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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
Eukaryote Anatomy
General differences between prokaryotes and eukaryotes
- 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
- 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
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.
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.
Note: many fungi are dimorphic -- grow as yeasts under some conditions, molds under others.
- 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.
View Candida albicans undergoing dimorphic growth; both hyphae (mold) and yeast forms are visible
Take a Self-Quiz on this material (Ch. 4)
Take a Self-Quiz on this material (Ch. 25)
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