2024 Cell Cycle - Mitosis PDF

THE CELL CYCLE AND CELL DIVISION Presented by: APRIL JOY A. TALAS  LESSON OBJECTIVES By the end of this session, the learners will be able to: 1. Characterized the phases of the cell cycle and their control points (STEM_BIO11/12-Id-f-6) 2. Described the stages of mitosis/meio...

THE CELL CYCLE AND CELL DIVISION Presented by: APRIL JOY A. TALAS  LESSON OBJECTIVES By the end of this session, the learners will be able to: 1. Characterized the phases of the cell cycle and their control points (STEM_BIO11/12-Id-f-6) 2. Described the stages of mitosis/meiosis given 2n=6 (STEM_BIO11/12-Id-f-7) 3. Compared mitosis and meiosis, and their role in the cell-division (STEM_BIO11/12-Id-f-7) Have you ever wondered how a tiny fertilized egg grows into a fully developed human being? Cell division is key to life: from the moment we are first conceived, we are continually changing and growing.  Are the terms "cell cycle" and "cell division" interchangeable, or do they refer to different processes in the life of a cell? The Cell Cycle The cell cycle is an ordered series of events involving cell growth and cell division. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division. The cell cycle has two major phases: interphase and the mitotic phase. During interphase, the cell grows, and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated, and the cell divides.  CELL DIVISION Cell division is a fundamental process found in both prokaryotes (bacteria) and eukaryotes, leading to the creation of two new cells. In organisms, there are three primary types of cell division: Prokaryotes (bacteria) — Binary fission Divides forming two new identical cells  PROKARYOTIC CELL DIVISION 1. Binary Fission Three (3) major steps; DNA Replication DNA is copied resulting into two identical chromosomes Chromosome Segregation Chromosomes separate and move towards ends (poles) of cell Cytokinesis (Separation) Cytoplasm divides forming two (2) cells Each new daughter cell is Genetically Identical to parent cell Prokaryotic Cell Division ▪ Eukaryotes — Mitosis essential for growth, development, and repair in multicellular organisms, as well as reproduction in single-celled organism. — Meiosis formation of sex cells, or gametes  EUKARYOTIC CELL DIVISION Cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent cell. 1. MITOSIS: Two (2) main steps: 1. Mitosis Fours steps; [Prophase, Metaphase, Anaphase, Telophase] 2. Cytokinesis Cytoplasm divides forming two new daughter cells Mitosis yields two daughter cells, each with the same number and type of chromosomes as the parent cell.  Eukaryotic Cell Division Cell division that results in four daughter cells 1. MEIOSIS: Consists of two consecutive cell divisions 1. Meiosis I Mitosis: Fours steps; [Prophase I, Metaphase I, Anaphase I, Telophase I] Cytokinesis: Results in two haploid daughter cells, each with half the original chromosome number 2. Meiosis II – without DNA replication Mitosis: Fours steps; [Prophase II, Metaphase II, Anaphase II, Telophase II] Cytokinesis: takes place in both haploid daughter cells, yielding a total of four haploid daughter cells, each with a unique genetic makeup. These cells are considered gametes. Resulting in four non-identical daughter cells, each containing half the number of chromosomes as the parent cell. WHY DO CELLS DIVIDE? Cell division is a fundamental process with various vital roles in the functioning of our bodies and the continuation of life. It plays a crucial role in our growth, development, repair of worn-out tissues, and even in reproduction.  1. Growth and Development: Growth and development require continuous cell division to produce new cells. This process enables us to increase our size, add height, build muscle, and develop various organs and tissues throughout our lifespan. 2. Tissue Repair: Tissue repair relies on cell division to replace damaged cells. When accidents occur, such as skin abrasions or nail breakage, cell division is essential for the production of new cells to heal and regenerate the injured tissue.  3. Maintaining Tissue Integrity: As cells age and wear out, they need to be replaced to maintain tissue integrity and functionality. Cell division ensures that our organs and tissues remain in optimal working condition. 4. Disease Prevention: Proper regulation of cell division is crucial for preventing diseases, as uncontrolled cell division can lead to conditions like psoriasis or, more dangerously, cancer. Strict checkpoints and stages in the cell division cycle help prevent these aberrations by ensuring that cell division proceeds accurately and safely. Examples: Skin Regeneration Blood Cell Renewal Intestinal Lining Liver Regeneration The outer layer of Our blood is composed The cells lining our The liver has a our skin, the of various types of intestines have a high remarkable ability to epidermis, constantly cells, including red turnover rate due to the regenerate. When a undergoes cell blood cells, white constant exposure to portion of the liver is division to replace blood cells, and food and digestive damaged or dead skin cells. This platelets. Cell division processes. Cell division removed, the ensures that the skin in the bone marrow in the intestinal lining remaining cells remains intact, continuously produces replenishes these cells, undergo rapid cell protective, and these blood cells, allowing for efficient division to replace capable of healing ensuring a steady absorption of nutrients the lost tissue, wounds and supply to support and maintaining a ensuring the organ's abrasions. bodily functions like healthy gut barrier. continued oxygen transport and functionality. immune response.  