microbiology unit 2

List advantages and disadvantages to phenolic compounds.

Advantages of Phenolic Compounds: Economical, eliminates fecal contamination Disadvantages of Phenolic Compounds:Highly irritating to skin, noxious odor, respiratory tract irritant, limited to disinfection of noncritical item.

Identify advantages and disadvantages of cold and desiccation.

Advantages: Cold treatment merely retards the growth of most microbes. Disadvantages: some psychrophiles grow very slowly even at freezing temps. Antimicrobial effects are erratic and uncertain.

List the essential nutrients of a bacterial cell. Use acronym CHONPS.

All organisms require carbon, hydrogen, oxygen, nitrogen, phosphate and sulfur.

Describe the function and structure(s) of viral capsids. Review Figure 5.3

All viruses have a protein capsid, or shell, that surrounds the nucleic acid in the central core. When a virus is magnified, the capsid is the most prominent geometric feature. Each capsid is constructed from identical subunits called capsomers that are constructed from protein molecules. The capsomers spontaneously self-assemble into the finished capsid, resulting in either helical or icosahedral shape.

Autotroph

An organism that uses inorganic carbon dioxide as its carbon source. They have the ability to convert carbon dioxide into other organic compounds. They are not nutritionally dependent on other living things.

. Discuss characteristics of biofilms that differentiate them from planktonic bacteria. Give some patient examples. Review Figure 6.7.

Biofilms are mixed communities of bacteria and other microbes that are attached to a surface and each other. They form a multilayer conglomerate of cells and intracellular material. The attached cells are stimulated to release chemicals as the cell population grows. Ex: biofilm grown on a gauze bandage

What is DNA recombination? Define recombinant.

DNA recombination is any event in which one bacterium donates DNA to another bacterium. The end result is a new strain different from both the donor and the original recipient strain. Recombinant: any organism that contains the genes that originated in another organism

Moist heat methods

Moist heat methods: occurs in the form of hot water, boiling water, or steam. The temperature ranges from 60 to 135 degrees Celsius. Moist heat operates at lower temperatures and lower exposure times to achieve the same effectiveness as dry heat.

. Discuss the primary reason that antiviral drugs are more difficult to design than antibacterial drugs.

Most antiviral drugs are aimed to block virus replication by targeting the function of the host cells and therefore would cause severe side effects.

Name the desirable characteristics of chemical control agents.

Rapid action even in low concentrations Solubility in water or alcohol and long-term stability Broad- spectrum microbial action without being toxic to human and animal tissues Penetration of inanimate surfaces to sustain a cumulative or persistent action Resistance to becoming inactivated by organic matter Noncorrosive or non-staining properties Sanitizing and deodorizing properties Affordability and ready availibiiity

Explain the mode of action of chlorhexidine.

Targets both bacterial membranes, where selective permeability is lost, and proteins, resulting in denaturation.

Identify important structural and functional differences between RNA and DNA.

The basic unit of DNA structure is a nucleotide. Each nucleotide is composed of a phosphate, a deoxyribose, and a nitrogenous base. The nucleotides covalently bond to each other in a sugar- phosphate linkage that becomes the backbone of each strand. RNAs: single stranded in helical form. The single strand can assume secondary and tertiary levels of complexity due to bonds within the molecule, leading to specialized forms of RNA. RNA contains uracil instead of thymine as a base pair for adenine. The sugar in RNA is ribose instead of deoxyribose.

List and describe the five types of associations microbes can have with their hosts.

The concept map on page 154 may help. a) Mutualism: both members benefit b) Commensalism: one partner benefits, the other member is not harmed c) Parasitism: parasite is dependent and benefits, the host is harmed d) Synergism: members cooperate and share nutrients e) Antagonism: some members are inhibited or destroyed by others

Hypotonic

The solute concentration of the external environment is lower than that of the cell's internal environment. The net direction of osmosis is from the hypotonic solution into the cell. Cells without walls can swell and burst.

Discuss the size of viruses relative to other microorganisms. Review Figure 5.1

Viruses represent the smallest infectious agent. More than 2000 bacterial viruses could fit into a bacterial cell. An average human cell could accommodate more than 50 million polioviruses. The smallest virus is the parvovirus (around 20 nm in diameter). The largest virus is the mimivirus (around 450 nm in length). 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.

