Transcript
How cells are studied Microscopy Light microscopes – higher magnification Dissecting magnification – larger objects Electron microscopes – use electrons Only dead organisms Largest magnification Cell theory Unified cell theory All living things are composed of one or more cells that the cells is the basic unit of life and that all new cells arise from existing cells Comparing Prokaryotic and Eukaryotic cells Components of prokaryotic cells All cells share four components: 1. Plasma membrane – an outer covering that separates the cell’s interior from surrounding environment Cytoplasm – a jelly-like region within the cell in which other cellular components are found DNA – genetic material of the cell Ribosomes – particles that synthesize proteins Prokaryotic cell – simple, single-celled organism that lacks a nucleus or any other membrane bound organelle Eukaryotic cell – cell that has a membrane bound nucleus and other membrane bound compartments or sacs, called organelles (organelles- have specialized functions) Cell size Prokaryotic cells are smaller than eukaryotic cells Prokaryotic cells – size allows for ions and organic molecules that enter them to quickly spread to other parts of the cell Eukaryotic cells – structural adaptations to enhance cellular transport Eukaryotic cells Plasma membrane Made up of the phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment Regulates the passage of some substances Organic molecules, ions, water Cytoplasm Comprises the contents of a cell between the plasma membrane and the nuclear envelope Made up of organelles suspended in the gel-like cystol, the cytoskeleton, and various chemicals 70-80% water Semi-solid consistency – from proteins Other organic molecules found: Glucose, other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids, and derivatives of glycerol Molecules dissolves in the cytoplasm: Ions of sodium, potassium, calcium Many metabolic reactions occur Ex: protein synthesis Cytoskeleton Network of protein fibers that: help maintain the shape of the cell secures certain organelles in specific positions allows cytoplasm and vesicles to move within the cell enables unicellular organisms to move independently three types of fibers microfilaments (actin filaments) thinnest function in moving cellular components maintain the structure of the microvilli intermediate filaments intermediate diameter maintain the shape of the cell anchors organelles microtubules thickest hollow tubes that can dissolve and reform quickly guide organelle movement structures that pull chromosomes to their poles during cell division structural complement of flagella and cilia flagella and cilia flagella – long, hair-like structures that extend from the plasma membrane and are used to move an entire cell cilia – short hair-like structures that are used to move entire cells or move substances along the outer surface of the cell Endomembrane system endomembrane system a group of membrane and organelles in eukaryotic cells that work together to modify, package, and transport lipids and proteins includes: nuclear envelope, lysosomes, vesicles, endoplasmic reticulum, and Golgi apparatus nucleus houses the cell’s DNA in the form of chromatic and directs the synthesis of ribosomes and proteins nuclear envelope double membrane structure that constitutes the outmost portion of the nucleus phospholipid bilayers pores that control the passage of ions, molecules, an RNA between the nucleoplasm and the cytoplasm nucleolus – darkly staining area within the nucleus that aggregates the ribosomal RNA with associated proteins to assemble the ribosomal subunits that are then transported through the nuclear pores into the cytoplasm endoplasmic reticulum (ER) series of interconnected membranous tubules that collectively modify proteins and synthesize lipids Lumen/cisternal space – hollow portion of the ER tubules Rough ER Ribosomes attached to its cytoplasmic surface give it a studded appearance when viewed through an electron microscope Transfer newly synthesized proteins into the lumen of the RER Undergo modifications; folding or adding sugars Makes phospholipids for cell membranes Smooth ER Has few or no ribosomes on its cytoplasmic surface Synthesize carbohydrates, lipids, steroid hormones Detoxification of medications and poisons Alcohol metabolism Storage of calcium cells Golgi apparatus Series of flattened membranous sacs Receive vesicles from ER, fuse with it, and empty contents into the lumen of the golgi apparatus Travel through Golgi, undergo further modifications, addition of shorts chains and sugar molecules Tagged with smaller molecular groups to enable them to be routed to their proper destinations Lysosomes Cells’ garbage disposal Digestive enzymes within the lysosomes aid the breakdown of proteins, polysaccharides, lipids, nucleic acid, and even worn-out organelles Digestion of food, infest and recycle organelles Use hydrolytic enzymes to destroy disease causing organisms Vesicles and vacuoles Membrane-bound sacs that function in storage and transport Vacuoles > vesicles Vacuoles membrane do not fuse with other membranes Vesicles can fuse with other membranes Ribosomes Cellular structures responsible for protein synthesis Consist of large and small subunits Found in practically every cell May be attached to either the cytoplasmic