Postlab Cell and Cell Transport Mechanisms PDF

Lab Activity 3 Human Transport Cheek Cell Mechanism  Human Cheek Cell cytoplasm nucleus Cell membrane Human cheek cells (unstained) Hu...

Lab Activity 3 Human Transport Cheek Cell Mechanism  Human Cheek Cell cytoplasm nucleus Cell membrane Human cheek cells (unstained) Human cheek cells (stained)  Cell The basic structural and functional unit of every organism Types of cells (based on the presence or absence of true nucleus) – Eukaryotic – Prokaryotic A eukaryotic ANIMAL cell Major Parts of the Cell (Eukaryotic) Plasma membrane (or cell membrane) – Plants, fungi, and some protists have cell wall Nucleus Cytoplasm – Endoplasmic reticulum – Ribosomes – Golgi bodies (or golgi apparatus) – Mitochondria – Peroxisomes – Cytoskeleton  Plasma membrane the outermost component of a cell encloses the cytoplasm and forms the boundary between material inside the cell and materials outside it, hence it is called the “gatekeeper of the cell” Selectively permeable which regulates the exchange of essential substances between the cell’s contents and the external environment  Nucleus the most distinct (usually the largest) organelle in a eukaryotic cell averaging about 5 um in diameter usually situated at the center of the cell, bounded by a double membrane (nuclear membrane) contains most of the genes in the eukaryotic cell (some genes are located in mitochondria and chloroplasts).  Three distinct parts of nucleus Nuclear envelope/ membrane – Double membrane that encloses the nucleus separating its contents from the cytoplasm – isolates the nucleus from the rest of the cell and allows selective exchange of materials – perforated with tiny membrane-lined channels called nuclear pores. Nucleolus diffuse body with no surrounding membrane that is found at the center of the nucleus Functions: Ribosomal RNA (rRNA) synthesis and Site of ribosome assembly Chromatin  Three distinct parts of nucleus Nuclear envelope/ membrane Nucleolus Chromatin materials – Within the nucleus, the DNA is organized into discrete units called chromosomes, structures that carry the genetic information. – Each chromosome is made up of a material called chromatin, a complex of proteins and DNA. Note: The cytoplasm of the nucleus is referred to as nucleoplasm or karyoplasm.  Functions of nucleus Controls and regulates the functions of other organelles, thus called the “governor or the control center of the cell” Information central  Cytoplasm consists of all materials inside the plasma membrane and outside the nucleus Has semifluid, jellylike substance called cytosol the most active region of the cell because most of the cell’s metabolic activities---the biochemical reactions that support life--- occur in cell cytoplasm Contains the different organelles of the cell – Organelles are physiologically active, permanent sub- cellular structures performing metabolic functions  Ribosomes spherical bodies that may be attached to the Endoplasmic Reticulum or nuclear envelope (Bound ribosomes) or free in the cytoplasm (Free ribosomes). – The two types of ribosomes are structurally identical aggregates of rRNA and protein Function: site of protein synthesis in the cell Proteins synthesized from free ribosomes function within the cytosol (e.g. enzymes) Proteins from bound ribosomes are used for: membrane components export from the cell or for secretion  Endoplasmic reticulum (ER) Endoplasmic means "within the cytoplasm”, and reticulum is Latin for "little net” network of membranous tubules and sacs called cisternae accounts for more than half the total membrane in many eukaryotic cells the ER membrane is continuous with the nuclear membrane  Two types of Endoplasmic Reticulum Smooth ER- without ribosomes Functions: – synthesis of lipids (oils, phospholipids, and steroids) – metabolism of carbohydrates – detoxification of drugs and poisons – Store calcium ions – Transport by vesicle formation – Abundant in liver and muscle cells  Two types of Endoplasmic Reticulum Rough ER- with ribosomes Function – The ribosomes on the outside of rough ER are used to synthesize both secretory proteins and phospholipids – Membrane factory of the cell (grows in place by adding membrane proteins and phospholipids to its own membrane) – Transport by vesicle formation  Golgi apparatus/ Golgi complex named for the Italian physician and cell biologist Camilo Golgi, who discovered in the late 1800s membrane-bound vesicles of flattened sacs and stacks (cisternae) parallel to each other – Unlike in ER, the cisternae of Golgi appartus are not physically connected derived from endoplasmic reticulum Golgi apparatus/ Golgi complex § Entry or cis face (convex) § a cisterna that faces the rough ER § Exit or trans face (concave) § a cisterna that faces the plasma membrane § Medial cisternae § Sacs between the entry and exit faces.  