Chapter 3: Cells Learning Objectives Describe what a cell is and the two general types of cells. Describe the structure and functions of cell membranes. Describe several ways in which molecules move across membranes. Describe how cells are connected and how they communicate with each other. Describe nine important landmarks in eukaryotic cells. Cell Theory 1. All living organisms are made up of one or more cells. 2. All cells arise from other pre-existing cells. The cell: The smallest unit of life that can function independently and perform all the necessary functions of life, including reproducing itself. Cells Robert Hooke, a British scientist, mid-1600s A cell is a three-dimensional structure, like a fluid-filled balloon, in which many of the essential chemical reactions of life take place. Nearly all cells contain DNA (deoxyribonucleic acid). Prokaryotic cells are structurally simple, but there are many types of them. Every cell falls into one of two basic categories: 1. A eukaryotic cell has a central control structure called a nucleus, which contains the cell s DNA. eukaryotes 2. A prokaryotic cell does not have a nucleus; its DNA simply resides in the middle of the cell. prokaryotes 1
Eukaryotic cells have compartments with specialized functions: organelles Which feature below is not found in a prokaryote? 1. Plasma membrane 2. Nucleus 3. Ribosomes 4. Cell wall 5. Flagellum Endosymbiosis Theory Developed to explain the presence of two organelles in eukaryotes, chloroplasts in plants and algae, and mitochondria in plants and animals. Humans may be part bacteria Which answer below supports the theory that mitochondria and chloroplasts were originally bacteria? 1. Circular DNA is present in both organelles. 2. Both organelles are larger than other organelles in the cell. 3. Both organelles are surrounded by a single lipid bilayer. 4. All of the above. 2
Every cell is bordered by a plasma membrane. Plasma membranes are complex structures? They perform critical functions take in food and nutrients dispose of waste products build and export molecules regulate heat exchange regulate flow of materials into and out of cell Molecules embedded within the plasma membrane help it perform its functions. Which arrow indicates a protein or part of a protein that is hydrophobic? There are four primary types of membrane proteins, each of which performs a different function. 1. Arrow A 2. Arrow B 3. Arrow C 4. Arrow D A B C D 3
The Plasma Membrane Fluid Mosaic In addition to proteins, two other molecules are found in the plasma membrane: 1. Short, branched carbohydrate chains 2. Cholesterol Lipids that make up the cell membrane are hydrophobic. Hydrophilic molecules, like glucose, cannot cross this barrier. What major component of the plasma membrane helps glucose get into and out of the cell? 1. Phospholipids 2. Carbohydrates 3. Nucleic acids 4. Proteins 5. Fatty acids Which protein found on the plasma membrane likely contributes to rejection of a transplanted organ or tissue? 1. Receptor proteins 2. Recognition proteins 3. Transport proteins 4. Enzymatic proteins Membrane surfaces have a fingerprint that identifies the cell. Cells with an improper fingerprint are recognized as foreign and are attacked by your body s defenses. Molecules move across membranes in several ways. Passive transport is the spontaneous diffusion of molecules across a membrane. There are two types of passive transport: 1. Diffusion 2. Osmosis 4
Diffusion and Concentration Gradients Solutes Solvents Facilitated Diffusion Most molecules can t get through plasma membranes on their own. Molecules move down their concentration gradient Carrier molecules transport proteins Summary In passive transport which includes simple and facilitated diffusion and osmosis the molecular movement occurs spontaneously, without the input of energy. Osmosis is the passive diffusion of water across a membrane. This occurs as molecules move down their concentration gradient. Cells in Solution Tonicity the relative concentration of solutes outside of the cell relative to inside the cell Hypertonic Hypotonic Isotonic 5
The Direction of Osmosis Determined only by a difference in total concentration of all the molecules dissolved in the water It does not matter what solutes they are. How do laxatives relieve constipation? Milk of magnesia and magnesium salts Water moves via osmosis from the cells into the intestines. An amoeba (a single-celled protist) is placed in a solution. The volume of the cell increases (cell swells). Which statement below is the correct interpretation of this result? 1. The amoeba is in a hypertonic solution. 2. Water is moving into the amoeba. 3. The amoeba is in a isotonic solution. 4. Water is moving out of the amoeba. In active transport, cells use energy to move small molecules. Primary active transport: uses energy directly from ATP Two distinct types of active transport: 1. Primary 2. Secondary Secondary Active Transport The transport protein simultaneously moves one molecule against its concentration gradient while letting another flow down its concentration gradient. No ATP is used directly. At some point energy from ATP was used to pump one of the types of molecules involved against their concentration gradient. A normal cell has a high concentration of potassium on the inside and a low concentration of potassium on the outside. Also, a normal cell has a low concentration of sodium on the inside and a high concentration on the outside. Yet, the net movement of potassium is into the cell and the net movement of sodium is out of the cell. What type of transport is involved? 1. Osmosis 2. Facilitated transport 3. Active transport 4. Simple diffusion 5. Secondary active transport 6
