Cell Biology PDF

Cell death is a natural physiological process in which cells die through either programmed cell death or cell injury. Cell death is essential for maintaining tissue homeostasis. Programmed cell death, known as apoptosis, plays a crucial role in development and immune system...

Cell death is a natural physiological process in which cells die through either programmed cell death or cell injury. Cell death is essential for maintaining tissue homeostasis. Programmed cell death, known as apoptosis, plays a crucial role in development and immune system regulation. Cell injury, caused by external factors such as toxins or physical trauma, can lead to necrosis, an unregulated form of cell death. The removal of dead cells is important for preventing inflammation and tissue damage. Mitosis Mitosis is a process of cell division resulting in two genetically identical daughter cells each having the same number and kind of chromosomes as the parent nucleus. Mitosis occurs in somatic (body) cells. Consists of four phases: prophase, metaphase, anaphase, and telophase. Enables growth, repair, and asexual reproduction in organisms. Abnormalities in mitosis can lead to cancer. Types of reproduction Reproduction can be either sexual, involving two parents and genetic variation, or asexual, where a single parent produces genetically identical offspring. Sexual reproduction involves meiosis and the fusion of gametes from two parents. Asexual reproduction includes methods such as binary fission, budding, and fragmentation. Sexual reproduction leads to genetic diversity, aiding in adaptation to changing environmental conditions. Asexual reproduction is more efficient in terms of energy and resources as only one parent is involved. Key Terms Anaphase Anaphase is the stage of cell division where chromatids separate and move towards opposite ends of the cell. Anaphase follows metaphase and precedes telophase in the cell cycle. The separation of chromatids in anaphase is facilitated by the shortening of microtubules. Proteins called cohesins hold the sister chromatids together until they are degraded during anaphase. The separation of chromatids in anaphase ensures that each daughter cell receives a complete set of chromosomes. Asexual reproduction Asexual reproduction is a form of reproduction where an organism can produce offspring without the involvement of another organism. Asexual reproduction only requires one parent organism. The offspring produced through asexual reproduction are genetically identical to the parent organism. Asexual reproduction is a common method of reproduction in organisms like bacteria, fungi, and plants. It allows for rapid population growth as there is no need to find a mate or go through the process of sexual reproduction. Chemotherapy Chemotherapy is a treatment method that uses drugs to destroy cancer cells in the body. Chemotherapy can be used alone or in combination with other treatments like surgery or radiation therapy. The drugs used in chemotherapy may be administered orally, by injection, or through IV infusion. Chemotherapy drugs work by targeting rapidly dividing cells, which includes cancer cells. Side effects of chemotherapy can include nausea, hair loss, fatigue, and weakened immune system. Chromatin Chromatin is the DNA-protein complex found within the nucleus of a cell, which is responsible for packaging and condensing the DNA.  Chromatin plays a crucial role in gene expression and regulation. During cell division, chromatin condenses further into visible chromosomes. Different types of chromatin exist, including euchromatin and heterochromatin. Histones are the proteins that help in organizing and stabilizing chromatin structure. Chromosome A chromosome is a thread-like structure made up of DNA and proteins found in the nucleus of a cell, carrying genetic information in the form of genes. A human cell typically contains 23 pairs of chromosomes, for a total of 46 chromosomes. In prokaryotes, such as bacteria, the chromosome is a circular DNA molecule. Chromosomes are visible under a microscope during cell division when they condense and become tightly coiled. Abnormalities in chromosome structure or number can lead to genetic disorders, such as Down syndrome. Cytokinesis Cytokinesis is the final stage of cell division where the cytoplasm of a parent cell is divided into two daughter cells. Cytokinesis occurs after mitosis or meiosis. It ensures equal distribution of organelles and cytoplasm in the daughter cells. In animal cells, a contractile ring constricts the cell membrane during cytokinesis. In plant cells, cell plate formation separates the daughter cells. Interphase Interphase is the phase in the cell