Microbiology Exam 2 Combine Sets

NCLEX Prep - Test Bank Question: Please read the clinical scenario, and then answer the questions that follow to become familiar with the traditional NCLEX question format.Mr. Olson arrived in the emergency department with his 10-month-old son. Mr. Olson states he had difficulty waking his son from a nap this afternoon. Additionally, the infant was unable to hold his spoon at dinner and did not seem to be chewing correctly. You observe that the patient has a very weak cry. Mr. Olson noted that the only difference in his son's diet was the ingestion of fresh honey on his toast at breakfast yesterday. You suspect Clostridium botulinum infection due to the ingestion of bacterial endospores. A bacterium acquiring a new trait from a bacteriophage is a phenomenon called

lysogenic conversion.

A(n) _____ originates from the Golgi apparatus as one type of vesicle that contains a variety of enzymes for intracellular digestion.

lysosome

Which of the following is not true of the cytoskeleton?

made of cilia

Oncoviruses include all the following except

measles virus

Viruses completely lack the genes for synthesis of

metabolic enzymes,This does not prove to represent an obstacle, as viruses have adapted to completely take over their host's metabolic resources

Seawater can contain 100 million viruses per

milliliter (extremely abundant)

Asexual spores are the products of

mitotic division of a single parent cell

•Main limiting factor for growth of protozoa is availability of

moisture

Filamentous fungi are called

molds

The woven, intertwining mass of hyphae that makes up the body of a mold is a(n)

mycelium

Toxins produced by poisonous mushrooms can induce

neurological disturbances and even cause death

•An average-size Escherichia coli cell can contain up to 200

new phage units

However, viruses exhibit a wide variety of configurations

of DNA or RNA

Examination of cells and tissues for cytopathic effects can be an important part of the diagnosis

of viral infections

For many years, the cause of viral infections was unknown (even though it was clear that the diseases were transmitted from

person to person

Which is not a characteristic of fungi?

photosynthetic

Aspergillus flavus (mold) produces a

potentially lethal poison to animals who eat contaminated grain

Two noncellular agents, smaller than viruses, are the infectious proteins called _____ and the infectious RNA strands called _____.

prions, viroids

Reproductive or fertile hyphae

produce spores (fungal reproductive bodies)

•A common feature of spongiform encephalopathies is distinct

protein fibrils in brain tissue called prions.

•Viruses bear no resemblance to cells and lack any of the

protein-synthesizing machinery found in cells

cell walls are not usually found in

protozoa

•Viruses infect every type of cell, including bacteria, algae, fungi,

protozoa, plants, and animals

Protoza can move through fluids by means of

pseudopods, flagella, or cilia

Septa

segments or cross walls found in most fungi that allow the flow of organelles and nutrients between adjacent compartments → Hyphae with these known as septate

•Cytoplasmic membrane serves as a

selectively permeable barrier

The first primitive eukaryotes were probably

single-celled and independent

•Viral outer surface is composed of regular, repeating

subunits that give rise to their crystalline appearance

•Upon release, virulent phages can spread to other

susceptible bacterial cells and begin a new cycle of infection

Which is not a typical capsid shape?

tetrahedral

First important hints about the unique characteristics of viruses came in

the 1890s

For many years, animal viruses were classified on the basis of their hosts and

the diseases they caused

•If even a small number of these virions happen to meet another susceptible cell and infect it

the potential for rapid viral proliferation is immense

The flexible cell membrane of the host is penetrated by

the whole virus or its nucleic acid

The primary purpose of viral cultivation is

to isolate and identify viruses in clinical specimens. to prepare viruses for vaccines. to do detailed research on the viral structure, lifestyle, genetics, and effects on host cells.

•The life cycle of a parasitic protozoa dictates its mode of

transmission to other hosts

Some protozoan groups exist only in the

trophozoite phase

All algae have chloroplasts.

true

Prophages can be activated into viral replication and enter the lytic cycle.

true

Viruses are the most common cause of acute infections that do not result in hospitalization.

true

Viruses are used to produce vaccines for prevention of certain viral infections.

true

All of the following are helminths except

trypanosomes

The process of dissolving the envelope and capsid to release the viral nucleic acid is

uncoating

Mycoses (fungal infections)

vary in the way the pathogen enters the body and the degree of tissue involvement

10 - 20% of bacterial DNA contains

viral sequences

Ivanovski and Beijerinck showed that a disease in tobacco was caused by a

virus (tobacco mosaic virus)

Not all noncellular infectious agents are

viruses

•Smallest infectious agents (More than 2,000 bacterial viruses could fit into a bacterial cell

while over 50 million polioviruses could fit in a human body cell.

