Chapter 27: Bacteria and Archaea Flashcards
What is the typical size range for most prokaryotic cells?
Prokaryotic cells typically have diameters of 0.5–5 µm.
What is the typical size range for most eukaryotic cells?
Eukaryotic cells typically have diameters of 10- to 100-µm.
What are the most common shapes of prokaryotes?
Cocci (singular, coccus) are spherical prokaryotes. They can occur singly, in chains of two or more cells, and in clusters resembling bunches of grapes. Bacilli (singular, bacillus) are rod-shaped prokaryotes. They are usually solitary, but in some forms the rods are arranged in chains. Spiral prokaryotes include spirochetes, which are corkscrew-shaped. Other spiral prokaryotes resemble commas or loose coils.
What is peptidoglycan? What cells contain peptidoglycan cell walls?
In contrast, most bacterial cell walls contain peptidoglycan, a polymer composed of modified sugars cross-linked by short polypeptides. This molecular fabric encloses the entire bacterium and anchors other molecules that extend from its surface. Archaeal cell walls contain a variety of polysaccharides and proteins but lack peptidoglycan.
What is Gram-stain?
Using a technique called the Gram-stain, developed by the 19th-century Danish physician Hans Christian Gram, scientists can categorize many bacterial species according to differences in cell wall composition.
What is gram-positive?
Gram-positive bacteria have relatively simple walls composed of a thick layer of peptidoglycan.
What is gram-negative?
The walls of gram-negative bacteria have less peptidoglycan and are structurally more complex, with an outer membrane that contains lipopolysaccharides (carbohydrates bonded to lipids).
What is a capsule?
In many prokaryotes, a dense and well-defined layer of polysaccharide or protein that surrounds the cell wall and is sticky, protecting the cell and enabling it to adhere to substrates or other cells.
What are the various functions of a bacterial capsule?
Both kinds of sticky outer layers enable prokaryotes to adhere to their substrate or to other individuals in a colony. Capsules and slime layersalso protect against dehydration, and some capsules shield pathogenic prokaryotes from attacks by their host’s immunesystem. In another way of withstanding harsh conditions, certain bacteria develop resistant cells called endospores when they lack water or essential nutrients (Figure 27.5). The original cell produces a copy of its chromosome and surrounds that copy with a multilayered structure, forming the endospore. Water is removed from the endospore, and its metabolism halts. The original cell then lyses, releasing the endospore.
What is the function of fimbriae?
Finally, some prokaryotes stick to their substrate or to one another by means of hair-like appendages called fimbriae (singular, fimbria) (Figure 27.6). For example, the bacterium that causes gonorrhea, Neisseria gonorrhoeae, uses fimbriae to fasten itself to the mucous membranes of its host.
What is chemotaxis?
About half of all prokaryotes are capable of taxis, a directed movement toward or away from a stimulus (from the Greek taxis, to arrange). For example, prokaryotes that exhibit chemotaxis change their movement pattern in response to chemicals. They may move toward nutrients or oxygen (positive chemotaxis) or away from a toxic substance (negative chemotaxis).
What do prokaryotic cells use to move?
Of the various structures that enable prokaryotes to move, the most common are flagella (Figure 27.7). Flagella (singular, flagellum) may be scattered over the entire surface of the cell or concentrated at one or both ends.
Prokaryotes do not have chloroplasts and mitochondria. What structures do they utilize for processes such as aerobic respiration and photosynthesis?
Prokaryotic cells lack the complex compartmentalization associated with the membrane-enclosed organelles found in eukaryotic cells. However, some prokaryotic cells do have specialized membranes that perform metabolic functions (Figure 27.8). These membranes are usually infoldings of the plasma membrane. Infoldings of the plasma membrane, reminiscent of the cristae of mitochondria, function in cellular respiration in some aerobic prokaryotes. Photosynthetic prokaryotes called cyanobacteria have thylakoid membranes, much like those in chloroplasts.
Compare the differences in shape, volume of DNA, and location of the genome of eukaryotic and prokaryotic cells.
What is a plasmid?
A small, circular, double-stranded DNA molecule that carries accessory genes separate from those of a bacterial chromosome; in DNA cloning, plasmids are used as vectors carrying up to about 10,000 base pairs (10 kb) of DNA. Plasmids are also found in some eukaryotes, such as yeasts.
