Lec. 6 Structure of a typical Animal Cell PDF

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 6 Title: Structure of a typical animal cell Ribosomes Ribosomes are cellular structures responsible for protein synthesis in...

College of Medicine, University of Mosul/ Department of Anatomy Subject: Medical Biology Stage: 1 st Lec. 6 Title: Structure of a typical animal cell Ribosomes Ribosomes are cellular structures responsible for protein synthesis in all living cells, from simple bacteria to complex eukaryotes. They are often referred to as the "protein factories" or "protein synthesis machines" of the cell. Ribosomes play a fundamental role in the translation of genetic information from messenger RNA (mRNA) into functional proteins. Here are key points about ribosomes: Structure:  Ribosomes are composed of two subunits: a small subunit and a large subunit. In eukaryotic cells, such as those found in humans, these subunits are designated as 40S (small) and 60S (large).  These subunits are made up of ribosomal RNA (rRNA) molecules and numerous ribosomal proteins. The rRNA serves as a scaffold for ribosomal proteins and is essential for ribosome function.  Ribosomes have a two-lobed structure that can come together to form a functional ribosome during protein synthesis and then dissociate when the process is complete. Features:  Protein Synthesis: Ribosomes are responsible for the translation of genetic information from mRNA into proteins. This process involves reading the genetic code in the mRNA and linking together amino acids in a specific sequence to form a polypeptide chain. The sequence of amino acids determines the protein's structure and function. 1   tRNA and Amino Acids: Transfer RNA (tRNA) molecules transport individual amino acids to the ribosome, where they are added to the growing polypeptide chain in accordance with the mRNA's instructions.  Ribosomal RNA: Ribosomes contain rRNA, which plays a crucial role in the ribosome's catalytic activity during protein synthesis. rRNA molecules within the ribosome help catalyze the formation of peptide bonds between amino acids. ribosome-structure-interaction-mrna-54691349 Vacuole Vacuoles are membrane-bound organelle found in the cells of plants, fungi, some protists, and certain animal cells. Structure:  Vacuoles are typically large, fluid-filled sacs enclosed by a lipid bilayer membrane known as the tonoplast.  The content of vacuoles, called cell sap, consists of water, ions, sugars, amino acids, enzymes, pigments, and other dissolved substances.  The tonoplast selectively regulates the passage of molecules in and out of the vacuole. Functions:  Storage: Vacuoles are often involved in the storage of various substances, including: 2   Vacuoles can store excess water, helping regulate turgor pressure in plant cells and maintaining cell rigidity.  In some plant cells, vacuoles store sugars and starches, which can be used for energy or structural purposes.  Vacuoles can contain pigments that give color to plant tissues, such as the red pigments in flower petals.  Some vacuoles in plants store toxic compounds as a defense mechanism against herbivores.  Waste Management: Vacuoles can serve as storage sites for cellular waste products, preventing them from accumulating in the cytoplasm and potentially harming the cell. cross-section-yeast-cell-structure-fungal-vector-diagram-educational-biological-science-use-130577197 Lysosome Lysosomes are membrane-bound organelles found in the cytoplasm of eukaryotic cells, including animal cells. They are often referred as the "garbage disposals" or "recycling centers" of the cell due to their essential role in breaking down and recycling cellular waste materials, as well as performing various other functions. Structure:  Lysosomes are small, spherical organelles enclosed by a lipid bilayer membrane.  The lysosomal membrane is highly stable and contains proteins known as lysosomal membrane proteins that help maintain the organelle's integrity.  Inside the lysosome, there is an acidic environment created by the presence of hydrolytic enzymes. 3 Function: 1. Digestion of Cellular Waste: Lysosomes contain a variety of hydrolytic enzymes, including proteases (enzymes that break down proteins), nucleases (enzymes that degrade nucleic acids), lipases (enzymes that digest lipids), and glycosidases (enzymes that break down carbohydrates). These enzymes work together to break down cellular waste materials, such as damaged organelles, proteins, lipids, and nucleic acids. 2. Autophagy: Lysosomes play a crucial role in autophagy, a cellular process in which the cell engulfs and digests its own damaged or obsolete organelles and proteins. This recycling process helps maintain cellular health and removes potentially harmful components. 3. Phagocytosis: In certain immune cells like macrophages and neutrophils, lysosomes are involved in the process of phagocytosis. They fuse with phagosomes (vacuoles containing engulfed pathogens or debris) to digest and break down the ingested material. 4. Exocytosis: Lysosomes can also be involved in exocytosis, where they fuse with the cell membrane to release their contents outside the cell. This process is important in some secretory cells for the release of digestive enzymes or other substances. 5. Lysosomal Storage Disorders: Mutations that affect the function of lysosomal enzymes or transporters can lead to lysosomal storage disorders, a group of rare genetic diseases. These disorders result in the accumulation of undigested substrates within lysosomes, causing various health problems. Acidic Environment:  The acidic pH within lysosomes (usually around pH 4.5 - 5.0) is essential for the optimal activity of lysosomal enzymes. It ensures that these enzymes function efficiently in breaking down cellular waste.  The low pH also helps prevent the leakage of hydrolytic enzymes into the cytoplasm, where they could damage cellular structures. 4  Types of lysosomes: Primary Lysosomes: Newly formed lysosomes containing hydrolytic enzymes. They have inactivated enzymes derived from Golgi complex. Secondary Lysosomes: They formed when primary lysosomes fuse with vesicles containing materials to be digested. Secondary lysosomes are two types: 1-Autophagosomes: It is an early stage in autophagy process, which is a self- digestion process carried out by the cell to get rid of damaged such as cell's cytoplasm components or a damaged organelle to be recycled. 2- Heterophagosomes: Primary lysosome fused with phagosome containing external particles or bacteria to be digested by lytic enzymes. Secondary Granules in Neutrophils: Contain lysosomal enzymes for pathogen destruction in white blood cells. Residual Bodies: Accumulate undigested waste in aging cells. Peroxisome Peroxisomes are typically small, spherical organelles enclosed by a single lipid bilayer membrane. They contain various enzymes, including peroxidases and catalases, which are crucial for their functions. The enzymes within peroxisomes are responsible for performing specific chemical reactions. Functions: 1. Fatty Acid Metabolism: Peroxisomes play a significant role in lipid metabolism, particularly in the breakdown of long-chain fatty acids. This process, called beta- oxidation, generates energy in the form of ATP and produces molecules that can be used for cellular processes. 5  2. Detoxification: Peroxisomes are involved in the detoxification of harmful substances, especially hydrogen peroxide (H2O2), which is a toxic byproduct of various metabolic reactions. Peroxisomes contain catalase, an enzyme that breaks down H2O2 into water and oxygen, preventing its buildup and potential damage to the cell. 3. Synthesis of Lipids: Some peroxisomes are involved in the synthesis of specific lipids, such as plasmalogens and ether phospholipids. These lipids are important components of cell membranes. 4. Biosynthesis of Bile Acids: In the liver, peroxisomes are involved in the biosynthesis of bile acids, which are essential for the digestion and absorption of dietary fats. 5. Peroxisomal Disorders: Mutations in genes encoding peroxisomal enzymes or peroxisome biogenesis can lead to peroxisomal disorders, a group of rare genetic diseases. These disorders result in liver and kidney problems, nervous problems, vision and hearing problems, and Hormonal disorders. animal-cell-fungal-yeast-cell-structure-animal-cell-fungal-yeast-cell-structure-cross-section-anatomy-cell-biology- 189467026 Figures are for illustration only. 6