e. Cells stained with fluorescent dyes f. Multiple plane images are assembled by software to form 3D images FIGURE 4.11 4. Transmission Electron Microscope (TEM) a. Very thin layer of specimen stained with heavy metal b. Application: observation of internal cell structure 5. Scanning Electron Microscope (SEM) a. Specimen receive electron beam and then reflect it b. Specimens need to be coated with a noble metal ex. Gold c. SEM has a greater depth than TEM: 3D image 6. Atomic Force Microscope (AFM) a. Specimen scanned by a cantilevered probe b. Doesn’t require coating LIVE images c. Provides extremely high resolution images of cells and structures d. Resolution of 0.05 micrometers e. 3D images of cells and surface structures October 02, 2007 VARIOUS SHAPES/MORPHOLOGY of BACTERIA and ARCHAEA -Cocci: round in shape. Can form as clusters, pairs, or chains. - Bacilli or rods - Curved and Helical Cells: not as common as cocci or rods. Ex: H. pylori - Mycelial: longer and branched, VERY rare - Filamentous Bacteria - Biofilms : in microbial communities, can survive in harsh conditions Ex: plaque on teeth
-most bacteria have a cell size range from 0.5 – 2.0 µm Some are small. ie: mycoplasms 0.2 µm **NO CELL WALL IN MYCOPLASM Others are LARGE ie: Thiomargarita ~700 µm -cell size and shape is maintained by cell wall and is determined by genetics and nutritional state STRUCTURE/FUNCTION What is in the cytoplasm ? -essential components: enzymes, DNA, ribosomes Ribosomes: protein synthesis CYTOPLASM is a crowded place . It includes: Intracellular enzymes: biosynthetic, catabolic, and repair enzymes Small molecule pools: essential nutrients and building blocks (ex. Amino acids, nucleotides, ions) Macromolecules: DNA, RNA, proteins, ribosomes DNA -prokaryote chromosome DNA= circular double strand (NOT linear) - one chromosome in most prokaryotes (NOT TWO) -prokaryotic DNA is not bound by a membrane, the region is called a nucleoid -in the cytoplasm, DNA is wound in supercoils- to pack it all into the cell Typical prokaryote chromosomes are ~ 4 x 10 6 base pairs (bp) = 4 megabase pairs Humans are 3.2 GB (1000 times more) Plasmids : extrachromosomal elements -are double stranded circular DNA -usually exist in multiple copies -contain feature that may enhance the survival of the cell allow them to degrade antibiotics or help the cell block antibiotics -genetic material can be transferred from one organism to another Transformation : DNA released into environment and taken up by another cell Conjugation : transfer in cell-to-cell contact Transduction : Viruses transfer the DNA to another cell Ribosomes : site of protein synthesis -contain protein and ribosomal RNA (rRNA) -present in cytoplasm of both prokaryotes and eukaryotes Prokaryote ribosome: 70S Eukaryote ribosome: 80S
STRUCTURES of SOME CELLS Bacterial Endospores - a resting stage formed within cell - can survive extended periods of dessication, high temps, UV radiation FUNCTION: survival - many soil bacteria form endospores - major genera: Bacillus, Clostridium - Endospore : spore inside of cytoplasm - low water content - high calcium ion -
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