Chapter 3 Cell Structure & Function Part 1 2024-2025 PDF

Chapter 3 Cell Structure and Function (Part I) 1  Outlines of part I 3.1 Cell Theory 3.2 Structure and Composition of the Cell Membrane 3.3 Transport across the Cell Membrane ❑ Passive transport ❑ Active transport...

Chapter 3 Cell Structure and Function (Part I) 1  Outlines of part I 3.1 Cell Theory 3.2 Structure and Composition of the Cell Membrane 3.3 Transport across the Cell Membrane ❑ Passive transport ❑ Active transport 2 Human Biology (BIOL-105), Health track  Objectives of chapter 3 After studying this chapter, students will be able to:  State the cell theory  Compare and contrast prokaryotic and eukaryotic cells  Describe the relative sizes of different cells  Describe the structure and function of the cell membrane, including its regulation of materials into and out of the cell  Describe the functions of the various cytoplasmic organelles  Explain the structure and contents of the nucleus 3 Human Biology (BIOL-105), Health track  Objectives  Describe the structure and function of the cellular organelles associated with the endomembrane system, including the endoplasmic reticulum, Golgi apparatus, and lysosomes  Describe the structure and function of mitochondria and peroxisomes  Explain the three components of the cytoskeleton, including their composition and functions 4 Human Biology (BIOL-105), Health track  Lesson 1 Human Biology (BIOL-105), Health track 5  3.1 Cell Theory  The microscopes we use today are far more complex than those used in the 1600s, later advances in lenses and microscope construction enabled other scientists to see different components inside cells.  By the late 1830s, scientist were studying tissues and proposed the unified cell theory:  All living things are composed of one or more cells.  Cell is the basic unit of life.  All new cells arise from existing cells.  These principles still stand today. 6 Human Biology (BIOL-105), Health track  Cells fall into one of two broad categories:  Prokaryotic: (pro- = before; -karyon- = nucleus, the predominantly single-celled organisms of the domains Bacteria and Archaea.  Eukaryotic: (eu- = true), the word eukaryotic means “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. Animal cells, plant cells, fungi, and protists. 7 Human Biology (BIOL-105), Health track  Prokaryotic Cells A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. All cells share four common components: 1) plasma membrane (outer covering): separates the cell’s interior from its surrounding environment 2) cytoplasm: consisting of a jelly-like region within the cell in which other cellular components are found 3) DNA: the genetic material of the cell. Prokaryotic DNA is found in the central part of the cell, a darkened region called the nucleoid 4) Ribosomes: particles that synthesize proteins. Figure 3.2. This figure shows the generalized structure of 8 a prokaryotic cell. Human Biology (BIOL-105), Health track  Eukaryotic Cells A eukaryotic cell is a cell that has a membrane-bound nucleus and organelles. Organelles; (little organs): membrane-bound compartments or sacs which have specialized functions. 9 Human Biology (BIOL-105), Health track  Comparison between prokaryotic and eukaryotic cells Prokaryotic Cells Eukaryotic Cells Have plasma membrane, genetic material Have plasma membrane, genetic material (DNA) and cytoplasm. (DNA) and cytoplasm. Cell Size: 0.1–5.0 µm in diameter have diameters ranging from 10–100 µm The small size of prokaryotes allows ions Larger eukaryotic cells have evolved and organic molecules that enter them to different structural adaptations to quickly spread to other parts of the cell enhance cellular transport and any wastes can quickly move out. Have no nucleus; have DNA region Have nucleus: compartment that houses (nucleoid) the DNA Have no membrane bound organelles. Have membrane bound and non membrane bound organelles. Bacterial cells are prokaryotic cells Protists, Fungi, Plants and Animals including human are eukaryotes Human Biology (BIOL-105), Health track ❑ Cell size The small size of prokaryotes allows ions and organic molecules to enter the cells and wastes produced within the cell to move out. Larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport: Some cells have microscopic projections called microvilli to increase surface area relative to volume. Small cells have a higher surface area-to-volume ratio which promotes efficiency in ✓ Acquisition of nutrients ✓ Disposal of wastes Human Biology (BIOL-105), Health track 11 Figure 3.4. This figure shows the relative sizes of different kinds of cells and cellular components. An adult human is shown for comparison. 12 Human Biology (BIOL-105), Health track  Lesson 2 Human Biology (BIOL-105), Health track 13 3.2 Structure and Composition of the Cell Membrane  All living cells in multicellular organisms have a surrounding cell membrane which separates the inner content of a cell from its exterior environment.  Cell membrane (plasma membrane) provides a protective barrier around the cell and regulates which materials can pass in or out.  It is selectively permeable (selective permeability allows only substances meeting certain criteria to pass through it ).  The cell membrane is an extremely pliable structure composed primarily of back-to- back phospholipids “bilayer”.  Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions. 14 Human Biology (BIOL-105), Health track 3.2 Structure and Composition of the Cell Membrane Plasma Membrane consists of: 1. Lipids: (lipid bilayer forms the basis of the cell membrane) Two adjacent layers of phospholipids which form the lipid bilayer Cholesterol 2. Proteins 3. Carbohydrates Intracellular fluid (ICF) is the fluid interior of the cell. The phosphate groups are also attracted to the extracellular fluid. Extracellular fluid (ECF) is the fluid environment outside the enclosure of the cell membrane. (extracellular fluid outside blood vessels is Figure 3.6. Phospolipid Bilayer. The phospholipid bilayer consists of two referred to as interstitial fluid “IF”) adjacent sheets of phospholipids, arranged tail to tail. The hydrophobic tails associate with one another, forming the interior 15 of the membrane. The polar heads contact the fluid inside and outside of the cell. Human Biology (BIOL-105), Health track 3.2 Structure and Composition of the Cell Membrane ❑ A single phospholipid molecule has a phosphate group on one end, called the “head,” and two side-by-side chains of fatty acids that make up the lipid tails. ❑ It is an amphipathic molecule containing both a hydrophilic and -ve charge A hydrophobic region. Head: Polar & Hydrophilic (water loving) One layer faces the watery solution outside the cell (extracellular fluid) and the other uncharged layer faces the watery cytoplasm. Tails: Figure 3.5. Phospholipid Structure. A phospholipid molecule consists of a polar phosphate “head,” which is hydrophilic and a non-polar lipid “tail,” which is Nonpolar & Hydrophobic (water fearing) hydrophobic. Unsaturated fatty acids result in kinks in the hydrophobic tails Meet in the center of the membrane 16 Human Biology (BIOL-105), Health track 3.2 Structure and Composition of the Cell Membrane Fluid Mosaic Model An important feature of the membrane is that it remains fluid; the lipids and proteins in the cell membrane are not rigidly locked in place. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—in which the components are able to flow and change position, while maintaining the basic integrity of the membrane. Phospholipid molecules and embedded proteins are able to diffuse rapidly and laterally in the membrane. The fluidity of the plasma membrane is necessary for the activities of certain enzymes and transport molecules within the membrane. 17 Human Biology (BIOL-105), Health track 3.2 Structure and Composition of the Cell Membrane Membrane Proteins  Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein.  Integral proteins : are permanently embedded in the plasma membrane. 1) Channel protein: a protein that selectively allows particular materials, such as certain ions, to pass into or out of the cell. 2) Cell recognition proteins: a protein which serves to mark a cell’s identity so that it can be recognized by other cells. A receptor is a type of recognition protein that can selectively bind a specific molecule outside the cell, this binding induces a chemical reaction within the cell. 3) Glycoprotein: a protein that is attached with carbohydrate molecules which extends into the extracellular matrix, that aids in cell recognition. 18 Human Biology (BIOL-105), Health track 3.2 Structure and Composition of the Cell Membrane Membrane Proteins  The carbohydrates that extend from membrane proteins and from some membrane lipids collectively form the glycocalyx. ❑ The glycocalyx is a fuzzy-appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane. It have various roles: 1- It may have molecules that allow the cell to bind to another cell. 2- It may contain receptors for hormones or have enzymes to break down nutrients. 3- It found in a person’s body are products of that person’s genetic makeup. They give identity to each of the individual’s trillions of cells person’s body. This identity is the primary way that a person’s immune defense cells not to attack own body cells, but it also is the reason organs donated by another person might be rejected. 19 Human Biology (BIOL-105), Health track  Lesson 3 Human Biology (BIOL-105), Health track 20 3.2 Structure and Composition of the Cell Membrane Membrane Proteins  Peripheral protein: found on the inner or outer surface of the lipid bilayer but can also be attached to the internal or external surface of an integral protein. They are loosely attached and can be released by relatively small changes in PH or ionic strength. These peripheral proteins perform a specific function for the cell. Some peripheral proteins on the surface of intestinal cells, for example, act as digestive enzymes to break down nutrients to sizes that can pass through the cells and into the bloodstream. Figure 3.7 21 Human Biology (BIOL-105), Health track  3.3 Transport across the Cell Membrane  Cell membrane have the ability to regulate the concentration of substances inside the cell, such as Ca++, Na+, K+, and Cl– ; nutrients including sugars, fatty acids, and amino acids; and waste products, particularly carbon dioxide (CO2).  Only relatively small, nonpolar materials can move through the lipid bilayer such as other lipids, oxygen and carbon dioxide gases, and alcohol.  However, water-soluble materials—like glucose, amino acids, and electrolytes—need some assistance to cross the cell membrane because they are repelled by the hydrophobic tails of the phospholipid bilayer.  All substances cross through cell membrane in:  Passive transport is the movement of substances across the membrane without the expenditure of cellular energy.  Active transport is the movement of substances across the membrane using energy from adenosine triphosphate (ATP). 22 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Passive transport Principles:  Concentration gradient is the difference in concentration of a substance across a space. Molecules (or ions) will spread/diffuse in a place from high concentration to low concentration until they are equally distributed in that space, this is called “move down their concentration gradient”  Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. 