Chapter 2: The Cell PDF

CHAPTER 2: THE CELL  LEARNING OBJECTIVES At the end of the chapter, the students should be able to: A. Understand the basic structure and function of cells. B. Differentiate between prokaryotic and eukaryotic cells. C. Identify the major organelles and their functions. D. Describe the excha...

CHAPTER 2: THE CELL  LEARNING OBJECTIVES At the end of the chapter, the students should be able to: A. Understand the basic structure and function of cells. B. Differentiate between prokaryotic and eukaryotic cells. C. Identify the major organelles and their functions. D. Describe the exchange of substances within the cell.  CELL ❖It is defined as the smallest, basic unit of life that is responsible for all of life’s processes. ❖A cell is the basic structural and functional unit of life. ❖The study of cells from its basic structure to the functions of every cell organelle is called Cell Biology.  ❖ In 1665, Robert Hooke first discovered a cell by observing very thin slices of cork under a HISTORY OF THE microscope. CELL  ❖ Henamed the compartment s cell from the Latin word “cellula” which means small rooms. HISTORY OF THE CELL  ❖ Antonie van Leeuwenhoek observed cells under a compound microscope with higher magnification. ❖ As per observation, the cells exhibit some form of movement HISTORY OF THE (motility)- living entities, which he CELL later named as “animalcules”.  ❖ Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. ❖ He was able to describe the HISTORY OF THE nucleus present in the cells of CELL orchids.  In 1838, Matthias Schleiden, study a sample of plant tissue and discovered that plants are made up of cells. He showed that all the development of the vegetable tissue HISTORY OF THE is because of the activity of the cell. CELL  In 1839, Theodore Schwann concluded similarly that all animals are made up of cells. Together with Schleiden, they theorized that all HISTORY OF THE living things are made up of cells. CELL  In 1855, Rudolph Virchow observed cells dividing into new cells. He theorized that cells come from existing HISTORY OF THE living cells CELL (“Omnis cellula e cellula”).  The cell theory states that: ❖ The cell is the basic unit of structure and function in Tenets of living things. Cell theory ❖ All living things are made up of one or more cells. ❖ All living cells come from other living cells through cell division.  A modern version of the cell theory was eventually formulated, and it contains the Tenets of following postulates: Modern ❖ Energy flows within the cells. Cell theory ❖ Genetic information is passed on from one cell to the other. ❖ The chemical composition of all the cells is the same. TYPES OF CELL  Prokaryotic Cells Pro-before; karyon- nucleus. They lack distinct nuclei and have few organelles that are not membrane-bound. They all are single-celled microorganisms.  Prokaryotic Cells The cell size ranges from 0.1 to 0.5 µm in diameter. The hereditary material can either be DNA or RNA. Prokaryotes reproduce by binary fission, a form of asexual reproduction. Eukaryotic Cells Eu-true; karyon- nucleus. They have distinct nuclei and contain several membrane-bound organelles. They are multicellular organisms. Eukaryotic Cells The size of the cells ranges between 10–100 µm in diameter. They reproduce sexually as well as asexually. CELL ORGANELLES AND ITS FUNCTION  Nucleus - It is the control center of the cell; it directs and coordinates all cellular activities; contains nucleolus and chromosomes.  Nucleolus ❖ Is a dense spherical body inside the nucleus. ❖ It is where the synthesis of RNA and production of ribosomes happen.  Plasma Membrane - It is selectively permeable; it regulates the entry and exit of materials like ions and organic molecules.  Mitochondrion The mitochondrion is a rod-shaped organelle that serve as the “powerhouse of the cell.”  Endoplasmic Reticulum The endoplasmic reticulum is an organelle that looks like a network of tiny canals extending from the nucleus. There are two types of endoplasmic reticulum: the rough ER (Protein synthesis) and smooth endoplasmic reticulum (Lipid synthesis).  Golgi Apparatus ❖ The Golgi apparatus function in the packaging of proteins and lipids. ❖ They form tiny membrane bound spheres called vesicles for the packaging and transport of materials.  Vacuole ❖ It stores water, food or waste for the cells. ❖ Vacuole of animal cells are smaller compared to the vacuoles of plant cells.  Lysosome ❖ Itbreaks down complex materials for it contains strong digestive enzymes and is referred to as the “suicidal bag” of the cell.  