18.1 Section Objectives – page 475

• Identify the different kinds of viruses and their structures.

Section Objectives: 18.1

• Compare and contrast the replication cycles of viruses.

• You’ve probably had the flu—influenza—at some time during your life.

• Viruses are composed of _____ ______ enclosed in a ______ coat and are smaller than the smallest bacterium.

• Nonliving particles called _______ cause influenza.

• Most biologists consider viruses to be _______ because they don’t exhibit all the ______ for life.

• They don’t carry out respiration, grow, or develop. All viruses can do is _______—make copies of themselves—and they can’t even do that without the help of living cells.

• A cell in which a virus replicates is called the _____cell.

• Viruses, such as _____ viruses and _____ viruses, were named after the diseases they cause.

• Other viruses were named for the _____ or ______ they infect.

• Today, most viruses are given a ______ name ending in the word “virus” and a ______ name.

• However, sometimes scientists use ____ numbers to distinguish among similar viruses that infect the same ____.• A virus that infects a bacterium is called a __________ (bak TIHR ee uh fayj), or phage for short.

• A virus has an inner core of nucleic acid, either ___ or ___, and an outer protein coat called a ____.

Capsid

Nucleic acid

Envelope

• Some relatively large viruses, such as human ___ viruses, may have an additional layer, called an _______, surrounding their capsids.

Capsid

Nucleic acid

Envelope

• Envelopes are composed primarily of the same materials found in the ______ membranes of all cells.

Capsid

Nucleic acid

Envelope

• ___ nucleic acid is either DNA or RNA and contains instructions for making copies of the virus.

• Some viruses have only four _____, while others have hundreds.

Nucleic acid

Capsid

• The _____ _____ virus has a long, narrow _______ shape.

Nucleic acid

Capsid

• The arrangement of _____ in the capsid of a virus determines the virus’s _____.

Nucleic acidCapsid

• ________ viruses resemble small crystals.

• The protein arrangement also plays a role in determining what cell can be _______ and how the virus infects the cell.

Nucleic acidCapsid

• Before a virus can replicate, it must ____ a host cell.

• A virus recognizes and ______ to a host cell when one of its ______ interlocks with a molecular shape that is the ______ site on the host cell’s plasma membrane.

• A protein in the ___ fibers of the bacteriophage __ recognizes and attaches the T4 to its bacterial host cell.

Capsid

Nucleic acid

Tail

Tail fiber

• In other viruses, the attachment protein is in the ____ or in the envelope.

Capsid

Nucleic acid

Tail

Tail fiber

• Each virus has a ________ shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells.

• In general, viruses are species specific, and some also are ____-type specific. For example, polio viruses normally infect only intestinal and nerve cells.

• The species specific characteristic of viruses is significant for controlling the spread of _____ diseases.

• Once attached to the plasma membrane of the host cell, the virus _____ the cell and takes over its ________.

• Only then can the virus ________.

• Viruses have ____ways of getting into host cells.

• The virus may _____its nucleic acid into the host cell like a syringe injects a vaccine into your arm.

• The _____ of the virus stays attached to the outside of the host cell.

• An ________ virus enters a host cell in a different way.

• After attachment, the plasma membrane of the host cell surrounds the virus and produces a virus-filled vacuole inside the host cell’s cytoplasm.

• Then, the virus bursts out of the vacuole and releases its nucleic acid into the cell.

• Once inside the host cell, a virus’s genes are _________ and the substances that are produced take over the host cell’s genetic material.

• The ____ genes alter the host cell to make new viruses.

Nucleic acid

Bacterial host cell

Bacteriophage Bacterial DNA

B. Entry

The bacteriophage injects its nucleic acid into the bacterial cell.

A. Attachment

C. ReplicationD. Assembly

E. Lysis and Release

The host’s metabolic machinery makes viral nucleic acid and proteins.

New virus particles are assembled.

The host cell breaks open and releases new virus particles.

• The host cell uses its own _______, raw materials, and energy to make copies of viral genes that along with viral proteins are assembled into new viruses, which _____ from the host cell, killing it.

• The new viruses can then infect and kill other host cells. This process is called a ____ (LIH tik) _____.

• Not all viruses ____ the cells they infect.

• Some viruses go through a ________ cycle, a replication cycle in which the virus’s nucleic acid is ________ into the host cell’s chromosome.

• A ________ cycle begins in the same way as a lytic cycle.

• However, in a lysogenic cycle, instead of _________ taking over the host’s genetic material, the viral DNA is integrated into the host cell’s chromosome.