5. Reproduction: Reproduction relies on cell division to create new organisms. Without cell division, there would be no generation of offspring, leading to the eventual extinction of a species and the end of life as we know it. 6. Controlling DNA Overloading: Cell division controls DNA overloading by ensuring that each daughter cell receives an identical and manageable portion of the genetic material, preventing genetic instability and potential harm. CELL CYCLE Introduction The cell cycle is a precisely regulated series of events encompassing phases of growth, rest, and cell division. It spans from the moment a cell emerges following division to the point when it divides itself. This cycle comprises distinct stages, each serving a specific purpose. Phases of the Cell Cycle Growth and Development: The cell grows and develops its functionality. DNA Replication: The cell duplicates its genetic material to prepare for division. Preparation for Division: This stage readies the cell for division, ensuring that all components are in order. Cell Division: The cell divides into two daughter cells, each with an identical genetic makeup. Following division, a new cell cycle commences  CONTROL OF THE CELL CYCLE It is essential that daughter cells be exact duplicates of the parent cell. Mistakes in the duplication or distribution of the chromosomes lead to mutations that may be passed forward to every new cell produced from the abnormal cell. To prevent a compromised cell from continuing to divide, there are internal control mechanisms that operate at three main cell cycle checkpoints at which the cell cycle can be stopped until conditions are favorable.  CONTROL OF THE CELL CYCLE Regulatory proteins called cyclins control the cell cycle at checkpoints: Cyclins are a family of regulatory proteins that control the progression of the cell cycle. Cyclins activate cyclin dependent kinases (CDKs), which control cell cycle processes. A critical control point in the Cell Cycle where ‘stop’/halt the cycle (negative regulation) and ‘go-ahead’/ next phase (positive regulation) signals can regulate the cell cycle is called the checkpoint. The concentrations of cyclin proteins change throughout the cell cycle. Regulation of the Cell Cycle by External Events Three major checkpoints are found in the G1, G2, and M phases of the Cell Cycle.  The first checkpoint (G1) determines whether all conditions are favorable for cell division to proceed. This checkpoint is the point at which the cell irreversibly commits to the cell- division process. In addition to adequate reserves and cell size, there is a check for damage to the genomic DNA. A cell that does not meet all the requirements will not be released into the S phase. The second checkpoint (G2) bars the entry to the mitotic phase if certain conditions are not met. The most important role of this checkpoint is to ensure that all of the chromosomes have been replicated and that the replicated DNA is not damaged.  The final checkpoint (M) occurs in the middle of mitosis. This checkpoint determines if all of the copied chromosomes are arranged appropriately to be separated to opposite sides of the cell. If this doesn’t happen correctly, incorrect numbers of chromosomes can be partitioned into each of the daughter cells, which would likely cause them to die.  The Cell Cycle Consist of two(2) main periods: G1 phase I. Interphase (G0, G1, S, G2) M phase II. Mitotic Phase (M) S phase G2 phase Interphase involves regular growth processes, DNA replication, and preparation for cell division (mitosis). It is sometimes called the "daily living" or metabolic phase due to its role in maintaining normal cellular functions. Surprisingly, despite its previous designation as the "resting phase," Interphase is highly active. Cells spend about 90% of their time in Interphase, making it the longest phase in the cell cycle. The name changed from "resting phase" to "Interphase" because cells actively prepare for cell division during this stage, rather than simply resting. Interphase consists of three sub-phases: Gap 1 (G1): The cell's first phase, dedicated to growth. Synthesis (S): The second phase, focused on DNA replication. Gap 2 (G2): The third phase, where further cell growth occurs.  G0 phase G0 represents a phase where cells temporarily exit the active cell cycle and enter a quiescent (inactive) state. Cells in G0 are not actively preparing for cell division, but they continue to perform their usual functions. The duration of G0 can vary widely depending on cell type and environmental conditions.  