Interphase
n., plural: interphases
[ˈɪn tərˌfeɪz]
Definition: the phase of the cell cycle wherein the nucleus is not dividing but may prepare for a subsequent cell division
Table of Contents
Interphase is the critical period in the eukaryotic cell cycle characterized by a sequence of events like the G1 phase where the cell undergoes growth, the S phase where the cell makes a copy of its DNA and the G2 phase where the cell continues to grow, and then prepares for cell division (parent cell divides and gives rise to two genetically identical daughter cells).
As we observe the natural world around us, we are left in awe of how living organisms continue to grow and maintain their biological identity. The process that allows for this incredible feat is known as the cell cycle, which is integral to the normal growth processes and regular repair of living organisms.
At the very core of this process and the subject of cell biology lays the cell itself, “the fundamental unit of life”. Different types of eukaryotic cells come together to form tissues, and these tissues further manifest as organs, which work in unison to form organ systems. The integrity of each cell is crucial for the proper functioning of these organ systems (as the cell functions at its optimum when it’s in a particular form), and the continuous maintenance of this integrity is vital for the survival of all biological beings.
Every cell in the body has a limited lifespan, and the process of cell division ensures that every parent cell gives rise to two daughter cells, which take up the mantle of running and functioning to sustain life. Whether they are plant cells or animal cells, cell division is an essential process that allows for the continuity of life.
When we delve deeper into the cell cycle, we can identify two key stages: the interphase and the mitotic phase, also known as the M-phase. Interphase is a vital stage during which the cellular components are replicated in preparation for cell division. This crucial step is what makes the M-phase possible, as the division of the replicated components, including membranes, nuclear materials, and cytoplasmic content, takes place during this stage. The final step of cell division, cytokinesis, is also counted in the M-phase.
The sole purpose of the M-phase is to divide the nuclear material in the form of replicated chromosomes, ensuring that each daughter cell has a complete set of genetic information. However, the interphase is equally important, as it lays the groundwork for the successful completion of the M-phase. This is why understanding the intricacies of interphase is crucial to understanding the cell cycle as a whole.
In this article, we will take a closer look at the fascinating world of interphase and its role in the cell cycle. We will explore the different stages of interphase, the cell’s complex processes that take place within it, and its significance in the functioning of biological organisms.
Interphase Definition
Interphase is like a ‘bustling city preparing for a big event’.
It’s the phase in the cell cycle where the cell is busy growing and preparing for cell division. During this period, the cell replicates its DNA, and all the necessary materials for cell division are produced. It’s a time of intense activity and growth, much like the buildup to a grand celebration. Without the interphase, the cell would not have the necessary resources to divide and produce genetically identical daughter cells.
In short, interphase is the critical period in the cell cycle where the cell gears up for division, ensuring the continuity of life. Duration-wise, interphase is a longer period than cell division.
Watch this vid about interphase:
Interphase is the phase in the cell cycle consisting of three sub-phases — Gap 1 (G1), Synthesis (S), and Gap 2 (G2) phases. In the cell cycle, it is the period before mitosis. It is when the chromosomes are decondensed and the cell continues to grow, actively metabolizing, and could subsequently replicate DNA in preparation for the ensuing mitosis. The period of interphase is generally longer than mitosis.
Word origin: inter (between) + phase (from phasis, appearance)
Synonym(s): Interkinesis
See also: mitosis, meiosis, cell cycle
Some important pointers for Interphase
» No characteristic or notable features are observed under the microscope.
» Characterized by the synthesis of a variety of proteins
» Characterized by the transcription process (DNA to RNA)
» Characterized by the engulfment of large amounts of extracellular material
» Characterized by several processing signals
» Dominant phase of any cell as a typical cell spends the longest time of its life in this phase.
» Also called the “daily living phase” of the cell
» Also called the “metabolic phase” of the cell
» The phase in which a cell obtains the nutrients and elements required for cell growth.
» Common misconceptions:
- Misconception 1: Interphase is the phase when the cell is resting or in a quiescent state.
Explanation: No, the above stamen is not true as the cell in interphase is not quiescent or dormant. In contrast to the common idea, the cell is undergoing a lot of changes and preparations for the upcoming cell division process. So, when we call interphase the quiescent phase or resting phase, it is only concerning cell division that no active division is occurring in this phase. - Misconception 2: Interphase is the first stage of mitosis.
Explanation: No, the above stamen is not true as the first stage of mitosis is prophase and not interphase. Interphase precedes mitosis and is not a part of it. You can read learn more details in our article on Prophase here.
- Misconception 1: Interphase is the phase when the cell is resting or in a quiescent state.
Stages of Interphase
As introduced above, there are three stages of interphase — Gap-1 (G1), Synthesis (S), and Gap-2 (G2) phases. Overall, 2 gap phases and 1 S-phase make up the entire interphase.
STAGE 1: Gap 1
» 1st stage of interphase
» Also called the G1 phase
» No major notable microscopic change
» Activity state of the cell: Quite active at the biochemical level
» Major activities:
- Cell grows intensively
- Accumulation of the building blocks of chromosomal DNA (nucleotides, sugar, and phosphate groups)
- Accumulation of DNA-associated proteins
- Accumulation of energy resources to ensure successful completion of DNA replication.
STAGE 2: Synthesis
» 2nd stage of interphase
» Also called the S phase
» The longest phase of interphase
» Marked by the complexities involved in the duplication of genetic material via the DNA replication process.
