10.3c: Regulatory molecules of the cell cycle (2023)

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    Learning Objectives
    • Distinguish between the molecules that regulate the cell cycle
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    Cell cycle control molecules

    In addition to the internally controlled checkpoints, there are two groups of intracellular molecules that regulate the cell cycle. These regulatory molecules promote or progress the cell to the next phase (positive regulation) or stop the cycle (negative regulation). May affect the impact activity or production of other regulatory proteins. Therefore, failure of a single regulator may have almost no impact on the cell cycle, especially if more than one mechanism regulates the same event. And possibly be fatal to the cell if several processes are affected.

    Positive regulation of cell cycle

    Two groups of proteins, called cyclins and cyclin-dependent kinases (CDKs), are responsible for cell progression through the various checkpoints. The levels of the four cyclin proteins fluctuate throughout the cell cycle in a predictable pattern. Increases in the concentration of cyclin proteins are activated by both external and internal signals After the cell has moved to the next phase of the cell cycle, the cyclins that were active in the previous phase are degraded.

    10.3c: Regulatory molecules of the cell cycle (2)

    Cycliner only regulates the cell cycle when tightly tied to CDKs.To be fully active, the CDK/Cycline complex must also be phosphorylated in specific places.Like all kinases, CDKs are enzymes (kinases) that phosphorylate other proteins.Phosphorylation activates protein by changing its form. The proteins phosphorylated by CDKs are involved in promoting the cell to the next step.The levels of CDK proteins are relatively stable throughout the cell cycle, but the cycline concentrations swing and determine when CDK/Cycline complexes are formed. The different cycliner and CDKs bind at specific points in the cell cycle and thus adjust different control points.

    10.3c: Regulatory molecules of the cell cycle (3)

    Although Cycliner is the most important regulatory molecules that determine the forward -looking momentum of the cell cycle, there are various other mechanisms that improve the development of the cycle with negative rather than positive effects.This mechanisms block in the essential progress of the cell cycle until the problematic circumstances are resolved.Molecules that prevent complete activation of CDKs are called CDK inhibitors.controlled.

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    Negative regulation of the cell cycle

    The second group of cell cycle regulating molecules are negative regulators.Negative regulators stop the cell cycle.Remember, in positive regulation causes active molecules cycle to develop.

    The best understood negative regulatory molecules are retinoblastom protein (RB), P53 and P21.Retinoblastom proteins are a group of tumor suppressor proteins found in many cells.Much of what you know about cell cycle control comes from research done with cells that have regulatory control lost.All three of these regulatory proteins were discovered to be damaged or non-functional in cells that had begun to replicate uncontrolled (became cancer).In each case, the main reason for the uncontrolled progression through the cell cycle was a defective copy of the regulatory protein.

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    RB, P53 and P21 mainly work on g1Checkpoint.p53 is a multifunctional protein that has a major impact on the dedication of the cell for division;It works when damaged DNA in cells undergoing the preparatory processes during g1If damaged DNA is detected, p53 stops the cell cycle and recruits enzymes to repair the DNA. If the DNA cannot be repaired, p53 can activate apoptosis (suicide cell) to prevent duplication of damaged chromosomes. The production of p21 is activated. P21 maintains the stop in the cycle determined by p53 by binding and slowing the activity of the CDK/Cycline complexes. A cell exposed to more stress accumulates higher levels of p53 and p21, making it less likely that the cell will enter S phase.

    RB exerts its regulatory influence on other positive regulator proteins. RB monitors cell size. In the active, deposited phosphorylated state, RB binds proteins called transcription factors, usually to E2F. Transcription factors "switch" specific genes so that they Production of proteins This gene codes. When RB is bound to E2F, production of proteins required for G1/S transition has been blocked.The cell rises in size, RB is slowly phosphorylated until it is inactivated.RB releases E2F, which can now turn on the gene, that the transitional protein is produced and this specific block has been removed.All positive supervisory authorities must be "committed" from the control points and all negative supervisors must be "turned off".

