Chapter 7: Cell Structure ProkaryoticEukaryotic Cell Size Smallest living entity. Many different types: Simple bacteria Single celled organisms Complex organisms An important thing to note is that most bacteria are 10x smaller than common eukaryotic cells. Microscopes Light Microscopes Use light to view specimens Electron Microscopes Use an electron beam to create an image on a screen. Microscopes Advantages of light microscopes: Can easily view slide preps up to 1000x Can view living organisms Wide variety of uses Disadvantages of light microscopes: Can only view slide preps up to 1000x Limitations in resolving power 0.2m Fathers of the Microscope Hans and Zacharias Janssen Self proclamation Galileo Made a scope with 2 lenses, had a lot of aberration. Fathers of the Microscope Antoine van Leeuwenhoek Considered the father of the scope, but actually did so with many other people. Was selfish. His scopes were giant lenses ~266x Very detailed specimens, brought microscopy to forefront of biology. Christian Huygans Corrected for chromatic aberration Cell Who actually saw the first cell is in dispute, but suffice it to say that it was probably some time in the mid 1600s. In 1665, Robert Hooke built a microscope and looked at thin slices of cork. He coined the term cell. Cell Theory present Matthias Schleidan and Theodor Schwaan and Rudolf Virchow Cells are fundamental units of all living things Living organisms consist of one or more cells All cells arise from pre-existing cells Genetic material is passed from one cell to the next during division All cells are essentially the same chemically Spontaneous Generation Most people believed this was the way in which organisms arose. Worms from meat Beetles from dirt Rodents from grain A number of experiments were going on at the time that didnt support this, but many people still believed in it. Experiments against Spontaneous Generation Francesco Redi Experiment using rotten meat Lorenzo Spallanzani Boiled broth and sealed it shut showing no growth Images taken from Microbiology Principles and Practices, Jackie Black. Louis Pasteur Helped lend credence to cell theory. Disproved the notion of spontaneous generation Used swan necked flasks to trap microorganisms Poured the broth to mix in with the trapped microorganisms and got bacterial growth Louis Pasteur Disproved the notion of spontaneous generation Used swan necked flasks to trap microorganisms Images taken from Microbiology Principles and Practices, Jackie Black. Two Main Types of Cells: Prokaryotes Kingdom Eubacteria Kingdom Archea Contain no membrane bound nucleus or organelles About 10x smaller than typical eukaryotes Eukaryotes Kingdom Eukarya Contain a membrane bound nucleus and other organelles. About 10x larger than prokaryotes. Similarities between Prokaryotes & Eukaryotes 1. They are bound by a plasma membrane 2. They contain cellular fluid called cytoplasm 3. They contain chromosomes 4. They contain ribosomes (although they are different) Cell Size Limitations Cell size is limited by the surface area to volume ratio. As the cell becomes larger, this ratio becomes smaller and it becomes more difficult for the cell to adequately perform its functions. Recall the importance of a cells surface in allowing things in and out of the cell. Organelles Recall that organelles are found in eukaryotic cells and perform various functions. Many similarities, some differences: *Animal cells contain lysosomes, centrioles and flagella, plants dont. *Plant cells have a cell wall, central vacuole and a tonoplast, animals dont. Nucleus Control center of a cell, contains DNA in the form of chromosomes. Chromatin-DNA/protein complex Surrounded by nuclear envelope--regulates entry and exit of macromolecules. Nucleolus (little nucleus) Contains rRNA Makes ribosomes which end up on the cytoplasm Ribosome factories The Nucleus Within the nucleus are the chromosomes and one or more nucleoli which function in ribosome synthesis. Ribosomes Found in both prokaryotes and eukaryotes They synthesize proteins by using the mRNA to produce the 1 structure of the protein. Found freely in the cytoplasm and also are found attached to the ER or nuclear envelope. Ribosomes Free ribosomes: Make proteins for use within the cell Bound Ribosomes: Make proteins which are inserted into membranes, packaging within certain organelles, or to be exported from the cell. Endomembrane System Membrane system found within the cell and carries out a variety of functions: Synthesis and transport of proteins Detoxification and movement of intracellular products. Endoplasmic Reticulum The ER is an extensive network of membranous tubules and sacs (cisternae). The ER is continuous with the nuclear envelope. It has a