Biology Chapter 3 Part 1 PDF

Biology Fall 2024/2025 Chapter 3 Cells & Tissues Part 1  Chapter 3: Cells & Tissues Learning objectives (pages 86-104) Upon completion of this section, students must be able to: Discuss the cell theory and the idea that cells are the basic units of structure an func...

Biology Fall 2024/2025 Chapter 3 Cells & Tissues Part 1  Chapter 3: Cells & Tissues Learning objectives (pages 86-104) Upon completion of this section, students must be able to: Discuss the cell theory and the idea that cells are the basic units of structure an function Describe the detailed anatomy of the cell Define structural & functional features of cellular components Describe the structural and functional diversity of human cells Describe the concept and mechanisms of plasma membrane transport: selective permeability of plasma membranes, passive / active transport; vesicular transport;  The cell theory Robert Hook in the 17th century was the first person to see plant cells under his crudely-made microscope: Cork cells As they looked to him like cells of Monk’s in the monastery, so he named them cells.  In the 19th century, the cell theory was formulated: – Cell is basic unit of structure and function – Activity of organisms depends on collective activity of cells that make them – Cell biochemical activity is related to its sub- cellular structure – Continuity of life is based on cellular growth and reproduction  Anatomy of a Generalized Cell In general, all cells have three main regions: The nucleus Cytoplasm Plasma membrane  The Nucleus Contains the genetic material (DNA) which is responsible for production of proteins in the cells Nuclear envelop: – Consists of a double membrane that bounds the nucleus – Contains nuclear pores that allow for exchange of material with the rest of the cell – Encloses the jellylike fluid called the nucleoplasm – Nucleoplasm is rich with  The Nucleus Nucleoli: (cont.) One or more small dark staining bodies; sites of ribosome synthesis & assembly Ribosomes migrate into the cytoplasm through nuclear pores to serve as the site of protein synthesis Chromatin: Chromatin is the combination of DNA + proteins in resting cells. As cells prepare for dividing, chromatin threads become Plasma membrane Structure  Plasma membrane Border between cell environment and outside Fluid mosaic model: A tail-to-tail phospholipid bilayer with cholesterol (in animal cells) + proteins + glycoproteins placed in various configurations ( = mosaic). Tail-to-tail = polar heads (hydrophilic) facing water, nonpolar tails (hydrophobic) away from water.  Plasma membrane Phospholipids align together (no chemical linking)  free to move in a lateral fashion (fluid). Glycoproteins in plasma membrane function as structural proteins, enzymes, transport proteins, ion channels, receptors, etc. Sugars and glycoproteins are sticky  give plasma membrane a fuzzy appearance  glycocalyx (sugar coated)  Membrane junctions Although some cells (blood cells) are loose, most other body cells are knitted together in one of 3 ways: – Glycoproteins present in the glycocalyx act as an adhesive or cellular glue (cells are sticky) – Wavy contours of plasma membranes of adjacent cells help them stick together – Special membrane junctions  next slide  Membrane junctions Tight junctions: plasma membranes of adjacent cells fuse at certain points forming leak-proof sheets of cells (e.g. cells forming wall of small intestine) Gap junctions: hollow protein cylinders (connexons) that directly connect adjacent cells and enable them to exchange substances (nutrients, ions, etc).  Membrane junctions (cont.) Desmosomes: anchoring junctions, function like rivets (nails), hold cells under stress from breaking off (e.g. heart muscle and skin cells). They are thickened plasma membrane of adjacent cells (plaque); connected together by fine protein filaments. Thicker filamentous proteins extend from inside the cell to reach plaques of an  Cytoplasm Cellular constituents located between nuclear envelop and plasma membrane. Most of the cell is basically cytoplasm  manufacturing area of the cell (where cells produce and metabolize substances and molecules) The cytoplasm consists of: – Cytosol: (water + dissolved nutrients and other elements) – Cellular organelles: mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, …etc. – Cytoplasmic inclusions: stored fat in fat cells (adipocytes), glycogen in liver cells (hepatocytes), pigments in skin cells (keratinocytes), et. Cytoplasmic Organelles  Mitochondria Mitochondrial wall is a double membrane: equal to two plasma membranes, placed side by side. Consists of outer membrane + inter-membrane space + inner membrane Outer membrane is smooth and featureless Inner membrane has protrusions called cristae, helps to increase surface area of inner membrane Contains enzymes dissolved in the fluid inside the mitochondria