Unit 4 PDF: Cell Communication

Intro to Unit 4 Your body is made up of TRILLIONS of cells that all have different responsibilities. That is a LOT of cells!! In order for your body to function correctly, these cells need to work in unison by communicating with each other. Your cells also go through a proce...

Intro to Unit 4 Your body is made up of TRILLIONS of cells that all have different responsibilities. That is a LOT of cells!! In order for your body to function correctly, these cells need to work in unison by communicating with each other. Your cells also go through a process called the cell cycle in order to generate new cells. Before we begin… A good way to remember the importance of regulation in cell communication and the cell cycle is to think of a checklist. In order for these processes to be done correctly, there must be correct timing and coordination within the cell. 4.1 Cell Communication 3 min read Last Updated on November 18, 2024 Skills you’ll gain in this topic: Describe how cells communicate using direct contact and signaling molecules. Differentiate between types of signaling, including autocrine, paracrine, and endocrine. Explain how cells receive and interpret signals. Relate signal reception to specific cellular responses. Predict the effects of successful cell signaling on cellular function. Mechanisms of Cell Signaling The cells in your body communicate in many different ways. Cells must communicate with each other and the environment in order to complete tasks. They communicate through chemical signals. These signals are usually proteins. Multicellular organisms have trillions of cells that communicate in the following ways. Juxtacrine Signaling Direct contact is also called juxtacrine signaling. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the plasmodesmata connect one plant cell to another. In animal cells, gap junctions directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules. Memory Tip: Think of direct contact like a handshake because both people must have direct contact with each other during a handshake! Direct contact is also called juxtacrine signaling. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the plasmodesmata connect one plant cell to another. In animal cells, gap junctions directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules. Memory Tip: Think of direct contact like a handshake because both people must have direct contact with each other during a handshake! Image courtesy of Giphy. Paracrine Signaling Another way that cells communicate is through paracrine signaling. Paracrine signaling is communication over short distances. Cell sends out signals to nearby cells which causes a change in the behavior of nearby cells. An example of paracrine signaling is contracting muscles. Chemical signals are sent from the nerve to the muscle. This causes the response of changes in the behavior of muscle so that the muscle contracts. Another example would be synaptic signaling involves a synapse which is the gap between 2 nerve cells. Signaling occurs when a neuron releases a neurotransmitter. Then, the neurotransmitter moves across the synapse. After it reaches the end of the gap, the neurotransmitter stimulates the adjacent neuron to fire. Memory Tip: Think of paracrine signaling as crossing the street. Crossing the street is a short distance and helps me remember that paracrine signaling is between nearby cells. Takes the “right down the street” phrase into a new perspective!  Image courtesy of Giphy. Autocrine Signaling Autocrine signaling is essentially a cell sending chemical messages to itself. It would involve the cell releasing a chemical and then having a receptor that receives this message. An example of this would be cancer cells. Cancer cells release their own growth hormones so that they can keep on growing, instead of relying on growth hormones from the host organism. In this way, the cancer cells can keep growing faster and more efficiently. Memory Tip: "Auto" means self, so autocrine signaling must be signaling to yourself. Think of other words that involve the root "auto" like autopilot. Endocrine Signaling Here, we have endocrine signaling, which is signaling another cell by sending the ligand through the bloodstream, perhaps to a different organ cell. This is different from paracrine signaling because that only involved sending it off to a cell nearby. Endocrine signaling is like sending a something to a different country. It's much more far away, so the ligand is also equipped to have a longer lifespan. An example of this would be the pancreas cells releasing insulin when blood sugar levels are too high. This insulin is then received by the liver cell and glucose is converted to glycogen as a response. Memory Tip: Think of this as sending a letter or package to a different country so your letter or package must travel by water to reach its destination. auto loading next study guide stay on this page Key Terms to Review (16) Autocrine Signaling: Autocrine signaling is a form of cell communication in which a cell produces and releases signals that bind to receptors on its own surface, leading to changes within the same cell. Cancer Cells: Cancer cells are abnormal cells that divide uncontrollably and have the ability to infiltrate and destroy normal body tissue. Endocrine Signaling: Endocrine signaling refers to the process where endocrine cells