9.1 Cell Cycle, Stem Cells and Cancer

This set covers the biological principles of the cell cycle, intestinal and liver stem cells, regulatory proteins like cyclins and p53, and the characteristics of cancer stem cells.

Cell proliferation

A key process precisely controlled to produce the diverse shapes of organs and tissues; disruption of this control can lead to cancer.

Stem cells

Cells that reside in tissues like the intestine to replenish them throughout life; they divide rarely but give rise to transit amplifying (progenitor) cells.

Intestinal epithelium

A tissue that constantly renews throughout life, with maintenance depending on generating new cells from the stem cell population at the base of crypts and cell death at the villus tip.

Crypt base columnar (CBC) cells

Cells located between the Paneth cells at the base of intestinal crypts that possess stem cell properties.

Paneth cells

Specific cells in the intestinal crypt base between which stem cells are located.

Partial hepatectomy

The removal of part of the liver, after which the remaining lobes enlarge to compensate, regenerating up to $70\%$ of the lost tissue.

Fibrosis

Scarring and loss of organ function that can result from repeat injury or chronic disease, such as in the liver.

Cell cycle

A tightly regulated sequence of events where a cell duplicates its contents through interphase ($G_1/S/G_2$) and physically divides in two during mitosis ($M$).

Gap 1 ($G_1$) phase

The longest period of the cell cycle where the cell functions normally and synthesises proteins and organelles to double its size.

$G_0$ state

A state entered by non-dividing cells, such as nerve cells, that never leave the $G_1$ phase.

Synthesis ($S$) phase

The part of interphase where DNA is replicated to produce two identical copies of each chromosome and checked for incorrect copying.

Gap 2 ($G_2$) phase

The period after $S$ phase where the cell prepares for mitosis by synthesising components to ensure functionality of daughter cells.

Interphase

domThe non-dividing stage of the cell cycle comprising the $G_1$, $S$, and $G_2$ phases.

Mitosis

The process of cell division that efficiently segregates genetic material equally into two daughter cells, subdivided into 5 stages.

Cell cycle checkpoints

Control system points that arrest the cell at specific stages to ensure preceding events, like DNA replication or repair, are completed before proceeding.

Cyclins

Proteins whose oscillating amounts control the timing of events and the transition from one phase of the cell cycle to the next.

Cyclin-dependent kinases (Cdks)

Protein kinases that form complexes with cyclins and phosphorylate other proteins to trigger phase-specific events.

p53

Known as the 'gatekeeper' of the genome; it is a normally unstable protein stabilised by damaged DNA that induces transcription of $p21$.

p21

A CKI (Cyclin-dependent kinase inhibitor) induced by $p53$ to halt the cell cycle until DNA damage is repaired.

Flow cytometric analysis

A visualization method where cells are labelled with a fluorescent marker and separated based on DNA content, which is proportional to the signal on the x-axis.

BrdU

A marker that incorporates into newly synthesised DNA and is used with antibodies to identify proliferating cells.

Metastasize

The process in malignancy where cancer cells migrate to many parts of the body to continue growing.

Cancer Stem Cells

A subset of tumor cells capable of self-renewal and generating diverse cells within a heterogeneous solid tumor; they are often resistant to chemotherapy.