chapter 4 microbiology PowerPoint

The History of Eukaryotes

• The first eukaryotic cells appeared 2 to 3 billion years ago.

• Bacteria, archaea, and eukarya all evolved from the Last Common Ancestor.

• First primitive eukaryotes were likely single-celled and independent.

• Over time cells aggregated, forming colonies

The History of Eukaryotes

• Cells within colonies became specialized to perform a specific function.

• Complex multicellular organisms evolved as individual cells lost the ability to survive separately from the intact colony

Appendages for Moving: Cilia and Flagella

Eukaryotic flagella:

• Different from bacterial flagella.

• About ten times thicker.

• Structurally more complex.

• Covered by an extension of the cell membrane.

• Long, sheathed cylinder containing regularly spaced microtubules.

Eukaryotic cilia:

• Similar to flagella in structure, but are smaller and more numerous.

• Found only in a single group of protozoa and certain animal cells

The Glycocalyx

An outermost layer that comes into direct contact with the environment.

Composed of polysaccharides.

Appears as:

• A network of fibers.

• A slime layer.

• A capsule.

Contributes to protection, adherence, and signal reception

Boundary Structures: The Cell Wall

Protozoa and helminths do not have cell walls.

Cell walls of fungi:

• Rigid and provide structural support and shape.

• Different in chemical composition from bacterial and archaeal cell walls.

• Thick inner layer of polysaccharide fibers composed of chitin or cellulose.

• Thin outer layer of mixed glycans

Boundary Structures: The Cell Membrane

Typical bilayer of phospholipids in which protein molecules are embedded.

Contain sterols of various kinds:

• Relative rigidity give stability to the membrane.

• Important in cells that do not have a cell wall.

Cytoplasmic membranes of eukaryotes have a similar function as those in bacteria and archaea, serving as selectively permeable barriers

Internal Structures: The Nucleus

Most prominent organelle of eukaryotic cells.

Separated from the cell cytoplasm by an external boundary called the nuclear envelope:

• Composed of two parallel membranes (lipid-bilayers) separated by a narrow space.

• Perforated with small, regularly spaced pores, formed at sites where the membranes unite.

• Macromolecules migrate through the pores to the cytoplasm and vice versa

The Nucleus

Nucleolus:

• Found in the nucleoplasm.

• Site for ribosomal RNA synthesis.

• Collection area for ribosomal subunits.

Chromatin:

• Made of linear DNA and histone proteins.

• Genetic material of the cell

Internal Structures: Endoplasmic Reticulum

A series of membrane tunnels used in transport and storage.

Rough endoplasmic reticulum (RER):

• Allows transport materials from the nucleus to the cytoplasm and to the cell's exterior.

• Ribosomes attached to its membrane surface.

Smooth endoplasmic reticulum (SER):

• Closed tubular network without ribosomes.

• Functions in nutrient processing and in synthesis and storage of nonprotein macromolecules such as lipids

Internal Structures: Golgi Apparatus

The site in the cell in which proteins are modified and then sent to their final destinations.

Consists of several flattened, disc-shaped sacs called cisternae.

Always closely associated with the endoplasmic reticulum:

• Transitional vesicles from the endoplasmic reticulum are picked up at the face of the Golgi apparatus.

• Proteins are modified within the cisternae by the addition of polysaccharides and lipids.

• Condensing vesicles pinch off of the Golgi apparatus and are then conveyed to lysosomes or transported outside the cell

Nature's Assembly Line

Nucleus, endoplasmic reticulum, and Golgi apparatus:

• A segment of DNA containing the instructions for producing a protein is copied into RNA, and this RNA transcript is passed out through the nuclear pores directly to the ribosomes on the endoplasmic reticulum.

• Specific proteins on the RER are deposited in the lumen and transported to the Golgi apparatus.

• Proteins in the Golgi apparatus are chemically modified and packaged into vesicles to be used by the cell

Vesicles

Lysosomes:

• Bud off the Golgi apparatus as a vesicle.

• Contain a variety of enzymes involved in the intracellular digestion of food particles and protection against invading microorganisms

• Participate in the removal of cell debris in damaged tissue.

Vacuoles:

• 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.

• Contents of a food vacuole are digested through a merger of a vacuole with a lysosome

Mitochondria

Generate energy for the cell.

Composed of a smooth, continuous outer membrane with an inner folded membrane.

Folds on the inner membrane are called cristae:

• Hold the enzymes and electron carriers of aerobic respiration.

• Extracts chemical energy contained in nutrient molecules and stores it in the form of high-energy molecules, or ATP.

Unique organelles.

• Divide independently of the cell.

• Contain circular strands of DNA.

