Basic Concepts Of Microbiology

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Acids

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substances that have an excess of H+ ions

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adenine

Back 2

a base that opposes thymine (T) within the 2 strands of DNA

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bases

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substances that have an excess of OH- ions

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cholesterols

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waxy, lipid, substances found in the bloodstreams and cells of animals

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chromosome

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A single piece of double-stranded DNA composed of thousands of genes. The 2 strands are complementary so that they always pair in a certain order.

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cytosine

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A base that opposes guanine within the 2 strands of DNA.

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deoxyribonucleic acid

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A variety of nucleic acid and, along with ribonucleic acid, 1 of 2 types of molecules that encode genetic information.

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enzymes

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Proteins that serve to break down complete nutrients into smaller, useful molecules according to the energy requirements of each cell.

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ergosterols

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Lipid components found in fungi that serve the same purpose as cholesterol in animals.

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gene

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A string of 3-letter codons that is usually 300 to 1000 base pairs long

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guanine

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A base that opposes cytosine within the 2 strands of DNA.

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lipids

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Relatively small macromolecules that span the membrane of every cell. Most membrane lipids contain phosphate and are called phospholipids.

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macromolecules

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Large types of molecules found in numbers of 1 to 100,000 copies per cell. Macromolecules include proteins, polysaccharides, nucleic acids, and lipids.

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messenger RNA

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A single-strand structure that contains the sugar ribose and uridine (U) in place of the thymine present in DNA. Messenger RNA is used as the actual template for protein synthesis.

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nonpolar

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A molecule in which there is no charge differential between each end.

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nucleic acid

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A macromolecule consisting of a sugar-phosphate repeating structure that is usually large and can be millions of units long. Each sugar has 1 of 4 possible basic molecules, called bases or nucleotides, attached.

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polar

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A molecule in which there is a positive charge at 1 end and a negative charge at the other

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polysaccharides

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Macromolecules in which sugars are polymerized into long chains. Polysaccharides provide strength to microbial cells to keep them from breaking open.

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proteins

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Macromolecules that comprise 100 to 600 amino acid residues. The majority of proteins are enzymes.

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ribonucleic acids

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A variety of nucleic acid and, along with deoxyribonucleic acid, 1 of 2 types of molecules that encode genetic information.

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sterols

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A type of lipid useful as targets for antibiotic therapy of fungi.

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thymine

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A base that opposes adenine (A) within the 2 strands of DNA.

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translation

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the process of protein synthesis

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uridine

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A material found in messenger RNA, as opposed to the thymine that exists in DNA.

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Distinguish between polar and nonpolar

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Water is polar because there is a positive charge at 1 end of the molecule and
a negative charge at the other. Water molecules are polar, much like a
magnet with positive and negative poles. Oil, on the other hand, has no
charge differential and is nonpolar. Thus, oil (or any lipid) does not dissolve
(interact) in water because a charged solvent (water) will not associate with
an uncharged solute (oil). All types of cells (i.e., bacteria, fungal, and
human) are bathed in a water (aqueous) environment; however, a membrane
layer comprised of lipids, a type of oil, delimits all cells.

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Describe the pH of bases and acids.

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Acids supply an excess of H+ ions that make the water solution acidic.
Bases, on the other hand, supply an excess of OH ions, making the solution
basic or alkaline because many of the free H+ ions are used by the OH ions
to form water (H2O). pH is a measurement of the acid or alkaline properties
of a molecule. High pHs (above 8) are basic and low pHs (below 6) are
acidic. The neutral point is pH 7.

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Identify the 4 types of macromolecules found in all living cells.

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Macromolecules include proteins, polysaccharides, nucleic acid, and lipids.

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Describe the role of enzymes.

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Enzymes facilitate the breakdown of nutrients into smaller molecules that
are combined by other enzymes into the complex materials required by the
cell. Enzymes also derive energy from chemicals for use by the growing
cell.

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Distinguish between DNA and RNA.

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Nucleic acids come in 2 varieties: DNA (deoxyribonucleic acid) and RNA
(ribonucleic acid). Thousands of genes make up a single piece of double-
stranded DNA called a chromosome. The 2 strands are complementary so
that they always pair in a certain order. The bases adenine (A) and thymine
(T) are always opposed to each other in the 2 strands; likewise, the bases
cytosine (C) and guanine (G) are opposed. It is notable that DNA will always have equal numbers of A and T and equal numbers of C and G. RNA differs from DNA in that RNA is always single-stranded, has the sugar ribose (not the deoxyribose found in DNA), and has uridine (U) in place of thymine. Messenger RNA is used as the actual template for protien synthesis or translation. Since RNA is single stranded, there is no constraint for the numbers of As and Us or Cs and Gs to be equal.

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Explain the main function of lipids in the cell membrane.

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Lipids are small macromolecules that span cell membranes. They provide a
nonpolar boundary to keep cellular contents in and unwanted materials out.

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active transport

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A pumping mechanism that runs on the cell’s energy resources and uses protein transporters in the membrane to bring desirable chemicals into the cell.

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bacillus

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A common morphology of bacteria composed of a rod-shaped cell.