release hormones directly into the bloodstream. These hormones then travel to target cells located in different parts of the body. Gap Junctions: Gap junctions are specialized intercellular connections between certain animal cell-types that directly connect the cytoplasm of two cells, allowing various molecules, ions and electrical impulses to pass freely between cells. Glucose: Glucose is a simple sugar (monosaccharide) that serves as the main source of energy for cells in living organisms. Glycogen: Glycogen is a polysaccharide that serves as the primary form of energy storage in animals and fungi. It's similar to starch but has more extensive branching. Growth Hormones: Growth hormones are substances produced by our bodies that regulate growth, metabolism, and body composition. Insulin: Insulin is a hormone produced by the pancreas that regulates the amount of glucose in the blood. It allows cells to take in glucose from the bloodstream and use it as energy. Juxtacrine Signaling: Juxtacrine signaling is a type of cell communication that involves direct contact between the signaling and responding cells. This means that the cells must be touching each other for the signal to be passed. Ligand: A ligand is a molecule that binds to another (usually larger) molecule. In cell communication, it's often the signal molecule that binds to a receptor. Liver Cell: Liver cells, also known as hepatocytes, are responsible for protein synthesis, detoxification and production of biochemicals necessary for digestion among other functions. Neurotransmitter: A neurotransmitter is a chemical substance produced in the body that transmits nerve impulses across synapses between neurons. Pancreas Cells: Pancreas cells are specialized types of cells found in pancreas which produce important enzymes and hormones like insulin and glucagon that regulate blood sugar levels. Paracrine Signaling: Paracrine signaling is a type of cell communication where a cell produces a signal to induce changes in nearby cells, altering the behavior or differentiation of those cells. Plasmodesmata: Plasmodesmata are microscopic channels traversing the cell walls of plant cells and some algal cells, enabling transport and communication between them. Synaptic Signaling: Synaptic signaling is an interaction between two nerve cells where an electrical signal or neurotransmitter molecule released from one neuron will stimulate another neuron, allowing for rapid transmission of information across synapses. Direct contact is also called juxtacrine signaling. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the plasmodesmata connect one plant cell to another. In animal cells, gap junctions directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules. Memory Tip: Think of direct contact like a handshake because both people must have direct contact with each other during a handshake! Image courtesy of Giphy. Paracrine Signaling Another way that cells communicate is through paracrine signaling. Paracrine signaling is communication over short distances. Cell sends out signals to nearby cells which causes a change in the behavior of nearby cells. An example of paracrine signaling is contracting muscles. Chemical signals are sent from the nerve to the muscle. This causes the response of changes in the behavior of muscle so that the muscle contracts. Another example would be synaptic signaling involves a synapse which is the gap between 2 nerve cells. Signaling occurs when a neuron releases a neurotransmitter. Then, the neurotransmitter moves across the synapse. After it reaches the end of the gap, the neurotransmitter stimulates the adjacent neuron to fire. Memory Tip: Think of paracrine signaling as crossing the street. Crossing the street is a short distance and helps me remember that paracrine signaling is between nearby cells. Takes the “right down the street” phrase into a new perspective! Image courtesy of Giphy. Autocrine Signaling Autocrine signaling is essentially a cell sending chemical messages to itself. It would involve the cell releasing a chemical and then having a receptor that receives this message. An example of this would be cancer cells. Cancer cells release their own growth hormones so that they can keep on growing, instead of relying on growth hormones from the host organism. In this way, the cancer cells can keep growing faster and more efficiently. Memory Tip: "Auto" means self, so autocrine signaling must be signaling to yourself. Think of other words that involve the root "auto" like autopilot. Endocrine Signaling Here, we have endocrine signaling, which is signaling another cell by sending the ligand through the bloodstream, perhaps to a different organ cell. This is different from paracrine signaling because that only involved sending it off to a cell nearby. Endocrine signaling is like sending a something to a different country. It's much more far away, so the ligand is also equipped to have a longer lifespan. An example of this would be the pancreas cells releasing insulin when blood sugar levels are too high. This insulin is then received by the liver cell and glucose is converted to glycogen as a response. Memory Tip: Think of this as sending a letter or package to a different country so your letter or package must travel by water to reach its destination. auto loading next study guide stay on this page Key Terms to Review (16) Autocrine