CHAPTER 3 The Cell Chapter 3 Learning Objectives Compare and contrast the features of prokaryotic and eukaryotic cells. Explain why surface area-to-volume ratios constrain cell size. Contrast light microscopy with electron microscopy. Label the features of a plasma membrane, and describe the function of each component. Explain the functions of the plasma membrane. Compare movement of materials across the plasma membrane by simple diffusion, facilitated diffusion, osmosis, and active transport. Explain the differences between hypertonic, hypotonic, and isotonic solutions, and predict the movement of water in or out of a cell in each case. Describe the function and structural features of each of the following organelles: nucleus, endoplasmic reticulum, Golgi complex, lysosomes, and mitochondria. Compare and contrast the structure and function of the three fibers that compose the cytoskeleton. Explain how the food we eat is converted into cellular energy as ATP. Describe the role of ATP as the energy currency of the cell. Describe the four phases of cellular respiration, indicating the reactants and products of each phase. Explain how the electron transport chain generates such a large quantity of ATP. Describe the products of fermentation. Cell Theory 1. A cell is the smallest unit of life 2. Cells make up all living things, from unicellular to multicellular organisms 3. New cells can arise only from preexisting cells Typical Bacteria Cell Feature Prokaryotic Cells Eukaryotic Cells Organisms Bacteria, archaea Plants, animals, fungi, and protists Size 1-10 µm across 10-100 µm across Membrane-bound organelles Absent Present DNA form Circular Coiled, linear strands DNA location Cytoplasm Nucleus Internal membranes Rare Many Cytoskeleton Present Present Eukaryotic Cells: Plant vs Animal Surface-to-volume ratio Most cells are limited in size What about a chicken egg? As a cell gets larger, its surface increase increases much more slowly than its volume 1
Microscopes are required to visualize cells Types of microscopes Light microscopes- compound light microscopes Can resolve structures 200 nm apart Electron microscopes Can resolve structures 0.2 nm apart 2 types SEM (scanning electron microscope) Forms 3-D images by beaming electrons onto the surface of the specimen TEM (transmission electron microscope) Also uses a beam of electrons that are transmitted through an ultra thin specimen, interacting with the specimen as it passes through it The use of stains aids in viewing cell structure Plasma membrane functions Imposes boundary and maintains structural integrity Regulates movement of substances into and out of cell Selectively permeable Cell-cell recognition Communication between cells Binding pairs or groups of cells together to form tissues and organs Cell adhesion molecules (CAMs) Fluid Mosaic Model- PM made up of lipids, proteins, and carbohydrates Passive Transport Simple diffusion: random movement of a substance from a region of higher concentration to a region of lower concentration Concentration: number of molecules of substance in particular volume Concentration gradient: difference in relative number of molecules or ions in two adjacent areas Facilitated diffusion: movement of substance from a region of higher concentration to lower concentration with the aid of a membrane protein Example: Movement of glucose by carrier protein or oxygen by hemoglobin Osmosis: type of diffusion that moves water across a plasma membrane from high water concentration to low water concentration Examples of Passive Transport How solute concentration is maintained inside cells Hypertonic: solute concentration is higher Hypotonic: solute concentration is lower Isotonic: equal solute and solvent concentration 2
Active Transport Na+ K+ pump 3 Na+ ions pumped out of the cell and 2 K+ ions pumped into the cell Endocytosis Movement of large molecules into the cell Phagocytosis Pinocytosis Receptor mediated endocytosis Exocytosis Movement of large molecules out of the cell Sodium-potassium pump 3 types of endocytosis Exocytosis Nucleus Endoplasmic Reticulum Contains most of the cell s genetic information Nuclear envelope Nuclear pores Chromosomes Nucleolus Rough Attached ribosomes Modifies proteins made by ribosomes Smooth Lacks ribosomes Stores Ca+ Detoxification Produces lipids 3
Golgi Complex Series of interconnected, flattened membrane like sacs Cell s protein processing and packaging center Lysosomes Site of intracellular digestion Roughly spherical organelles consisting of single membrane with about 40 different digestive enzymes Tay-Sachs caused by absence of the lysosomal enzyme HEX A which breaks down lipids in nerve cells Capable of digesting old organelles, macromolecules, and foreign matter Mitochondria Site of cellular respiration Most cells contain several 100 to 1000 of mitochondria Inner folds called cristae Contain ribosomes and DNA Environmental Issue: Deadly interaction between asbestos and lysosomes Asbestos is a fibrous, silicate material found in nature Very strong, flexible, and resistant to heat and corrosion Used widely in construction Can be inhaled by lungs, remain in lungs for life Causes lung cancer and mesothelioma Asbestosis- dangerous interaction between asbestos and lysosomes Lysosomes can t break down particles and release enzymes into respiratory tract No effective treatment Mainly Prevention Question 1: Cigarette smoking worsens disease caused by exposure to asbestos. If a worker who smokes is exposed over many years to asbestos in the workplace and subsequently develops lung cancer, when who is responsible for his developing cancer? Is the employer responsible, or does the worker bear some personal responsibility? Question 2: What information would you consider when assessing responsibility? Cytoskeleton Microtubules-thickest Straight hollow rods made up of the protein tubulin Centrioles-microtubule organization center involved in cell division Cilia and flagella Microfilaments or actin: thinnest Solid rods of the protein actin Muscle contraction Intermediate: diverse group in between Cellular Respiration Metabolism- all chemical reactions that take place in a cell Catabolic pathways: complex molecules broken down Anabolic pathways: build complex molecules from simpler ones Oxygen-requiring pathway by which cells break down glucose 4 phase Glycolysis Transition Reaction Citric Acid Cycle Electron Transport Chain 4
Phase Location Description Start Material Main Products Net ATP Glycolysis Cytoplasm Several-step process by which glucose is split into 2 pyruvate Transition Reaction Citric Acid Cycle ETC Mt Mt matrix Mt inner membrane Glucose 2 pyruvate 2 NADH One CO2 is removed from each pyruvate, the resulting molecule binds to CoA, forming 2 acetyl CoA 2 pyruvate 2 acetyl CoA 2 NADH Cyclic series of 8 chemical reactions by which acetyl CoA is broken down Electrons from NADH and FADH 2 are passed from 2 acetyl CoA 2 FADH 2 6 NADH 10 NADH 2 FADH2 H 20 2 0 2 ATP 32 ATP 26 27 28 Fermentation Breakdown of glucose without oxygen Begins with glycolysis Ends with 2 ATP molecules Lactic acid fermentation occurs in the human body in muscles Strenuous exercise causes oxygen to run low Use lactic acid fermentation to produce ATP Muscle pain is caused by an accumulation of lactic acid Disappears as lactic acid moves into bloodstream where it is converted to pyruvate Mitochondrial disease 40 illnesses Results in less energy, cell function compromised, and cell death 1000 to 4000 babies born with mt diseases Fatigue and failure to gain weight Brain: seizures, developmental delays, and dementia Sensory organs: decline or complete loss of vision or hearing Skeletal muscle: muscle weakness, cramps, and exercise intolerance No known cures, alleviating symptoms and slowing progression Question 1: A woman had an inherited, adult-onset mitochondrial disease that was diagnosed only after she had two sons and a daughter. Her symptoms are relatively mild, and her disease has been traced to a mutation in her mt DNA. Which, if any, of her children will inherit the mutation? Question 2: What factors determine the extent of symptoms in any afflicted child? If all of her children reach adulthood and have families of their own, which of her children will pass on the mutation? 5