The Fungi

•Approximately 100,000 species of fungi •Macroscopic fungi: Mushrooms, puffballs, gill fungi •Microscopic fungi: Molds, yeasts •Forms - Unicellular - Colonial (form colonies) - Complex/multicellular (mushrooms, puffballs)

Viruses that Infect Bacteria

•Bacteriophage

Life Cycles and Reproduction

•Complete life cycle includes the fertilized egg (embryo), larval, and adult stages •Adults derive nutrients and reproduce sexually in a host's body

On the basis of body type, the two major groups of pathogenic helminths are

•Flatworms (Phylum Platyhelminthes) •Roundworms (Phylum Aschelminthes)

Mitochondria

•Generate energy for the cell •Appear as round or elongated particles scattered throughout the cytoplasm •Composed of a smooth, continuous outer membrane •Inner membrane has tubular inner folds called cristae - Hold the enzymes and electron carriers of aerobic respiration - Extracts chemical energy contained in nutrient molecules and stores it as ATP •Unique organelles: - Divide independently of the cell - Contain circular strands of DNA - Have prokaryotic-sized 70S ribosomes *These characteristics have caused scientists to suggest that mitochondria were once bacterial cells that developed into eukaryotic organelles over time

General Worm Morphology

•Multicellular animals equipped with organs and organ systems •In pathogenic helminths, most developed organs are found in the reproductive tract •Reduction in the digestive, excretory, nervous, and muscular systems

The Protozoa

•Name comes from the Greek for "first animals" •65,000 species of single-celled organisms that have startling properties when it comes to movement, feeding, and behavior •Most are harmless, free-living inhabitants of water and soil •A few species of parasites are responsible for hundreds of millions of infections each year •Protozoa are categorized together because of their similar physical characteristics rather than their genetic relatedness

Ribosomes

•Numerous, tiny particles that give a "dotted" appearance to the cytoplasm •Distributed throughout the cell - Scattered freely in the cytoplasm and cytoskeleton - Intimately associated with rough endoplasmic reticulum - Inside mitochondria and chloroplasts •Can be found in short chains of polyribosomes •Size and structure - Large and small subunits of ribonucleoprotein - Eukaryotic ribosome is the larger 80S, a combination of 60S and 40S subunits (Because of this difference in size compared to a bacterial ribosome, we can use antibiotics to target prokaryotic ribosomes without harming our own eukaryotic ribosomes) • Staging areas for protein synthesis

Detection of Viral Growth in Culture

•One way to detect the growth of a virus in culture is the observation of degeneration and lysis of infected cells in the monolayer of cells

Satellite Viruses

•Other virus-like particles that are dependent on other viruses for replication

Treatment of Animal Viral Infections

•The nature of viruses makes it difficult to design effective therapies against them •Antibiotics designed to disrupt prokaryotic cells have no effect on viruses •Antiviral drugs that block viral replication by targeting the function of host cells can have severe side effects (on the host) •Almost all antiviral drugs so far licensed have been designed to target one of the steps in the viral life cycle

The Cytoplasmic Membrane

•Typical bilayer of phospholipids in which protein molecules are embedded •Contain sterols (a type of lipid) of various kinds - Relative rigidity give stability to the membrane (making the membranes of eukaryotic cells more stable than those of non-eukaryotic cells) - Important in cells that do not have a cell wall swwwwwwwwwwwwwwwwwwwwwwwwwwww

Cell Cultures and Avian Influenza

•Vaccine strains of the influenza virus have been grown in chicken eggs since the 1950's •Recent worries about avian influenza have prompted scientists to look for faster and more efficient ways to grow the virus - Scientists were able to propagate the virus in dog kidney cells - In 2009, plans were made to produce flu vaccine from cell culture, but they were mostly thwarted (FDA approved general use of cell-culture -based vaccine in 2012) - During the run up to the 2009 flu season, only one vaccine company was using cell culture for vaccines, the rest were still using chicken eggs

Viroids

•Virus-like agents that parasitize plants •About one-tenth the size of an average virus •Composed only of naked strands of RNA, lacking a capsid or any other type of coating •Significant pathogens in economically important plants: tomatoes, potatoes, cucumbers, citrus trees, chrysanthemums

•Bovine spongiform encephalopathy (BSE)

"Mad cow disease" - Recent crisis in Europe when researchers found that humans could contract the disease by consuming contaminated beef - Infected individuals developed a variant of CreutzfeldtJacob disease - As of 2011, only three BSE-positive cows have been found in the US compared to over 184,000 cows in the UK

Cultivation of viruses is difficult, as they require living cells as their

"medium"

•Cause spoilage of fresh produce during shipping and storage

(40% of yearly fruit crop consumed by fungi)

Creutzfeldt-Jacob disease

(First of these diseases discovered in humans) - Infects the human nervous system - Causes gradual degeneration and death

•Cells became specialized within colonies

(adapting to perform a particular function advantageous to the whole colony, such as movement, feeding, or reproduction)

•Cell shape can remain constant

(most ciliates), or change constantly (most amoebas)

Louis Pasteur postulated that a "living thing" smaller than bacteria caused these diseases

(specifically rabies, developing a vaccine for it in 1884) - Also proposed the term virus, which is Latin for "poison."