membrane that separates the lumen from the cytosol. There are two types: Rough endoplasmic reticulum (RER) Smooth endoplasmic reticulum (SER) Endoplasmic Reticulum RER is studded with ribosomes. SER is not. Two types of ER RER: Studded with ribosomes Proteins made go to the lumen where they take on their 3 structure. Secretory proteins, wrapped in a membrane bound vesicle to be shipped out of the cell. SER: Involved in the synthesis of lipids, phospholipids and steroids. Detoxify drugs and poisons, assist in removal from the body. Golgi Apparatus Shipping and receiving center of the cell. After leaving the ER, products are dumped into the Golgi at the cis face (closest to the ER). Here they are sometimes modified and then head to the trans side of the Golgi. These products then bud off from the trans face of the Golgi and head to their destination. Lysosomes Membrane bound organelle that stores hydrolytic enzymes that break down macromolecules. They also do clean up functions within the cell. Vacuoles Found in plant cells and store a variety of compounds, both good and bad. (Nutrients and poisons). It isolates the cytoplasm of the plant cell from the water, food, or other things. Mitochondria Sites of cellular respiration that generate ATP for a cell. Have an inner and an outer membrane. Mitochondria Outer membrane: Smooth and surrounds the entire mitochondria. Inner membrane: Has many foldings called cristae which increases the surface area of the organelle. Good for a lot of cellular respiration. Chloroplasts Sites of photosynthesis found in plants and algae. Have an inner and an outer membrane. Chloroplasts Outer membrane: Houses all of the structures of the chloroplast. Inner membrane: Contains a membranous system of thylakoids, grana, and stroma. Images taken from Microbiology Principles and Practices, Jackie Black. Chloroplasts, Inner Membrane Thylakoid: often found in stacks like poker chips. Each stack is called a granum. These are the sites of the light reactions. These reside in the stroma--the liquid inside the chloroplast. The stroma is the site of the dark reactions (Calvin cycle). Chloroplast and Peroxisome Peroxisomes contain catalase and are involved in breaking down H 2 O 2 --a toxic compound formed as a normal part of cellular metabolism. Mitochondria and Chloroplasts Not part of the endomembrane system. They have their own DNA which synthesizes proteins on their own ribosomes. Peroxisomes Membrane bound and add H + from certain substrates to O - creating H 2 O 2 (hence the name). Peroxisomes have two main jobs: Create products that can be used by cellular respiration. Detoxify. The cell contains enzymes that break down H 2 O 2 into H 2 O and O 2. The Cytoplasm It is a fibrous network of microtubules, microfilaments and intermediate fibers (called the cytoskeleton). Provides structural support, (no cell walls) Serves as an anchor point for organelles. Allows substances to be transported throughout the cell. Cytoskeleton A TEM of the cytoskeleton. Microtubules and microfilaments are evident, intermediate filaments are not. Microtubules Provide structural support for the cell. Serve as transport tracks along which many products move as they transfer to the plasma membrane for discharge from the cell. (neurotransmitters, etc.) Microtubules Microtubules make up cilia and flagella in eukaryotes. Microfilaments Smallest fibers and built from actin protein. Provide structural support and are involved in motility. Work closely with myosin in muscle cells allowing it to contract. A Structural Role of Microfilaments The surface of this nutrient- absorbing intestinal cell is increased by its many microvilli, cellular extensions reinforced by bundles of microfilaments. These actin filaments are anchored to a network of intermediate filaments. Microfilaments and Motility Microfilaments are involved in muscle contraction, amoeboid movement and the streaming of particles within the cytoplasm of plant cells. Intermediate Filaments Provide permanent structural support for the cell. Microtubules and microfilaments are often broken down and built back up when and where needed. Intermediate filaments are not. Plant Cells Contain a cell wall. Provides support for the plant. Young plants secrete a primary cell wall rich in polysaccharide. Glues the cells together. Animal Cells No cell wall. Do have an extracellular matrix composed of glycoproteins (collagen) and proteoglycans (found in cartilage). Levels of Organization Cells are organized in many organisms to form tissues--cells that have similar structures and functions. Tissues are arranged into organs--a structure with a particular function. Organ systems are a group of organs that carry out major body functions.