5 ( cytoplasm .pdf)

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 5 Title: Structure of a typical animal cell The cytoplasm The cytoplasm is a jelly...

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 5 Title: Structure of a typical animal cell The cytoplasm The cytoplasm is a jelly-like substance that fills the interior of animal cells. It is a vital component of the cell and plays several crucial roles in cellular processes. Here is some information about the cytoplasm of animal cells: 1. Cytosol Composition: The cytoplasm consists of water, ions, organic molecules, and various cellular structures suspended within it. It is primarily composed of water, making up around 70-80% of its content. 2. Organelles: Various organelles are suspended. These include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, Cytoskeleton, lysosomes, peroxisomes, and more. 3. Cellular Metabolism: Many metabolic pathways and enzymatic reactions take place in the cytoplasm. These include glycolysis, which is the breakdown of glucose for energy production, and various biosynthesis processes, such as the synthesis of fatty acids and some amino acids. 4. Support and Transport: The cytoplasm provides structural support to the cell and helps maintain its shape. It also plays a role in intracellular transport, facilitating the movement of organelles and molecules within the cell. 5. Storage: Some materials, such as glycogen and lipids, are stored in the cytoplasm as energy reserves. Additionally, certain ions and molecules are stored temporarily in the cytoplasm before being transported to specific organelles or used in cellular processes. 6. Regulation: The cytoplasm is involved in cellular signaling and regulation. It contains proteins and enzymes that control various cell functions, including gene expression, cell growth, and cell division. 7. Protein production and preserve: While the ribosomes responsible for protein synthesis are found on the surface of the endoplasmic reticulum or freely floating in the cytosol, the process of translation, where mRNA is translated into proteins, occurs in the cytoplasm. 1  Cellular Organelles The Endoplasmic reticulum The endoplasmic reticulum (ER) is a complex organelle composed of a network of membranes that form interconnected tubules and flattened sacs called cisternae. The ER membranes are composed of lipids, primarily phospholipids, and are embedded with proteins that perform various functions. Types: There are two types of endoplasmic reticulum, each with distinct characteristics and functions: Rough Endoplasmic Reticulum (RER): Studded with ribosomes on its outer surface, giving it a rough appearance. Major functions of the RER include protein synthesis by ribosomes, post-translational modification, protein folding, sorting, and transporting the proteins outside the cell to their proper destinations. Smooth Endoplasmic Reticulum (SER): Lacks ribosomes on its surface, giving it a smooth appearance. Functions of the SER include lipid metabolism, detoxification, and calcium ion storage and release. In lipid metabolism, the SER is involved in the synthesis of lipids and phospholipids, which are crucial for cell membrane formation and lipid storage. In detoxification, the SER plays a role in the breakdown and removal of drugs and toxins from the cell. Muscle cells have specialized SER called sarcoplasmic reticulum, which stores and releases calcium ions needed for muscle contraction. General Functions of ER: The endoplasmic reticulum has several vital functions in eukaryotic cells: Protein Synthesis (RER): The ribosomes on the rough ER are responsible for protein synthesis. They translate mRNA into proteins that are either secreted from the cell, inserted into cell membranes, or sent to other organelles. The RER also assists in post-translational modifications of proteins. 2  Lipid Metabolism (SER): The smooth ER is involved in lipid metabolism, including the synthesis of lipids and phospholipids. These lipids are essential for the formation of cell membranes and are stored in the SER. Detoxification (SER): The SER plays a crucial role in the detoxification of drugs and toxins. It contains enzymes that break down these substances, making them less harmful and aiding in their removal from the cell. Calcium Storage and Release (SER in Muscle Cells). _https://www.dreamstime.com/stock-illustration-cell-nucleus-endoplasmic-reticulum-detailed-anatomy-description-image63549497# Golgi body: The Golgi apparatus, also known as the Golgi complex or Golgi body, is a cellular organelle found in eukaryotic cells. Structure: The Golgi apparatus consists of a series of flattened, membrane-bound sacs called cisternae. These cisternae are stacked on top of each other like pancakes. The function: 1. Processing and Modification: The primary function of the Golgi apparatus is to modify and process molecules, primarily proteins and lipids. This includes glycosylation (adding sugar molecules) and phosphorylation (adding phosphate groups). 