Peroxisome ❖ Itprotect cells by isolating and breaking down harmful hydrogen peroxide into water and oxygen. Cell Wall ❖ The cell wall is a rigid lining outside the cell membrane. ❖ This makes the plant cells appear to be more rectangular and is mainly composed of cellulose.  Cytoplasm Cytoplasm is the gelatinous liquid (fluid) that fills the inside of a cell.  Chromosomes ❖ Are highly coiled structures that form a network over the nucleoplasm. ❖ They are gene carriers responsible in transmitting hereditary characteristics.  Chloroplastids ❖ Are double- membrane structure that contains chlorophyll pigments. ❖ It provides the green color of plants; functions for photosynthesis.  Centrioles Parts of the Cell ❖ Are two small rods that lie at a right angles to each other. ❖ They are microtubules that assist animal cells during cell division.  Comparison of the Structures of Prokaryotic, Animal, and Plant Cells Structures Prokaryotic Animal Cell Plant Cell Cell Nucleus Absent Present Present Cell membrane Present Present Present Cytoplasm Present Present Present Mitochondrion Absent Present Present Ribosomes Present Present Present Endoplasmic reticulum Absent Present Present  Comparison of the Structures of Prokaryotic, Animal, and Plant Cells Structures Prokaryotic Animal Cell Plant Cell Cell Golgi apparatus Absent Present Present Lysosomes Absent Present Present Vacuoles Absent Present Present Cell wall Present Absent Present Plastids/chloropla Absent Absent Present st Centrioles Absent Present Absent Flagella/Cilia Present Present Absent  Other Functions of the Cell Facilitate Growth in Allows Transport of Mitosis Substances Energy Production Aids in Reproduction Exchange of Substances Between a Cell and its Environment  DIFFUSION ❖Diffusion is the process in which a higher concentration of particles moves to the area with a lower concentration of particles. ❖For example, the reason you can smell perfume is because the particles diffuse into the air, making their way to your nose. ❖ Simple diffusion shows as a timeline with the outside of the cell (extracellular space) separated from the inside of the cell (intracellular space) by the cell membrane. ❖ In the beginning of the timeline there are many molecules outside of the cell and none inside. ❖ Over time, they diffuse into the cell until there is an equal amount outside and inside.  DIFFUSION Concentration gradient results from the unequal distribution of ions between intracellular fluid and extracellular fluid. Once the molecules become uniformly distributed, dynamic equilibrium exists. DIFFUSION  OSMOSIS Osmosis is a specific type of diffusion; it is the passage of water from a region of high water concentration through a semi- permeable membrane to a region of low water concentration.  OSMOSIS Cell membranes allow small molecules such as oxygen, water carbon dioxide and glucose to pass through, but do not allow larger molecules like sucrose, proteins and starch to enter the cell directly.  OSMOSIS If there was a semi-permeable membrane with more water molecules on one side as there were on the other, water molecules would flow from the This would continue until the side with a high concentration of concentration of water on both water to the side with the lower sides of the membrane were concentration of water. equal (dynamic equilibrium is established).  Osmotic Pressure Adding sugars to water will result in a decrease in the water concentration because the sugar molecules displace the water molecules.  Osmotic Pressure If the two containers are connected, but separated by a semi- permeable membrane, water molecules would flow from the area of high water concentration (the solution that does not contain any sugar) to the area of lower water concentration (the solution that contains sugar).  Osmotic Pressure This movement of water would continue until the water concentration on both sides of the membrane is equal and will result in a change in volume of the two sides. The side that contains sugar will end up with a larger volume.  The classic example used to demonstrate osmosis and osmotic pressure is to immerse red blood cells into sugar solutions of various concentrations. 1. The concentration of solute in the solution can be equal to the concentration of solute in cells. ❖In this situation the cell is in an isotonic solution (iso = equal or the same as normal). ❖A red blood cell will retain its normal shape in this environment as the amount of water entering the cell is the same as the amount leaving the cell.  