An intestinal epithelial cell powers the movement of glucose into the cell against its concentration gradient by simultaneously transporting sodium down its concentration gradient. Which transport mechanism is responsible? 1. Osmosis 2. Facilitated transport 3. Active transport 4. Simple diffusion 5. Secondary active transport Endocytosis and exocytosis are used for bulk transport of particles. Three types of endocytosis: 1. Phagocytosis Cell Eating 2. Pinocytosis Cell drinking 3. Receptor-mediated endocytosis Lots of small particles When a woman nurses her baby, proteins are released from the mammary cells, accumulate in the ducts of the breast, and flow out of the nipple. Which process listed below is involved? 1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis 4. Exocytosis 7
Connections between cells hold them in place and allow communication with each other Tight Junctions form continuous, water-tight seals around cells and also anchor cells in place particularly important in the small intestine where digestion occurs Desmosomes are like spot welds or rivets that fasten cells together into strong sheets Gap Junctions pores surrounded by special proteins that form open channels between two cells function like Velcro : they hold cells together but are not water-tight found in much of the tissue-lining cavities of animal bodies Gap junctions are an important mechanism for cell-to-cell communication. Your skin cells form a waterproof barrier, therefore they are held together by 1. Tight junctions 2. Desmosomes 3. Gap junctions 4. Glue Plasmodesmata Tube-like channels connecting the cells to each other and enabling communication and transport between them Consider a plant as one big cell? 8
Nine important landmarks distinguish eukaryotic cells. The nucleus is the cell s genetic control center. The nucleus the largest and most prominent organelle in most eukaryotic cells. The nucleus has two primary functions: genetic control center storehouse for hereditary information Chromatin - a mass of long, thin fibers consisting of DNA & proteins Nucleolus an area near the center of the nucleus where subunits of the ribosomes are assembled Cytoskeleton: Three Chief Purposes Shape (support), intracellular movement, and cell Movement Ribosomes are factories for proteins. Cilia and Flagellum Which type of cytoskeletal protein is involved in the tail movement of a swimming human sperm (flagella)? 1. Microtubules 2. Intermediate filaments 3. Microfilaments 9
Mitochondria: the cell s energy converters Bag-within-a-Bag Structure: the intermembrane space and the matrix Endosymbiosis Mitochondria may have existed as separate single-celled, bacteria like organisms billions of years ago. Mitochondria have their own DNA! Lysosomes are the cell s garbage collectors Round, membrane-enclosed, acid-filled vesicles Digestive system of the cell Why is Tay-Sachs (Genetic disorder) disease like a strike by trash collectors? 50 different enzymes necessary for lysosomes to function well Malfunctions sometimes occur Lipid-digesting enzyme made incorrectly Lipid buildup in cells The Endomembrane System Rough Endoplasmic Reticulum Where cells build proteins and disarm toxins 10
The Smooth Endoplasmic Reticulum Critical Responsibilities of the Smooth ER Another critical responsibility of the smooth ER particularly the smooth ER in human liver cells is to help protect us from dangerous molecules that get into our bodies. Alcohol, antibiotics, barbiturates, amphetamines, and other stimulants, along with toxic metabolic waste products produced in our bodies, are made less harmful by detoxifying enzymes in the smooth ER Which organ below is likely composed of cells with the greatest amount of SER? The Golgi apparatus processes products and ships them throughout the body. 1. Heart 2. Lungs 3. Kidney 4. Liver 5. Brain Vacuoles: multipurpose storage sacs for cells The cell wall provides additional protection and support for plant cells. The central vacuole can play an important role in five different areas of plant life: 1. Nutrient storage 2. Waste management 3. Predator deterrence 4. Sexual reproduction 5. Physical support 11
