The Structure within Cytoplasm

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The Structure within Cytoplasm
Prokaryotic structure cell

1. Cytoplasm
2. The Nucleoid
3. Plasmid
4. Ribosomes
5. Endospore

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• A typical bacterium usually consists of
• a cytoplasmic membrane surrounded by a
  peptidoglycan cell wall and maybe an outer
  membrane
• a fluid cytoplasm containing a nuclear region
  (nucleoid) and numerous ribosomes and
• often various external structures such as a
  glycocalyx, flagella, and pili. 

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Cytoplasm

• In bacteria, the cytoplasm refers to everything
  enclosed by the cytoplasmic membrane. About 80
  of the cytoplasm of bacteria is composed of
  water.
• Within the cytoplasm can be found nucleic acids
  (DNA and RNA), enzymes and amino acids,
  carbohydrates, lipids, inorganic ions, and many
  low molecular weight compounds.
• The liquid component of the cytoplasm is called
  the cytosol.

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The Nucleiod

• The bacterial genome is composed of chromosomal
  deoxyribonucleic acid or DNA and represents the
  bacterium's nucleoid.
• the bacterial nucleoid has no nuclear membrane or
  nucleoli
• the bacterial nucleoid does not divide by mitosis
•  In general it is thought that during DNA
  replication, each strand of the replicating
  bacterial DNA attaches to proteins at what will
  become the cell division plane.

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• The nucleoid is one long, single molecule of
  double stranded, helical, supercoiled DNA 
•  The chromosome is generally around 1000 µm long
  and frequently contains as many as 3500 genes 
• E. coli, a bacterium that is 2-3 µm in length,
  has a chromosome approximately 1400 µm long.

Electron Micrograph of Nucleiod DNA
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• Function of nucleiod?
• The nucleoid is the genetic material of the
  bacterium. Genes located along the DNA are
  transcribed into RNA that, in the case of mRNA,
  is then translated into protein at the ribosomes.
  
• In other words, DNA determines what proteins and
  enzymes an organism can synthesize and,
  therefore, what chemical reactions it is able to
  carry out.

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Plasmid

• Plasmid- Small molecules of autonomously
  replicating, circular, extrachromosomal DNA found
  in many bacteria.
• F They are transferable genetic elements that
  can be transferred from one organism to another
• - through a process called conjugation, the
  conjugation pilus enables the bacterium to
  transfer a copy of the R-plasmids(g-ve) to other
  bacteria, making them also multiple antibiotic
  resistant and able to produce a conjugation pilus.

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Ribosome

• Ribosomes are composed of ribosomal RNA (rRNA)
  and protein.
• Composed of two subunits with densities of 50S
  and 30S. ("S" refers to a unit of density called
  the Svedberg unit.) 
• The two subunits combine during protein synthesis
  to form a complete 70S ribosome about 25nm in
  diameter.
• A typical bacterium may have as many as 15,000
  ribosomes.

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• Ribosomes function as a workbench for protein
  synthesis, that is, they receive and translate
  genetic instructions for the formation of
  specific proteins. During protein synthesis, mRNA
  attaches to the 30s subunit and amino
  acid-carrying transfer RNAs (tRNA) attach to the
  50s subunit (see Fig. 1). Protein synthesis is
  discussed in detail in Microbial Genes Chapter.

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Endospore

• Endospores are dormant alternate life
  forms produced by the genus Bacillus, the
  genus Clostridium, and several other genera of
  bacteria including Desulfotomaculum,
  Sporosarcina, Sporolactobacillus,
  Oscillospira, and Thermoactinomyces.
• Bacillus species are obligate aerobes that live
  in soil while Clostridium species are obligate
  anaerobes often found as normal flora of the
  gastrointestinal tract in animals.

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• Under conditions of starvation, especially the
  lack of carbon and nitrogen sources, a single
  endospores form within some of the bacteria. The
  process is called sporulation.
• The completed endospore consists of multiple
  layers of resistant coats (including
  a cortex, a spore coat, and sometimes
  an exosporium) surrounding a nucleoid, some
  ribosomes, RNA molecules, and enzymes.
• Endospores are quite resistant to high
  temperatures (including boiling), most
  disinfectants, low energy radiation, drying, etc.
  
• The endospore can survive possibly thousands of
  years until a variety of environmental stimuli
  trigger germination, allowing outgrowth of a
  single vegetative bacterium 

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Organelles Used in Bacterial PhotosynthesisOrgan
elles Used in Bacterial Photosynthesis

• There are three major groups of photosynthetic
  bacteria cyanobacteria, purple bacteria, and
  green bacteria.
• The cyanobacteria carry out oxygenic
  photosynthesis, that is, they use water as an
  electron donor and generate oxygen during
  photosynthesis.The photosynthetic system is
  located in an extensive thylakoid membrane system
  that is lined with particles called
  phycobilisomes.
• Photograph of the cyanobacteria Anabaena.
• Photograph of the cyanobacteria Oscillatoria.