While fungi have many complex reproductive strategies, most can reproduce through the outward growth of hyphae or by fragmentation

, in which a separated piece of mycelium can generate into a whole new colony

•Locomotion via cilia and flagella is common in protozoa

, many algae, and a few fungal and animal cells

Corynebacterium diphtheriae

- Diphtheria toxin is a bacteriophage product → C. diphtheriae without the phage are harmless

Detection of Viral Growth in Culture (cont'd) •This same technique is used to detect and count bacteriophages

- Viruses released by an infected cell radiate out to adjacent host cells → Leading to plaque development - New cells become infected, they die and release more viruses, and the process continues - Plaque manifests as a macroscopic, round, clear space that correspond to areas of dead cells → Due to the gradual and symmetrical spread from the original point of infection

• Smooth endoplasmic reticulum

-Closed tubular network without ribosomes -Nutrient processing -Storage of nonprotein macromolecules such as lipids

•Three types of fungal diseases in humans:

1) Community-acquired infections → Environmental pathogens 2) Hospital-associated infections → Pathogens in clinical setting 3) Opportunistic infections → Low-virulence species infecting already weakened individuals

Life Cycle of animal viruses

1. absorption 2. penetration 3. uncoating 4. synthesis 5. assembly 6. release

•Poliovirus-infected cell

100,000 virions

The History of Eukaryotes: Evidence from paleontology indicates the first eukaryotic cells appeared approximately

2 billion years ago

Parvoviruses around

20 nm in diameter

•Many fungi are part of the normal human microbiome, yet nearly

300 species of fungi can cause human disease

The length of the replication cycle varies from 8 hours in polioviruses to

36 hours in herpesviruses

•The number of viral genes is quite small compared with that of a cell

4 genes in hepatitis B virus - Hundreds of genes in some herpes viruses - Possess only the genes needed to invade host cells and redirect their activity *A human body cell has approximately 20,000 genes, allowing these cells to carry out complex metabolic activity necessary for independent life

•International Committee on the Taxonomy of Viruses (Most recent update issued in 2016)

8 orders - 38 families (+84 families not yet assigned to an order) *Prior to 2000, there was only a single recognized order of viruses

Oncogenic Viruses

: Experts estimate that up to 13% of human cancers are caused by viruses

Sporangiospores

: Formed by successive cleavages within a sac-like head called a sporangium, which is attached to the stalk, the sporangiophore

Conidiospores or conidia:

: Free spores not enclosed by a spore-bearing sac → Develop by either the pinching off of the tip of a special fertile hypha, or by the segmentation of a preexisting vegetative hypha

•Parasitic

: Grow on the bodies of living animals or plants, although very few require a living host

Tropisms

: Specificities of viruses for certain tissues (The hepatitis B virus targets the liver, the mumps virus targets the salivary glands

Nucleocapsid

: The capsid together with the nucleic acid - Naked viruses consist only of a nucleocapsid

The Cytoskeleton

A flexible framework of molecules criss-crossing the cytoplasm •Functions: - Anchoring organelles - Moving RNA and vesicles - Permitting shape changes - Movement

•Virion

A fully formed virus that is able to establish an infection in a host cell

•Provirus

A persistent infection in which the viral DNA is incorporated into the DNA of the host - One of the more serious complications occurs with the measles virus → May remain hidden in brain cells for many years, causing progressive damage and loss of function

Nucleus, Endoplasmic Reticulum, and Golgi Apparatus: Nature's Assembly Line

A segment of genetic code of DNA from the nucleus is copied onto RNA and passed through the nuclear pores to the rough endoplasmic reticulum •Synthesized proteins on the RER (via ribosomes) are deposited into 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

Endoplasmic Reticulum

A series of microscopic tunnels used in transport and storage

Adsorption

A virus can invade its host cell only through making an exact fit with a specific host molecule → Because of this, the range of hosts it can infect is limited

Harmless spores can cause opportunistic infections in

AIDS patients, cancer, or diabetes

Distribution and Importance of Parasitic Worms

About 50 species of helminths parasitize humans •Distributed in all areas of the world that support human life •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

Heterotrophic:

Acquire nutrients from a wide variety of organic substrates (sources of nutrition) → ALL fungi

It is impossible to estimate the number of viruses that occur on a worldwide basis, but the number is in the billions

Acute infections: colds, hepatitis, chickenpox, influenza, herpes, warts - Prominent viral infections found in certain regions of the world: Dengue fever, Rift Valley fever, yellow fever - Viruses with high mortality rates: rabies, AIDS, Ebola - Viruses that cause long-term debility: polio, neonatal rubella - Viruses with possible connection to chronic afflictions with an unknown cause: type 1 diabetes, multiple sclerosis, various cancers, Alzheimer's disease, obesity

T-even Bacteriophage Life Cycle

Adsorb to host bacteria using specific receptors on the bacterial surface •Although the enter phage does not enter the host cell, nucleic acid penetrates after being injected through a rigid tube inserted through the cell wall and membrane - Nucleic acid entry causes cessation of host cell DNA replication & protein synthesis •No uncoating is necessary •Host machinery used for viral replication and synthesis of viral proteins •Parts spontaneously assemble into bacteriophages

•General phases of the animal viral replication cycle

Adsorption - Penetration - Uncoating - Synthesis - Assembly - Release

•Roundworms (Phylum Aschelminthes)

Also know as nematodes - Have an elongated, cylindrical, unsegmented body

The exceptional and curious nature of viruses raises many questions

Are they organisms; that is, are they alive? •What role did viruses play in the evolution of life? •What are their distinctive biological characteristics? •How can particles so small, simple, and seemingly insignificant be causing disease and death? •What is the connection between viruses and cancer?

