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Transcript
Cells: The Basic Units of Life • • • • • • • • • The Cell: The Basic Unit of Life Prokaryotic Cells Eukaryotic Cells Organelles that Process Information The Endomembrane System Organelles that Process Energy Other Organelles The Cytoskeleton Extracellular Structures • Life requires a structural compartment separate from the external environment in which macromolecules can perform unique functions in a relatively constant internal environment. • These “living compartments” are cells. The average human being is composed of around 100 Trillion individual cells!!! It would take as many as 50 cells to cover the area of a dot on the letter. Discovery of Cells 1665- English Scientist, Robert Hooke, discovered cells while looking at a thin slice of cork. He described the cells as tiny boxes or a honeycomb He thought that cells only existed in plants and fungi Anton van Leuwenhoek 1673- Used a handmade microscope to observe pond scum & discovered single-celled Organisms. He called them “animalcules” He also observed blood cells from fish, birds, frogs, dogs, and humans Therefore, it was known that cells are found in animals as well as plants Between the Hooke/Leuwenhoek discoveries and the mid 19th century, very little cell advancements were made. This is probably due to the widely accepted, traditional belief in Spontaneous Generation. Examples: -Mice from dirty clothes/corn husks -Maggots from rotting meat 19th Century Advancement Much doubt existed around Spontaneous Generation Conclusively disproved by Louis Pasteur Redi’s experiment Pasteur’s experiment Development of Cell Theory 1838- German Botanist, Matthias Schleiden, concluded that all plant parts are made of cells 1839- German physiologist, Theodor Schwann, stated that all animal tissues are composed of cells. M. Schleiden T. Schwann 1858- Rudolf Virchow, German physician, after extensive study of cellular pathology, concluded that cells must arise from preexisting cells. Cell Shapes 11 Cell Shapes 2 • • • • • • • • • Squamous = thin and flat Polygonal = irregularly angular with 4 or more sides Cuboidal = squarish Columnar = taller than wide Spheroid = round Discoid = disc-shaped Stellate = starlike Fusiform = thick in middle, tapered at ends Fibrous = threadlike 12 Cell Theory 1. All organisms are composed of one or more cells -Organisms can be unicellular or multicellular. 2. The cell is the basic unit of organization of organisms. 3. All cells come from pre-existing cells -Cells reproduce to make exact copies of themselves Exceptions to cell theory • Protozoans do not have cellular body. They are acellular. • Bacteria and blue green algae (cynobacteria) do not possess an organised nucleus. Their genetic material lies uncovered in the cytoplasm. They also lack membrane bound organelles. • Some tissues such as connective tissues, have-non-living material called matrix in which living cells remain embedded. Cell theory does not cover such cases. • RBC’s and seive tube cells live without nucleus and other cell organelles • Protoplasm is replaced by non-living materials in the surface cells of skin and cork. • Viruses do not have a cellular machinery. They consist of a nucleic acid (DNA or RNA) core surrounded by protein sheath. They are inert, except, when present in a living cell of some organism where they multiply by using cell’s mateials and machinery. Modern Cell Theory Modern Cell Theory contains 4 statements, in addition to the original Cell Theory: - The cell contains hereditary information(DNA) which is passed on from cell to cell during cell division. - All cells are basically the same in chemical composition and metabolic activities. - All basic chemical & physiological functions are carried out inside the cells.