• Have bacteria-sized 70S ribosomes

Ribosomes

Distributed throughout the cell:

• Scattered freely in the cytoplasm and cytoskeleton.

• Attached to the rough endoplasmic reticulum.

• Appear inside mitochondria and chloroplasts.

Multiple ribosomes are often found arranged in short chains called polyribosomes (polysomes).

Size and structure:

• Large and small subunits of ribonucleoprotein.

• Eukaryotic ribosome is 80S, a combination of 60S and 40S subunits

The Cytoskeleton

Functions:

• Anchoring organelles.

• Moving RNA and vesicles.

• Permitting shape changes and movement.

Three main types of cytoskeletal elements:

• Actin filaments: long, thin protein strands.

• Intermediate filaments: ropelike structures.

• Microtubules: long, hollow tubes

Fungal Cells

Yeasts:

• Round to oval shape.

• Asexual reproduction, budding Hyphae:

• Long, threadlike cells found in the bodies of filamentous fungi.

Pseudohypha: chain of yeast cells.

Some fungal cells are considered dimorphic and can take either form, depending on growth conditions

Fungi and Human Disease

Nearly 300 species of fungi can cause human disease.

Three types of fungal disease in humans:

• Community-acquired infections caused by environmental pathogens.

• Hospital-associated infections caused by fungal pathogens in clinical settings.

• Opportunistic infections caused by low-virulence species infecting already-weakened individuals

Fungi and Human Disease

• Harmless spores can cause opportunistic infections in AIDS patients.

• Fungal cell walls give off chemical substances that can trigger allergies.

• Toxins produced by poisonous mushrooms can induce neurological disturbances and even death.

• Aspergillus flavus synthesizes a poison called aflatoxin, potentially lethal to animals who eat contaminated grain

Agricultural Impact of Fungi

A number of species are pathogenic to corn and grain:

• Reduces crop production.

• Can cause disease in domestic animals consuming contaminated feed crops.

Fungi rot fresh produce during shipping and storage:

• 40% of yearly fruit crop is consumed by fungi

Benefits of Fungi

• Play an essential role in decomposing organic matter and returning minerals to the soil.

• Form stable associations with plant roots and increase their ability to absorb water and nutrients.

• Fungi have been engineered to produce large quantities of antibiotics, alcohol, organic acids, and vitamins.

• Some fungi are eaten or used to provide flavoring to food

Fungal Nutrition

• Heterotrophic: acquire nutrients from a wide variety of organic substrates.

• Saprobic: these substrates from the remnants of dead plants and animals in soil or aquatic habitats.

• Parasitic: grow on the bodies of living animals or plants, although very few require a living host.

• Fungi penetrate the substrate and secrete enzymes that reduces it to small molecules that can be absorbed by the cells.

• Fungi are often found in nutritionally poor or adverse environments, and those with high salt or sugar content

Morphology of Fungi

• Cells of most microscopic fungi grow in loose associations or colonies.

• Colonies of yeasts are much like bacteria: they have a soft, uniform texture and appearance.

• Colonies of filamentous fungi are noted for the striking cottony, hairy, or velvety texture

Morphology of Fungi

Mycelium: the woven, intertwining mass of hyphae that makes up the body or colony of a mold.

Septa: the nature of the septa varies from solid partitions with no communication between the compartments to partial walls with small pores that allow the flow of organelles and nutrients between adjacent compartments:

• Nonseptate hyphae consist of one, long, continuous cell.

Vegetative hyphae are responsible for the visible mass of growth that appears on a substrate.

Reproductive, or fertile, hyphae produce spores

Reproductive Strategies and Spore Formation

Most can propagate by the outward growth of existing hyphae or by fragmentation.

Spores:

Primary reproductive mode of fungi.

• Can be dispersed through the environment by air, water, and living things.

• Will germinate upon finding a favorable substrate and produce a new fungus colony in a short time

Asexual Spore Formation

• Sporangiospores: formed by successive cleavages within a saclike head called a sporangium, which is attached to a stalk, the sporangiophore.

• Conidiospores or conidia: free spores not enclosed by a spore-bearing sac

Sexual Spore Formation

• Mixing of DNA from two parent fungi creates offspring with combinations of genes different from that of the parents.
  Variations lead to potentially advantageous adaptations.

• Sexual spores vary from simple fusion of fertile hyphae of two different strains, or as a complex union of male and female structures

The Protozoa

• Name comes from the Greek for "first animals".

• About 12,000 species of single-celled creatures.

• Most are harmless, free-living inhabitants of water and soil.

• Afew species are pathogens responsible for hundreds of millions of infections each year

Protozoan Form and Function

Single cells containing all of the major eukaryotic organelles.

