16 public questions tagged with this topic.
During G1, the ll grows, carries out metabolic activities, and prepares for DNA replication in the S phase. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Cyclins constitute regulatory subunits that impose temporal order on constitutively expressed but inactive cyclin-dependent kinases. In mammals, D-type cyclins respond to mitogens via Ras-MAPK induction, E-type governs G1/S boundary, A-type controls S and G2 progression, B-type drives mitosis. Binding of cyclin to CDK induces conformational change in T-loop exposing activation site for phosphorylation by CAK complex CDK7-cyclin H-Mat1, stabilizing fully active kinase competent for substrate phosphorylation. Substrate specificity derives from cyclin hydrophobic patch interacting with RXL motifs
Ref: Morgan, The Cell Cycle: Principles of Control, Chapter 3: Cyclin-CDK Regulation. Alberts 7th ed., Chapter 17.
Cellular metabolism is tightly coupled to cell cycle progression, with G1 phase exhibiting maximal biosynthetic activity to support doubling of mass before DNA replication. Upon growth factor binding, PI3K-Akt-mTORC1 pathway stimulates glucose uptake through GLUT1, increases glycolytic flux and pentose phosphate pathway for nucleotide precursors, enhances mitochondrial biogenesis via PGC1-alpha and mitochondrial transcription factor TFAM, and activates ribosome biogenesis through RNA polymerase I mediated rDNA transcription and S6K phosphorylation of ribosomal protein S6. Translation initiatio
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: G1 Metabolism and Growth.
p27Kip1 product of CDKN1B gene exemplifies Cip/Kip family that imposes G1 arrest and integrates nutrient availability with size control. In quiescent and early G1 cells, p27 accumulates due to low proteasomal turnover and binds cyclin E-CDK2 heterodimer, inserting 3_10 helix into ATP-binding pocket, preventing catalysis and blocking Rb phosphorylation, maintaining E2F repression. This prevents premature S-phase entry when growth factors limited. Mitogen signaling induces cyclin D-CDK4/6 complexes that sequester p27 in trimeric assembly without fully inhibiting them, lowering free p27 pool. Sub
Ref: Sherr & Roberts, Genes & Dev 2004, p27 Biology. Morgan, Cell Cycle, Chapter 4, G1 Control.
Specificity and timing of APC/C activity arise from sequential association with two adaptors, Cdc20 and Cdh1, both containing seven WD40 repeats forming beta-propeller that binds D-box and KEN motifs. During prometaphase and metaphase, APC/C-Cdc20 polyubiquitinates securin and cyclin B to trigger anaphase and mitotic exit. At telophase, cyclin B degradation reduces CDK1 activity, allowing Cdc14 phosphatase to dephosphorylate Cdh1, enabling its binding to APC/C core. APC/C-Cdh1 then operates from late mitosis through entire G1, continuously ubiquitinating mitotic cyclins A and B, mitotic kinase
Ref: Peters, Nature Reviews Mol Cell Biol 2006, APC/C Mechanisms. Alberts 7th ed., Chapter 17.
Cyclins earned name due to fluctuating concentrations through cell cycle while CDKs remain relatively constant. Function is to activate CDKs by allosteric remodeling and to direct substrate choice through additional binding motifs. In G1, Cyclin D with CDK4/6 senses mitogens, Cyclin E with CDK2 triggers S-phase entry, Cyclin A with CDK2 drives S-phase progression and later with CDK1 primes mitosis, Cyclin B with CDK1 executes mitosis. Each cyclin contains conserved cyclin box domain and hydrophobic patch recognizing RXL motifs on substrates, plus localization signals determining nuclear or cen
Ref: Murray, Cyclins: Roles in Cell Cycle and Evolution, Cell; Alberts et al., Molecular Biology of the Cell, Chapter 17, Cyclin-CDK Functions.
Late G1 restriction point defines irreversible commitment to divide independent of external growth factors. Its molecular basis revolves around retinoblastoma protein Rb and E2F transcription factors. In quiescence, hypophosphorylated Rb binds E2F-DP1 heterodimers, recruiting histone deacetylases, SWI/SNF remodelers and H3K9 methyltransferases to repress genes needed for S phase. Mitogen signaling induces Cyclin D synthesis via Ras-MAPK and PI3K pathways. Cyclin D-CDK4/6 complexes accumulate, phosphorylate Rb at multiple C-terminal residues, partially reducing repression and derepressing limit
Ref: Weinberg, Retinoblastoma Protein and Cell Cycle Control, Cell 1995; Alberts et al., Molecular Biology of the Cell, Chapter 17, Rb-E2F Switch.
Chromosome segregation occurs during mitosis, whereas interphase is mainly for growth, DNA replication, and preparation for division.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Cell Cycle - Phases G1 S G2 M and Regulation
G1 phase comes before the S phase, not after it.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Cell Cycle - Phases G1 S G2 M and Regulation
DNA replication does not occur in G1 phase; it happens in the S phase.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Cell Cycle - Phases G1 S G2 M and Regulation
Interphase is the longest phase of the cell cycle, not the shortest.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Cell Cycle - Phases G1 S G2 M and Regulation
G1 phase occurs before the S phase, not after it.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Cell Cycle - Phases G1 S G2 M and Regulation
