Chapter 4 - Prokaryotic Cell Structure & Function I Flashcards
The prokaryotic cell is ______ and structurally ____________.
Small
Structurally simple
You must be familiar with all of the structures listed in the following image.
Identify the labeled parts of the basic prokaryotic cell.
A. Pilus
B. Ribosome
BB. Storage granule
C. Flagellum
E. Cytoplasm
F. Cell membrane
G. Murein layer
GG. Outer membrane
T. Nucleoid
Prokaryotic organisms are in many ways the dominant life on earth. In terms of total protoplasmic volume, they make up about ___%.
90%
Why are prokaryotic organisms so successful from an evolutionary perspective?
They have very simple cell structures
What is the typical volume of a prokaryotic cell?
1 µm3
Structural simplicity does not mean ____________ simplicity.
Molecular simplicity
There is a range of sizes for prokaryotic cells. What are the ranges?
0.25 µm to 120 µm in diameter
Most prokaryotes are unicellular. True or false?
True
What are the three common cell shapes of prokaryotes?
- Cylindrical rods (bacillus)
- Spheres (cocci)
- Helical (spirilla)
Some prokaryotes are multicellular and are commonly _________________, made of a chain of identical cells attached end to end. Some are __________, meaning they are branching tubes of cytoplasm contained within walls.
Filamentous
Mycelial
Multicellular prokaryotes generally lack cell differentation. If they do, they usually are ____________, which merely have a different function, or in the case of cyanobacteria, _______________, which fix nitrogen and have a different metabolism.
Spores
Heterocysts
True of false: almost all prokaryotic cells have a cell envelope.
True
True or false: cell envelope structure and chemistry are the same among different groups of prokaryotes.
False - cell envelope strucutre and chemistry can differ among different groups of prokaryotes
True or false: the cell envelope is composed of a single layer.
False. The cell envelope can be a single homogeneous layer or a complex, multilayered structure.
What is the difference between a cell envelope and a cell wall?
The cell envelope comprizes the cell membrane, the cell wall and an outer membrane if present
How do prokaryotic cells protect themselves against osmotic lysis?
Via a cell envelope
Why do prokaryotic cells require protection against osmotic lysis?
Most of them live in environments in which solute concentration is less than their highly concentrated cytoplasm
Why strategy do prokaryotic cells use to protect against osmotic lysis?
The strategy is to contain the cell’s turgor pressure with a layer external to the cell membrane that resists expansion of the cell volume
Who developed the Gram stain process?
Hans Christian Gram in 1884
What is the Gram stain useful for?
Distinguishing some prokaryotic envelopes from each other
Outline the general steps of the Gram stain process.
- Stain with crystal violet (purple)
- Add iodine
- Add decolorizer, either ethanol or acetone
- Stain with safranin (pink)
Gram-positive cells stain _______________.
Purple
Gram-negative cells stain ___________.
Pink
What is the conventional theory regarding the mechanism of the Gram-stain process?
- Crystal violet and mordant freely crossed the outer membrane (OM), the peptidoglycan mesh (PM), and cell membrane (CM), binding to anions within the periplasm and cytosol
- Alcohol dissolves lipid membranes, attacking the structural integrity of the OM and CM. Because the PM of Gram-negative cells is covalently bound to the OM, it is significantly disrupted with the OM is torn away. Thus the crystal violet precipitate is washed away.
- In Gram-positive cells, there is no OM and only a thick PM coating the CM. Thus, the PM remains largely undisturbed when subjected to the decolorization process, retaining the crystal violet stain.
What does recent research suggest about the mechanism of the Gram-stain process?
Recent research,suggests that crystal violet slowly diffuses across the peptidoglycan mesh and does not penetrate the cell membrane; that crystal violet becomes “stuck” within the peptidoglycan layer; and that the crystal violet and mordant precipitate forms within the peptidoglycan layer
What method did researchers use to show that crystal violet does not, in fact, cross the cell membrane?