Functions of Golgi complex § Modifies, sorts, packages, and transports proteins received from the rough ER. § Forms secretory vesicles that discharge processed proteins via exocytosis into extracellular fluid § Forms membrane vesicles that ferry new molecules to the plasma membrane § Forms transport vesicles that carry molecules to other organelles, such as lysosomes  Golgi apparatus/ Golgi complex Functions separates (sorts) proteins and lipids received from the ER according to their destinations modifies some molecules – For instance, it adds sugars to proteins to make glycoproteins manufactures certains molecules (polysaccharides) ‘Shipping and receiving center’ of the packages these materials into vesicles that are then transported to other parts cell of the cell or to the plasma membrane for export Three general destinations for proteins that leave the Golgi complex Secreted from the cell by exocytosis Incorporated into the plasma membrane Occupy storage vesicles that become lysosomes  Endomembrane system Includes the: – Nuclear membrane/ envelope – Endoplasmic reticulum – Golgi appratus – Lysosomes (found only in animal cell) – Various kinds of vacuoles (lysosomes in plants) – Plasma membrane (not actually an endomembrane in physical location, but nevertheless related to the endoplasmic reticulum and other internal membranes) The membranes of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane).  Peroxisomes are small, single membrane-bound vesicle containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2) Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell. The enzymes in peroxisomes break down hydrogen peroxide to water and oxygen. § Peroxisomes in the liver detoxify alcohol and other harmful compounds by transferring hydrogen from the poisons to oxygen.  Mitochondria Singular: ‘mitochondrion’ Pair of membranes double-membrane organelle, enclosing two fluid smooth outer membrane and compartments: folded inner membrane the intermembrane (cristae) found in almost all compartment living cells between the outer and inner membrane matrix within the inner membrane  Mitochondria Abundant in liver cells Also contain ribosomes Have their own DNA (capable of self-replication). Functions: – Site of cellular aerobic respiration (convert energy stored in sugar to ATP) – major site of ATP synthesis – “powerhouse of the cell” – found in large number of metabolically active cells  Cytoskeleton network of protein fibers that support the cell, hold organelles in place, and enable the cell to change to shape Functions: – Cell support – Cell shape – Cell and organelle motility (movement) – Cell division  Types of cytoskeleton 1.thin microfilaments- small fibrils formed from protein subunits – Cell shape – Cell motility (movement) – Cell division 2.medium-sized intermediate filaments- provide mechanical support to the cell and maintenance of cell shape 3.thick microtubules- hollow structures formed from protein subunits – Cell shape – Cell motility (movement) – Chromosome movements in cell division – Organelle movements – Forming essential components of certain organelles, such as cilia and flagella (in animal cells) Structures Present in Animal Cell but not in plant cell Lysosomes – Central vacuole in plants Centrosomes and Centrioles Flagella Cilia  Lysosomes membrane-enclosed vesicles formed from Golgi apparatus containing numerous digestive enzymes – Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing. At least some lysosomes probably arise by budding from the trans face of the Golgi apparatus. Main function: Intracellular digestion – Lysosomes contain digetsive enzymes called hydrolases, which catalyse the digestion of proteins, nucleic acids, some carbohydrates and fats into their component subunits – Digest food particles, which range from individual proteins to complete microorganisms Also digest excess cellular membranes and defective and malfunctioning organelles – Serve as the cell’s digestive system and known as the “suicide bags” Vesicles formed by endocytosis may fuse with lysosomes. The enzymes within the lysosomes break down the materials in the endocytotic vesicle. Lysosomes digest food in a process known as phagocytosis or cell eating. Lysosomes also use their hydrolytic enzymes to recycle the cell's own organic material, a process called autophagy. Phagocytic white blood cell (macrophage) is best for studying lysosomes.  