Viruses and Monerans

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Viruses and Monerans

• Chapter 18

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What is a Virus?

• Viruses are composed of nucleic acids enclosed in
  a protein coat and are smaller than the smallest
  bacteria.
• Viruses are non living particles.
• Most viruses do not fit the criteria for being
  alive. Because they do not
• Carry our respiration
• Grow
• Move
• Reproduce unless in host

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Structure and Shape of Viruses

• Host Cell - The cell in which they reproduce.
• Because viruses are non living, they are not
  given Latin names.
• Most viruses are named for the cells they affect.
• Bacteriophage is a virus that infects bacteria.

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Structure of Viruses

• Inner core of nucleic acid and an outer protein
  coat called a capsid.
• Larger viruses such as human flu viruses may have
  an additional layer called an envelope.
• The nucleic acid core of a virus contains the
  viruses genetic material.
• Some viruses have DNA, others RNA, but never
  both.
• The arrangement of proteins plays a role in
  determining the viral shape and structure.

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Attachment to a host cell.

• Before a virus can replicate, it must enter a
  host cell.
• Before it can enter, it must recognize and attach
  to a receptor site on the plasma membrane of the
  host cell.
• Attachment is a specific process because each
  virus has a specifically shaped attachment
  protein.

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Recognition of Host Cell

• Recall the Bi Lipid Layer and its surface
  proteins.
• Viruses capsule also contains 3-D portions that
  only bond with specific surface Proteins.
• Attachment is a specific Process dictated by the
  amino acids that make up the shape.

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Chicken Pox- caused by lysogenic virus
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Herpes Simplex 1
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Smallpox
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Smallpox
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Smallpox
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Warts---caused by virus
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Wart
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Warts
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STD wart
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Genital Warts
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Staph is a bacterial infection
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Staph
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STD
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MRSA
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Small Pox
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Various Shapes of Viruses

• Polyhedral
• Cylindrical
• Enveloped with studded projections
• Head and tail configurations

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Polyhedral
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Cylindrical
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Enveloped with studded projections
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Head and tail configurations
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Viral Reproductive Cycle

• Once attached to the plasma membrane a virus must
  reproduce.
• The way it enters the cell is dependant on the
  virus shape.
• Once inside the cell the virus destroys the
  hosts DNA and reprograms the cell metabolic
  activity to copy the viral genes.

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Lytic Cycle

• Lytic
• Lyein (Greek) to break down
• The host cell is always broken down during this
  cycle.
• Page 479 fig 18.3

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The Lytic Cycle
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Lysogenic Cycle

• Not all virus infections are fatal to their
  hosts.
• Non Fatal viruses go through a cycle called the
  Lysogenic Cycle.
• Also referred to as a provirus formation.
• Does not interfere with the normal functioning of
  the host cell, which is capable still of carrying
  out its normal metabolic activity.

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Proviruses explain symptoms of disease

• Example Cold Sores
• The virus Herpes Simplex 1 remains in the host
  cell as a provirus
• When the virus pops out and enters a Lytic cycle,
  you get another cold sore.
• No one knows the exact conditions that cause the
  provirus to pop out.

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Retroviruses

• RNA viruses with the most complex reproductive
  cycles.
• When they inject their nucleic acid into the host
  cell, they also inject a molecule of the enzyme
  reverse transcriptase.
• Reverse transcriptase then copies viral RNA into
  the DNA.

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HIV Infection of White Blood Cells

• Once inside a human host HIV infects white blood
  cells.
• An HIV infected person can experience no AIDS
  symptoms for a really long time.
• Most people infected from HIV eventually develop
  AIDS.
• Because white blood cells are a vital part of the
  human disease fighting system, the persons
  immunity weakens, and eventually they succumb to
  a opportunistic infection or cancer.
• HIV Human Immunodeficiency Virus
• AIDS Acquired Immunodeficiency Syndrome.

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Cancer and Viruses

• Some viruses have been linked to certain cancers
  in humans and animals.
• The hepatitis B virus has been shown to play a
  role in causing liver cancer.
• These viruses disrupt the normal growth and
  division of cells in a host, causing abnormal
  growth.

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Origin of Viruses

• Just because they are simple doesnt mean they
  are from primitive forms of life.
• Remember viruses need hosts, therefore they have
  evolved after the hosts.
• Science suggests that viruses may have developed
  from the host DNA.

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Prions and Viroids

• Researchers have recently discovered some
  particles that behave like viruses and cause
  infection and disease.
• Prions are composed of proteins but have no
  nucleic acid to carry genetic info.
• Prions are responsible for many animal diseases
  such as mad cow disease.
• Viroids are composed of a single circular strand
  of RNA with no protein coat.

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Monerans (bacteria)

• Classified into two groups
• Archaebacteria
• Usually found where no free oxygen is available.
• The earliest forms of Monerans
• Found in extreme habitats
• Fig 18.8 page 485 shows some examples of habitats
• Eubacteria
• Three types
• Heterotrophs need to consume organic molecules
  to live.
• Autotrophs make their own food from
  photosynthesis.
• Chemoautotrophs use chemicals to make their
  energy.
• Wide array of habitats and metabolism
• Need organic molecules for energy, thus some live
  as parasites others as saprobes (feed on dead
  organisms)

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Eubacteria Photosynthetic Autotrophs

• Obtain their energy from sunlight
• Cyanobacteria are in this group. (blue green
  algae)
• Cyanobacteria are not unicellular.

