1 Bacterial Anatomy and Physio (54) Flashcards
What structure of the bacterial cell envelope is marked as 2? Refer to the image.
1 Peptidoglycan layer
2 Outer membrane
3 Mesosomes
4 Inner cell membrane
5 Capsule
Peptidoglycan layer
Refer to second image for identified structures.
Structure 2 is the cell wall composed of peptidoglycans: the peptidoglycan layer. The cell wall is involved in maintaining the overall shape of a bacterial cell. Most gram-positive bacteria have a relatively thick cell wall composed largely of peptidoglycan. In contrast, the peptidoglycan layer in the gram-negative bacteria is relatively thin. This structure provides the basis for the gram reaction.
Outside the peptidoglycan layer in the gram-negative envelope is a structure called the outer membrane. This membrane structure is anchored non-covalently to lipoprotein molecules (Braun’s lipoprotein), which in turn are covalently linked to the peptidoglycan. The lipopolysaccharides of the gram-negative cell envelope form part of the outer leaflet of the outer membrane structure.
The capsule is a region of material that extends beyond the outer membrane of some bacteria. Bacterial capsule contributes directly to the pathogenicity or virulence of an organism. They confer resistance to phagocytosis; they provide protection to the bacterial cell against host defenses to invasion. Encapsulated species are found among both gram-positive and gram-negative bacteria.
The inner cell membrane is a lipid bilayer that surrounds and contains the cytosol.
Mesosomes are invaginations of the plasma membrane/inner cell membrane. These structures are much more prominent in gram-positive than in gram-negative organisms.
In the accompanying diagram of a bacterial cell envelope, identify the structure marked 5.
1 Nucleoid
2 Peptidoglycan layer
3 Outer membrane
4 Inner cell membrane
5 Mesosomes
Outer membrane
Arrow 5 points to the outer membrane, which is the structure found outside the peptidoglycan layer/cell wall. This structure is anchored non-covalently to lipoprotein molecules (Braun’s lipoprotein), which in turn, are covalently linked to the peptidoglycan. Like other membranes, the outer membrane is composed of proteins and phospholipids. Unlike other membranes, it contains an additional molecule, lipopolysaccharide, which displays endotoxin activity. The lipopolysaccharides of the Gram-negative cell envelope form part of the outer leaflet of the outer membrane structure, while the lipoprotein and the phospholipids form the inner leaflet of the outer membrane bi-layer. The outer membrane possesses several major outer membrane proteins; the most abundant is called porin. A capsule is often seen extending beyond this structure and contributes to bacterial virulence.
Peptidoglycan is a major component of the bacterial cell wall, particularly in gram-positive species. These complex carbohydrate polymers provide structural integrity to the cell and are a major factor in the Gram stain reaction.
The inner cell membrane surrounds and contains the bacterial cytosol.
Nucleoid refers to the bacterial DNA and associated proteins that appear within discrete areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
Mesosomes are invaginations of the plasma membrane/inner cell membrane. These structures are much more prominent in Gram-positive than in Gram-negative organisms.
A Gram stain has been performed on a bacterial isolate taken from a sheep blood agar plate. Upon observation, the cells appear to be red to pink rods. The organism is presumptively identified as Citrobacter koseri. What is the most likely reason for the red color of the cells in the stain?
1 Peptidoglycan layer of the cell wall is relatively thin
2 Peptidoglycan layer of the cell wall is relatively thick
3 Organisms in this genus have a lipopolysaccharide outer membrane
4 Organisms in this genus have only a cytoplasmic membrane
5 Capsule tends to capture the safranin from the Gram stain reagent
Peptidoglycan layer of the cell wall is relatively thin
The Gram stain is a differential stain utilizing two dyes: crystal violet (blue) and safranin (red). Gram negative organisms stain red and Gram positive organisms stain blue. The cell wall of the organism is the determining factor that makes an organism’s Gram positive or Gram negative. Gram positive organisms have a thick peptidoglycan layered wall that tends to complex with Gram’s iodine and remains captured in the complex layer. Gram negative cells have a much thinner peptidoglycan layer that allows the crystal violet-iodine complex to be easily removed by the decolorizer. Thus, the subsequent addition of safranin stains the wall red. Bacterial membranes and capsules do not play a role in the Gram reaction.
