Biology: Cytology PDF

## **Biology: Cytology** **Prepared by: Dr. Mohammed Elshebly** ### **Cell Science: Cytology** - The science that studies the cell. - The cell is the unit of composition and function in living organisms. - The cell is linked to the discovery of the microscope, which was invented by Anthony Levin...

## **Biology: Cytology** **Prepared by: Dr. Mohammed Elshebly** ### **Cell Science: Cytology** - The science that studies the cell. - The cell is the unit of composition and function in living organisms. - The cell is linked to the discovery of the microscope, which was invented by Anthony Levinhock in **1591**. - Levinhock became more involved in science, and, with his new improved microscope, was able to see things that no man had ever seen before. - He saw bacteria, yeast, blood cells, and many tiny animals swimming about a drop of water. ### **Cell Structure** - A cell is the smallest unit of the living thing. - A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an **organism**. - Cells vary in size. - Cells cannot be seen with the naked eye, so scientists use microscopes to study them - **Microscope**: an instrument that magnifies an object. - Pictures of the cell taken with a microscope are called **micrographs**. ### **Cell Theory** - Botanist Mathias Schleiden and zoologist Theodor Schwann studied tissues and proposed this unified cell theory: - All living things are composed of one or more cells - The cell is the basic unit of life. - New cells arise from existing cells ### **Basic Structure of the Cell** - All cells share four common components: - **Cytoplasm**: where the cellular components are found. - **DNA**: the genetic material of the cell. - **Plasma (Cell) membrane**: an outer covering that separates the cell's interior from its surrounding environment. - **Ribosome**: which synthesize proteins. ### **Main Types of Cells** - **Prokaryotic:** - A simple type of cell found in bacteria and archea (unicellular organisms). - Lacks a nucleus and membranous organelles - The DNA is found in the central part of the cell, called the **nucleoid**. - Most prokaryotes have a cell wall made up of peptidoglycan. - Contains a capsule made up of polysaccharide. - **Eukaryotic:** - More complex cell type. - Cells of animals, plants, fungi, and protists are all eukaryotic. - Have true nucleus, membranous organelles such as mitochondria, endoplasmic reticulum, golgi, and chloroplasts. - Have several rod-shaped chromosomes. ### **Diagram of a Prokaryotic Cell** **Contains the following:** - **Capsule** - **Cell wall** - **Plasma membrane** - **Cytoplasm** - **Ribosomes** - **Plasmid** - **Pili** - **Bacterial flagellum** - **Nucleoid** (circular DNA) ### **Functions of the Cell Wall:** - Prevents dehydration. - Provides extra protection. - Helps the cell maintain its shape. - Enables the cell to attach to surfaces in its environment. ### **Functions of the Capsule:** - Some prokaryotes have flagella for locomotion, and pili are used to exchange genetic material during a type of reproduction called **conjugation **. ### **Diagram of a Eukaryotic Cell** **Contains the following:** - **Intermediate filament** - **Ribosomes** - **Rough endoplasmic reticulum** - **Nucleus** - **Nucleolus** - **Chromatin** - **Mitochondria** - **Plasma membrane** - **Microtubule** - **Centrosome** - **Microfilament** - **Golgi apparatus** - **Golgi vesicle** - **Lysosome** - **Smooth endoplasmic reticulum** - **Secretory vesicle** - **Peroxisome** - **Vacuole** - **Cytoplasm** ### **Comparison of Prokaryotic and Eukaryotic Cells** | Feature | Prokaryotic | Eukaryotic | |---|---|---| | Size | Small (0.3 - 5 mm) | Large (10 - 100 mm) | | Cell wall | Contains peptidoglycans | Made up of cellulose if present | | Flagella | Made of single microtubules. | Made of 9+2 arrangement of microtubules if present. | | Ribosomes | Small (70S), scattered | Large (80S) attached to endoplasmic reticulum | | Nucleus | No true nucleus | True nucleus | ### **Cell Components** - **Nucleus:** - The genetic material DNA exists in the form of filaments. - Usually spherical in shape and large in size. - Surrounded by a nuclear envelope composed of two layers of membranes separated by a distance of 20-40 nm. - The two layers merge in many places to form nuclear pores. - **Functions of the nucleus:** - Contains genetic material inherited from one cell to another via cell division. - Regulates the activity of the cell. ### **Diagram of the Nucleus** **Contains the following:** - **Endoplasmic reticulum** - **Nucleolus** - **Chromatin** - **Nucleoplasm** - **Nuclear pore** - **Nuclear envelope** - **Ribosomes** - **Cytoplasm** - Located between the cell membrane and the nucleus. - Consists of about 80% water, 15% proteins, 