•Plaques

Areas where virus-infected cells have been destroyed and show up as a clear, well-defined patches in the cell sheet - Microscopic manifestation of cytopathic effects (CPEs)

Nucleic Acids

At the core of a virus

Opportunistic pathogens:

Attack persons who are already weakened in some way

•Bacteriophage

Bacterial viruses were discovered in 1915 by Twort and d'Herelle (it appeared as if the bacterial host cells were being eaten by some unseen parasite) - From the Greek phage meaning "eating" - Most contain double-stranded DNA, but some RNA types exist as well - Every bacterial species is parasitized by various specific bacteriophages - Often make the bacteria they infect more pathogenic for humans

Using Bird Embryos

Bird eggs containing embryos provide: - Intact and self-supporting unit - Sterile environment - Contain their own nourishment •Furthermore, it furnishes several embryonic tissues that readily support viral multiplication •Chicken, duck, and turkey eggs are the most common choices for inoculation •Virus is injected through the eggshell by drilling a small hole or making a small window

Clostridium botulinum

Botulinum toxin

Primary pathogens

Can sicken even healthy persons

•Viruses are obligate intracellular parasites

Cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses

Viral Components

Capsids, Nucleic Acids, and Envelopes

•Persistent infections

Cell harbors the virus - Not immediately lysed - Can last from a few weeks to the remainder of the host's life - Can remain latent in the cytoplasm, or incorporate into the DNA of the host

•Enveloped viruses can bud from:

Cell membrane - Nuclear envelope - Endoplasmic reticulum

In vitro

Cell or tissue culture methods (cultivated in the lab)

•Sexual reproduction also occurs in most protozoa

Ciliates participate in conjugation in which two cells fuse and exchange micronuclei (genetic exchange) - This results in new and different genetic combinations that can be advantageous in evolution

Ectoplasm

Clear outer layer involved in locomotion, feeding, and protection

Characteristics of Prions

Composed entirely of protein •Contain no nucleic acid (Revolutionized our ideas about what can constitute an infectious agent) •Questions still remain as to how the agent is propagated/replicated, since all other infectious agents require nucleic acid

•Lysosomes

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 and damaged tissue (a similar-acting organelle being the peroxisome)

Reverse transcriptase synthesizes

DNA from RNA

•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 *If provided with moisture and nutrients, a cyst breaks open and releases the active trophozoite.

•RNA viruses

Double-stranded - More often single-stranded - Positive-sense RNA: Ready for immediate translation (protein synthesis) - Negative-sense RNA: Must be converted before translation can occur - Segmented → Meaning that the individual genes exist on separate pieces of RNA - Retroviruses: Carry their own enzymes to create DNA out of RNA

Life Cycle of dsDNA Viruses •Synthesis phase divided into two parts

Early Phase and Late Phase

•Cytoplasm divided into two parts

Ectoplasm Endoplasm

•DNA viruses

Enter the host cell's nucleus and are replicated and assembled there

•Penetration through endocytosis

Entire virus is engulfed by the cell and enclosed in a vacuole or vesicle

•Uncoating

Enzymes in the vacuole dissolve the envelope and capsid - Virus fuses with the wall of the vesicle - Viral nucleic acid is released into the cytoplasm

•Eukaryotic vs. prokaryotic flagella

Eukaryotic flagellum is 10x thicker - Covered by an extension of the cell membrane - A long, sheathed cylinder containing regularly spaced microtubules - Microtubules slide past each other creating a whipping motion that requires the expenditure of energy

Contain only those parts needed to invade and control a host cell

External coating - Core containing one or more nucleic acid strains of DNA or RNA - Sometimes one or two enzymes

•Envelope

External covering of a nucleocapsid, usually a modified piece of the host's cell membrane (not all viruses, but most viruses that infect humans

Nucleolus

Found in the nucleoplasm - Site of RNA synthesis - Collection area for ribosomal subunits (which are then transported through the nuclear pores to the cytoplasm for final assembly into ribosomes)

Cestodes

Generally hermaphroditic

Endoplasm

Granular inner region housing the nucleus, mitochondria, and food and contractile vacuoles

Types of CPEs include

Gross changes in shape and size - Development of intracellular changes - Inclusion bodies: Compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm - Syncytia aka Giant Cells: Fusion of multiple host cells into single large cells containing multiple nuclei (come about as a result of some viruses' ability to fuse membranes)