A successful Gram stain would use, in order
1 Crystal violet, alcohol, iodine, safranin
2 Methylene blue, iodine, alcohol, safranin
3 Crystal violet, iodine, alcohol, congo red
4 Methylene blue, iodine, saline, safranin
5 Crystal violet, iodine, alcohol, safranin
Crystal violet, iodine, alcohol, safranin
The Gram stain is the work horse of microbiology, but adherence to accurate technique is absolutely essential to obtaining the correct results. In fact, for some specimens that represent life-threatening illnesses, e.g. spinal fluid, the Gram stain can detect the etiologic agent directly in the specimen in time to direct empiric therapy and have a positive impact on the prognosis of the patient. The agents used in order are crystal violet (deep blue to purple), iodine (serves as a mordant), alcohol (or a mix of acetone and alcohol) which is the most critical of the steps and is the decolorizing procedure followed by the addition of safranin (red), the final stain to be added.
If you observe an organism microscopically to be unicellular, motile, and without a membrane-bound nucleus, it will most likely be a
1 Fungus
2 Bacterium
3 Virus
4 Protozoan
5 Yeast
Bacterium
Most living cells are either prokaryotic or eukaryotic. Probably the most distinguishing feature that separates these two classes of organisms, especially the microscopic ones, is that prokaryotic cells do not have a membrane-bound nucleus. The DNA of bacterial cells essentially floats in the cytoplasm but is attached to the inner membrane. Fungi, yeasts, and protozoa are eukaryotic cells and have membrane-bound nuclei. Viruses are not cells in the classic sense and are classed differently.
The medical importance of spores lies in the fact that:
1 They have keratin-like coats.
2 They contain bacterial DNA.
3 They are extremely resistant to heat and chemicals.
4 They are formed in adverse conditions.
They are extremely resistant to heat and chemicals.
Spore formation occurs in the medically important gram-positive rods (Bacillus and Clostridium) when nutrients such as carbon and nitrogen are depleted. The spore is remarkably resistant to heat, dehydration, radiation, and chemicals. This resistance is thought to be mediated by dipicolinic acid, a calcium ion chelator found only in spores. As a result of their resistance to heat, sterilization cannot be achieved by boiling. Autoclaving at 121°C for 30 minutes is required to ensure the inactivation of spores.
Endotoxin is
1 The enzyme lysozyme present in human tears, mucus, and saliva.
2 The lipopolysaccharide (LPS) of the outer layer of the cell wall of gram negative bacteria.
3 Toxin released by Clostridia.
4 Always freely released from bacteria.
The lipopolysaccharide (LPS) of the outer layer of the cell wall of gram negative bacteria.
The LPS of the outer layer of the cell wall of gram negative bacteria is called endotoxin. It is an integral part of the cell wall and causes many features of disease, such as fever and shock. The toxic effect is caused by 1 of its 3 distinct units, lipid A. LPS is also composed of a core polysaccharide of 5 sugars and an outer polysaccharide consisting of up to 25 repeating units of 3 to 5 sugars. The outer polysaccharide is the somatic or O antigen of gram negative bacteria.
Mycobacteria are called acid-fast bacilli because
1 They have unusual cell walls and they resist decolorization with acid alcohol after being stained with carbol-fuchsin
2 They lack endotoxins
3 They have thick walls
4 They have capsules
They have unusual cell walls and they resist decolorization with acid alcohol after being stained with carbol-fuchsin
Mycobacteria have a high concentration of cell wall lipids called mycolic acids. The high mycolic acid content makes these bacteria resistant to decolorization with acid alcohol after being stained with carbol-fuchsin, and hence these bacteria are said to be acid fast.
Which of the following events is most likely the effect of bacterial conjugation?
1 A gene encoding resistance to chloramphenicol in the Escherichia coli chromosome appears in the genome of a virulent bacteriophage that has infected E.coli.
2 An encapsulated strain of Streptococcus pneumoniae acquires the gene for capsule formation from an extract of another encapsulated strain.
3 A strain of Corynebacterium diphtheriae produces a toxin encoded by a prophage.
4 A strain of Pseudomonas aeruginosa produces β-lactamase encoded by a plasmid identical to a plasmid of another gram negative organism.