5% fats, sugars, and mineral salts. - Cytoplasm is the medium in which chemical reactions occur. - **Cytosol**: the part of the cytoplasm that doesn't contain organelles. - **Functions of the cytoplasm:** - Most important activities of the cell occur in the cytoplasm. - Responsible for giving the cell its shape. It helps fill out the cell and keeps organelles in place. Without cytoplasm, the cell would be deflated. - **Endoplasmic reticulum (ER)** - Multifold membranous structure. - There are two types of ER: rough and smooth. - The two types are separate entities and not joined together. - Cells producing proteins have more rough ER (RER). - Cells producing fats and steroids have more smooth ER (SER). - The ER plays a role in the synthesis of complex molecules required by the cell. - The RER has many ribosomes, giving it a rough appearance. - **The main functions of RER and SER:** - **Rough ER:** synthesis of proteins and modification of some proteins produced by ribosomes. - **Smooth ER:** plays a major role in the synthesis of lipids, and reproductive organs produce steroid hormones testosterone and estrogen. - **Golgi apparatus (Body or complex):** - Composed of flat sacs known as **cisternae**, and associated small hollow spheres of membrane called **vesicles**. - Responsible for the manufacturing, warehousing, shipping, modification, packaging, and certain cellular products, particularly those from the endoplasmic reticulum (ER). - Cells that specialize in secreting a variety of substances typically have a high number of Golgi. ### **Diagram of the Golgi Apparatus** **Contains the following:** - **Nucleus** - **Nuclear envelope** - **Ribosomes** - **Smooth endoplasmic reticulum** - **Rough endoplasmic reticulum** - **Mitochondria:** - Rod-shaped or spherical - Considered among the largest cell organelles in size. - Surrounded by a double membrane, where the inner membrane folds inwards, forming folds called **cristae**. - The cavity of the mitochondria is filled by a thick liquid called the **matrix**. - The matrix contains some enzymes that are involved in chemical processes like **cellular respiration** and the **Krebs cycle**. - The greater the need for the cell to power itself, the greater the number and size of mitochondria. - **Functions of mitochondria:** - The site where energy (ATP) is produced. - Contains mitochondrial DNA, which is capable of self-cleavage. ### **Diagram of the Mitochondria** **Contains the following:** - **ATP synthase particles** - **Intermembrane space** - **Matrix** - **Cristae** - **Ribosomes** - **Granules** - **DNA** - **Inner membrane** - **Outer membrane** - **Ribosome:** - Non-membranous organelle. - **Consist of 2 units:** one large and one small. - The two units don't unite only when synthesizing protein (peptide). - There are large numbers of ribosomes in the cells that create proteins, because they are the only place where amino acids are created. ## **Diagram of a Ribosome** **Contains the following:** - **Large subunit** - **Small subunit** - **Instructions to make a protein** (written on a mRNA molecule in the nucleus) ### **Ribosome Diameter** - 10 nm - **Lysosomes:** - Small vesicles are formed in the Golgi apparatus. - Contains enzymes that break down carbohydrates, proteins, and lipids. - Found in cells that are phagocytic (these are cells that carry out the process of phagocytosis). - Lysosomes are formed by the inclusion of digestive enzymes such as **proteases** and **lipases**. - It is important to isolate enzymes from the rest of the cell inside a lysosome membrane, otherwise their release will result in self-digestion of the cell. ### **Example of Lysosome-Related Disease:** - **Rheumatoid arthritis**: where the cartilage of the joint is attacked by lysosomal enzymes. ### **Diagram of Lysosomes in a Phagocytic Cell** - **Phagocytic particle** - **Food particle** - **Food vacuole** - **Exocytic vesicle containing undigested material** - **Phagocytosis** - **Pseudopods** - **Lysosome containing digestive enzymes** ### **Peroxisomes:** - Vesicles contain enzymes that crash toxic organic compounds, such as **hydrogen peroxide**, and then decompose these toxic compounds into water and oxygen. ### **Diagram of a Peroxisome** **Contains the following:** - **Single membrane** - **Peroxisome** - **Urate oxidase crystalline core** ### **Cytoskeleton:** - The cytoskeleton has three different types of protein elements. - From narrowest to widest, they are: - **Microfilaments (Actin filaments)** - **Intermediate filaments** - **Microtubules** - **Microfilaments:** Often associated with myosin. They provide rigidity, shape, and facilitate cellular movements in the cell. - **Intermediate filaments:** Bear tension and anchor the nucleus