• Many disease-causing ______ have lysogenic cycles.

• Three examples of these viruses are ____ _____ I, herpes simplex II that causes ______ herpes, and the _______ B virus that causes hepatitis B.

• Another lysogenic virus is the one that causes _____ ___.

• Having chicken pox, which usually occurs before age ten, gives lifelong protection from another infection by the ___. However, some chicken pox viruses may remain as _________ in some of your body’s nerve cells.

• Later in your life, these proviruses may enter a lytic cycle and cause a disease called _______—a painful infection of some nerve cells.

• Either lysis, the bursting of a cell, or ______, the active transport process by which materials are expelled from a cell, release new viruses from the host cell.

• In exocytosis, a newly produced virus approaches the inner surface of the host cell’s _______ membrane.

• The plasma membrane surrounds the virus, enclosing it in a _____ that then fuses with the host cell’s plasma membrane.

• Then, the ______are released to the outside.

• Many viruses, such as the _____ _______________ ____(HIV) that causes the disease AIDS, are RNA viruses—RNA being their only nucleic acid.

HIV virus

• Once inside a human host, HIV infects _____ blood cells.

• Newly made viruses are released into the blood stream by ________ and infect other white blood cells.

Normal white blood cells

• Infected host cells still function normally because the viral genetic material is a ______ that produces only a small number of new viruses at a time.

• Because the infected cells are still able to function normally, an infected person may not appear _____, but they can still ____ the virus in their body fluids.

• Most people with an HIV infection eventually get ____ because, over time, more white blood cells are infected and produce new viruses.

• Because white blood cells are part of a body’s ______-fighting system, their destruction interferes with the body’s ability to protect itself from organisms that cause disease, a symptom of AIDS.

• Some viruses have been linked to certain ______ in humans and animals.

• These viruses disrupt the normal growth and division of cells in a host, causing abnormal growth and creating _______.

• Researchers have recently discovered some particles that behave somewhat like viruses and cause infectious diseases.

• Prions are composed of proteins but have no nucleic acid to carry genetic information.

• Prions are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning.

• Prions are responsible for many animal diseases, such as mad cow disease and its human equivalent, Creutzfeldt-Jakob disease.

• Viroids are composed of a single circular strand of RNA with no protein coat.

• Viroids have been shown to cause infectious diseases in several plants.

• The amount of viroid RNA is much less than the amount found in viruses.

• The first virus to be identified was a plant virus, called tobacco mosaic virus, that causes disease in tobacco plants.

Tobacco mosaic virus causes yellow spots on tobacco leaves, making them unmarketable.

• Viruses cause as many as 1000 plant diseases and are named according to their host plant.

• Viruses can cause stunted growth and yield losses in their host plants.

• Plant viruses require wounds or insect bites to enter and infect a host, and do not use surface recognition.

• They do not undergo lytic or lysogenic phases.

• Not all viral plant diseases are fatal or even harmful.

• Some mosaic viruses cause striking patterns of color in the flowers of plants.

Rembrandt tulips

• For replication, viruses need host cells; therefore, scientists suggest that viruses might have originated from their host cells.

• Some scientists suggest that viruses are nucleic acids that break free from their host cells while maintaining an ability to replicate parasitically within the host cells.

Section Objectives 18.2

• Explain the characteristics and adaptations of bacteria.

• Compare the types of prokaryotes.

• Evaluate the economic importance of bacteria.

• Recall that prokaryotes are _________organisms that do not have a nucleus or membrane-bound organelles.

• They are classified in two kingdoms—_________ and ________.

• Many _________ differences exist between these two types of prokaryotes.

• Because they are so different, many scientists propose that archaebacteria and eubacteria arose from a _______ ancestor several billion years ago.

• There are ____ types of archaebacteria that live mainly in extreme habitats where there is usually no free ______ available.• One type of archaebacterium lives in

oxygen-free environments and produces ______ gas.

• These methane-producing archaebacteria live in marshes, lake sediments, and the digestive tracts of some ________, such as cows.

• They also are found at sewage disposal plants, where they play a role in the ______ of sewage.

• A second type of archaebacterium lives only in water with ____ concentrations of salt.

Dead Sea

• A third type lives in the hot, acidic waters of ______ springs.

• This type of anaerobic archaebacterium also thrives near cracks deep in the ocean floor, where it is the _______ producer for a

unique animal community’s food chain.

• ________, the other kingdom of prokaryotes, includes those prokaryotes that live in places more hospitable than archaebacteria inhabit and that vary in nutritional needs.