Note: About lysosomes Lysosomal enzymes work best in the acidic environment found in lysosomes. If a lysosome breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a neutral pH. However, excessive leakage from a large number of lysosomes can destroy a cell by autodigestion.  Centrosomes a region that is often located near the nucleus Function: – “microtubule-organizing center” in animal cells Where microtubules grow out from Within the centrosome are a pair of centrioles  Centrioles short barrel-shaped ring consisting of nine microtubule triplets, with no microtubules in the center (9+0 arrangement). Functions: – Cell division – move to the plasma membrane and provides a center for the formation of cilia or flagella (formation of basal body) Before an animal cell divides, the centrioles replicate. Although centrosomes with centrioles may help organize microtubule assembly in animal cells, they are not essential for this function in all eukaryotes; yeast cells and plant cells lack centrosomes with centrioles but have well-organized microtubules.  Cilia and flagella Singular- cilium; flagellum slender extensions of the plasma membrane consists of microtubules arising from the basal body Each cilium and flagellum contain microtubules arranged in an outer ring of nine fused pairs of microtubules surrounding a central unfused pair (9+2 arrangement). Function: for locomotion (movement)  Difference between cilia and flagella Cilia Flagella Length Shorter Longer Number on cell surface Numerous usually limited to just one or a few per cell Beating patterns Alternating power and Undulating motion that recovery strokes generates force in generating force in a the same direction as the direction perpendicular flagellum's axis. to the cilium’s axis, much as the oars of a crew boat extend outward at right angles to the boat's forward movement. Beating patterns and direction of movement of cilia and flagella Transport Across the Plasma Membrane Types of Transport Mechanism PASSIVE TRANSPORT ACTIVE PROCESSES § Simple diffusion § Active transport § Transport in vesicles (Bulk § Facilitated diffusion Transport) § Osmosis § Endocytosis § Phagocytosis § Pinocytosis § Exocytosis  Passive transport § A substance moves down its concentration or electrical gradient (from higher concentration to lower concentration) to cross the membrane using only its own kinetic energy (energy of motion). § Kinetic energy is intrinsic to the particles that are moving. Requires NO expenditure of energy EXAMPLES OF PASSIVE TRANSPORT  The Principle of Diffusion § Diffusion is a passive process in which the random mixing of particles in a solution occurs because of the particles’ kinetic energy. § Both the solutes and the solvent undergo diffusion. § They move down their concentration gradient  Simple diffusion § Movement of solute molecules from an area of higher concentration to an area of a lower concentration of that solute in solution § results from the constant random motion of all solutes in a solution § A passive process in which substances move freely through the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins  Diffusion within a liquid Solutes diffuse faster in hot water.  Brownian Motion § The constant movement of all particles of matter § Discovered by Scotish scientist Robert Brown § Brownian motion drives passive transport process (diffusion) Diffusion through a membrane The cornstarch solution turned purple-black in color Iodine diffuses from the outside (greater concentration) to the inside (lesser concentration)  Diffusion through a membrane The color change indicates that the iodine reacts with starch Starch molecules did not pass through the membrane because of their large size. The cellophane serves as semipermeable membrane  Simple diffusion § Nonpolar, hydrophobic § Small, uncharged polar molecules molecules such as: § Such molecules include: § water, § oxygen, § urea § carbon dioxide § small alcohols § and nitrogen gases § fatty acids § steroids § fat-soluble vitamins (A, D, E, and K)  Factors affecting diffusion § Steepness of the concentration gradient. § The greater the difference in concentration between the two sides of the membrane, the higher is the rate of diffusion § Temperature. § The higher the temperature, the faster the rate of diffusion § Mass of the diffusing substance. § The