Lecture Exam 2 Flashcards
Prokaryotic Cell
Simple structure
No organelles, No nucleus
DNA is in cell wall
Peptidoglycan in cell wall
Diameter Size <1-5m
Reproduce process: Binary fission
Eukaryotic Cell
Complex structure
Many organelles
DNA inside nucleus
No Peptidoglycan
Diameter size 10-100m
Reproduce process: Mitosis
The cell wall of a bacterial cell is
Complex and semirigid
The 3 major groups of bacteria:
Gram-positive bacteria, Gram-negative bacteria, and Mycoplasmas
How do the 3 major groups of bacteria differ?
The structure of their cell walls
Gram-negative bacteria has the most complex wall structure
The cell wall of gram-negative bacteria is composed of
An OUTER MEMBRANE component and a THIN layer of peptidoglycan molecule.
The outer membrane is a bilayer composed of an outer layer and an inner layer.
Outer layer consists of: LPS, phospholipids, and membrane protein molecules
Inner layer consists of: phospholipid and membrane protein molecules
Each phospholipid molecule has a
Hydrophilic HEAD and 2 hydrophobic tails
The liquid portion of the LPS molecule
Lipid A
Endotoxin
LPS
Bacterial toxin
Endotoxin
Connects the outer membrane to the layer of peptidoglycan molecules
Lipoprotein molecule
The cell wall of gram positive consists of
A THICK layer of peptidoglycan molecules
NO outer membrane component
Mycoplasmas
DO NOT contain a cell wall
Mycoplasmas shapes:
are irregular or undefined due to lack of cell wall
Bacteria Mycoplasmas pneumoniae causes
Atypical pneumonia (pneumonia without its typical clinical symptoms
Why are mycoplasmas considered the third group of bacteria?
Because the lack of cell wall
Why do mycoplasmas stain PINK at the end of Gram-staining even though they are Gram-Positive?
The lack of cell wall makes it difficult for them to retain the purple crystal violet dye. The CV-I complex can be easily washed out of the cell after alcohol wash during the Gram Staining.
What are the functions of a bacterial cell wall?
Protection, Cell shape, Turgor pressure
What are the major cell shapes of bacteria?
Coccus, bacillus, and spiral shape (vibrio, spirillum, or spirochete)
What is turgor pressure?
aka osmotic pressure (water pressure inside a cell)
Cytoplasmic membrane (Plasma membrane)
The membrane that encloses the cytoplasm (the interior of the cell).
What is the function of the cytoplasmic membrane?
To regulate what comes in and out of the cell
Selective permeability
Specific and selective
What is the structure of cytoplasmic membrane?
A bilayer of phospholipid molecules with membrane proteins in between.
A fluid-filled space found between the outer membrane component and the cytoplasmic membrane.
Periplasm
Periplasm is ONLY found in
Gram-negative bacteria
What are the bacteria appendages?
Fimbriae, pili and flagella
Sit on the ends of the cell or are evenly distributed
Shorter, straighter and thinner than flagella
Fimbriae
Longer than fimbriae
Pili
Protein molecules that make up Fimbriae and Pili
Pilins
Joining two bacterial cells
Sex pili
Functions of Fimbriae and pili
For attachment purpose
Functions of Flagella
For locomotive purposes
Single flagellum at one end
Monotrichous
One or more flagella at both ends of cell
Amphitrichous
Many flagella at one end of cell
Lophotrichous
Flagella all over the surface of a cell
Peritrichous
A slippery mucoid substance that forms the outermost layer
Glycocalyx
Organized and firmly attached
Capsule
Unorganized and loosely attached
Slime layer
Function of a capsule
Protection of drying out and protection from phagocytosis
Forms inside the cell when environmental conditions are not favorable for growth
Endospore
Can be released to outside once formed
Endospore
Belonging to bacterial special genus Clostridium and genus Bacillus
Endospore
Do not form endospores
Vegetative cells
Formed by the process of sporulation
Endospore
The differences between endospores and spores tbc
Endospores are dormant, resting, and non-growing structures formed by certain bacterial species when environmental conditions are not favorable for growth. When conditions become favorable the endospores will germinate to form actively growing vegetative cells. Endospores are infectious and cause disease.
Staining
Coloring
Why do we need to stain microorganisms?
Because most microbes are colorless, and we use brightfield microscope in out lab to observe microbes. A stain must be used in order to create a light dark contrast between the background and the microbial specimen.
What are stains?
Stains are dye-molecules that bind to microbial cells or microbial cellular structures.
Stains are chemical salts
composed of a positively charged ion and a negatively charged ion. One of the two is responsible for the actual color in the dye.
Chromophore
The colored portion of a stain.
Could be negative or positive.
When color is in the positive ions
basic dye
when color is in the negative ions
acidic dye
Bacterial cells are
negatively charged and pH7
How does the basic dyes work?
Basic dyes are attached to the negatively charged bacteria and binds to the surface due to opposite electrical charges
How does the acidic dyes work?
Two negatives repel each other, therefore, the acidic dye stains the background.
Procedure for basic staining
- Prepare a microbial smear on a microscope slide
- Fix it
- Apply the stain
- Rinse with tap water
- Blot dry
- Observe
Why do we need to fix the microbes before staining?
Fixing is to kill the microbes and to attach them to the slide.
How do we fix the microorganisms?
By using heat provided by bacti-cinerator
What are the staining techniques?
Simple, Differential, and Special
What is the purpose of simple staining?
To highlight the entire microorganism so the cell shape and basic structures are visible.
What are the 2 most frequently used differential staining techniques?
Gram staining and Acid-fast staining
What does the Gram staining technique do?
It differentiates gram-positive bacteria from gram-negative bacteria
Gram staining procedure
- Apply Crystal violet to Heat fixed bacteria smear
- Rinse
- Cover with iodine
- Rinse
- Wash with alcohol
- Rinse
- Apply safranin
- Rinse
- Blot dry
- Observe
A stain that will stain ALL microbes the SAME color
Primary dye
What is a mordant?
a color intensifier
What is an example of a mordant?
Iodine
What is an example of a decolorizing agent?
Alcohol
A secondary stain is
also known as a counterstain
At the end of Gram-staining,
Gram-Positive bacteria RETAIN the primary dye. Gram-Negative RETAINS the counterstain. Gram-negative stays PURPLE. Gram-positive is not PINK
What is the concept behind Gram-Staining?
The results are dependent upon the structure of the cell wall of the bacteria.
How does acid-fast staining work?
Acid-fast bacteria can RETAIN the carbolfuchsin (red primary stain) in their waxy cell walls. Non-acid fast bacteria appears blue after alcohol wash and being stained with counterstain methylene blue.
What are examples of acid-fast bacteria?
Mycobacterium tuberculosis and Mycobacterium leprae
What is the purpose of special staining?
To color, detect, and demonstrate the presence of various structures in bacteria like capsule, endospore, and flagella.