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Bio 111 Fall 2010 Unit 2 - Unit 2 Unit 2 Bio 111 All Cells...

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Unformatted text preview: Unit 2 Unit 2 Bio 111 All Cells Share Common All Cells Share Common Features A plasma membrane encloses all cells and regulates material flow Cytoplasm is the fluid interior where a cell’s metabolic reactions occur Contains organelles Fluid portion (cytosol) contains water, salts, and organic molecules 2 All Cells Share Common All Cells Share Common Features All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint All cells use RNA (ribonucleic acid) to copy DNA to make protein All cells obtain energy and nutrients from the environment All cells use common building blocks to build the molecules of life 3 Prokaryotic Cells Prokaryotic Cells A stiff cell wall is usually present Some bacteria are propelled by flagella Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces Pili and fimbriae are protein projections in some bacteria that further 4 enhance adhesion Prokaryotic Cells Prokaryotic Cells Can take the shape of rods, spheres, or helices Single, circular chromosome of DNA Chromosome found coiled in an area called the nucleoid Small rings of DNA (plasmids) located in the cytoplasm 5 Prokaryotic Cells Prokaryotic Cells No nuclear membrane or membrane­bound organelles present Some have internal membranes used to capture light Cytoplasm may contain food granules 6 Prokaryotic Cell Prokaryotic Cell 7 Major Features Major Features Eukaryotic cells are > 10 µm long A variety of membrane­ enclosed organelles perform specific functions The cytoskeleton provides shape and organization 8 Major Features Major Features Animal and plant cells differ with regards to cell walls chloroplasts plastids central vacuoles centrioles 9 Cell Walls Cell Walls Stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists are cell walls Cells walls support and protect fragile cells and are usually porous Cell walls are composed of polysaccharides like cellulose (plants) or chitin (fungi) 10 The Cytoskeleton The Cytoskeleton Cytoskeleton forms a network of protein fibers within the cytoplasm Composed of microfilaments, intermediate filaments, and microtubules 11 The Cytoskeleton The Cytoskeleton 12 Cilia and Flagella Cilia and Flagella Cilia and flagella are extensions of the plasma membrane Cilia and flagella are composed of microtubules Cilia are short and numerous while flagella are long but few in any cell 13 Cilia and Flagella Cilia and Flagella Functions Cilia or flagella may be used to move cell about Cilia may be used to create currents of moving fluid in their environment 14 The Nucleus The Nucleus The nucleus is an organelle that contains three major parts Nuclear envelope Chromatin Nucleolus 15 The Nucleus The Nucleus The nuclear envelope separates chromosomes from cytoplasm Envelope is a double membrane with nuclear pores for transport Outer membrane is studded with ribosomes 16 The Nucleus The Nucleus The nucleus contains DNA in various configurations Compacted chromosomes (during cell division) Diffuse chromatin (as DNA directs reactions through an RNA intermediate by coding for proteins) 17 The Nucleus The Nucleus Darker area within the nucleus called the nucleolus Functions as the site of ribosome synthesis Ribosomes synthesize proteins 18 19 System of Membranes System of Membranes Membrane system includes the plasma membrane and organelle membranes Plasma membrane isolates cell and allows for regulation of transport Vesicles are membranous sacs that transport substances among the separate regions of the membrane system 20 System of Membranes System of Membranes Endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell There are two forms of ER Smooth ER Rough ER 21 System of Membranes System of Membranes Smooth ER has no ribosomes Contains enzymes that detoxify drugs (in liver cells) or synthesizes lipids Rough ER is studded with ribosomes on outside Produces proteins and phospholipids destined for other membranes or for secretion (export) 22 Rough vs Smooth ER Rough vs Smooth ER 23 System of Membranes System of Membranes Golgi Apparatus is a set of stacked flattened sacs Receives proteins from ER (via transport vesicles) and sorts them by destination Modifies some molecules (e.g. proteins to glycoproteins) Packages material into vesicles for transport 24 25 System of Membranes System of Membranes Three fates of substances made in the membrane system: 1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane 26 System of Membranes System of Membranes 1. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell Lysosomes fuse with food vacuoles and digest food into basic nutrients 27 System of Membranes System of Membranes 1. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes 28 Vacuoles Serve Many Functions Vacuoles Serve Many Functions Fluid­filled sacs with a single membrane Functions of vacuoles Contractile vacuoles in freshwater organisms used to collect and pump water out 29 Vacuoles Serve Many Functions Vacuoles Serve Many Functions Functions of vacuoles Plant central vacuoles used in several ways Maintain water balance Store hazardous wastes, nutrients, or pigments Provide turgor pressure on cytoplasm to keep cells rigid 30 Mitochondria Extract Food Mitochondria Extract Food Energy Mitochondria are round, oval, or tubular sacs of double­membranes Inner membrane is folded into cristae Intermembrane compartment lies between inner and outer membranes Matrix space within inner membrane 31 32 Mitochondria Extract Food Mitochondria Extract Food Energy Function as the “powerhouses of the cell” Mitochondria extract energy from food molecules Extracted energy is stored in high­energy bonds of ATP Energy extraction process involves anaerobic and aerobic reactions 33 Chloroplasts Chloroplasts Chloroplasts are specialized organelles surrounded by a double membrane Outer membrane Inner membrane encloses the stroma space Stacked hollow membranous sacs (grana) within stroma are called thylakoids 34 35 Chloroplasts Chloroplasts The thylakoid membranes contain chlorophyll and other pigments that capture sunlight and make sugar, CO2, and water (photosynthesis) 36 Plants Use Plastids for Storage Plants Use Plastids for Storage Plastids found only in plants and photosynthetic protists Surrounded by a double membrane Functions Storage for photosynthetic products like starch Storage of pigment molecules giving color to ripe fruit 37 38 Plasma Membrane Plasma Membrane Functions of the plasma membrane Isolates the cell’s contents from environment Regulates exchange of essential substances Communicates with other cells Creates attachments within and between other cells Regulates biochemical reactions 39 Membranes Are “Fluid Membranes Are “Fluid Mosaics” “Fluid mosaic” model of a membrane proposed in 1972 A lumpy, constantly shifting mosaic of “tiles” or proteins Proteins float around in a sea of phospholipids 40 The Phospholipid Bilayer The Phospholipid Bilayer Phospholipids are the basis of membrane structure Polar, hydrophilic head Two non­polar, hydrophobic tails 41 The Phospholipid Bilayer The Phospholipid Bilayer The cell exterior and interior face watery environments Hydrophobic and hydrophilic interactions drive phospholipids into bilayers Double row of phospholipids Polar heads face outward and inward Non­polar tails mingle within the membrane 42 Membrane Proteins Form a Membrane Proteins Form a Mosaic Proteins are embedded in the phospholipid bilayer Some proteins can float and drift Other proteins are anchored by protein filaments in the cytoplasm Many proteins have attached carbohydrates (glycoproteins) 43 Membrane Proteins Form a Membrane Proteins Form a Mosaic Receptor Proteins Trigger cellular responses upon binding specific molecules, e.g. hormones Recognition Proteins Serve as identification tags on the surface of a cell 44 Membrane Proteins Form a Membrane Proteins Form a Mosaic Enzymes Promote chemical reactions that synthesize or break apart biological molecules Attachment Proteins Anchor the cell membrane to inner cytoskeleton, to proteins outside the cell, and to other cells 45 Membrane Proteins Form a Membrane Proteins Form a Mosaic Transport Proteins Include channel and carrier proteins Regulate import/export of hydrophilic molecules 46 47 Movement Across Membranes Movement Across Membranes Concentration gradients of ions and molecules exist across the plasma membranes of all cells There are two types of movement across the plasma membrane Passive transport Energy­requiring transport 48 Movement Across Membranes Movement Across Membranes Passive transport Substances move down their concentration gradients across a membrane No energy is expended Membrane proteins and phospholipids may limit which molecules can cross, but not the direction of movement 49 Passive Transport Passive Transport Simple Diffusion Lipid soluble molecules (e.g. vitamins A and E, gases) and very small molecules diffuse directly across the phospsholipid bilayer 50 Passive Transport Passive Transport Facilitated Diffusion Water soluble molecules like ions, amino acids, and sugars diffuse with the aid of channel and carrier transport proteins 51 Passive Transport Passive Transport Osmosis – the special case of water diffusion Water diffuses from high concentration to low concentration across a membrane Dissolved substances reduce the concentration of free water molecules in a solution 52 Passive Transport Passive Transport The flow of water across a membrane depends on the concentration of water in the internal or external solutions 53 Passive Transport Passive Transport Isotonic solutions have equal concentrations of water and equal concentrations of dissolved substances No net water movement occurs across the membrane 54 Passive Transport Passive Transport A hypertonic solution isone with lower water concentration or higher dissolved particle concentration Water moves across a membrane towards the hypertonic solution 55 Passive Transport Passive Transport A hypotonic solution is one with higher water concentration or lower dissolved particle concentration Water moves across a membrane away from the hypotonic solution 56 Active Transport Active Transport Cells need to move some substances against their concentration gradients Active Transport: membrane proteins move molecules across using ATP Proteins span the entire membrane Often have a molecule binding site and an ATP binding site Often referred to as pumps 57 Endocytosis Endocytosis Cells import large particles or substances via endocytosis Plasma membrane pinches off to form a vesicle in endocytosis Types of endocytosis Pinocytosis Receptor­mediated endocytosis Phagocytosis 58 Endocytosis Endocytosis Types of endocytosis Pinocytosis (“cell drinking”) brings in droplet of extracellular fluid 59 Endocytosis Endocytosis Types of endocytosis Receptor­mediated endocytosis moves specific molecules into the cell 60 Endocytosis Endocytosis Types of endocytosis Phagocytosis (“cell eating”) moves large particles or whole organisms into the cell 61 Exocytosis Exocytosis Exocytosis Vesicles join the membrane, dumping out contents in