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Bio1140 Textbook + Lecture Notes

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University of Ottawa
Kathleen Gilmour

What is a cell? a fundamental unit of life every organisms consists of cells or is a cell key characteristics of a cell: genetic material that runs the cell surrounded by a cell membrane has a control centre contains cytoplasm ~ semi-fluid liquid made up of water and contains sugars, salts, organic molecules smallest functional unit of life structures within the cell that allow it to synthesize proteins responds to external influences come from other cells wide variety of cells can be eukaryotic or prokaryotic metabolism can evolve ~ heritable changes that are passed down from one generation to the next 3 tenets to the cell theory: proposed by Theodor Schwann and Matthias Shleiden Cells are diverse in terms of shapes, functions, some are general while others are specialized, size most cells are small, but not all ex: ostrich egg = single cell (average diameter = 13cm) Why can we generalize from one cell to another? There are commonalities between cells that allow us to do this when broken down to their subunits they all contain the same building blocks Metabolism - the use of ATP as a general “currency" Use of DNA for genetic information Size matters cell are small, usually: prokaryote = 1-5 um eukaryote = 10-30 um Surface area - determines area of exchange volume ratio - determines how much needs to be created for exchange As cells get larger to surface area to volume ratio gets smaller, this means as the cell is getting larger and aquiring more things the surface area allowing these in/out gets smaller (ratio wise) things within a cell move by diffusion as distance gets longer, the time required for diffusion increases very rapidly (it is cubed, diffusion^3) this poses limitations on the rate of the metabolism of the cell As cells get larger they require more molecules of the substrate in order to reach adequate concentrations It may not be able to synthesize everything needed for biochemical reactions to sustain life Prokaryotes 1-5um simple cells cell membrane bounded by a cell wall simple cytoplasm - consists of cytosol that contains ribosomes for protein synthesis and genetic material no membrane around the genetic material (no nuceus), called nucleoid 2 broad groups of prokaryotic cells Archaea (extremophiles) Bacteria ex: e. coli, saphylococus, helicobactr… Best known prokaryotes is Escherichia coli (E. coli) can survive without O2, found in lower gut of mammals, most strains of it don’t cause problems some strains cause disease it is easy to grow in a lab ~ incubator can grow very rapidly (divides about every 20mins) people have used/modified E. coli to produce things of interest, for example: genetically manipulating bacteria to produce compounds like vitamins or to break down things in the environment Eukaryotes larger than prokaryotes size of around 10-30um membrane bound organelles - overcome the limitations of adequate concentrations transport system - don’t have to rely on diffusion - carried out by microtubules cytoplasm is more complex than the prokaryotic cytoplasm this comes at an energetic cost, this is balanced due to the fact that eukaryotic cells can generate ATP much more efficiently than prokaryotes ~ mitochondria protists (single-celled eukaryotic organisms) Fungi, animals, plants (multicellular eukaryotic organisms Arabidopsis thaliana - weed in the mustard family, grow easily and quickly, relatively small genome Saccharomyces cerevisiae - baker’s yeast, brewer’s yeast, bread, bear, easy to grow in a lab, shares metabolic pathways with other eukaryotes Mus musculus - mouse, most common organism used for biomedical research, small, easy to keep in a lab setting, reproduce every three months, large numbers in small spaces Drosophila melanogaster - fruitfly, can grow lots in small dishes, reproduce quickly, many of the genetic differences have observable phenotypes Danio rerio - zebrafish, uses external fertilization, quite rapid in terms of development, go from fertilized egg to adult in about 24 hours, they reproduce easily, can microinject the clear embryos to see effects of substances, becoming more popular for biomedical research, they can also regenerate their heart tissue Caenorhabditis elegans - roundworm, nematoad, shows aging, development, behaviours, can study things relevant to humans How did eukaryotic cells arise? the endosymbiont theory (around 1905) widely accepted as the most plausible explanation as to how eukaryotic cells arose an original prokaryotic cell that somehow incorporated an aerobic bacteria into itself which become mitochondria Later on, this eukaryotic cell underwent another change ~ it engulfed photosynthetic bacteria (algae) which became chloroplasts = plants and some protists, other eukaryotes = animals, fungi, some protists this can explain the relatively sudden appearance of eukaryotic organisms one of the strongest line of evidence is the similarities between the mitochondria and chloroplasts to prokaryotic cells both have their own ribosomes chloroplasts and mitochondria can only exist through cell divisions = binary fission this supports the endosimboint theory functions of mitochondria oxidative metabolism - nutrients to ATP 2 membranes, own and cell's Chloroplasts convert light energy to glucose for the plants 2 membranes, own and cell’s At the sequence level, the mitochondria and chloroplasts are more similar to prokaryotes than eukaryotes. cytoplasm is more complex in eukaryotic cells than prokarotic cells cytosol is the same in eukaryotic cells and prokaryotic cells endosymbiotic theory fossil record strong similarities sequence homology present day examples of endosymbiosis - some sponges, hydra, “solar-powered” sea slug sea slug - extracts chloroplasts from its food and incorporates them into the cells that line its intestine - in the end the entire body appear green - once they’ve been incorporated the chloroplast’s function - allowing it to get energy from the sun - chloroplasts do not divide & are not passed down to the next generation (kleptoplasty - “stealing chloroplasts from its food”) How does kleptoplasty in Elysia chlorotica differ from the endosymbiotic origin of chloroplasts? endosymbiont = 2 cells (1 cell incorporated a 2nd cell into it) - in this case a cell organelle was incorporated and not a cell kleptoplasty - no reproduction of the chloroplasts endosymbiont - cell was able to reproduce in the host cell kleptoplasty - no transmission of chloroplasts form one generation to the next endosymbiont - it was transmissable to next generation CHAPTER 2 (except 2.5) Prokaryotic cell - particular cell architecture lacking a nucleus bacteria, archaea 3 shapes are common to prokaryotic cells: spherical rodlike spiral DNA is a single circular molecule the DNA molecule is the prokaryotic chromosome DNA is copied into mRNA (messenger RNA) which is then used by ribosomes to assemble amino acids ino proteins Each ribosome consists of a large and small subunit the cell wall is coated with an external layer of polysaccharides (outer most layer) called the glycocalyx gelatinous = slime layer firmly attached to cells = capsule flagellum - pushes the cell through a liquid medium pili- attach the cell to other cells or surfaces Eukaryotes - cells’ whose DNA is bound in a compartment - the nucleus protists, fungi, animals, plants have a true nucleus and cytoplasmic organelles enclosed within a plasma membrane cytosol - energy metabolism, molec
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