2. Sorting and Packaging: The Golgi apparatus acts as a central sorting and packaging station within the cell. It receives proteins and lipids from the ER and 3  then directs them to their final destinations including lysosomes, the cell membrane, or secretory vesicles for export from the cell. 3. Formation of Lysosomes: The Golgi apparatus plays a critical role in the formation of lysosomes. The Golgi apparatus packages enzymes and other components necessary for lysosome function. 4. Secretory Vesicles: In cells that secrete substances, such as hormones or digestive enzymes, the Golgi apparatus packages these molecules into secretory vesicles for release from the cell through exocytosis. 5. Protein Trafficking: The Golgi apparatus is involved in the regulation and trafficking of cell membrane proteins. It helps transport and maintain the balance of membrane proteins between the cell's various compartments, including the plasma membrane. golgi-apparatus-golgi-body-complex-plays-important-role-modification-transport-proteins-cell-55680598 (1) Mitochondria Mitochondria are double-membraned organelles found in eukaryotic cells. They have a unique structure consisting of distinct components: 1. Outer Membrane: The outer membrane is a smooth, semi-permeable barrier that encloses the entire organelle. It contains a variety of transport proteins that allow for the passage of ions and small molecules. 2. Inner Membrane: The inner mitochondrial membrane is highly folded into structures called cristae, which increase its surface area. This membrane is impermeable to most ions and molecules. It contains numerous protein complexes 4  involved in energy production through electron transport chain by process called (oxidative phosphorylation). 3. Matrix: The innermost compartment of mitochondria is the matrix. It contains enzymes responsible for several metabolic pathways, including the citric acid cycle (Krebs cycle), fatty acid oxidation, and amino acid metabolism. The matrix also contains mitochondrial DNA (mtDNA), specific ribosomes called (mitoribosome), and other essential molecules. 4. Intermembrane Space: The region between the outer and inner mitochondrial membranes is called the intermembrane space. This space is a preserve location for proton gradients from electron transport chain called (proton motive force). Function of Mitochondria: Mitochondria are often referred to as the "powerhouses of the cell" due to their central role in energy production and numerous other functions: 1. ATP Production: Mitochondria generate the majority of a cell's adenosine triphosphate (ATP), which serves as the primary source of chemical energy for cellular activities. ATP is produced through oxidative phosphorylation, a process that occurs in the inner mitochondrial membrane. 2. Citric Acid Cycle (Krebs Cycle): Mitochondria host the citric acid cycle, a key metabolic pathway involved in the breakdown of carbohydrates, fats, and proteins to produce energy in the form of ATP. 3. Fatty Acid Oxidation: Mitochondria are responsible for the breakdown of fatty acids, a process known as beta-oxidation. This provides energy when glucose is scarce. 4. Amino Acid Metabolism: Mitochondria play a role in the metabolism of amino acids, particularly in the removal of amino groups (deamination) and their subsequent entry into energy-generating pathways. 5. Calcium Regulation: Mitochondria are involved in calcium ion homeostasis within the cell. They can sequester and release calcium ions, which are important for various cellular processes, including muscle contraction and apoptosis (cell death). 5  6. Apoptosis: Mitochondria are central to the initiation of apoptosis (programmed cell death). When certain signals trigger apoptosis, mitochondria release pro-apoptotic proteins, leading to cell death. 7. Heat Production: In some specialized cells, such as brown adipocytes, mitochondria generate heat through a process called thermogenesis, which helps regulate body temperature. mitochondria-vector-illustration-section-70961539 Mitochondrial DNA Mitochondria are independent organelles. They have their own DNA and ribosomes. They can replicate and multiply on their own and make their own proteins. They have circular DNA similar to bacteria and replicate by fission. Mutations in the mitochondrial DNA leads to a number of diseases such as:  Young-adult blindness.  Progressive muscular disorders.  Some cases of Alzheimer’s disease.  Type -two diabetes mellitus. 6