cycle where a cell prepares for division by duplicating its DNA and growing in size. It's divided into three stages: G1, S, and G2. G1 and G2 are periods of cell growth, while S-phase is when DNA replication occurs. Interphase typically takes up about 90% of the complete cell cycle. Certain cells, like neurons, can exit the cell cycle and stay in G0 phase, a resting state. Metaphase During Metaphase, chromosomes align along the cell's equator, forming a metaphase plate, facilitating their orderly separation into two daughter cells. Spindle fibers from opposite poles attach to centromeres of sister chromatids. Checkpoint ensures proper alignment before proceeding to Anaphase. Chromosomes are maximally condensed during Metaphase. Errors in chromosome alignment can result in genetic abnormalities. Prophase Prophase is the initial phase in the process of cell division (Mitosis and Meiosis), marked by the condensation of chromosomes, increase in spindle fiber formation and nucleoli disappearance. Chromosomes become visible and duplicate, creating two sister chromatids connected by a centromere. Centrioles move towards opposite ends of the cell, beginning spindle formation. The nuclear envelope breaks down, enabling spindle fibers to interact with the chromosomes. Prophase stage sets the stage for the alignment of chromosomes during Metaphase. Radiation Radiation is the emission or transmission of energy in the form of particles or electromagnetic waves, which can be harmful or beneficial to living organisms. There are two types of radiation: ionizing radiation, which has enough energy to remove tightly bound electrons from atoms, and non-ionizing radiation, which does not have enough energy to do so. Common sources of ionizing radiation include X-rays, gamma rays, and radioactive materials such as uranium and radon gas. Exposure to high levels of ionizing radiation can damage cells and DNA, leading to health effects such as cancer and radiation sickness. However, non-ionizing radiation, such as visible light and radio waves, is generally considered to be safe and is used in various forms of technology and communication. Sexual reproduction Sexual reproduction is a process involving the combination of genetic material from two parent organisms to create offspring with varied genetic composition. Sexual reproduction typically involves two parents, each contributing half of the offspring's genetic material. It promotes genetic diversity, enhancing a species' adaptability to changing environments. Meiosis, a special form of cell division, facilitates sexual reproduction by producing haploid gametes. The process involves fertilization, where a sperm and an egg unite to form a zygote. Sister chromatids Sister chromatids refer to identical copies of a single chromosome which are connected at a region called the centromere. Produced during S phase of cell cycle. Separated during mitosis or meiosis II. Once separated, each can function as an individual chromosome. Each chromatid carries identical genetic information. Spindle fibers Spindle fibers are microscopic structures involved in cell division. Emanating from cell poles, they attach to chromosomes and segregate them during mitosis and meiosis. Formed of proteins called microtubules during cell division. Collectively referred to as the spindle apparatus in dividing cells. Help ensure each new cell gets the appropriate number of chromosomes. Disruption in spindle fiber function leads to incorrect chromosome separation, potentially causing genetic disorders. Telophase During Telophase, nuclear envelopes re-form around the separated daughter chromosomes at opposite poles, and the chromosomes begin to uncoil. Cytokinesis typically occurs concurrently. In animal cells, cytokinesis is achieved through the formation of a cleavage furrow constricting the cell into two.  In plant cells, a cell plate forms in the middle, dividing the cell into two distinct daughter cells. Telophase marks the final stage of mitosis where the chromosomes have reached the poles of the cell. Nucleoli reappear, and the spindle fibers disassemble during Telophase. Tumour A tumour is an abnormal mass of tissue formed by cells that grow and divide uncontrollably; it can be benign or malignant. Benign tumours are non-cancerous, do not spread to other parts of the body, and have well-defined borders. Malignant tumours are cancerous, invade nearby tissues, and have the potential to spread to other parts of the body. Tumours can arise from different types of cells, such as epithelial cells or connective tissue cells. Metastasis occurs when cancer cells break away from a malignant tumour and spread through the bloodstream or lymphatic system.