Cytoplasm divided into two parts:

• Ectoplasm: clear outer layer involved in locomotion, feeding, and protection.

• Endoplasm: granular inner region housing the nucleus, mitochondria, and food and contractile vacuoles

Protozoan Form and Function

Some organelles act as a primitive nervous system to coordinate movement.

Can move through fluids by means of pseudopods ("false feet").

Cell membrane regulates food, wastes, and secretions.

Cell shape can remain constant (as in most ciliates), or change constantly (as in amoebas).

Size of most protozoans range from 3 to 300 um:

• Giant amoebas and ciliates range from 3 to 4 mm

Nutritional and Habitat Range

• Heterotrophic, require food in a complex organic form.

• Free-living species scavenge dead plant or animal debris or graze on bacteria and algae.

• Some have special feeding structures, such as oral grooves.

• Some absorb food directly through the cell membrane.

• Pathogenic species may live on the fluids of their host, such as plasma and digestive juices, or actively feed on tissues.

• Main limiting factor is availability of moisture.

• Predominant habitats are fresh and marine water, soil, plants, and animals.

• Can survive in extremes of temperature and pH

Life Cycles

Trophozoite: motile feeding stage requiring ample food and moisture to stay active.

Cyst:

• Dormant, resting stage when conditions in the environment become unfavorable.

• Resistant to heat, drying, and chemicals.

• Can be dispersed by air currents.

• Important factor in the spread of disease

Life Cycles and Transmission

• Some protozoan groups exist only in the trophozoite phase.

• Many alternate between the trophozoite and cyst stage, depending on the habitat.

• Trichomonas vaginalis, a common STD, does not form cysts and must be transmitted by intimate contact.

• Entamoeba histolytica and Giardia lamblia form cysts ano are readily transmitted in contaminated water and foods

Reproduction

All protozoa reproduce by relatively simple, asexual mitotic cell division or multiple fission.

Sexual reproduction also occurs in most protozoa:

• Ciliates participate in conjugation in which two cells fuse and exchange micronuclei.

• This results in new and different genetic combinations that can be advantageous in evolution

The Helminths

• Include tapeworms, flukes, and roundworms.

• Adult specimens are usually large enough to be seen with the naked eye.

• Not all flatworms and roundworms are parasites; many live free in soil and water.

• Disease-causing helminths spend part of their lives in the gastrointestinal tract

Flatworms and Roundworms

Flatworms (phylum Platyhelminthes):

• Very thin, often segmented body plan.

• Divided into cestodes (tapeworms) and trematodes (flukes).

Roundworms (phylum Aschelminthes):

• Also called nematodes.

• Elongated, cylindrical, unsegmented body

General Worm Morphology

• Multicellular animals that are equipped to some degree with organs and organ systems.

• In pathogenic helminths, the most developed organ is the reproductive tract.

• Therefore, there is a reduction in the digestive, excretory, nervous, and muscular systems

Life Cycles and Reproduction

• Complete life cycle includes the fertilized egg, larval, and adult stages.

• Adults derive nutrients and reproduce sexually in a host's body.

• Nematodes: sexes are separate and different in appearance.

• Trematodes: sexes can be separate or hermaphroditic.

• Cestodes: generally hermaphroditic

Life Cycles and Reproduction

Helminth life cycle:

• Must transmit an infective form (egg or larva) to the body of another host.

• The host in which the larva develops is known as the intermediate (secondary) host.

• Adulthood and mating occur in the definitive (final) host.

• Transport host is an intermediate that experiences no parasitic development.

Sources for human infection are contaminated food, soil, and water or infected animals

Egg Laying

Fertilized eggs:

• Released to the environment.

• Provided with a protective shell and extra food to aid their development into larvae.

• Vulnerable to heat, cold, drying, and predators.

Certain helminths can lay from 200,000 to 25 million eggs a day to assure successful completion of their life cycle

A Helminth Cycle: The Pinworm

Enterobius vermicularis:

• Pinworm or seatworm.

• Common infestation of the large intestine.

• Range from 2 to 12 mm long with a tapered, curved cylindrical shape

A Helminth Cycle: The Pinworm

Life cycle:

• Microscopic eggs are swallowed: picked up from another infected person or objects they have touched.

• Eggs hatch in the intestine.

• Larvae mature into adults within 1 month.

• Male and female worms mate.

• Female migrates to the anus to deposit eggs.

• Intense itching ensues.

• Scratching spreads the eggs

Distribution and Importance of Parasitic Worms

• About 50 species of helminths cause disease in humans.

• Distributed in all areas of the world.

• Higher incidence in tropical areas.

• Yearly estimate of cases is in the billions and are not confined to developing countries.

• Conservative estimate of 50 million helminth infections in North America alone