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Unit 2: Lesson 3- The Prokaryotic Cell- External Structures

Terms in this set (91)

-consists of lipopolysaccharides (LPS), lipoproteins, and phospholipids
-Functions of outer membrane:
-its strong negative charge is an important factor in evading phagocytosis and the actions of complement (lyses cells and promotes phagocytosis), two components of the defenses of the host
-provides a barrier to certain antibiotics (for example, penicillin), digestive enzymes such as lysozyme, detergents, heavy metals, bile salts, and certain dyes.
-does not provide a barrier to all substances- still allows nutrients to pass through to sustain metabolism of the cell
-permeability partly is due to proteins in the membrane called porins that form channels
-porins-permit passage of molecules such as nucleotides, disaccharides, peptides, amino acids, vitamin B12, and iron.
-The lipopolysaccharide (LPS) of the outer membrane is a large complex molecule that contains lipids and carbohydrates and consists of three components: (1) lipid A, (2) a core polysaccharide, and (3) an O polysaccharide.
- Lipid A is the lipid portion of the LPS and is embedded in the top layer of the outer membrane.
-When gram-negative bacteria die, they release lipid A, which functions as an endotoxin
-responsible for the symptoms associated with infections by gram-negative bacteria such as fever, dilation of blood vessels, shock, and blood clotting.
- core polysaccharide is attached to lipid A and contains unusual sugars.
-Its role is structural—to provide stability.
-O polysaccharide extends outward from the core polysaccharide and is composed of sugar molecules.
-functions as an antigen and is useful for distinguishing species of gram-negative bacteria.
- role is comparable to that of teichoic acids in gram-positive cells.

-Lipopolysaccharide is known to make a pivotal contribution to the signs and symptoms of disease resulting from infection by gram-negative bacteria. Because of its structure (the association of a core polysaccharide, known as O polysaccharide and a lipid component, called lipid A), lipopolysaccharide is known to be highly toxic when introduced into the blood circulation of animals and humans. The reaction to the introduction of this substance is known as endotoxic shock.
-Chief distinguishing characteristics of Prokaryotes:
1. Their DNA is NOT ENCLOSED WITHIN A MEMBRANE and is usually a SINGULAR circularly arranged chromosome. (Some bacteria, such as Vibrio cholerae, have two chromosomes, and some bacteria have a linearly arranged chromosome.)
2. Their DNA is NOT associated with histones (special chromosomal proteins found in eukaryotes); other proteins are associated with the DNA.
3. They LACK membrane-enclosed organelles.
4. Their cell walls almost always contain the complex polysaccharide peptidoglycan.
5. They usually divide by BINARY FISSION. During this process, the DNA is copied, and the cell splits into two cells. Binary fission involves fewer structures and processes than eukaryotic cell division.

• -Chief distinguishing characteristics of Eukaryotes:
1. Their DNA is found in the cell's NUCLEUS, which is separated from the cytoplasm by a nuclear membrane, and the DNA is found in MULTIPLE chromosomes.
• 2. Their DNA is consistently associated with chromosomal proteins called HISTONES and with NONHISTONES.
• 3. They have a number of MEMBRANE-ENCLOSED ORGANELLES, including mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, and sometimes chloroplasts.
• 4. Their cell walls, when present, are chemically SIMPLE.
• 5. Cell division usually involves MITOSIS, in which chromosomes replicate and an identical set is distributed into each of two nuclei. This process is guided by the mitotic spindle, a football-shaped assembly of microtubules. Division of the cytoplasm and other organelles follows so that the two cells produced are identical to each other.