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Unit 2: Lesson 3- The Prokaryotic Cell- External Structures

Terms in this set (91)

Objectives
1. compare the structural features of prokaryotic and eukaryotic cells.
2. describe the general size of bacteria.
3. draw three basic shapes of bacteria.
4. draw and distinguish between monomorphic and pleiomorphic microorganisms.
5. define glycocalyx, capsule, and slime layer.
6. draw four types of flagellar orientation, using line drawings of a bacillus.
7. describe how bacteria move.
8. explain the action of axial filaments used by spirochetes.
9. differentiate between fimbriae and pili.
10. describe the composition and major function of the bacterial cell wall.
11. compare the major structural features of gram-positive and gram-negative cell walls.
12. define porin.
13. describe two characteristics of the lipopolysaccharide component of the outer membrane of the bacterial cell wall.
14. explain why bacteria containing lipopolysaccharide are easily distinguished in a Gram stain.
15. describe the general appearance of mycoplasma and archaeobacteria in terms of cell wall structure.
16. explain the action of lysozyme and antibiotics on bacterial cell walls.
Prokaryotes and Eukaryotes
-2 groups of cells Prokaryotes & Eukaryotes
-Prokaryotes- simpler and smaller
- DNA of P - single, circularly arranged chromosome;
not surrounded by a membrane;
-the DNA of E-found in multiple chromosomes;
in membrane-enclosed nucleus.
-P lack membrane-enclosed organelles
-E include: Plants & Animals, Fungi, Protozoa, and Algae
-P include: Bacteria & Archaea
-Both E & P have a sticky glycocalyx surrounding them
-Bacteria- usually sticking to solid surfaces (including other cells) rather than free floating
- glycocalyx-glue that holds the cells in place.

- P&E both contain nucleic acids, proteins, lipids, and carbohydrates.
- use the same kinds of chemical reactions to metabolize food, build proteins, and store energy.

-Things that distinguish E &P: structure of cell walls and membranes, and the absence of organelles
Chief distinguishing characteristics of Prokaryotes:
1. Their DNA is not enclosed within a membrane and is usually a singular circularly arranged chromosome. (Some bacteria, such as Vibrio cholerae, have two chromosomes, and some bacteria have a linearly arranged chromosome.)
2. Their DNA is not associated with histones (special chromosomal proteins found in eukaryotes); other proteins are associated with the DNA.
3. They lack membrane-enclosed organelles.
4. Their cell walls almost always contain the complex polysaccharide peptidoglycan.
5. They usually divide by binary fission. During this process, the DNA is copied, and the cell splits into two cells. Binary fission involves fewer structures and processes than eukaryotic cell division.
Chief distinguishing characteristics of Eukaryotes
1. Their DNA is found in the cell's nucleus, which is separated from the cytoplasm by a nuclear membrane, and the DNA is found in multiple chromosomes.
• 2. Their DNA is consistently associated with chromosomal proteins called histones and with nonhistones.
• 3. They have a number of membrane-enclosed organelles, including mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, and sometimes chloroplasts.
• 4. Their cell walls, when present, are chemically simple.
• 5. Cell division usually involves mitosis, in which chromosomes replicate and an identical set is distributed into each of two nuclei. This process is guided by the mitotic spindle, a football-shaped assembly of microtubules. Division of the cytoplasm and other organelles follows so that the two cells produced are identical to each other.
An overview of comparing Eukaryotic and Prokaryotic Cells
• 1. Prokaryotic and eukaryotic cells are similar in their chemical composition and chemical reactions.
• 2. Prokaryotic cells lack membrane-enclosed organelles (including a nucleus).
• 3. Peptidoglycan is found in prokaryotic cell walls but not in eukaryotic cell walls.
• 4. Eukaryotic cells have a membrane-bound nucleus and other or ganelles.
Prokaryotic Cells
-unicellular
-Bacteria(majority) & Archaea
Bacteria
-differ by morphology(shape), chemical composition, nutritional requirements, biochemical activities, and source of energy
-99% are biofilms
- diameter:0.2-2.0um; length:2-8um
-Shapes:
-coccus (spherical)
-bacilli (rods)
-spiral
Cocci
-spherical- can be oval, or flattened on one side
-cells remain attached when they divide
-Diplococci-remain in pairs after dividing
-Streptococci-divide and remain attached in chainlike patterns
-Tetrads-divide in two planes ;remain in groups of 4
--Sarcinae-divide in three planes ; remain attached in cubelike groups of 8
-Staphylococci-Those that divide in multiple planes ; form grapelike clusters or broad sheets
Bacilli shape
-divide across short axis- fewer groupings than cocci
-often form long, twisted chains of cells
-shaped: determined by heredity
-most are MONOMORPHIC- maintain single shape
-shape can be altered by environmental conditions
-Pleomorphic- have many shapes