Signaling: Autocrine signaling is a form of cell communication in which a cell produces and releases signals that bind to receptors on its own surface, leading to changes within the same cell. Cancer Cells: Cancer cells are abnormal cells that divide uncontrollably and have the ability to infiltrate and destroy normal body tissue. Endocrine Signaling: Endocrine signaling refers to the process where endocrine cells release hormones directly into the bloodstream. These hormones then travel to target cells located in different parts of the body. Gap Junctions: Gap junctions are specialized intercellular connections between certain animal cell-types that directly connect the cytoplasm of two cells, allowing various molecules, ions and electrical impulses to pass freely between cells. Glucose: Glucose is a simple sugar (monosaccharide) that serves as the main source of energy for cells in living organisms. Glycogen: Glycogen is a polysaccharide that serves as the primary form of energy storage in animals and fungi. It's similar to starch but has more extensive branching. Growth Hormones: Growth hormones are substances produced by our bodies that regulate growth, metabolism, and body composition. Insulin: Insulin is a hormone produced by the pancreas that regulates the amount of glucose in the blood. It allows cells to take in glucose from the bloodstream and use it as energy. Juxtacrine Signaling: Juxtacrine signaling is a type of cell communication that involves direct contact between the signaling and responding cells. This means that the cells must be touching each other for the signal to be passed. Ligand: A ligand is a molecule that binds to another (usually larger) molecule. In cell communication, it's often the signal molecule that binds to a receptor. Liver Cell: Liver cells, also known as hepatocytes, are responsible for protein synthesis, detoxification and production of biochemicals necessary for digestion among other functions. Neurotransmitter: A neurotransmitter is a chemical substance produced in the body that transmits nerve impulses across synapses between neurons. Pancreas Cells: Pancreas cells are specialized types of cells found in pancreas which produce important enzymes and hormones like insulin and glucagon that regulate blood sugar levels. Paracrine Signaling: Paracrine signaling is a type of cell communication where a cell produces a signal to induce changes in nearby cells, altering the behavior or differentiation of those cells. Plasmodesmata: Plasmodesmata are microscopic channels traversing the cell walls of plant cells and some algal cells, enabling transport and communication between them. Synaptic Signaling: Synaptic signaling is an interaction between two nerve cells where an electrical signal or neurotransmitter molecule released from one neuron will stimulate another neuron, allowing for rapid transmission of information across synapses. 4.3 Signal Transduction 3 min read Last Updated on June 18, 2024 Skills you’ll gain in this topic: Explain how phosphorylation cascades and second messengers amplify signals. Describe how transduction pathways lead to diverse cellular responses. Analyze the role of second messengers in transmitting information. Relate signal amplification to efficient cellular responses. Predict cell function changes based on variations in signal transduction. Signal Amplification and Cellular Responses As we talked about earlier, cells communicate and respond to changes in the environment. The environment also has the ability to influence cells in order to elicit a response. Many things in the environment can alter the cell cycle. Some examples of factors are temperature, light, and chemicals. When these factors are present, it can influence how the cell responds to the environment. Signal transduction can also result in changes in types of cellular response such as gene expression and cell function. A good example of cell communication is "quorum sensing" done by bacteria cells. The bacteria infect a host with toxin and produce a ligand. Once the concentration of the ligands reaches a certain amount, it becomes an indicator that the bacteria population is sufficient, thereby allowing the bacteria to act accordingly to the environment. Gene Expression Gene expression is when the instructions of our DNA is converted into a product. Signal transduction pathways can affect gene expression by altering the amount of product that is being made. This is related to the idea of protein synthesis. The number of proteins made is altered through signal transduction pathways if less signals are received by the cell to make these proteins. Signal Transduction Pathways The signal transduction pathways can also alter a large number of cell functions such as death, differentiation, shape, and metabolism. Because of this, it is very important that all processes occur correctly in order to avoid harmful disorders and diseases. A good example is the blood sugar level regulation through the use of insulin. Image Courtesy of News Medical When you eat food, blood glucose level rises from the sugar you just ate. The pancreas has a sensor attached to it in the blood stream, so when glucose level rises, it senses the increase. It in turn releases insulin into the blood. Insulin travels through the bloodstream and signals the liver that there is too much glucose in the blood stream. The liver then takes