A strain of Pseudomonas aeruginosa produces β-lactamase encoded by a plasmid identical to a plasmid of another gram negative organism.
Conjugation is the mating of two bacterial cells during which DNA is transferred from the donor to the recipient cell.
Transduction is defined as
1 Transfer of cell DNA by means of a bacterial virus
2 Mating of two bacterial cells
3 Release of DNA by bacterial cells
4 Transfer of cell DNA by means of a plasmid
Transfer of cell DNA by means of a bacterial virus
Transduction is the transfer of cell DNA by means of a viral infection of a bacterial cell. During viral growth within the cell, a piece of bacterial DNA is incorporated into the virus particle and is carried into the recipient cell at the time of infection.
Which of the following media are considered to be most useful for the cultivation of fastidious pathogens?
1 Chocolate agar
2 MacConkey agar
3 Colistin-nalidixic acid agar
4 Eosin methylene blue agar
5 Thioglycollate broth
Chocolate agar
Chocolate agar is a highly enriched medium composed of heated sheep blood in which the red cells have lysed due to gentle heating, spilling their nutritious contents into the basal medium. This agar is normally incubated in a carbon dioxide atmosphere to further enhance the growth of fastidious pathogens. MacConkey agar and Eosin methylene blue are designed only for the isolation of enteric, gram-negative rods. Colistin-nalidixic acid agar is an inhibitory medium that prevents the growth of gram-negative organisms and allows gram-positive organisms to grow. Thioglycollate is a broth medium designed to encourage the growth of anaerobic organisms.
Gram negative rods are often capable of producing beta-lactamases to facilitate their survival in the presence of therapy. The beta-lactamases that are produced are often stored in the bacterial cell
1 In the teichoic acid moiety of the cell wall
2 In the protein components of the phospholipid membrane
3 In the cytoplasm of the cell
4 In the periplasmic space between the cell wall and the membrane
5 In the transposons of the cell
In the periplasmic space between the cell wall and the membrane
The periplasmic space serves as a storage site for beta-lactamases and some other enzymes that are produced in the cell. Therefore, any beta-lactam antibiotic attempting to penetrate the cell wall will be inactivated by the beta-lactamase. Teichoic acid is found in Gram positive organisms and is not involved in storage. Protein moieties of membranes are associated with membrane transport, not storage. The cytoplasm is the site of production of beta-lactamases by plasmids. Transposons are genetic elements that may, in fact, contribute to production of beta-lactamases but not storage.
After studying an isolate in the laboratory, it was determined that the organism actually grows well at 4-8° C. Under these conditions, most pathogens are unable to multiply, although a few, like Yersinia enterocolitica, do. Organisms that grow under these conditions are called
1 Psychrophiles
2 Mesophiles
3 Capnophile
4 Thermophile
Psychrophiles
A psychrophile grows best at 4-20° C, a mesophile grows best at 20-40° C, and a thermophile grows best at 40-90° C. A capnophile refers to an organism that requires carbon dioxide for survival. Most bacteria, especially bacterial pathogens, are mesophiles. Routine laboratory incubators should be set at 35° C to accommodate these pathogens. Unfortunately, some mesophiles may survive very well at refrigerator temperatures and grow slowly. Both Staphylococcus aureus and Salmonella spp. can survive in refrigerated foods and produce toxins that are responsible for food “poisoning”.
In a private practice office in a rural area, you must make your own broth in order to culture a specimen from a patient that would normally be sent to a local laboratory. In the process of making the medium, you discover that the portion of the label regarding pH of the medium has been torn off and the information is unavailable. Knowing the growth characteristics of most bacterial pathogens, the pH you would most likely use for your medium is
1 5.1-6.3
2 6.8-7.2
3 7.5-7.8
4 7.9-8.3
5 8.5-8.8
6.8-7.2
The optimum pH for the growth of most bacteria isolated from humans is 6.8-7.2. Growth is substantially reduced at pH levels above and below this level. In fact, as bacteria grow in the laboratory, one of the factors that limits their growth is the increasing acidity created by normal metabolic processes. Enteric bacteria can produce acids that lower the pH of the broth in which they are growing to pH 4 and lower.