-Single Bacilli-Most bacilli appear as single rods
-Diplobacilli-appear in pairs after division
-Streptobacilli-occur in chains
-Coccobacilli-oval and look much like cocci

-Spiral bacteria have one or more twists; they are never straight.

-Vibrios-bacteria that look like curved rods
-Spirilla-helical, corkscrew shape w/ fairly rigid bodies; use propeller-like external appendages called flagella to move
-Spirochetes-helical and flexible; move by means of axial filaments, which resemble flagella but are contained within a flexible external sheath.

-Star shaped
-Rectangular, flat shaped
-Triangular shaped
Vibrios, Sprilla, Spirochetes
-Vibrios-bacteria that look like curved rods
-Spirilla-helical, corkscrew shape w/ fairly rigid bodies; use propeller-like external appendages called flagella to move
-Spirochetes-helical and flexible; move by means of axial filaments, which resemble flagella but are contained within a flexible external sheath.
Prokaryotic Cell: summary
• 1. Bacteria are unicellular, and most of them multiply by binary fission.
• 2. Bacterial species are differentiated by morphology, chemical composition, nutritional requirements, biochemical activities, and source of energy.
The Size, Shape, and Arrangement of Bacterial Cells Summary
• 1. Most bacteria are 0.2 to 2.0 µm in diameter and 2 to 8 µm in length.
• 2. The three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted).
• 3. Pleomorphic bacteria can assume several shapes.
prokaryotes: Structures external to cell wall
glycocalyx,
flagella,
axial filaments,
fimbriae, and
pili.
All bacteria contain....
-cytoplasm,
-ribosomes,
-plasma membrane
-nucleoid.
-Almost all bacteria have cell walls.
Capsules play specific role in
bacterial virulence
Cell walls or flagella play specific roles in
bacterial identification
Cell walls also play specific roles in
targets of antimicrobial agents
Plasmids
-encode information (such as genes) for resistance to antibiotics or the production of toxins.
-may be exchanged between bacteria.
-a genetic structure in a cell that can replicate independently of the chromosomes, typically a small circular DNA strand in the cytoplasm of a bacterium or protozoan. Plasmids are much used in the laboratory manipulation of genes.
Glycocalyx
-substance secreted on prokaryotes surface
-means sugar coat
-viscous(sticky), gelatinous polymer,
-external to cell wall,
-composed of polysaccharide, polypeptide or both
-made inside cell and secreted to surface
-important component of biofilms
-can protect a cell against dehydration
-its viscosity may inhibit the movement of nutrients out of the cell.
-Capsule & Slime Layer
Glycocalyx Summar
• 1. The glycocalyx (capsule, slime layer, or extracellular polysaccharide) is a gelatinous polysaccharide and/or polypeptide covering.
• 2. Capsules may protect pathogens from phagocytosis.
• 3. Capsules enable adherence to surfaces, prevent desiccation, and may provide nutrients.
Capsule
-organized glycocalyx
-firmly attached to cell wall
-presence determined by NEGATIVE STAINING
-important in contributing to bacterial virulence (the degree to which a pathogen causes disease).
-protect pathogenic bacteria from phagocytosis by the cells of the host
--Bacillus anthracis produces a capsule of D-glutamic acid.
- only encapsulated B. anthracis causes anthrax,
- capsule may prevent its being destroyed by phagocytosis.
--Streptococcus pneumoniae- causes pneumonia only when the cells are protected by a polysaccharide capsule. -Unencapsulated S. pneumoniae- cells cannot cause pneumonia and are readily phagocytized.
Slime Layer
-unorganized glycocalyx
-loosely attached to cell wall
extracellular polymeric substance (EPS)
-glycocalyx that helps cells in a biofilm attach to their target environment and to each other
--protects cells within it
-facilitates communication among cells
-enables the cells to survive by attaching to various surfaces in their natural environment
Flagella
-filamentous appendages that propel bacteria
-atrichous, peritrichous, polar
-semirigid; helical structure
atrichous
bacteria that lack flagella
peritrichous
flagella distributed over entire cell
polar flagella
flagella at one or both poles or ends of the cell
If polar, flagella may be
-monotrichous (a single flagellum at one pole)
-lophotrichous (a tuft of flagella coming from one pole)
-amphitrichous(flagella at both poles of the cell)
monotrichous
lophotrichous
amphitrichous
parts of flagella
-Filament
-Hook
-Basal Body
Filament
-long outermost region
-contains the globular (roughly spherical) protein flagellin arranged in several chains that intertwine and form a helix around a hollow core
- 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
-anchors flagellum to the cell wall and plasma membrane.
-small central rod inserted into series of rings
-Gram-negative: 2 pairs of rings- outer pair of rings is anchored to various portions of the cell wall; inner pair of rings is anchored to the plasma membrane
-Gram-positive: only inner pair is present
Flagella movement
