Biochemistry Block 2.2: Hormones and Signal Transduction

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Questions and Answers

What second messenger is produced when adenylyl cyclase is activated?

cGMP

IP3

cAMP (correct)

DAG

Which role does diacylglycerol (DAG) play in cellular signaling?

It activates protein kinase C (PKC). (correct)

It opens Ca2+ channels in the endoplasmic reticulum.

It binds and activates adenylyl cyclase.

It directly phosphorylates protein substrates.

What is the primary effect of calcium ions in the cytosol?

They cause the dissolution of cellular membranes.

They activate calmodulin and related proteins. (correct)

They inhibit protein synthesis.

They degrade second messengers.

What is produced when guanylyl cyclase is activated?

cGMP Signup and view all the answers

Which of the following processes does not involve phospholipase C?

Activation of protein kinase A (PKA). Signup and view all the answers

What defines Group I hormones?

They are lipid soluble and bind to intracellular receptors. Signup and view all the answers

How do Group II hormones initiate signal transduction?

By binding to membrane receptors and utilizing second messengers. Signup and view all the answers

Which mechanism is primarily used by lipophilic hormones for signal transduction?

Binding to intracellular receptors and affecting gene transcription. Signup and view all the answers

What role does the enzyme cascade play in signal transduction?

It amplifies the signal and leads to multiple cellular responses. Signup and view all the answers

What type of receptors are involved with G protein coupled receptors?

Receptors that facilitate signal transduction via cAMP. Signup and view all the answers

Which of the following is NOT a group of secondary messengers?

Insulin Signup and view all the answers

What effect does the activation of a catalytic receptor have?

It alters the activity of intracellular enzymes. Signup and view all the answers

What is the main function of signal transduction at the cellular level?

To move signals from outside the cell to inside. Signup and view all the answers

What is the primary function of the cGMP-dependent protein kinase (PKG)?

To phosphorylate smooth muscle proteins Signup and view all the answers

Which enzyme catalyzes the conversion of GTP to cGMP?

Guanylyl cyclase Signup and view all the answers

Which pathway directly leads to an increase in intracellular calcium concentration?

Hormones binding with calcium channels Signup and view all the answers

What characterizes the Na/Ca pump in terms of capacity and affinity?

High capacity, low affinity Signup and view all the answers

Which of the following is produced in the cardiac atrial tissue?

Atrial Natriuretic Factor Signup and view all the answers

What is the role of phospholipase C in calcium signaling?

Activates IP3 and DAG formation Signup and view all the answers

Which of the following pumps has a high affinity for calcium but low capacity?

Ca/proton ATPase Signup and view all the answers

What effect does increased cGMP have on smooth muscle tissue?

It promotes relaxation of smooth muscle Signup and view all the answers

What is the primary function of adenylyl cyclase in the signal transduction mechanism?

Convert ATP to cAMP Signup and view all the answers

Which type of G protein is considered inhibitory?

G alpha i Signup and view all the answers

What activates the effector enzyme adenylyl cyclase?

GTP binding Signup and view all the answers

How are the heterotrimeric G proteins characterized?

By possessing three subunits Signup and view all the answers

Which of the following is NOT a characteristic of heterotrimeric G proteins?

Active in their native state Signup and view all the answers

What happens to the alpha subunit of G proteins when the hormone dissociates from its receptor?

It is hydrolyzed to GDP Signup and view all the answers

Which G protein subunit is capable of interacting with specific enzymes?

Alpha subunit only Signup and view all the answers

Which of the following receptors does NOT require second messengers for their action?

Catalytic activity receptors Signup and view all the answers

What distinguishes catalytic receptors from other types of receptors?

They activate protein kinase without the need for second messengers. Signup and view all the answers

Which of the following hormones does NOT utilize the signaling pathway involving nonreceptor tyrosine kinases?

Insulin Signup and view all the answers

What initiates the action of nuclear receptors bound to HRE?

The dissociation of the corepressor. Signup and view all the answers

What characterizes the action of cytoplasmic receptors when they bind to hormones?

They contain a nuclear localization sequence. Signup and view all the answers

What is one of the primary characteristics of the hormone response elements (HRE)?

They can resemble enhancer elements. Signup and view all the answers

Which family of nonreceptor tyrosine kinases is particularly well characterized?

JAK family Signup and view all the answers

What happens to nuclear receptors when they are inactive?

They are bound to corepressors. Signup and view all the answers

Which of the following correctly describes the characteristics of signaling for lipid-soluble hormones?

They diffuse through the cell membrane to bind with intracellular receptors. Signup and view all the answers

Study Notes

Signal Transduction

Refers to the process by which external signals are transmitted to the interior of a cell.
Signals can activate effector enzymes, causing a cascade of cellular changes.
Key players include G proteins, which bind GTP and hydrolyze it to GDP.

Classes of Hormones

Group I: Lipid-soluble (lipophilic), pass through cell membranes and bind to intracellular receptors, influencing gene transcription.
Group II: Water-soluble (hydrophilic) hormones bind to membrane receptors, triggering secondary messenger systems for intracellular signaling.

G Protein Coupled Receptors (GPCR)

Largest family of cell surface receptors in humans.
Comprises heterotrimeric G proteins (three subunits: α, β, γ) and the Ras superfamily (monomeric).
G alpha subunits determine the type of signaling pathway; distinct subunits correspond to specific enzymes like adenylyl cyclase.

Mechanism of Signal Transduction

Hormone binds to its receptor, activating the G protein.
G protein activation leads to GDP release and GTP binding on the alpha subunit, which then dissociates from beta and gamma subunits.
Subsequent activation of enzymes such as adenylyl cyclase produces secondary messengers like cAMP.

Second Messengers

cAMP activates protein kinase A (PKA), modulating various cellular functions.
Calcium ions (Ca2+) released from the endoplasmic reticulum activate enzymes via calmodulin.
Diacylglycerol (DAG) activates protein kinase C (PKC).

Guanylyl Cyclase

Catalyzes the conversion of GTP to cGMP, involved in signaling for smooth muscle relaxation and vasodilation.
Exists in membrane-bound and soluble forms; atriopeptins increase cGMP levels.

Catalytic Receptors

Activate protein kinases directly without requiring second messengers.
Examples include nonreceptor tyrosine kinases like JAK, which associate with hormone receptors.

Nuclear Receptors

Bind hormones and specific DNA response elements (HREs), acting as transcription factors.
Typically exist in an inactive state with a corepressor that is released upon hormone binding.

Key Functional Domains in Receptors

Ligand Binding Domain: Where hormones bind.
Gene Regulatory Domain: Contains motifs that interact with DNA to regulate transcription.
DNA Binding Domain: Involved in binding the hormone-receptor complex to target DNA sequences.

Calcium Regulation

Calcium levels are altered through channels that hormones can directly open.
Phospholipase C cascades lead to calcium influx and production of inositol trisphosphate (IP3) and DAG influencing cellular responses.

Summary of Hormonal Actions

Different hormones can influence cellular processes like gene transcription, protein modification, and enzymatic activity based on their structure and receptors used.

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Description

This quiz covers essential concepts in biochemistry related to hormones, including their classes and mechanisms of action through signal transduction. You'll learn about the different groups of hormones and their lipid-soluble properties. Prepare to test your knowledge on how hormones function within biological systems.