    10.3c: Regulatory molecules of the cell cycle (4)


    • Two groups of proteins, cyclines and cycline-dependent kinases (CDKs) are responsible for promoting the cell cycle.
    • Cyclins regulate the cell cycle only when bound to CDKs; to be fully active, the CDK/cyclin complex must be phosphorylated, enabling it to phosphorylate other cell cycle-promoting proteins.
    • Negative regulatory molecules (RB, P53 and P21) work mainly on g1Checkpoint and prevents the cell from continuing to divide until damaged DNA has been repaired.
    • P53 stops the cell cycle and recruit enzymes to recover damaged DNA;If DNA cannot be repaired, P53 activates apoptosis to prevent double work.
    • The production of P21 is triggered by P53; P21 stops the cycle by tying and inhibiting the activity of the CDK/Cycline complex.
    • Defosphorylated RB binds to E2F, which stops the cell cycle;As the cell grows, RB is fosphorylated and releases E2F, which promotes the cell cycle.
    (Video) CBSE board Exam Class 12th Biology Revision Topic

    Main relationship

    • Cycline: one of a group of proteins that regulate the cell cycle by forming a complex with kinases
    • Cyclin-dependent kinase: (CDK) A member of a family of proteininases that was first discovered for its role in regulating the cell cycle through phosphorylation
    • Retinoblastoomeiwit: (RB) a group of tumor suppressor proteins that regulate the cell cycle by monitoring cell size

    Contributions and attributes


    What are the regulatory molecules in the cell cycle? ›

    Two groups of proteins, cyclins and cyclin-dependent kinases (Cdks), are responsible for promoting the cell cycle.

    What is 10% of the cell cycle? ›

    Mitosis accounts for about 10 percent of the cell cycle (may last only one to two hours) and is much shorter than the interphase. Mitotic errors can cause cell death through apoptosis or mutations that may induce cancer. Prophase: During the Prophase, nuclear envelope disintegrates and the nucleolus disappears.

    What is 2C and 4C in cell cycle? ›

    AS WE MEASURE THINGS IN KILOGRAM , DNA IS MEASURED IN PICOGRAM {c}. WHEN DNA CONTENT DOUBLES WE CALL IT AS DNA CONTENT HAS CHANGED FRON 2C TO 4C. C is nothing, just a unit for DNA amount . In diploid it is consider as 2C And during replication in the S phase.. it becomes 4C .

    What is 10 the phase of the cell cycle in which DNA replication occurs? ›

    S phase is the period during which DNA replication occurs.

    What is regulation of the cell cycle quizlet? ›

    The cell cycle is regulated to ensure cells only divide as and when required. At each checkpoint in the cell cycle, a set of conditions determines whether or not the cell will continue into the next phase. Cyclins and CDK's are molecules that check the cell cycle at various points.

    What are 2 types of regulatory molecules? ›

    There are three types of regulatory molecules: repressors, activators, and inducers.

    What is 90% of the cell cycle? ›

    During interphase, the cell undergoes normal growth processes while also preparing for cell division. It is the longest phase of the cell cycle, cell spends approximately 90% of its time in this phase.

    What are the 11 phases of cell cycle? ›

    The correct sequence of cell cycle stages in the cell is G1 → S → G2 → M. On the other hand, meiosis includes interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II.

    What are the 7 stages of the cell cycle? ›

    prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. metaphase, prometaphase, prophase, anaphase, telophase, and cytokinesis.

    What is the C value cell cycle? ›

    C-value is the amount, in picograms, of DNA contained within a haploid nucleus (e.g. a gamete) or one half the amount in a diploid somatic cell of a eukaryotic organism.

    What does C mean in cell cycle? ›

    We use “c” to represent the DNA content in a cell, and “n” to represent the number of complete sets of chromosomes. In a gamete (i.e. sperm or egg), the amount of DNA is 1c, and the number of chromosomes is 1n.

    What is 3.2 the cell cycle? ›

    There are two main stages in the cell cycle. The first stage is interphase during which the cell grows and replicates its DNA. The second phase is the mitotic phase (M-Phase) during which the cell divides and transfers one copy of its DNA to two identical daughter cells.

    How many stages are in mitosis? ›

    Mitosis is conventionally divided into 5 phases, which include prophase, prometaphase, metaphase, anaphase and telophase and cytokinesis.

    What is DNA replication in cell life cycle? ›

    DNA replicates in the S phase of the cell cycle and initiates at specific regions in the DNA sequence known as DNA replication 'origins'. A number of proteins participate in DNA replication and the process is subject to scrutiny by cell surveillance mechanisms called cell cycle checkpoints.

    Why is regulation of the cell cycle? ›

    The cell replicates itself in an organized, step-by-step fashion known as the cell cycle. Tight regulation of this process ensures that a dividing cell's DNA is copied properly, any errors in the DNA are repaired, and each daughter cell receives a full set of chromosomes.

    How is the cell cycle regulated answer? ›

    Cell-cycle control depends exclusively on post-transcriptional mechanisms that involve the regulation of Cdk activity by phosphorylation and the binding of regulatory proteins such as cyclins, which are themselves regulated by proteolysis.