» State of nuclear DNA during entire interphase: Semi-condensed chromatin configuration
» Characteristic features of the S phase:
- Formation of sister chromatids ( the identical pairs of DNA)
- Attachment of sister chromatids at the centromeric region
- Duplication of centrosome
- Formation of mitotic spindle apparatus (apparatus facilitating the movement of chromosomes during mitosis or meiosis) from the two duplicated centrosomes)
Note it!
Centrioles, Animal Cells, and Interphase
Did you know that centrioles are unique structures found only in animal cells?
These cylindrical organelles are composed of microtubules and are involved in organizing the microtubules that form the spindle fibers during cell division. Centrioles play a critical role in the separation of chromosomes during mitosis, making them an essential component of the cell cycle.
Centrioles are characteristic of animal cells. Interestingly, centrioles are absent in plant and fungi cells, and instead, these normal cells use other structures to organize their microtubules during cell division.
But centrioles aren’t only important during cell division. During interphase, the centrioles play a crucial role in the organization of the cell’s cytoskeleton. They form the basis of the microtubule organizing structure/center (MTOC), which is responsible for arranging the microtubules that help maintain the cell’s shape and transport organelles and other molecules around the cell.
Hence the role played by centrioles in the organization of the cytoskeleton during interphase can’t be overemphasized. These structures are indispensable for the maintenance of cell structure and function in animal cells!
STAGE 3: Gap 2
» 3rd stage of interphase
» Also called the G2 phase
» Marked by cell’s replenishment activities
» High protein synthesis levels
» Number of chromosome manipulation events
» Duplication of several cell organelles
» Dismantling of the cytoskeleton (for the provision of resources needed in the upcoming mitotic phase)
» Some spurts of additional cell growth
» Cell finally polishes and prepares for the mitotic phase
Gap 0 – A Complex Cell State
Is Gap 0 (G0) part of the interphase? Is it even part of the cell cycle? The allocation of the G0 in the life of a cell is quite complex. Defining G0 (resting phase) in the cell cycle is not an easy feat. Some references consider G0 (resting phase) as part of the cell cycle; others imply otherwise (that G0 is not part of the cell cycle).
- Gap 0 is part of the cell cycle, but not implicitly part of the Interphase:
It can be argued that some cells enter G0 as the quiescent period or the resting phase but may subsequently proceed and enter the stages prior to cell division as seen in certain cells, such as the hematopoietic stem cells that remain arrested in the G0 for extended periods of time and eventually become mitotically active upon receiving “signals” (e.g., interleukin-3 binding to the stem cell, thereby, activating it). In such a case, G0 can be considered as part of the cell cycle.
Cooper and Hausman (2019) explained that G0 is part of the cell cycle especially when a mature or differentiated cell reverts to becoming mitotically active. However, they considered interphase as a phase distinct from G0:
“G0 is the state that represents a divergence from the normal cell cycle, but it is nevertheless related to cell division. It represents a quiescent state in which cells can remain for an indefinite period of time, but the cell retains the ability to re-enter the cell cycle phases and undergo division.”
- Gap 0 is neither a part of the interphase nor part of the cell cycle:
While there are cells that can revert to becoming mitotically active, there are also cells that will persist in the G0 throughout the lifespan of an individual and will no longer divide. Examples of such cells are the neurons in the cerebral cortex, the cardiac muscle cells, the lens of the eye, and so on.
This, therefore, implies that G0 is not a part of a cell cycle, especially when the cells have fully differentiated. They will not re-enter the cell cycle and will merely degenerate or die by apoptosis in time.
A quote from Alberts et al. (2015) below is shown as they defined interphase as being made up of three distinct phases — G1, S1, and G2 — and G0 as not part of the cell cycle:
“Interphase is the period of the cell cycle when the chromosomes are decondensed and most cellular growth, replication of chromosomes, and other metabolic processes occur. This is a period of active cell metabolism and DNA synthesis, and is subdivided into three distinct phases: G1, S, and G2.Cells that exit the cell cycle enter a non-proliferative state known as G0, which is characterized by decreased metabolic activity and differentiation into specialized cell types.” (p. 105)
How about G0 as part of the interphase? There is no widely accepted notion about G0 being part of the interphase. But should the cell cycle be divided merely into two — interphase and cell division (mitosis) — then, G0 would have been a part of the interphase, which in such a case might arguably be divided into a proliferative sub-phase (G1, S, and G2) and G0 as a non-proliferative, quiescent sub-phase.
The point is G0 is a distinct state and to answer whether G0 is part of the cell cycle (or part of the interphase) or not will highly depend on how these concepts are interpreted or contextually defined.
Take the Interphase – Biology Quiz!
Further Reading
References
- Liu, S., & Pellman, D. (2020). The coordination of nuclear envelope assembly and chromosome segregation in metazoans. Nucleus, 11(1), 35-52.
- The Cell Cycle & Mitosis Tutorial. The Biology Project – Cell Biology. The University of Arizona.
- Derenzini, M., & Trerè, D. (1992). Importance of interphase nucleolar organizer regions in tumor pathology. Virchows Archiv B, 61, 1-8.
- Babil, P. K., Kikuno, H., Shiwachi, H., TOYOHARA, H., FUJIGAKI, J., FUJIMAKI, H., & Asiedu, R. (2010). The optimum time for collection of root samples for chromosome observation in yams (Dioscorea spp.). Tropical Agriculture and Development, 54(3), 71-75.
- Chin, C. F., & Yeong, F. M. (2010). Safeguarding entry into mitosis: the antephase checkpoint. Molecular and cellular biology, 30(1), 22-32.
- Cooper GM, Hausman RE. The Cell: A Molecular Approach. 8th edition. Sunderland, MA: Sinauer Associates; 2019.
- Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2015). Molecular Biology of the Cell (6th ed.). Garland Science.
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