Chapter 27: Bacteria and Archaea(1) Flashcards
How do prokaryotes live in extremely salty habitats?
Their ability to tolerate such high salt levels is due to the compensatory activity of K+
pumps, which help balance the ionic concentration inside the cell so that the cells don’t lose water through osmosis
What are the extreme habitats prokaryotes live in?
Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms
How can prokaryotes be divided?
Bacteria and Archaea.
What is a key feature of nearly all prokaryotic cells and what is its function?
A key feature of nearly all prokaryotic cells is the cell wall:-
- which maintains cell shape
- protects the cell
- prevents it from bursting in a hypotonic environment
Why can we preserve food by keeping it in salt ?
In a hypertonic environment, most prokaryotes lose water and shrink away from their wall (plasmolyze). Such water
losses can inhibit cell reproduction.
Thus, salt can be used to preserve foods because it causes prokaryotes to lose water, preventing them from rapidly multiplying.
What is a bacterial and archaeal cell wall made up of?
Most bacterial cell walls contain peptidoglycan, a polymer composed of modified sugars cross-linked by short polypeptides.
Archaeal cell walls contain a variety of polysaccharides and proteins but lack peptidoglycan.
What is the technique used to classify bacterial groups?
Gram stain can be used to classify bacteria by cell wall composition
What are the common shapes of prokaryotic cells?
- Cocci (singular, coccus) are spherical prokaryote
- Bacilli (singular, bacillus) are rod-shaped prokaryotes
- Spiral prokaryotes include spirilla, which range from comma-like shapes to loose coils.
Differentiate between gram-positive and negative bacteria.
- Gram-positive bacteria have simpler walls with a large amount of peptidoglycan
– Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic
Why is gram-negative bacteria more resistant to antibiotics?
Gram-negative bacteria also tend to be more resistant than gram-positive species to antibiotics because the outer membrane impedes entry of the drugs.
How do antibiotics destroy pathogens without harming human cells? a
The effectiveness of certain antibiotics, such as penicillin, derives from their inhibition of peptidoglycan cross-linking.
The resulting cell wall may not be functional, particularly in gram-positive bacteria. Such drugs destroy many species of pathogenic bacteria without adversely affecting human cells, which do not have peptidoglycan
What is a capsule?
The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharides or proteins.
This layer is called a capsule if it is a dense and well-defined slime layer.
What is the function of the sticky layer surrounding the cell wall of bacteria i.e capsule?
- Both kinds of sticky outer layers enable prokaryotes to adhere to their substrate or other individuals in a colony.
- Some capsules and slime layers
protect against dehydration and some shield pathogenic prokaryotes from attacks by their host’s immune system.
What is fimbriae and pilli?
Some prokaryotes stick to their substrate or one another using hairlike appendages called fimbriae.
Fimbriae are usually shorter and more numerous than pili appendages that
pull two cells together before DNA transfers from one cell to the other pili are sometimes referred to as sex pili.
What are endospores?
Many prokaryotes form metabolically inactive endospores, which can remain viable in harsh conditions for centuries.
The cell creates an endospore by enclosing a copy of its chromosome in a multilayered structure. The metabolism halts and water is removed from the endospore.
