Chapter 4 - Eukaryotic Cells and Microorganisms

Nearly all eukaryotic microbial cells have a

Cell membrane, nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, cytoskeleton, cytoplasm, and glycocalyx.

Only some have a cell wall, locomotor appendages, and chloroplasts.

eukaryotic cells

Larger, complex, with nucleus, membrane bound organelles, DNA tightly wrapped around histone proteins in chromosomes, cellulose in plant cell walls.

Motility

Allows microorganisms to locate nutrients and to migrate toward positive stimuli such as sunlight; also enables them to avoid harmful substances and stimuli. eukaryotic microbes move by using flagella or cilia, common in protozoa, many algae, few fungal and animal cells.

Eukaryotic flagella are very different from those of bacteria, 10 times thicker, structurally more complex, covered by extension of cell membrane. Long, sheathed cylinder containing regularly spaced hollow tubules extending along its entire length.

Cilia are shorter, more numerous, upwards of several thousand for some cells. Found only in single group of protozoa and in certain animal cells. Ciliated protozoa have cilia occurring in rows over cell surface, which beat back and forth in oar-like strokes. Among the fastest of all motile cells. Some cilia on other cells function as feeding and filtering structures.

Glycocalyx

The outermost layer found in direct contact with the environment, found in many eukaryotic cells. usually composed of polysaccharides, appearing as network of fibers, slime layer, or capsule. Contributes to protection, adherence of cells to surface, reception of signals from other cells. Fungi and most algae have thick, rigid cell wall surrounding cell membrane; protozoa, few algae, and all animal cells do not have cell wall but only cell membrane.

Cell wall

Found in fungi, protozoa and helminths do not have it. Cell walls of fungi are rigid, providing structural support and shape, different in chemical composition from bacterial and archaeal cell walls. Inner layer of polysaccharide fibers composed of chitin or cellulose, with an outer layer of mixed glycans.

Cell membrane (cytoplasmic)

Typical bilayer of phospholipids with imbedded proteins for eukaryotic cells. Also contains sterols of various kinds, which are a different form of lipid from phospholipids in both structure and behavior. Fairly rigid, making eukaryotes more stable structurally than non-eukaryotes, which is extremely important in cells that don't have a cell wall. Eukaryotic cytoplasmic membranes function as selectively permeable barriers.

Internal structures

Eukaryotic cells have internal structures accumulating to 60-80% of their volume, contained in fluid called cytosol. All content outside of nucleus is termed cytoplasm.

Nucleus

Most prominent organelle of eukaryotic cells, separated from cytoplasm by nuclear envelope, which is comprised of 2 parallel membranes (2 lipid bilayers) separated by a narrow space. There are regularly spaced openings/pores which are formed by connection of inner and outer nuclear membranes. These pores serve as passageways through which macromolecules move from nucleus to cytoplasm and vice versa. Nucleus is filled with nucleoplasm and nucleolus - nucleolus is the site for ribosomal RNA synthesis and collection area for ribosomal subunits, which are transported through nuclear pores into cytoplasm for final assembly into ribosomes.

Chromatin is a feature of nucleoplasm, network of dark fibers, made of linear DNA. When wound around histone proteins, chromatin forms structures called chromosomes.

Endoplasmic reticulum (ER)

Series of membrane tunnels used in transport and storage. Rough endoplasmic reticulum (RER) is a continuation of outer membrane of nuclear envelope, extending to continuous network through cytoplasm, al the way to cell membrane. Such a structure permits the space in the RER (called cisternae) to transport materials from nucleus to cytoplasm and ultimately the cell's exterior. Appears rough due to large number of ribosomes attached to membrane surface. Protein synthesized on ribosomes are shunted into inside space lumen) of RER and held for later packaging and transport.

The smooth endoplasmic reticulum (SER) is a closed tubular network without ribosomes, functions in nutrient processing, synthesizing and storing nonprotein macromolecules (such as lipids).