Missense

any change in the code that leads to placement of a different amino acid. They can do one of the following: create a faulty, nonfunctional protein, produce a protein that functions in a different manner, or cause no significant alteration in protein function

Death phase

as the limiting factors intensify, cells begin to die at an exponential rate an they are unable to multiply. The speed in which death occurs depends on the relative resistance of the species and how toxic the conditions are.

Aerobes

can use gaseous oxygen in their metabolism and possess the enzymes needed to process toxic oxygen products. An organism that cannot grow without oxygen is an obligate aerobe.

Persistent infections

cell harbors the virus, it is not immediately lysed, it can last from a few weeks to the remainder of the host's life, and can remain latent in the cytoplasm.

Nonsense

changes a normal codon into a stop codon that does not code for an amino acid and stops the production of the protein wherever it occurs. A nonsense mutation almost always results in a nonfunctional protein.

Sanitization

cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels.

decontamination

cleansing technique that mechanically removes microorganisms as well as other debris to reduce contamination to safe levels.

inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus or cytoplasm.

Describe and define three forms of horizontal gene transfer used in bacteria

conjugation, transformation, transduction

Parasite

derive nutrients from the cells or tissues of a living host Examples: bacteria, fungi, protozoa, animals. Range from viruses to worms (helminths) The can live on the body as ectoparasites or in the organs and tissues as endoparasites, or within cells as intracellular parasites.

Microaerophiles

do not grow at normal atmospheric concentrations of oxygen but require a small amount of it in the metabolism.

Faculative anaerobes

do not require oxygen for metabolism but use it when it is present. They can also perform anaerobic metabolism.

Aerotolerant anaerobes

don't utilize oxygen but survive and grow to a limited extent in its presence. They are not harmed by oxygen, mainly because they possess alternative mechanisms for breaking down peroxidases and superoxide.

Transforming infections

effect on the cell caused by oncogenic viruses. They have an increased growth rate, alterations in chromosomes, changes in the cell's surface molecules, and capacity to divide for an indefinite period.

disinfection

physical process or chemical agent to destroy vegetative pathogen but not bacterial endospores. Removes harmful products of microorganisms from material.

Lag phase

population appears to not be growing or is growing at less than the exponential rate.

Osmotic pressure

preserving food. Adding large amounts of salt or sugar to foods creates a hypertonic environment for bacteria in the foods, causing plamoylsis and making it impossible for bacteria to multiple. Meats are cured. High surag concentration in foods like jelly.

Sterilization

process that removes or destroys all viable microorganisms

Antisepsis

reduces the number of microbes on the human skin.

synthesis

replication and protein production: DNA viruses enter the host cell's nucleus and are replicated and assembled there. RNA viruses are replicated and assembled in the cytoplasm. Retroviruses turn their RNA genomes into DNA.

conjugation

requires the attachment of two related species and the formation of a bridge that can transport DNA

Exponential growth phase

the curve increases geometrically. This phase will continue as long as cells have adequate nutrients and the environment is favorable.

Diagram the possible configurations that nucleic acid viruses may possess. Review Table 5.3

1. double-stranded DNA 2. single-stranded DNA 3. single-stranded (+) polarity 4. single-stranded (-) polarity 5. doube-stranded RNA 6. single-stranded RNA reverse transcriptase

Summarize the steps of bacterial DNA replication, and identify the enzymes used in the process. Review Table 8.2

1. the origin of replication is a short sequence rich in adenine and thymine bases that are held together by only two hydrogen bonds rather than three. Because the origin of replication is AT-rich, less energy is required to separate the two strands than would be required if the origin were rich in guanine and cytosine 2. helicases break the hydrogen bonds holding the two strands together, resulting in two separate strands. 3. single stranded binding proteins keep the strands apart. 4. DNA polymerase is correctly orientated for synthesis only in the 5' to 3' direction of the new molecule (blue) strand, only one strand, called the leading strand, can be synthesized as a continuous, complete strand. The strand with the opposite orientation is the lagging strand. On this strand the polymerase adds nucleotides a few at a time in the direction away from the nucleotides a few at a time in the direction away from the fork. As the fork opens up a bit, the next segment is synthesized backward to the point of the previous segment, a process repeated until synthesis is complete. In this way, the DNA polymerase is able to synthesize the two strands simultaneously. This manner of synthesis produces one strand containing short fragments of DNA called okazaki fragments. These fragments are attached to the growing end of the lagging strand by another enzyme called DNA ligase. 5. in all cases, initiation of DNA synthesis requires "jump-starting" with a length of RNA manufactured by RNA primase. DNA polymerase can then add DNA nucleotides to that primer sequence. The primer sequence Is later removed through enzymatic action. The RNA primer is not seen on the leading strand as it appeared closer to the origin, which is not pictured. RNA priers are required at the beginning of each fragment of DNA synthesized on the lagging strand.

