Lecture_02_Cell Structure and Function.pdf

Muhammad Ali Nawaz, PhD Department of Biological and Environmental Sciences Cell Structure and Function Lecture 02 Chapter 3 1  Points to ponder § What is a cell? § What are the common micros...

Muhammad Ali Nawaz, PhD Department of Biological and Environmental Sciences Cell Structure and Function Lecture 02 Chapter 3 1  Points to ponder § What is a cell? § What are the common microscopes used? § What do prokaryotic and eukaryotic cells have in common? § How are cells organized? § How do things move across the plasma membrane? § What is the role of an enzyme in a metabolic reaction? § What is cellular respiration? 2  The Cell Theory The cell theory. Cell—the basic unit of life. All living things are made up of cells. New cells arise only from preexisting cells. Cells Vary in Structure and Function 33  Cell Size Cells are small because of their surface- area-to-volume ratio. Smaller cells have a larger amount of surface area compared to the volume. An increase in surface area allows for more nutrients to pass into the cell and more wastes to exit the cell. There is a limit to how large a cell can be while remaining efficient and metabolically active. 44 Surface-Area-to-Volume Ratio Limits Cell Size Total surface area 96 cm² 192 cm² 384 cm² (height × width × number of sides × number of cubes) Total volume 64 cm³ 64 cm³ 64 cm³ (height × width × length × number of cubes) Surface area: 1.5:1 3:1 6:1 Volume per cube (surface area ÷ volume) 55 3.1 What is a Cell? Microscopy provide a deeper look into how cells function 6 3.1 What is a Cell? What are some common microscopes used to view cells? 1. Light microscope 2. Transmission electron microscope (TEM) 3. Scanning electron microscope (SEM) 7 3.1 What is a Cell? Light Microscope vs Electron Microscope 8 3.1 What is a Cell? What are some common microscopes used to view cells? Light microscope – Lower magnification (magnification= ratio between the observed size of an image and its actual size) – Uses light beams to view images – Can view live specimens 9 3.1 What is a Cell? What are some common microscopes used to view cells? Transmission electron microscope – 2-D image – Uses electrons to view internal structure – High magnification, no live specimens Scanning electron microscope – 3-D image – Uses electrons to view surface structures – High magnification, no live specimens 10 Light Microscope vs Electron Microscopes 11 Micrographs of Human Red Blood Cells 1212  Cells viewed with SEM Human Breast Neutrophil Pollen Grains engulfing fungus Cancer Cells 13 3.2 How Cells are Organized What are the 2 major types of cells in all living organisms? Prokaryotic cells (Represented mainly by bacteria) – Lack a nucleus – Have plasma membrane – Have cytoplasm – Have DNA – Have very few organelles (e.g. ribosomes) – Have capsule – Have hair-like extensions (Pilli) found on the surface Eukaryotic cells (human, animal, plant, protozoa, fungus) – Have a nucleus that houses DNA – Have many membrane-bound organelles ‫اﻟﻌﺿﯾﺎت‬ – Have more complex structures than Prokaryotic cells 14 3.2 How Cells are Organized Prokaryotic vs Eukaryotic cells DNA Bacteria Human Cell 15 3.2 How Cells are Organized What do prokaryotic and eukaryotic cells have in common? 1) Plasma membrane that surrounds and delineates the cell 2) Cytoplasm: the semi-fluid substance inside the cell 3) DNA & RNA 4) Ribosomes 16  Prokaryotic vs Eukaryotic Cells https://www.youtube.com/watch?v=RQ-SMCmWB1s 17 3.3 The Plasma Membrane and How Substances Cross It The plasma membrane All human cells are surrounded by a plasma membrane The plasma membrane marks the boundary between the outside and the inside of the cell The integrity and function of the plasma membrane are necessary to the cell’s life 18 3.3 The Plasma Membrane and How Substances Cross It What are some characteristics of the plasma membrane? It is a phospholipid bilayer (made of 2 layers). It is embedded with proteins. It contains cholesterol for support. It contains carbohydrates on proteins and lipids. It is selectively permeable (‫)اﻧﺗﻘﺎﺋﻲ‬. 19 Organization of the Plasma Membrane 20 3.3 The Plasma Membrane and How Substances Cross It What does selectively permeable mean? + charged molecules The plasma membrane – and ions allows some substances to H2O enter the cell while keeping other substances out aquaporin noncharged molecules In general, plasma macromolecule membrane is permeable to + – non-polar and non-charged molecules and impermeable to large, polar and charged molecules phospholipid molecule protein Figure 3.7 Selective permeability of the plasma membrane. 21 3.3 The Plasma Membrane and How Substances Cross It 22 3.3 The Plasma Membrane and How Substances Cross It How do things move across the plasma membrane? 