and anchored to inner membrane Has own genetic material that is maternally inherited Major function: “Powerhouse of  Ribosomes Small bi-lobed structures (small subunit + large subunit) Made of proteins and rRNA Sites for protein synthesis (mRNA translation) Free floating or attached to outer surface of ER (rough endoplasmic reticulum)  Endoplasmic reticulum (ER) Accounts for ½ of cell’s membrane system Rough (RER) & Smooth (SER) types ER switches between RER and SER RER: ribosomes attached to ER surface; participate in proteins synthesis synthesized protein buds off RER in transport vesicles  attaches to receiving phase of GA (Golgi apparatus) RER is the cell membrane  Endoplasmic reticulum (ER) SER: Plays no role in protein synthesis Participates in lipid metabolism (cholesterol and fat synthesis and breakdown) Detoxification of drugs and pesticides (liver cells are very rich in SER) Body cells producing steroid hormones such as male testes producing testosterone  Golgi Apparatus Stack of flattened membranous sacs with many vesicles fusing in and budding off. Modifies and package incoming proteins for final shipping to target location (folding, glycosylation, etc) Vesicles from GA move in 1 (one) of 3 pathways – Pathway 1: trafficking of mature proteins to final destination (cytoplasm, cell membrane, secretory proteins) – Pathway 2: Empty vesicles bud out of GA  fuse with plasma membrane enable cells to increase in size – Pathway 3: Vesicles containing digestive enzymes become lysosomes, fuse with ingested substances to degrade them (e.g. pathogens)  Rough ER Cisterns Proteins in cisterns Membrane Lysosome fuses with ingested Transport substances. vesicle Golgi vesicle containing digestive enzymes becomes a lysosome. Pathway 3 Pathway 2 Golgi vesicle containing Golgi membrane components apparatus Secretory vesicles fuses with the plasma Pathway 1 Proteins membrane and is Golgi vesicle containing incorporated into it. proteins to be secreted Plasma membrane becomes a secretory Secretion by vesicle. exocytosis Extracellular fluid Interaction of ribosomes, ER, and GA in protein synthesis, packaging and export Figure 3.6 Role of the Golgi apparatus in packaging the products of the rough ER.  Lysosomes Membranous bags filled with digestive enzymes Often called breakdown bodies Degraded, damaged or no-longer-needed molecules for recycling purposes (e.g., protein  amino acids  exit for reuse in protein synthesis) Abundant in certain types of cells that are know for their ability to degrade macromolecules (pathogen-degrade phagocytes, macrophages, etc.) Enzymes that fill lysosomes form on ribosomes (pathway 3)  Peroxisomes Membranous bags of oxidative enzymes (oxidases) that use molecular oxygen (O2) to detoxify poisons, alcohol, & other harmful substances) Oxidases in peroxisomes neutralize harmful free radicals like superoxide[O2-], hydroxyl radical [OH-]. Free radicals are normal by-products of cellular metabolism; should not accumulate as they are very reactive chemicals that can damage proteins and DNA Peroxisomes convert free radicals into H2O2; excess H2O2 is converted into H2O by the catalase enzyme Numerous in liver and kidney cells (major organs of drug and poison detoxification) Peroxisomes do not arise from GA. They replicate  Cytoskeleton A network of fibers and filaments that form internal frameworks within cells Gives cells shape, supports organelles & furnishes the machinery to transport substances inside cells and for cells to move (e.g. cilia, flagella, etc.) 3 different types: – Microfilaments: mostly involved in cell mobility and in changing shape of cell (e.g. ACTIN & MYOSIN) – Intermediate filaments: form desmosomes, act like internal anchors that resist pulling forces on the cell. – Microtubules: give cell its overall shape, help in distributing & locking organelles in place inside cells. Very important during cell division  (a) Microfilaments (b) Intermediate filaments (c) Microtubules Tubulin subunits Fibrous subunits Actin subunit 7 nm 10 nm 25 nm Microfilaments form the blue Intermediate filaments form Microtubules appear as gold batlike network. the purple network networks surrounding the surrounding the pink nucleus. cells’ pink nuclei. Figure 3.7 Cytoskeletal elements support the cell and help to generate movement. Cytoskeleton  Structures related to cytoskeleton Centrioles: paired rod-shaped bodies near nucleus; form microtubules and the spindle fibers which play a major in the nuclear phase of cell division Cell extensions with microtubules or actin filaments as the core structure – Cilia: multiple whip-like projections that move liquid (water) current along surface of cells expressing them; originate from Centrioles (microtubuless) e.g. ciliated cell of respiratory system – Flagella: longer / thicker / smaller in number than cilia, consist of microtubules (sperm cells, bacterial flagella, etc.) – Microvilli: are tiny, fingerlike extensions of cell membrane. – abundant on cells involved in absorption (epithelial cells of small intestine) – have actin filament cores that extend to inside of cells Cell diversity Over 200 different types of cells make the body Cells vary in size, shape, structure, function, etc. Can be divided into several groups based on general function  Cell Physiology Cells have the ability to: – Metabolize – Digest food – Dispose of wastes – Reproduce – Grow – Move – Respond to a stimulus © 2015 Pearson Education, Li mited.  