Golgi apparatus

Also called Golgi complex/Golgi body, site in cell for modifying proteins and sent to final destinations. Consisting of several stacked, flattened disc-shaped sacs called cisternae, which are comprised of both membranes and cavities similar to what's found in ER, but do not form a continuous network. Consistently closely associated with ER, which buds off tiny membrane-bound packets of protein (transitional vesicles) which are then picked up by the face of the Golgi apparatus. Proteins are then typically modified by addition of polysaccharides and lipids once in the Golgi body. From there, it is pinched off and out of the Golgi body into condensing vesicles designed to carry modified proteins to organelles such as lysosomes or outside the cell as secretory vesicles.

DNA translation

Segment of DNA containing instructions for producing a protein is copied into RNA transcript, which is passed out through nuclear pores directly to ribosomes on the endoplasmic reticulum. Specific proteins from there are then synthesized from RNA code and deposited in the lumen of the endoplasmic reticulum. After being transported to Golgi apparatus, protein products are chemically modified and packaged into vesicles that can be used by the cell in a variety of ways. Some of the vesicles contain enzymes to digest food inside the cell; other vesicles are secreted to digest materials outside the cell, and others are important in the enlargement and repair of the cell wall and membrane.

Lysosome

A vesicle that buds off Golgi apparatus, containing variety of enzymes. Involved in digestion of food particles inside cell and in protection against invading microorganisms. Also participate in digestion and removal of cell debris in damaged tissue.

Peroxisome is a type of vesicle containing wide variety of enzymes (these do not originate from Golgi). Vacuoles are another type of vesicle which are membrane-bound sacs containing fluids or solid particles to be digested, excreted, or stored. Found in phagocytic cells in response to food and other substances that have been engulfed. Content of a food vacuole are digested through merger of vacuole with lysosome, creating a phagosome. Other types of vacuoles store fats and glycogen. Contractile vacuoles are found in freshwater protozoa and regulate osmotic pressure; they systematically expel excess water that diffused into the cell.

Mitochondria

A double-membrane organelle of eukaryotes that is the main site for aerobic respiration, therefore responsible for generating the bulk of a cell's energy. Appears as round or elongated particles scattered throughout cytoplasm. Folds of inner membrane are called cristae, may be tubular, or folded into shelf-like bands.

Cristae membranes hold enzymes and electron carriers needed in aerobic respiration. Mitochondria and chloroplasts are unique because they divide independently of the cell, containing circular molecules of DNA, and have bacteria-sized 70S ribosomes.

Chloroplasts

Are organelles containing chlorophyll that is found in photosynthetic eukaryotes (plant and algae specifically. While resembling mitochondria, chloroplasts are larger, and contain special pigments, in addition to being much more varied in shape.

Ribosomes

Numerous, tiny particles with "dotted" presentation to cytoplasm. Ribosomes are distributed throughout cell: some are scattered freely in cytoplasm and cytoskeleton, others are attached to rough endoplasmic reticulum as previously described. Others appear inside mitochondria and chloroplasts. Often found arranged in short chains called polyribosomes (polysomes). Composed of large and small subunits of ribonucleoproteins. Eukaryotic ribosomes differ from bacterial (except in mitochondrion) by having the larger 80S variety that is a combination of 60S and 40S subunits. This difference allows the use of antibiotics that target prokaryotic ribosomes without harming eukaryotic ribosomes found naturally throughout human cells. As is in bacteria, eukaryotic ribosomes are the staging areas for protein synthesis.

Cytoskeleton

Eukaryotic cells have criss-crossed flexible framework of cytoplasm. Aids in anchoring organelles, moving RNA and vesicles, permitting shape changes and movement in some cells. 3 main types of cytoskeletal elements are actin filaments, intermediate filaments, and microtubules.

Actin are long thin protein strands (7 nm in diameter), found throughout cell but mostly highly concentrated just inside cell membrane, responsible for cell movements such as contraction, crawling, pinching (during cell division), and formation of cellular extensions.

Microtubules are long, hollow tubes maintaining shape of eukaryotic cells that don't have walls, transporting substances from one part of cell to another. Spindle fibers playing essential role in mitosis are actually microtubules attached to chromosomes and separate them into daughter cells. Also responsible for movement of cilia and flagella.

Intermediate filaments are ropelike structures (about 10nm in diameter), intermediate size between actin and microtubules. Structurally reinforce cell and organelles (for example, supporting structure of nuclear envelope).