the glucose and stores it as glycogen (long chain of sugar). Then, blood glucose level declines, brining it back to the regular sugar level allowed by the body. But what if your body is low on glucose level? This could cause problems too, so the body will respond to this stimulus. This time, the pancreas will sense the change again and release glucagon into the blood. Glucagon will travel through the blood stream and signal the liver that the blood sugar level is low. The liver will break down the stored glycogen back into glucose and release it into the blood stream. As a result, blood glucose level rises, brining the body back to the regular sugar level. Every time insulin or glucagon travel through the blood stream to signal the liver or the pancreas, signal transduction pathway is in activity. It's a crucial way to sustain life, and it's used everywhere. Even this second, your body is probably signaling an organ for metabolism. It's essential and it's crucial. Image courtesy of WikiMedia Commons. auto loading next study guide stay on this page Key Terms to Review (15) Blood Sugar Level Regulation: This is the process by which the body maintains a balanced concentration of glucose in the bloodstream. It's crucial for providing energy to cells and maintaining overall health. Cell Communication: Cell communication is the process by which cells interact and respond to signals from their environment or other cells. This involves a series of steps including signal reception, transduction, and response. Cell Death: Cell death is a process where a cell ceases to function and ultimately dies. This can occur naturally as part of an organism's growth or development, or it can be triggered by disease or injury. Cell Differentiation: Cell differentiation is the process by which a less specialized cell becomes a more specialized cell type. This happens during development of an organism, allowing cells to take on specific functions. Gene Expression: Gene expression is the process by which information from a gene is used to create a functional product, usually a protein. Glucagon: Glucagon is a hormone produced by the pancreas that raises blood sugar levels by stimulating the breakdown of glycogen into glucose. Glucose: Glucose is a simple sugar (monosaccharide) that serves as the main source of energy for cells in living organisms. Glycogen: Glycogen is a polysaccharide that serves as the primary form of energy storage in animals and fungi. It's similar to starch but has more extensive branching. Insulin: Insulin is a hormone produced by the pancreas that regulates the amount of glucose in the blood. It allows cells to take in glucose from the bloodstream and use it as energy. Ligand: A ligand is a molecule that binds to another (usually larger) molecule. In cell communication, it's often the signal molecule that binds to a receptor. Metabolism: Metabolism refers to all chemical reactions involved in maintaining the living state of cells and organisms. It can be divided into two categories - catabolism (breaking down molecules) and anabolism (building up molecules). Pancreas: The pancreas is an organ located behind stomach that produces enzymes used in digestion, as well as hormones like insulin and glucagon that regulate blood sugar levels. Protein Synthesis: Protein synthesis is the process by which cells build proteins. This involves two main stages - transcription (where DNA is converted into RNA) and translation (where RNA is used to produce proteins). Quorum Sensing: Quorum sensing is a system of stimulus and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to local population density. Signal Transduction Pathways: Signal transduction pathways are series of chemical reactions within a cell that are triggered by signals at its surface, leading to changes inside the cell such as activation of genes or alteration in cellular metabolism. 4.4 Changes in Signal Transduction Pathways 3 min read Last Updated on June 18, 2024 Skills you’ll gain in this topic: Explain how mutations in receptors or pathway proteins alter signaling. Describe how external factors, like drugs or toxins, affect signal transduction. Relate signaling disruptions to diseases like cancer.  Analyze how feedback loops can compensate for signaling changes. Predict the effects of altered pathways on cell function. Impacts of Disruptions in Signaling Cellular Processes Changes to any structure in the cell cycle can affect the signal transduction pathway. As we talked about earlier, the signal transduction pathway has the ability to alter cellular processes. Specifically, mutations can lead to detrimental effects on later responses. Mutations Mutations have the ability to greatly impact the cell cycle. It can disturb the production of proteins, which could be crucial to the cell's survival. Or, for example, mutations in the signal transduction pathway can prevent the cell from regulating its cell cycle. When the cell cycle is unregulated, it can result in unrestricted cell division that could lead to harmful conditions like cancer. Let's look at an example. Insulin is a type of ligand that tells the liver to store glucose as glycogen and reduce the level of sugar in the bloodstream. It travels through the blood stream, and it binds to a receptor protein on the surface of a liver cell. Accordingly, the liver cell activates a sequence to link the glucose molecules