Membrane Transport The inside of a cell and the environment in which cells live is water + substances dissolved in water = solution A solution is a homogenous mixture of >2 substances Most abundant substance in a solution is the solvent (water), the rest are solutes Common examples of solutions in the human body ‒ Blood plasma: the liquid phase of blood; rich in proteins and other substances (minerals, vitamins, hormones, etc.); can move out of circulation to become interstitial fluid ‒ Intracellular fluid: located inside cells (nucleoplasm and cytosol), contain gases, nutrients, and salts dissolved in water  Membrane Transport Plasma membrane is Selectively Permeable: only specific substances can get in or out of the cell according to certain rules. These rules are imposed by the basic structure of the plasma membrane: hydrophilic heads facing aqueous solutions from both sides + hydrophobic tails in the facing each other within the membrane. Therefore, a substance that needs to move into/out of the cell will face a set of problem that require specific solutions  Membrane Transport Small substance that can pass through membrane components enter/exit cells by one of two mechanisms depending on the chemical/physical features of the molecule ‒ Passive transport (e.g., diffusion, filtration, and facilitated diffusion). No energy (ATP) needed ‒ Active transport: (e.g., ion channels like the Na+/K+ pump). Energy (ATP) required Vesicular transport (endocytosis & exocytosis): for large molecules that cannot squeeze themselves through membrane components.  Passive Transport It is energy-independent Substance moves according to its concentration gradient (from area of [high] to area of [low]. The force is the kinetic energy of molecules in the substance, smaller molecules pass faster than larger ones Different forms: simple diffusion, filtration, facilitated diffusion, Osmosis Molecules will move across plasma membrane by diffusion if any of the following applies: —The molecules are small enough to pass through the membrane’s pores (channels formed by membrane proteins) —The molecules are lipid-soluble —The molecules are assisted by a membrane  simple diffusion Figure 3.9 Diffusion.  Passive Processes Types of diffusion – Simple diffusion (lipid-soluble or small molecules) – Osmosis (movement of water) – Facilitated diffusion (carrier-mediated and channel-mediated) © 2015 Pearson Education, Li mited.  Passive Processes Osmosis—A Closer Look – Isotonic solutions have the same solute and water concentrations as cells and cause no visible changes in the cell – Hypertonic solutions contain more solutes than the cells do; the cells will begin to shrink – Hypotonic solutions contain fewer solutes (more water) than the cells do; cells will plump © 2015 Pearson Education, Li mited.  Active transport (solute pumping) Like facilitated diffusion, it requires special transport proteins but unlike facilitated diffusion it is Energy- Dependent (that is why they call it active and not passive) A substance could move against its concentration gradient especially if the cells needs it Energy that move substances = cellular energy in the form of ATP (ATP hydrolysis) The special proteins use ATP to change channel configuration that would allow a specific substance to pass. Examples include the Na/K pump, the proton pump,  Slide 1 Extracellular fluid Na+ Na + K+ Na+-K+ pump Na+ Na+ Na+ K+ P P K+ ATP Na+ 1 2 3 K+ ADP 1 Binding of cytoplasmic Na+ 2 The shape change expels 3 Loss of phosphate to the pump protein stimulates Na to the outside. Extracellular + restores the original phosphorylation by ATP, which K+ binds, causing release of the conformation of the pump causes the pump protein to phosphate group. protein. K+ is released to the change its shape. cytoplasm, and Na+ sites are ready to bind Na+ again; the cycle repeats. Cytoplasm Figure 3.11 Operation of the sodium-potassium pump, a solute pump.  Vesicular transport Is a type of active transport where substances are moved without actually crossing the plasma membrane. – Exocytosis – Endocytosis Phagocytosis Pinocytosis  Active Processes Vesicular transport (continued) – Exocytosis o Moves materials out of the cell o Material is carried in a membranous sac called a vesicle o Vesicle migrates to plasma membrane o Vesicle combines with plasma membrane o Material is emptied to the outside o Refer to Pathway 1 in Figure 3.6 © 2015 Pearson Education, Li mited.  