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Eubacteria Chemosynthetic Autotrophs

• Obtain energy from chemosynthetic breakdown of
  inorganic molecules.
• Some of these are important in the conversion of
  nitrogen in the atmosphere to forms that can be
  used by plants. (Nitrogen Cycle)

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Oops that changed our world

• 1928 Sir Alexander Fleming accidentally
  discovered penicillin.
• He was growing bacteria when an airborne mold
  contaminated his culture plates.
• He noticed that the mold secreted a substance
  that is now known as penicillin.
• The penicillin killed the bacteria and prevented
  it from growing.
• This discovery is one of the major contributions
  to human life spans being almost 80 years now.

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Structure of Monerans

• Smallest and simplest of living things
• Prokaryotes that lack membrane bound organelles
• Ribosomes are smaller than eukaryotes
• Bacteria are commonly classified based on the
  shape of their cells.

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Identifying Bacteria

• Scientist have developed ways to distinguish
  among bacteria.
• One way is to classify them based on how they
  react to gram staining.
• Gram staining is a technique that distinguishes
  two kinds of bacteria, because the color reflects
  a difference in the cell walls of the bacteria.
• Gram positive bacteria are purple after staining,
  while gram negative are pink.
• Gram positive bacteria are affected by different
  antibiotics than gram negative bacteria.
• The shape of the bacteria also distinguishes its
  type.

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Three Most Common Shapes

• Spheres cocci
• Streptococcus, Coccus Sphere
• Rods
• Bacillus
• Spirals
• Spirillium

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Streptococcus pneumoniae
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Streptococcus pyogenes
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Bacillus Rods
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Bacillus
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Spirillium
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Classification by arrangement

• Diplo refers to an arrangement in which cells
  are paired.
• Staphylo is an arrangement that is
  characterized by grapelike clusters.
• Strepto Characterized by long chains.

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Diplo
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Staphylo
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Strepto
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What are these?
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Reproduction

• Bacteria reproduce by a process called binary
  fission.
• The bacteria first copies its single chromosome,
  then the original and copy attach to the plasma
  membrane on opposite sides.
• As the bacteria grows, eventually it splits into
  two bacteria.
• Binary fission can be a very rapid process
  depending on the bacteria and conditions it lives
  in.
• Under ideal conditions some bacteria can
  reproduce every 20 minutes.

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Sexual Reproduction

• Sexual reproduction of bacteria is called
  conjugation.
• One bacterium transfers all or part of its
  chromosome to another cell through a bridge like
  structure called a pillus, that connects the two
  cells.
• The cell that receives the genetic info can then
  undergo binary fission to produce a new bacteria
  type.

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Obligate aerobes

• Many bacteria require oxygen for respiration.
• These bacteria are called obligate aerobes.
• Obligate anaerobes are those that are killed by
  oxygen.
• The bacteria Treponema pallidum, is an obligate
  anaerobe, which is responsible for the sexually
  transmitted disease called syphilis.

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Survival Mechanisms

• Some bacteria, when faced with unfavorable
  environments produce endospores.
• Endospores are tiny structures that contain a
  bacterias DNA and a small amount of its
  cytoplasm, encased by a tough outer covering that
  resists drying out, temp extremes, and harsh
  chemicals.
• Endospores are like seeds that allow a bacteria
  to germinate when conditions become favorable.
• The only way to kill endospores is by
  sterilization.

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Importance of Bacteria

• Nitrogen fixation is a process that converts
  atmospheric nitrogen, to ammonia, nitrate, or
  nitrite which make nitrogen useful to other
  organisms.
• Recycling of nutrients that is discarded as waste
  by organisms.
• Food and medicines the action of bacteria can
  affect the way that food tastes as well as looks
  (holes in Swiss cheese), as well as the medicinal
  benefits of antibiotics.
• Our digestive systems would not function without
  a base bacteria called the normal digestive flora.

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Bacteria and disease

• In the past bacterial infections had a great
  effect on human populations than they do now.
• In 1900, the life expectancy in the US was 47
  years, and now is 75 years and this is the result
  of the discovery of antibiotics.
• Bacteria become resistant quickly to antibiotics
  because of their fast life cycles, so it is
  important to follow instructions carefully when
  taking antibiotics to ensure that you to not
  inadvertently create a super strain of a
  bacteria.

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Terminology

• an epidemic (from Greek epi- upon demos people)
  is a disease that appears as new cases in a given
  human population, during a given period, at a
  rate that substantially exceeds what is
  "expected", based on recent experience (the
  number of new cases in the population during a
  specified period of time is called the "incidence
  rate").
• A pandemic (from Greek pan all demos people) is
  an epidemic (an outbreak of an infectious
  disease) that spreads worldwide, or at least
  across a large region.

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Antibiotic resistance

• Antibiotic-resistant "superbugs" may also revive
  diseases previously regarded as "conquered."
• Cases of tuberculosis resistant to all
  traditionally effective treatments have emerged
  to the great concern of health professionals.
• Such common bacteria as Staphylococcus aureus,
  Serratia marcescens and species of Enterococcus
  that have developed resistance to the strongest
  available antibiotics such as vancomycin emerged
  in the past 20 years as an important cause of
  hospital-acquired nosocomial infections (acquired
  in a hospital), and are now colonizing and
  causing disease in the general population.

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HIV
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Food Poisoning

• Staphylococcus aureus

• Staphylococcus aureus

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Salmonella
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E. Coli
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Ebola
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Influenza
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Cholera

• Cholera (also called Asiatic cholera) is a
  water-borne disease caused by the bacterium
  Vibrio cholerae, which is typically ingested by
  drinking contaminated water, or by eating
  improperly cooked fish, especially shellfish.

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The End