of plasma membrane or cytoplasmic side of the ER Mitochondria Powerhouse of the sell Responsible for making adenosine triphosphate (ATP); cells main energy carrying molecule Cellular respiration – formation of ATP from the breakdown of glucose Oval-shaped, double membrane organelles Heave their own ribosomes and DNA Each membrane is a phospholipid bilayer embedded with proteins Inner layer (cristae) – increase the surface area of the inner membrane Mitochondrial matrix – area surrounded by the folds Peroxisomes Small round organelles enclosed by single membranes Carry out oxidation reactions that break down fatty acids and amino acids Detoxify many poisons/alcohol that may enter the body Animal cells versus plant cells Animal cells – have centrioles, centrosomes, and lysosomes Plant cells – have a cell wall, chloroplasts, plasmodesmata, and plastids, large central vacuole Cell wall structure external to the plasma membrane rigid covering that protects the cell provides structural support gives shape to the cell cellulose – major organic molecule in cell walls chloroplast have their own DNA and ribosomes function in the photosynthesis have outer and inner membranes inner membrane thylakoids - set of interconnected fluid filled membrane sacs each stack is called a granum stoma – fluid enclosed by the inner membrane and surrounding the grana contain chlorophyll – green pigment captures the energy of sunlight for photosynthesis central vacuole plants cells each have a large central vacuole that occupies most of the cell central vacuole plays a key role in regulating the cells concentration of water in changing environmental conditions to store proteins in developing seed cells 286512013716000Extracellular matrix of animal cells most animal cells release materials into the extracellular space extracellular space – glycoproteins and the protein collagen holds the cells together to form a tissue allows the cells within the tissue to communicate with each other Intercellular junctions communication between cells by direct contact plant cells plasmodesmata – junctions between plant cells numerous channels that pass between the cells walls of adjacent plants, connecting their cytoplasm and enabling signal molecules and nutrients to be transported form cell to cell animal cells tight junction – water tight seal between two adjacent animal cells proteins hols the cells tightly against each other prevents materials from leaking between cells found in epithelial tissues; lines internal organs and cavities, composes most of the skin desmosome – spot welds between adjacent epithelial cells keep cells together in a sheet-like formation in organs and tissues that stretch, skin, heart, and muscles gap junction – channels between adjacent cells that allow for transport of ions, nutrients, and other substances that enable cells to communicate Cell Component Function Present in Prokaryotes? Present in Animal Cells? Present in Plant Cells? Plasma membrane Separates cell from external environment; controls passage of organic molecules, ions, water, oxygen, and wastes into and out of the cell Yes Yes Yes Cytoplasm Provides structure to cell; site of many metabolic reactions; medium in which organelles are found Yes Yes Yes Nucleoid Location of DNA Yes No No Nucleus Cell organelle that houses DNA and directs synthesis of ribosomes and proteins No Yes Yes Ribosomes Protein synthesis Yes Yes Yes Mitochondria ATP production/cellular respiration No Yes Yes Peroxisomes Oxidizes and breaks down fatty acids and amino acids, and detoxifies poisons No Yes Yes Vesicles and vacuoles Storage and transport; digestive function in plant cells No Yes Yes Centrosome Unspecified role in cell division in animal cells; organizing center of microtubules in animal cells No Yes No Lysosomes Digestion of macromolecules; recycling of worn-out organelles No Yes No Cell wall Protection, structural support and maintenance of cell shape Yes, primarily peptidoglycan in bacteria but not Archaea No Yes, primarily cellulose Chloroplasts Photosynthesis No No Yes Endoplasmic reticulum Modifies proteins and synthesizes lipids No Yes Yes Golgi apparatus Modifies, sorts, tags, packages, and distributes lipids and proteins No Yes Yes Cytoskeleton Maintains cell’s shape, secures organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently Yes Yes Yes Flagella Cellular locomotion Some Some No, except for some plant sperm. Cilia Cellular locomotion, movement of particles along extracellular surface of plasma membrane, and filtration No Some No The Cell Membrane Cell membrane plasma membrane defines the boundary of the cell determines the nature of its contact with the environment exclude some/take in others dynamic and constantly in flux sufficiently flexible to allow certain cells to change shape as they as through narrow capillaries Surface of plasma membrane Carries markers that allow cells to recognize one another Carries receptors – attachment sites for specific substances that interact with the cell Fluid mosaic model Singer Garth Structure and functions of the plasma membrane as a mosaic of components Phospholipids, cholesterol, proteins, and carbohydrates Components are ale to flow and change position Fluidity of plasma membrane is necessary for the activities of certain enzymes and transport molecules in the