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Transcript
PAP and Biology A Look at Cells—Cell Theory, Structure, & Function NOTES Cells are the smallest unit of life that can carry out all the functions of a living organism; not discovered until the invention of the microscope. Organisms can be very broadly classified on the number of cells they are made of. Unicellular organisms are made of only 1 cell; they are the smallest of all living organisms. Ex) some bacteria, many protists Other living organisms are made of many cells and are called multicellular Ex) Plants, animals, and fungi Shape is related to function Blood cells (hemocytes) - round to move through vessels Nerve - long to carry message to spinal cord Muscle cells - for contracting and relaxing Categories/Types of Cells Cells can be separated into two broad categories or types based on their internal structures: Prokaryotic cells and Eukaryotic Cells Prokaryotic cells- do not have a nucleus or other membrane-bound organelles. - cell’s DNA is suspended in the cytoplasm - most prokaryotes are microscopic, single-celled organisms - Bacteria are the ONLY prokaryotes! Eukaryotic cells – have a nucleus and other membrane bound organelles - cell’s DNA is enclosed in the nucleus - Eukaryotes can be unicellular or multicellular organisms - Animals (including humans), plants, fungi, and protists are ALL eukaryotes! Discoveries In 1665 Robert Hooke observed a thin slice of cork from an oak tree What he saw reminded him of the rooms in which monks lived so he called what he saw under the microscope a “cell”; Hooke is credited with naming the “cell” In 1670 Anton van Leeuwenhoek used the first “real” microscope to view pond water He saw living creatures that we now call singled celled organisms In 1840, Robert Brown discovered the nucleus of a cell; He observed the epidermal cells of orchids and the anthers of Tradescantia (spiderwort plant) Looking at Cells -Cells are the smallest unit of life that can carry out all the functions of a living organism -Not discovered until the invention of the microscope Cell Theory The Cell Theory was established by 3 men: • Schleiden 1838, botanist, “all plants are made of cells” • Schwann 1839, zoologist, “all animals/organisms are made of cells” • Virchow 1855, physician, “all new cells come from other cells” (biogenesis) Cell Theory • Cells are the basic units of all life • All organisms are made of 1 or more cells • All cells come from other cells Cell Structure • • • Many components make up a cell and carry out specific activities Each component works together, like a factory, to keep the cell functioning These components are called organelles Typical Animal Cell: Typical Plant Cell: 5 structures in ALL cells (prokaryotes and eukaryotes) 1. Cell Membrane 2. Cytoplasm 3. Cytoskeleton 4. DNA 5. Ribosomes When comparing just plants and animal cells: Only plants - Only Animals Central Vacuole Chloroplast Cell Wall - lysosome* centriole* Cell Organelles Structure & Function Cell Membrane: Structure: Made of phospholipids and proteins -2 phospholipid layers called a bilayer - Semipermeable (a.k.a. selectively permeable) - Hydrophilic (H2O loving) head - Hydrophobic (H2O fearing) tail - Thin layer of lipids embedded with protein Function: maintain homeostasis 1. Controls what enters and leaves 2.Boundary separating the cell from its environment Cell Wall Structure: - Found in plant, algae, fungi and most bacterial cells - In plants and algae made of cellulose - In fungi made of chitin - In eubacteria made of peptidoglycan - In archaebacteria made of lipids Function: - Provides support and protection - Helps maintain square shape Cytoplasm: Structure: Jelly like base throughout the cell - consists of mainly water and cytosol (an organic compound) - contains the cytoskeleton Function: -Contains or “suspends” organelles inside the cell - Site of many chemical reactions where water is the solvent Polar Non-polar Cytoskeleton Structure-composed of flexible protein fibers 3 types: • microtubules –act as tracks for movement of organelles (largest) • intermediate filaments – give the cell its strength (medium) • microfilaments – tiny threads that allow cells to move and divide (smallest) Function- provides support and a place to “anchor” other structures Centrioles Structure -Found in animal cells and some algae - made of microtubules - shaped like a cylinder Function - Aid in the division of chromosomes in mitosis. Nucleus Structure: - Found in the cytoplasm - Contains the genetic material (chromosomes made of DNA & proteins) - Surrounded by a nuclear envelope (double membrane) -Contains the nucleolus that makes ribosomes Function: Control headquarters for the cell (brain) Nucleolus -Found inside of nucleus Structure - Dense knot of chromatin Function - Produces ribosomes Nuclear Envelope Structure- double lipid bilayer. It has small holes called nuclear pores. Function- encloses genetic material (DNA) in eukaryotic cells and the holes allow mRNA to leave during transcription Ribosomes Structure- spheres composed of RNA and protein (assembled in the nucleolus) Function-site of protein synthesis • Free ribosomes make proteins that remain inside the cell • Attached ribosomes make proteins that become part of the cell membrane or are exported or secreted from the cell (usually attached to the ER) Endoplasmic Reticulum (ER) Two types: 1. The rough ER - has ribosomes attached 2. The smooth ER - does not have ribosomes 1. Rough ER Structure: - Network of folded membranes near nucleus - Contains ribosomes on surface Function: -Transports proteins that were made by the attached ribosomes through the cell to the golgi. 2. Smooth ER Structure: - Network of folded membranes throughout cell - Contains no ribosomes on surface Function: - Makes lipids and breaks down toxic substances, (such as drugs and alcohol) Golgi Apparatus Structure - Closely stacked, flattened membrane sacs - Found in the cytoplasm - Near nucleus Function - Stores, packages, and transports products inside for use outside -Releases vesicles(a bit of the golgi pinched off) for transport of stored protein. Vesicles Structure - bits of membrane from the plasma membrane or from the golgi apparatus - found inside or outside of the plasma/cell membrane Function - Vesicles fuse with the cell membrane - may be used to release or transport chemicals in or out of the cells: o Exocytosis out of the cell o Endocytosis into the cell - Transports chemicals to lysosomes or vacuole Lysosomes Structure - found in animal cells - saclike - contain digestive enzymes Function - Digests food particles - Digests old organelles - Defends cells from bacteria and viruses Vacuole Structure - Found in cytoplasm - Sac of fluid surrounded by a membrane Plants: Large in size (have one central vacuole) Animals: small in size (have many) Function - Sites of storage of water, ions and some nutrients. - Plants: allows plants to maintain turgor pressure; plant wilts when large central vacuole is empty Mitochondria Structure - Oval - Inside is a complex matrix of folded membranes to increase surface area. - Has own ribosomes and DNA Function - Changes energy stored in food into a more useful form - ATP is formed inside as a product of cellular respiration - powerhouse of the cell Chloroplast Structure - Found in plant cells (and some protists) - Double phospholipid bilayer. Inner layer Disc like structure containing chlorophyll = thylakoid Stacks of thylakoids = grana Non stacked area = stroma Function - Capturing radiant energy and converting it to chemical energy during photosynthesis. - Chlorophyll is the green pigment that traps the energy from the sun Cilia Structure - Found outside of the cell - short hair-like Function Locomotion (movement) • tiny, flutters of movement. Flagella Structure - Found outside of the cell - long whip-like Function Locomotion (movement) • one big wave motion will cause a large amount of movement