•Cell cultures

Grown in sterile chambers with special media that contain the correct nutrients for cells to survive - Cells form a monolayer, or single, confluent sheet of cells that supports viral multiplication - Allows for the close inspection of culture for signs of infection

Transformation: Effect on the cell caused by oncogenic viruses

Increased rate of growth - Alterations in chromosomes - Changes in the cell's surface molecules - Capacity to divide for an indefinite period - Oncoviruses: Mammalian viruses capable of initiating tumors

T-even Bacteriophage

Infect Escherichia coli - Icosahedral capsid head - Central tube - Collar - Base plate - Tail pins - Fibers

Poliovirus

Intestinal and nerve cells of primates

•Primary purposes of viral cultivation

Isolate and identify viruses in clinical specimens - Prepare viruses for vaccines - Do detailed research on viral culture, multiplication cycles, genetics, and effects on host cells

In vivo

Laboratory-bred animals and embryonic bird tissues

•Both prokaryotes and eukaryotes evolved from a precursor cell called the

Last Common Ancestor

•Sexual spore formation

Linking of genes from two parent fungi creates offspring with combinations of genes different from that of the parent - Variations lead to potentially advantageous adaptations - Sexual spores vary from simple fusion of fertile hyphae to a complex union of male and female structure

Hepatitis B

Liver cells of humans

•Microtubules

Long hollow tubes - Maintain the shape of eukaryotic cells without cell walls - Transport substances from one part of the cell to another - Spindle fibers play a role in mitosis (centrioles)

•Actin filaments

Long, thin protein strands, about 7 nm in diameter - Found throughout the cell, but most highly concentrated just inside the cell membrane - Responsible for cellular movements such as contraction, crawling, pinching during cell division, and formation of cellular extensions

•Hyphae (Molds)

Long, threadlike cells found in the bodies of filamentous fungi - Pseudohypha: Chain of yeast cells that forms when buds remain attached in a row

Vesicles

Lysosomes, •Vacuoles

Chromatin

Made of DNA and histone proteins - Genetic material of the cell

The Danger of Lysogeny in Human Disease

Many bacteria that infect humans are lysogenized by phages •Occasionally phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human

Which of the following occurs during assembly?

Nucleocapsid is formed. New viral nucleic acid is formed. Viral spikes insert in host cell membrane. A nucleocapsid is formed and viral spikes insert in host cell membrane.

Saprobic

Obtain nutrients from the remnants of dead plants and animals in soil or aquatic habitats → MOST fungi

•Direct fusion of the viral envelope with the host cell membrane

Occurs with influenza and mumps viruses - Envelope merges directly with the cell membrane - Whole nucleocapsid is released to the cell's interior (cytoplasm), and the virus is not uncoated until later in the process

Cilia are similar in structure to flagella but are shorter and more numerous

Only found in a single group of protozoa and in certain animal cells - Occur all over the cell surface (could be thousands) - Beat in oar-like strokes - Also function as feeding and filtering structures

•Adeno-associated virus (AAV)

Originally thought that it could only replicate in cells infected with the adenovirus - Can also infect cells that are infected with other viruses or that have had their DNA disrupted through other means

•Rough endoplasmic reticulum (RER)

Originates from the outer membrane of the nuclear envelope and extends in a continuous network to the cell membrane - Allows transport materials from the nucleus to the cytoplasm and ultimately to the cell's exterior - Ribosomes are attached to its membrane surface - Proteins synthesized on the RER are transported into the lumen and held for packaging and transport

•Late phase

Other parts of the viral genome are translated into proteins required to form the capsid and other structures - New viral genomes and capsids are assembled - Mature viruses are released by budding or cell disintegration *In some viruses, the viral DNA becomes silently integrated into the host's genome by insertion at a particular site on the host genome. This integration may later lead to the transformation of the host cell into a cancer cell and the production of a tumor.

Largest viruses

Pandora virus around 1 um in length

•Cancer-causing viruses

Papillomaviruses → Genital warts are associated with cervical cancer - Epstein-Barr virus (herpesvirus) → Burkitt's Lymphoma - HTLV-1 (virus related to HIV) → Involved in human cancers

Who developed a rabies vaccine by separating bacteria from virus using a filter?