and other organelles in place. - **Microtubules:** - Help the cell resist compression. - Serve as tracks for motor proteins that move vesicles through. - Pull chromosomes during cell division. - Act as structural elements of centrioles, flagella, and cilia. ### **Diagram of the Cytoskeleton** **Contains the following** - **Intermediate filaments** - **Microfilaments** - **Microtubules** ### **Centrioles:** - Small, hollow, cylindrical non-membranous organelles present in pairs. - Each one is made up of nine triple microtubules. - During cell division, the centrioles replicate themselves and migrate to opposite poles of the cell. - Play a role in the formation of the **spindle fibers**. ### **Diagram of a Centriole** **Contains the following:** - **Microtubule triplet** - **Mother centriole** - **Distal appendages** - **Subdistal appendages** - **Proximal ends** - **Interconnecting fibers** - **Daughter centriole** - **Distal ends** ### **The Endomembrane System and Proteins** - A group of membranes and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins. - Includes the nuclear envelope, lysosome, vesicles, endoplasmic reticulum, golgi, cell membrane. - **Note:** The endomembrane system does not include membranes of either mitochondria or chloroplasts.. ### **Diagram of the Endomembrane System** **Contains the following:** - **Nucleus** - **Rough ER** - **Golgi apparatus** - **Transitional ER** - **Cisternae** - **Cis face** - **Trans face** - **Transport vesicle** - **Plasma membrane** ### **Cilia and Flagella** - Organelles: thin cytoplasmic threads projecting from the surface of the cell, also containing microtubules, and have a similar structure. - **Flagella:** longer (100mm) and are fewer in number. - **Cilia:** shorter (5-10 mm) and are present in larger numbers. - Cilia are present in large numbers on the surface of some cells, such as epithelial lining the trachea. Their function is to beat backwards and forwards in one direction. - Flagella normally moves the whole cell or organism, as in sperm cells, which have a single flagellum. - Cilia and flagella both contain a characteristic arrangement of nine outer pairs and two central ones, referred to as a 9+2 arrangement. ### **Diagram of Cilia and Flagella** **Contains the following:** - **Plasma membrane** - **Axoname** - **Basal body** - **Outer doublet microtubules** - **Central microtubules** - **Dynein Arms** ### **Microvili** - Finger-like projections present in the outer surface of the cell. - Increase the surface area of the cell, allowing for increased absorption of materials, for example, in the small intestine. - The microvilli of the epithelium allow faster uptake of the products of digestion. - The microtubules contained within the microvilii help the cell maintain its shape. ### **Diagram of a Microvili** **Contains the following:** - **Microvilli** - **Cell membrane** - **Mitochondrion** - **Golgi apparatus** - **Nucleus** - **Rough endoplasmic reticulum** - **Nucleolus** - **Intestinal epithelial cell** ### **Plasma (cell) Membrane** - All cell membranes have similar structures. - Some organelles have a single membrane (golgi complex), but others have a double membrane (nucleus, mitochondria). - Membranes are composed of phospholipids with proteins. - The plasma membrane is **selectively permeable**, meaning it allows some materials to freely enter or leave the cell, while others cannot. ### **Phospholipids in Cell Membrane** - Phospholipids molecules are made up of a phosphate head and a fatty acid tail. - The phosphate head is attracted to water (hydrophilic). - The fatty acid tail is repelled by water (hydrophobic). - Phospholipids molecules naturally consist of bilayers. ### **Diagram of the Plasma Membrane** **Contains the following:** - **Hydrophilic region of protein** - **Hydrophobic region of protein** - **Phospholipid bilayer** - **Glycoprotein:** protein with carbohydrate attached - **Glycolipid:** lipid with carbohydrate attached - **Peripheral membrane protein** - **Integral membrane proteins** - ** Cholesterol** - **Protein channel** - **Cytoskeletal filaments** - **Phospholipid bilayer** ### **Functions of Phospholipids in Cell Membrane** - The main purpose of the hydrophobic center of the membrane is to prevent the free diffusion of water and polar molecules through the membrane. - The membrane acts as a barrier to free movement. - If the membrane is disrupted by molecules passing through it, it quickly springs back into its original position, with the phosphate head on the outside and the fatty acid tails on the inside. ### **Proteins on Cell Membrane** - Proteins float in the cell membrane between phospholipids. ### **Functions of Proteins on Cell Membrane** - Provide support and stability