• The ____________ eubacteria live almost everywhere and use organic molecules as their food source.

• Some bacterial heterotrophs are ______, obtaining their nutrients from living organisms.

• Others are _______—organisms that feed on dead organisms or organic wastes.

• A second type of eubacterium is the ___________ autotroph.

• These eubacteria live in places with ________ because they need light to make the organic molecules that are their food.

• ___________ are photosynthetic autotrophs.

• Most cyanobacteria are _______ and some are red or yellow in color.

Cyanobacteria

• Cyanobacteria commonly live in ponds, streams, and moist areas of land.

• They are composed of chains of independent cells.

Cyanobacteria

• A third type of eubacterium is the _________ autotroph.

• Unlike the photosynthetic bacteria, the chemosynthetic bacteria do not obtain the energy they need to make food from _______.

• Instead, they break down and release the energy of inorganic compounds containing

sulfur and nitrogen in the process called ____________.

• A _________ consists of a very small cell.

• Although tiny, a bacterial cell has all the ________ necessary to carry out its life functions.

• Prokaryotic cells have ribosomes, but their ribosomes are smaller than those of eukaryotes.

• They also have genes that are located for the most part in a single circular chromosome, rather than in paired chromosomes.

Ribosome

Cytoplasm

Chromosome

Gelatinlikecapsule

Cell Wall

Cell Membrane

Flagellum

• A typical bacterium, such as _____________would have some or all of the structures shown in this diagram of a bacterial cell.

Capsule Cell Wall

Chromosome

Flagellum

PlasmidPilus

Plasma membrane

• A bacterial cell remains intact as long as its cell ____ is intact.

• If the cell wall is damaged, ____ will enter the cell by osmosis, causing the

cell to burst.

• Scientists used a bacterium’s need for an intact cell wall to develop a weapon against bacteria that cause ________.

• In 1928, Sir Alexander Fleming accidentally discovered _______, the first antibiotic—a substance that destroys bacteria—used in humans.

• Later, biologists discovered that penicillin can _______ with the ability of some

bacteria to make cell walls.

• When such bacteria grow in penicillin, holes develop in their cell walls, water enters their cells, and they rupture and die.

• One trait that helps categorize bacteria is how they react to _____ stain.

• Gram staining is a technique that distinguishes ___ groups of bacteria because the stain reflects a basic difference in the composition of bacterial cell walls.

• After staining, Gram-_______ bacteria are _____ and Gram-_______ bacteria are _____.

Gram-positive bacteria Gram-negative bacteria

• Gram-positive bacteria are affected by different antibiotics than those that affect Gram-negative bacteria.

Gram-positive bacteria Gram-negative bacteria

• Bacterial cell walls also give bacteria different _____.

• The three most common shapes are spheres, called _____; rods, called _____; and spirals, called ________.

• In addition to having one of these shapes, bacterial cells often grow in characteristic _______ that provide another way of categorizing them.

• _____–is a prefix that refers to a paired arrangement of cell growth.

• The prefix _______–describes an arrangement of cells that resemble grapes.

• _______–is a prefix that refers to an arrangement of chains of cells.

• Bacteria reproduce ______ by a process known as ______ _______.

• To reproduce in this way, a bacterium first copies its chromosome. Then the original chromosome and the copy become attached to the cell’s plasma membrane for a while.

• The cell grows ____, and eventually the two chromosomes separate and move to opposite ends of the cell.

• Then, a _______ forms between the chromosomes. This partition separates the cell into ___ similar cells.

• Because each new cell has either the original or the copy of the chromosome, the resulting cells are genetically identical.

• Under ideal conditions, some bacteria can reproduce every ___ minutes, producing enormous numbers of bacteria quickly.

• But bacteria don’t always have ideal growing conditions. They run out of nutrients and water, they poison themselves with their own ______, and predators eat them.

• In addition to binary fission, some bacteria have a form of sexual reproduction

called ______________.

• During conjugation (kahn juh GAY shun), one bacterium ______ all or part of its chromosome to another cell through or on a bridge-like structure called a ____ that connects the two cells.

• Conjugation results in a bacterium with a ___ genetic composition.

• This bacterium can then undergo binary fission, producing more cells with the same genetic makeup.

• Based on fossil evidence, some scientists propose that ______ bacteria were probably among the first photosynthetic organisms, producing not only their own food but also

oxygen.

• As the concentration of oxygen increased in Earth’s atmosphere, some bacteria probably _______ over time to use oxygen

for respiration.

• Modern bacteria have diverse types of ______________.

• Many bacteria require ________ for respiration. These bacteria are called ______ _________.