together into a long chain, making glycogen. Then, the blood sugar level is decreased. However, when mutations happen with creating the insulin, recepting the insulin or activating a response. This might be because the DNA was deleted, missing or damaged. Type 1 Diabetes comes from the inability to create insulin. This type of mutation causes patients to be unable to regulate their blood sugar level. Type 2 Diabetes, on the other hand, comes from the inability to recognize insulin. This means that the liver cell is unable to recognize what the insulin is trying to say, thus unable to follow through with a response and store glucose. This may be due to a mutation with the receptor protein when it was being made. We will go over more effects that mutations can have on cells in section 4.7 Regulation of Cell Cycle. Image courtesy of Giphy. Chemicals Along with mutations, chemicals have the ability to alter the signal transduction pathway. These chemicals can either activate or hamper the pathway’s response. For example, chemicals such as lead, polychlorinated biphenyls (PCBs), and ethanol have the ability to have neurotoxic effects with specific signal transduction pathways. Things like temperature, chemicals and pH can cause disruptions too. Remember denatured proteins? The same applies here. Without proteins, the signal transduction pathway is a complete failure. If the proteins, therefore, are damaged or denatured in any way shape or form, the signal transduction pathway could be significantly altered. Like the insulin example, the receptor might not recognize a ligand, or maybe a cell won't be able to produce a ligand. This can cause the cell to fail to response more effectively. Lastly we have inhibitors. These inhibitors can block the sites of the receptor proteins, so the ligand can't bind. This will, again, cause great disruptions to the signal transduction pathways. This is actually how most medications are made. They usually take place of a ligand so that a specific part of the body functions are not being processed. Key Terms to Review (22) Blood Sugar Level: The concentration of glucose present in the blood. It is usually measured in milligrams per deciliter (mg/dL). Cellular Processes: Cellular processes are the biochemical mechanisms that occur within living cells to maintain life, such as cell division, protein synthesis, and energy production. Chemicals: Substances produced by different processes involving changes at molecular level. They have specific properties and play crucial roles in biological processes. Denatured Proteins: Denatured proteins have lost their native shape and biological function due to stress factors like heat, pH changes, or chemicals. DNA: DNA (Deoxyribonucleic Acid) is a molecule that carries most of the genetic instructions used in development, functioning and reproduction of all known living organisms. Ethanol: Ethanol, also known as ethyl alcohol, is a type of alcohol produced by yeast during fermentation. It's found in alcoholic beverages and used as a biofuel. Glucose Molecules: Glucose molecules are simple sugars that serve as primary energy sources for living organisms. They can be broken down during cellular respiration to provide energy for cells. Glycogen: Glycogen is a polysaccharide that serves as the primary form of energy storage in animals and fungi. It's similar to starch but has more extensive branching. Inhibitors: Inhibitors are substances that reduce the activity of enzymes, slowing down or even stopping certain reactions in the body. Insulin: Insulin is a hormone produced by the pancreas that regulates the amount of glucose in the blood. It allows cells to take in glucose from the bloodstream and use it as energy. Lead: Lead is a heavy metal that is naturally occurring in the earth's crust. It is toxic to humans and animals when ingested or inhaled, causing damage to the nervous system and other organs. Ligand: A ligand is a molecule that binds to another (usually larger) molecule. In cell communication, it's often the signal molecule that binds to a receptor. Liver Cell: Liver cells, also known as hepatocytes, are responsible for protein synthesis, detoxification and production of biochemicals necessary for digestion among other functions. Neurotoxic Effects: Neurotoxic effects refer to the damage or disruption of the structure and function of neurons, which are the nerve cells in our brain and nervous system, due to exposure to natural or artificial toxic substances. Polychlorinated Biphenyls (PCBs): PCBs are man-made organic chemicals consisting of carbon, hydrogen and chlorine atoms. They were used in numerous industrial applications but were banned due to their environmental persistence and potential health risks. Proteins: Large biomolecules consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms. Receptor Protein: A receptor protein is a molecule found on the surface of cells that binds to specific substances, triggering a specific response in the cell. Receptor Protein Mutation: A change or alteration in receptor proteins which can affect their function. This can lead to various diseases if these proteins fail to perform their normal functions. Receptor Proteins: Receptor proteins are special structures within cells or situated on their exterior surfaces that bind specific substances, triggering changes in the behavior of the cells. Signal Transduction Pathway: A signal transduction pathway is a series of molecular events through which cells respond to external signals. These pathways convert these signals into cellular responses. Type 1 Diabetes: An autoimmune disease where pancreas produces little or no insulin due to destructions of insulin-producing cells by immune system. This leads to high levels of sugar (glucose) in bloodstream. Type 2 Diabetes: A chronic condition that affects the way your body metabolizes sugar (glucose), resulting in too much sugar circulating in your blood. It's often associated with obesity and lack of exercise. 