(movement, digestion,etc) - Cell activity depends on the activities of sub-cellular structures within the cell(organelles, nucleus, plasma membrane) -Cell size is limited by the surface area-tovolume ratio. - The surface of a cell is the area that interfaces with the cell’s environment. The volume of a cell is a measure of the space inside a cell. - Surface area-to-volume ratio is defined as the surface area divided by the volume. For any given shape, increasing volume decreases the surface area-to-volume ratio. ● Because most cells are tiny, with diameters in the range of 1 to 100 m, microscopes are needed to visualize them. ● With normal human vision the smallest objects that can be resolved (i.e., distinguished from one another) are about 200 m (0.2 mm) in size. The scale of life The scale of life Two Types of Cells • Prokaryotic Cells: – No nucleus – No organelles – Mostly unicellular organisms – Cell wall or membrane Specialized features of some prokaryotic cells: - A cell wall just outside the plasma membrane (made of carbohydrates). - Some bacteria have another membrane outside the cell wall, a polysaccharide-rich phospholipid membrane. - Some bacteria have an outermost slimy layer made of polysaccharides and referred to as a capsule. Some bacteria, including cyanobacteria, can carry on photosynthesis. The plasma membrane is infolded and has chlorophyll. Some bacteria have flagella, locomotory structures shaped like a corkscrew. Some bacteria have pili, threadlike structures that help bacteria adhere to one another during mating or to other cells for food and protection. Three types of prokaryotic cells 1. Bacteria without Cell Walls – Mycoplasma- PPLO • Lack a rigid cell wall during their entire life cycle • Smallest known organisms – smallest genomes (other than viruses) – Diameter ranges from 0.15 m to 0.30 m • Do not stain with the Gram stain. • May be saprophytic or parasitic. • Pleomorphic – Tiny pleomorphic cocci, short rods, short spirals, and sometimes doughnut shape • Mycoplasma pneumoniae – Atypical pneumonia in humans. 23 2. Kingdom Eubacteria • • • • Unicellular (single-cell) Prokaryotes (no membrane-bound organelles) Cell Walls contain peptidoglycan, not cellulose First appeared approximately 3.7 BYA Nutrition Autotrophs- manufacture organic compounds – Photoautotrophs- use light energy & CO2 – Chemoautotrophs-use inorganic substances like H2S, NH3, and other nitrogen compounds • Heterotrophs- obtain energy by consuming organic compounds – parasites- get energy from living organisms – saprobes (saprophytes)- get energy from dead, decaying matter; also called decomposers. • Bacteria cells digest foods by releasing enzymes (which are usually poisonous) outside the cells and into their food. This is called Extra-cellular digestion. • • The digested foods are then absorbed by diffusion or active transport. Oxygen Preferences • obligate aerobes must have oxygen • obligate anaerobes cannot live in oxygen • facultative anaerobes can grow with or without oxygen General Characteristics • are found almost everywhere • are often pathogenic (they make us sick!) • are divided into groups according to: – their shape – grouping – cell wall – ability to absorb stains Shapes • Coccus = spherical (coccus came from the Greek word for berries!) • Bacillus = rod-shaped • Spirilla = spiral-shaped. Examples of Spherical-shaped cells Cyanobacteria Gram negative phototrophs - Oxygenic photosynthesis 12H2O + 6CO2 C6H12O6 + 6H2O + 6O2 - Existed for 2.3 bya - Largest and one of the most important groups of bacteria on Earth Extremely diverse group - Unicellular, colonial & filamentous form - Some species fix N2 in heterocysts - Some species produce akinete Analogous to a endospore - Most species are found in fresh water ▪ Marine ▪ Damp soil ▪ Temporarily moistened desert rocks ▪ Endosymbionts in lichens, plants, various protists or sponges Two Types of Cells • Eukaryotic Cells: – Nucleus – Organelles surrounded by membranes – Mostly multicellular – organisms – Cell wall or membrane Eukaryotic cells Prokaryotic cells Vesicles: Mitochondria: Chloroplasts: Plasma membrane with steriod Golgi apparatus: Endoplasmic reticulum: Differentation: Ribosomes: Cytoskeleton: Vacoules: Number of chromosomes: Present Present Present (in plants) Present Absent Absent Yes Usually no Present Absent Present Absent Tissue and organs 80S especially in Mitochondria and chloroplast Present Present Radimentary More than one One 70S May be absent Present DNA complexed histones: True Membrane bound Nucleus: Yes No Present Absent Cell wall: Chemically simpler Nucleolus: Mitosis Occurs: Genetic Recombination: Present Yes Mitosis and fusion gametes Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlets Flagella: Lysosomes and peroxisomes: Microtubules: Usually chemically complexed Absent No Partial, undirectional transfers DNA Submicroscopic in size, composed of only one fiber Present Absent Present Absent or rare Cell Organelles • Cytoplasm: – Structure: gel-like material found inside the cell, made of water, salts, and organic materials. – Function: holds the organelles, keeps them separate. • Cell wall: – Structure: a tough outer covering made of cellulose, small holes are present that allow materials to enter and exit the cell. – Function: maintains shape, supports, strengthens – Only plant cells have cell walls. • Cell membrane: a protective covering that surrounds the cell. – Materials entering the cell must pass through the cell membrane. Some materials can easily enter while others cannot cross at all. – Selectively permeable. – Made of a phosopholipid bilayer: The heads of the lipids are hydrophilic (water loving) while the tails are hydrophobic (water fearing). – Both plant and animal cells have cell membranes • Nucleus: – Structure: round, large organelle. Surrounded by a membrane. Contains the DNA, nucleolus, and chromatin. – Function: controls the cell – Nickname: “brain” • Nuclear membrane: surrounds and protects the nucleus. • Ribosomes: – Structure: made of RNA – Function: produce proteins – Location: attached to the endoplasmic reticulum. – Nickname: food source • Endoplasmic Reticulum: Structure: made of membranes, flattened sacs Location: located next to the nuclear membrane Nickname: highway, subway system, … Smooth ER: does not contain ribosomes, makes lipids and membrane proteins, transports proteins – Rough ER: contains ribosomes, makes proteins. – – – – • Golgi Body: – Structure: stack of membranes. – Function: packages proteins from the ER and distribute them around or outside of the cell. – Nickname: UPS or shipping center, … • Mitochondria: – Structure: outer membrane is a phospholipid bilayer, inner membrane is permeable to oxygen, carbon dioxide, and water. Wrinkled appearance – Function: transform the energy in food to energy the cell can use to drive chemical reactions. – Nickname: “powerhouse” of the cell. • Lysosomes: – Structure: sac filled with enzymes and liquids. – Function: involved in digestion of old cell organelles as well as breaking large molecules into smaller ones. – Location: found in all animal cells, rare in plant cells. – Nickname: garbage person, stomach. • Vacuoles: – Structure: cell membrane surrounding a fluid. – Function: storage area • Plant cells: very large organelle, contains pigments, waste, salts, water. Maintains turgor pressure • Animal cells: smaller organelle, primarily responsible for general storage. – Nickname: storage tank. Difference Between Plant Cell And Animal Cell • • • • • • • • • • • PLANT CELL ************ Shape Size Cell Wall Vacuole Plastid Centrosome Mitochondria Amino Acid Cell Division • • • • • • • • • • • ANIMAL CELL ************** Shape Size Cell Wall Vacuole Plastid Centrosome Mitochondria Amino Acid Cell Division Plant cell 1. Rectangular in shape. 2. Plant cell is covered by a thick cell wall. Cell wall is made up of cellulose and hemicellulose. 3. Plant cell is larger than Animal cell. 4. Vacuole is big, prominent and permanent. 5. Plastids are present . 6. Centrosome is absent. 7. The number of Mitochondria is less in plant cell than animal cell. 8. Cell Division occurs by cell plate . Animal cell -Spherical in shape - Animal cell is covered by a thin cell membrane. It is made up of Lipoprotein. - Animal cell is smaller than plant cell. - Vacuole is small, temporary and not so prominent. -Plastids are absent. -Centrosome is present. -The number of Mitochondria is approximately more in animal cell. -Cell Division occurs by furrow in spite of cell plate. Plant cell 9. Nucleus is pushed to one side of the cell by central vacuole. 10. Crystals are mostly present. 11. Can synthesize all amino acids, coenzymes and vitamins. 12. Glyoxysomes may be present. 13. Store carbohydrates as starch. Animal cell - The nucleus is mostly located in the centre of the cell. -Crystals mostly lacking. -Incapable of synthesizing all amino acids, coenzymes and vitamins. -Glyoxysomes not present. - Carbohydrates are stored as glycogen.