Endosymbiosis

The theory that eukaryotic cells came to be when primordial cell types engulfed bacteria or other primordial cell types that later became organelles inside the more complex cells.

Fungi

Majority are either unicellular or colonial, however a few (such as mushrooms and puffballs) are truly multicellular. Microscopic fungi are yeasts or hyphae. Yeast is round/ovular, asexual in reproductive activities. Grows swellings (called buds) which then separate into new cells. Hyphae are long, threadlike, found in fungi of filamentous type, called molds. Some form pseudohypha. Some are classified as dimorphic (can take either form depending on growth conditions).

Pseudohypha

A chain of easily separated, spherical to sausage-shaped yeast cells partitioned by constrictions rather than by septa.

Mycoses

Fungal infections. Varies by way pathogen enters body.

Saccharomyces

Yeast that produces the alcohol in beer and wine and gas that causes bread to rise.

Heterotrophic

An organism relying upon organic compounds for carbon and energy needs.

Fungal nutrition

All are heterotrophic, acquiring from wide variety of organic materials (sources are called substrates). Most are saprobes, also can function as parasites on bodies of animals or plants, although very few require a living host. Fungus primarily secretes enzymes to reduce substrate to smaller molecules to then be absorbed.

Saprobe

A microbe that decomposes organic remains from dead organisms. Also known as a saprophyte or saprotroph.

Morphology of fungi

Most microscopic fungi grow in loose associations or colonies. Yeast colonies are much like bacteria in having soft, uniform texture and appearance. Colonies of filamentous fungi are noted for striking cottony, hairy, velvety textures arising from microscopic organization and morphology. Hyphae contain usual eukaryotic organelles, but they do also have unique features. Hyphae is usually septate (can divide into segments by cross walls).

Hyphae can also be classified by particular function, such as vegetative and reproductive/fertile hyphae. Vegetative responsible for visible mass of growth appearing on surface of substrate. These are hyphae responsible for producing spores.

Mycelium

The filamentous mass that makes up a mold. Composed of hyphae.

Spores

A differentiated, specialized cell form that can be used for dissemination, for survival in times of adverse conditions, and/or for reproduction. Spores are usually unicellular and may develop into gametes or vegetative organisms.

Spore formation

Fungi have complex reproductive strategies. Most propagate by simple outward growth of existing hyphae, separating piece of mycelium to generate new colony.

Primary method involves production of various types of spores. Spores disperse easily by air, water, living things. Once finding substrate, will germinate, producing new fungus colony in little time.

Asexual spores produce via mitotic division of single parent cell, sexual spores formed through process involving fusion of 2 parental nuclei followed by meiosis. Important consequence of meiosis and sexual reproduction is that it serves to increase genetic variation among spores.

Vaginal candidiasis

Yeast infection, caused by overgrowth of Candida albicans. Causes irritation, itching, vaginal discharge, infection, easily treatable with antifungal medicine.

Asexual spore formation

2 types - sporangiospores and conidiospores (called conidia).

Sporangiospore

A form of asexual spore in fungi; enclosed in a sac. Formed by sporangium (the sac), which is attached to the stalk, sporangiophore.

Conidiospores/conidia

Asexual fungal spores shed as free units from the tips of fertile hyphae. Develop either by pinching off tip of special fertile hypha or by segmentation of preexisting vegetative hypha. Many forms of conidia.

Sexual spore formation

Fungi are very reproductive with millions of asexual spores. Sexual reproduction for fungi is imperative for diversifying genetic material across species, majority of fungi produce sexual spores at some point. Details of process vary greatly.

Protozoa

Greek for "first animals", far from being simple, primitive organisms. Comprised of very large group (~12k species), single-celled. Most are free-living of water and soil, a few are pathogens responsible for hundreds of millions of infections annually. Typically contain all the major eukaryotic organelles, however, such parts can be highly specialized for feeding, reproduction, locomotion. Can move through fluids by pseudopods, flagella, or cilia. Lacking cell wall, therefore semi-flexible. Cell shape can remain constant (most ciliates) or can change (such as amoebas). Some amoebas encase themselves in hard shells of calcium carbonate (CaCO3). Size falls within range of 3-300um). Giant amoebas and ciliates can be 3-4mm in length.