Chocolate agar and 5% sheep blood agar are examples of
1 Differential media
2 Selective media
3 Hypertonic media
4 Enriched media
5 One-purpose media
Enriched media
Chocolate agar and 5% sheep blood agar (SBA) are both made from a basal medium enriched with sheep blood. Chocolate agar is prepared by heating SBA prior to preparation of the plates. By heating (not boiling), the red cells lyse, releasing their hemoglobin-containing contents and the enrichments found within the red cells. SBA is prepared by adding the appropriate amount of sheep blood to autoclaved basal medium that has been cooled to about 50° C. The red cells are not destroyed at this temperature and they retain their bright red color, thus imparting a red color to SBA. Chocolate agar, on the other hand, is brown in color, thus its name as “chocolate”. Chocolate agar is more enriched than SBA. In fact, some fastidious organisms will grow on chocolate agar but not on SBA. Both media are usually incubated in a carbon dioxide atmosphere.
Smooth strains (S) of Streptococcus pneumoniae are encapsulated and are pathogenic. Rough strains (R) are not encapsulated and are generally not pathogenic. When mice are injected with live S strains they die; when injected with live R strains, the mice survive. Mice also survive when injected with dead S strains. Interestingly, when **dead S strains and live R strains are mixed together **and then injected into mice, the mice die and colonies of S and R strains can be isolated from the dead mice.
What is the most likely explanation for these laboratory results?
1 Transportation
2 Transformation
3 Conjugation
4 Transduction
5 Transposition
Transformation
In 1928, an English bacteriologist named Frederick Griffith published the results of the experiment described above. While the results were curious and unusual in 1928, this experiment became a classic example of the genetic event now known as transformation. In transformation, soluble DNA from a donor cell (in this case, the dead S strain) is taken up by a recipient cell of the same species but a different genotype (in this case, the R strain). The DNA from the donor recombines with the DNA of the recipient resulting in the expression of genetic characteristics of the donor (the ability to manufacture capsular material).
Conjugation and transduction are also important mechanisms of DNA transfer, but soluble DNA is not involved in these processes.
Transportation and transposition are unrelated to the genetic events described above.
The toxin of Corynebacterium diphtheriae is responsible for the vaccine-preventable childhood illness diphtheria. Toxin production in this organism is mediated by chromosomal genes that originated from a bacteriophage. When incorporated into the DNA of a host cell, bacteriophage DNA is called a prophage. Organisms that contain the prophage produce the toxin and cause diphtheria, while those that do not contain the prophage are probably nonpathogenic.
This mechanism of DNA transfer from one cell to another by way of a bacteriophage is called
1 Transduction
2 Transformation
3 Conjugation
4 Transfection
5 Recombination
Transduction
Transduction is the transfer of a fragment of donor chromosome to a recipient cell by a temperate bacteriophage produced in the donor cell. The recipient may, by recombination, exchange the transduced gene for its own corresponding gene, eliminating the latter. The other two types of genetic transfer, transformation and conjugation, do not involve bacteriophages. Transfection and recombination are not involved in the transfer of DNA between bacterial cells.
Prokaryotic cytoplasm consists of
1 Mitochondria
2 Golgi bodies
3 70S ribosomes
4 Endoplasmic reticulum
70S ribosomes
Prokaryotic cytoplasm consists of 70S ribosomes.
Mitochondria, golgibodies, and endoplasmic reticulum are part of eukaryotic cytoplasmic structures.
Protein synthesis in prokaryotes, as well as eukaryotes, takes place on ribosomes that are complex of protein and ribonucleic acid. However, eukaryotic ribosomes are larger and heavier (80S ribosome) than prokaryotic ribosomes (70S ribosomes).
Gram positive bacterial cell wall is composed of
1 Peptidoglycan and outer membrane only
2 Peptidoglycan, teichoic acids and lipoteichoic acid
3 Phospholipid membrane and teichoic acids
4 Thin layer of peptidoglycan only
5 Lipids and proteins only
Peptidoglycan, teichoic acids and lipoteichoic acid
Gram positive bacterial cell wall comprises multiple layers of cross-linked peptidoglycan, teichoic acids anchored to the peptidoglycan and lipoteichoic acid anchored to the plasma membrane. Teichoic acids are water soluble polymers of polyol phosphates and are important factors in virulence. Gram-positive cell walls usually lack lipids and proteins with few exceptions. Long-chain fatty acids are part of cell wall of Corynebacterium diptheriae, Mycobacterium tuberculosis, and Nocardia asteroides.