G0 phase Cells in G0 can be prompted to re-enter the active cell cycle when they receive appropriate signals or stimuli. G0 is critical for cells with specialized functions that do not require continuous division, such as mature nerve cells, muscle cells, and certain immune cells. Chromosome and Centrioles  A single length of DNA undergoes intricate packaging to form the structures known as nucleosomes, with many proteins called histones involved in this process. Histones primarily facilitate the compaction of DNA. These nucleosomes coil tightly together, creating chromatin loops. These chromatin loops, in turn, wrap around each other, culminating in the formation of a complete chromosome.  Each chromosome exhibits a distinct structure, featuring two short arms referred to as p arms, two longer arms known as q arms, and a centromere situated at the center, which plays a crucial role in holding the chromosome together.  Human chromosomes can be represented in two forms: as a single component or replicated. During interphase, chromosomes duplicate, resulting in two sister chromatids. A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division. The two “sister” chromatids are joined at a constricted region of the chromosome called the centromere. 1  Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms. This is the relaxed form of DNA found in the nucleus of a cell when it is not dividing. It's like a tangled string of genetic material. Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). When a cell is getting ready to divide, the chromatin coils up tightly to form chromosomes. These are the X-shaped structures that hold your genetic information. A chromatid is one of two identical halves of a replicated chromosome. Sister chromatids are identical copies of DNA that remain connected by a central point called the centromere until they are separated during mitosis.  Before duplication: A chromosome is composed of a single chromatid. This is when the cell is not preparing to divide, and the chromosome consists of just one copy of DNA. After duplication: The chromosome has two chromatids. These chromatids are identical copies of each other, connected at a region called the centromere. During cell division, these chromatids will separate to ensure that each new cell gets a complete set of chromosomes. So, when duplicated, the chromosome has two chromatids, and when not duplicated, it has just one.  In humans, the genetic material is organized into 23 pairs of chromosomes, amounting to a total of 46 chromosomes. These chromosomes come in two sets: one set inherited from the mother and the other from the father. Among these 23 pairs, one pair is comprised of sex chromosome (allosomes), and their composition varies based on an individual's gender—XX for females and XY for males. The remaining 22 pairs are termed autosomes, representing non-sex chromosomes, and remain identical in appearance for both males and females.  Each of our chromosomes contains a multitude of genes, the fundamental units of genetic information that govern various aspects of our traits and functions. Moreover, at the ends of each chromosome, there are specialized sections of DNA known as telomeres. Telomeres serve a critical role in safeguarding the chromosome ends during the process of DNA replication. They function as protective caps, much like the plastic tip on the end of a shoelace, ensuring the stability and integrity of our genetic material. Centrosome is the point of origin of the mitotic spindle Gap 1 (G1) It is the first part of the cell cycle wherein the cell carries out its normal metabolic function. During this phase, cells also increased in size as their organelles increase in number. Cells spend most of their life cycle in this phase. The G1 checkpoint ensures that the cell is large enough to divide, the nutrients are enough to support the resulting daughter cells and the DNA is not damaged.  If a cell receives a ‘go-ahead’ signal at the G1 checkpoint, it will usually continue with the Cell Cycle. If the cell does not receive the ‘go-ahead’ signal, it will exit the Cell Cycle and switch to a non-dividing state called G0. In G0, a cell is not actively preparing to divide, it’s just doing its job, for instance, a neuron conducting nerve impulses or a liver cell storing carbohydrates. Most cells in the human body are in the G0 phase. Centriole Replication A centrosome is composed of two, barrel-shaped centrioles embedded in an amorphous proteinaceous matrix, known as the pericentriolar material (PCM). Like DNA, centrosome duplication is a semi-conservative process that occurs once, and only once, per cell cycle. G1 phase cells possess a single centrosome containing two centrioles. They take part in cell division for the formation of spindle fibers necessary for the movement of chromosomes towards opposite poles during the separation of sister chromatids. S phase (DNA Replication) The cell makes a copy of genetic material in the form of nuclear DNA. During this stage, the cell spends considerable amount of time and energy to make copies of its chromosome. Each chromosomes contains one DNA molecule that is copied with enough accuracy