Chloroplasts: the plant cell s solar power plant The stroma and interconnected little flattened sacs called thylakoids (stack called a granum) Endosymbiosis Theory Revisited Chloroplasts resemble photosynthetic bacteria Circular DNA Dual outer membrane Almost all eukaryotic organisms derive energy directly or indirectly from the sun. Therefore, which organelle is the most important for life as we know it? 1. Nucleus 2. Endoplasmic reticulum 3. Golgi 4. Chloroplast 5. Mitochondria Learning Objectives Understand and be able to explain the following: Chapter 4: Energy How energy flows from the sun and through all life on earth How photosynthesis uses energy from sunlight to make food How cellular respiration converts food molecules into ATP, a universal source of energy Alternative pathways to energy acquisition Energy flows from the sun and through all life on earth. Biofuels and Fossil Fuels Chains of carbon and hydrogen atoms Energy is stored in the bonds Animal fats and oils How do fuels provide energy? The activities of living organisms are fueled by breaking chemical bonds and harnessing the released energy. 12
Energy Conversions All life depends on capturing energy from the sun and converting it into a form that living organisms can use. Two key processes Photosynthesis Cellular respiration Plants convert the energy of the sun into bonds in carbohydrates using a process called. 1. Covalent bonds; photosynthesis 2. Ionic bonds; photosynthesis 3. Hydrogen bonds; cellular respiration 4. Covalent bonds; cellular respiration 5. Ionic bonds; cellular respiration What is energy? The capacity to do work Work Moving matter against an opposing force Water flowing through a dam can be used to generate electricity, which is an example of 1. Energy being used to do work 2. Kinetic energy 3. Potential energy 4. 1 and 2 5. 2 and 3 Energy Conversions Only ~1% of the energy released by the sun that earth receives is captured and converted by plants. Converted into chemical bond energy What happens to the other 99%? As energy is captured and converted, the amount of energy available to do work decreases. 13
Thermodynamics First Law of Thermodynamics Energy can never be created or destroyed. It can only change from one form to another. Second Law of Thermodynamics Conversion of energy includes the transformation of some energy into heat. Heat is almost completely useless to living organisms. Given that every energy conversion is inefficient, which type of food below would feed the most people? 1. Steak 2. Fish 3. Rice 4. Ice cream How do cells directly fuel their chemical reactions? Structure of ATP None of the light energy from the sun can be used directly to fuel cellular work. First it must be captured in the bonds of a molecule called adenosine triphosphate (ATP). Adenosine Triphosphate Pop off the third phosphate group ATP ADP + Phosphate group + energy release Release a little burst of energy! Use this energy to drive chemical reactions necessary for cellular functioning. Building muscle tissue Repairing a wound Growing roots Recycling in the Cell ADP + phosphate group + energy = ATP ATP molecules are like rechargeable batteries cells. 14
Which answer is an example of potential energy? Where does plant matter come from? Photosynthesis: the big picture. 1. Heat 2. Converting ATP to ADP 3. A candy bar 4. ATP 5. 3 and 4 From a seed to a tree: Where does the mass come from? Photosynthetic Organisms Photosynthesis: The Big Picture 3 inputs 2 products Photosynthesis take place in the chloroplasts. Organelles found in plant cells A Closer Look at Chloroplasts 15
Light energy travels in waves: plant pigments absorb specific wavelengths. Light Energy A type of kinetic energy Made up of little energy packets called photons Different photons carry different amounts of energy, carried as waves. Shorter waves = more energy. Electromagnetic Spectrum Range of energy that is organized into waves of different lengths. Shorter the wavelength, higher the energy. Visible Spectrum Range of energy humans see as light ROYGBIV Red, Orange, Yellow, Green, Blue, Indigo, Violet Pigments = molecules that absorb light UV light can damage the DNA in your cells, while visible light cannot. Why? 1. UV light has a longer wavelength than visible light. 2. The wavelength of UV light is within the visible spectrum. 3. UV light contains more energy than visible light. 4. UV light contains less energy than visible light. Plant pigment Chlorophyll Absorbs certain wavelengths of energy (photons) from the sun - can only absorb specific wavelengths of energy. Therefore, plants produce several different types of pigments Absorbed energy excites electrons Chlorophyll a Chlorophyll b Carotenoids Plant Pigments 16
Why are leaves of deciduous trees not green in the fall? 1. Less green light is reflected due to less chlorophyll. 2. More green light is reflected due to increased carotenoids. 3. More red, orange, yellow light is reflected due to carotenoids. 4. 1 and 3 Photons cause electrons in chlorophyll to enter an excited state. Electron Excitation Conversion of electromagnetic energy into chemical energy of bonds between atoms Two Potential Fates of Excited Electrons 1) Electron returns to resting, unexcited state. 2) Excited electrons are passed to other atoms. Photons of specific wavelengths bump electrons up a quantum level into an excited state 17