• There are other bacteria, called obligate _________, that are killed by oxygen.

• There are still other bacteria that can live either with or without oxygen, releasing the energy in food _________ by cellular respiration or anaerobically by _______.

• Some bacteria, when faced with unfavorable environmental conditions, produce _______.

• An _________ is a tiny structure that contains a bacterium’s ___ and a small amount of its ________, encased by a tough outer covering that resists drying out, temperature extremes, and harsh chemicals.

• When environmental conditions improve, the endospore ________, or produces a cell that begins to grow and reproduce.

• As an ________, the bacterium rests and does not _________.

• __________ can survive a temperature of 100˚C, which is the boiling point of water.

• To kill endospores, items must be ________—heated under high pressure in either a pressure cooker or an _______.

• This is because the endospores of the bacterium called ________ ________ easily get into foods being canned.

• Canned food must be sterilized and _______.

• Bacteria grow in the ________ environment of the can and produce a powerful deadly poison, called a _____, as they grow.

• If the endospores of C. botulinum get into improperly sterilized canned food, they germinate.

• This deadly toxin saturates the food and, if eaten, causes the disease called

_______.

• B. anthracis causes ______, a disease that commonly infects cattle and sheep, but can also infect humans.

• A different bacterium, Bacillus _______, lives in the soil.

• Most human anthrax infections are fairly harmless and occur on the ___ as a result of handling animals.

• This infection is more serious than a skin infection and often _______.

• The bacterial _________ can become airborne, however, and if inhaled in large amounts, can germinate in a person’s lungs, causing an infection.

• Bacteria help to _______ fields, to recycle nutrients on Earth, and to produce foods and ________.

• Disease-causing bacteria are few compared with the number of harmless and beneficial bacteria on Earth.

• Yet few organisms, including most plants, can directly use _______ from the air.

• All organisms need ________ because the element is a component of their proteins, ____, ____, and ___.

• Other bacteria then convert the ammonia into nitrite ____and nitrate ______which plants can use.

• Several species of bacteria have enzymes that convert __into ammonia (___) in a process known as _______ _______.

• _______ are the only organisms that can perform these chemical changes.

• Farmers grow legume crops after the harvesting of crops such as _____, which depletes the soil of nitrogen.

• Some nitrogen-fixing bacteria live ________ within

the roots of some trees and ______.

• This food is passed from one _________ to the next in food chains and webs.

• ________ bacteria and also plants and algae, which are at the bottom of the food chains, use the nutrients in the food they make.

• In the process of making food, many autotrophs replenish the supply of ______ in the atmosphere.

• Some foods that you eat—mellow Swiss cheese, crispy pickles, tangy yogurt—would not _____ without bacteria.

• Specific bacteria are used to make different foods, such as ______, cheeses, and ________.

• Bacteria also inhabit your _______ and produce _______ and _______ that help digest food.

• ________, ________, bacitracin, and neomycin are some of these antibiotics.

• In addition to food, some bacteria produce important ________ that destroy other types of bacteria.

• Bacteria also cause many human diseases.

• Bacteria cause diseases in plants and animals, causing crops and livestock losses that impact humans indirectly.

• Disease-causing bacteria can enter human bodies through openings, such as the mouth.

• The growth of the bacteria can interfere with the normal function of body _)___, or

it can release a _____ that directly attacks the host.

• Bacterial diseases harm people in two ways.

Diseases Caused by BacteriaDisease Transmission Symptoms Treatment

Strep throat

(Streptococcus)

Inhale or ingest throughmouth

Fever, sore throat,swollen neck glands

Antibiotic

Tuberculosis Inhale Fatigue, fever, nightsweats, cough, weight loss, chest pain

Antibiotic

Tetanus Puncturewound

Stiff jaw, musclespasms, paralysis

Open and clean wound,antibiotic; give antitoxin

Lyme disease Bite ofinfected tick

Rash at site of bite,chills, body aches,joint swelling

Antibiotic

Dentalcavities (caries)

Bacteriain mouth

Destruction of toothenamel, toothache

Remove and fill thedestroyed area of tooth

Diptheria Inhale orclose contact

Sore throat, fever,heart or breathingfailure

Vaccination to prevent, antibiotics

• In the last 100 years, human life expectancy has increased to about __ years.

• In the past, bacterial illnesses had a greater effect on human populations than they do now.

• This increase is due to many factors, including better public health systems, improved ____ and sewage treatment, better ________, and better medical

care.• These improvements, along with

_________, have reduced the death rates from bacterial diseases to low levels.