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Photograph of the cyanobacteria Oscillatoria.
Photograph of the cyanobacteria Anabaena.
Cyanobacteria, as well as algae and green plants,
use hydrogen atoms from water to reduce carbon
dioxide to form carbohydrates, and during this
process oxygen gas is given off (an oxygenic
process). Cyanobacteria were the first organisms
on earth to carry out oxygenic photosynthesis.
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• The green bacteria carry out anoxygenic
  photosynthesis. They use reduced molecules such
  as H2, H2S, S, and organic molecules as an
  electron source and generate NADH and NADPH. The
  photosynthetic system is located in ellipoidal
  vesicles called chlorosomes that are independent
  of the cytoplasmic membrane.
• The purple bacteria carry out anoxygenic
  photosynthesis. They use reduced molecules such
  as H2, H2S, S, and organic molecules as an
  electron source and generate NADH and NADPH. The
  photosynthetic system is located in spherical or
  lamellar membrane systems that are continuous
  with the cytoplasmic membrane.

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Structure Outside The Cell Wall

1. Glycocalyx
2. Flagella
3. Pili

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a) TheGlycocalyx (Capsules and Slime Layers 

• All bacteria secrete some sort of glycocalyx (an
  outer viscous covering of fibers extending from
  the bacterium).
• The possession of a glycocalyx on bacteria is
  associated with the ability of the bacteria to
  establish an infection.
• Can assume several forms.
• If in a condensed form that is relatively tightly
  associated with the underlying cell wall, the
  glycocalyx is referred to as a capsule.
• A more loosely attached glycocalyx that can be
  removed from the cell more easily is referred to
  as a slime layer.

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Capsule stain of Streptococcus lactis
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2 important functions of Glycocalyx

• The glycocalyx enables certain bacteria to resist
  phagocytic engulfment by white blood cells in the
  body or protozoans in soil and water.
• The glycocalyx also enables some bacteria
  to adhere to environmental surfaces (rocks, root
  hairs, teeth, etc.), colonize, and resist
  flushing.

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2) Flagella

• Outside cell wall
• Made of chains of flagellin
• Attached to the protein hook
• Anchored to the wall and membrane by the basal
  body

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• The filament of the bacterial flagellum is
  connected to a hook which, in turn, is attached
  to a rod.
• The basal body of the flagellum consists of a rod
  and a series of rings that anchor the flagellum
  to the cell wall and the cytoplasmic membrane.
• In gram-negative bacteria, the L ring anchors the
  flagellum to the lipopolysaccharide layer of the
  outer membrane
• while the P ring anchors the flagellum to the
  peptidoglycan portion of the cell wall.
• The MS ring is located in the cytoplasmic
  membrane and the C ring in the cytoplasm. The Mot
  proteins surround the MS and C rings of the motor
  and function to generate torque for rotation of
  the flagellum.

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Arrangement of Bacterial Flagella

• 1. monotrichous a single flagellum, usually at
  one pole
• 2. amphitrichous a single flagellum at both ends
  of the organism
• 3. lophotrichous two or more flagella at one or
  both poles
• 4. peritrichous flagella over the entire surface

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• Flagella are the organelles of locomotion for
  most of the bacteria that are capable of
  motility.
• The bacterial flagellum can rotate both
  counterclockwise and clockwise. A protein switch
  in the molecular motor of the basal body controls
  rotation. 
• Clockwise rotation results in a tumbling motion
  and changes the direction of bacterial movement.
  On the other hand, counterclockwise rotation
  leads to long, straight or curved runs without a
  change in direction

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3) Fimbriae and Pili

• Fimbriae allow attachment
• They are found in virtually all gram-negative
  bacteria but not in many gram-positive bacteria.
• There are two basic types of pili
• 1) short attachment pili, also known as fimbriae,
  that are usually quite numerous and (fig.a).
• 2) long conjugation pili, also called "F" or sex
  pili  that are very few in number (fig.b).

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a)
b)
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Function of pili

• The short attachment pili or fimbriae are
  organelles of adhesion allowing bacteria
  to colonize environmental surfaces or cells and
  resist flushing. . Because both the bacteria and
  the host cells have a negative charge, pili may
  enable the bacteria to bind to host cells without
  initially having to get close enough to be pushed
  away by electrostatic repulsion. Once attached to
  the host cell, the pili can depolymerize and
  enable adhesions in the bacterial cell wall to
  make more intimate contact.