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basal body

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Two to 4 rings mounted on a rod; they secure the flagellum to the cell envelope

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capsule

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A covering, usually a polysaccharide, of the whole cell that makes the cell slippery, preventing white blood cells from capturing it and antibodies from binding to it.

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cell envelope

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All the covering layers of a bacterium, including the cytoplasmic membrane and cell wall.

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cell wall

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A layer of the cell outside the cell membrane that confers rigidity and shape.

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chemotaxis

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A process in which bacterium moves toward or away from chemicals.

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coccus

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A common morphology of bacteria composed of a spherical-shaped cell.

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colony

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A visible clump of cells; the colony’s color and appearance are often helpful in eliminating possibilities to assist in identification.

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cytoplasm

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The content within the cytoplasmic membrane.

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cytoplasmic membrane

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A boundary structure present in all living cells that defines inside and outside; is also called the cell membrane or plasma membrane

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endospores

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Thick spore structures that grow inside cells and are therefore protected from heat, drying, freezing, and harsh living conditions.

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filament

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The major part of a flagellum that contains long, helical structures made of the polymerized protein flagellin.

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fimbriae

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Small, hairlike appendages present on the external surface of many bacteria and usually seen in hundreds per cell. Fimbriae specifically refer to “attachment factors” (or “holdfasts”) that attach to host cells.

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flagella

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Hairlike appendages that allow bacteria to attach to sites for the purpose of growth and motility functions.

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flagellin

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Corkscrew-shaped polymerized proteins present in filament that are normally several times longer than the entire bacterial cell.

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glycocalyx

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Another name for capsule or sugar coat.

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gram stain

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The microscopic staining procedure discovered by Hans Christian Gram used to differentiate between Gram-positive and Gram-negative bacteria. The 4 steps of Gram’s staining are: Stain with the primary stain, crystal violet; fix the crystal violet with Gram’s iodine so that it aggregates; wash the aggregates from the porous Gram-negative bacteria with acetone-alcohol; and counterstain with safranin to make the Gram-negative cells readily visible.

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gram-negative

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Bacteria with 3-layered cell walls.

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gram-positive

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Bacteria with 2-layered cell envelopes.

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granules

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Polysaccharides or polyphosphates in the cytoplasm that usually provide an energy source and are available when the cell has a special energy need; also called inclusions.

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hook

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A flexible piece at the proximal end of filament that can bend to function as a universal joint.

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lipid A

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The proximal end in the outer half of the membrane on Gram-negative bacteria that anchors it to the cell

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lipopolysaccharide

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A material that composes the outer membrane of 3-layered Gram-negative bacterial cells.

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lysis

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A process in which bacteria with damaged cell walls explode due to increased internal osmotic pressure.

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organelles

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Membrane-bound sacks that are smaller than a cell.

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peptidoglycan

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A polysaccharide called glycan that is cross-linked to other polysaccharide molecules by short peptide cross-bridges to form a fishnet-like structure.

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pili

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Small, hairlike appendages present on the external surface of many bacteria.

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plasmids

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Small pieces of DNA that normally contain only a few genes, often for highly specialized functions.

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proteinaceous flagella

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The organelle of motility present in many bacteria.

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random-biased walk

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A process in which bacteria try to move randomly in different directions and only go a significant distance when the result is favorable to them.

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ribosomes

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Enzymes that perform translation; ribosomes include bacteria and eukaryotes.

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spirochete

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A common morphology of bacteria composed of a helical-shaped cell.

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spores

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The most stable form of life, spores are wrapped in multiple layers of peptidoglycan and protein; there may also be other polysaccharide layers. Unlike vegetative (growing) cells, spores contain very little water.

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vibrio

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Short spirochetes that contain less than a full helical turn or are comma shaped

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Identify the morphology of coccus, bacillus, and spirochete.

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A spherical cell is called a coccus; a rod-shaped cell, a bacillus; and a helical
cell, a spirochete. Short spirochetes—those that contain less than a full
helical turn or are comma shaped—are called vibrio.

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Describe how the terms diplo, tetra, staphylo, and strepto indicate types of
cell clustering.

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The morphological names of bacteria may include a prefix that designates
the type of clustering: mono- means single cell; diplo- means 2 linked cells;
tetra- means 4 linked cells in a square formation; strepto- means chains of
cells; and staphylo- means clusters of cells organized like a cluster of grapes.

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Explain the function of the cytoplasmic membrane.

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The cytoplasmic membrane controls what enters and exits the cell because it
is a semipermeable barrier; in essence, it allows few molecules to cross
freely.

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Describe the bacterial cell structure.

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There are no membrane-bound organelles (membrane-bound sacks that are
smaller than a cell) in bacteria. Photosynthetic bacteria have an extension or
folding of the cytoplasmic membrane, but they do not have a separate
organelle to carry out photosynthesis. Also, bacterial replication and
transcription occur simultaneously in the cytoplasm. Bacteria also have other
layers outside the membrane, including a cell wall that confers rigidity and
shape to the bacteria. Many bacteria have a 3rd layer (an outer membrane)
that covers the peptidoglycan.

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Describe the structure of peptidoglycan.

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The structure of peptidoglycan is like a fishnet because the long polymers of
glycan are cross-linked by shorter pieces of peptides.