The classic example used to demonstrate osmosis and osmotic pressure is to immerse red blood cells into sugar solutions of various concentrations. 2. The concentration of solute in the solution can be greater than the concentration of solute in the cells. ❖This cell is described as being in a hypertonic solution (hyper = greater than normal). ❖In this situation, a red blood will appear to shrink as the water flows out of the cell and into the surrounding environment.  The classic example used to demonstrate osmosis and osmotic pressure is to immerse red blood cells into sugar solutions of various concentrations. 3. The concentration of solute in the solution can be less than the concentration of solute in the cells. ❖This cell is in a hypotonic solution (hypo = less than normal). ❖A red blood cell in this environment will become visibly swollen and potentially rupture as water rushes into the cell.  ACTIVE TRANSPORT In Active transport the molecules are moved across the cell membrane, pumping the molecules against the concentration gradient using energy (ATP). Molecules will move across the membrane from a lower to a higher concentration.  PASSIVE TRANSPORT In Passive transport, the molecules are moved within and across the cell membrane and thus transporting it through the concentration gradient, without using energy (ATP). Molecules move from an area of high concentration to an area of low concentration without the need of energy.  FACILITATED DIFFUSION Facilitated diffusion is the diffusion of solutes through transport proteins in the plasma membrane. Facilitated diffusion is a type of passive transport. Even though facilitated diffusion involves transport proteins, it is still passive transport because the solute is moving down the concentration gradient.  Types of Transport Proteins A channel protein, a type of transport protein, acts like a pore in the membrane that lets water molecules or small ions through quickly. ❖Water channel proteins (aquaporins) allow water to diffuse across the membrane at a very fast rate. ❖Ion channel proteins allow ions to diffuse across the membrane.  Types of Transport Proteins A gated channel protein is a transport protein that opens a "gate," allowing a molecule to pass through the membrane. A carrier protein is a transport protein that is specific for an ion, molecule, or group of substances. ❖Carrier proteins "carry" the ion or molecule across the membrane by changing shape after the binding of the ion or molecule.  TYPES OF FACILITATED DIFFUSION Uniport: Movement of one molecule independent of the other molecules. Symport: Movement of two molecules in the same direction through a protein channel. Antiport: Movement of two molecules in the opposite direction through a protein channel. TYPES OF FACILITATED DIFFUSION  TYPES OF BULK/VESICLE TRANSPORT Some molecules or particles are just too large to pass through the plasma membrane or to move through a transport protein, so cells use two other active transport processes to move these macromolecules (large molecules) into or out of the cell. TYPES OF BULK/VESICLE TRANSPORT  ENDOCYTOSIS AND EXOCYTOSIS Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane. The membrane folds over the substance and it becomes completely enclosed by the membrane.  ENDOCYTOSIS AND EXOCYTOSIS At this point a membrane-bound sac, or vesicle, pinches off and moves the substance into the cytosol. There are three main kinds of endocytosis: ❖Phagocytosis ❖Pinocytosis ❖Receptor-Mediated Endocytosis  ENDOCYTOSIS AND EXOCYTOSIS Phagocytosis (cellular eating) ❖Occurs when the dissolved materials enter the cell. ❖The plasma membrane engulfs the solid material, forming a phagocytic vesicle. Pinocytosis (cellular drinking) ❖Occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell. ❖When the channel is closed, the liquid is encircled within a pinocytic vesicle.  ENDOCYTOSIS AND EXOCYTOSIS Receptor-Mediated Endocytosis (clathrin-mediated endocytosis) ❖Is a process by which receptors are applied for transferring antigenic proteins from extracellular matrix into the cells. ❖Is an active targeting method, in which macromolecules (ligands) bind to a specific type of receptor found on target cells. What does a cell "eat"? This image depicts a cancer cell being attacked by a cell of the immune system.  ENDOCYTOSIS AND EXOCYTOSIS Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell. Exocytosis occurs when a cell produces substances for export, such as a protein, or when the cell is getting rid of a waste product or a toxin. EXOCYTOSIS