4.1 Cell Communication - Developing Questions

In signal transduction, what is typically responsible for 'turning off' or terminating a signaling event once it has been initiated?

• Phosphatases remove phosphate groups from proteins, thus

  inactivating them.

• Kinases add phosphate groups to other enzymes, continuously

  activating them.

• Ligands bind irreversibly to receptors, permanently activating them.

• Secondary messengers increase indefinitely, perpetuating activation

  signals.‬

Answer explanation

Phosphatases are enzymes that can deactivate other proteins by removing phosphate groups from them; this process is essential for turning off signaling events and preventing overstimulation of cellular responses.

Tags

NGSS.HS-LS1-3

How does an ion channel receptor transmit information across a membrane without physical transport of signaling molecules?

• By changing conformation upon ligand binding which allows specific

  ions through.

• Transporting secondary messenger molecules into intracellular space.

• Direct involvement in gene transcription similar to steroid receptors.

• Using carrier proteins that shuttle signaling molecules across.

Answer explanation

Ion channel receptors open or close in response to ligand (signaling molecule) binding, allowing ions such as Na+ or Ca² to flow into or out of cells, thus transmitting signals without transporting actual signaling molecule types.

How does signal amplification occur within a cell after it has received an external signal?

• Activation of cascades involving multiple enzymes.

• Increased mutation rates in response to environmental cues.

• Reduction in chromosome number through meiosis.

• Direct stimulation of DNA polymerase activity by external signals.

Answer explanation

Signal amplification involves activation cascades where one activated enzyme activates multiple molecules of another enzyme; this is unrelated to meiosis or DNA replication directly stimulated by external signals or increased mutation rates due to environmental changes which do not describe processes involved in signal transduction pathways within cells upon receiving an external signal.

In signal transduction pathways, what best explains why a small number of hormone molecules can have a large effect on a cell?

• Signal amplification via cascade effects.

• Hormones serve as energy sources for cellular reactions.

• Direct genetic alteration by hormones.

• Immediate destruction of hormones after signaling prevents

  overstimulation.

Answer explanation

Signal amplification occurs when one hormone molecule activates multiple enzymes or second messengers, leading to a cascade effect where one signal molecule can induce a large-scale response within the cell.

In an experiment involving epidermal growth factor (EGF), researchers found that after EGF was added, there was an increase in cell division rates; this suggests EGF likely initiates which type of cellular sequence?

• A metabolic pathway increasing ATP synthesis for cellular functions

• A differentiation pathway causing specialized cell types formation

• Apoptotic signals resulting in programmed cell death

• A signal transduction pathway promoting mitosis

Answer explanation

Epidermal Growth Factor typically binds to its receptor on cells, triggering a signal transduction pathway that stimulates cell division (mitosis) rather than apoptosis, energy production or differentiation processes which are not directly related to increased division rates as observed.

Tags

NGSS.HS-LS1-4

Which type of cell signaling would be most effective for a single-celled organism in a low-density population to communicate with others of its kind?

• Paracrine signaling

• Quorum sensing

• Endocrine signaling

• Synaptic Signaling

Answer explanation

Quorum sensing is a mechanism that enables communication among individual cells, particularly in bacteria, which allows them to detect their density and coordinate behavior when there is a sufficient concentration of signaling molecules, making it ideal for low-density populations.

If a researcher observes that the application of adrenaline to cardiac muscle cells increases their rate of contraction, this observation is best explained by what cellular process?

• Receptor activation leading to signal transduction and increased heart

  muscle activity.

• Increased permeability of the plasma membrane to calcium ions

  without receptor involvement.

• Direct entry of adrenaline into the cytoplasm and binding to DNA to

  alter gene expression.

• Inhibition of phosphodiesterase activity leading to reduced cAMP

  levels within the cells.

Answer explanation

Adrenaline binds to receptors on cardiac muscle cells, activating them and initiating a signal transduction pathway that ultimately leads to increased heart rate; this specific response does not involve direct gene alteration or pathways mentioned in the incorrect answers.

How could cancerous tumors utilize paracrine signaling during angiogenesis?

(Angiogenesis is the formation of new blood vessels)

• Tumors absorb inhibitors preventing local tissue vascularization

• Tumors secrete growth factors stimulating nearby blood vessels

  formation

• Tumors enhance immune responses clearing surrounding vessel tissue

• Tumors release neurotransmitters inhibiting distant neuron synapses

Answer explanation

Cancerous tumors can secrete various paracrine factors like VEGFs encouraging new blood vessel growth nearby providing nutrients needed; other options pertain less directly tumor-related angiogenesis activities

Why are protein kinases critical components within many signal transduction pathways?

• They produce cAMP from ATP upon activation.

• They bind DNA directly and initiate transcription.

• They act as second messengers inside target cells.

• They phosphorylate other proteins, altering activity/function.

Answer explanation

Protein kinases transfer phosphate groups from ATP onto specific amino acids (usually serine/threonine or tyrosine) within target proteins, changing those targets' activity/function.

Which of the following best describes the role of cyclic AMP (cAMP) in a typical G-protein coupled receptor (GPCR) signaling pathway?

• Secondary messenger that amplifies the signal inside the cell.

• Protein that transports ions across the cell membrane.

• Receptor that binds to extracellular ligands.

• Enzyme that directly deactivates the G-protein.

Answer explanation

Cyclic AMP acts as a secondary messenger within cells during signal transduction pathways, helping to amplify and spread the signal internally after it is initiated by an external ligand binding to a receptor like GPCR on the cell surface.