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Cell Biology Ground Rules: • Respect for your fellow students • Turn off mobile phones in class • Arrive on time, if you do need to leave do so with out disturbing other students • Do not interrupt a fellow student when speaking My Details Dr. Colin Stack (Cell Biology unit coordinator) Office: Building 21 Room no: 1.07 Tel: 4620-3237 Email: c.stack@uws.edu.au You will need to use your student e-mail All unit requirements will be explained at this week’s tutorial Cell Biology Week 1 lectures Tour of the Cell Cell Structure & Function These lectures correspond to chapter 6 in Biology 8th ed. by Campbell pgs 95-124 • • • • • • • • What is Cell Biology' What is a cell' Are all cells the same' How big are cells' Where do they come from' How do cells reproduce' How do cells “talk” to each other' Why should you care' Cell Biology Overview: Cell Biology is the study of individual cells & their interactions with each other. Intended Learning Outcomes: By the end of this lecture, you should be able to: • Explain Cell Theory • Relate the use of microscopy in cell biology • Distinguish between prokaryotic & eukaryotic cells • Describe the structures of a cell Overview: the fundamental units of life • All organisms are made of cells. • The cell is the simplest collection of matter that can live. • Cell structure is correlated to cellular function. • All cells are related by their descent from earlier cells. 1 So the big question: What makes one cell different to another' ANS: Same Genome but different proteome, tells you what’s happing So what is a cell' In the 1600s, Robert Hooke was studying a section of cork under a light microscope and saw that it was composed of tiny chambers. He coined the term cell, which comes from the Latin word cella, meaning “storeroom” or “small container”. Black Swallowtail- larvae & butterfly Timeline: Cell Theory Cells were discovered in 1665 by Robert Hooke. (a long time before acceptance) Early studies of cells were conducted by - Mathias Schleiden (1838) - Theodor Schwann (1839) Schleiden and Schwann proposed the Cell Theory. Cell Theory Cell Theory 1. All organisms are composed of cells (one or more). 2. Cells are the smallest living things 3. Cells arise only from pre-existing cells. All cells today represent a continuous line of descent from the first living cells. If a cell is the basic unit of life, what about viruses are they living' Cell Theory Cell size is limited. -As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell. Cell Size: As the surface area increases by a factor of n2, the volume increases by a factor of n3. Picture of cell describing effect of size Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area 2 Cell Size • Human cell size – most from 10 - 15 µm in diameter • egg cells (very large)100 µm diameter • nerve cell (very long) at 1 meter long Cell Size The logistics of carrying out a cell’s functions sets limits on size. (THIS IS KEY) • At a min, a cell must be able to house enough DNA, proteins, & internal structures to survive & reproduce. • The max size is influenced by its requirements for enough surface area to obtain adequate nutrients and oxygen & dispose of wastes. As cell size inc the length of time for diffusion from the cell surface to the interior increase. • Limitations on cell size – cell growth increases volume faster than surface area • nutrient absorption and waste removal utilize surface Microscopy • Scientists use microscopes to visualise cells too small to see with the naked eye. • In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image. • Enables us to see the overall shape and structure of a cell magnifies an image by up to 1500 times its original size Microscopy & the size range of cells Most cells are microscopic but not all e.g. nerve cell can be 1 m. Most of what we know about Cells has been dependent on the development of microscopes. Picture showing the scale of different Cells and objects Picture of a microscope Size, Does it really matter' Common misconceptions • Science student’s often believe that everything in science has been discovered • The more we find out the less we actually really know Size does matter if you are a disease causing microorganism e.g. viruses, bacteria even parasites! Artist’s impression of malaria Parasites rupturing a RBC 3 – Light microscopes • Magnify cells, living and preserved, up to 1,000 times Essentially cells are the biological building blocks of living things. Picture of a simple cell Light microscopes can resolve structures that are 200nm apart. Electron microscopes can resolve structures that are 0.2nm apart. Microscopy • Two basic types of electron microscopes (EMs) are used to study subcellular structures (magnification of up to 1 million times): – scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing 3-D images; – transmission electron microscopes (TEMs) focus a beam of electrons through a specimen, and are used mainly to study the internal structure of cells. Electron Microscopy Importance of Cilia SEM & TEM pictures Electron microscope is used to reveal ultrastructure (the fine detail) Microscopy • Electron microscopes have truly revolutionised the study of cells and their structures. • BUT have not replaced light microscopes. EM cannot be used to study living specimens due to specimen preparation. Quick Check Which type of microscope would you use to study a) The changes in shape of a living human white blood cell; b) the finest details of the surface texture of a human hair; c) the detailed structure of an organelle in a human liver cell' Talk in groups for a minute & Write your answer down. 4 ONLY TWO TYPES OF CELL Bacteria, fungi and animals are all made of cells, all of these show the tremendous diversity of cell types i.e. cells come in all shapes and sizes. Humans have over 260 cell “types/forms” (30 trillion cells) e.g. RBCs (erythrocytes) are amongst our smallest, 2 um thick and 7 um in diameter. While a single nerve cell can be 1 m in length. There are only “2 types” of cells Which type is based on the organisation of their internal structures/complexity. • All cells are either prokaryotic or eukaryotic. • Pro- means “before” and karyoto means “nucleus” hence the term prokaryotic meaning “before the nucleus” i.e. lacks a nucleus. • Prokaryotic cells lack internal membranes. Comparing prokaryotic and eukaryotic cells • Some basic features common to all cells include: – a plasma membrane, – a semifluid substance called cytosol, – chromosomes (which carry genes), – and ribosomes (which make proteins). • Prokaryotic cells are structurally simpler than eukaryotic cells – There are two kinds of cells • Prokaryotic and eukaryotic Picture of prokaryotic and eukaryotic cells Make sure you know the differences and similarities between these two cell types! Comparing Prokaryotic and Eukaryotic Cells • What is the main structural feature that eukaryotic cells possess but prokaryotic cells are lacking' A typical prokaryotic cell Picture of a typical prokaryotic cell – a. Cell membrane – b. Cytoplasm – c. Nucleus – d. Ribosomes ANSWER – Prokaryotic cells are small, relatively simple cells • That do not have a membrane-bound nucleus • Lack many of the major organelles 5 Eukaryotic Cells Eukaryotic cells -possess a membrane-bound nucleus -are more complex than prokaryotic cells -compartmentalize many cellular functions within organelles and the endomembrane system -possess a cytoskeleton for support and to maintain cellular structure Eukaryotic Cells Picture of a prokaryotic cell Internal Structures of Prokaryotic Cells • Which of the following is a function of the cytoplasmic membrane' – a. To control the passage of substances into and out of the cell – b. To prevent the passage of substances into and out of the cell – c. To produce a capsule for the cell – d. To contain the DNA of the cell ANSWER Eukaryotic Cells Picture of a plant cell What differences can you see' Cell Shapes – Eukaryotic cells are distinguished by the presence of a true nucleus – Membranes form the boundaries of many eukaryotic cells • Compartmentalizing the interior of the cell and facilitating a variety of metabolic activities • Organelles are surrounded by a viscous substance called the cytosol Picture of the various cell types 6 So how do cell become different' Quick Check List three features that are common to prokaryotic and eukaryotic cells. Figure of how cells become different List three features that differ. Talk in groups for 2 minutes & Write your answer down. Why should you care about prokaryotes' Prokaryotes are very important. Right at this moment in time our bodies are covered in millions of different types of bacteria (they are on us & inside us) in fact we have a number of bacterial genes incorporated into our DNA (genome). Some bacteria are beneficial while others can cause disease or even kill us. Modern Cell Theory expanded • All organisms composed of cells and cell products. • Cell is the simplest structural and functional unit of life. • Organism’s structure and functions are due to the activities of its cells. • Cells come only from preexisting cells. • Cells of all species have many fundamental similarities. Next week we’ll discuss the role of the cell membrane Now we’ll discuss the organelles the nucleus & mitochondrion Table comparing prokaryotes and eukaryotes (animal and plant cells) Figure taken from Raven, Biology 8th ed McGraw-Hill 7 Eukaryotic Cells Nucleus -stores the genetic material of