. Summarize the steps of cell division used by most bacteria. Review Figure 6.8.

1. young cell 2. chromosomes are replicated and new and old chromosomes move to different sides of the cell. 3. protein band forms in center of cell 4. septum formation begins 5. when septum is complete, cells are considered divided. Some species will separate completely, while others remain attached, forming chains and doublets.

Degermation

A form of decontamination but on living tissues.

Identify better terms for viruses than "alive" or "dead."

Active or inactive

Explain methods of moist heat control.

Boiling: relied on for decontamination and not sterilization. Exposing materials to boiling water will kill most non-endospore forming pathogens, including resistant species such as staphylococci. The greatest disadvantage is that items can easily be re-contaminated. Pasteurization: technique in which heat is applied to liquids to kill potential agents of infection and spoilage, while at the same time retaining the liquid's flavor and food value. Used for milk, fruit juices, wine, and more. These methods don't kill endospores or heat-resistant bacteria. Steam under pressure: pressure is increasing, causing the temp at which water boils and the temp of the steam to rise. An autoclave is used to raise pure steam pressures greater than one atmosphere.

Explain the importance of viral surface proteins, or spikes. Review Figure 5.4

Both naked and enveloped viruses possess proteins on their outer surfaces that project from either the nucleocapsid or the envelope. They are molecules that allow viruses to dock with their host cells. The configuration of the spike has a complementary fit for cell receptors.

chlorine

Chlorine can kill endospores and all other microbes. It is less effective if exposed to light, alkaline pH, and excess organic matter. in solution, combines with water and releases hypochlorous acid: denature enzymes permanently and suspend metabolic reactions. Chlorine kills bacteria, endospores, fungi, and viruses. Liquid or gaseous types can disinfect drinking water, sewage. Hypochlorites used in health care treat wounds, disinfect bedding, and sanitize food equipment. It is also used to clean pools and spas.

Phenolic Compounds

Concentrate w/ detergent additives and diluted w/ tap water. It Disinfects general health-care facilities

Explain what cytopathic effects are and list types. Review Figure 5.7

Cytopathic effects are virus-induced damage to the cell that alters its microscopic appearance. Individual cells can undergo a change in shape or size, or develop intracellular changes. Types: inclusion bodies and synctia

Provide an overview of the relationship among DNA, RNA, and proteins. Relate the new and old versions of the "central dogma" of biology.

DNA-> transcription-> RNA->translation->protein The classic view of the central dogma of biology states that "the coded genetic information hard-wired into DNA is transcribed into individual transportable cassettes, composed of messenger RNA (mRNA); each mRNA cassette contains the program for synthesis of a particular protein (or small number of proteins)." As a general rule, the classic view of central dogma of biology reflects how molecular biology data are organized within the databases (e.g, by molecule type such as genomic DNA, mRNA, protein). However, many exceptions to this dogma are now known as a result of genomic studies in recent years. For example, much of the DNA that does not encode proteins is now known to encode various types of functional RNAs

Compare and contrast the process of diffusion and osmosis.

Diffusion is when atoms or molecules move in a gradient from an are of higher concentration or density to an area of lower concentration or density. Osmosis is diffusion of water through a selectively permeable membrane. In an osmotic system, the membrane is selectively permeable, having passageways that allow free diffusion of water but can block other certain dissolved molecules. Water will diffuse at a faster rate from the side that has more water to the side that has last water.

Dry heat

Dry heat: refers to hot air or an open flame. Temperature ranges from 160 to several thousand degrees Celsius. Dry heat dehydrates the cell, removing the water necessary for metabolic reactions, also denaturing the proteins. Dry heat is not as versatile or as widely used, but it has several sterilization applications. Ex: incinerator

. Identify the microorganisms that are most resistant and least resistant to control measures. Figure 9.2 may help you. Order from least to most resistant:

Enveloped viruses most gram positive bacteria non-enveloped viruses fungi and fungal spores most gram negative bacteria protozoan trophozoites protozoan cysts Staphylococcus and Pseudomonas mycobacterium bacterial endospores prions

Identify applications for ethylene oxide sterilization.