Pasteur

A Helminth Cycle: The Pinworm • Enterobius vermicularis → A type of roundworm

Pinworm or seatworm - Causes a common infestation of the large intestine - Range from 2 - 12 cm long with a tapered, curved cylindrical shape - The condition they cause, enterobiasis, is usually a simple, uncomplicated infection that does not spread beyond the intestine

•Enzymes for specific operations within their host cell

Polymerases that synthesize DNA and RNA - Replicases that copy RNA - Reverse transcriptase synthesizes DNA from RNA (Seen in Human Immunodeficiency Virus)

Eventually the cell becomes so packed with viruses that it lyses (splits open), releasing mature virions

Process hastened by viral enzymes produced late in the infection cycle that digest the cell envelope, weakening it

Spikes can be found on naked or enveloped viruses

Project from the nucleocapsid or the envelope - Allow viruses to dock with host cells

Capsid

Protein shell that surrounds the nucleic acid

•Only disease-causing eukaryotes will be discussed in this chapter

Protozoa, Fungi, Helminths

•DNA usually exists as a double-stranded molecule and

RNA as a single-stranded molecule

•A number of fungal species are pathogenic to field plants (such as corn and grain)

Reduces crop production & can also cause disease in domestic animals that eat the contaminated food crops

•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, which leads to many being destroyed an unable to reach a new host •Certain helminths (Ascaris) can lay from 200,000 to 25 million eggs a day to assure successful completion of their life cycle

•RNA viruses

Replicated and assembled in the cytoplasm (Retroviruses are an exception to this rule, and turn their RNA genomes into DNA)

•Spores

Responsible for reproduction - 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

•Cell walls of fungi:

Rigid and provide structural support and shape - Different in chemical composition from prokaryotic cell walls - Thick layer of polysaccharide fibers composed of chitin or cellulose - Thin outer layer of mixed glycans

•Intermediate filaments

Rope-like structures 10 nm in diameter - Structural support to the cell and organelles

•Yeasts (Fungal Cell)

Round to oval shape - Asexual reproduction - Budding (swellings on the surface of the cell that become separate cells

•Sexual spores are formed by a process involving the fusing of two parental nuclei followed by meiosis →

Serves to increase the genetic variation among spores

•Nematodes

Sexes are separate and different in appearance

Trematodes

Sexes can be separate or hermaphroditic (male and female sex organs are in the same individual worm)

Two sides of the debate about the connection between viruses and the rest of the microbial world

Since viruses are unable to replicate independently from the host cell, they are not living things and should be called "infectious molecules" - Even though viruses do not exhibit most of the life processes of cells, they can direct them, andthus are certainly more than inert and lifeless molecules

Protozoan Form and Function

Single cells containing all of the major eukaryotic organelles except chloroplasts

•DNA viruses

Single-stranded (ss) - Double-stranded (ds) - Linear - Circular

Golgi Apparatus

Site of protein modification and shipping •Consists of several flattened, disc-shaped sacs called cisternae •Cisternae do not form a continuous network •Always closely associated with the endoplasmic reticulum - Transitional vesicles (tiny membrane-bound packets of protein 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

The number of viruses released by infected cells is variable, controlled by

Size of the virus - Health of the host cell

•Spongiform encephalopathies

Smaller and simpler than viruses - Implicated in chronic, persistent diseases in humans and animals - Brain tissue removed from affected animals resembles a sponge - Long period of latency before first clinical signs appear - Signs range from mental derangement to loss of muscle control - Diseases are progressive and universally fatal

Viruses and Cancer

Some animal viruses enter a host cell and permanently alter its genetic material, leading to cancer

Viral envelope differs significantly from the host's membranes

Some or all of the regular membrane proteins are replaced with viral proteins - Some envelope proteins attach to capsid proteins - Glycoproteins are exposed on the outside of the envelope (these spikes are essential for the attachment of viruses to the next host cell)

Using Live Animal Inoculation

Specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits are the usual choices for viral cultivation in animals • Occasionally, invertebrates such as insects or nonhuman primates are used •Because viruses exhibit host specificity, certain animals can propagate viruses more readily than others

•Asexual spore formation (Two types of asexual spores)

Sporangiospores Conidiospores or conidia:

•Host range:

The limited range of cells that a virus can infect (Can be highly restrictive, moderately restrictive, or broad)

Endosymbiosis

The more complex cell type most likely emerged when a Last Common Ancestor cell engulfed smaller prokaryotic cells and coexisted with them

The Glycocalyx

The outermost layer that comes into direct contact with the environment •Usually composed of polysaccharides and appears as a network of fibers, a slime layer, or a capsule •Functions: - Protection - Adherence of cells to surfaces - Reception of signals from other cells and the environment

•The nature of the viral replication cycle dictates

The way the virus is transmitted - What it does to the host - Responses of immune defenses - Human measures to control viral infections

Mycelium

The woven, intertwining mass of hyphae that makes up the body or colony of a mold

Some fungi are eaten or used to impart flavoring to food

The yeast Saccharomyces produces the alcohol in beer and wine and the gas that causes bread to rise -Blue cheese, soy sauce, and cured meats derive their unique flavors from the actions of fung

•Filterable virus

These early researchers found that when fluids from host organisms passed through porcelain filters designed to trap bacteria, the filtrate remained infectious - This result proved that a cell-free fluid could contain agents that could cause infection

Last Common Ancestor

This cell was neither prokaryotic nor eukaryotic - Gave rise to both prokaryotic and eukaryotic cells

•Encystment

Trophozoite cell rounds up into a sphere - Ectoplasm secretes a tough, thick cuticle around the cell membrane

