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Transcript
Cell Unit Notes The Cell Theory All living things are composed of cells Cells are the basic functional units of life New cells are produced from existing cells Prokaryotes vs. Eukaryotes Prokaryotes smaller & simpler Contain a cell membrane & cytoplasm Sometimes a cell wall Also have ribosomes No nucleus All bacteria are prokaryotes DNA is “free – floating” Eukaryotes Have a nucleus containing DNA Most have specialized structures called organelles All plants, animals, protists, and fungi are eukaryotes Larger and more complex Prokaryote vs. Eukaryote Cell membrane Cytoplasm Prokaryotic Cell Cell membrane Eukaryotic Cell Cytoplasm Nucleus Organelles Prokaryotes Prokaryotes are simple, living organisms that can reproduce on their own They have diverse ways of obtaining nutrients: Photosynthesis Chemosynthesis Heterotrophic consumers Prokaryotes Bacteria (prokaryotes) live in every habitat possible and are the most numerous of all living things on our planet All living things depend upon bacteria – including, especially, humans! Prokaryotes represent the “ancient bacteria” and they live in extreme environments such as boiling water or extremely salty environments They are the oldest living organisms on this planet. Evidence suggests that they were present during the early stages of Earth over 3.9 billion years ago Archea Prokaryotes Bacteria have cell membranes and most have a cell wall Their DNA is one circular molecule They often have many plasmids Small circular rings of DNA usually containing one gene Pili help bacteria “stick” to things Many bacteria have a flagellum or many flagella to help them move Prokaryotes & Viruses Viruses are extremely small particles not considered to be “alive” They act like parasites because they can ONLY reproduce in a host They consist of a protein coat and contain either DNA or RNA inside Eukaryote Cell Structures Cell Wall Found in many organisms including plants, algae, fungi, and nearly all prokaryotes Not found in animal cells Cell Wall The main function of the cell wall is to provide support and protection for the cell Plant cell walls are made of cellulose The Nucleus The nucleus is the “control center” of the cell The nucleus controls most cell processes and contains the hereditary information of DNA Almost all eukaryotic cells, including plant and animal, contain a nucleus The Nucleus Nucleolus – small dense region in nucleus where ribosomes are produced Nuclear envelope – double membrane layer surrounding the nucleus (aka. Nuclear membrane) The Cytoskeleton A network of protein filaments that help the cell maintain it’s shape It is also involved in many forms of Microtubule movement Microfilament The Cytoskeleton Made up of three types of structures: Microtubules – hollow tubes of protein that help maintain cell shape and serve as “tracks” for organelles to travel on Intermediate Filaments – smaller than microtubules – gives a cell its strength Microfilaments – long thin fibers that support cell movement and support Organelles in the Cytoplasm Ribosomes Organelle that “assembles” proteins (Protein Synthesis) A ribosome is made up of 2 parts: • a protein • rRNA (ribosomal RNA) Ribosomes make proteins from the “coded” instructions of the DNA inside the nucleus Ribosomes Endoplasmic Reticulum An internal membrane where parts of the cell membrane are made and some proteins are modified Rough endoplasmic reticulum The Rough Endoplasmic Reticulum is where protein synthesis occurs Ribosomes are on it’s surface making it appear “rough” Endoplasmic Reticulum The Smooth Endoplasmic Reticulum does not have any ribosomes on it’s surface It contains enzymes that make lipids (fats) Smooth endoplasmic reticulum Golgi Apparatus Golgi apparatus After proteins are assembled and produced by the Rough ER they move to the Golgi Complex where : Carbohydrates (sugars) and lipids (fats) are attached to the protein They are then sent to their final destination Lysosomes Small organelles that are filled with digestive and other enzymes They break down lipids (fats), carbohydrates (sugars), and proteins from food particles so it can be used by the rest of the cell Lysosomes also break down “old” organelles that have outlived their function Basically, they “take out the trash” Vacuoles Serve as a storage for water, salts, proteins, and “carbs” (plant and animal cells) In Plants : They usually have one large vacuole filled with water to support structures like leaves and flowers Vacuole Chloroplasts The producer! They use sunlight to power a familiar process called Photosynthesis The green pigment (color) chlorophyll is what gives leaves their color and is found inside chloroplasts Chloroplast Mitochondria The “powerhouse” of the animal and plant cell! Mitochondria use energy from food to make highenergy compounds (ATP) The cell uses these highenergy compounds for growth, development, and movement In that way, the mitochondria makes “fuel” for the cell Typical Plant Cell Typical Animal Cell The Cell Membrane The cell membrane regulates what enters and leaves the cell It also provides support and protection The cell takes in food and water and eliminates wastes through the cell membrane The cell membrane is selectively permeable Selective Permeability The Lipid Bilayer Most cell membranes are made up of a doublemembrane layer called the lipid bilayer Along with lipids the membrane also has proteins that are “stuck” in it (see below) The Lipid Bilayer Along with the proteins are “carbohydrate chains” that are attached to the protein These “chains” act like an identification card or “face” so the cell can be recognized Carbohydrate chains Protein channel Diffusion All living cells are surrounded by and full of liquid Even a cactus in the desert has moist cells in it’s living tissue One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other Diffusion Diffusion The concentration of a solution is the relative “purity” of a liquid There can be a high concentration to a low concentration A solution will move in the direction of high concentration to low concentration and this is called Diffusion Diffusion Diffusion allows substances to cross the cell membrane without requiring the cell to use energy This is very important since energy must be conserved – even at the cellular level! What is Osmosis Osmosis is the movement of water across a semi-permeable membrane. Important part of homeostasis Osmosis Selective permeability means that only select “things” can pass through the membrane Osmosis is “the diffusion of water across a selectively permeable membrane” Osmosis (cont.) Tonicity: Ability of a solution to cause a cell to gain or lose water. Is dependent on the concentration of solutes that cannot cross a membrane (nonpenetrating solutes). The more of these solutes there are, the higher the tendency that water will exit the cell and vice versa. Isotonic solution: No net movement of H2O occurs. The concentration of solutes is equal outside & inside of cell. This is an indicator of a stable cell environment. Water will still flow across the membrane at the same rate in both directions. Osmosis (cont.) Hypertonic solution: H2O will move out of the cell (lose H2O). Concentration of solutes is greater outside of cell. Increases in salinity causes cells to lose H2O such as a freshwater plant placed into saltwater. Hypotonic solution: H2O will enter cell. Concentration of solutes is greater inside of cell. This can cause cells to lyse (burst) & die. Osmosis (cont.) Osmotic Pressure Isotonic – means that on both sides of the cell membrane it is the same “concentration” Hypotonic – the cell fills up with water and is in danger of “bursting” Hypertonic – the cell loses much of its water concentration and can “shrink” (Animal Cells react differently than plant cells because of the cell wall that plant cells have) Osmotic Pressure Osmosis (cont.) Osmoregulation: Control of H2O balance. Paramecium lives in pond water (hypotonic to cell). It has a plasma membrane that is less permeable to H2O to slow the uptake of H2O. • Also has a contractile vacuole that pumps out H2O as fast as it enters. Osmosis (cont.) Plant cells are very turgid (very firm) when they are surrounded by a hypotonic solution. Allows the plant to stay upright = Healthy. If plant cells are in an isotonic environment, the cells will become flaccid (limp) = Unhealthy. If plant cells are in a hypertonic environment, they will undergo plasmolysis. Causes the plant cell to lose water & turgor pressure, resulting in cell death. Bacteria & fungi cells can also undergo plasmolysis. Facilitated Diffusion This is diffusion across the cell membrane with the “help” of proteins It still flows from a high to low concentration Facilitated Active and Passive Transport Active Transport Active transport requires “action” or energy in order to move these particles across the cell membrane The input of energy along with special proteins on the surface of the cell can move any particles across any “gradient” Gradient – relative concentration of a solution Endocytosis & Exocytosis Exocytosis The removal of large amounts of material from the cell is known as exocytosis The vesicle fuses with the cell membrane and forces its contents out of the cell