Ethylene oxide is a colorless gas at room temp. it reacts with functional groups of DNA and proteins, blocking both DNA replication and enzymatic actions. It is sued to disinfect plastic materials and delicate instruments. Also used to sterilize syringes, surgical supplies, and medical devices that are prepackaged.

Define doubling time and how it relates to exponential growth.

Figure 6.9 may help you understand. Doubling time: The time required for a complete fission cycle- from parent cell to two new daughter cells. Generation increases the population by a factor of two. As long as the environment remains favorable, the doubling effect continues at a constant rate. The growth pattern is exponential and population numbers can be expressed in terms of logarithms.

Differentiate between genotype and phenotype.

Genotype: distinctive genetic makeup Phenotype: expression of genotype traits

Discuss the disadvantages of aldehyde agents.

Glutaraldehyde is somewhat unstable, especially with increased pH and temperature. Formaldehyde is extremely toxic and it irritating to skin and mucous membranes.

Explain the applications of hydrogen peroxide agents.

Hydrogen peroxide agents kill endospores and all other microbes. It is a colorless, caustic liquid that decomposes the presence of light metals or catalase into water, and oxygen gas. Pxygen forms free radicals, which are highly toxic and reactive to cells. As an antiseptic, it can be used for cleaning skin wounds, mouthwash, and bedsore care. Others can be used in low temp sterilizing cabinets for delicate instruments.

Differentiate between macronutrients and micronutrients.

Macronutrients are required in relatively large quantities and play principle roles in cell structure and metabolism. Examples are carbon, hydrogen, and oxygen. Micronutrients, or trace elements, are present in much smaller amounts and are involved in enzyme function and maintenance of protein structure. Examples include zinc, manganese, and nickel.

Identify some heavy metal control agents.

Mercury, silver

Summarize three ways in which microorganisms function in the presence of differing oxygen conditions.

Microbes can either: 1. Can use oxygen and detoxify it 2. Can neither use oxygen nor detoxify it 3. Can not use oxygen but can detoxify it

Chemotroph

Microbes that gain energy from chemical compounds

Compare the action of microbiocidal and microbiostatic agents, providing an example of each.

Microbiocidal: chemical agents that kill microorganisms. Ex: fungicide kills fungal spores Microbiostatic: materials used to control microorganisms in the body have microbiostatic effects because the compounds can be highly toxic to human cells. Ex: aspetics and drugs

Define the term mutation, and discuss one positive and one negative example of it in microorganisms.

Mutation: any change to the nucleotide sequence in the genome Positive: A small number of spontaneous mutations contribute to the success of the individual and the population by creating variant strains with alternative ways of expressing a trait. The organisms with beneficial mutations can readily adapt, survive and reproduce Negative: mutations are permanent and heritable and will be passed on to the offspring of organisms and new viruses and become a long-term part of the gene pool.

Distinguish between enveloped and naked viruses. Review Table 5.2

Naked viruses are the simplest viruses consisting of a geometric capsid around a nucleic acid strand. An enveloped virus is composed of a nucleocapsid surrounded by a flexible membrane called an envelope. The envelope usually has special receptor spikes inserted into it. When enveloped viruses are released from the host cell, they take with them a bit of its membrane in the form of an envelope.

Explain what it means when viruses are described as "filterable."

When fluids from host organisms passed through porcelain filters designed to trap bacteria, the filtrate remained infectious. This proved that a cell-free fluid containing agents smaller than bacteria could cause an infection.

lytic

a cell can contain so many viruses that it lyses (splits open), releasing mature virions. This process can speed up by viral enzymes produced late in the infection cycle that digest the cell envelope, weakening it. Upon release, virulent phages can spread to other bacterial cells and begin a new cycle of infection.

Syncytia

a result of some viruses' ability to fuse membranes causing multiple host cells to fuse into single large cells.

Anticodon

a sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA

Codon

a sequence of three nucleotides that together form a unit of genetic code in a DNA or RNA molecule.

Name six methods of physical control of microorganisms.

a) Boiling water: disinfection b) Pasteurization: disinfection of beverages c) steam under pressure: autoclaving d) incineration e) hot air oven f) radiation

Name four categories of cellular targets for physical and chemical agents. Review Table 9.3

a) Cell wall b) cytoplasmic membrane c) cellular synthesis d) proteins

List the three principal purposes of cultivating viruses.

a) Isolate and identify viruses in clinical specimens b) Prepare viruses for vaccines c) do detailed research on viral structure, multiplication cycles, genetics and effects on host cells.