Gram negative bacterial cell wall is made up of two layers. Inner membrane is made up of thin layer of peptidoglycan, and outer membrane consists of proteins, phospholipids, and lipopolysaccharide.
Turbidimetric density measurement for bacterial cell concentration involves
1 Serial dilution followed by colony forming units on an agar plate
2 Viable cell count
3 Nonviable cell count
4 A and C
5 B and C
B and C
Cell concentration measurement by viable cell count involves serial dilution, followed by determination of colony forming units on an agar surface. This method is used in determining bacterial cell count in urine cultures.
Turbidimetric density measurement for bacterial cell concentration includes viable cell count and nonviable cell count. This method is used to prepare a standard inoculum for antimicrobial susceptibility testing.
The differential growth media
1 Is composed of compounds that select the growth of one type of bacteria over other
2 Contain nutrients and pH indicators to allow visual distinction of bacterial growth
3 Is a type of enrichment media
4 A and C
5 B and C
B and C
Enrichment medium is a growth medium that contains added growth factors like vitamins and blood.
Selective growth medium is a type of enrichment medium that contains additives that select the growth of one type of bacteria and inhibit others.
The differential growth media contains a combination of nutrients and pH indicators to visually differentiate bacteria (like giving a distinctive color) that grow on it.
In the accompanying diagram of a bacterial cell envelope, identify the overall structure marked as “2.”
1 Lipoprotein
2 Outer protein coat
3 Peptidoglycan
4 Inner cell membrane
5 Capsule
Lipoprotein
Structure “2” indicates the lipoproteins, which **function to bridge between the outer cell membrane and the peptidoglycan component of gram-negative bacterial cell walls. **
The capsule is a region of material that extends beyond the outer protein coat of most bacteria and helps them adhere to eukaryotic cell surfaces. Bacterial capsules often contribute directly to the pathogenicity of the organism.
The inner cell membrane is a lipid bilayer, which *surrounds and contains the overall cellular cytosol. *
Peptidoglycan is a major structural component of the bacterial cell wall and is independent of the membrane.
The **outer protein coat **refers to the structure found at or near the overall surface of the cell (a capsule is often seen extending beyond this feature).
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “1.”
1 Nucleoid
2 Peptidoglycan
3 Outer protein coat
4 Inner cell membrane
5 Polyribosomes
Peptidoglycan
Structure “1” is the peptidoglycan layer of gram-negative bacterial cell walls. This layer is surrounded by the periplasmic gel and is attached to the outer membrane by lipoproteins.
The inner cell membrane surrounds and contains the bacterial cytosol. Polyribosomes are units within the cytosol, which translate mRNA into proteins. The outer protein coat refers to the structure found at or near the overall surface of the cell (a capsule is often seen extending beyond this feature). Nucleoid refers to the bacterial DNA and associated proteins, which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “5”
1 Nucleoid
2 Peptidoglycan
3 Outer protein coat
4 Inner cell membrane
5 Polyribosomes
Inner cell membrane
Arrow “5”, points to the inner cell membrane which surrounds and contains the bacterial cytosol.
The outer protein coat is the structure found at or near the overall surface of the cell. A capsule is often seen extending beyond this feature and contributes to bacterial pathogenicity and host cell trophism. Peptidoglycan is a major component of the bacterial cell wall, particularly in gram positive species. These complex carbohydrate polymers provide structural integrity to the cell and are a major factor in the Gram stain reaction. Polyribosomes are units within the cytosol which translate mRNA into proteins. Nucleoid, refers to the bacterial DNA and associated proteins which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “4”
1 Nucleoid
2 Peptidoglycan
3 Outer cell membrane
4 Inner cell membrane
5 Polyribosomes
Outer cell membrane
Arrow “4”, points to the outer cell membrane of the gram-negative bacterial cell envelope. The outer leaflet of this membrane is made up of LPS (lipopolysaccharide) which is also called endotoxin and contributes to gram-negative bacterial pathology. Peptidoglycans are complex carbohydrate polymers which provide structural integrity to the cell wall and are a major factor in the Gram stain reaction. Gram-negative cells have a relatively thin cell wall which contains a compact layer peptidoglycan. The inner cell membrane surrounds and contains the bacterial cytosol. Polyribosomes are units within the cytosol which translate mRNA into proteins. Nucleoid refers to the bacterial DNA and associated proteins which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
Identify the bacterial classification that applies to a cell with the type of envelope shown in the attached image.
