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The S phase, short for synthesis phase, is a period in the cell cycle
Cell cycle

The cell cycle, or cell-division cycle, is the series of events that take place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission....
 during interphase
Interphase

Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division....
, between G1 phase
G1 phase

The G1 phase is a period in the cell cycle during interphase, after cytokinesis and before the S phase. For many cells, this phase is the major period of cell growth during its lifespan....
 and the G2 phase
G2 phase

G2 phase is the third, final, and usually the shortest subphase during interphase within the cell cycle in which the cell undergoes a period of rapid growth to prepare for mitosis....
. Following G1, the cell enters the S stage, when DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 synthesis
DNA synthesis

DNA synthesis commonly refers to:*DNA replication - DNA biosynthesis *Polymerase chain reaction - enzymatic DNA synthesis *Oligonucleotide synthesis - chemical synthesis of nucleic acids...
 or replication
DNA replication

DNA replication, the basis for heredity, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative replication" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand....
 occurs. At the beginning of the S stage, each chromosome
Chromosome

A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
 is composed of one coiled DNA double helix
Double helix

In geometry a double helix typically consists of two congruence helix with the same axis, differing by a translation along the axis, which may or may not be half-way....
 molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
, which is called a chromatid
Chromatid

A chromatid is one among the two identical copies of DNA making up a replicated chromosome, which are joined at their centromeres, for the process of cell division ....
. The enzyme DNA helicase splits the DNA double helix down the hydrogen bonds (the middle bonds). DNA polymerase follows, attaching a complementary base pair to the DNA strand, making two new semi-conservative strands.






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The S phase, short for synthesis phase, is a period in the cell cycle
Cell cycle

The cell cycle, or cell-division cycle, is the series of events that take place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission....
 during interphase
Interphase

Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division....
, between G1 phase
G1 phase

The G1 phase is a period in the cell cycle during interphase, after cytokinesis and before the S phase. For many cells, this phase is the major period of cell growth during its lifespan....
 and the G2 phase
G2 phase

G2 phase is the third, final, and usually the shortest subphase during interphase within the cell cycle in which the cell undergoes a period of rapid growth to prepare for mitosis....
. Following G1, the cell enters the S stage, when DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 synthesis
DNA synthesis

DNA synthesis commonly refers to:*DNA replication - DNA biosynthesis *Polymerase chain reaction - enzymatic DNA synthesis *Oligonucleotide synthesis - chemical synthesis of nucleic acids...
 or replication
DNA replication

DNA replication, the basis for heredity, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative replication" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand....
 occurs. At the beginning of the S stage, each chromosome
Chromosome

A chromosome is an organized structure of DNA and protein that is found in Cell . A chromosome is a single piece of DNA that contains many genes, regulatory sequence and other genetic sequence....
 is composed of one coiled DNA double helix
Double helix

In geometry a double helix typically consists of two congruence helix with the same axis, differing by a translation along the axis, which may or may not be half-way....
 molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
, which is called a chromatid
Chromatid

A chromatid is one among the two identical copies of DNA making up a replicated chromosome, which are joined at their centromeres, for the process of cell division ....
. The enzyme DNA helicase splits the DNA double helix down the hydrogen bonds (the middle bonds). DNA polymerase follows, attaching a complementary base pair to the DNA strand, making two new semi-conservative strands. At the end of this stage, each chromosome has two identical DNA double helix molecules, and therefore is composed of two sister chromatids (joined at the centromere
Centromere

A centromere is a region of DNA typically found near the middle of a chromosome where two sister chromatids come in contact. It is involved in cell division as the point of mitotic spindle....
). During S phase, the centrosome
Centrosome

In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression....
 is also duplicated. These two events are unconnected, but require many of the same factors to progress. The end result is the existence of duplicated genetic material in the cell, which will eventually be divided into two.

Damage to DNA often takes place during this phase, and DNA repair
DNA repair

DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolism activities and environmental factors such as UV light and Radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell pe...
 is initiated following the completion of replication. Incompletion of DNA repair may flag cell cycle checkpoint
Cell cycle checkpoint

Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division in eukaryotic cell . These checkpoints verify whether the processes at each phase of the cell cycle have been accurately completed before progression into the next phase....
s, which halts the cell cycle. However, after the cell has completed this phase, it is very likely that the cell will continue on to complete the cell cycle
Cell cycle

The cell cycle, or cell-division cycle, is the series of events that take place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission....
. the cell preperates its self for cell division, mitosis

See also

  • S phase index (SPI)