AP BIO U4 - Cell Communication & Cell Cycle (STUDY GUIDE)

Signal transduction pathway

A series of steps that converts an external signal into a specific cellular response.

Ligand

A signaling molecule that binds to a receptor on a target cell.

Hormone

A signaling molecule transported through the bloodstream to distant target cells.

Reception

The stage where a ligand binds to a receptor.

Transduction

The stage where the signal is converted into intracellular steps.

Response

The final cellular action triggered by the signal.

Second messenger

A small molecule that relays and amplifies a signal inside the cell.

G protein

A membrane protein that relays signals from receptors to other proteins.

G-protein-linked receptor

A receptor that activates a G protein when a ligand binds.

Adenylyl cyclase

An enzyme that converts ATP into cAMP.

Cyclic AMP (cAMP)

A second messenger formed from ATP that activates protein kinases.

Protein kinase

An enzyme that phosphorylates proteins using ATP.

Phosphorylation cascade

A series of protein kinases activating one another.

What is local signaling?

Signaling that affects nearby cells through diffusion.

How do animal hormones travel to target cells?

Through the circulatory system (endocrine signaling).

What are the three stages of cell signaling?

Reception, transduction, and response.

How does ligand binding initiate signaling?

Binding causes a receptor shape change that starts transduction.

Where are receptors located?

On the plasma membrane or inside the cell.

Compare GPCRs and ligand-gated ion channels

GPCRs activate G proteins and cascades, ion channels open directly.

Two advantages of multistep pathways

Signal amplification and regulation.

How can a signal work without entering the cell?

By activating membrane receptors that trigger cascades.

How does phosphorylation cause a response?

It activates or deactivates proteins.

Why are many protein kinases needed?

To allow specificity and multiple responses.

What is a second messenger’s role?

Amplifies and relays signals inside the cell.

How is cAMP formed?

Adenylyl cyclase converts ATP into cAMP.

How does cAMP propagate signals?

It activates protein kinases.

How are cytoplasmic responses triggered?

By activating enzymes or structural proteins.

How are nuclear responses triggered?

By activating transcription factors.

What is signal amplification?

One signal activates many molecules.

Why do cells respond differently to the same signal?

They have different receptors and pathways.

What triggers apoptosis?

DNA damage, lack of survival signals, or developmental cues.

Role of apoptosis in development

Removes unnecessary cells.

Role of apoptosis in disease prevention

Eliminates damaged cells to prevent cancer.

Cell cycle

The ordered sequence of events leading to cell division.

Cell division

Formation of two daughter cells.

Interphase

G1, S, and G2 phases.

G1 phase

Cell growth and normal function.

S phase

DNA replication.

G2 phase

Final preparation for mitosis.

G0 phase

Non-dividing resting state.

M phase

Mitosis and cytokinesis.

Mitosis

Division of the nucleus.

Cytokinesis

Division of the cytoplasm.

Chromatin

Uncondensed DNA and proteins.

Chromosome

Condensed DNA molecule.

Sister chromatids

Identical copies of a chromosome.

Centromere

Region joining sister chromatids.

Centrosome

Microtubule organizing center.

Mitotic spindle

Structure that separates chromosomes.

Kinetochore

Protein complex attaching chromosomes to spindle fibers.

Metaphase plate

Plane where chromosomes align.

Prophase

Chromosomes condense and spindle forms.

Metaphase

Chromosomes align at the metaphase plate.

Anaphase

Sister chromatids separate.

Telophase

Nuclear envelopes reform.

Cell plate

Structure that forms the new cell wall in plants.

Cleavage furrow

Indentation that divides animal cells.

Cytokinesis in plants vs animals

Plants form a cell plate, animals form a cleavage furrow.

Binary fission

Prokaryotic cell division.

Checkpoint

Control point where cell cycle progression is regulated.

G1 checkpoint

Checks size, nutrients, and DNA damage.

G2 checkpoint

Ensures DNA replication is complete.

M checkpoint

Ensures spindle attachment.

Cyclin

Protein that activates CDKs.

Cyclin-dependent kinase (Cdk)

Enzyme that drives cell cycle progression.

Growth factor

External signal that stimulates cell division.

Density-dependent inhibition

Cells stop dividing when crowded.

Benign tumor

Noncancerous growth.

Malignant tumor

Cancerous growth that spreads.

Cancer

Loss of cell cycle control.

Positive feedback

A response that amplifies the original stimulus.

Negative feedback

A response that counteracts a stimulus.

Stimulus

A change that triggers a response.

Receptor

A protein that receives a signal.

Effector

A protein that carries out the response.

Difference between positive and negative feedback

Positive amplifies, negative stabilizes.

Homeostasis maintained by which feedback?

Negative feedback.