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UW-Milwaukee BIOSCI 152 - Cell Structure and Function

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BIO SCI 152 1st Edition Lecture 2BioSci-152 Lecture 2 Cell Structure and FunctionProkaryotic Cells and the Importance of being smallProkaryotes are usually small (usually 0.5-2 m in diameter.).Eukaryotic cells are larger, usually 10-50 m diameterTo give you some idea of size of these organisms, note that:1000 m = 1 mm1000 mm = 1 mSo, a typical bacterium is 1000 times smaller than a millimeter, and thus cannot be seenwith naked eye.Small size of prokaryotes is an advantage when it comes to utilizing scarce nutrients.Smaller cells generally transport and utilize scarce nutrients more rapidly resulting in faster growth rates.B. Bacterial Cell Structure1. CytoplasmDNA, called nucleoidRNARibosomesSoluble proteinsSmall molecules2. Cytoplasmic membranephospholipid bilayer with proteins embedded- fluid mosaic structure bacterial phospholipids are made of fatty acids and glycerol-phosphate-Membrane displays selective permeability- allows nutrients in, wastes out-Many enzymes of metabolism in membrane (for example for generation of ‘proton motive force’ and of ATP)3. Cell wall-give cell shape and prevents cell lysisMain structural component is peptidoglycanpeptidoglycan is composed of sugars and amino acidssugars: N-acetyl muramic acid (NAM), N-acetyl glucosamine (NAG) D and L amino acids(N-acetyl muramic acid and D amino acids are not commonly found elsewhere in nature.)lysozyme is an enzyme that cleaves peptidoglycan between sugar residues.penicillin is an antibiotic that prevents amino acid cross bridge formation thus preventing synthesis of peptidoglycan.a. Gram positive cell wall has thick layer of peptidoglycan (up to 25 layers thick)b. Gram negative cell wall has thin layer of peptidoglycan (1 or 2 layers thick) and an outer membraneouter membrane (OM) -protects the cell by excluding toxic moleculesstructure of outer membrane:-lipid bilayer with proteins embedded-composition is very different from cytoplasmic membrane -phospholipids make up innerleaflet of OM-Lipopolysaccharide (LPS, also known as 'endotoxin') constitutes the bulk of the outer face of the OM-'Porins' in outer membrane allow nutrients in and wastes out. Porins are made of protein.periplasm- space between cytoplasmic and outer membrane of Gram negative cell.some proteins involved in nutrient uptake are found in the periplasm.Bacterial Flagella -Structure:-long rigid propellers that extend from the cell-bulk of the structure is composed of multiple copies of the protein flagellin -complex motor in the cell envelope composed of many different proteins anchors the flagellum to the cell-Rotation of the flagellum results in cell movement-H+ (proton) gradient across the membrane (proton motive force) is the energy source used by the flagellar motorSpirochetes are a type of bacteria that have unusual flagella that do not extend from the cell but rather are enclosed within the periplasm of the cell. Some spirochetes cause disease- A member of the genus Borrelia causes Lyme disease. A member of the genus Treponema causes the sexually transmitted disease syphilis.5. Pili (singular ‘pilus’)- long filamentous structures composed of protein that extend from the cellFunctions:-attachment to surfaces-some pili involved in transfer of DNA between cells by conjugation-some pili involved in twitching motility (unrelated to bacterial flagellar motility)1)pilus extends from cell and tip attaches to surface 2) retraction of pilus pulls cell over the surfaceArchaeal Cell structureSimilar in gross appearance to Bacterial cells, but have major differences:1. Unusual lipids make up Archaeal membranesether linked isoprene hydrocarbons instead of the ester linked fatty acids that are found inmembrane lipids of bacteria and eukaryotes2. Archaeal cell walls do not have PeptidoglycanDepending on the organism cell walls may be made of polysaccharide, protein, or other polymers.Lysozyme and penicillin have no effect on archaea (fortunately, no archaea are known to cause disease in humans)3. Archaeal flagella. Gross structure and function (rotation of flagellum to propel cell) similar to bacterial flagella but they evolved independently and are not evolutionarily related to bacterial flagella. The components of archaeal flagella are related to components of bacterial pili, and rotation of the archaeal flagellum is powered by ATP hydrolysis rather than by proton motive force.4. Other unique features of archaeaMany have unique metabolism. Methanogens are strict anaerobes that generate methane gas (CH4) as waste product of their energy generating metabolism.Many live in harsh environments (halophiles live in saturated salt brines, hyperthermophiles live in very hot water)D. Eukaryotic cell structureDifferences from prokaryotes:size- typically 10-50 m diameter (compare to prokaryotes which are typically 0.5-2 m diameter) No peptidoglycan (may have cell walls though, composed of cellulose, chitin, other) DNA enclosed in nucleus Well-developed cytoskeleton composed of microtubules, microfilaments and intermediate filaments Cytoskeleton involved in cell shape, movement, cell division.5. Eukaryotic flagella or cilia have different structure and mode of action than bacterial or archaeal flagellacomposed of microtublesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.much larger than prokaryotic flagellapowered by ATP hydrolysis (unlike bacterial flagella which are powered by proton motive force)beat like a tail rather than rotating like a propeller6. Many organelles in eukaryotic cell such as:Endoplasmic reticulum and golgi- (protein synthesis and processing) mitochondria-(energy generation, ATP synthesis) chloroplasts-(photosynthesis)Endosymbiotic theory for origin of mitochondria and chloroplastsevidence:-both organelles have DNA and ribosomes that resemble DNA and ribosomes of bacteria-rRNA genes of mitochondria and chloroplasts are similar in sequence to those of


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