Unit 4 - Reading Comprehension

These flashcards cover key concepts in signal reception, transduction, and the cell cycle control system necessary for understanding cellular communication and regulation.

What explains why similar signaling pathways are found in diverse organisms?

They originated in early prokaryotes and were inherited by later eukaryotic lineages.

What best defines a target cell?

A cell containing the receptor specific to the ligand.

Why is noncovalent ligand-receptor binding advantageous?

It allows rapid reversal once signaling is complete.

What does allosteric regulation in signal transduction involve?

A molecule binding to one site and altering protein shape at another site.

What distinguishes ligands of intracellular receptors from those of membrane receptors?

They are small or hydrophobic and diffuse across the membrane.

How do activated intracellular hormone-receptor complexes function?

They act as transcription factors that turn on genes.

Which type of molecule would most likely serve as a ligand for a membrane receptor?

A large polar peptide.

What is the immediate effect when a ligand-gated ion channel opens?

Specific ions move across the membrane, altering cellular ion concentrations.

What activates a G-protein during signaling?

Replacement of GDP with GTP when a ligand binds the receptor.

Which structure of all eukaryotic G-protein linked receptors spans the membrane?

They span the membrane once.

What is the first step of cell signaling?

Binding of a chemical messenger to a receptor protein.

Why do shared G-protein structures across eukaryotes support evolutionary theory?

It suggests G-protein mechanisms originated early and were conserved.

What is a major advantage of multistep signal transduction pathways?

They allow for signal amplification and increased regulatory control.

What is the role of protein phosphatases in signal transduction?

They remove phosphate groups to turn off pathways and reuse kinases.

What characteristic allows secondary messengers to rapidly activate proteins?

Their small, hydrophilic nature allowing quick diffusion.

What occurs after cAMP levels rise inside a cell?

Protein kinase A becomes activated.

Which factor most determines a cell's response to a signaling molecule?

The cell's specific collection of receptors and relay proteins.

How do morphogens create distinct cell fates during embryonic development?

By forming a concentration gradient that activates different amounts of receptors.

What initiates the positive feedback loop in childbirth?

The baby pushing on the cervix.

What distinguishes endocrine signaling from other communication types?

It uses hormones traveling long distances through blood.

Which checkpoint is considered most important in mammalian cells?

G1 checkpoint.

What happens to a cell that does not receive a go-ahead signal at the G1 checkpoint?

It enters a non-dividing state called GO.

What stimulates the G1 checkpoint?

Growth factors increasing G1 cyclin concentrations.

What occurs if DNA cannot be repaired at the G2 checkpoint?

The cell undergoes apoptosis.

What happens to mitotic cyclin after the cell enters M phase?

It is degraded.