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Chapter 6 Cells Dr. Joseph Silver
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It was only in the 1500 and 1600s that people actually began to exam what the body was made up of blood carried a vital force semen carried the vital force the brain made the vital force but nothing was really known about cells
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in 1665 Robert Hooke using a primitive magnifying system saw little compartments in samples of cork and called them cells meaning “little rooms”
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a few years later (1674) Anton van Leeuwenhoek using a better primitive microscope was the first to observe little things moving in drops of water he called them “animalcules”
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further advances in light microscopy allowed for better contrast, resolution, and greater magnification
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in 1838 Matthias Schleiden stated that all plants are made up of cells and in 1839 Theodor Schwann stated that all animals are made up of cells and the cell theory was born
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the cell theory 1. all living things are made up of one or more cells 2.cells are the basic building block of all organisms 3. cells come from other cells
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most cells are vey small large (thick) cells are not as efficient why? Read fig. 6.7 page 98
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cells are small because it of the ratio between surface area compared to volume surface area is represented by the cell membrane volume is represented by the cytoplasm (liquid in the cell) and it’s contents
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in every cell there is a cell membrane which regulates what goes in and out of the cell and the inside of the cell where all of the work that the cell does takes place in the cytoplasm the membrane and the cytoplasm must work together but as the cell gets larger problems take place
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as a cell grows the surface area increases but not as fast as the cytoplasm inside the cell eventually the cell becomes too big and the cell membrane can no longer keep up with the needs of the inside of the cell and this becomes the stimulus for the cell to divide and become two smaller cells
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volume is 4 x 4 x 4 = 64 surface area = 4 x 4 = 16 x 6 = 96 ratio = sa /vol = 96/64 = 1.5
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scientists use microscopes and biological stains (chemicals which stain specific cell parts) to study the make up of cells
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the ability of scientists to see inside of a cell is limited by the wavelength of the beam or energy passing through a cell the wavelengths of light are much larger than the smaller wavelengths of an electron beam electron beams allow electron microscopes to show structures almost down to the level of an atom
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what is a cell? every cell in a multicellular organism has exactly the same genes but most genes in a cell are turned off only the genes needed by a cell to do the work of that cell are turned on
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cells are divided into two groups prokaryotes and eukaryotes
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prokaryotes primitive cells - a simple but effective structure - one (1) strand of DNA some have a second - cell membrane and cell wall - move by pili and flagella - pili also used for attachment and gene exchange - have free ribosomes - no membrane bound organelles - no nucleus scavengers, carnivores, photosynthetic, decomposers
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eukaryotes advanced cells compartmentalized organelles nucleus protects genetic material internal endomembrane system internal transport system you have eukaryotic cells in your bodies
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terms you should be able to describe and explain cell membrane – nucleus – nuclear membrane – nucleolus – chromatin – nuclear pores – ribosome – rough endoplasmic reticulum – smooth endoplasmic reticulum – vesicle – Golgi apparatus – cisternae -mitochondria – peroxisome – lysosome – cytoplasm – centriole – cytoskeleton – filaments –microtubules – actin – nucleoplasm – chloroplast – central vacuole – DNA – RNA – mRNA – rRNA – tRNA – endocytosis – exocytosis – phagocytosis – endosymbiosis – molecular motor – flagella – extracellular matrix -
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in chapter 7 we will study the structure and functions of the cell membrane in more detail and put knowledge of all of these terms together to understand how a cell responds to a message from in or out of the cell to produce a product or produce a change in the cell
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every cell has a cell membrane made up of a double phospholipid layer the polar phosphate ends are in contact with the liquid material inside and outside of the cell the lipid part is present inside the membrane (we saw this in chapter 5)
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the cell membrane separates the cell components from the fluids outside of the cell the many structures found in the membrane regulate what goes in and out of the cell many membrane structures act as receptors to hormones, nutrients, and other chemicals and by interacting with these chemicals begins the process of gene activation and cell response
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the nuclear membrane surrounds the nucleus it has pores which allow material to go in and out it keeps the genetic material separate from the cytoplasm the DNA is present as chromatin (an unwound state) dark areas called nucleolus are areas where RNAs are being made
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DNA contains the genetic code(for many genes) one gene makes one kind of RNA mRNA goes to the cytoplasm and a protein is made many of the proteins are enzymes there are thousands of mRNAs rRNAs form ribosomes in the cytoplasm (protein factories) tRNAs bring amino acids to ribosomes to make up a protein
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mRNA leaves the nucleus links up with a free ribosome or a ribosome on the rough endoplasmic reticulum and stimulates the production of proteins and enzymes
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the enzymes then link up with other cell components and cause the chemical reactions of those components to work millions of times faster then when the enzymes are not present in other words enzymes tell the cell what work to do when done the enzymes are recycled
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completed products from the RER, SER or free ribosomes are secreted as transport vesicles which fuse with the Golgi apparatus
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some enzymes go to the smooth endoplasmic reticulum where manufacture of lipids takes place calcium is stored, steroids are made, chemicals are rearranged, non protein products are produced
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materials enter the Golgi apparatus from the RER and the SER as transport vesicles are rearranged and are packaged (made ready for delivery to where they are needed) these products are pushed out of the Golgi at the ends of the membranes (cisternae) in the from of secretory vesicles
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the vesicles which leave the Golgi can be used outside of the cell or in the cell many secretory vesicles combine with the cell membrane and by exocytosis are moved out of the cell
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a cell is very sensitive to its internal and external environment when a structure or compound is no longer necessary a membrane bound vesicle called a lysosome which contains digestive enzymes break down and recycle structures and chemicals for new uses
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another important vesicle is the peroxisome it contains enzymes for destroying lipids when activated the enzymes in peroxisomes produce hydrogen peroxide
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the various vesicles which have many cytoplasmic functions are collectively known as microbodies
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in order to survive a cell needs energy mitochondria produce a high energy phosphate molecule known as ATP adenosine tri phosphate which produces the energy used by cells to do work
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when a cell is not doing too many things the cell contains few mitochondria but when a cell is very active there are many mitochondria
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mitochondria are -sausage shaped organelles -have an inner and outer membrane -the inner membrane is very folded -the folds are known as cristae -the space in the cristae is the matrix -the space between the layers is the intermembrane space -the inner membrane contains enzymes for making ATP -mitochondria have their own (non human) DNA
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mitochondrial DNA rarely mutates it is like having a visitor within a cell which makes many of the enzymes the cell needs to generate energy from braking down glucose we cannot live without them!!!!