1 Gram-negative
2 Spheroplast
3 Mycoplasma
4 Gram-positive
5 Protoplast
Gram-positive
The gram-positive bacterial cell envelope diagramed in this illustration contains a single inner cell membrane and a very substantial cell wall structure. This wall is anchored to the membrane and displays numerous complex layers. This represents the peptidoglycan layers characteristic of these cells.
**Gram-negative **cells lack such a thick cell wall and have both an inner and outer cell membrane.
Mycoplasma lack a cell wall altogether, as do protoplasts and spheroplasts, which are simply gram-positive or gram-negative cells that have had the cell wall removed artificially.
In the accompanying diagram of a bacterial cell envelope, identify the overall structure marked as “2”.
1 Cell wall
2 Outer protein coat
3 Peptidoglycan
4 Inner cell membrane
5 Capsule
Cell wall
Structure “2” is the cell wall which is made up of several layers of complex carbohydrates and associated proteins. This structure is very thick in many species of bacteria and provides the basis for the gram reaction.
The capsule is a region of material which extends beyond the outer protein coat of most bacteria and help them adhere to eukaryotic cell surfaces.
Bacterial capsules often contribute directly to the pathogenicity of an organism.
The inner cell membrane is a lipid bilayer which surrounds and contains the cytosol.
**Peptidoglycan is a major structural component of the bacterial cell wall and is independent of the membrane. ** NOTE: Some sources say its attached to the outer membrane via lipoproteins, it’s composed of alternatine NAG and NAM subunits.
The outer protein coat refers to the structure found at or near the overall surface of the cell (a capsule is often seen extending beyond this feature).
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “1.”
1 Nucleoid
2 Peptidoglycan
3 Outer protein coat
4 Inner cell membrane
5 Ribosomes
Inner cell membrane
Structure “1” is the inner cell membrane that surrounds and contains the bacterial cytosol. Ribosomes are units within the cytosol, which translate mRNA into proteins. The outer protein coat refers to the structure found at or near the overall surface of the cell (a capsule is often seen extending beyond this feature). Peptidoglycan is a major structural component of the bacterial cell wall and is independent of the membrane. Nucleoid refers to the bacterial DNA and associated proteins, which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “5”.
1 Nucleoid
2 Peptidoglycan
3 Outer protein coat
4 Inner cell membrane
5 Polyribosomes
Outer protein coat
Arrow “5”, points to the outer protein coat which is the structure found at or near the overall surface of the cell. A capsule is often seen extending beyond this feature and contributes to bacterial pathogenicity and host cell trophism. Peptidoglycan is a major component of the bacterial cell wall, particularly in gram positive species. These complex carbohydrate polymers provide structural integrity to the cell and are a major factor in the Gram stain reaction. The inner cell membrane surrounds and contains the bacterial cytosol. Polyribosomes are units within the cytosol which translate mRNA into proteins. Nucleoid, refers to the bacterial DNA and associated proteins which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
In the accompanying diagram of a bacterial cell envelope, identify the structure marked “4.”
1 Nucleoid
2 Peptidoglycan
3 Outer protein coat
4 Inner cell membrane
5 Ribosomes
Peptidoglycan
Arrow “4” points to the peptidoglycan layers of the bacterial cell wall. These complex carbohydrate polymers provide structural integrity to the cell and are a major factor in the Gram stain reaction. Gram positive cells have a thick cell wall, which contains high levels of peptidoglycan. The inner cell membrane surrounds and contains the bacterial cytosol. Ribosomes are units within the cytosol, which translate mRNA into proteins. The outer protein coat refers to the structure found at or near the overall surface of the cell (a capsule is often seen extending beyond this feature). Nucleoid refers to the bacterial DNA and associated proteins, which appear within discreet areas of the cytosol. Unlike eukaryotic cell nuclei, the nucleoid is not membrane bound.
