Chp. 4 Bacterial Structure & Chp. 3 Gram Stain Flashcards
8 Identify, describe, and draw the various shapes and cell arrangements of bacteria.
Bacterial Shapes
Bacterial Shapes
a. Rod-Bacillus- cyllinder shape
b. Coccus- spherical bacteria
c. spiral
- spirillum–has flagella e.g. Spirillum volutans
- Spirochete–has axial filaments (internal) that rotate
- axial filaments- flagella on inside and twist, corkscrew motion
d. star
e. pleimorphic
- e.g. Corynebacterium diphtheriae- causes diphtheria (many shapes
f. coccobacillus- a bacillus that looks like a coccus (oval shape)
8 Identify, describe, and draw the various shapes and cell arrangements of bacteria.
Cell arrangements
Bacterial Cell Arrangements
a. strepto- chains of cells
- e.g. streptobacilli
b. tetard- group of 4 cells
c. staphylo- grapelike clusters
d. palisade- “picket fence” [][][]
e. diplococcus- attached in pairs OO
- Vibrios- bacteria that look like curved rods
- Spirilla- have a helical shape, look like a corkscrew, and fairly rigid bodies
- Spirochetes- another group of spirals, helical and flexible
- Monomorphic- most bacteria that maintain a single shape
- Pleomorphic- many shapes, not just one
e. g. staphylococci - grapelike spherical clusters
e. g. streptobacilli- chain of cells
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Cell Wall
-Their cell walls almost always contain the complex polysaccharide
peptidoglycan.
- The Cell Wall of the bacterial cell is a complex, semirigid structure responsible for the shape of the cell. The Cell Wall surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and the interior of the cell from adverse changes in the outside environment.
- Almost all prokaryotes have cell walls
- The function of the cell wall is to prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that outside the cell.
- Also helps maintain the shape of a bacterium and serves as a point of anchorage for flagella.
- As the volume of a bacteria cell increases, its plasma membrane and cell wall extend as needed
- The cell wall is important because it contributes to the ability of some species to cause disease and is the site of action of some antibiotics.
- the chemical composition of the cell wall is used to differentiate major types of bacteria
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Cell Membrane
- The plasma membrane encloses the cytoplasm and is a lipid bilayer
with peripheral and integral proteins (the fluid mosaic model). - The plasma membrane is selectively permeable.
- Plasma membranes contain enzymes for metabolic reactions, such
as nutrient breakdown, energy production, and photosynthesis. - Mesosomes, irregular infoldings of the plasma membrane, are
artifacts, not true cell structures. - Plasma membranes can be destroyed by alcohols and polymyxins.
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Flagellum
-Flagella are long filamentous appendages that propel bacteria.
- Flagella are relatively long filamentous appendages consisting of a
filament, hook, and basal body. - Prokaryotic flagella rotate to push the cell.
- Motile bacteria exhibit taxis; positive taxis is movement toward
an attractant, and negative taxis is movement away from a repellent. - Flagellar (H) protein is an antigen.
11 Describe: (a) the parts of the flagellum, (b) what the filament is made of (c) how the flagellum produces runs and tumbles. Define chemotaxis
3 basic parts
- Filament- long, outermost region, in constant diameter and contains the globular (roughly spherical) protein FLAGELLIN arranged in several chains that intertwine and form a helix around a hollow core. In most bacteria, filaments are not covered by a membrane or sheath, as in eukaryotic cells
- Hook- filament is attached to a slightly wider hook, consisting of a different protein.
- Basal body- third portion of a flagellum, which anhors the flagellum to the cell wall and plasma membrane
- Basal body is composed of a small central rod inserted into a series of rings.
- Gram-negative bacteria contain two pairs of rings; the outer pair of rings is anchored to various portions of the cell wall, and the inner pair of rings is anchored to the plasma membrane. Only the inner-pair is present in GP (gram-positive)
- semirigid, helical structure that moves the cell by rotating from the basal body. The rotation of a flagellum is either clockwise or counterclockwise around its long axis
- The movement of a prokaryotic flagellum results from rotation of its basal body and is similar to the movement of the shaft of an electric motor.
- As the flagella rotate, they form a bundle that pushes against the surrounding liquid and propels the bacterium.
- Flagella rotation depends on the cell’s continuous generation of energy
- Bacterial cells can alter the speed and direction of roatation of flagella, and thus are capable of various patterns of MOTILITY- the ability of an organism to move by itself.
- When a bacterium moves in one direction for a length of time, the movement is called a “run” or “swim”
- “Runs” are interrupted by periodic, abrupt, random changes in direction called “Tumbles”, then a “Run” resumes.
- “Tumbles” are caused by a reversal of flagella rotation.
- One advantage of motility is that it enables a bacterium to move toward a favorable environment or away from an adverse one.
- TAXIS- movement of a bacterium toward or away from a particular stimulus
- Chemotaxis- chemical stimiulus
- Photoaxis- light stimulus
- Motile bacteria contain receptors in various locations, such as in or just under the cell wall. These receptors pick up chemical stimuli, such as oxygen, ribose, and galactose.