4.6 Cell Cycle 3 min read Last Updated on June 18, 2024 Skills you’ll gain in this topic: Describe the stages of the cell cycle, including interphase, mitosis, and cytokinesis. Explain how cells ensure accurate DNA replication and division. Relate the cell cycle to growth, development, and tissue repair. Illustrate the importance of checkpoints in regulating cell division. Predict the effects of cell cycle disruptions on organismal health. Phases and Functions of the Cell Cycle The cell cycle is the sequence of steps prior to cell division. Cell division is crucial to survival because it replaces bad cells, and plays a role in growth and tissue repair. Mitosis (the process of cell division) is an asexual reproduction, which means the parent cell will produce two identical daughter cells that are also identical to the parent cell. This does not bring diversity within the cells, but it is an efficient way to create cells that will replace old cells. In eukaryotic cells, the cell cycle is highly regulated through the growth and reproduction of cells. If this process is not regulated, the cell will continue to divide non-stop, which is what a cancer cell is. Therefore, there are checkpoints and signals to regulate the cell cycle throughout each phase. Depending on the cell type, the cell division can happen frequently or nearly never. The cell cycle consists of 5 phases: interphase (G1, S, and G2), mitosis, and cytokinesis.  Image courtesy of Bio LibreTexts/10%3A_Cell_Reproduction/10.2%3A_The_Cell_Cycle/10.2A%3A_Interphas e). Interphase Interphase contains the phases G1, S, and G2. Over 90% of the cell cycle is spent in interphase! During interphase, the chromatin of the cell is threadlike so when looking at a cell undergoing interphase, a centrosome can be spotted with 2 centrioles. During the S phase, the centrosome is duplicated. Now, let’s break down the phases. 1️⃣ G1 is a period of intense growth and activity.  2️⃣ S is used to stand for the synthesis of DNA. The DNA is replicated so the cell now has two sets of the same DNA. 3️⃣ G2, the cell continues to grow in order to finish cell division. Image courtesy of Doc Kaiser's Microbiology. Keep in mind, a cell can go into the G0 phase, which is a phase where a cell never divides. These G0 phase cells can reenter the cell cycle when they receive appropriate signals, and dividing cells can exit the cell cycle at any given time. Because the cell cycle is highly regulated, cells are only told to divide when it receives a growth factor via the signal-response pathway. Mitosis can also be contagious, because a currently-mitosis-cell can activate mitosis in another cell nearby. Mammalian cells are able to sense cells around it and tell others to divide and stop dividing when there are enough cells. Mitosis Mitosis is the part of the cell cycle when the nucleus of the cell is divided. Even though mitosis is one process, it is broken down into prophase, metaphase, anaphase, and telophase.  Prophase is the first phase of mitosis. In prophase, the nuclear membrane begins to disintegrate, chromosomes condense, and the spindle begins to form. Because DNA is a bunch of tangled mess, the DNA is nicely wrapped into chromosomes so equal dividing will become a little easier. During metaphase, chromosomes begin to line up in the middle of the cell. Also, the centrosomes move to the ends of the cell. Anaphase is when the centromeres finally separate. The spindle pulls apart the now sister chromosomes (identical copies). Telophase begins when the chromosomes move to opposite ends of the cell. The chromosomes begin to uncoil and return to their threadlike shape. Mitosis is complete once the cell separates and 2 separate nucleoli form. Image courtesy of BioNinja. Cytokinesis The process of cytokinesis is different in plant and animal cells. After mitosis occurs, cytokinesis begins. Cytokinesis is when the cytoplasm is divided. The process of cytokinesis is different in plant and animal cells.  For plant cells, a cell plate made of stiff sugars is formed and surrounds the cell membrane. In plant cells, the daughter cells do not separate from each other. Instead, a new cell wall is created. For animal cells, a cleavage furrow is formed. A cleavage furrow is a groove that is created in the middle of the cell surface. The cytoplasm then begins to separate. auto loading next study guide stay on this page Key Terms to Review (25) Anaphase: Anaphase is a phase of mitosis and meiosis following metaphase, in which sister chromatids separate into two new nuclei. Cancer Cell: A cancer cell is a type of abnormal cell that divides uncontrollably and can invade nearby tissues or spread to other parts of the body through blood and lymph systems. Cell Cycle: The cell cycle is the series of events that take place in a cell leading