-rotation is either clockwise or counterclockwise around its long axis.
(Eukaryotic flagella- a wavelike motion.)
-motility-ability of an organism to move by itself
-advantage of motility: enables a bacterium to move toward a favorable environment or away from an adverse one.
-runs- counterclockwise- -"run" or "swim"-when a bacteria moves in one direction for a length of time
--"Tumbles" -periodic, abrupt, random changes in direction -clockwise- reversal of flagellar rotation
-"swarm," -to show rapid wavelike movement across a solid culture medium
Taxis
-movement of a bacterium toward or away from a particular stimulus
-Chemotaxis-chemical stimuli
-Phototaxis-light stimuli
-bacteria contain receptors in various locations -will pick up chemical stimuli such as oxygen, ribose, and galactose
-info is passed to flagella from stimuli
-attractant; repellant
attractant
-chemotactic signal is positive;
-bacteria move toward the stimulus with MANY RUNS and few tumbles
repellant
chemotactic signal is negative;
-frequency of TUMBLES INCREASES as the bacteria move away from the stimulus.
H antigen
-flagellar protein
-useful for distinguishing among SEROVARS-variations within a species, of gram-negative bacteria
Flagella Summary
• 4. Flagella are relatively long filamentous appendages consisting of a filament, hook, and basal body.
• 5. Prokaryotic flagella rotate to push the cell.
• 6. Motile bacteria exhibit taxis; positive taxis is movement toward an attractant, and negative taxis is movement away from a repellent.
• 7. Flagellar (H) protein is an antigen.
Axial Filaments
-Spirochetes -move by axial filaments, or endoflagella, bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell
-anchored at one end of the spirochete
-rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion.
- similar to the way a corkscrew moves through a cork.
-allows effective movement through body fluids
Axial Filaments Summary
• 8. Spiral cells that move by means of an axial filament (endoflagellum) are called spirochetes.
• 9. Axial filaments are similar to flagella, except that they wrap around the cell.
Fimbraie and Pili
-Many gram-negative bacteria contain hairlike appendages that are shorter, straighter, and thinner than flagella and are used for:
-attachment and transfer of DNA rather than for motility. -consist of a protein called pilin
-arranged helically around a central core,
-divided into two types, fimbriae and pili
Fimbraie
-can occur at the poles of the bacterial cell or
- can be evenly distributed over the entire surface of the cell
-can number anywhere from a few to several hundred per cell
-have a tendency to adhere to each other and to surfaces. -involved in forming biofilms
-can also help bacteria adhere to epithelial surfaces in the body
Pili
-longer than fimbriae- about 1-2 per cell
-involved in motility and DNA transfer
-Twitching Motility
-Gliding Motility
-Some pili are used to bring bacteria together allowing the transfer of DNA from one cell to another, a process called conjugation--> Bacteria Sex
-the 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.
- The two cells make physical contact, and
-DNA from the F+ cell is transferred to the other cell.
-The exchanged DNA can add a new function to the recipient cell, such as antibiotic resistance or the ability to digest its medium more efficiently.
twitching motility
-pilus extends, makes contact w/ surface or another cell, then retracts (power-stroke)
-called GRAPPLING HOOK MODEL of twitching motility
-results in short, jerky, intermittent movement
Gliding Motility
-smooth gliding movement of myxobacteria
-provides a means for microbes to travel in environments with a low water content, such as biofilms and soil
Fimbriae & Pili Summary
• 10. Fimbriae help cells adhere to surfaces.
• 11. Pili are involved in twitching motility and DNA transfer.
The Prokaryotic Cell Wall
-complex, semirigid structure responsible for the shape of the cell.
-surrounds fragile plasma (cytoplasmic) membrane
-protects it and the interior of the cell from adverse changes in the outside environment
-most prokaryotic cells have cell walls
-eukaryotes- cell walls are similar but are more simple and less rigid
Functions of Cell Wall
-prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that outside the cell
-helps maintain the shape of a bacterium
-serves as a point of anchorage for flagella
-contributes to the ability of some species to cause disease and is the site of action of some antibiotics
Cell wall composition
-composed of peptidoglycan
-Peptidoglycan: consists of repeating disaccharides attached by polypeptides -forms lattice around cell
-Disaccharide portion: made up of monosaccharides called NAG and NAM--- related to glucose
NAG NAM
-Alternating NAM and NAG molecules are linked in rows of 10 to 65 sugars
- form a carbohydrate "backbone"
- (the glycan portion of peptidoglycan).
Polypeptides
Adjacent rows are linked by polypeptides (the peptide portion of peptidoglycan).
-includes tetrapeptide side chains, which consist of four amino acids attached to NAMs in the backbone.