- Attractant- if the chemotactic signal is positive. the bacteria move toward the stimulus with many runs and few tumbles.
- Repellent- if the chemotactic signal is negative. the frequency of tumbles increases as the bacteria move away from the stimulus
- H Antigen- flagellar protein, useful for distinguishing among SEROVARS, or variations within a species, of gram-negative bacteria.
12 Define and draw the various arrangements of flagella
- Atrichous- bacteria that lack flagella
- Peritichous (distributed over the entire cell;) or Polar (at one or both poles or ends of the cell
- Monotrichous- polar, single flagellum at one pole
- Lophotrichous- a tuft of flagella coming from one pole
- Amphitrichous- flagella at both poles of the cell
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Fimbriae
- can occur at the poles of the bacterial cell or can be evenly distributed over the entire surface of the cell.
- they can number anywhere from a few to several hundred per cell.
- Fimbriae have a tendency to adhere to each other and to surfaces
- As a result, they are involved in forming biofilms and other aggregations on the surfaces of liquids, glass, and rocks.
- Fimbriae can also help bacteria adhere to epithelial surfaces in the body
- For example, fimbriae on the bacterium Neisseria gonorrhoeae, help the microbe colonize mucous membranes. One colonization occurs, the bacteria can cause disease
- When fimbriae are abset (because of genetic mutation), colonization cannot happen, and no disease ensues
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Pili
- Usually longer than fimbriae and number only one or two per cell
- Involved in motility, called Twitching Motility, a pilus extends by the addition of subunits of pilin, makes contact with a surface or another cell, and then retracts (power stroke) as the pilin subunits are disassembled.
- This is called the Grappling Hook Model of twitching motility and results in short, jerky, intermittent movements.
- The other type of motility associated with pili is Gliding Motility, the smooth gliding movement of myxobacteria.
- Although the exact mechanism is unknown for myxobacteria, some utilize pilus retraction.
- Gliding motility provides a means for microbes to travel in environments with a low water content, such as biofilms and soil
- Some pili are used to bring bacteria together allowing the transfer of DNA from one cell to another, a process called CONJUGATION.
- Conjugation (sex) pili- Conjugation pilus of one bacterium called an F+ cell connects to receptors on the surface of another bacterium of its own species or a different species. Two cells make physical contact, and DNA from the F+ cell is transferred to the other cell. The exchanged DNA can add new function to the recipient cell, such as antibiotic resistance or the ability to digest its medium more efficiently.
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Cytoplasm
-Cytoplasm is the fluid component inside the plasma membrane.
-The cytoplasm is mostly water, with inorganic and organic
molecules, DNA, ribosomes, and inclusions
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Nucleoid
-The nucleoid contains the DNA of the bacterial chromosome.
-Bacteria can also contain PLASMIDS, which are circular,
extrachromosomal DNA molecules.
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Ribosomes
-The cytoplasm of a prokaryote contains numerous 70S ribosomes;
ribosomes consist of rRNA and protein.
-Protein synthesis occurs at ribosomes; it can be inhibited by
certain antibiotics.
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Inclusions
-Inclusions are reserve deposits found in prokaryotic and eukaryotic cells.
-Among the inclusions found in bacteria are metachromatic granules (inorganic phosphate), polysaccharide granules (usually
glycogen or starch), lipid inclusions, sulfur granules, carboxysomes (ribulose 1,5-diphosphate carboxylase), magnetosomes (Fe3O4),
and gas vacuoles.
9 Identify, describe the components and functions and draw a picture of these bacterial structures: cell wall, cell membrane, flagellum, capsule, endospore, pili, fimbriae, nucleoid, plasmid, inclusion body/cytoplasmic body, ribosomes, cytoplasm.
Endospores
-Endospores are resting structures formed by some bacteria; they allow survival during adverse environmental conditions.
-The process of endospore formation is called sporulation; the return of an endospore to its vegetative state is called
germination.
10 a) describe and draw a gram negative bacterial cell wall and a gram positive bacterial cell wall. list and describe all of the chemical components of each type of cell wall.
b) what are the differences
c) what is the procedure for a Gram Stain
d) how does the Gram stain allow you to differentiate between cells
Gram-Positive Cell Walls
- In most gram-positive bacteria, the cell wall consists of many layers of peptidoglycan, forming a thick, rigid structure.
- cell walls contain TEICHOIC ACIDS, which consist of primarily of an alcohol (such as glycerol or ribitol) and phosphate, and there are two classes
- LIPOTEICHOIC ACID, which spans the peptidoglycan layer and is linked to the plasma membrane
- WALL TEICHOIC ACID, which is linked to the peptidoglycan layer.
- because of their negative charge (from the phosphate groups), teichoic acids may bind and regulate the movement of cations (+) into and out of the cell.
- Mayalso assume a role in cell growth, preventing extensive wall breakdown and possible cell lysis.
- Finally, Teichoic acids provide much of the wall’s anitgenic specificity and thus make it possible to identify gram-positive bacteria by certain lab tests.
- Similarly, the cell walls of gram-positive streptococci are covered with various polysaccharides that allow them to be grouped into medically significant types