List the three types of RNA directly involved in translation. Table 8.4 may help you.

a) Messenger RNA b) Transfer RNA c) Ribosomal RNA

Name two noncellular infectious agents besides viruses.

a) Spongiform encephalopathies b) viroids

Describe three ways in which viruses are cultivated.

a) Using live animal inoculation: specially bred strains of white mice, rats, hamsters are usually the choices for viral cultivation. b) Using bird embryos: provide intact and self-supporting unit, sterile environment, and contain their own nourishment. Use chicken, duck or turkey eggs. c) Using cell (tissue) culture techniques: isolated animal cells are grown in virto; in cell or tissue culture rather than in animal or egg. Cell cultures are grown in sterile chambers with special media that contain the nutrients for cells to survive. Cells form a monolayer, or single, confluent sheet of cells that supports viral multiplication. This allows for the close inspection of culture or signs of infection. Review

Explain two methods of dry heat control. Table 9.6

a) incineration: perhaps the most rigorous of all heat treatments. Direct exposure to such intense heat reduces microbes to ashes and gas. Using loops and needles on a Bunsen burner is common. This method is fast and effective, but also presents hazards to flamer and environment. b) Hot-air oven: has coils that radiate heat within an enclosed compartment. Heated, circulated air transfers its heat to the materials in the oven. Heating for 2 to 4 hours ensures destruction of endospores.

Identify three important environmental factors (other than temperature and oxygen) with which organisms must cope

a) pH b) Osmotic Pressure c) Radiation anf Hydrostatic/ atmospheric pressure

Identify three methods besides a growth curve to analyze and count bacteria.

a) turbidity b) counting c) genetic probing

Diagram the five-step life cycle of animal viruses. Review Table 5.4

absorption, penetration, synthesis, assembly, release

Silent

alters a base but does not change the amino acid and thus has no effect.

Heterotroph

an organism that must obtain carbon in an organic form

Filtrations

effective method to remove microbes form air and liquids. A fluid is strained through a filter with openings large enough for the fluid to pass through but too small for microorganims to pass through. Used to prepare liquids that cannot withstand heat, inlcuding serum and other blood products, avvines, drugs, IV fluids, enzymes, and media. Alternative method for decontaminating milk and beer without altering flavor. Water purification. Removes airborne contaminates that are a common source of infection and spoilage.

transformation

entails the transfer of naked DNA and requires no special vehicle

Icosahedral capsids

form a three dimensional 20-sided figure with 12 evenly spaced corners.

Saprobe

free- living microorganisms that feed primarily on organic detritus from dead organisms Examples: fungi, bacteria (decomposers)

Ionizing radiation

gamma rays and x rays. It is a highly effective alternative for sterilizing materials that are sensitive to heat or chemicals. ionzing radiation if the radiation ejects orbital electrons from an atom, it causes ions to form (gamma rays, x rays, high-speed electrons). Radiation ejects orbital electrons from an atom, causing ions to form. Causes the most damage to proteins. COLD sterilization is used for materials sensitive to heat or chemicals. Breaks DNA.

Extreme thermophile

grow between 80 and 121 degrees Celsius.

Psychotrophs

grow slowly in the cold but have an optimum temp between 15 and 30 degrees Celsius. Bacteria such as Staphylococcus aureus can grow in refrigerated food and cause food-borne illness.

Thermophile

grows optimally at temps greater than 45 degrees Celsius. They live in soil and water associated with volcanic activity, compost piles, and in habitats directly exposed to the sun. They vary in heat requirements with a range of growth of 45 to 80 degrees Celsius. Most eukaryotic forms cannot survive above 60 degrees Celsius.

Helical capsids

have rod shaped capsomers that bond together to form a series of hollow discs resembling a bracelet.

Iodine

iodine can kill endospores and all other microbes. It penetrates cells of microbes where it interferes with a variety of metabolic functions; interferes with the hydrogen and disulfide bonding of proteins. It can be extremely irritating to the skin and is toxic when absorbed.

Anaerobes

lack the metabolic enzyme systems for using oxygen in respiration.

