13). Cell Cycle Regulation and Growth Control Flashcards

Vocabulary flashcards covering cell cycle regulation, mitosis, cell cycle checkpoints, cyclin-Cdk complexes, and DNA damage control based on the lecture material.

Hayflick limit

The finite replicative limit of most normal cells, dividing approximately 20-50 times before dying.

Cell cycle

The controlled sequence of events by which a cell duplicates its genome, doubles its content, and eventually divides into two identical daughter cells.

Interphase

The long, non-dividing phase of the cell cycle that prepares the cell for mitosis, comprising G1, S, and G2 phases.

G1 phase

The interphase stage where cells are metabolically active, grow continuously, and carry out active RNA and protein synthesis.

S phase

The stage of interphase during which DNA replication takes place and total DNA content doubles.

G2 phase

The final stage of interphase involving protein synthesis in preparation for division and duplication of centrosomes.

Mitosis

Equatorial division in somatic cells wherein replicated chromosomes are equally divided between daughter cells.

Karyokinesis

The division of the cell nucleus during mitosis, occurring across four stages.

Cytokinesis

The process of dividing the cytoplasm of a parental cell into two daughter cells.

Prophase

The initial stage of mitosis characterized by condensation of duplicated chromosomes, disintegration of the nuclear envelope and nucleolus, disassembly of the cytoskeletal network, and migration of centrosomes to opposite poles.

Metaphase

The mitotic stage during which spindle fibers attach to kinetochores and chromosomes align along the equator of the spindle to form the metaphase plate.

Kinetochore

A protein structure composed of over 100 proteins on centromeres that allows attachment of spindle fibers to sister chromatids.

Anaphase

The mitotic stage where centromeres split, sister chromatids separate into daughter chromosomes, and shorten spindle fibers pull them toward opposite poles.

Telophase

The stage of mitosis where chromosome clusters arrive at opposite poles, nuclear envelopes and nucleoli assemble, and a contractile ring appears.

Cleavage furrow

A groove formed during cytokinesis by parallel sliding microfilaments of actin and myosin that pinches the cell inward.

Midbody

A thin intercellular bridge formed as the cleavage furrow deepens prior to complete separation into two daughter cells.

Checkpoints

Surveillance mechanisms and binary switches in the cell cycle consisting of event sensors, signaling pathways, and effectors that halt cycle progression and activate repair mechanisms.

Restriction point

The major, rate-limiting checkpoint in G1 phase that determines whether a cell passes into S phase or exits into the G0 state.

Quiescent cells

Reversibly inactive stem cells or tissue cells in the G0 state that retain the ability to re-enter the cell cycle upon receiving proper growth signals.

Senescent cells

Aged cells in the G0 state that are permanently withdrawn from the cell cycle.

Terminally differentiated cells

Fully functioning cells (such as neurons, myocytes, and osteocytes) permanently withdrawn from the cell cycle that never divide.

Cyclins

Regulatory subunits whose synthesis and degradation fluctuate cyclically to regulate Cdk activity throughout the cell cycle.

Cyclin-dependent kinases (Cdks)

Enzymes that, when activated by cyclin binding and phosphorylation, phosphorylate target proteins to drive transitions between cell cycle phases.

Cyclin kinase inhibitors (CKIs)

Inhibitory proteins that bind cyclin-Cdk complexes and distort their active sites, blocking enzymatic activity.

Retinoblastoma protein (Rb)

A protein that forms an inhibitory complex with E2F in non-dividing cells; its phosphorylation by G1-Cdks releases E2F to drive cell cycle progression.

E2F

A transcription factor bound by Rb in G0/G1 that, when released, stimulates the transcription of genes required for G1/S phase progression and DNA replication.

SPF (S phase promoting factor)

The S phase-Cdk complex that phosphorylates helicase and recruits helicase activators to replication origins to start DNA replication.

MPF (Mitosis promoting factor)

Mitotic cyclin-Cdk complex generated during G2 phase that triggers entry into mitosis.

Wee1 kinase

A kinase that maintains MPF in an inactive state via inhibitory phosphorylation until DNA replication is complete.

Cdc25 phosphatase

A phosphatase that dephosphorylates MPF, reversing Wee1 inhibition and activating MPF for entry into mitosis.

APC/C (Anaphase-Promoting Complex/Cyclosome)

A ubiquitin ligase complex activated by MPF that marks mitotic cyclins and securin for degradation, facilitating exit from mitosis and sister chromatid separation.

Cohesins

Protein complexes containing Smc1 and Smc3 that tether sister chromatids together during metaphase.

Separase

A protease that cleaves cohesin proteins (Smc1 & Smc3) to break sister chromatid attachment following dephosphorylation induced by APC/C activity.

p53

A tumor suppressor protein stabilized by ATM/ATR in response to DNA damage that induces p21 expression, activates DNA repair, or triggers apoptosis.

p21

A CKI produced via p53 activation that binds Cdk2/Cyclin E complexes to halt cell cycle progression upon DNA damage.

ATM and ATR

Protein kinases activated by double-strand (ATM) or single-strand (ATR) DNA breaks that stabilize p53 to initiate cell cycle arrest and DNA repair.