AP Biology Unit 4 – Cell Communication and Cell Cycle: Ultimate Study Notes (CED aligned)

Cell Communication

Types of Cell Signaling

Local and Long-Distance Signaling

• Autocrine: cell signals itself

• Paracrine: signals nearby cells

• Endocrine: long-distance signaling via hormones in bloodstream

• Cause → Effect

  • Signal released → travels to target cell → response triggered

• Tips

  • If distance is involved → mention endocrine signaling

  • Always identify source and target cell

Signal Reception

Receptor Binding

• Ligand (signal molecule) binds to receptor protein

• Receptor changes shape when ligand binds

• Only specific ligands bind specific receptors

• Types of receptors:

  • Cell surface receptors (for large/polar molecules)

  • Intracellular receptors (for small/nonpolar molecules)

• Cause → Effect

  • Ligand binding → receptor shape change → initiates signaling

• Tips

  • Use terms: ligand, receptor, specificity

Signal Transduction

Signal Cascade

• Series of steps inside the cell

• Often involves phosphorylation (adding phosphate groups)

• Amplifies the signal

• Cause → Effect

  • One signal → cascade → large response

• Tips

  • Use term: phosphorylation cascade

  • Emphasize signal amplification

Cellular Response

Types of Responses

• Changes in gene expression

• Activation or inhibition of enzymes

• Cell movement or secretion

• Cause → Effect

  • Signal → transduction → response (gene/protein change)

• Tips

  • Always connect response to protein activity or gene expression

Feedback Mechanisms

Negative Feedback

Maintaining Stability

• Reduces or shuts down a process

• Maintains homeostasis

• Example:

  • High product levels → inhibit pathway

• Cause → Effect

  • Increase in output → system slows → balance restored

Positive Feedback

Amplifying Responses

• Increases or enhances a process

• Leads to rapid change

• Example:

  • Blood clotting cascade

• Cause → Effect

  • Initial stimulus → increased response → rapid outcome

• Tips

  • Negative = stabilizes

  • Positive = amplifies

Cell Cycle

Cell Cycle Phases

Interphase

• G1: cell growth

• S: DNA replication

• G2: preparation for division

Mitosis

• Division of nucleus

• Produces identical daughter cells

• Cause → Effect

  • DNA replication → ensures identical genetic information

• Tips

  • Interphase = longest stage

Mitosis Stages

PMAT Stages

• Prophase:

  • Chromosomes condense

  • Nuclear membrane breaks down

• Metaphase:

  • Chromosomes line up in middle

• Anaphase:

  • Sister chromatids separate

• Telophase:

  • Nuclear membranes reform

• Cause → Effect

  • Proper chromosome separation → identical cells

• Tips

  • Memory trick: PMAT

  • Metaphase = “middle”

Cytokinesis

Cytoplasmic Division

• Division of cytoplasm

• Animal cells: cleavage furrow

• Plant cells: cell plate

Regulation of Cell Cycle

Checkpoints and Control

Cell Cycle Regulation

• Checkpoints at G1, G2, and M phase

• Ensure DNA is correct before division

• Cause → Effect

  • Errors detected → cycle stops → prevents damage

Cyclins and CDKs

Molecular Control

• Cyclins regulate timing

• CDKs (cyclin-dependent kinases) control progression

• Cause → Effect

  • Cyclin/CDK activity → cell cycle progression

Cancer and Cell Cycle Disruption

Loss of Regulation

• Mutations in regulatory genes

• Cells divide uncontrollably

• Can form tumors

• Cause → Effect

  • Mutation → loss of checkpoint control → uncontrolled division

• Tips

  • ALWAYS mention:

    • “loss of regulation”

    • “uncontrolled cell division”