Compare and contrast the four phases of growth in a bacterial growth curve.

lag phase, exponential growth phase, stationary growth phase, death phase

Phototroph

microbes that photosynthesize

Release

non-enveloped and complex viruses that reach maturation in the cell nucleus or cytoplasm are released when the cell lyses or ruptures. Enveloped cells are released by budding from the membranes of the cytoplasm, nucleus, ER or vesicles. The nucleocapsid binds to the membrane, which curves completely around it and forms a small pouch. Pinching off the pouch releases the virus with its envelope.

Frameshift

one or more bases are inserted into or deleted from a newly synthesized DNA strand. They nearly always result in a nonfunctional protein because every amino acid after the mutation is different from what it coded for in the original DNA.

psychrophile

optimum temperature is below 15 degrees Celsius. They are capable of growth at 0 degrees Celsius. They cannot grow above 20 degrees Celsius. They are rarely pathogenic. Storage in a refrigerator incubates them rather than inhibiting them. Natural habitats of psychrophilic bacterial, algae and fungi include lakes, rivers, snow fields, polar ice, and the deep ocean.

Name two types of passive transport and one type of active transport. Table 6.4 may help you.

passive transport a) simple diffusion b) facilitated diffusion active transport a) carrier-mediated active transport

Hypertonic

the environment has a higher solute concentration than the cytoplasm. Water will be forced out of the cell and have high osmotic pressure or potential. The cell will likely shrink and become distorted.

Isotonic

the environment is equal in solute concentration to the cell's internal environment, and because diffusion of water proceeds at the same rate in both directions, there is no net change in cell volume.

penetration and uncoating

the flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid. Penetration through endocytosis occurs when the entire virus is engulfed by the cell and enclosed in a vacuole or vesicle. Enzymes in the vacuole then dissolve the envelope and capsid. The virus fuses with the wall of the vesicle. Viral nucleic acid is released into the cytoplasm.

Gene

the fundamental unit of heredity responsible for a given trait in an organism. In the molecular and biochemical sense, it is a site on the chromosome that provides information for a certain cell function

Thermal death point

the lowest temperature required to kill all microbes in a sample in ten minutes

Mesophiles Thermoduric microbes

the majority of medically significant organisms. They grow at temps between 20 and 40 degrees Celsius. They inhabit animals and plants as well as soil and water in temperate, subtropical and tropical regions. can survive short exposure to high temps, but are normally mesophiles. They are common contaminants of heater or pasteurized foods. Examples include heat resistant cysts such as Giardia and sporeformers such as Bacillus and clostridium

Assembly

the new nucleic acids and capsids are put together to form new viruses. Viral spikes are inserted into the host cell's membrane so that they can be picked up as the virus buds off with its envelope.

Stationary growth phase

the population enters a period during which the rates of cell birth and death are more or less equal. At this time, the division rate is slowing down.

Thermal death time

the shortest length of time required to kill all test microbes at a certain temperature

Genome

the sum of the total genetic material of an organism Gene: the fundamental unit of heredity responsible for a given trait in an organism. In the molecular and biochemical sense, it is a site on the chromosome that provides information for a certain cell function

transduction

the transfer of DNA from one bacterium to another via a bacterial virus

Nonionizing radiation

ultraviolet rays. It is not as penetrating is ionizing radiation. UV radiatin passes only through air, slightly liquids and poorly solids, so the object must be directly exposed to it to be disinfected. Exemliefied by ultraviolet, excites atoms by raising them to a higher energy state, but it does not ionize them. Leads to the formation of abnormal bonds within molecules such as DNA and is source of mutations. Excites atoms, raising them to higher energy state. Leads to the formation of abnormal bonds (pyrimidine dimers) within molecules such as DNA (T-T or C-C)

Absorption

virus absorbs specifically to receptor sites on the cell membrane of a host cell. The membrane receptors are usually glycoproteins. Glycoprotein spikes on the envelope bind to the cell membrane receptors

lysogenic infections

virus in a lysogenic cell becomes activated and progresses into viral replication. Lyogeny is considered the least deadly form of parasitism 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. Occasionally phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human. The lysogenic conversion is when a bacterium requires a new trait from its template phage.

Analyze the relative importance of viruses in human infection and disease. Scan Table 5.6

viruses are extremely common causes for acute infections such as colds, hepatitis, chicken pox, influenza, herpes, and warts. Some viruses have high mortality rates, such as Ebola and AIDS. Others can lead to long term debility such as polio.