Chapter 5: Eukaryotic cell structure

eukaryotes

• prominent members of ecosystem

• major human pathogens

• two groups in microbiology:

  • protists

  • fungi

features of eukaryotic cells

• membrane delimited nuclei

• membrane bound organelles

  • allows to perform specific functions within the celland independent control of cellular processes

• large intracytoplasmic membrane complex

  • a large surface area allowing greater respiratory and photosynthetic activity

  • serves as a transport system to move materials to different cell locations

eukaryotic cell envelopes

• phospholipid bilayers with sphingolipids and sterols

  • lipids in the outer layer are different from those in the inner layer

• cell wall composition:

  • polymers, cellulose, glucan, or chitin, while others have a rigid silica shell

cytoplasmic matrix

provides the complex structured environment required for many cellular activities

cytoskeleton

network of interconnected filaments and tubules important for motion and act as a scaffold for maintaining cell organization

microfilaments

• 4 to 7 nm

• composed of actin, may be scattered or organized into networks and parallel arrays

• play a major role in cell motion and changes in cell shape

microtubules

• hollow cylinders (25 nm) of tubulin help maintain cell shape, and are also involved with microfilaments in cellular movement

• participate in the intracellular transport of substances, participate in organelle movements

• from the mitotic spindle during cell division and present in cilia and flagella

intermediate filaments

• 8 to 10 nm

• major components of the cytoskeleton and are particularly prominent in the nuclear lamina

endoplasmic reticulum

• complex interconnected array of internal membranous tubes and sacs that may have ribosomes attached

• transports proteins, lipids, and other materials within the cell, and it is a major site of membrane synthesis

• begins at the nuclear membrane

golgi apparatus

• set of membranous sacs (cisternae) that is involved in the modification, packing, and secretion of materials

• cisternae exist in stacks called dictyosomes

lysosomes

membrane-bound vesicles that contain hydrolase enzymes needed for intracellular digestion of all types of macromolecules

secretory pathway

the cellular machinery responsible for synthesizing, modifying, packaging, and transporting proteins and lipids

• proteins are transported from the cell membrane, lysosomes, or secreted in vesicles that bud off the ER and join the face of golgi apparatus

  • proteins are modified and transported in vesicles off/away of the golgi apparatus

• transport vesicles move the material to the cell membrane of lysosome

  • secretory vesicles fuse with the plasma membrane upon signal

endocytosis

process in which the cell takes up solutes or particles by enclosing them in vesicles pinched off from the plasma membrane

phagocytosis

endocytosis of large particles by engulfing them into a phagocytic vacuole

pinocytosis

endocytosis of small amounts of liquid with its solute molecules

• three types:

  • fluid phase endocytosis

  • receptor mediated endocytosis using clathrin coated pits and vesicles

  • type of endocytosis that forms special vesicles (caveolae), contents are not degraded

endocytic pathway

1. endocytosis

2. most endosomes fuse with early lysosomes

organelles involved in genetic control of the cell

• nucleus and nuclear structure

  • house most of the genetic material of the cell

• eukaryotic ribosomes

  • are 80S with 60S and 40S subunits either free or bound to ER

chromatin

dense fibrous material seen within the nucleoplasm of the nucleus; when dividing, chromatin condenses into visible chromosomes

nucleus and nuclear structure

• chromatin

• nucleus bounded by the nuclear envelope, a double membrane structure (two lipid bilayers) allows to be penetrated by nuclear pores = allow materials to be transported into or out of the nucleus

• nucleolus is involved in the synthesis of rRNA and the production of ribosomes

eukaryotic ribosomes

• are 80S with 60S and 40S subunits, either free or bound to ER

• ER-associated ribosomes synthesize integral membrane proteins or proteins that are secreted out of the cell

• free ribosomes synthesize nonsecretory, nonmembrane proteins

organelles involved in energy conservation

• endosymbiotic hypothesis

• mitochondria

• hydrogenosomes

• chloroplasts

endosymbiotic hypothesis

holds that the mitochondria, chloroplasts, and hydrogenosomes are derived from bacterial cells engulfed by host cells early in evolutionary history

mitochondria

• site of the TCA cycle and electron transport chain

• an outer and inner membrane enclosing a fluid matrix

  • enzymes of the TCA cycle are within the matrix and ETC, and oxidative phosphorylation occurs only in the inner mitochondrial membrane

• reproduce by binary fission and use their own DNA and their own ribosomes to synthesize some of their proteins

  • DNA and ribosome are similar to bacteria

hydrogenosomes

• small organelles in some anaerobic protists that conserve energy by fermentation and generate hydrogen

• composed of a double membrane, they share some features with mitochondria

chloroplasts

• site of photosynthesis in protists and higher plants

• surrounded by two membranes

  • stroma: inner membrane encloses a fluid matrix

  • thylakoid: within the stroma is a system of flattened membrane sacs

  • grana: stacks of thylakoid

• formation of carbohydrates from carbon dioxide and water occurs in stroma

• trapping of light energy to generate ATP, NADPH, and oxygen occurs in the thylakoid in the grana

external structures in eukaryotic cells

cilia and flagella

cilia and flagella

• locomotor structures that differ in length and how they move the cell with cilia like oars and flagella like propellers

• structurally similar, both membrane bound cylinders composed of microtubules in a 9+2 arrangement = embedded in a matrix, basal bodies have a 9+0 microtubule pattern

protist

• single celled eukaryotes with specialized organelles

• a cell membrane called the plasmalemma toward the center of the cell

  • gelatinous layer of cytoplasm, the ectoderm

  • fluid region of cytoplasm inside the plasmalemma, the endoplasm

• aerobic chemoorganotrophic species have mitochondria

• anaerobic protists lack mitochondria, cytochromes and the TCA cycle

• many protists have flagella or cilia

protist encystment

• protists can differentiate (simpler) into cysts, a dormant form with a cell wall and little metabolic activity

  • protects the organism from adverse environments

  • can be reproductive

  • used to transfer to new hosts

protist excystment

• escape from cysts

• triggered by a change to favorable conditions

protists reproduction

• asexually by binary fission or budding

• sexually by producing haploid gametes

  • conjugation: nuclear material exchanged between individuals

  • autogamy: genetically distinct nuclei in a single individual

fungal structure

• thallus

• yeast

• mold

thallus

• body or vegetative structure of a fungus

• fungal cell walls are usually composed of chitin, a nitrogen-containing polysaccharide consisting of N-acetylglucosamine residues

yeast

• unicellular fungus with single nucleus

• reproduces asexually by budding or sexually by spore formation

• daughter cells may separate after budding or may aggregate to form colonies

mold

• fungus with long, branched, threadlike filaments

  • hyphae: filaments of a mold

    • coenocytic (no cross walls) or septate (cross walls)

  • mycelia: bundles or tangled masses of hyphae

fungal reproductive cells and structures: asexual reproduction

• reproduction occurs by several mechanisms:

  • transverse fission

  • budding of somatic vegetative cells

  • sport production

    • hyphal fragmentation: resulting cells behave as arthrospores

    • sporangiospores: produced in a sporangium (sac)

    • conidiospores: enclosed spores produced at the hypha tip

    • blastospores: produced from a vegetative mother cell by budding

fungal reproductive cells and structures: sexual reproduction

• union of compatible nuclei

• homothallic: some are self fertilizing

  • producing male and female gametes on the same mycelium

• heterothallic: require outcrossing between different but sexually compatible mycelial mating types

• zygote formation proceeds by fusion of gametes of hyphae