through DNA replication. Semi-conservative replication because two copies of the original DNA molecule are produced, each copy conserving (replicating) the information from one half of the original DNA molecule. S phase (DNA Replication) This process ensures that the daughter cell receives exact copies of the parent’s genetic material during the cell division. Aside from the DNA, it also produces protein complex called microtubules- will help in organizing the cell. Centrioles duplicate during the S phase of the cell cycle, and it results in the formation of four centrioles prior to cell division. They help in distributing the duplicated genetic material equally. Also, during S phase, DNA replication occurs inside the nucleus. Gap 2 or G2 The critical checkpoint before transitioning to the next stage. It make sure that, it grows in correct size and duplicating DNA without damage. For most cells the G2 phase is relatively short; once complete, the cell is ready to divide. During interphase, a cell grows larger. The cell replicates its DNA, forming sister chromatids. Each is joined by a centromere. A collection of microtubules (structural proteins) called a centrosome also replicates. There are two gap stages during interphase. During gap 1 (G1), the cell grows, while during gap 2 (G2), the cell finishes growing and performs a quick check of the replicated DNA to make sure it was copied correctly.  MITOSIS The mitotic phase, also known as M phase, is the stage where the cell undergoes division, ultimately leading to the creation of two genetically identical daughter cells. This phase is a complex, multi-step process encompassing the division of both the nucleus (karyokinesis) and the cytoplasm (cytokinesis). Karyokinesis: Division of the Nucleus Mitosis, a critical component of the mitotic phase, involves the division of the nucleus. Duplicated chromosomes are carefully aligned, separated, and move towards opposite poles of the cell. The process can be broken down into four distinct stages: Prophase, Metaphase, Anaphase, and Telophase (PMAT).  Cytokinesis: Division of the Cytoplasm The second part of the mitotic phase is cytokinesis, which involves the physical separation of cytoplasmic components into the two daughter cells. Cytokinesis is responsible for creating two distinct and complete daughter cells from the parent cell. It marks the final step in the cell cycle, completing the goal of distributing an identical set of genetic instructions to each daughter cell. As a result, each daughter cell receives one copy of each chromosome, ensuring that they have the same full set of DNA as the parent cell. INTERPHASE  PROPHASE (START OF MITOSIS) Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms. Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). A chromatid is one of two identical halves of a replicated chromosome. Sister chromatids are identical copies of DNA that remain connected until they are separated during mitosis.  A centromere, the point on a chromosome that attaches to the spindle fibers with a kinetochore during cell division, attaches the sister chromatids. It is the region where the cell's spindle fibers attach. The centromere is aided in binding sister chromatids together by several proteins called cohesins and condensins. Once the DNA has been replicated, the cell moves to the second gap phase.  During mitosis, the genetic material that has been replicated during the synthesis phase is affected by the actions of two types of proteins called cohesins and condensins. Prior to mitosis, the DNA is found spread out inside the nucleus. A cohesin protein helps bind sister chromatids together at the centromere until they separate during anaphase. A condensin is a protein that helps condense DNA into chromosomes during prophase of mitosis. Condensin reorganizes chromosomes when they get compacted during prophase. This reduces the amount of space the DNA takes up..  PROPHASE (START OF MITOSIS) Prophase is the first phase of mitosis, in which sister chromatids condense the mitotic spindle begins to form, and centrosomes (the structures that coordinate the formation of microtubules, which allow cell division to proceed) segregate to opposite poles.  PROPHASE (START OF MITOSIS) During prophase, the sister chromatids condense until they are tightly packed. This makes them appear X-shaped, which is the representation of chromosomes with which most people are familiar. The centrosomes segregate to the ends of the cell, called the poles. The centrosomes then start to organize the formation of the mitotic spindle, the bundle of spindle fibers attached at one end to the centrosome.  