-amino acids occur in an alternating pattern of D and L forms
--unique because the amino acids found in other proteins are L forms.
--Parallel tetrapeptide side chains may be directly bonded to each other or linked by a peptide cross-bridge, consisting of a short chain of amino acids.
Penecillin interferes with...
-Penicillin interferes with the final linking of the peptidoglycan rows by peptide cross-bridges
Result: cell wall is greatly weakened and the cell undergoes lysis, destruction caused by rupture of the plasma membrane and the loss of cytoplasm.
gram positive gram negative cell wall
*see figure in notes
Cell wall: composition and characteristics summary
• 1. The cell wall surrounds the plasma membrane and protects the cell from changes in water pressure.
• 2. The bacterial cell wall consists of peptidoglycan, a polymer consisting of NAG and NAM and short chains of amino acids.
• 3. Penicillin interferes with peptidoglycan synthesis.
• 4. Gram-positive cell walls consist of many layers of peptidoglycan and also contain teichoic acids.
• 5. Gram-negative bacteria have a lipopolysaccharide-lipoproteinphospholipid outer membrane surrounding a thin peptidoglycan layer.
• 6. The outer membrane protects the cell from phagocytosis and from penicillin, lysozyme, and other chemicals.
• 7. Porins are proteins that permit small molecules to pass through the outer membrane; specific channel proteins allow other molecules to move through the outer membrane.
• 8. The lipopolysaccharide component of the outer membrane consists of sugars (O polysaccharides), which function as antigens, and lipid A, which is an endotoxin.
NAG and NAM backbone is specific to ___________ cells
prokaryotic
the feature of alternating D and L amino acid side chains that link the backbone together is unique to __________
prokaryotes, since D forms of peptide are seldom seen in nature
combination of the carbohydrate backbone, together with covalent linkage by the D and L forms of the tetrapeptides, contribute to ...
the rigidity of bacteria.
Gram-Positive Cell Walls
- THICK, RIGID, peptidoglycan layer
-cell walls contain TEICHOIC ACIDS, which consist primarily of an alcohol (such as glycerol or ribitol) and phosphate.
Teichoic Acid
-two classes of teichoic acids:
-lipoteichoic acid- spans the peptidoglycan layer and is linked to the plasma membrane,
-wall teichoic acid- 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 (positive ions) into and out of the cell.
-may also assume a role in cell growth, preventing extensive wall breakdown and possible cell lysis.
-teichoic acids provide much of the wall's antigenic specificity and thus make it possible to identify gram-positive bacteria by certain laboratory tests
Gram-Negative Cell Walls
-THIN peptidoglycan layer and OUTER MEMBRANE
-peptidoglycan -bonded to lipoproteins (lipids covalently linked to proteins) in the outer membrane and is in the periplasm
--periplasm-a gel-like fluid between the outer membrane and the plasma membrane
-contains a high concentration of degradative enzymes and transport proteins
--cell walls DO NOT contain teichoic acid
--due to thin layer of peptidoglycan, more susceptible to mechanical breakage
-outer membrane: consists of lipopolysaccharides (LPS), lipoproteins, and phospholipids
Outer Membrane
-consists of lipopolysaccharides (LPS), lipoproteins, and phospholipids
-Functions of outer membrane:
-its strong negative charge is an important factor in evading phagocytosis and the actions of complement (lyses cells and promotes phagocytosis), two components of the defenses of the host
-provides a barrier to certain antibiotics (for example, penicillin), digestive enzymes such as lysozyme, detergents, heavy metals, bile salts, and certain dyes.
-does not provide a barrier to all substances- still allows nutrients to pass through to sustain metabolism of the cell
-permeability partly is due to proteins in the membrane called porins that form channels
-porins-permit passage of molecules such as nucleotides, disaccharides, peptides, amino acids, vitamin B12, and iron.
-The lipopolysaccharide (LPS) of the outer membrane is a large complex molecule that contains lipids and carbohydrates and consists of three components: (1) lipid A, (2) a core polysaccharide, and (3) an O polysaccharide.
- Lipid A is the lipid portion of the LPS and is embedded in the top layer of the outer membrane.
-When gram-negative bacteria die, they release lipid A, which functions as an endotoxin
-responsible for the symptoms associated with infections by gram-negative bacteria such as fever, dilation of blood vessels, shock, and blood clotting.
- core polysaccharide is attached to lipid A and contains unusual sugars.
-Its role is structural—to provide stability.
-O polysaccharide extends outward from the core polysaccharide and is composed of sugar molecules.
-functions as an antigen and is useful for distinguishing species of gram-negative bacteria.
- role is comparable to that of teichoic acids in gram-positive cells.

