Cell Proliferation

The cell cycle is the process that cells use to grow and divide. It helps living things make new cells for growth and repair. In many cases, it is also the way single cells reproduce.

The cycle has two main parts: interphase and cell division. During interphase, the cell grows and prepares for division. During cell division, one cell splits into new cells. This sequence keeps cells in a repeating pattern of growth, copying, and splitting.

Interphase is the part of the cell cycle when a cell grows and prepares to divide. It is a major stage in the life of a cell, and it includes the phases G1, S, and G2.

During G1, the cell grows and carries out its normal functions. In the S phase, the cell copies its DNA. During G2, the cell continues to grow and gets ready for mitosis, the stage when the cell divides.

Interphase takes up most of the cell cycle. It gives the cell time to build materials, make a copy of its genetic...

The cell cycle is the organized process that controls cell division. It helps one cell divide into two daughter cells with chromosomes that match the parent cell. This process is essential for growth from a single-cell zygote and for tissue renewal in adult multicellular eukaryotes.

Cell division also supports repair and replacement in the body. In bone marrow, stem cells divide to make new blood cells. When cell division happens without control, it can lead to cancer and many genetic diseases.

Cyclins and cyclin-dependent kinases help control how cells move through the cell cycle. These positive regulator molecules keep mitotic cell division on schedule so daughter cells can match the parent cell. When this control fails, errors in DNA replication or in the distribution of genetic material can create mutant cells that pass those changes to every new cell they form.

Cell cycle checkpoints limit the spread of these abnormal cells. A checkpoint is a control point at a specific stage of...

Cdk4/6 blockers help control the cell cycle by stopping the signals that push cells from G1 into S phase. Cdks, or cyclin-dependent kinases, must bind cyclins to become active, and cyclin D often pairs with Cdk4/6 to form this active complex. The cyclin D-Cdk4/6 complex then phosphorylates the retinoblastoma protein, or Rb, which normally acts as a tumor suppressor.

When Rb is inactivated, cells can move into the next stage of division. In normal cells, Cdk activity is carefully regulated so...

Cdk control of DNA replication timing helps cells copy DNA once each cycle. The cell cycle has four main stages: G1, S, G2, and M. In G1, the cell grows. In S phase, it copies its DNA. In G2, it prepares to divide. In M phase, mitosis divides the cell content into two daughter cells.

In eukaryotes, DNA replication starts at many sites on the chromosomes called origins of replication. These origins switch between two states during the cell cycle. In G1, a multiprotein pre-replicative complex,...

Cell cycle kinases help control the move from G2 into M phase. Checkpoints act as safeguards and gatekeepers, so the cell cycle can continue in good conditions and slow down or stop when problems appear. This regulation is called the cell cycle control system.

Cyclin-dependent kinases, or Cdks, work with cyclins to manage cell cycle transitions. A key example is M-Cdk, which is made of Cdk1 bound to M cyclin. M-Cdk helps drive the shift from G2 to M phase by preparing the cell for mitosis.

M...

Epidermal growth factor, or EGF, is a mitogen that helps control cell division. Its receptor, EGFR, sits in the cell membrane and sends a growth signal when EGF binds to it. EGFR is part of the ErbB family of tyrosine kinase receptors, and this signaling helps decide whether a cell will keep proliferating.

In healthy tissue, the number of EGFR molecules on the cell surface is tightly regulated. This balance helps cell division match the tissue’s needs. In cancer cells, however, EGFR is often...

Telomeres and telomerase help control how many times a cell can divide. Telomeres are short, repetitive DNA sequences at the ends of chromosomes. They are covered by proteins that form a protective cap. In many human body cells, this cap gets a little shorter after each round of cell division.

This shortening is part of replicative senescence, the point at which a cell stops dividing permanently. Embryonic stem cells make telomerase, an enzyme that adds telomeric repeats and supports repeated...

Ras and MYC can drive abnormal cell proliferation, which is uncontrolled cell growth. Under normal conditions, most adult cells stay non-proliferative unless they receive internal or external signals to replace lost cells. In abnormal proliferation, cell division continues even after those signals stop. This persistent growth can lead to tumors.

The tumor forms from damaged cells that keep copying themselves. Those cells pass the damage to daughter cells and to later generations of daughter...

Cell size control helps cells keep their shape, function, and fitness. Many dividing cells grow and then double their mass before they divide. This coordination depends on checkpoints between cell cycle phases, which help the cell stay in balance.

When checkpoint control fails, cells may grow without proper control. That loss of coordination can lead to uncontrolled growth and reduced cellular function. In adult tissues, non-dividing cells also adjust size based on metabolic state.

Adult...