Cell signalling

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Questions and Answers

What is the first step in the process of cell signaling?

Respond to signal

Transduce the signal

Receive the signal (correct)

Convert the signal to intracellular info

Which type of signaling involves cells communicating over short distances using secreted messenger molecules?

Paracrine signaling (correct)

Juxtracrine signaling

Autocrine signaling

Endocrine signaling

What type of receptors can trigger multiple signal transduction pathways at once?

Intracellular receptors

G protein-coupled receptors

Ion channel receptors

Receptor tyrosine kinases (correct)

Which process describes signaling between the same cell?

Autocrine signaling Signup and view all the answers

What is a defining feature of G protein-coupled receptors?

They associate with a G protein Signup and view all the answers

What is required for a cell to respond to a specific signal?

The presence of a receptor specific to that signal Signup and view all the answers

Which of the following is NOT a type of membrane receptor?

Intracellular receptors Signup and view all the answers

What does cortisol primarily aid in regarding metabolism?

Increasing blood sugar through gluconeogenesis Signup and view all the answers

What is the primary role of a kinase enzyme in cell signaling?

To add a phosphate group to a target protein Signup and view all the answers

What happens when a ligand binds to a ligand-gated ion channel?

It induces a shape change allowing specific ions to flow Signup and view all the answers

How do intracellular receptors operate when activated by small hydrophobic chemical messengers?

They directly alter gene expression as transcription factors Signup and view all the answers

In signal transduction, what is the significance of protein phosphorylation?

It represents a mechanism for regulating protein activity Signup and view all the answers

Which of the following is NOT a common second messenger in signaling pathways?

ATP Signup and view all the answers

What initiates the activation of protein kinase A (PKA) in a signaling pathway involving cyclic AMP?

Conversion of ATP to cAMP Signup and view all the answers

What is the primary consequence of increased calcium ion concentrations in animal cells?

Secretion of substances and cell division Signup and view all the answers

What occurs during the nuclear response of a signal transduction pathway?

Gene expression is regulated through transcription factors Signup and view all the answers

Why is signaling termination important in cellular pathways?

It allows cells to remain responsive to new signals Signup and view all the answers

What would likely happen if molecular changes in signaling pathways became locked in one state?

The cell might exhibit disrupted functions Signup and view all the answers

Study Notes

Cell Signaling Overview

Cell signaling is a complex communication system that governs cellular activities
Cells receive, transduce, and respond to signals
Signals can be proteins, peptides, small molecules, or inorganic ions
Types of signaling: autocrine (same cell), paracrine (nearby cell), endocrine (distant cell), juxtacrine (cell contact dependent)

Paracrine Signaling

Local signaling using secreted messenger molecules over short distances
Growth factors (cytokines) are examples

Endocrine Signaling

Long-distance signaling using hormones
Specialized cells release hormones into the circulatory system to target distant cells
Cellular response depends on receptor presence

Receptor Classification

Receptors are categorized as intracellular or cell surface
Intracellular receptors: in cytoplasm or nucleus, suitable for lipophilic signals
Cell surface receptors: on the plasma membrane, for hydrophilic signals.

Receptor Types

G protein-coupled receptors (GPCRs): largest family, associate with G proteins. Bind various signals like epinephrine and neurotransmitters
Receptor tyrosine kinases (RTKs): phosphorylate tyrosine residues, trigger multiple pathways affecting growth and reproduction. Abnormal RTK function can cause cancer.
Ligand-gated ion channels: act as gates responding to ligand binding, allow ion flow, regulate cell activities

Intracellular Receptors

Located in the cytoplasm or nucleus.
Small, hydrophobic signals like steroid and thyroid hormones cross the membrane and bind.

Signal Transduction

Signal binding triggers a cascade of conformational changes. Often involves phosphorylation.
Second messengers: small, non-protein, water-soluble molecules (e.g., cAMP, calcium ions) amplify and relay the signal.

Protein Phosphorylation

Protein kinases add phosphates to proteins for activation or inactivation, often creating cascades.
Protein phosphatases remove the phosphates. This acts as a molecular on/off switch.
This is common in nearly all signaling pathways

Second Messenger cAMP

GPCR activation leads to adenylyl cyclase activation
Adenylyl cyclase converts ATP to cAMP
Cyclic AMP activates protein kinase A signaling pathway.

Second Messenger Ca²⁺

Cytoplasmic Ca²⁺ concentration is lower than outside.
Increased Ca²⁺ can cause muscle contraction, substance secretion, and cell division.

Signal Response

Signal transduction pathways regulate cellular activities
Cytoplasmic responses (enzyme activation, ion channel opening)
Nuclear responses (protein synthesis, gene expression changes in the nucleus)

Signal Termination

Deactivation mechanisms are essential for cell signaling.
Molecular changes must be short-lived for cell alertness
Inactivation prevents signalling pathway components from permanently locking in one state preventing proper cell function.