    What is the regulation of the cell cycle answer? ›

    The cell cycle is controlled by a number of protein-controlled feedback processes. Two types of proteins involved in the control of the cell cycle are kinases and cyclins. Cyclins activate kinases by binding to them, specifically they activate cyclin-dependent kinases (CDK).

    What are the regulatory molecules? ›

    Regulatory molecules. Enzymes can be regulated by other molecules that either increase or reduce their activity. Molecules that increase the activity of an enzyme are called activators, while molecules that decrease the activity of an enzyme are called inhibitors.

    What are 2 examples of regulatory proteins? ›

    There are several different categories of regulatory proteins. Enzymes, like peptidase or amylase, help speed up chemical reactions. Antibodies and cytokines play an important role in the immune system. Hormones are chemical messengers that can affect gene expression and functioning of their target cells.

    What are the types of regulatory DNA? ›

    Regulatory regions in DNA: promoters, enhancers, silencers, and insulators.

    What are all 4 cell cycles? ›

    The cell cycle is a 4-stage process consisting of Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M), which a cell undergoes as it grows and divides. After completing the cycle it either starts the process again from G1 or exits through G0.

    What are the 4 cell cycles? ›

    In eukaryotes, the cell cycle consists of four discrete phases: G1, S, G2, and M. The S or synthesis phase is when DNA replication occurs, and the M or mitosis phase is when the cell actually divides. The other two phases — G1 and G2, the so-called gap phases — are less dramatic but equally important.

    What are the 5 cell cycles? ›

    Today, mitosis is understood to involve five phases, based on the physical state of the chromosomes and spindle. These phases are prophase, prometaphase, metaphase, anaphase, and telophase.

    What are the 6 cell cycles? ›

    • 1.1 G0 phase (quiescence)
    • 1.2 Interphase. 1.2.1 G1 phase (First growth phase or Post mitotic gap phase) 1.2.2 S phase (DNA replication) 1.2.3 G2 phase (growth)
    • 1.3 Mitotic phase (chromosome separation)
    • 1.4 Cytokinesis phase (separation of all cell components)

    What are the 3 types of the cell cycle? ›

    The cell cycle of a eukaryotic cell has three stages: interphase, mitosis, and cytokinesis. The first stage of the cell cycle is called interphase.

    What is cell cycle grade 12 biology? ›

    The cell cycle is a repeating series of events that cells go through. It includes growth, DNA synthesis, and cell division. In eukaryotic cells, there are two growth phases, and cell division includes mitosis and cytokinesis. The cell cycle is controlled by regulatory proteins at three key checkpoints in the cycle.

    What are the 9 stages of the cell cycle in order? ›

    Include the following stages:
    • Interphase - G1.
    • Interphase - S.
    • Interphase - G2.
    • Prophase.
    • Prometaphase.
    • Metaphase.
    • Anaphase.
    • Telophase.

    What are the 8 stages of meiosis? ›

    In this video Paul Andersen explains the major phases of meiosis including: interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II.

    What is mitosis grade 10? ›

    Mitosis is the process of cell division wherein the chromosomes replicate and get equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division.

    What does C stand for in DNA? ›

    There are four nucleotides, or bases, in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T).

    What does the C-value represent? ›

    C-value is the amount of nuclear DNA in the unreplicated gametic nucleus, irrespective of the ploidy level of the species.

    What are C values in mitosis? ›

    If the cell undergoes mitosis, each daughter cell will return to 2c and 2n, because it will receive half of the DNA, and one of each pair of sister chromatids.

    What does C mean in meiosis? ›

    The "c" refers to the number of copies of each chromosome. In meiosis the progression of chromosomes is as follows: 2n, c: 1 cell. 2n, 2c: 1 cell where the DNA has been copied. n, 2c: 2 cells, each with 2 copies of only half the chromosomes.

    Which organism has the largest C-value? ›

    This is known as the C-value paradox. The largest genome is found in an amoeba, a one-cell organism, with 686,000 Mb, 200 fold larger than the human genome and 20,000 fold larger than the one found in yeast.

    What is the 10.2 cell cycle? ›

    The cell cycle consists of interphase and the mitotic phase. During interphase, the cell grows and the nuclear DNA is duplicated. Interphase is followed by the mitotic phase. During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei.

    How do you measure cell cycle? ›

    The cell cycle profile of a sample can be determined by staining the DNA with a fluorescent dye and measuring its intensity. The dye stains DNA stoichiometrically, allowing differentiation of cells in G0/G1, S phase, and G2/M, as well as identification of aneuploid populations.

    How do you calculate cell cycle time? ›

    Calculate the percentage of time spent in each phase by counting the total number of cells in each phase (total in interphase, in prophase, etc.) and dividing each by the total number of cells you counted.