to its division and duplication. It consists of stages such as interphase (growth), mitosis (nuclear division), and cytokinesis (cell division). Cell Division: Cell division is the process by which a parent cell divides into two or more daughter cells. It's essential for growth, repair, and reproduction in organisms. Cell Plate: A plate that develops at midline of dividing plant cell during cytokinesis, eventually becoming the cell wall for each of the two daughter cells. Centrioles: Centrioles are cylindrical structures found in most eukaryotic cells, involved in cellular division and the formation of spindle fibers that separate chromosomes during mitosis. Centrosome: A centrosome is an organelle found in most eukaryotic cells near their nuclei. It's responsible for pulling apart sister chromatids during cell division. Checkpoints: In cell biology, checkpoints are control mechanisms in the cell cycle that ensure each phase is completed accurately before proceeding to the next. Chromatin: Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. It condenses to form chromosomes during cell division and decondenses for gene expression. Cleavage Furrow: The cleavage furrow is a shallow groove in the cell membrane where cytoplasmic division will occur. It's the first sign of cytokinesis during cell division in an animal cell. Cytokinesis: Cytokinesis is the process during cell division where the cytoplasm divides into two daughter cells after mitosis or meiosis. DNA Synthesis: DNA synthesis refers to the process by which copies of DNA molecules are made within cells, enabling genetic information to be passed from generation to generation. Eukaryotic Cells: These are complex cells with a nucleus and other organelles, all enclosed within membranes. They make up organisms in the Protista, Fungi, Plantae, and Animalia kingdoms. G0 Phase: The G0 phase is a period in the cell cycle where cells exist in a quiescent (inactive) state. Cells in this stage are not preparing for or undergoing division. G1 Phase: The G1 phase is part of interphase within the cell cycle during which cellular content excluding chromosomes gets duplicated. G2 Phase: The G2 phase is the third subphase of interphase in the cell cycle directly preceding mitosis. It follows successful completion of DNA synthesis and chromosomal replication during the S phase. Interphase: Interphase is the phase in the cell cycle where a cell prepares for division. It's divided into three stages - G1 (first gap), S (synthesis), and G2 (second gap). Metaphase: Metaphase is a stage in both mitosis and meiosis during which all chromosomes align at the center (equator) of the cell before being separated into two new cells. Mitosis: Mitosis is a part of the cell cycle where replicated chromosomes are separated into two new nuclei resulting in genetically identical cells with equal distribution of genetic material. Nucleoli: The nucleolus is a small dense spherical structure in the nucleus of a cell during interphase. It's involved in protein synthesis, and produces and assembles ribosome components. Prophase: Prophase is the first stage of mitosis during which chromosomes condense and become visible under light microscopy; spindle fibers form and the nuclear envelope breaks down. S Phase: The S phase, or synthesis phase, is a part of the cell cycle where DNA replication occurs. During this phase, each chromosome is duplicated to ensure that both new cells will have complete sets of chromosomes. 4.7 Regulation of Cell Cycle 4 min read Last Updated on June 18, 2024 Skills you’ll gain in this topic: Explain how checkpoints regulate cell cycle progression and prevent errors. Describe how proteins like cyclins and CDKs control cell division. Relate cell cycle regulation to conditions like cancer. Analyze the consequences of disrupted cell cycle regulation. Predict the impact of cell cycle dysregulation on cell and tissue health. Cell Cycle Checkpoints Mistakes in duplication can lead to mutations that can lead to cells being abnormal and develop into cancer. Because of this, cell cycle checkpoints are done. At checkpoints, the progression of the cell cycle is halted until all parts are checked and conditions are correct to continue with duplication. Checkpoints are at the end of G1, at the G2 and M transition, and during metaphase.  Image courtesy of BioNinja. At G1, there is a cell growth checkpoint. This check occurs at the end of the G1 growth phase. During this checkpoint, it checks whether the cell is big enough and has the proper proteins and nutrients for the synthesis phase. If the cell is not big enough or not ready to go onto the next phase, they enter the G0 phase as you can see on the diagram. In G0, the cell is in a resting phase until it is ready to move on. At the G2 checkpoint, there is a DNA synthesis checkpoint during the S phase. Here, there is a check to make sure that the DNA has been replicated correctly. If the DNA is replicated correctly, it moves on to the M (Mitosis) phase. The final checkpoint is the metaphase checkpoint. This occurs in the (M) Mitosis phase and checks whether metaphase is complete. If it is complete, the cell divides and the process repeats. Cdk-Cyclin Complex The entire cell division process is regulated through the Cdk-Cyclin complex. Image Courtesy of BioNinja Cdk is always within the cytoplasm; it doesn't disappear. The number of cyclin goes