Temperate phages can participate in a lytic phase or in the very different lysogenic cycle

Undergo adsorption and penetration into bacterial host - Do not undergo replication or release immediately • Instead, the viral DNA enters an inactive prophage state (reminiscent of the provirus state in animal viruses) - Inserted into bacterial chromosome - Copied during normal bacterial cell division so that the cell's progeny will also have the temperate phage DNA - Lysogeny: a condition in which the host chromosome carries viral DNA • Because viral particles are not produced, the bacterial cells carrying temperate phages do not lyse, and they appear entirely normal

Rabies

Various cells of all mammals

•Early phase

Viral DNA enters the nucleus where genes (usually the ones that make proteins needed to make new viral DNA) are transcribed into a messenger RNA - RNA transcript moves into the cytoplasm to be translated into viral proteins (enzymes) needed to replicate viral DNA (this replication occurring in the nucleus) - Host cell's DNA polymerase is involved in this phase

Chronic latent state (Several types of viruses remain in this state, periodically becoming reactivated)

Viruses go into a period of inactivation in cells - Later periodically emerge under the influence of various stimuli to cause recurrent symptoms - Examples are herpes simplex virus (cold sores and genital herpes) and herpes zoster virus (chickenpox and shingles)

Lysogenic conversion:

When a bacterium acquires a new trait from its temperate phage

The three main types of cytoskeleton elements are:

actin filaments, microtubules, & intermediate filaments

Cells that lack compatible virus receptors are resistant to

adsorption and invasion by that virus (For example, human liver cells are not infected by the canine hepatitis virus, and vice versa)

•Viruses are better described as active or inactive rather than

alive or dead (although, terming them alive or dead does not really matter)

Motility

allows microorganisms to move toward nutrients and positive stimuli and away from harmful substances and stimuli

•Some fungal cells are considered dimorphic

and can take either form depending on growth conditions (such as changing temperature

Cells later began to aggregate

and form colonies

Viruses are minute parasites that seize control of the synthetic

and genetic machinery of cells

•Form stable associations with plant roots (forming structures called mycorrhizae)

and increase their ability to absorb water and nutrients

•Complex organisms later evolved

and individual cells lost the ability to survive on their own

Play an essential role in decomposing organic matter

and returning essential minerals to the soil

Thrive in nutritionally poor or adverse environments

and those with high salt or sugar content, or high temperatures

•Isolated animal cells are grown in vitro; in cell or tissue culture rather than in an

animal or egg (The most important early discovery that led to easier cultivation of viruses in the lab

Fungi have been engineered to produce large quantities of

antibiotics, alcohol, organic acids, and vitamins

The group of protozoa that have gliding motility are the

apicomplexa/sporozoa.

•Entamoeba histolytica and Giardia lamblia form cysts and

are readily transmitted in contaminated water and food

Vegetative hyphae

are responsible for the visible mass of growth that appears on the surface of a substrate and penetrates it to digest and absorb nutrients → Can give rise to reproductive hyphae during the development of a fungal colony

•Fungus penetrates the substrate and secretes enzymes that reduce it to small molecules that can

be absorbed by cells (Fungus have enzymes for digesting an incredible array of substances, including: feathers, hair, cellulose, petroleum products, wood, & rubber)

Some cylindrical viruses can be relatively long (800 nm)

but are so narrow in diameter (15 nm) that their visibility is limited without an electron microscope

•Unlike cells, viruses contain DNA or RNA

but not both

NCLEX Prep - Test Bank Question: Please read the clinical scenario, and then answer the questions that follow to become familiar with the traditional NCLEX question format.Mrs. Hammond is a 79-year-old woman who has been a resident on your floor for the past 5 years. She has been complaining of pain, burning, and tingling on her left side. Today, you observe fluid-filled blisters wrapping around the left side of her torso in a single line. The physician diagnoses her with shingles and places her on contact precautions. Viruses contain the necessary tools to invade and control a host cell. These tools may consist of a

capsid or envelope, nucleic acid strands of DNA or RNA, and enzymes.

•Protozoa and helminths do not have

cell walls

•Accumulated damage from a virus infection kills most

cells. •However, some cells maintain a carrier relationship:

Fungal cell walls give off

chemical substances that cause allergies

Vibrio cholerae -

cholera toxin

When a eukaryotic cell is not undergoing mitosis, the DNA and its associated proteins appear as a visible network of dark fibers called the

chromatin

Non-septate hyphae

consist of one, long, continuous cell not divided into individual compartments via cross walls

Some organelles act as a primitive nervous system to

coordinate movement

•Trichomonas vaginalis, a common STD, does not form

cysts (more delicate) and must be transmitted by intimate contact

Which of the following is not a characteristic of a transformed cell?

decreased growth rate

•Many protozoan groups alternate between trophozoite and cyst stage

depending on the habitat

•All protozoa reproduce by simple, asexual mitotic cell

division or multiple fission (multiple rounds of cell division)