1. Passive Transport Diffusion Osmosis Facilitated Transport 2. Active Transport 3. Endocytosis and Exocytosis (Bulk Transportation) 23 3.3 The Plasma Membrane and How Substances Cross It 1- Diffusion and Osmosis 1. Diffusion is the random movement of molecules from a higher concentration (of solute molecules) to a lower concentration (of solute molecules) until they are equally distributed -No cellular energy is required 2. Osmosis is the movement of water molecules (from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules) -No cellular energy is required 24 3.3 The Plasma Membrane and How Substances Cross It Net movement of solutes Net movement of water 25 MEMBRANE TRANSPORT: OSMOSIS 26 3.3 The Plasma Membrane and How Substances Cross It 2-What is facilitated transport? Ø Facilitated transport is the transport of molecules across the plasma membrane from higher concentration to lower concentration via a protein carrier called transporter. No cellular energy is required Ø Some form of Diabetes may occur when a number of glucose transporters are altered Figure 3.10 Facilitated transport across a cell membrane. 27 3.3 The Plasma Membrane and How Substances Cross It What is active transport? Active transport is the movement of molecules from a lower to higher concentration using ATP as energy; it requires a protein carrier called pump Na+/K+ pump transports 3 Na+ out of the cell and 2 K+ into the cell from low to high concentrations respectively, using ATP Active transport and the sodium–potassium pump. 28 ACTIVE TRANSPORT 29  3- What is endocytosis? plasma membrane Endocytosis transports molecules or cells into the cell via invagination of the plasma membrane to form a vesicle. vesicle a) phagocytosis: “Cell Eating” ‫اﻟﺑﻠﻌﻣﺔ‬. Cell a. Phagocytosis engulfs solid matter either to destroy it or to feed on it. b) pinocytosis: “Cell Drinking” ‫اﻹﺣﺗﺳﺎء‬. Cell solute engulfs fluid matter either to destroy it or to vesicle feed on it. b. Pinocytosis c) receptor-mediated endocytosis: Cell receptor protein ingests matter by binding to a specific membrane receptor solute coated vesicle coated pit Figure 3.12 Movement of large molecules across the membrane. c. Receptor-mediated endocytosis 30 3.3 The Plasma Membrane and How Substances Cross It 3- What is exocytosis? Exocytosis transports molecules outside the cell via the fusion of a vesicle with the plasma membrane. Figure 3.12 Movement of large molecules across the membrane. 31  Isotonic, hypotonic, and hypertonic solutions Solute Extracellular Intracellular Isotonic Solution – Extracellular and intracellular ionic concentrations are equal Hypotonic Solution – Extracellular ionic concentration is less than intracellular Hypertonic Solution – Extracellular ionic concentration is higher than intracellular 32 Effects of Changes in Tonicity on Red Blood Cells No effect Cell bursting Cell shrinking and lysis 3333 3.4 The Nucleus and Endomembrane System Gene expression: from DNA to protein Messenger RNA m ( by the ribosomes) 34 3.4 The Nucleus and Endomembrane System What is the structure and function of the nucleus? Bound by a porous nuclear envelope Houses DNA: The genetic material Controls nearly all the activities of the cell 35 3.4 The Nucleus and Endomembrane System Figure 3.13 The nucleus and endoplasmic reticulum. 36  What is the structure and function of ribosomes? Ribosome Organelles made of RNA and Protein Found bound to the endoplasmic reticulum and free floating in the cytoplasm Sites of protein synthesis 37 3.4 The Nucleus and Endomembrane System What is the endomembrane system? It is a series of membranes and vesicles that work together to produce, package, secrete, and digest protein, lipids, and carbohydrates. It consists of: 1) Nuclear envelope 2) Endoplasmic reticulum (rough and smooth) 3) Golgi apparatus 4) Lysosomes 5) Vesicles 38 3.4 The Nucleus and Endomembrane System How does the endomembrane system function? secretion plasma membrane incoming vesicle secretory vesicle enzyme Golgi apparatus lysosome modifies lipids and proteins from the ER; sorts and packages contains digestive enzymes them in vesicles that break down cell parts or substances entering by vesicles protein transport vesicle transport vesicle takes proteins to takes lipids to Golgi apparatus Golgi apparatus lipid rough endoplasmic smooth endoplasmic reticulum reticulum synthesizes proteins and synthesizes lipids and has packages them in vesicles various other functions Nucleus ribosome Figure 3.14 The endomembrane system. 39 3.4 The Nucleus and Endomembrane System How can we summarize the parts of the endomembrane system? Rough endoplasmic reticulum – studded with ribosomes used to make proteins Smooth endoplasmic reticulum – lacks ribosomes but aids in making lipids and carbohydrates Golgi apparatus – flattened stacks that process, package, and deliver proteins and lipids from the ER 40 41 3.4 The Nucleus and Endomembrane System How can we summarize the parts of the endomembrane system? Lysosomes – membranous vesicles produced by the Golgi that contain digestive enzymes that breakdown cell debris or foreign particles. Vesicles – small membranous sacs used for transport of molecules from one part of the system to another. 