-Lipopolysaccharide is known to make a pivotal contribution to the signs and symptoms of disease resulting from infection by gram-negative bacteria. Because of its structure (the association of a core polysaccharide, known as O polysaccharide and a lipid component, called lipid A), lipopolysaccharide is known to be highly toxic when introduced into the blood circulation of animals and humans. The reaction to the introduction of this substance is known as endotoxic shock.
Gram-positive and Gram-negative characteristics
Carefully study Table 4.1 (p. 87).
Cell Walls and the Gram Stain Mechanism Summary
• 9. The crystal violet-iodine complex combines with peptidoglycan.
• 10. The decolorizer removes the lipid outer membrane of gram-negative bacteria and washes out the crystal violet.
Atypical Cell Walls
-include members of the genus Mycoplasma
-Mycoplasmas - the smallest known bacteria that can grow and reproduce outside living host cells
-Because of their size and because they have no cell walls, they pass through most bacterial filters and were first mistaken for viruses.
-plasma membranes are unique among bacteria in having lipids called sterols- thought to help protect them from lysis (rupture).

-Archaea may lack walls or may have unusual walls composed of polysaccharides and proteins but not peptidoglycan
- contain a substance similar to peptidoglycan called pseudomurein.
-contains N-acetyltalosaminuronic acid instead of NAM and lacks the D-amino acids found in bacterial cell walls.
-Archaea generally cannot be Gram-stained but appear gram-negative because they do not contain peptidoglycan.
Atypical Cell Walls Summary
• 11. Mycoplasma is a bacterial genus that naturally lacks cell walls.
• 12. Archaea have pseudomurein; they lack peptidoglycan.
• 13. Acid-fast cell walls have a layer of mycolic acid outside a thin peptidoglycan layer.
Damage to the Cell Wall
-Chemicals that damage bacterial cell walls, or interfere with their synthesis, often do not harm the cells of an animal host because the bacterial cell wall is made of chemicals unlike those in eukaryotic cells.
-cell wall synthesis is the target for some antimicrobial drugs.
Ways cell walls can be damaged
-exposure to the digestive enzyme lysozyme (a constituent of perspiration, tears, mucus, and saliva)
- active on the major cell wall components of most gram-positive bacteria, making them vulnerable to lysis.
-catalyzes hydrolysis of the bonds between the sugars in the repeating disaccharide "backbone" of peptidoglycan. This act is analogous to cutting the steel supports of a bridge with a cutting torch: the gram-positive cell wall is almost completely destroyed by lysozyme.
-cellular contents that remain surrounded by the plasma membrane may remain intact if lysis does not occur; this wall-less cell is termed a protoplast.
Protoplast
-protoplast-is spherical and is still capable of carrying on metabolism.
Damaged cell walls continued...
-genus Proteus, as well as other genera, can lose their cell walls and swell into irregularly shaped cells called L forms
-may form spontaneously or develop in response to penicillin (which inhibits cell wall formation) or lysozyme (which removes the cell wall).
- L forms can live and divide repeatedly or return to the walled state.
-lysozyme is applied to gram-negative cells, usually the wall is not destroyed to the same extent as in gram-positive cells; some of the outer membrane also remains.
-cellular contents, plasma membrane, and remaining outer wall layer are called a spheroplast, also a spherical structure.
- For lysozyme to exert its effect on gram-negative cells, the cells are first treated with EDTA (ethylenediaminetetraacetic acid). EDTA weakens ionic bonds in the outer membrane and thereby damages it, giving the lysozyme access to the peptidoglycan layer.
-Protoplasts and spheroplasts burst in pure water or very dilute salt or sugar solutions because the water molecules from the surrounding fluid rapidly move into and enlarge the cell, which has a much lower internal concentration of water. This rupturing, called osmotic lysis,
Effects of penecillin
-certain antibiotics (penicillin) destroy bacteria by interfering with the formation of the peptide cross-bridges of peptidoglycan- preventing the formation of a functional cell wall.
--Most gram-negative bacteria -not as susceptible to penicillin as gram-positive bacteria are because the outer membrane of gram-negative bacteria forms a barrier that inhibits the entry of this and other substances, and gram-negative bacteria have fewer peptide cross-bridges
-gram-negative bacteria are quite susceptible to some β-lactam antibiotics that penetrate the outer membrane better than penicillin.
Damage to the cell wall summary
• 14. In the presence of lysozyme, gram-positive cell walls are destroyed, and the remaining cellular contents are referred to as a protoplast.
• 15. In the presence of lysozyme, gram-negative cell walls are not completely destroyed, and the remaining cellular contents are referred to as a spheroplast.
• 16. L forms are gram-positive or gram-negative bacteria that do not make a cell wall.
• 17. Antibiotics such as penicillin interfere with cell wall synthesis.
1. Distinguish between prokaryotic and eukaryotic cells in terms of DNA packaging, organelles, cell wall structure, and reproduction.
-Chief distinguishing characteristics of Prokaryotes:
1. Their DNA is NOT ENCLOSED WITHIN A MEMBRANE and is usually a SINGULAR circularly arranged chromosome. (Some bacteria, such as Vibrio cholerae, have two chromosomes, and some bacteria have a linearly arranged chromosome.)
2. Their DNA is NOT associated with histones (special chromosomal proteins found in eukaryotes); other proteins are associated with the DNA.
3. They LACK membrane-enclosed organelles.
4. Their cell walls almost always contain the complex polysaccharide peptidoglycan.
5. They usually divide by BINARY FISSION. During this process, the DNA is copied, and the cell splits into two cells. Binary fission involves fewer structures and processes than eukaryotic cell division.