Second harmonic light scattering
What is second harmonic light scattering?
It is a type of nonlinear optical spectroscopy. A nonlinear vibrational spectroscopy in which two colors of light, one in the visible and one in the infrared, are mixed at an interface to create the sum frequency. The generated sum frequency light carries structural information about the molecules and chemical functionalities present at the interface.
What are the seven steps in the gram staining process?
- Crystal violet
- Iodine
- 95% ethanol
- Safranin
- Blot semi-dry, air dry, and/or heat fix
- Coverslip
- Oil
After each step in the gram staining process, what do you do?
Rinse with distilled water
How long do you saturate the sample with crystal violet?
60 seconds
How long do you saturate the specimen with iodine?
60 seconds
How long do you saturate with 95% ethanol?
Until the specimen becomes clear or 15 seconds
How long do you saturate the specimen with safranin?
30 seconds
What are three ways that a gram stain can go wrong?
- Excessive heat during fixation
- Low concentration of crystal violet
- Excessive washing between steps
Why should you avoid excessive heating during the gram staining process?
Heat fixing the cells, when done to excess, alters the cell morphology and makes the cells more easily decolorized
Why do low concentrations of crystal violet disrupt the gram stain process?
Concentrations of crystal violet up to 2% can be used successfully; however, low concentrations result in stained cells that are easily decolorized
Why does excessive washing disrupt the gram stain process?
The crystal violet stain is susceptible to wash out with water (but not the crystal violet- iodine complex.
How long should you rinse with water during each rinse in the gram stain process?
No longer than 5 seconds
What three results can occur from a gram stain?
- Gram positive - stain purple
- Gram negative - stain pink
- Gram variable - PITB (pilus backbone protein)
What seven microbe species can stain pink even though they are gram positive?
- Actinomyces
- Arthrobacter
- Corynebacterium
- Propionibacterium
- Bacillius
- Butyrivibrio
- Clostridium
Why do Actinomyces, Arthrobacter, Corynebacterium, and Propionibacterium stain pink even though they are gram positive?
Because they are part of a genera with cell walls that break during division
Why do Bacillus, Butyrivibrio, and Clostridium stain pink even though they are gram positive?
Because growing and elongating cells decrease their cell wall thickness
How old are most cultures that undergo gram staining?
Less than 24 hours
What bacterium is diplococci?
Neisseria gonorrhoeae
What does “diplococci” mean?
Refers to a bacterium that occurs as a pair of cocci
There are different types of cell envelopes among bacteria. Which is the most common?
The gram-negative envelope
Most bacteria have a _____ _____________ that consists of a thin rigid layer (the cell wall), overlain with a membrane, termed the outer membrane.
Cell envelope
In gram-______________ bacteria, the cell wall is between one to three layers thick.
Gram negative
What makes up the cell wall in bacteria?
Peptidoglycan
In what type of bacteria is the cell wall between 10 and 20 layers thick?
Gram-positive
One group of bacteria, the _______________________, has an envelope that appears to be a combination of gram-negative and -positive structures: a thick murein layer, overlain with an outer membrane; yet they stain gram positive.
Deinococci
The ________________________ group of bacteria has an envelope that consists of a layer of protein. These bacteria generally stain gram-negative because the thin layer of protein is unable to prevent the gram stain from rinsing out.
Planctomyces
Although planctomyces stain Gram negative - due to the thin layer of protein that surrounds their cell membrane - recent studies have suggested what about the structure of their cell envelopes?
Evidence of a cell wall with peptidoglycan
How many types of archael cell walls are there?
Three
What is the most common type of archael cell wall?
A layer of protein
Which archaea have a rigid wall made of a murein-like compound termed pseudomurein?
The methanogens
Some archae have walls that consist of what types of polysaccharides? Simple or complex?
Complex polysaccharides
True or false?
No archaea have been shown to contain true murein
True
What are the three types of archaeal cell envelope?
- A layer of protein
- Rigid wall of pseudomurein
- Wall of complex polysaccharide