the cell in the form of multiple, linear chromosomes -surrounded by a nuclear envelope composed of 2 phospholipid bilayers -in chromosomes – DNA is organized with proteins to form chromatin Picture displaying the functions of the various cellular components Eukaryotic Cells The nucleus: information central • In the nucleus, DNA and proteins form genetic material called chromatin. • Chromatin condenses to form discrete chromosomes. • The nucleolus is located within the nucleus, and is the site of ribosomal RNA (rRNA) synthesis. Picture of the nucleus and nuclear membrane Central Dogma The big picture Mitochondria (the cells power stations) Mitochondria -organelles present in all types of eukaryotic cells -contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP (the cell’s energy currency) -found in all types of eukaryotic cells Figure displaying how DNA is converted to RNA and then to Protein 8 Mitochondria -surrounded by 2 membranes -smooth outer membrane -folded inner membrane with layers called cristae -matrix is within the inner membrane -intermembrane space is located between the two membranes -contain their own DNA Picture of a mitochondria Peroxisomes: oxidation (these are the detox centres) • Peroxisomes are specialised metabolic compartments bounded by a single membrane. • Peroxisomes produce hydrogen peroxide and convert it to water. • Oxygen is used to break down different types of molecules. • Peroxisomes are abundant in liver cells Other organelles Ribosomes -the site of protein synthesis in the cell -composed of ribosomal RNA and proteins -found within the cytosol of the cytoplasm and attached to internal membranes Fig. 6-11 from campbell of a ribosome Endomembrane System Endomembrane system -a series of membranes throughout the cytoplasm -divides cell into compartments where different cellular functions occur 1. endoplasmic reticulum 2. Golgi apparatus 3. lysosomes Endomembrane System Rough endoplasmic reticulum (RER) acts as a quality control centre -membranes that create a network of channels throughout the cytoplasm -attachment of ribosomes to the membrane gives a rough appearance -synthesis of proteins to be secreted, sent to lysosomes or plasma membrane 9 Endomembrane System Smooth endoplasmic reticulum (SER) -relatively few ribosomes attached -functions: -synthesis of membrane lipids -calcium storage (cell signaling) -detoxification of foreign substances Endomembrane System Picture of the system Endomembrane System Golgi apparatus -flattened stacks of interconnected membranes -packaging and distribution of materials to different parts of the cell -synthesis of cell wall components Diagram of transport inside and outside the cell Internal Structures of Eukaryotic Cells • What is the function of the smooth endoplasmic reticulum' – a. Excretion of wastes from the cell – b. Lipid synthesis and transport – c. Protein synthesis – d. Photosynthesis ANSWER Internal Structures of Eukaryotic Cells •What organelle is sometimes called the “powerhouse of the cell”' – – – – a. Mitochondria b. Nucleus c. Ribosomes d. Centriole ANSWER 10 Endomembrane System Lysosomes (intracellular digestion) -membrane bound vesicles containing digestive enzymes to break down macromolecules (acidic environment) -destroy cells or foreign matter that the cell has engulfed by phagocytosis -Lysosome means “body that lyses” and contain up to 40 different enzymes - Disease (Tay-Sachs disease) Endomembrane System Microbodies -membrane bound vesicles -contain enzymes -not part of the endomembrane system -peroxisomes contain oxidative enzymes and catalase The Big Picture A panoramic view of the eukaryotic cell • A eukaryotic cell has internal membranes that partition the cell into organelles. • Plant and animal cells have most of the same organelles. Diagram of how a protein produced in the cell is shipped outside BioFlix: tour of an animal cell BioFlix: Evolution of Mitochondria & Chloroplasts Endosymbiosis -proposal that eukaryotic organelles evolved through a symbiotic relationship -one cell engulfed a second cell and a symbiotic relationship developed -mitochondria and chloroplasts are thought to have evolved this way 11 Mitochondria & Chloroplasts Much evidence supports this endosymbiosis theory. 1st proposed by Lynn Margulis Mitochondria and chloroplasts: -have 2 membranes -possess DNA and ribosomes -are about the size of a prokaryotic cell -divide by a process similar to bacteria Mitochondria & Chloroplasts Diagram displaying the endosymbiont theory of mitochondria and chloroplasts FINAL ROUND Question • What theory did Lynn Margulis propose as a way to explain the formation of eukaryotic cells' – a. Theory of Relativity – b. Life Theory – c. Endosymbiotic Theory – d. Theory of Mitochondria ANSWER 12