    What are the 6 enzymes in DNA replication? ›

    The enzymes involved in the replication of prokaryotic DNA are DNA polymerase I to III, helicase, ligase, primase, sliding clamp, topoisomerase, and single-strand binding proteins (SSBs). The basics of DNA replication are similar in prokaryotes and eukaryotes, but eukaryotes have many more enzymes involved.

    What enzyme unzips DNA? ›

    Key enzyme involved in DNA replication, it is responsible for 'unzipping' the double helix structure by breaking the hydrogen bonds between bases on opposite strands of the DNA molecule.

    What does meiosis make? ›

    Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction.

    Is mitosis haploid or diploid? ›

    Mitosis produces two diploid (2n) somatic cells that are genetically identical to each other and the original parent cell, whereas meiosis produces four haploid (n) gametes that are genetically unique from each other and the original parent (germ) cell.

    Is mitosis Asexual? ›

    Mitosis is essential for asexual reproduction, regeneration, and growth. It does not make sex cells or gametes.

    Are humans meiosis or mitosis? ›

    As sexually-reproducing, diploid, multicellular eukaryotes, humans rely on meiosis to serve a number of important functions, including the promotion of genetic diversity and the creation of proper conditions for reproductive success.

    What phase does the cell grow? ›

    A cell spends most of its time in what is called interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division.

    Does DNA replicate before meiosis? ›

    DNA replication occurs in both mitosis and meiosis. In meiosis, the cell undergoes two divisions, i.e. meiosis I and II. Meiosis I is reduction division and meiosis II is similar to mitosis but DNA replicates only once during meiosis, i.e. before meiosis I in S phase.

    Do cells spend 10% of their time in mitosis? ›

    Most cells spend about 90% of their time in interphase. Note that mitosis and meiosis comprise only about 10% of the cell cycle.

    How do you calculate cell cycle percentage? ›

    Calculate % of cell by taking total number of cells for that phase and dividing it by 36 (total # cells observed). Multiple this number by 100 to get percent.

    What percent of cell cycle is prophase? ›

    We get 69.6 % cells in interphase, 12.5% in prophase, 8.9% in metaphase, 5.4% in anaphase, and 3.6% in telophase. It takes about 24 hours, or one-thousand, four-hundred and forty minutes, for an onion root-tip cell to complete the cell cycle.

    Does a cell have 10 chromosomes after mitotic cell division? ›

    Given that the parent cell has 10 chromosomes, the number of chromosomes in the daughter cell after mitotic cell division will be the same as the parent cell, which is 10. This is because during mitosis, the chromosomes are duplicated, and each daughter cell gets a complete set of chromosomes.

    What happens if a cell has 10 chromosomes and undergoes mitosis? ›

    The number of chromosomes that each of the new cells will have is c. 10 chromosomes each. Mitotic division results in two daughter cells with an identical chromosomal number and genetic content to the parental cell.

    What stage of cell cycle takes 10 hours of cell growth? ›

    G1 is typically the longest phase of the cell cycle. This can be explained by the fact that G1 follows cell division in mitosis; G1 represents the first chance for new cells have to grow. Cells usually remain in G1 for about 10 hours of the 24 total hours of the cell cycle.

    What is the cell cycle limit? ›

    The Hayflick Limit is a concept that helps to explain the mechanisms behind cellular aging. The concept states that a normal human cell can only replicate and divide forty to sixty times before it cannot divide anymore, and will break down by programmed cell death or apoptosis.

    What percentage of the cell cycle is G1? ›

    In this part of interphase, the cell synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis. G1 phase ends when the cell moves into the S phase of interphase. Around 30 to 40 percent of cell cycle time is spent in the G1 phase.

    How much time is spent in each phase of the cell cycle? ›

    Cells spend 95% of their cell division cycle in interphase (G1-, S-, and G2-phases) with average durations of 4 hr, 9 hr, and 5 hr to complete G1-, S-, and G2-phases, respectively. This results in cells spending only 5% of their cell-cycle time (less than 1 hr) in mitosis (Figures 1B–1D).

    What percent of total cells are in interphase? ›

    Roughly 90 percent of the cell cycle is spent in interphase.

    How is mitosis different from meiosis? ›

    There are two kinds of cell division: mitosis and meiosis. What's the Difference? Mitosis produces two genetically identical “daughter” cells from a single “parent” cell, whereas meiosis produces cells that are genetically unique from the parent and contain only half as much DNA.

    Is meiosis part of the cell cycle? ›

    Meiosis, in contrast, is a specialized kind of cell cycle that reduces the chromosome number by half, resulting in the production of haploid daughter cells.


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