By infecting cells and influencing their genetic makeup, viruses have shaped the way cells, tissues, bacteria, plants, and animals have

evolved

All fungi have hyphae. True or False.

false

Cell membrane regulates

food, water, and secretions (Lacking a cell wall gives them a certain range of flexibility)

Loeffler and Frosch discovered an animal virus causes

foot-and mouth disease in cattle

Predominant habitats for Protozoa are

fresh and marine water, soil, plants

Colonies of filamentous fungi have a cottony, hairy, or velvety texture that arises

from their microscopic organization and morphology

The sum total of the genetic information carried by an organism is its

genome

•Colonies of yeasts are much like bacteria;

have a soft, uniform texture and appearance

•Because the envelope is more flexible than the capsid, enveloped viruses are pleomorphic;

have a variable shape and range from spherical to filamentous

Larvae and eggs are developmental forms of

helminths

Most protozoa fall within 3-300 um (micrometers),

however some are large enough to be seen swimming in a pond (3-4 mm)

8-10% of the human genome consists of sequences that come from viruses that have inserted their genetic material permanently into

human DNA

Host cells of viruses include

humans and other animals. plants and fungi. bacteria. protozoa and algae.

Protozoa can survive

in extremes of temperature and pH - Many protozoa can convert to a resistant, dormant stage called a cyst

Which of the following does not pertain to helminths?

in kingdom Protista

Types of cytopathic effect?

inclusions in the nucleus multinucleated giant cells inclusions in the cytoplasm cells change shape

Which of the following is a type of cytopathic effect?

inclusions in the nucleus multinucleated giant cells inclusions in the cytoplasm cells change shape

The envelope of enveloped viruses is

is obtained by viral budding or exocytosis.

•Cells of most microscopic fungi grow

loose associations or colonies

When a bacterium acquires a trait from its temperate phage, it is called

lysogenic conversion

•Vaccines stimulate immunity and are extremely valuable, but are only available for a limited number of viral diseases →

Nearly all of the vaccines available today are targeted at viral diseases

•Flatworms (Phylum Platyhelminthes)

Have a thin, often segmented body plan - Divided into cestodes (tapeworms → long, ribbonlike arrangement) and trematodes (flukes → flat, ovoid bodies)

•Two different types of capsid (Depending on how the capsomeres are shaped and arranged)

Helical - Icosahedral

Nutritional and Habitat Range

Heterotrophic, requiring food in a complex organic form •Free-living species scavenge dead plant or animal debris or graze on bacteria and algae •Some species have special feeding structures, such as oral grooves which carry food particles into a passageway or gullet that packages the captured food into vacuoles for digestion •Some protozoa absorb food directly through the cell membrane •Parasites live on fluids of their host (Such as plasma or digestive juices

•Newer classification systems emphasize the following

Hosts and diseases they cause - Structure - Chemical composition - Similarities in genetic makeup

The Helminths

Include tapeworms, flukes, and roundworms •Adult specimens are usually large enough to be seen with the naked eye (the largest tapeworm measuring ~25 meters) •Included in the study of microbes mainly due to their infective abilities and the fact that they produce microscopic eggs and larvae •Not all flatworms and roundworms are parasites; many live free in soil and water •Parasitic helminths spend part of their lives in the gastrointestinal tract

Vacuoles

Membrane bound sacs containing fluids or solid particles to be digested, excreted, or stored - Formed 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 and a lysosome (this merged structure is called a phagosome)

A Helminth Cycle: The Pinworm (cont'd) • 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 contaminates the fingers, which, in turn, transfers eggs to bedclothes and other inanimate objects, and other people

•Capsid

Most prominent feature of viruses - Composed of identical protein subunits called capsomeres - Capsomeres spontaneously self-assemble into the finished capsid

The Nucleus

Most prominent organelle of eukaryotic cells •Separated from the cytoplasm by the nuclear envelope - Composed of two membranes 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

•Trophozoite

Motile feeding stage requiring ample food and moisture to stay active

•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 host - Adulthood and mating occur in the definitive host aka "final" host •Sources for human infection are contaminated food, soil, and water or infected animals •Routes of infection are by oral intake or penetration of unbroken skin

•Delta agent

Naked circle of RNA - Expressed only in the presence of the hepatitis B virus - Worsens the severity of liver damage

•Interferon

Naturally occurs in human cells and is used with some success in treating and preventing viral infections

•Enveloped viruses (Mostly animal)

Take a bit of the cell membrane when they are released from a host cell

Lysogeny:

The Silent Virus Infection

•Ways that viruses cause cancer in animals

Virus carries genes that directly cause cancer - Virus produces proteins that induce a loss of growth regulation in the cell

•Induction

Virus in a lysogenic cell becomes activated and progresses directly into viral replication and the lytic cycle •Lysogeny considered the least deadly form of parasitism than the full lytic cycle because it allows the virus to spread without killing the host •Scientists believe there are more bacteriophages than all other life in the biosphere combined

•Cytopathic Effects (CPEs)

Virus-induced damage to the cell that alters its microscopic appearance