Cell Biology and Microbiology Basics

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Questions and Answers

What is an essential and definitive characteristic of a cell?

  • Cell wall
  • Cell envelope
  • Plasma membrane (correct)
  • Cell protoplasm

What type of bacteria has a thick cell wall?

  • Gram-positive (correct)
  • Gram-negative
  • Coccus
  • Spirillum

What type of molecules are found in the cell wall of Gram-negative bacteria?

  • Lipoprotein
  • Peptidoglycan (correct)
  • Sterols
  • Capsule

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Study Notes

  • All living things are made of one or more cells.
  • Cells are the basic unit of structure and function in living things.
  • All cells come from other cells.
  • Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles.
  • Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus (that holds genetic material) as well as membrane-bound organelles.
  • Genetic material in eukaryotes is contained within a nucleus within the cell and DNA is organized into chromosomes.
  • Eukaryotic organisms may be multicellular or single- celled organisms.
  • Eukaryotic cell membrane contains sterols, whereas no prokaryotes except the wall of Mycoplasma, has sterol in its membrane.
  • All animals are eukaryotes. Other eukaryotes include plants, fungi.
  • Structure of bacterial cell: - The most elemental structural property of bacteria is cell morphology (shape). Typical examples include: coccus (spherical) , bacillus (rod-like) , spirillum (spiral) .
  • Cell shape is generally characteristic of a given bacterial species, but can vary depending on growth conditions.
  • Structurally, a bacterial cell has three architectural regions: appendages (attachments to the cell surface) in the form of flagella and pili (or fimbriae); a cell envelope consisting of a capsule, cell wall and plasma membrane; and a cytoplasmic region that contains the cell chromosome (DNA) and ribosomes and various sorts of inclusions.
  • Cell envelope:
  • The cell envelope is a descriptive term for the several layers of material that envelope or enclose the protoplasm of the cell. The cell protoplasm (cytoplasm) is surrounded by the plasma membrane, a cell wall and a capsule. The cell wall itself is a layered structure in Gram-negative bacteria. All cells have a plasma membrane, which is the essential and definitive characteristic of a "cell". Almost all prokaryotes have a cell wall to prevent damage to the underlying protoplast. Outside the cell wall, foremost as a surface structure, may be a polysaccharide capsule or glycocalyx.
  • Most prokaryotes have a rigid cell wall.
  • Bacteria are classified according to the response to the gram staining procedure as either Gram-positive or Gram-negative.
  • The cell wall of Gram-positive bacteria is thick (15-80 nanometers) and consists of several layers of peptidoglycan.
  • The cell wall of Gram-negative bacteria is relatively thin (10 nanometers) and is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane.
  • LPS, which is toxic to animals, is found in Gram-negative bacteria.
  • Lipoprotein, and phospholipid are also found in Gram-negative bacteria.

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