AP Biology Review Sheet: The Cell Cycle & Cell Cycle Regulation

Unit 4 Quiz Focus Sheet

"Cell cycle definition"

"An ordered series of events that eukaryotic cells undergo to grow replicate their DNA and divide into two genetically identical daughter cells | ensures proper growth tissue maintenance and reproduction"

"Main stages of the cell cycle"

"Interphase (G₁ S G₂) where the cell grows and duplicates DNA followed by the M phase which includes mitosis and cytokinesis | tightly regulated to maintain genomic integrity"

"G₁ phase key events"

"Cell increases in size | synthesizes RNA and proteins essential for DNA replication | organelles replicate | cell assesses environmental signals such as nutrients and growth factors"

"S phase key event"

"DNA replication occurs producing identical sister chromatids | replication enzymes such as DNA polymerases ensure high fidelity genome duplication"

"G₂ phase key events"

"Cell continues growing | synthesizes proteins required for mitosis such as microtubule components | performs extensive DNA damage checks to ensure replication was accurate"

"Mitosis definition"

"A multistep process in which the replicated genome is evenly separated so that each daughter cell receives one complete set of chromosomes"

"Prophase events"

"Chromatin condenses into distinct chromosomes | nuclear envelope begins to break down | mitotic spindle fibers start forming from centrosomes which move to opposite poles"

"Metaphase events"

"Spindle fibers attach to kinetochores | chromosomes align at the metaphase plate | checkpoint ensures all chromatids are correctly attached to spindle fibers"

"Anaphase events"

"Cohesin proteins are cleaved | sister chromatids separate and are pulled toward opposite poles by shortening spindle fibers | ensures equal chromosome distribution"

"Telophase events"

"Chromosomes reach opposite poles and decondense | new nuclear envelopes reform | cell prepares for physical division"

"Cytokinesis definition"

"Division of the cytoplasm into two separate daughter cells | involves cytoskeletal elements such as actin and microtubules"

"Cytokinesis in animal cells"

"Contractile ring of actin filaments tightens forming a cleavage furrow that pinches the cell into two"

"Cytokinesis in plant cells"

"Vesicles from the Golgi apparatus fuse in the center forming a cell plate which develops into a new cell wall separating the two daughter cells"

"G₀ phase definition"

"A non dividing state where cells exit the cell cycle | some cells such as neurons remain in G₀ permanently while others can reenter the cycle if stimulated"

"S checkpoint purpose"

"Monitors accuracy of DNA replication | detects replication stress or DNA damage and pauses the cycle to allow repair"

"G₂ checkpoint purpose"

"Ensures DNA replication is fully completed and accurate | prevents entry into mitosis if errors or breaks are detected"

"M spindle checkpoint purpose"

"Monitors attachment of spindle fibers to kinetochores during metaphase | prevents anaphase onset until all chromatids are properly attached ensuring equal segregation"

"Cyclins"

"Regulatory proteins whose concentrations fluctuate through the cycle | bind to and activate CDKs to drive progression through checkpoints"

"CDKs"

"Cyclin dependent kinases that phosphorylate target proteins to initiate specific cell cycle transitions | active only when bound to cyclins"

"MPF definition"

"Maturation promoting factor consisting of cyclin and CDK | triggers entry into mitosis by phosphorylating proteins involved in chromosome condensation nuclear envelope breakdown and spindle formation"

"Effect of cyclin degradation"

"Cyclins are rapidly degraded by proteasomes which inactivates CDKs | ensures cell cycle events proceed in one direction and prevents reentering earlier stages"

"Proto oncogenes definition"

"Normal genes that promote controlled cell growth and division by coding for growth factors receptors or signaling proteins | may become oncogenes if mutated"

"Oncogene effect"

"Mutation converts proto oncogenes into permanently active forms leading to uncontrolled cell proliferation | contributes to cancer development"

"Tumor suppressor genes"

"Genes that inhibit cell cycle progression repair DNA or trigger apoptosis when damage is detected | act as brakes on cell division"

"p53 function"

"Protein that senses DNA damage | halts cell cycle by activating CDK inhibitor p21 | recruits DNA repair enzymes or initiates apoptosis if damage is severe"

"Effect of mutated p53"

"Loss of p53 prevents damaged cells from arresting or undergoing apoptosis | leads to accumulation of mutations | found in over half of human cancers"

"Purpose of mitosis"

"Ensures growth tissue repair and asexual reproduction in multicellular organisms | produces two genetically identical diploid daughter cells"

"Quick summary of prophase"

"Chromosomes condense and spindle apparatus begins forming"

"Quick summary of metaphase"

"Chromosomes align at the metaphase plate and attach to spindle fibers"

"Quick summary of anaphase"

"Sister chromatids separate and move to opposite poles"

"Quick summary of telophase"

"Chromosomes decondense and nuclear membranes form around each set"

"When does DNA replication occur?"

"During the S phase of interphase when the entire genome is duplicated"

"Which checkpoint is the restriction point?"

"The G₁ checkpoint where a cell commits to division after assessing conditions"

"What do cyclins activate?"

"Cyclins activate CDKs enabling progression through specific cell cycle stages"

"In which phase do sister chromatids separate?"

"Anaphase when cohesin is cleaved and chromatids are pulled apart"

"What happens if p53 is nonfunctional?"

"Cells with DNA damage continue dividing | mutations accumulate | greatly increases cancer risk"

"Difference in cytokinesis: plants vs animals"

"Plants form a cell plate that becomes the cell wall | animals use a contractile ring to form a cleavage furrow"