Chapter 27: Bacteria and Archea Flashcards

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1
Q

Prokaryotic shapes

A

Cocci- spherical shaped

Bacilli- rod-shaped

Spiral- corkscrew-shaped or can resemble commas or loose coils

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2
Q

Prokaryotic cell walls

A

Bacterial cell walls are composed of peptidoglycan- a polymer composed of modified sugars cross-linked by short polypeptides

  • Consist of interlocking chains of identical peptidoglycan monomers N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with a pentapeptide coming off of the NAM
  • Pentapeptide amino acids show some slight variation among the bacteria
  • Peptidoglycan monomers are synthesized in the cytosol of the bacterium where they attach to a membrane carrier molecule called bactoprenol that escorts them across the cytoplasmic membrane
  • Enzymes insert the monomers into existing peptidoglycan network, enabling bacterial growth following binary fission.
  • Found in all bacteria except Mycoplasma

Archaeal cell walls contain a variety of polysaccharides and proteins but lack peptidoglycan

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3
Q

Gram stain

A

Used to classify bacteria by cell wall composition

Gram-positive bacteria have simpler walls with a larger amount of peptidoglycan

  • Teichoic acids are found within the cell wall of gram positive bacteria

Gram-negative bacteria are structurally more complex and have less peptidoglycan with an outer membrane composed of lipopolysaccharides

  • Lipopolysaccharides of some gram-negative bacteria can be toxic
  • Gram-negative bacteria are more likely to be antibiotic resistant
  • Outer membrane helps protect it from the body’s defences

Antibiotics target peptidoglycan and damage bacterial cell walls

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4
Q

Capsule

A

A mucopolysaccharide coating around cell surface

  • Termed a capsule if well-defined or a slime layer if not well organized
  • Encapsulated bacteria are usually “mucoid”

Enable prokaryotes to adhere to their substrate or other individuals in colony

Virulence factor that blocks phagocytosis

Blocks antigenic sites on the bacterial cell wall from immune responses

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5
Q

Endospores

A

Allows bacterial cell to survive in harsh conditions such as a lack of water or essential nutrients

Cell forms a spore by replicating its DNA and sequestering it within a mulltilayered structure that forms the endospore

Aids in organism classification based on the position, size, and shape of the spore.

Metabolically inactive endospores, can remain viable in harsh conditions for centuries

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6
Q

Fimbriae

A

Short and numerous hairlike appendages that allow some prokaryotes to stick to their substrate or other cells

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7
Q

Pili

A

Appendages that pull two cells together prior to DNA transfer

Sometimes referred to as sex pili

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8
Q

Prokaryotic motility

A

In a heterogeneous environment many bacteria exhibit taxis- the ability to move toward or away from a stimulus

  • Chemotaxis thange their movement pattern in response to chemicals

Most motile bacteria propel themselves by flagella scattered about the surface or concentrated at one or both ends

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9
Q

Prokaryotic flagellum

A
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10
Q

Plasmids

A

Smaller rings of DNA seperate from primary DNA

Facilitate genetic transfer between organisms

Contain genes for antibiotic resistance

Can increase a strain’s pathogenicity

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11
Q

Prokaryotic genetic diversity

A

Three factors contribute to prokaryotic genetic diversity:

  1. Rapid reproduction- short generation times allows prokaryotes to evolve quickly
  2. Mutation- low frequency but because of rapid reproduction mutations can accumulate quickly in a population
  3. Genetic recombination- the combination of DNA from two sources
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12
Q

Bacterial growth curve

A

Reproducible growth pattern that results when microorganisms are grown in a closed culture in which no nutrients are added and most waste is not removed

Composed of four phases:

  1. Lag phase- period after cells are first added to culture medium during which cells are gearing up for the next phase of growth
  2. Log phase- cells are actively dividing by binary fision and their numbers increase exponentially
  3. Stationary phase- waste accumulation and depletion of resources contribute to a slowing growth rate that eventually plateaus; rate of cell division is equal to death rate resulting in stagnant growth
  4. Death phase- cell death exceeds rate of division due to further accumulation of waste and nutrient depletion; some cells can persist and form endospores
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13
Q

Genetic recombination

A

The combination of DNA from two sources that contributes to genetic diversity

Occurs via three mechanisms:

  1. Transformation
  2. Transduction
  3. Conjugation

Movement of genes among individuals from different species is called horizontal gene transfer

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14
Q

Transformation

A

The uptake and incorporation of foreign DNA from the surrounding environment by a cell

Many bacteria have cell-surface proteins that recognize DNA from closely related species and transport them into the cell

Once inside the cell the foreign DNA can be incorporated into the genome by homolgous DNA exchange

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15
Q

Transduction

A

The movement of genes between bacteria by bacteriophages

Usually occurs as an error during the phage replicative cycle when it incorporates a piece of the bacterial chromosome into its capsid

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16
Q

Conjugation

A

Pocess in which genetic material is transferred between two prokaryotic cells that are temporarily joined

A donor cell attaches to a recipient via a pilus, pulls it closer, and transfers DNA

A piece of DNA called an F factor (fertiilty factor) is required for the production of pili; may exists as a plasmid or be incorporated in the chromosome

  • Cells containing the F plasmid function as DNA donors during conjugation
  • Cells with the F factor built into its chromosome are called Hfr cells (High Frequency of Recombination)

R plasmids carry genes for antibiotic resistance

17
Q

Major nutritional modes

A
18
Q

Prokaryotic oxygen demands

A

Obligate aerobes- require oxygen for cellular respiration

Obligate anaerobes- are poisoned by oxygen and rather use fermentation or anaerobic respiration in which sources other than oxygen serve as the final electron acceptors such as nitrate (NO3 ) or sulfate (SO4 2−) ions

Facultative anaerobes- can survive with or without oxygen

19
Q

Nitrogen metabolism

A

Nitrogen is essential for the production of amino acids and nucleic acids

Nitrogen fixation is the process by which some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)

Individual cells cannot carry out both photosynthesis and nitrogen fixation

Specialized cells called heterocysts perform nitrogen fixation and exchange metabolic products with neighboring cells that perform photosynthesis

20
Q

Biofilms

A

Surface-coating colonies of one or more species that cooperate metabolically

Cells produce polysaccharides and proteins that attach the cells to the substrate and to one another and form the capsule or slime layer

Channels in the biofilm allow nutrients to reach cells in the interior and wastes to be expelled

21
Q

Culture

A

Method that allows the multiplication of bacterial cells in or on a culture medium under controlled laboratory conditions

22
Q

Streak

A

Method by which bacteria are spread out for better visualization

23
Q

Endotoxins

A

Lipopolysaccharide components of the outer membrance of gram-negative bacteria

Are only released when the bacteria die and their cell walls break down

24
Q

Exotoxins

A

Proteins secreted by certain bacteria and other organisms that are poisonous and can cause illness

25
Q

Archea

A

Many archea live and thrive in extreme environments

Halophiles- live in highly saline environments

Thermophiles- thrive in very hot environments

Methanogens- populate more moderate environments and release methane as a byproduct of the they obtain energy

26
Q

Bacterial kingdoms

A
  1. Proteobacteria
  2. Chlamydias
  3. Spirochetes
  4. Cyanobacteria
  5. Gram-positive
    bacteria