Cellular Level of Organization Prokaryotic vs. Eukaryotic Cells Cell Structures Cellular Level of Organization Prokaryotic vs. Eukaryotic Cells This Photo by Unknown Author is licensed under CC BY-NC

Important people in Cell Theory Robert Brown (1773-1858) – discovered the nucleus and its role Matthias Schleiden (1804 – 1881) – discovered plants are made of cells Theodore Schwann (1810-1882) – discovered animals are made of cells Rudolph Virchow (1821-1902) – showed cells self reproduce and come from preexisting cells Important people in Cell Theory

Cell Theory All organisms are composed of cells Cells are the basic units of structure and function in organisms Cells come only from preexisting cells because cells are self- reproducing This Photo by Unknown Author is licensed under CC BY

Structure of Prokaryotes Prokaryotes are quite small Three basic shapes are most common Bacillus – Rod-shaped Coccus – Spherical shaped bacterium Long rods that are twisted into spirals Rigid ones are called Spirilla Flexible ones are called Spirochetes This Photo by Unknown Author is licensed under CC BY-SA-NC

Prokaryote Cell Envelope Envelope consists of the plasma membrane, the cell wall, and the glycocalyx Plasma membrane – phospholipid bilayer with embedded proteins Cell wall – maintains the shape of the cell Glycocalyx – a layer of polysaccharides that lies outside the cell wall When this layer is well organized, and not easily washed off, it is called a capsule It helps bacteria resist a host’s immune system Protects against drying out This Photo by Unknown Author is licensed under CC BY-SA-NC

Prokaryotic Cells Inside Cytoplasm - A semifluid solution composed of water and inorganic and organic molecules Nucleoid – The DNA, found in a single, coiled chromosome is located in the nucleoid Plasmid – extrachromosomal pieces of circular DNA Ribosomes – synthesize proteins using RNA This Photo by Unknown Author is licensed under CC BY-SA-NC

Appendages Flagella – consists of a filament, a hook, and a body, the hook rotates, propelling the bacteria Fimbriae – small bristle-like fibers that sprout from the cell surface, that attach bacteria to a surface Conjugation Pili – rigid tubular structures used to pass DNA from cell to cell Bacteria reproduce asexually, but can exchange DNA This Photo by Unknown Author is licensed under CC BY-SA-NC

Two Theories Evidence from fossil record suggests prokaryotic cells first appeared on Earth between 3 and 3.5 billion years ago Eukaryotic cells appeared between 1 and 1.5 billion years ago. What do you think would be a possible explanation for how cells became more complex over time? This Photo by Unknown Author is licensed under CC BY-SA-NC

Autogenous Theory According to the autogenic theory, eukaryotes evolved from prokaryotes through the accumulation of changes over time Gradually, the plasma membrane of the prokaryote folded inward, creating organelles such as the ER and golgi bodies, and the nucleus Evidence to support this theory are the similarities among the cell membrane and the organelle membranes

Endosymbiotic Theory 1960’s Lynn Margulis suggested that mitochondria and chloroplasts have ore in common with prokaryotes than eukaryotes She suggests that chloroplasts and mitochondria were once prokaryotic cells that evolved into a mutualistic relationship with their eukaryotic cells Evidence to support this theory, is that mitochondrial DNA is similar to a parasitic endosymbiont bacteria, and chloroplast DNA is similar to photosynthetic bacteria This Photo by Unknown Author is licensed under CC BY

Eukaryotic cells Are more complex Contain a nucleus and other membrane bound organelles that perform specific functions that contribute to the overall metabolism and growth of the cell Metabolism – the process by which cells make, store, and transport chemicals This Photo by Unknown Author is licensed under CC BY

Structures Cell wall – surrounds the cell and maintains its shape, in plant, fungi, and protist cells only Cell Membrane – surrounds the cell and helps move materials into and out of the cell Cytoplasm – takes up much of the space inside the cell This Photo by Unknown Author is licensed under CC BY-SA-NC

More Structures Nucleus – organelle that holds DNA Mitochondria – transforms the energy in food, to a useable form of energy called ATP. ATP is used for growth and cellular reproduction This Photo by Unknown Author is licensed under CC BY-NC More Structures

More structures ER – helps transport proteins and produces lipids Golgi Body – helps package and distribute proteins and lipids within the cell Ribosomes – are larger in eukaryotic cells and also manufacture proteins This Photo by Unknown Author is licensed under CC BY-SA More structures

Structures Lysosomes – contains enzymes that help break down food, or recycle parts of the cell Chloroplast – contain the green pigment chlorophyll, which captures energy of sunlight for photosynthesis Vacuoles – store water, food, and waste, larger in plant cells than in animal This Photo by Unknown Author is licensed under CC BY-SA

Vocabulary to remember: Lipid – an organic compound that stores energy – aka fats Enzyme – a protein in organisms that helps control a chemical reaction Photosynthesis – the process by which certain organisms use energy from the sun to make food Protein – a polymer of amino acids Amino Acid – contains an amino group and an acid group This Photo by Unknown Author is licensed under CC BY-SA-NC