptor activation Signup and view all the answers

What occurs in the cell when no external signaling molecules are present?

G alpha is in an inactive state bound to GDP Signup and view all the answers

What is the role of Gq proteins in cellular signaling?

Increase calcium channel activity Signup and view all the answers

Which type of receptors are located in the cytoplasm or nucleus and respond to lipid soluble messengers?

Intracellular receptors Signup and view all the answers

What is required for a drug to bind to intracellular receptors?

Ability to cross cell membrane Signup and view all the answers

How do intracellular receptors typically alter gene expression?

By binding to specific genes Signup and view all the answers

Which G protein type is responsible for decreasing cAMP levels?

Gi Signup and view all the answers

What is the primary function of Gs proteins in signaling pathways?

Increase cAMP levels Signup and view all the answers

What is one of the methods by which Gi proteins decrease cAMP levels?

Opening potassium channels Signup and view all the answers

How does the action of intracellular receptors compare to other classes of receptors?

It takes time for gene expression changes Signup and view all the answers

What defines a full agonist in terms of receptor activity?

Has affinity and maximal intrinsic activity Signup and view all the answers

What characterizes a partial agonist?

Has affinity and submaximal intrinsic activity Signup and view all the answers

Which statement best describes antagonists?

They have affinity but no intrinsic activity Signup and view all the answers

In the context of receptor types, where are intracellular receptors typically located?

In the cytoplasm or nucleus Signup and view all the answers

What is the primary difference between full agonists and partial agonists in terms of effect?

Full agonists produce maximal effects, while partial agonists produce submaximal effects Signup and view all the answers

How are receptors primarily classified based on their location?

As cell-surface or intracellular receptors Signup and view all the answers

What kind of response do antagonists produce when they bind to a receptor?

No response at all Signup and view all the answers

Which of the following correctly categorizes receptor types?

Enzyme-linked receptors can be cell-surface receptors Signup and view all the answers

What is the primary result of receptor desensitization?

Decreased response to stimulation Signup and view all the answers

What does the therapeutic index represent in pharmacology?

The safety margin between drug effectiveness and toxicity Signup and view all the answers

Which of the following can be a consequence of desensitization?

Altered receptor levels and expression Signup and view all the answers

In the context of drug holidays, what is the purpose of temporarily stopping a medication?

To allow the body to reset its response to the drug Signup and view all the answers

What is the relationship described by the dose-effect curve?

Increased doses correlate with increased effects Signup and view all the answers

What does LD50 represent in the context of the therapeutic index?

The dose at which 50% of animals experience lethal effects Signup and view all the answers

Which of the following terms describes the minimum dose required to achieve a therapeutic effect?

ED50 Signup and view all the answers

What mechanism might lead to decreased therapeutic efficacy over time?

Changes in receptor conformation Signup and view all the answers

What does the therapeutic index measure?

The safety margin of a drug based on dose Signup and view all the answers

Which of the following statements is true about drugs with a narrow therapeutic index (NTI)?

They require frequent monitoring of blood levels. Signup and view all the answers

If Drug A has an LD50 of 300 mg and an ED50 of 100 mg, what is its therapeutic index?

3 Signup and view all the answers

What can be a consequence of a narrow therapeutic index drug?

Serious therapeutic failures may occur Signup and view all the answers

Which of the following is characteristic of drugs with a wide therapeutic index?

They are less likely to cause significant disability. Signup and view all the answers

What is indicated by the ratio of TD50 to ED50 in the context of drug safety?

The safety margin of the drug Signup and view all the answers

Why are drugs with a narrow therapeutic index not preferred?

They may lead to significant adverse drug reactions. Signup and view all the answers

How can the therapeutic index be improved for existing drugs?

By improving drug formulation and delivery Signup and view all the answers

Study Notes

G Protein Signaling Pathways

Gs: Increases cAMP levels.
Gi: Decreases cAMP levels and opens potassium channels.
Gq: Increases calcium channel activity.

Types of G Proteins

G proteins linked to calcium increase are primarily associated with Gq subtypes.
Gi type causes a reduction in cAMP via two mechanisms: opening potassium channels and decreasing cAMP in selected tissues.

Intracellular Receptors

Located in cytoplasm; respond to lipid-soluble chemical messengers that cross cell membranes.
These receptors bind specific genes to modulate their expression, leading to slower responses compared to cell surface receptors.

Receptor Types

Agonists: Have both affinity and maximal intrinsic activity.
Partial Agonists: Display affinity and sub-maximal intrinsic activity.
Antagonists: Possess affinity but no intrinsic activity.

Drug Concentration Response

Full Agonist: Maximum response at high concentrations.
Partial Agonist: Produces less than the maximum effect.
Antagonist: Binds but does not produce any effect on the receptor.

Classification of Receptors

Cell-Surface Receptors: Involves ligand-gated ion channels, enzyme-linked, and GPCR.
Intracellular Receptors: Includes cytoplasmic and nuclear receptors.
GPCRs consist of seven membrane-spanning helices and interact with G proteins upon ligand binding.

Receptor Activation Mechanism

Ligand binding induces a conformational change in GPCR, causing G protein activation (GDP exchanges for GTP).
G alpha subunit activates downstream signaling pathways, while G beta-gamma also plays a role.

Receptor Desensitization and Downregulation

Refers to reduced cellular response following prolonged exposure to agonists.
Mechanisms include transcriptional/translational changes, conformational alterations, and receptor localization changes.
Can necessitate dose adjustments or drug holidays to maintain therapeutic efficacy.

Dose-Effect Relationships

Increasing drug dose typically results in an enhanced effect on response.

Therapeutic Index

Calculated as the ratio of LD50 (lethal dose) to ED50 (effective dose) in animals.
In humans, calculated as TD50 (toxic dose) to ED50, without lethal dose considerations.
Narrow Therapeutic Index (NTI): Riskier as small dose changes can lead to adverse reactions.
Wide Therapeutic Index: Preferred due to a larger margin of safety.

Clinical Relevance

Understanding the therapeutic index helps assess drug safety and efficacy.
Knowledge of dose-response curves assists in determining appropriate therapeutic regimens.

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Description

This quiz covers the biochemical functions of ATP, including its conversion processes and roles in energy metabolism. Focuses on the relationship between ATP and other molecules such as GDP and gamma. Test your understanding of ATP's functions and significance in biological systems.