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Transcript
Chapter 4 Prokaryotic cell • Bacteria are prokaryotic organisms • DNA is not enclosed within a membrane • DNA is not associated with histone proteins ( no nucleosomes) • No membrane bound organelles. • Cell walls – peptidoglycan • Divide by binary fission Curved rod Bent rod Loose spiral Tight spiral Glycocalyx • Capsule – gelatinous substance – outside the cell wall. • Polysaccharides • Contribute to the virulence • Protect bacteria from phagocytosis • Capsulated Streptococcus pneumoniae – pneumonia • Uncapsulated – destroyed by WBCs • • • • • • • • • Streptococcs mutans – surface of teeth Tooth decay Flagella long filamentous Movement – motile Rotate their flagella to swim Exhibit chemotaxis Positive chemotaxis – towards substances Negative chemotaxis - move away Spirochetes Treponema pallidum syphilis Fimbriae • Gram - bacteria have hair like structures. • Shorter thinner than flagella • Numerous • Attachment – virulence • Neisseria gonorrhoeae – fimbriae – Mucous membrane – colonize the area • No fimbriae – cannot colonize Pili • • • • One or two pili Longer than fimbriae Used for conjugation Join two bacterial cells together for DNA transfer Cell wall • Protects internal structures and plasma membrane • Made up of peptidoglycan • Glycan – sugar – repeating units of disaccharide • N-acetylmuramic acid • N-acetylglucosamine • Peptido-peptide-amino acids • Rows are sugars are cross linked by amino acid chains. Lipoprotein Phospholipid lipopolysaccharide Lipid A Endotoxin Septic shock • • • • • • • • Mycoplasma has no cell walls Cell wall can be damaged Antibiotic penicillin Stops the formation of peptide cross bridges in peptidoglycan Lysozyme-enzyme-tears, saliva, mucus Breaks the bond between sugar molecules. Gram- more resistant – outer membrane Gram+ more sensitive – peptidoglycan is exposed to the environment Plasma membrane • • • • • • Encloses the cytoplasm Phospholipids and proteins No sterols – exception is mycoplasma Phospholipids are arranged in a bilayer Proteins are inserted Structure – fluid mosaic • Plasma membrane – selectively permeable (semipermeable) • Damaged by alcohol, polymyxin • Molecules constantly cross the membrane • Nutrients get into the cell • Waste products move out of the cell • Active process and passive process • Passive process – molecules move from an area of high concentration to low concentration. Energy is not used. • Active process – molecules move from an area of low concentration to high concentration Energy is used. • Passive process • Simple diffusion, facilitated diffusion, osmosis • Simple diffusion – molecules move from an area of high concentration to low concentration. • CO2 and O2 cross the membrane by means of simple diffusion. • Facilitated diffusion – molecules move from an area of high concentration to low concentration. Energy is not used. • Transport proteins are used. • Osmosis – movement of water molecules from an area of high concentration of water to an area of low concentration of water through a selectively permeable membrane. • hypotonic – solute concentration lower outside the cell. Water moves into the cell. • Cell swells up and breaks down. Osmotic lysis. • Cell walls are damaged – bacteria undergo osmotic lysis. • Hypertonic – solute concentration is higher outside the cell. • water moves out of the cell. Plasma membrane shrinks away from the cell wall. • Plasmolysis • Most bacteria cannot survive in a hypertonic environment Active process • Active transport - molecules move from an area low concentration to high concentration. Energy is used. Transport proteins are involved. Ribose, histidine • Group translocation – molecules move from an are low concentration to high concentration. Energy is used. Transport proteins are involved. While the molecule is being transported, it is chemically altered. • Glucose transported across the membrane, phosphate is added. • Cytoplasm – carbohydrates, proteins, lipids, ribosomes, DNA, inclusions • Nuclear area (nucleoid) – long circular, double stranded DNA – chromosome • Genetic information needed for the structure and function of the cell. • Some bacterial cells – small circular DNA – plasmid • Plasmids make the bacterium resistant to antibiotics. • Ribosomes – two subunits • Each subunit is made up of proteins and ribosomal RNA. • 70S ribosomes – smaller, less dense than 80S ribosomes • Protein synthesis • Inclusions – organic or inorganic • Metachromatic granules – phosphate – used by the cell to make ATP. • Corynebacterium diphtheriae • Polysaccharide granules – glycogen or starch • Lipid inclusions – hydroxybutyric acid • Bacillus, Mycobacterium • Sulfur granules – Thiobacillus – uses sulfur for energy. • Carboxysomes – enzyme – ribulose diphosphate carboxylase. • Needed for photosynthesis • Cyanobacteria – photosynthetic bacteria • Gas vacuoles – hollow cylinders covered by protein. • Float at a certain depth in water - light Endospores • Clostridium and Bacillus • Dormant stage of the cell • Resistant to hostile environmental conditions • Heat, UV light, disinfectant, desiccation • Nutrient depletion • sporulation • Endospores – dehydrated • DNA, RNA, ribosomes, enzymes, dipicolinic acid, calcium ions. • Stay dormant for thousands of years. • When conditions are favorable, spores germinate into vegetative cells. • Sporulation is not reproduction. • One cell – one spore – germinates into a single cell. • No increase in the number of cells