exocytosis 62 Desomosomes Desomosomes Desmosomes attach cells together Found where cells need to adhere tightly together under the stresses of movement (e.g. the skin) Tight Junctions Tight Junctions Tight junctions make the cell leakproof Found where tubes and sacs must hold contents without leaking (e.g. the urinary bladder) Gap Junctions and Gap Junctions and Plasmodesmata Allow for communication Cell­to­cell channels allowing for passage of hormones, nutrients, and ions in animal cells are gap junctions Plant cells have cytoplasmic connections called plasmodesmata What Is Energy? What Is Energy? Energy is the capacity to do work The two fundamental types of Energy Kinetic energy is the energy of movement e.g. light, heat, electricity, moving objects Potential energy is stored energy e.g. chemical energy in bonds, electrical charge in a battery, a rock at the top of a hill 66 The Laws of Thermodynamics The Laws of Thermodynamics First Law of Thermodynamics Energy can neither be created nor destroyed The total amount of energy within a given system remains constant unless energy is added or removed from the system 67 The Laws of Thermodynamics The Laws of Thermodynamics Second Law of Thermodynamics The amount of useful energy decreases when energy is converted from one form to Entropy (disorder) increases 68 69 Chemical Reactions Chemical Reactions Chemical reactions are processes that form or break chemical bonds between atoms Chemical reactions convert reactants to products Reactants Products 70 Exergonic Reactions Exergonic Reactions Exergonic reactions release energy Reactants contain more energy than products in exergonic reactions 71 Exergonic Reactions Exergonic Reactions Exergonic reaction example: the burning of glucose 72 Exergonic Reactions Exergonic Reactions All chemical reactions require an initial energy input (activation energy) to get started Molecules need to be moving with sufficient collision speed The electrons of an atom repel other atoms and inhibit bond formation 73 Endergonic Reactions Endergonic Reactions Endergonic reactions require an input of energy Products contain more energy than reactants in endergonic reactions 74 Endergonic Reactions Endergonic Reactions Endergonic reaction example: photosynthesis 75 Energy Carrier Molecules Energy Carrier Molecules Food energy cannot be used directly to power energy­requiring reactions Adenosine triphosphate (ATP) is the most common energy carrying molecule 76 ATP ATP Energy is stored in the high­energy bond extending to the last phosphate Heat is given off when ATP breaks into ADP and P The energy released when ATP is broken down into ADP + P is transferred to endergonic reactions to help the cell do work 77 78 Metabolic Reactions Metabolic Reactions Enzyme molecules are employed to catalyze (speed up) chemical reactions in cells Catalysts speed up the rate of a chemical reaction without themselves being used up 79 Catalysts Reduce Activation Catalysts Reduce Activation Energy Catalysts speed up spontaneous reactions by reducing activation energy 80 Enzymes Are Biological Enzymes Are Biological Catalysts Enzymes orient, distort, and reconfigure molecules in the process of lowering activation energy Enzymes (proteins) differ from non­biological catalysts because: 1. 2. 3. Enzymes are very specific for the molecules they catalyze Enzyme activity is often enhanced or suppressed by their reactants or products Some enzymes require helper coenzyme molecules to function (e.g. certain B vitamins) 81 Enzyme Structure Enzyme Structure Enzymes have a pocket called an active site Reactants (substrates) bind to the active site Distinctive shape of active site is complementary and specific to the substrate Active site amino acids bind to the substrate and distort bonds to facilitate a reaction 82 Enzyme Structure Enzyme Structure Three steps of enzyme catalysis 1. Substrates enter the active site in a specific orientation 1. Upon binding, the substrates and enzyme change shape to promote a reaction 1. Products of the reaction leave the active site, leaving the enzyme ready for another catalysis 83 84 Cells Regulate Metabolism Cells Regulate Metabolism A given enzyme usually catalyzes a single step in a chain of metabolic reactions 85 Cells Regulate Metabolism Cells Regulate Metabolism Metabolic pathways are controlled in several ways 1. Control of enzyme synthesis regulates availability 1. Some enzymes are inactive when synthesized and must be “turned on” to be active 1. Small organic molecules can bind to enzymes and enhance/inhibit activity (allosteric regulation) 86 87 Cells Regulate Metabolism Cells Regulate Metabolism Adequate amounts of formed product inhibit enzyme activity (feedback inhibition) 88 Drugs and Poisons Drugs and Poisons Drugs and poisons often inhibit enzymes by competing with the natural substrate for the active site This process is known as competitive inhibition Some inhibitors bind permanently to the enzyme 89 Environmental Conditions Environmental Conditions Three­dimensional structure of an enzyme is sensitive to the environment Enzyme structure is distorted and function is destroyed when pH is too high or low Salts in an enzyme’s environment can also destroy function by altering structure Temperature also affects enzyme activity Low temperatures slow down molecular movement High temperatures cause enzyme shape to be altered, destroying function 90 Environmental Conditions Environmental Conditions Most enzymes function optimally only within a very narrow range of these conditions 91 92 ...
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