# The Cell Cycle: A Deep Dive

**URL:** <https://stemaway.com/t/the-cell-cycle-a-deep-dive/77>\
**Category:** Technical Resources\
**Created:** [September 1, 2019, 2:26am UTC](https://stemaway.com/t/the-cell-cycle-a-deep-dive/77 "2019-09-01T02:26:54Z")\
**Posts on this page:** 1\
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**Author:** ![anoori](https://d2nat51eddc6b4.cloudfront.net/user_avatar/stemaway.com/anoori/32/275_2.png) [@anoori](https://stemaway.com/u/anoori)\
**Post date:** [September 1, 2019, 2:26am UTC](https://stemaway.com/t/the-cell-cycle-a-deep-dive/77/1 "2019-09-01T02:26:56Z")

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# The Cell Cycle

### Ayush Noori | EduSTEM Advanced Biology
  

Interphase and Mitosis:

- The **cell cycle** is the life of a cell from the time it first form during division of a parent cell until its own division into two daughter cells.
- **Somatic cells** are **diploid** and have 46 chromosomes in humans, unlike the reproductive cells, or **gametes** , which are **haploid** and have 23 chromosomes in humans.
  - In somatic cells, the division of genetic material in the nucleus is called **mitosis**.

- The mitotic (M) phase is usually the shortest part of the cell cycle, and alternates with a much longer stage called interphase, which is divided into three phases.
  - During the first **G1 phase** , the cell prepares to divide by growing, producing proteins, and duplicating cytoplasmic organelles.
  - The DNA divides during the second **S phase**.
  - The cell continues to grow during the third **G2 phase** , which directly proceeds mitosis.
  - Image Credit: “The Cell Cycle: Figure 1” by OpenStax College, Biology (CC BY 3.0).

> **EXTENSION** This extension explores the molecular pathways which regulate mitosis, specifically in epidermal and epithelial cells.  
> **Kandasamy K, Mohan SS , Raju R, _et al._** **NetPath: A public resource of curated signal transduction pathways. _Genome Biol._ 2010 Jan 12;11(1):R3. doi: 10.1186/gb-2010-11-1-r3.**[**http://www.netpath.org/netslim/EGFR1\_pathway.html**](http://www.netpath.org/netslim/EGFR1_pathway.html)  
> Please see the above link for a comprehensive diagram of the epidermal growth factor receptor (EGFR) signaling pathways. Below is an excerpt from WikiPathways which elaborates on this:  
> “Epidermal growth factor receptor (EGFR) also known as ErbB1/HER1 is a member of the ErbB family of _receptor tyrosine kinases_, which also includes ErbB2 (Neu, HER2), ErbB3 (HER3) and ErbB4 (HER4). Several ligands such as epidermal growth factor, transforming growth factor-alpha, epigen, amphiregulin, betacellulin, heparin-binding EGF and epiregulin are known to specifically bind to EGFR. Epidermal growth factor (EGF) is one of the high affinity ligands of EGFR. _EGF/EGFR system induces growth, differentiation, migration, adhesion and cell survival through various inter-acting signaling pathways._ The binding of EGF to the extracellular domain of EGFR induces the dimerization, activation of intrinsic kinase activity and subsequent autophosphorylation of EGFR at multiple residues in the cytoplasmic region such as Tyr 1092, Tyr 1172, Tyr 1197, Tyr 1110, Tyr 1016). Activated EGFR recruits various cytoplasmic proteins which transduce and regulate the EGFR function. The proteins recruited to active EGFR include many Src homology 2 (SH2) and phosphotyrosine binding (PTB) domain containing proteins which binds to the tyrosine phosphorylated residues in EGFR, enzymes which act on EGFR and also various EGFR substrates. _One of the adapter proteins, GRB2, binds to the phosphotyrosine residue at 1068 and recruits SOS to the membrane. SOS activates GDP/GTP exchange which recruits RAF to the membrane. RAF phosphorylates MEKs, which then activates the extracellular signal regulated kinase (ERK). ERK activates a number of transcriptional regulators to induce cell growth and proliferation._”  
> Specifically, ERK2 (also known as MAPK) activates the Cyclin D and Cyclin-Dependent Kinase (CDK) 4/6 signaling pathway. Increased intracellular concentration of CDK4/6 causes the phosphorylation of retinoblastoma protein (pRb). Hypophosphorylated pRB sequesters E2F, therefore phosphorylating pRB releases E2F. The nuclear localization signal of E2F is then bound by the karyopherin importin-β and transported into the nucleus (using the RanGTP gradient), where it acts as a transcription factor to ultimately stimulate the transition from the G1 phase to the S phase and DNA replication.  
> **Wee P and Wang Z. Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways. _Cancers_ 2017, 9(5), 52. doi: 10.3390/cancers9050052.**[**https://www.mdpi.com/2072-6694/9/5/52**](https://www.mdpi.com/2072-6694/9/5/52)  
> Please click on the above link and see Figure 1 for a diagram which depicts the entire process.  
> “Epidermal growth factor receptor (EGFR) signaling pathways leading to G1/S cell cycle progression activated by EGF activation. Depicted are the RAS-RAF-MEK-ERK MAPK and PI3K-AKT-mTOR pathways. _EGF activation of the EGFR induces receptor dimerization and transphosphorylation of the C-terminal domain. The phosphorylated C-terminal domain binds SHC and GRB2_, along with PLC-γ1 at Y992 (not pictured). The GRB2 SH3 domain recruits the proline-rich domains of SOS or GAB1 _to initiate ERK MAPK or AKT signaling respectively_. SOS is also recruited to the plasma membrane (PM) by the interaction of its PH (pleckstrin homology) domains with PIP2 (phosphatidylinositol-4,5-bisphosphate) and PA (phosphatidic acid). SOS catalyzes the conversion of GDP to GTP of RAS. Active RAS uses its RAS RAF-binding domain (RBD) to recruit RAF-1. RAF-1 is activated by dephosphorylation and phosphorylation events, and activates MEK1/2. Activated MEK1/2 activates ERK1/2. _ERK1/2 has various cytoplasmic and nuclear targets, which aid in the transcription and translation of Cyclin D1._ For example, ELK-1 transcribes the c-FOS gene (not pictured), and the protein product together with c-JUN make up the AP-1 complex. The AP-1 complex as well as c-MYC induce the transcription of CYCLIN D1. _Increased levels of CYCLIN D1 correlates with increased CDK4/6 activity, which phosphorylates RB. Phosphorylated RB releases the E2F transcription factor, which participates in the transcription of Cyclin E and leads to G1/S progression._”

  

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With these courses, we hope to further our mission to make high-quality STEMX education accessible for all. For questions or support, please feel free to reach out to me at [anooristudent@outlook.com](mailto:anooristudent@outlook.com).

Best Regards,

Ayush Noori

_EduSTEM Boston Chapter Founder_

  

**Resources:**

1. [NCBI PubMed](https://www.ncbi.nlm.nih.gov/pubmed/)

The premier source of past and present medical literature. Most supplemental information in Extensions is available via PubMed. When searching PubMed, be sure to use the “Free full text,” and “Sort by: Best Match” filters to find relevant and accessible results.

1. [RCSB Protein Data Bank (PDB)](https://www.rcsb.org/)

A large database of useful 3D structures of large biological molecules, including proteins and nucleic acids. Use the search bar to find a molecule of interest, which can then be examined using the Web-based 3D viewer.

  

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