The Passing of Electrons in Their Excited State Chief way energy moves through cells Molecules that gain electrons always carry greater energy than before receiving them Can view this as passing of potential energy from molecule to molecule Photosynthesis in detail: the energy of sunlight is captured as chemical energy. FOLLOW THE ELECTRONS! The Photo Part Sunlight ATP A high-energy electron carrier Electrons That Leave the Photosystem Are Replenished Where does oxygen come from? An Electron Transport Chain Connects the two photosystems 18
Product #1 of the Photo Portion of Photosynthesis: ATP The Second Photosystem Follow the electrons Product #2 of the Photo Portion of Photosynthesis: NADPH ATP and NADPH Products from the Photo Portion Time for the synthesis part! Plants produce oxygen 1. during electron transport in photosystem 1. 2. during electron transport in photosystem 2. 3. by splitting water to replace electrons in chlorophyll a. 4. by splitting water to replace electrons in the electron transport chain. Review: Which answer is an example of a molecule with high potential energy? 1. NADPH 2. ATP 3. NADP + 4. H 2 O 5. Both 1 and 2 19
The Calvin Cycle SYNTHESIS Photosynthesis in detail: the captured energy of sunlight is used to make food. Series of chemical reactions Occurs in stroma Enzymes are recycled The Processes in the Calvin Cycle Occur in Three Steps: What component of photosynthesis is directly responsible for the increased weight of the plant? 1. Photosystem 1 providing ATP 2. Photosystem 2 providing NADPH 3. Calvin Cycle fixing carbon Evolutionary Adaptations Some plants thrive in hot, dry conditions Stomata Pores for gas exchange Adaptations that reduce evaporative water loss How do plants use water? How to get CO 2 when stomata are shut? 20
C4 Photosynthesis C4 plants produce ultimate CO 2 -sticky tape enzyme. C4 photosynthesis adds an extra set of steps. CAM Photosynthesis Close stomata during hot dry days At night, stomata open, CO 2 let in and temporarily bound to a holding molecule During day, CO 2 gradually released and used while stomata are closed All Three Photosynthetic Pathways 21
Reminder: The energy used by plants and animals ultimately came from 1. Food 2. Soil 3. Sun 4. Air How do living organisms fuel their actions? Cellular respiration: the big picture. Cellular Respiration The big picture ATP: Food molecules into ATP by cellular respiration Three-Step Process Biggest ATP payoff (90%) occurs during the electron transport chain. Cellular Respiration Requires (1) fuel and (2) oxygen. Potential energy stored in chemical bonds of sugar, protein, and fat molecules. Breaks bonds to release the high-energy electrons captured in ATP. Oxygen is electron magnet. Eat food Digest it A Human Example Absorb nutrient molecules into bloodstream Deliver nutrient molecules to the cells At this point, our cells can begin to extract some of the energy stored in the bonds of the food molecules 22
The first step of cellular respiration: glycolysis is the universal energyreleasing pathway. Glycolysis: the universal energy-releasing pathway Glycolysis Three of the ten steps yield energy quickly harnessed to make ATP. The Preparatory Phase to the Krebs Cycle High-energy electrons are transferred to NADH. Net result: each glucose molecule broken down into two molecules of pyruvate ATP molecules produced NADH molecules store high-energy electrons Payoff from the Krebs Cycle: ATP NADH FADH 2 23
The third step in cellular respiration: ATP is built in the electron transport chain. In the mitochondria: Two key features of mitochondria are essential to their ability to harness energy from molecules: Feature 1: mitochondrial bag-within-abag structure Feature 2: electron carriers organized within the inner bag The Bag-within-a-Bag Follow the Electrons Proton Gradients and Potential Energy Proton (H + ) concentration gradient represents a significant source of potential energy! The force of the flow of H + ions fuels the attachment of free-floating phosphate groups to ADP to produce ATP. Why can a proton gradient be used to make ATP? 1. The movement of protons from high to low concentration provides kinetic energy to make ATP from ADP. 2. The movement of protons from low to high concentration provides kinetic energy to make ATP from ADP. 3. The movement of protons from high to low concentration provides the potential energy to make ATP from ADP. 4. The movement of protons from low to high concentration provides the potential energy to make ATP from ADP. 24
Plants have both chloroplasts and mitochondria. Why? 1. The mitochondria also synthesize sugars. 2. The mitochondria are used to convert oxygen to carbon dioxide for the plant. 3. The mitochondria break down sugars produced by photosynthesis to provide energy for the cellular work of the plant. 4. The mitochondria break down fat produced by photosynthesis to provide energy for the cellular work of the plant. There are alternative pathways to energy acquisition. Beer, wine, and spirits are byproducts of cellular metabolism in the absence of oxygen. 25
Which activity below would produce lactic acid via anaerobic respiration? 1. Running 10 miles 2. Swimming 1 mile 3. Sprinting 100 meters 4. Making beer 5. 3 and 4 Eating a complete diet: cells can run on protein and fat as well as on glucose. 26