Cell Biology PDF

The cell ´ All organisms are made of cells, The basic unit of the human body. ´ Most of the cells are microscopic. ´ Limited size. ´ Most cells are between 1 and 100 μm in diameter. ´ The cells are similar in structure but modified in various ways to carry out specialized functions. ´ Some n...

The cell ´ All organisms are made of cells, The basic unit of the human body. ´ Most of the cells are microscopic. ´ Limited size. ´ Most cells are between 1 and 100 μm in diameter. ´ The cells are similar in structure but modified in various ways to carry out specialized functions. ´ Some nerve cells are very long, and specialized to transmit the message. ´ Ova (egg cells) are among the largest cells. The cell Cell size and shape are related to the function Examples: ´ Fat cells: are modified to store lipids. ´ Nerve cells: have long axons to transmit message ´ Muscle cells: are elongated. In muscle contraction, the length of the muscle shortens ´ Epithelial cells: are polyhedral or rectangular to form sheets for protection and absorption. ´ WBCs: change shape to move ´ Sperm: have a tail (flagellum) to move. The cell Why do the cells have a small size? Because small cells allow easy transport of molecules inside the cell than larger cells. Also, smaller cells have larger surface area to permit adequate Surface area 24 mm 48 mm exchange of materials. Volume 8 mm 8 mm Ratio (surf./Vol.) 3 (24/8) 6 (48/8) N.B. As the cell volume increases, the surface can not increase accordingly. Cell structure The eukaryotic cell composed of; A mass of protoplasm composed of cytoplasm and nucleoplasm. The cytoplasm comprises cytosol (the fluid part of the cytoplasm) and cell organelles (except the nucleus). All cells are bound by a plasma membrane which is a selective barrier. All cells have a nucleus that contains the chromosomes, that carry genes in the form of DNA. All cells have cell organelles (mitochondria, Golgi bodies, ribosomes, etc.) Types of cells ´ There are 2 types of cells, Eukaryotic & Prokaryotic cells Items Prokaryotic cell Eukaryotic cell DNA Is in a nucleoid a region that is not Is in a nucleus, bounded by double membrane-enclosed. membrane Membrane Absence of these organelles Present in the cytosol, with bounded specialized form and function organelles Size Smaller (1–10 µm ) Larger (10–100 µm ) Types of cells https://www.sciencefacts.net/prokaryotes-vs-eukaryotes.html Types of cells ´ Eukaryotic cells also have 2 types: plant cell and animal cell; Plant cell Animal cell Chloroplasts: the organelle that makes photosynthesis (converts Not present energy of sunlight to chemical energy) Central vacuole: present in older plant cells; its functions are; Not Present storage, breakdown of waste products, hydrolysis of macromolecules; enlargement of vacuole is a major mechanism of plant growth Cell wall: forms the outer layer of the plant cell maintains the Not Present cell’s shape and protects the cell from mechanical damage; made of cellulose, other polysaccharides, and protein Types of cells Plant cell Animal cell Not present Centrosome (a pair of centrioles): the cell’s microtubules originate from it. Not Present Lysosome: a membrane-bound organelle containing hydrolytic enzymes that help in the digestion of macromolecules. Not Present Flagellum: present only in some animal cells for locomotion its core is formed of microtubules, present in sperm cells. Types of cells https://byjus.com/biology/difference-between-plant-cell-and-animal-cell/ Cell components; The Nucleus https://www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and-eukaryotic-cells/a/nucleus- and-ribosomes The Nucleus ´ In the eukaryotic cell, The nucleus (plural, nuclei) is: ´ The site of synthesis for ribosomes (cellular machine that assemble s proteins), ´ Houses the cell’s genetic material, it contains most of the cell’s genes. (where some genes are present in mitochondria while some are in the chloroplast of plant cells). ´ Enclosed by the nuclear envelope (lipid bilayer double membrane, outer and inner), which separates the nucleoplasm (nucleus) from the cytoplasm. ´ The thin space between the two layers of the nuclear envelope is the perinuclear space which is directly connected to the interior of another membranous organelle, the rough endoplasmic reticulum (RER). The Nucleus ´ The nuclear envelope is interrupted by the nuclear pore complex (complex glycoproteins) that regulates the passage of molecules between the nuclear and cytoplasmic compartments. ´ The DNA is organized into separate units called chromosomes (structures that carry the genetic information). ´ The complex of DNA and proteins making up chromosomes is called chromatin. ´ The chromatin in the nucleus are Heterochromatin (inactive form) and Euchromatin (active form) ´ Within the non-dividing nucleus, the nucleolus (plural, nucleoli) is present. In which (rRNA) is synthesized. Ribosomes (Protein Factories) ´ The molecular machines responsible for protein synthesis. ´ Made up of ribosomal (rRNA) and protein. ´ Each ribosome consists of two separate RNA-protein complexes, known as the small and large subunits. The large subunit sits on top of the small subunit, with an RNA template sandwiched between the two subunits. ´ They are 2 types, free ribosomes that float around (suspended) in the cytoplasm, or attached (bounded), to the endoplasmic reticulum or the outside of the nuclear envelope. Ribosomes (Protein Factories) https://www.easynotecards.com/notecard_set/59566 https://www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and- eukaryotic-cells/a/nucleus-and-ribosomes Endomembranous system While each of the membranous organelles is distinct in terms of its structure and function. Many of these are considered together as an endomembrane system since their functions are coordinated. The Endomembrane system in the cell includes: ´ Nuclear envelope ´ Endoplasmic reticulum (ER) ´ Golgi apparatus ´ Lysosomes ´ Vesicles and Vacuoles, ´ Plasma membrane  Endomembranous system What is the endomembrane system? Is a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins https://www.sciencefacts.net/endomembrane-system.html Endomembranous system Connections between members of the endomembranous system: ´ Directly Like the connection between RER, and the nuclear envelope. ´ Indirectly (By Vesicles) Vesicles may be: 1. Transport vesicle: arises from RER and fuses in Golgi-complex. 