membrane Made up of primarily a bilayer of phospholipids with embedded proteins, carbohydrates, glycolipids, and glycoproteins (in animals, cholesterol) Main fabric of the membrane is composed of two layers of phospholipid molecules Polar ends in contact with aqueous fluid both inside/outside cell Hydrophilic Inner is hydrophobic or nonpolar Proteins make up the second major chemical component Integral proteins are embedded in the plasma membrane Serve as channels or pumps to move materials in/out cell Peripheral proteins are found on the exterior or interior attached to either integral proteins or phospholipids molecules Both may serve as enzymes Structural attachments for the fibers of the cytoskeleton Parts of the cell’s recognition sites Carbohydrates are the third major component Always found on the exterior surface, bound to either proteins or lipids Form specialized sites on the cell surface that allows cells to recognize each other Passive Transport Plasma membrane Plasma membranes Must allow certain substances to enter and leave a cell Preventing harmful materiel from enter, essential materiel from leaving Selectively permeable – allow substances through but not others If lost, cell would no longer be able to sustain itself, would be destroyed Passive transport Most direct form of membrane transport Naturally occurring phenomenon Does not require the cell to expend energy Diffusion substances move from an area of higher concentration to lower concentration until the concentration is equal across the space passive process of transport expends no energy factors that affect the rate of diffusion extent of the concentration gradient the greater the difference in concentration the more rapid the diffusion the closer the distribution of the materials get to the equilibrium the slower the rate of diffusion becomes mass of the molecules diffusing more massive molecules move more slowly it is more difficult to move between molecules temperature higher temperatures increase the energy and therefore the movement of the molecules, increasing rate of diffusion solvent density as density increases the rate of diffusion decreases. Molecules slow down because they have a difficult time getting through denser material concentration gradient physical space in which there is a different concentration of a single substance Facilitated transport facilitated diffusion material moves across the plasma membrane with the assistance of transmembrane proteins down a concentration gradient without using energy Osmosis movement of free water molecules through semipermeable membrane according to the waters concentration gradient across the membrane only transports water across a membrane solute cannot diffuse through membrane, but water can Tonicity tonicity - amount of solute in a solution osmolarity – total amount of solutes in a specific amount of solution hypotonic – extracellular fluid has lower concentration of solutes than the fluid inside the cell and water enters the cell hypertonic – extracellular fluid having a higher concentration of solutes than the cell’s cytoplasm fluid contains less water than the cell does isotonic – the extracellular fluid has the same osmolarity as the cell if the concentration of solutes of the cells matches that of the extracellular fluid there will be no net movement of water into or out of the cell Active Transport Active transport active transport – mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP) if a substance must move into the cell against its concentration gradient (if the concentration of the substance inside the cell must be greater than its concentration in the extracellular fluid) the cell must use energy to move the substance move small molecular weight materials (ions) Electrochemical gradient combined gradient that affects an ion important to move muscles and nerves cells contain proteins most of which are negatively charged ions move in/out cell – electrical gradient moving against a gradient cell must use energy harvested from ATP generated through cellular metabolism maintains concentrations of ions and other substances needed by living cells Endocytosis endocytosis - type of active transport that moves large molecules, parts of cells, and even whole cells into the cell plasma membrane of the cell invaginates forming a pocket around the target particle target pinches off, resulting in the particle being contained in a newly created vacuole that is formed from the plasma membrane phagocytosis – process by which particles such as cells are taken in by a cell pinocytosis – cell drinking, takes in solutes that the cell needs from the extracellular fluid receptor mediated endocytosis – targeted variation binding proteins in the plasma membrane that are specific for certain substances particles bind to the proteins and plasma membrane invaginates bringing the substance and the proteins to the cell. If ineffective; passage across the membrane = ineffective; it will not be removed from the tissue’s fluids or blood Wil stay in those fluids and increase in concentration Exocytosis Expel material from the cell in the extracellular fluid Particles enveloped in membrane fuses with the interior of the plasma membrane Fusion opens the membranous envelope to the exterior of the cell Particle is expelled into the extracellular space
