Quiz (Ch. 4) Quiz (Ch. 25);	Eucaryotic structure. Fungi
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Last revised: Monday, February 7, 2000
Ch. 4; Ch.25 (p. 523-530; skim rest) in Prescott et al, Microbiology, 4th Ed.

Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!

Copyright 2000. Thomas M. Terry

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Eukaryote Anatomy

General differences between prokaryotes and eukaryotes

1. Eukaryotes
   • Eucaryotes are typically larger
   • compartmentalized by membrane-bounded sacs or organelles
   • contain a nucleus with multiple chromosomes
   • divide by complex process of mitosis
   • usually have a sexual life cycle involving meiosis
   • View TEM of animal cell
2. Prokaryotes
   • Procaryotes are typically smaller
   • not compartmentalized
   • do not have a nucleus
   • divide by binary fission
   • no sex life
   • View TEM of bacterial cell

Note: exceptions to these generalizations. Some prokaryotes do have internal compartments. Some eukaryotic cells are very small. Some eukaryotes don't have sexual cycle.

Distinctive eucaryotic features

Nucleus

• Contains DNA complexed to histone proteins = chromatin.
• Note: Archaea have histone-like proteins (but don't have mitosis)
• During division, chromatin condenses by tight coiling into chromosomes, may be visible in light microscope.

Mitosis

• Process of cell division. Involves chromosome condensation, attachment to spindle fibers (made of microtubules), separation. Machinery can handle large numbers of chromosomes, from 2 to over 1000.
• Very different from bacterial DNA separation, no spindle involved, no chromosome condensation, only 1 circular DNA molecule/cell (unless replicated prior to division).
• View movie of mitosis (526K)

Meiosis

• Specialized cell division that reduces chromosome set by half.
• Necessary for sexual reproduction.

Cytoplasmic fibers = cytoskeleton

• Made of microtubules, microfilaments, intermediate fibers.
• Projections from cell surface include cilia (fine hairs) and flagella. Both have internal core of "9+2" microtubular rows.
• Contrast with procaryote flagella, about the size of a single microtubule).
• Also involved in cell division --> mitotic spindle

Endomembrane system

• Internal membranes include rough endoplasmic reticulum (rER), smooth ER, Golgi body, lysosomes, plasma membrane.
• Membranes are in common dynamic flux, pinch off and move to other regions.
• Many proteins are manufactured at rER for destinations other than cytoplasm; outside the cell (secretion), membrane proteins, lysosomal proteins, etc.
• Elaborate machinery for targeting and moving proteins around the cell.
• Membranes can pinch off, move material out of cell = exocytosis; also can invaginate, bring materials into cell = endocytosis. Very important in control of disease by white blood cells, "eat" bacteria by phagocytosis.

Organelles

• Cell structures such as mitochondria, chloroplasts.
• Mitochondria = sites of respiration, ATP synthesis. As many as 1000/cell.
• Don't arise from endomembrane system; instead, arise by binary fission.
• Mitochondria contain some DNA (not bound to histones like nuclear DNA), ribosomes, and manufacture some proteins from their own DNA-RNA-protein synthetic machinery.
• Surprise: mitochondrial ribosomes are 70S, not 80S as found in cytoplasm.
• Chloroplasts = sites of photosynthesis, found in all green plants.
• Like mitochondria, contain DNA, ribosomes, manufacture some of their own proteins

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Endosymbiont theory

• first proposed by Lynn Margulis (now at UMass)
• Core idea: mitochondria (and other organelles) derived from ancient colonization of large bacteria (became the eucaryotic cell) by smaller bacteria (became the mito, chloroplast, etc.)
• Symbiosis = "intimate living together".
• Eventually, organelles lost ability to exist as separate organisms, cannot be separated from cell and survive independently.
• Note: other evidence (16S RNA homology) supports this theory. Will discuss in lecture on bacterial taxonomy.

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Fungi: eukaryotic microbes

• One of 5 kingdoms.
• Eukaryotic, spore-bearing, non-photosynthetic.
• Found in soils & water everywhere; mold spores are most abundant component of dust (airborne soil).
• Many beneficial organisms: yeasts -> fermentations, make bread, wine, beer, cheeses, soy sauce.
• Many drugs derived from fungi: penicillin, etc.
• Many harmful organisms: many crop diseases, human diseases

Yeasts & Molds: 2 common morphologies.

• Yeasts are unicellular, divide by budding (asexual) or by spores (sexual).
• View light micrograph of yeasts from Univ. or Edinburgh
• Can be oval, triangular, etc. in shape, larger than bacteria (5 micrometer is typical).
• Some are facultative anaerobes (can grow with or without oxygen).
• View SEM of yeast cells. Note bud scars from previous buddings.

• Molds are multicellular, made of long, branched filaments (hyphae). View SEM of hyphae from aquatic mold.
• Mass of hyphae = mycelium.
• View SEM of mold mycelium; from athlete's foot fungus.
• Typically aerobic. Produce digestive enzymes, can attack many organic substrates (e.g. wood fibers).
• Eventually, mycelium produces spores (sexual or asexual) on some type of stalk.
• View SEM of penicillium mold ascospores
• View SEM of spore-bearing structure of bread mold, Aspergillus niger
• Shape & arrangement of spore-bearing structures is used for identification.

Note: many fungi are dimorphic -- grow as yeasts under some conditions, molds under others.
View Candida albicans undergoing dimorphic growth; both hyphae (mold) and yeast forms are visible

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