PROPHASE (START OF MITOSIS) The mitotic spindle is composed of microtubules that elongate from the centrosome to the centromeres, the point on a chromosome that attaches to the spindle fibers and at which the sister chromatids are attached. The mitotic spindle helps align the sister chromatids correctly for proper cell division, ensuring each daughter cell gets one copy. Prometaphase As the cell progresses from prophase to prometaphase, the nuclear envelope starts to dissolve. This breakdown of the nuclear envelope is a critical step that allows the chromosomes to become free to move within the cell. Additionally, during this process, the nucleolus, a structure inside the nucleus, disappears. Formation of Vesicles: The breakdown of the nuclear membrane results in the formation of small vesicles, which are remnants of the nuclear envelope. These vesicles play an essential role in providing access to the centromeres of the chromosomes for the mitotic spindle. Attachment of Spindle Fibers: When a spindle fiber finds a centromere, it attaches at the kinetochore, a group of proteins bound at the centromere. The spindle fibers tug the chromosomes back and forth as they position them correctly for the next stage. The spindle fiber that extends from the centrosome to the kinetochore on the centromere is known as a kinetochore microtubule End Prophase: The nuclear membrane has fragmented, centrioles microtubules have Microtubules invaded the nuclear area form a complete spindle Centrioles have moved to the chromatids opposite poles centrioles The spindle is completely formed. METAPHASE: the third phase of mitosis, where the chromosomes align themselves along the equator of the cell. In this stage, the chromosomes line up along the cell equator (also called the metaphase plate), an imaginary line in the center of a cell during mitosis, along which sister chromatids align.  METAPHASE Each chromosome is composed of a pair of identical sister chromatids Centrioles linked by the centromere. The sister chromatids are attached by their centromere to two spindle Chromosomes fibers: one leading to each centrosome at opposite ends—each pole—of the cell. The chromosomes Spindle no longer move back and forth but composed of microtubules stay aligned along the equator. In metaphase the third stage of mitosis, the sister chromatids of the replicated chromosomes line up along the cell equator or "metaphase plate" or "equatorial plate." The metaphase plate is significant because it marks a critical checkpoint in cell division. The cell checks to make sure that all the chromosomes are properly aligned before proceeding to anaphase, where the sister chromatids are pulled apart to opposite poles of the cell. Anaphase: where the sister chromatids separate and start to move towards opposite sides of the cell. Chromosome Separation: the paired chromosomes, also known as sister chromatids, undergo separation. Chromatid Movement: The separated chromatids swiftly move toward opposite poles of the cell. This movement is orchestrated by the shortening of kinetochore microtubules. Initiation of Cytoplasmic Division: Simultaneously, anaphase initiates a Chromatids are being pulled to partial division of the cell's opposite sides of cytoplasm. This early phase of the cell. cytokinesis lays the foundation for the eventual splitting of the cell into Shortening of the microtubules two daughter cells. Telophase: the nuclear membrane reforms and prepares the cell to divide in half during cytokinesis. Chromosomal Arrangement: Chromosomes reach poles within the cell. Nuclear Envelope Formation: Vesicles reform a new nuclear envelope around daughter cell DNA. Spindle Breakdown: Mitotic spindle begins to break down, causing spindle fibers to disappear.  Telophase Microtubule and Spindle Fiber Disintegration: Microtubules and spindle fibers disintegrate. Nuclear Membrane Reconstruction: Nuclear membrane Fragments and proteins rebuild the is nuclear membrane, defining two distinct returning nuclei. Chromatin Formation: Chromosomes gradually uncoil into chromatin, making DNA accessible. Chromosomal Visibility: Individual chromosomes are no longer visible, Telophase marks mitosis completion, leading to two separate having transitioned into a less compacted nuclei and preparing for cytokinesis, the final step in cell chromatin state. division Cytokinesis: the pinching off of the cytoplasm to form two new cells Involves the splitting of the cytoplasm into two daughter cells. It completes the cell cycle. Cytokinesis: in animal cells… In animal cells, cleavage furrow is formed inward by tiny strands of protein actin called “microfilaments” Slowly, the cell membrane begins to form. This final cell division marks the end of M phase of the cell cycle. At this point, each cell resumes the G1 phase or exits the cell cycle completely if the cell will no longer divide. Cytokinesis: in plant cells… In plant cells, the membrane cannot pinch because of cell wall. Instead, a cell plate will form between the two daughter cells. The cell plate is made by Golgi apparatus The vesicle supply new cell wall. Lipids to form plasma membrane Cytokinesis: Occurs at the end of mitosis Animal cells: a cleavage furrow separates the daughter cells Plant cell: a cell plate separates the daughter cells Daughter cells are genetically Cells return to interphase identical  The duration of these cell cycle phases varies considerably in different kinds of cells. For a typical rapidly proliferating human cell with a total cycle time of 24 hours, the G1 phase might last about 11 hours, S phase about 8 hours, G2 about 4 hours, and M about 1 hour. Thank You!