• -Chief distinguishing characteristics of Eukaryotes:
1. Their DNA is found in the cell's NUCLEUS, which is separated from the cytoplasm by a nuclear membrane, and the DNA is found in MULTIPLE chromosomes.
• 2. Their DNA is consistently associated with chromosomal proteins called HISTONES and with NONHISTONES.
• 3. They have a number of MEMBRANE-ENCLOSED ORGANELLES, including mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, and sometimes chloroplasts.
• 4. Their cell walls, when present, are chemically SIMPLE.
• 5. Cell division usually involves MITOSIS, in which chromosomes replicate and an identical set is distributed into each of two nuclei. This process is guided by the mitotic spindle, a football-shaped assembly of microtubules. Division of the cytoplasm and other organelles follows so that the two cells produced are identical to each other.
2. Complete the "Critical Thinking" problem 1 (p. 110).
How can prokaryotic cells be smaller than eukaryotic cells and still carry on all the functions of life?
1. Prokaryotes are small, so they don't require many resources or much space.
2. They are diverse, so they can occupy many niches.
3. They have the ability to reproduce quickly.
4. They can evolve quickly because of their fast generation time.
5. Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes.

Prokaryotic cells have a good surface area to volume ratio. They contain 1 circular chromosome and no membrane bound organelles. All of their chemical activity occurs in the cytoplasm and cell membrane. They have all they need at this minimal functional level.