larger the mass of the diffusing particle, the slower its diffusion rate  Factors affecting diffusion § Surface area. § The larger the membrane surface area available for diffusion, the faster is the diffusion rate § Diffusion distance. § The greater the distance over which diffusion must occur, the longer it takes  Osmosis § A type of diffusion in which there is net movement of a solvent through a selectively permeable membrane. § In living systems, the solvent is water, which moves by osmosis across plasma membranes from an area of higher water Water moves through a selectively concentration to an area permeable membrane from an area of of lower water lower solute concentration to an area concentration of higher solute concentration  Requirements: Osmosis Osmosis occurs only when: 1. Difference in concentration of water between two sides of the membrane 2. A membrane is permeable to water NOT permeable to certain solutes  Tonicity § A measure of the solution’s ability to change the volume of cells by altering their water content. § Three types of solution § Isotonic solution § Hypotonic solution § Hypertonic solution  Isotonic solution § “having the same strength” § Solution whose concentration of water and solute inside the cell (intracellular fluid) is THE SAME as the concentration outside the cell (extracellular fluid) § Example: 0.9% NaCl (normal physiologic saline solution)  Hypotonic solution § “having lesser strength” § Solution that has a LOWER concentration of solute and higher concentration of water than does a cell cytoplasm § It will cause water to enter the cell, and thus the cell will swell or even burst (lysis) § Example: pure water  Hypertonic solution § “having greater strength” § Solution that has a HIGHER concentration of solute and a lower concentration of water than does a cell cytoplasm § It will cause water to leave the cell will shrink or crenate (crenation) § Example: 2% NaCl solution  2.Active transport uses CELLULAR ENERGY to move molecules across the plasma membrane, often “uphill”AGAINST a concentration gradient (from lower concentration to higher concentration gradient) Example: Na+K+ pump  2.Active transport also a carrier-mediated processàuses active transport-proteins which span the width of the membrane and have two active sites:  3.Bulk transport particles are transported in large amounts or in bulk without actually passing or crossing the membrane Uses cellular energy Examples: endocytosis and exocytosis  Endocytosis particles are transported in large amounts or in bulk “into the cell” uptake of material through the cell membrane by formation of vesicle the cell membrane invaginates to form a vesicle containing the material to be taken by the cell. The vesicle then moves into the cytoplasm Three types: Ø Pinocytosis Ø Receptor-mediated endocytosis Ø Phagocytosis  Three types of Endocytosis Pinocytosis (“cell-drinking”) – the particle to be engulfed is in liquid form or a droplet of extracellular fluid Receptor-mediated endocytosis – selectively concentrate specific molecules inside a cell – Plasma membranes bear many receptor proteins on their outside surfaces, each with a binding site for a particular molecule – Example: cholesterol and growth factors Phagocytosis (“cell-eating”) – the particle to be engulfed is in solid form or chunks of matter. – Example: WBC and some other cell types phagocytize bacteria, cell debris, and foreign particles  Exocytosis particles are transported in large amounts or in bulk “out of the cell” A membrane-enclosed vesicle carrying material to be expelled moves to the cell surface, where the vesicle’s membrane fuses with the cell’s plasma membrane. The vesicle then opens to the extracellular fluid, and its contents diffuse out used to dispose of unwanted materials such as products of digestion  Transport Needs carrier Movement Requires energy? Mechanism molecule? Simple Diffusion Higher to lower concentration of No No solute Osmosis Higher to lower concentration of No No water (solvent) Facilitated Higher to lower diffusion concentration of Yes No molecules Active transport Lower to higher concentration of Yes Yes substance Endocytosis “into the cell” No Yes Exocytosis “out of the cell” No Yes  Summary Types of Transport Mechanisms across plasma membrane Carrier-mediated transport 1. Passive Transport Facilitated diffusion Diffusion Active transport Osmosis Facilitated Diffusion Energy-requiring transport 2. Active Transport Active transport Bulk transport 3. Bulk Transport Endocytosis Exocytosis