in the fluid structure. - Transport of molecules across the membrane. ### **Types of Proteins in Cell Membrane** - Transport proteins - Channel proteins - Receptors - Carrier proteins - Enzymatic - Recognition proteins ### **Glycoproteins and Glycolipids** - **Glycoproteins:** a protein with a polysaccharide attached. - **Glycolipids:** a lipid with a polysaccharide attached. - The polysaccharide is always on the outside of the cell's surface membrane. ### **Functions of Glycoproteins and Glycolipids** - They form hydrogen bonds with water molecules outside the cell, helping to stabilize the cell membrane. - They participate in cell-to-cell recognition, enabling cells of similar type to group together to form tissue. - The carbohydrate tails of both glycoproteins and glycolipids can act as receptor sites, binding the molecules to the plasma membrane, and triggering a variety of events. ### **The Way in Which Materials Are Transferred Across The Cell** - There are two basic types of transport: - **Passive transport:** No energy. - **Active transport:** Employs ATP (adenosine triphosphate). ### **Transport Mechanisms** - **Active transport:** - **Sodium-potassium pump:** - The function of the sodium-potassium pump (Na,K-ATPase) is to actively transport sodium and potassium across the cell membrane, against concentration gradients. - For each ATP molecule the pump breaks down, two potassium ions are transported into the cell, and three sodium ions are transported out of the cell. - **Passive transport:** - **Simple diffusion:** Movement of substances from a high concentration to a low concentration. - **Facilitated diffusion:** Movement of substances from a high concentration to a low concentration assisted by protein carriers. - **Osmosis:** Net movement of water from a high water concentration to a low water concentration, through a partially permeable membrane. ### **Types of Solution ** - **Hypertonic Solution:** The solution surrounding the cell has a higher solute concentration. - **Hypotonic Solution:** The solution surrounding the cell has a lower solute concentration. - **Isotonic Solution:** The solution surrounding the cell has the same solute concentration. ### **Table of Solution Type, Direction of Osmosis** | Solution | Direction of Osmosis | |---|---| | Hypotonic | Into cell | | Hypertonic | Out of cell | | Isotonic | No net movement | ### **Bulk Transport (Vesicle Mediated Transport)** - **Phagocytosis:** The process by which a cell engulfs solid particles. - The cell membrane invaginates around the solid particle, eventually pinching off and leaving the particle entirely enclosed by the plasma membrane. - **Pinocytosis:** The process by which a cell absorbs fluids outside the cell and brings them inside. - **Exocytosis:** A process by which materials are transported out of the cell. - **The plasma membrane invaginates and pinches off, producing a small envelope of fluid from outside the cell** ### **Extracellular Matrix of Animal Cells** - **The primary components of the ECM are proteins, and the most abundant protein is collagen**. - **Collagen fibers are interwoven with carbohydrate-containing proteins called proteoglycans.** - **All of this material is called extracellular matrix.** - **The extracellular matrix holds cells together to form tissue and allows the cells to communicate with each other** ### **Diagram of the Extracellular Matrix** **Contains the following:** - **Collagen fiber** - **Proteoglycan complex** - **Carbohydrates** - **Protein** - **Polysaccharide** - **Fibronectin** - **Plasma membrane** - **Integrin** - **Microfilaments of the cytoskeleton** ### **Intercellular Junctions** - Cells can communicate with each other via direct contact, referred to as **intercellular junctions**. - **Plasmodesmata:** Junctions between plant cells. - **Tight junctions, gap junctions, and desmosomes:** Junctions between animal cells. ### **Diagram of a Tight Junction** **Contains the following:** - **Cell A** - **Cell B** - **Tight junctions** - **Groups of tight junction proteins** - **Extracellular space** - **Plasma membrane** ### **Gap Junctions** - Present in animal cells. - Channels between adjacent cells that allow transport of ions, nutrients, and other substances. ### **Diagram of a Gap Junction** **Contains the following:** - **Connexon** - **Closed** - **Open** - **Plasma membrane of cell 1** - **Plasma membrane of cell 2** - **Gap junction channel** - **Extracellular space** ### **Role of Gap Junctions in Cardiac Muscle** - Gap junctions are particularly important in **cardiac muscle**. - The electrical signals for the muscle to contract are passed through gap junctions. ### **Closing Remarks** - Good luck to all my future doctors! - Dr. Mohammed Elshebly