. Essentially, prokaryotes require the apparatus necessary to metabolize simple nutrients and to reproduce. Given their small size and the simplicity of their basic structures, one would expect that the intracellular components would also be simple.
3. Define monomorphic and pleomorphic
-Monomorphic- most bacteria- maintain single shape

--environmental conditions can alter shape- identification becomes difficult

-Pleomorphic-have many shapes (not just one)
4. List three possible cell shapes and cell arrangements demonstrated by bacteria.
-Basic shapes:
- Cocci- spherical shaped (Cocci, Diplococci, Streptococci, Tetrads, Sarcinae, Staphylococci)
-Diplococci- Cocci that remain in pairs after dividing
-Streptococci-those that divide and remain attached in chainlike patterns
-Tetrads-Those that divide in two planes and remain in groups of four
-Sarcinae-Those that divide in three planes and remain attached in cubelike groups of eight

-Bacilli- rod shaped (Single Bacilli, Diplobacilli, Streptobacilli, Coccobacilli)
-Single Bacilli-Most bacilli appear as single rods
-Diplobacilli-appear in pairs after division
-Streptobacilli-occur in chains
-Coccobacilli-oval and look much like cocci

- spiral (Vibrio, Spirillium, Spirochette)
--Spiral bacteria have one or more twists; they are never straight.
-Vibrios-bacteria that look like curved rods
-Spirilla-helical, corkscrew shape w/ fairly rigid bodies; use propeller-like external appendages called flagella to move
-Spirochetes-helical and flexible; move by means of axial filaments, which resemble flagella but are contained within a flexible external sheath.
5. Why is the glycocalyx an important structural feature of bacteria infection?
- Capsule or Slime Layer
--capsules are important in contributing to bacterial virulence (the degree to which a pathogen causes disease).
--Capsules often protect pathogenic bacteria from phagocytosis by the cells of the host.
-helps cells in a biofilm attach to their target environment and to each other
-protects cells within it
-facilitates communication among cells
-enables the cells to survive by attaching to various surfaces in their natural environment.
-glycocalyx also can protect a cell against dehydration, and its viscosity may inhibit the movement of nutrients out of the cell.
6. What is the connection between a bacterial glycocalyx and a biofilm?
-Glycocalyx-important component of biofilms
- extracellular polymeric substance (EPS)- glycocalyx that helps cells in a biofilm attach to their target environment and to each other
-protects cells within it
-facilitates communication among cells
-enables the cells to survive by attaching to various surfaces in their natural environment.
7. Why will a rod-shaped bacterium become spherical if its cell wall is disrupted?
-environmental conditions can alter shape
-cell wall gives bacterium its cell shape- damage to the cell wall can alter the shape of the bacterium
8. Examine the pictures in Figure 4.7 (p. 80). Describe the four types of flagella arrangement.
-peritrichous- distributed over entire cell
-monotrichous-a single flagellum at one pole
-lophotrichous a tuft of flagella coming from one pole
-amphitrichous-flagella at both poles of the cell
9. Compare the type of motility of an organism that has an axial filament to that of an organism possessing fimbriae.
Axial Filament: rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion. This type of movement is similar to the way a corkscrew moves through a cork.
-allows effective movement through body fluids

Fimbriae:used for attachment and transfer of DNA rather than for motility
--have a tendency to adhere to each other and to surfaces. involved in forming biofilms
--can also help bacteria adhere to epithelial surfaces in the body
10. What is the predominant function of fimbriae and pili?
Fimbriae-for attachment and transfer of DNA
Pili-Motility and DNA transfer(conjugation)
11. What is the major difference between gram positive and gram negative cell walls?
Gram positive- Thick peptidoglycan wall; contains teichoic acids
Gram negative- thin peptidoglycan wall an LPS (lipopolysaccharide)outer membrane
12. What is peptidoglycan composed of? What antibiotic targets peptidoglycan?
-consists of a repeating disaccharide attached by polypeptides to form a lattice that surrounds and protects the entire cell.
-disaccharide portion is made up of monosaccharides called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) - related to glucose
--Alternating NAM and NAG molecules are linked in rows of 10 to 65 sugars to form a carbohydrate "backbone" (the glycan portion of peptidoglycan).
-Adjacent rows are linked by polypeptides (the peptide portion of peptidoglycan).
-always includes tetrapeptide side chains, which consist of four amino acids attached to NAMs in the backbone.
-amino acids occur in an alternating pattern of D and L forms
--unique because the amino acids found in other proteins are L forms.
-Parallel tetrapeptide side chains may be directly bonded to each other or linked by a peptide cross-bridge, consisting of a short chain of amino acids.
13. Study Table 4.1 (p. 87). On the basis of structural properties, explain why there are marked differences in the susceptibility of gram-positive and gram-negative bacteria to basic dyes, anionic detergent, and sodium azide.
-Marked differences are due to the difference in Gram-Positive and Gram-Negative bacteria's cell walls:
-Gram-Positive- Thicker peptidoglycan layer; techoic acid