Ectoplasm

Clear outer layer dividing the cytoplasm; endoplasm is the inner region.

Protozoa nutrition/habitat

Typically heterotrophic, usually requiring complex organic foods. Free-living species found on dead plant/animal debris, sometimes live bacteria and algae. Some have special feeding features (oral grooves). Primarily found in fresh and marine water, soil, plants, animals. Sometimes can withstand extreme temperature and pH.

Trophozoites

A vegetative protozoan (feeding form) as opposed to a resting (cyst) form.

Protozoa reproduction

Are trophozoites when in motile feeding stage, requiring ample food and moisture to remain active. Many can enter a dormant resting stage called a cyst when environment is unfavorable. During encystment, trophozoite rounds up into sphere. Cysts are more resistant to extreme environments than normal cells. Can also be dispersed by air currents.

All protozoa reproduce by relatively simple, asexual methods, using mitotic cell division. Some reproduce into host cell.

Helminths

Tapeworms, flukes, roundworms. Adult specimens can usually be seen by naked eye. Ranging from 1mm-25m. Helminths are also included in study of microbes mainly due to their infective abilities and that they can produce microscopic eggs and larvae.

2 major groups of pathogenic helminths are flatworms (phylum Platyhelminthes) and roundworms (phylum Aschelminthes, also called nematodes). Flatworms are very thin, segmented body. Roundworms have elongated, cylindrical, unsegmented body.

Flatworm group is subdivided into cestodes (tapeworms), and trematodes (flukes).

Not all flatworms and roundworms are parasites, many live free in soil and water. Most disease-causing helminths spend part of their lives in GI tract.

Worm morphology

All helminths are multicellular; pathogenic helminths have a reproductive tract, digestive, excretory, nervous, and muscular systems that are more developed than their other organs.

Life cycle of helminth

Includes fertilized egg (embryo), larval, and adult stages. Majority have adults derive nutrients and reproduce sexually in host's body. Sexes are separate and usually appear different in nematodes. Nematode sexes can either be separate or hermaphroditic. Cestodes are typically hermaphroditic.

Helminths complete life cycle by transmitting infective form (egg or larva) to body of another host which is known as the intermediate (secondary) host, and the host in which adulthood and mating occur for definitive (final) host.

Transport host is intermediate host experiencing no parasitic development, but is an essential link in completing the cycle.

Pathogenic worms

About 50 species of helminths cause disease in humans. Frequently called parasites.

Eukaryotic flagella differ from bacterial flagella because only eukaryotic flagella

Contain microtubules

Bacteria, archaea, and eukaryotes are believed to have evolved from a different kind of cell, known as the

Last common ancestor

The eukaryotic cell's glycocalyx is

Mostly polysaccharide

The Golgi apparatus

Modifies proteins

Fungal spores arise

When asexual reproduction produces sporangiospores and condiospores, and sexual reproduction produces spores, often from fruiting body.

Protozoan cysts

Are helpful in surviving unfavorable conditions.

Fungal infections are known as ___ and can be acquired from environmental or clinical sources.

Mycoses.

Fungi produce which structures for reproduction and multiplication?

Spores.

The county public health department is notified that an organism has been identified in a local lake, which is popular for water recreation and swimming. Acanthamoeba is familiar to the public health officials as an amoeba that can cause a fatal brain disease in both normal and immunocompromised individuals. An RN is a member of the taskforce assigned to the development and dissemination of community education. The team prepares information for the public to be released to media outlets and posted at the lake. The public health information flyer explains that an amoeba is which type of microorganism?

A eukaryotic protozoan.

An RN at an elementary school notices a second grade female scratching and pulling at her pants. The student complains that her buttocks itch. Upon further assessment, the patient reports that the itching worsened in the morning hours. Since another child in the student's class was recently diagnosed with Enterobius vermiucularis, or pinworm infection, the RN contacts the girl's mother and recommends following up with her pediatrician. Pinworm is characterized as which type of helminth?

Nematode