Rough ER Cisterns Proteins in cisterns Membrane Lysosome fuses with ingested Transport substances. vesicle Golgi vesicle containing digestive enzymes becomes a lysosome. Pathway 3 Pathway 2 Golgi vesicle containing Golgi membrane components apparatus Secretory vesicles fuses with the plasma Pathway 1 Proteins membrane and is Golgi vesicle containing incorporated into it. proteins to be secreted Plasma membrane becomes a secretory Secretion by vesicle. exocytosis Extracellular fluid Figure 3.6 Role of the Golgi apparatus in packaging the products of the rough ER.  Active Processes Vesicular transport (continued) – Exocytosis docking process Transmembrane proteins on the vesicles are called v-SNAREs (v for vesicle) Plasma membrane proteins are called t- SNAREs (t for target) v-SNAREs recognize and bind t-SNAREs Membranes corkscrew and fuse together SNARS: Soluble N-ethylmaleimide attachment protein receptor (SNARE) proteins © 2015 Pearson Education, Li mited. Figure 3.12a Exocytosis. Extracellular Plasma fluid membrane SNARE (t-SNARE) 1 Vesicle The membrane bound SNARE (v-SNARE) vesicle migrates to the Molecule plasma membrane to be secreted Secretory vesicle Cytoplasm Fusion pore formed There, v-SNAREs bind with 2 t-SNAREs, the vesicle and plasma membrane fuse, Fused and a pore opens up. SNAREs Vesicle contents are 3 released to the cell exterior (a) The process of exocytosis  (b) Electron micrograph of a secretory vesicle in exocytosis (190,000×) Figure 3.12b Exocytosis.  Active Processes Vesicular transport (continued) – Endocytosis Extracellular substances are engulfed by being enclosed in a membranous vesicle Vesicle typically fuses with a lysosome Contents are digested by lysosomal enzymes In some cases, the vesicle is released by exocytosis on the opposite side of the cell © 2015 Pearson Education, Li mited.  Slide 1 Extracellular fluid Cytosol Plasma membrane Vesicle Lysosome 1 Vesicle fusing with lysosome for digestion Release of contents to cytosol 2 Transport to plasma membrane and exocytosis of vesicle contents Detached vesicle Ingested substance 3 Membranes and receptors (if present) recycled to plasma Pit membrane (a) Figure 3.13a Events and types of endocytosis.  Active Processes Vesicular transport Extracellular Cytoplasm (continued) fluid Types of endocytosis Bacterium or other 1. Phagocytosis—“cell particle eating” Cell engulfs large particles such as bacteria Pseudopod or dead body cells Pseudopods are cytoplasmic extensions that separate substances (such as bacteria or dead body cells) from external © 2015 Pearson Education, Li environment mited.  Active Processes Vesicular transport (continued) – Types of endocytosis 2. Pinocytosis—“cell drinking” – Cell “gulps” droplets of extracellular fluid containing dissolved proteins or fats – Plasma membrane forms a pit, and edges fuse around droplet of fluid – Routine activity for most cells, such as those involved in absorption (small intestine) © 2015 Pearson Education, Li mited. Figure 3.13a Events and types of endocytosis. Extracellular fluid Cytosol Plasma membrane Vesicle Lysosome 1 Vesicle fusing with lysosome for digestion Release of contents to cytosol 2 Transport to plasma membrane and exocytosis of vesicle contents Detached vesicle Ingested substance 3 Membranes and receptors (if present) recycled to plasma Pit membrane (a)  Active Processes Vesicular transport (continued) 3. Receptor-mediated endocytosis Membrane Method for taking up specific receptor target molecules Receptor proteins on the membrane surface bind only certain substances Highly selective process of taking in substances such as enzymes, some hormones, cholesterol, and iron Both the receptors and target molecules © 2015 are Pearson in Education, a Li mited.  Components and functions of cell’s organelles Component Function Regulates the movement of substances in and out of the cell; Cell Membrane protects the cell Contains genetic material (DNA); controls cell activities and Nucleus gene expression Nucleolus Produces and assembles ribosomes Nuclear Envelope Surrounds the nucleus and controls substance movement Chromosomes Carry genetic information in the form of DNA Cytoplasm Suspends organelles and participates in cellular processes Ribosomes Site of protein synthesis Involved in protein synthesis, lipid metabolism, and ER detoxification processes Golgi Apparatus Modifies, sorts, and packages proteins and lipids for transport Mitochondria Produces energy (ATP) through cellular respiration Lysosomes Contain enzymes for waste breakdown Cytoskeleton Provides structural support and aids in cell movement Centrioles Involved in cell division and spindle fiber formation Vacuoles Store and transport substances Vesicles Membrane-bound sacs for transport and storage