23 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Passive transport (no energy)  Diffusion Tow main types: 1. Simple diffusion. 2. Facilitated diffusion.  Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient. 24 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport 1. Simple diffusion  It is easily diffusion through the lipid bilayer of the cell membrane, such as the gases oxygen (O2) and CO2.  Whenever a substance exists in greater concentration on one side of a semipermeable membrane (e.g cell membranes) it can move down its concentration gradient across the membrane.  O2 generally diffuses into cells because it is more concentrated outside of them, and CO2 typically diffuses out of cells because it is more concentrated inside of them. Neither of these examples requires any energy on the part of the cell, and therefore they use passive transport to move across the membrane.  Water can cross via simple diffusion due to their small size. 25 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport 1. Simple diffusion Figure 3.8. Simple Diffusion across the Cell (Plasma) Membrane. The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. 26 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport 2. Facilitated diffusion It is the diffusion process used for those substances that cannot cross the lipid bilayer due to their size, charge, and/or polarity. Figure 3.9. Facilitated Diffusion. (a) Facilitated diffusion of substances crossing the cell (plasma) membrane takes place with the help of proteins such as channel proteins and carrier proteins. Channel proteins are less selective than carrier proteins, and usually mildly discriminate between their cargo based on size and charge. (b) Carrier proteins are more selective, often only allowing one particular type of molecule to cross. 27 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Facilitated diffusion through protein channels  Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer. So, their movement is restricted to protein channels and specialized transport mechanisms in the membrane.  Channel: Proteins that span the entire lipid bilayer. Gated channels: open or close in response to specific stimuli. Are important in regulating the transport of ions such as sodium, Potassium, calcium, and chloride. Non gated channel proteins or '' Aquaporins, are always open. They allow water and other molecules to freely traverse the selectively permeable plasma membrane without the need for an external signal 28 or trigger. Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Examples of Facilitated diffusion Ex1. movement of glucose into the cell Although glucose can be more concentrated outside of a cell, it cannot cross the lipid bilayer via simple diffusion because it is large and polar. So, glucose transporter will transfer glucose molecules into the cell to facilitate its inward diffusion. Ex2. sodium ions (Na+) can move down their concentration gradient from outside to inside cells Although Na+ highly concentrated outside of cells, these electrolytes are charged and cannot pass through the nonpolar lipid bilayer of the membrane. Their diffusion is facilitated by sodium channels. 29 Human Biology (BIOL-105), Health track  Lesson 4 Human Biology (BIOL-105), Health track 30 3.3 Transport across the Cell Membrane- Passive transport Osmosis The movement of water molecules is not itself regulated by cells, so it is important that cells are exposed to an environment in which the concentration of solutes outside of the cells is equal to the concentration of solutes inside the cells. Figure 3.10. Osmosis. Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient. If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration). In the beaker on the left, the solution on the right side of the membrane is hypertonic. 31 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Osmosis Osmosis occurs when there is an imbalance of solutes outside of a cell versus inside the cell. Three types of solutions according to tonicity (solute conc.): Hypertonic: having more solutes less water. Isotonic solution: have the same solute concentration. Hypotonic: having fewer solutes more water. Pure water is the most hypotonic solution possible A critical aspect of homeostasis in living things is to create an internal environment in which all of the body’s cells are in an isotonic solution. Various organ systems, particularly the kidneys, work to maintain this homeostasis. 32 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Effects of Tonicity on RBCs Isotonic Hypotonic Hypertonic Extracellular solute Extracellular solute Extracellular solute concentration equals concentration is lower concentration is higher intracellular solute than intracellular solute than intracellular solute concentration concentration concentration No net movement of Water will diffuse into Water will diffuse out water occurs. the cell. of the cell. The size of the cell Cell may swell and burst, Cell may shrink and die doesn’t change. 33 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Passive transport Filtration  Another mechanism besides diffusion to passively transport materials between compartments is filtration.  Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area.  Filtration is an extremely important process in the body. For example, the circulatory system uses filtration to move plasma  Filtration pressure in the kidneys provides the mechanism to remove wastes from the bloodstream. 34 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport Active transport  ATP is required to move a substance across a membrane often with the help of protein carriers, and usually against its concentration gradient. Figure 3.12. Sodium-Potassium Pump. The sodium-potassium pump is found in many cell (plasma) membranes. Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from and two potassium ions are imported into 35 the cell. Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport Active transport The sodium-potassium pump, which is also called Na+/K+ ATPase, transports sodium out of a cell while moving potassium into the cell. The Na+/K+ pump is an important ion pump found in the membranes of many types of cells. These pumps are particularly abundant in nerve cells, which are constantly pumping out sodium ions and pulling in potassium ions to maintain an electrical gradient across their cell membranes. 36 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport © 2017 Pearson Education, Ltd. 37 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport © 2017 Pearson Education, Ltd. 38 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport Other forms of active transport do not involve membrane carriers  Endocytosis : is the process of a cell ingesting material by enveloping it in a portion of its cell membrane, and then pinching off that portion of membrane. Once pinched off, the portion of membrane and its contents becomes an independent, intracellular vesicle. Endocytosis often brings materials into the cell that must to be broken down or digested. A vesicle is a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer membrane 39 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport Other forms of active transport do not involve membrane carriers  Phagocytosis (cell eating) is the endocytosis of large particles, Ex. Many immune cells engage in phagocytosis of invading pathogens.  Pinocytosis (cell drinking) brings fluid containing dissolved substances into a cell through membrane vesicles. Phagocytosis and pinocytosis take in large portions of extracellular material, and they are typically not highly selective in the substances they bring in Receptor-mediated endocytosis is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance. Once the surface receptors have bound sufficient amounts of the specific substance, the cell will endocytose the part of the cell membrane containing the receptor-ligand complexes. Ex. Iron. it is bound to a protein called transferrin in the blood. Specific transferrin receptors on red blood cell surfaces bind the iron-transferrin molecules, and the cell endocytoses the receptor-ligand complexes. 40 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport © 2017 Pearson Education, Ltd. 41 Human Biology (BIOL-105), Health track 3.3 Transport across the Cell Membrane- Active transport Other forms of active transport do not involve membrane carriers  Exocytosis : (taking “out of the cell”) is the process of a cell exporting material using vesicular transport. Ex.1 Cells of the stomach and pancreas produce and secrete digestive enzymes through exocytosis. Ex. 2 Endocrine cells produce and secrete hormones that are sent throughout the body. Ex. 3 Immune cells produce and secrete histamine. 42 Human Biology (BIOL-105), Health track  Summary 3.1 Cell Theory Principles: All living things are composed of one or more cells, cell is the basic unit of life, all new cells arise from existing cells. Cells fall into one of two broad categories; prokaryotic and eukaryotic cells 3.2 Structure and Composition of the Cell Membrane All living cells in multicellular organisms have a surrounding cell membrane that separates the inner contents of a cell from its exterior environment. Cell membrane (plasma membrane) provides a protective barrier around the cell and regulates which materials can pass in or out. It has selective permeability The cell membrane is an extremely pliable structure composed primarily of phospholipids bilayer. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components— including phospholipids, cholesterol, proteins, and carbohydrates—in which the components are able to flow and change position, while maintaining the basic integrity of the membrane. Two different types of proteins that are commonly associated with the cell membrane are the integral proteins and peripheral protein 43 Human Biology (BIOL-105), Health track  Summary 3.3 Transport across the Cell Membrane Passive transport is the movement of substances across the membrane without the expenditure of cellular energy. Active transport is the movement of substances across the membrane using energy from adenosine triphosphate (ATP). Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. Tow forms of passive transport across the cell membrane are: simple diffusion and facilitated diffusion (via protein channels, carrier proteins and specialized transport mechanisms. Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient. Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area. Phagocytosis (cell eating) is the endocytosis of large particles, Ex. Many immune cells engage in phagocytosis of invading pathogens. Pinocytosis (cell drinking) brings fluid containing dissolved substances into a cell through membrane vesicles. Exocytosis: (taking “out of the cell”) is the process of a cell exporting material using vesicular transport. 44 Human Biology (BIOL-105), Health track  Activity  Imagine being inside a closed bathroom, if a bottle of perfume were sprayed. Please illustrate how the scent spread?  A spoonful of sugar placed in a cup of tea, what will happen if the tea gets hotter?  Write the concept of the mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated is a form of passive transport. 45 Human Biology (BIOL-105), Health track  Activity  In this figure, which of the following are peripheral proteins? A. 1 and 2. B. 2 and 4. C. 1, 3, and 5. D. 4 and 5. 46 Human Biology (BIOL-105), Health track Thank you & Good Luck ☺ 47