Cell biology

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Cell biology

• Class-2

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Prokaryotic cell

• prokaryotes include the kingdoms of simple
  bacteria.
• Simply stated, prokaryotes are molecules
  surrounded by a membrane and cell wall

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• Prokaryotic cells lack membrane enclosed
  "organelles.
• Prokaryotic cells may have photosynthetic
  pigments
• Example - cyanobacteria ("blue bacteria").

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• Prokaryotic cells have external
• -Whip-like flagella for locomotion.
• -Hair like pili for adhesion.

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• Prokaryotic cells come in multiple shapes
• cocci (round),
• baccilli (rods), and
• spirilla or spirochetes (helical cells).

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Internal Structure

• Bacteria have a very simple internal structure,
  and no membrane-bound organelles.
• Nucleoid
• Ribosome's
• Storage granules
• Endospore

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Nucleoid

• DNA in the bacterial cell is generally confined
  to this central region.
• it isn't bounded by a membrane.
• it is visibly distinct from the rest of the
  cell interior.

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Ribosomes

• Ribosomes give the cytoplasm of bacteria a
  granular appearance.
• Though smaller than the ribosomes in eukaryotic
  cells.
• these inclusions have a similar function
  production of proteins.

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storage granules

• Nutrients and reserves may be stored in the
  cytoplasm in the form of glycogen, lipids etc.,

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Endospore

• Some bacteria form spores
• that are highly resistant to drought, high
  temperature and other environmental hazards.
• Once the hazard is removed, the spore germinates
  to create a new population.

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Surface Structure

• Beginning from the outermost structure and moving
  inward, bacteria have some or all of the
  following structures
• capsule
• outer membrane
• cell wall
• plasma membrane

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Capsule

• This layer (polysaccharide ) protects the
  bacterial cell .
• It serves as a barrier against phagocytosis by
  white blood cells (WBC).

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cell wall

• the cell wall maintains the overall shape of a
  bacterial cell.
• The three primary shapes in bacteria are coccus
  (spherical), bacillus (rod-shaped) and spirillum
  (spiral).
• Imp
• Mycoplasma are bacteria that have no cell wall
  and therefore have no definite shape.

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plasma membrane

• This is a lipid bilayer much like the cytoplasmic
  (plasma) membrane of other cells.
• primarily responsible for transport of ions,
  nutrients and waste across the membrane.

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Appendages

• - Pili
• Flagella

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Pili

• These are hollow, hairlike structures made of
  protein allow bacteria to attach to other cells.
• A specialized pilus, the sex pilus, allows the
  transfer from one bacterial cell to another.
• Pili (sing., pilus) are also called fimbriae
  (sing., fimbria).

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Flagella

• The purpose of flagella (sing., flagellum) is
  motility.
• Bacteria may have one, a few, or many flagella in
  different positions on the cell.

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Summary-1

• prokaryotes include kingdoms of simple bacteria.
• molecules surrounded by a membrane and cell wall
• 3. lack membrane enclosed "organelles.

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Summary-2

• Internal structures
• -Nucleoid
• Ribosome's
• Storage granules
• Endospore

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Summary-3