3 Questions
What is an essential and definitive characteristic of a cell?
Plasma membrane
What type of bacteria has a thick cell wall?
Gram-positive
What type of molecules are found in the cell wall of Gram-negative bacteria?
Peptidoglycan
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.
Test your knowledge on the basic concepts of cell biology and microbiology including cell structure, prokaryotic and eukaryotic cell characteristics, bacterial cell morphology, and classification based on gram staining. Explore the fundamental principles of living organisms at the cellular level.
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