42 3.5 The Cytoskeleton, Cell Movement, and Cell Junctions What is the cytoskeleton? A series of proteins that maintain cell shape, as well as anchors and/or moves organelles in the cell Made of 3 types of fibers: large microtubules, medium-sized intermediate filaments, and thin actin filaments 43 What is the cytoskeleton? 44  Cilia and Flagella Cilia: Short and many Flagella: Long and single Cilia are about 20´ shorter than flagella. Both are made of microtubules. Both are used in cell movement. Cilia are found in the lining of the trachea (windpipe), where they sweep mucus and dirt out of the lungs and in the lining of the fallopian tube (oviduct), where they convey released ova to the uterine cavity Figure 3.15 Structure and function of the flagellum and cilia. 45  A Tour of the Cell https://www.youtube.com/watch?v=0xe1s65IH0w 46 3.6 Metabolism and the Energy Reactions Metabolism Metabolism consists of all chemical reactions that occur in a cell Metabolism comprises of two major parts: anabolism and catabolism Catabolism is the set of metabolic processes that break down large molecules. It yields energy Anabolism is the set of metabolic pathways that construct molecules from smaller units. It requires energy input Metabolism requires metabolic pathways and is carried out by enzymes sequentially arranged in cells Metabolism = Catabolism + Anabolism 47 3.6 Metabolism and the Energy Reactions Enzymes are important for cellular respiration and many activities in the cell. Most enzymes are proteins. Enzymes are specific to what substrate they work on (Lock and Key). Enzymes have active sites where a substrate binds. Enzymes are not used up in a reaction but instead are recycled. Some enzymes are aided by non-protein molecules called coenzymes. 48 How do enzymes work? 49 3.6 Metabolism and the Energy Reactions What do mitochondria do and what do they look like? Highly folded organelles found in eukaryotic cells Produce energy in the form of ATP: powerhouse of the cell Thought to be derived from an engulfed prokaryotic cell Figure 3.17 The structure of a mitochondrion. 50  ATP-ADP Cycle Production of ATP in a cell. When energy is needed, ATP is broken down into ADP (adenosine diphosphate) and a phosphate. When energy is obtained from food, it is used to add a phosphate back onto ADP to make ATP. This cycles repeatedly. 5151  Cellular Respiration Cellular respiration breaks glucose down into carbon dioxide and water. Three pathways are involved: 1. Glycolysis: In the Cytoplasm 2. Citric Acid Cycle (Krebs cycle): In the Mitochondria 3. Electron Transport Chain: In the Mitochondria These pathways allow the energy to be released slowly; a tremendous amount of heat would be lost if glucose breakdown occurred all at once. 5252 3.6 Metabolism and the Energy Reactions Inside cell electrons transferred by NADH glucose electrons transferred by NADH Glycolysis Citric Electron acid transport glucose pyruvate cycle chain oxygen mitochondrion 2 ATP 2 ATP 32 ATP Outside cell Figure 3.19 Production of ATP. 53  Glycolysis Glycolysis. Breaks glucose, a 6-carbon sugar, into two 3- carbon pyruvates. Occurs in the cytoplasm of almost every cell type. Is anaerobic—does not require oxygen. Produces NADH and 2 ATP molecules. 5454 GLYCOLYSIS 55  Citric Acid Cycle (Krebs cycle) A cyclical series of enzymatic reactions. Occurs in the matrix of mitochondria. Completes the breakdown of glucose by breaking the bonds between carbons. Each pyruvate enters the citric acid cycle as acetyl CoA. Produces NADH and 2 ATP. Requires Oxygen Releases carbon dioxide. 5656 Krebs cycle 57  Electron Transport Chain NADH from glycolysis and the citric acid cycle deliver electrons to the electron transport chain. The members of the electron transport chain are carrier proteins embedded in the mitochondria cristae. Each carrier accepts two electrons and passes them on to the next carrier. Oxygen is the final acceptor of the electrons at the end of the chain (so the chain is aerobic). After oxygen receives the electrons, it combines with hydrogens and becomes water. The reason why we breathe in oxygen is so it can receive electrons at the end of the electron transport chain. The energy released during cellular respiration is used to make 36 to 38 ATP. 5858 Electron Transport Chain 59 60 3.6 Metabolism and the Energy Reactions What other molecules besides glucose can be used in cellular respiration? Carbohydrates (other than glucose) Lipids Proteins Fats have twice the energy of carbohydrates Proteins have same energy as carbohydrates 61 3.6 Metabolism and the Energy Reactions How can a cell make ATP without oxygen? Fermentation (anaerobic respiration; absence of oxygen) – Occurs in the cytoplasm – Does not require oxygen – Involves glycolysis step only – Makes 2 ATP and: 1) Lactic acid (Lactate) in human cells: painful sensation 2) Ethanol in yeast and bacteria - Can give humans a burst of energy for a short time. - Produces much less ATP than aerobic respiration 62 3.6 Metabolism and the Energy Reactions How can a cell make ATP without oxygen? Glucose (Glycolysis) (2) ATP Pyruvate Lactic acid/ ethanol buildup Mitochondrial metabolism blocked without oxygen Mitochondrion 63