up during interphase, and after the amount of cyclin reaches a certain threshold, mitosis is triggered. This leads to the degradation of cyclin, and Cdk is dephosphorylated. The number of cyclin is a great mechanism the cell uses to regulated mitosis activity. Genes and Proteins There are genes and proteins that can also regulate mitosis. The best example of a protein is p53. p53 was actually named the molecule of the year (1992) for its contribution to cancer research. p53 is essentially the toolbox of the cell. Any segment of DNA can be damaged by heat, radiation or chemicals. p53 will notice this damage and stop cell division. It then triggers enzymes that will repair the damaged region. If the DNA is properly repaired, p53 will allow for the DNA replication and cell division to continue. However, if p53 determines that the damage is beyond repair, it will trigger apoptosis, or cell programmed death. When your skin peels off, it's because of apoptosis, so you're actually witnessing p53 at work! Because p53 is so important, it can cause problems when it is malfunctioning. DNA damage will not be detected by a malfunctioning p53, and it will fail to stop cell division or repair DNA. Instead, the cell will continue to divide with damaged DNA. If this damage accumulates, the cell can turn cancerous. There are about 6 key genes that also regulate the division process. If there are mutations in these 6 genes, cancer is likely to develop. Keep in mind, these genes don't cause cancer. When turned on and off correctly, cancer does not develop. It's when these genes stay on or off that causes the issue. Growth Promoter Genes ON = unlimited growth Tumor Suppressor Gene (p53) OFF = ignore checkpoint stop signs Apoptosis Genes OFF = cell doesn't go through apoptosis Chromosome Maintenance Genes (telomerase) ON = unlimited divisions Touch-Sensor Gene OFF = overcome density dependence Cancerous Cells However, disruptions in the cell cycle can lead to cancerous cells. Cancerous cells are cells that are unregulated and divide uncontrollably. Cancerous cells have the ability to migrate or metastasize to other regions of the body that they didn’t originate in. Apoptosis Apoptosis is programmed cell death. Apoptosis is a normal and controlled process within multicellular organisms. It is very important because it maintains the balance of cells within an organism. Apoptosis happens when the lysosome bursts, causing the cell to burst and die from the acid. For example, apoptosis can occur during the development of new cells. If these cells are not divided correctly, they could lead to cancer or a virus. Without apoptosis, these harmful cells could continue dividing and multiplying which could cause an adverse effect on the organism. Apoptosis is very important because if damaged or mutated cells do not get the signal to go through apoptosis, cancer can form. Image courtesy of Giphy. auto loading next study guide stay on this page Key Terms to Review (14) Apoptosis: Apoptosis is a process of programmed cell death that occurs in multicellular organisms. It's a way for the body to get rid of old, unnecessary, or damaged cells. Apoptosis Genes: Apoptosis genes are responsible for initiating and executing apoptosis, which is programmed cell death. Cancerous Cells: Cancerous cells are abnormal cells that divide uncontrollably and have the ability to infiltrate and destroy normal body tissue. Cdk-Cyclin Complex: The Cdk-Cyclin complex is a key regulator of cell cycle progression, formed by cyclin-dependent kinases (Cdks) binding with cyclins. Cell Cycle Checkpoints: These are control mechanisms in the cell cycle that ensure each stage is completed accurately before proceeding to the next. They prevent errors such as DNA damage and incomplete replication. Chromosome Maintenance Genes: Chromosome maintenance genes are involved with repairing damaged DNA and ensuring proper segregation during cell division. G1 Checkpoint: This checkpoint occurs in the G1 phase of the cell cycle and checks for conditions favorable for DNA replication, including sufficient energy resources, nutrients, and absence of DNA damage. G2 Checkpoint: This checkpoint ensures that all chromosomes have been replicated without any damage before mitosis begins. It also checks that all necessary proteins are available for mitosis. Genes and Proteins: Genes are segments of DNA that code for specific proteins. Proteins carry out most cellular functions and make up majority of a cell's structure. Growth Promoter Genes: Growth promoter genes are genes that regulate cell growth and division. They play an essential role in organismal development and tissue repair. Metaphase Checkpoint: The metaphase checkpoint is a control mechanism in cell division that ensures all chromosomes are properly attached to the spindle fibers before proceeding to anaphase. P53 Protein: The p53 protein is a crucial regulator that prevents cancer formation. It promotes cell cycle arrest and apoptosis in response to DNA damage. Touch-Sensor Gene: A touch-sensor gene is a type of gene that allows organisms to respond to physical contact or pressure. It plays a crucial role in the development and function of sensory cells. Tumor Suppressor Gene: Tumor suppressor genes are protective genes that regulate cell growth. When these genes mutate, they may fail to control cell growth effectively, leading to cancerous tumors.