2. Secretory vesicle: arises from Golgi- complex and fuses with the plasma membrane. The Endoplasmic Reticulum (Biosynthetic Factory) ´ ER consists of a network of membranous tubules and flattened sacs called cisternae. ´ And because the ER membrane is continuous with the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER. ´ There are 2 types of the ER which are connected but differ in structure and function: q Smooth ER (SER) q Rough ER (RER)  The Endoplasmic Reticulum SER vs RER https://www.quora.com/What-is-the-definition-and-function-of-Smooth-Endoplasmic-Reticulum https://www.amboss.com/us/knowledge/the-cell  The Endoplasmic Reticulum (SER vs RER) SER RER Smooth as it has no attached ribosomes Rough as it has attached ribosomes Abundant in steroid hormone-secreting cells ( Abundant in protein-secreting cells (pancreatic, ex. Leydig & muscle cells) and plasma cells) Functions: Functions: Synthesis of lipids, steroid hormones, Synthesis of proteins by attached ribosomes, Metabolism of carbohydrates, Form transport vesicles that carry Detoxification of drugs and poisons, synthesized protein to other members of the Storage of calcium ions. (in muscle cells and endomembranous system. called sarcoplasmic reticulum Protein folding (by Chaperons). Modifying proteins by adding carbohydrates or lipids. Golgi Apparatus (bodies)(complex) Structure: Curved flattened membranous sacs called cisternae, It has 3 faces: A- Cis-cisternae (face): They receive newly synthesized protein from RER by microvesicles (small transport vesicles). B- The central cisternae are called the medial cisternae. C- Trans-cisternae (face): From it arise the large secretory vesicles, They are the site of protein glycosylation. Golgi Apparatus Golgi Apparatus (bodies)(complex) ´ Functions of Golgi Apparatus 1. Protein Modification: it modifies, and sorts proteins, This includes ´ Glycosylation, where sugar molecules are added to proteins to form glycoproteins, ´ Phosphorylation, ´ Sulfation. 2. Lipid Modification: It synthesizes lipids and also modifies them. 3. Vesicle Formation: forms vesicles that transport molecules to different parts of the cell or for secretion outside the cell. 4. Sorting and Trafficking: It sorts proteins and lipids into different vesicles destined for different cellular compartments or for secretion. 5. It packages proteins and carbohydrates into vesicles and directs them to the plasma membrane for exocytosis. Lysosomes (cell digestive system) ´ A membranous sac filled with hydrolytic enzymes (about 40) that animal cell uses to digest (hydrolyze) macromolecules, spent organelle (autophagy), and phagocytosed particles (phagocytosis). ´ It carries out intracellular digestion. ´ Lysosomal enzymes work best in the acidic environment found in lysosomes. ´ Lysosomes arise by budding from the trans face of the Golgi apparatus. Lysosomes (cell digestive system) ´ There are 2 types of lysosomes inside the eukaryotic cells: Primary Lysosomes Secondary Lysosomes Their content is homogenous. Their content is heterogenous. Small vesicle. Large vesicle. Still not participate in cellular Formed after fusion with the digestion. phagocytosed particles (Phagosomes) or the spent organelles. Still not share in digestion. The digestion products contain simple sugars, amino acids, and other monomers. Lysosomes (cell digestive system) ´ Macrophages are a type of human white blood cell that helps defend the body by engulfing and destroying bacteria in a process called (Phagocytosis) i.e. phagocytosis means engulfing large solid particles (bacteria) while the process of internalization of fluid by membrane–bounded vesicles (pinocytotic vesicle or endosome) is called (Pinocytosis). ´ When the lysosomes use their hydrolytic enzymes to recycle the cell’s own organic material, this process is called (Autophagy) where the spent organelle is wrapped in ER-derived membranes to form an autophagosome. Phagocytosis vs Autophagy https://preuniversity.grkraj.org/html/1_CELL_STRUCTURE.htm Phagocytosis vs Pinocytosis https://www.quora.com/Whats-the-difference-between-autophagic-and-phagocytic-processes Peroxisomes (Microbodies) Small spherical to ovoid membrane-bound vesicles Self–replicating organelles. Present in almost all animal cells. Contains more than 40 oxidative enzymes Functions of peroxisomes: They catabolize (Break down) the long fatty acid chains into acetyl Co-enzyme A, and Hydrogen ions that combine with oxygen ions to form hydrogen peroxide (H2O2). Hydrogen peroxide is able to detoxify various noxious substances (e.g.: ethanol), and kill microorganisms They are extensive in the Liver and Kidney. Proteasomes § Small organelles composed of protein complexes. § Responsible for cytosolic proteolysis of specific types of proteins. Functions § Degradation of proteins that act in metabolic regulation. § Elimination of denatured, damaged, or malformed proteins. § Cleavage of antigenic proteins into small polypeptide fragments.