Biochemistry Week 8: G Proteins

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Questions and Answers

What role does mRNA play in protein synthesis?

It dictates the sequence of amino acids for protein production. (correct)

It catalyzes the reaction of proteins during synthesis.

It serves as a receptor for extracellular signals.

It modifies the structure of membrane proteins directly.

Which class of receptors is characterized by being located on the plasma membrane and includes ion channel receptors?

Intracellular receptors

Plasma receptors (correct)

G-protein coupled receptors (GPCRs)

Catalytic receptors

What can the protein produced as a result of mRNA translation function as?

Only as a structural protein without metabolic impact.

Only as a membrane receptor.

An enzyme or a channel affecting physiological processes. (correct)

Only as an enzyme with no other roles.

In the context of signal transduction mechanisms, what is primarily influenced by the regulation of gene expression?

Metabolic and growth activities of the cell. Signup and view all the answers

Which of the following is a type of ligand involved in cell-to-cell communication?

Hormones and neurotransmitters. Signup and view all the answers

What characterizes autocrine signaling?

The sending cell also acts as the receiving cell. Signup and view all the answers

Which signaling type specifically involves transmitting signals between nerve cells?

Synaptic signaling Signup and view all the answers

Which component does the Tyrosine Kinase-Associated receptor lack?

Intrinsic signaling ability Signup and view all the answers

In endocrine signaling, what is a key feature regarding the chemical messenger?

It travels through blood vessels to reach target cells. Signup and view all the answers

What process follows the binding of a ligand to its receptor?

The signal is transmitted intracellularly. Signup and view all the answers

What initiates the phosphorylation process in Tyrosine Kinase-Associated receptors?

Ligand binding Signup and view all the answers

Which molecule is responsible for dimerizing with STAT after phosphorylation?

Phosphorylated receptor Signup and view all the answers

Which best describes the modulation associated with a single ligand?

It activates multiple effector proteins, enhancing the physiological effect. Signup and view all the answers

What happens to the ion channel when acetylcholine binds to its receptor?

The ion channel opens. Signup and view all the answers

Which of the following does NOT mediate transcription through Tyrosine Kinase-Associated receptors?

Receptor tyrosine kinases Signup and view all the answers

Which of the following is NOT a characteristic of paracrine signaling?

It requires the messenger to travel through the bloodstream. Signup and view all the answers

What is the primary function of the JAK family in the context of Tyrosine Kinase-Associated receptors?

Phosphorylate the receptor Signup and view all the answers

What is a significant outcome of signal transduction once a ligand binds to its receptor?

Activation of several effector proteins may occur. Signup and view all the answers

Which type of hormones primarily operate through intracellular receptors, as mentioned in the context?

Steroid and thyroid hormones Signup and view all the answers

What role does STAT play in the signaling pathway associated with Tyrosine Kinase-Associated receptors?

Formation of a transcription complex Signup and view all the answers

Which of the following best describes the process after a hormone binds to its receptor in the context of Tyrosine Kinase-Associated receptors?

The receptor-hormone complex enters the nucleus for transcription activation Signup and view all the answers

What is the role of protein kinase A in cell signaling?

To attach phosphates to proteins or enzymes Signup and view all the answers

Which G protein is specifically mentioned as being part of the phosphodiesterase pathway?

Gt Signup and view all the answers

What is the main function of cyclic AMP as a secondary messenger?

To phosphorylate proteins, affecting metabolic pathways Signup and view all the answers

Which of the following is NOT one of the types of secondary messengers mentioned?

Nitric oxide Signup and view all the answers

What determines whether protein kinase A will activate or inhibit a pathway?

The type of ligand and cell being activated Signup and view all the answers

Which component is a product of the phosphoinositide (PIP2) pathway?

DAG Signup and view all the answers

What initiates the activity of adenyl cyclase and cAMP in cell signaling?

Ligand binding to the receptor Signup and view all the answers

Which type of G protein is classified as stimulatory?

Gs Signup and view all the answers

What is the role of protein kinase A (PKA) when activated?

It activates certain enzymes. Signup and view all the answers

How does phospholipase C contribute to physiological responses?

By producing diacylglycerol and inositol triphosphate. Signup and view all the answers

What is the main function of phospholipase A2?

To release arachidonic acid. Signup and view all the answers

How is phospholipase C activated?

By Gq protein activation. Signup and view all the answers

What is the relationship between calcium and physiological effects?

Calcium acts through the Calmodulin complex. Signup and view all the answers

Which G protein is primarily associated with inhibiting pathways?

Gi. Signup and view all the answers

What secondary messenger can be increased by both Gs and phospholipase C pathways?

Calcium. Signup and view all the answers

Which statement about calcium's role in signaling is true?

Calcium's action requires the Calmodulin complex. Signup and view all the answers

Study Notes

Physiologic Response and G Proteins

Physiologic responses are mediated through G proteins attached to receptors.
Different types of G proteins include GRPn0 (effect not specified) and GNO (effect not specified).

Protein Kinase A (PKA)

PKA phosphorylates proteins or enzymes, leading to their activation or inhibition.
The effect of PKA activation depends on the specific ligand and cell type.
Activation of PKA influences various metabolic pathways.

Secondary Messengers

Key secondary messengers include:
- Cyclic AMP (cAMP) and cyclic GMP (cGMP).
- Arachidonic acid metabolites such as prostaglandins and leukotrienes.
- Calcium ions, which serve as secondary messengers, modulating various cellular processes.

Signaling Pathways

Adenyl Cyclase/cAMP/PKA Pathway:
- Activated by Gs (stimulatory G protein).

Types of Cell Signaling

Autocrine Signaling:
- The signaling cell also acts as the receiving cell.
Intracrine Signaling:
- Chemical messengers act within the cell without being released extracellularly.
Synaptic Signaling:
- Occurs specifically between nerve cells or between a nerve cell and another cell.
Endocrine Signaling:
- Relies on chemical messengers traveling through the bloodstream to reach target cells.

Signal Modulation

A single ligand can activate multiple effector proteins, leading to amplified physiological effects.

Receptor Types and Function

Receptors are crucial for signal transduction, and their interaction with ligands can lead to opening or closing ion channels.
Example: Acetylcholine binding opens an ion channel, while another G protein may inhibit this process.

Phospholipases and their Role

Phospholipases (notably A2 and C) hydrolyze phospholipids to release signaling molecules.
Phospholipase C generates diacylglycerol (DAG) and inositol triphosphate (IP3).
Calcium levels can be influenced by Gs signaling pathways.

Tyrosine Kinase Signaling

Tyrosine kinase-associated receptors do not have inherent tyrosine kinase activity; they depend on the activation of Janus Kinase (JAK).
Upon ligand binding, JAK phosphorylates the receptor, initiating transcription via STAT proteins.

Gene Expression Regulation

Gene expression is regulated during signaling transduction, affecting both metabolism and cell growth.
Various ligands and receptor types influence gene expression pathways.

Types of Receptors

Plasma Receptors:
- Include ion channel receptors, G protein-coupled receptors (GPCRs), and catalytic receptors.
Intracellular Receptors:
- Include those that respond to steroid and thyroid hormones.

Regulated Intramembrane Proteolysis (RIP)

Non-classical signaling mechanism involving membrane proteins that can convert extracellular signals into intracellular effects.

Summary Points

Understand mechanisms of cell-to-cell communication.
Familiarize with types of ligands and classes of receptors based on location and mechanism.

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Description

This quiz covers the physiological responses mediated by G proteins and their effects as related to receptor mechanisms. Test your understanding of the biochemical pathways discussed in Week 8 of the Biochemistry course.