-Gram-Negative- Thin peptidoglycan layer; LPS outer membrane.
-outer membrane has a strong negative charge- an important factor in evading phagocytosis and the actions of complement (lyses cells and promotes phagocytosis), two components of the defenses of the host

_Gram-Negative outer membrane provides a barrier to certain antibiotics (for example, penicillin), digestive enzymes such as lysozyme, detergents, heavy metals, bile salts, and certain dyes.
14. What is a porin?
-Porins are proteins that permit small molecules to pass through the outer membrane; specific channel proteins allow other molecules to move through the outer membrane.
-permeability partly is due to proteins in the membrane called porins that form channels
-porins-permit passage of molecules such as nucleotides, disaccharides, peptides, amino acids, vitamin B12, and iron.
15. Describe the structure of lipopolysaccharide (LPS) and indicate its clinical significance.
-Gram-negative bacteria have a lipopolysaccharide-lipoproteinphospholipid outer membrane surrounding a thin peptidoglycan layer.
-The lipopolysaccharide component of the outer membrane consists of sugars (O polysaccharides), which function as antigens, and lipid A, which is an endotoxin.
The lipopolysaccharide (LPS) of the outer membrane is a large complex molecule that contains lipids and carbohydrates and consists of three components: (1) lipid A, (2) a core polysaccharide, and (3) an O polysaccharide.
- Lipid A is the lipid portion of the LPS and is embedded in the top layer of the outer membrane.
-When gram-negative bacteria die, they release lipid A, which functions as an endotoxin
-responsible for the symptoms associated with infections by gram-negative bacteria such as fever, dilation of blood vessels, shock, and blood clotting.
- core polysaccharide is attached to lipid A and contains unusual sugars.
-Its role is structural—to provide stability.
-O polysaccharide extends outward from the core polysaccharide and is composed of sugar molecules.
-functions as an antigen and is useful for distinguishing species of gram-negative bacteria.
- role is comparable to that of teichoic acids in gram-positive cells.
16. What species of bacteria has an atypical cell wall? What is the cell wall of this organism composed of?
-include members of the genus Mycoplasma
-Mycoplasmas are the smallest known bacteria that can grow and reproduce outside living host cells
-Because of their size and because they have no cell walls, they pass through most bacterial filters and were first mistaken for viruses.
-plasma membranes are unique among bacteria in having lipids called sterols- thought to help protect them from lysis (rupture).

-Archaea may lack walls or may have unusual walls composed of POLYSACCHARIDES and PROTEINS but not peptidoglycan
- contain a substance similar to peptidoglycan called PSEUDOMUREIN
-contains N-acetyltalosaminuronic acid instead of NAM and lacks the D-amino acids found in bacterial cell walls.
-Archaea generally cannot be Gram-stained but appear gram-negative because they do not contain peptidoglycan.
17. Why are drugs that target cell wall synthesis useful?
-cell wall synthesis is the target for some antimicrobial drugs.
-The targeted effects of those antibiotics that affect cell wall synthesis (such as penicillin, cephalosporin, bacitracin, and vancomycin) are better suited to the destruction of gram-positive than gram-negative bacteria.
--Penicillin interferes with the final linking of the peptidoglycan rows by peptide cross-bridges (seeFigure 4.13a).
-As a result, the cell wall is greatly weakened and the cell undergoes lysis, destruction caused by rupture of the plasma membrane and the loss of cytoplasm.

Functions of cell walls:
-prevent bacterial cells from rupturing when the water pressure inside the cell is greater than that outside the cell
-helps maintain the shape of a bacterium
-serves as a point of anchorage for flagella
-contributes to the ability of some species to cause disease and is the site of action of some antibiotics

Without the cell wall, the bacteria will be susceptible to destruction by chemicals outside the plasma membrane (which is just inside the cell wall of bacteria), and it will not be able to survive.
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