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as with mitochondria plant chloroplasts which produce ATP and glucose by photosynthesis are double membrane and also have their own DNA plants also contain other organelles which have their own DNA collectively these are known as plastids
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mitochondria and plastids are believed to at one time been independent prokaryotic cells which when “eaten” by a eukaryotic cell provided some benefit to the eukaryotic cell so it was not destroyed and over time have each adapted to this beneficial relationship endosymbiosis
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the inside of a cell is a thin Jello-like cytoplasm the cell membrane is a thin layer of phospholipid if this was all that a cell had the cell would collapse but a cell has a cytoskeleton a series of actin filaments, microtubules, and intermediate filaments which allow a cell to retain a circular shape
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actin filaments allow cell and organelle movement and cell membrane extensions microtubules aid cell movement organize the cytoplasm are short lived and move materials about the cell
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intermediate filaments are tough long lasting fibrous stable proteins which provide -support for the membrane -anchor organelles in place -anchor the nucleus -acts as a true skeleton for the membrane, cytoplasm, and membrane projections
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many of the cells components are organized into functional complexes organelles, enzymes, microbodies, molecular motors and more are in close proximity to each other so that all of the things needed to do work are right next to each other
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but in many cases when a cell makes a product it is not always made exactly where it will be used a cell has an internal highway system which is used to move materials about the cell it is called a molecular motor
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https://video.search.yahoo.com/video/play;_ylt=A2 KLqICpuCpUng8A9S_7w8QF;_ylu=X3oDMTEwN WU3ZWNzBHNlYwNzcgRzbGsDdmlkBHZ0aWQD VjE3OQRncG9zAzEy?p=molecular+motor&vid=02 83e937c212c9e84bc1f247e4c1149d&l=1%3A07&t url=http%3A%2F%2Fts4.mm.bing.net%2Fth%3Fid %3DVN.608013154318287947%26pid%3D15.1&r url=http%3A%2F%2Fwww.youtube.com%2Fwatch %3Fv%3DKfEbuHCGIIo&tit=Myosin+V+%3Cb%3 Emolecular+motor%3C%2Fb%3E&c=11&sigr=11af iov7v&sigt=10vo2lhlr&age=0&fr=ytff1-&tt=b
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https://www.youtube.com/watch?v=7sRZy9PgPvg
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look at fig 6.21 page 113 actin and dynein are the same chemicals which allow movement of prokaryotes, sperm, and cell projections microtubules form an internal highway system this complex is used to move material to where it is needed
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a cell membrane is much more than a simple skin animal cells secrete an extracellular matrix which is made up of fibrous proteins (collagen) glycoproteins (receptors, transporters) elastin (membrane strength & shape) integrins (chemical & mechanical signals) which cover the outside of the cell membrane
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the extracellular matrix -connects the interior of the cell with the exterior of the cell -provides strength for cell shape -anchors internal and external structures -responds to external hormones & chemicals
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now let’s integrate all of this information and some which we will get from chapter 7 into a logical sequence of events of what happens in a cell
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-a chemical is floating in the liquid outside a cell -a membrane projection links up with the chemical -causes change in shape of a membrane chemical -cause chemical change in cytoplasm -change eventually causes chemical change in nucleus -one gene is opened up and copied as mRNA -mRNA leaves nucleus links up with ribosome -ribosome makes proteins and enzymes -enzyme stimulates 1 chemical reaction to work very fast -product goes to Golgi for rearrangement and packaging -Golgi releases vesicle which is moved by molecular motor -vesicle use in cell or is moved out of cell
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look at fig 6.8 fig 6.15 these figures show most of the structures and steps needed for reception of a chemical message to production of a cell product
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cell junctions cells that are next to each other interact with each other adhere to each other communicate with each other see fig. 6.30 page 120
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tight junctions = two cell membranes glued together desmosomes = rivets or screws holding two cell membranes close to each other and allowing some movement gap junctions = connects the cytoplasm of adjacent cells
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parts of chapter 6 not included here (centrioles or centrosomes) will be addressed when we study the cell cycle in chapter 12
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