Transcript bacteria
Welcome to Microbiology Learning Objectives: To be able to describe characteristics of bacteria and the functions of each structure What can you remember? • ALL bacteria are prokaryotes. What does this mean? • Without nucleus • Compare prokaryotes and eukaryotes: Prokaryotes Eukaryotes Small – less than 5 µm Always unicellular No nucleus or any membrane bound organelles DNA is circular, without proteins Large cells (>10 µm) Often multicellular Always have a nucleus and other membrane bound organelles DNA is linear and associated with proteins to form chromatin Ribosomes are large (80S) Ribosomes are small (70S) No cytoskeleton Motility by rigid rotating flagellum Cell division by binary fision Reproduction is always asexual Huge variety of metabolic pathways Always has a cytoskeleton Motility by flexible waving undulipodium made of tubilin Cell division by mitosis or meiosis Reproduction is sexual or asexual Common metabolic pathways • • • • How big? A metre (m) contains an thousand millimetres (mm) A millimetre contains a thousand micrometres (µm) A micrometre contains a thousand nanometres (nm) The size of an animal cell and some of its contents, in micrometres and nanometres is given below. Animal cell 20µm; mitochondrion 1µm; cell membrane (width) 8nm; nucleus 5µm; ribosome 15nm Imagine an animal cell is 5 metres across. How big would the various organelles inside it be? Real animal cell = 20µm. 5 metres = 5000 000µm, so the cell has been magnified 5000 000/20 = 250 000 – Size of nucleus • 5 µm x 250 000 = 1.25m – Size of mitochondria • 1 µm x 250 000 = 250 mm – Size of ribosome • 15nm x 250 000 = 3.75mm – Width of cell membrane • 8nm x 250 000 = 2mm Bacteria are classified according to their shape: Make a list of the shapes of bacteria that you can remember Cocci – spherical bacteria: •Cocci – smallest bacteria, occur as single spheres. •Diplococci – pairs of spheres, e.g. Diplococcus pneumoniae (pneumonia). •Staphylococci – clusters of spheres, e.g. Staphylococcus aureus (boils and food poisoning). •Streptococci – chains of spheres, e.g. Streptococcus pyogenes (sore throats). Bacilli – rod-shaped bacteria: •Individual rods – e.g. Escherichia coli, Salmonella typhi (typhoid fever). •Chains of rods – e.g. Azotobacter, Bacillus anthracis (anthrax). Spirilla – large, spiral-shaped bacteria (motile with flagella), e.g. Treponema pallidum (causes syphilis). Vibrio – crescent-shaped bacteria (motile), e.g. Vibrio cholerae (causes cholera). Structure Function Ribosomes Carries out protein synthesis Mesosome Site of respiration (formed by the intucking of the plasma membrane) Slime Capsule Physical barrier to predatory protazoa, white blood cells or bacteriophages Cell Wall Provides structure Flagellum Organelle of propulsion Pili or Fimbriae Bristle like projections that allow bacteria to stick to surfaces Cell surface membrane Plasmid Barrier between cell and environment Regulates transport of substances Loops carrying 10-30 genes enable production of antibiotics, or resistance to antibiotics Nuclear material within the nuclear zone Carries genetic material • Give four features that most bacteria have in common – – – – Cell wall made of peptidoglycan Reproduce asexually by binary fission No membrane bound organelles DNA is a circular molecule • Give three features that are only present in some bacteria – – – – Presence of flagella Mesosomes Pili or fimbriae Slime layer or capsule • The mitochondria found in eukaryotic cells contain their own loop of DNA as well as 70S ribosomes. Given this information suggest how mitochondria may have originated