Chapter 4 Objectives:

• Learn the characteristics of Cells
• Prokaryotic Profiles
  • Bacteria
  • Archaea
• Learn the external structures of Prokaryotes
• The Boundrary Layer of Bacteria: The Cell Envelope
• Learn the bacterial internal structure
• Learn the Bacterial shapes, arrangements and sizes
• Classification systems in the Prokaryote
• NONtypical cell walls
• several bacterial groups lack the cell wall structure of gram-positicve or gram-negative bacteria, and some bacteria have no cell wall at all.
• the cells of Myocobacterium and Nocardia contain peptidoglycan and stain gram positive, but bulk of the cell wall is composed of unique typea of lipids.
• Resistance is the basis for the acid-fast stain used to diagnose tuberculosis and leprosy.

Note from Kevin: this video is great for showing how a bacterial flagellum moves, so thanks for putting it in. I think I should point out, however, that the main point of the video is to highlight one of the main arguments from the Intelligent Design (Creationism) community against Darwin's Theory of Evolution. Evolutionists have strong counter-arguments, whose views are not represented here (if you really want details on the evolution of flagella, see here).



PROKARYOTE VS. EUKARYOTE:


Biologist believe that the characteristics most inherent to life are: Heredity and reproduction; growth and development; metabolism (cell synthesis and release of energy; movement/irritability; cell support, protection, and storage and the capacity to transport substances into and out of a cell. Unlike Eukaryotic cells (comes from Greek word for true nucleus) which have specific organelles to perform these functions, the Prokaryotic cells (comes from Greek word for pre-nucleus) must rely on a few simpler, multipurpose cellular components.

Q: What organisms are thought to be the first cells to appear on earth?
a. bacteria
b. archae
c. fungi
A: archae


Q: Which component is not found in the cytoplasm of the majority of procaryotes?
a. capsule
b. ribosomes
c. DNA
A: capsule


Prokaryotic Profile:

A Prokaryotic cell is also known as BACTERIA (unless otherwise noted). Prokaryotic cells evolutionary history extends clear back over 3. 5 billion years. The shear thought that these cells have endured such a variety of habitats is indicative of amazing adaptability and versatility with such simple cellular structure and functions is beyond amazing. What gives these such amazing living organisms such longevity to survive billions of years? To find the answers we need to explore how the Prokaryote is structured.

• EXTERNAL STRUCTURES:
  • Flagella
  • Pili
  • Fimbriae
  • Glycocalyx
    • Capsule, slimie layer
  • CELL ENVELOPE:
    • Cell Wall
      
    • Cell Membrane

• INTERNAL STRUCTURES:
  • Cytoplasmic matrix
  • Ribosomes
  • Inclusions
  • Nucleoid/chromosome
  • Actin Cytoskeleton
  • Endospore

External Structures:

HOME PAGE ~~ TOP of PAGE

Flagella:

• Provides the power of motility or self-propulsion, which allows a cell to swim freely through an aqueous habitat
• Composed of 3 parts:
  • Filament: a long, thin, helical structure composed of a protein called flagellin. It is inserted into a curved, tubular hook
  • The hook (sheath) anchors to the cell by the basal body
    
    • The hook and filaments are free to rotate 360 degrees.
    • Eukaryotic cells only move back and forth
      
  • Basal body -- stack of rings (2 rings in Gram positive, 4 rings in Gram negative) firmly anchored to the cell well to the cell membrane
• Q: In a peritrichous arrangement of flagella, how are the flagella distributed over the organism?

a. a single flagellum at one end of the cell
b. multiple flagella attached to both ends of the cell
c. multiple flagella randomly dispersed over the cell surface
A: multiple flagella randomly dispersed over the cell surface
How does the flagellum move?
The flagellum is spun around and around by a cellular "motor." This rotor can move very quickly if there is no filament attached (6,000-17,000 rpm), but with a filament attached it generally moves at 200-100rpm. Flagella can vary in both number and arrangments according to two generalized patterns.

• The POLAR arrangement
  • In a polar arrangement the flagella re attached at one or both ends of the cell.
• The PERITRICHOUS arrangement
  • Arrangement of flagella randomly dispersed around the cell.
    

Common Flagellum arrangements:

POLAR ARRANGEMENTS:
Monotrichous – one flagella. Sperm.
Lophotrichous – small bunches arising from one end of cell.

Amphitrichous – flagella at both ends of cell. Only one side or the other is working at once.

PERITRICHOUS ARRANGEMENT:
Peritrichous - Flagella are dispersed randomly all around the cell.



Harvard has made available many short movies of bacteria moving. They are taken with fluorescence microscopy and you can really see the flagella well.






Periplasmic flaggelum or axial filament is an unusual flagella.
This is a trait shared by all spirochetes, including Treponema pallidum, the cause of syphilis. Here is a video of dark-field microscopy being used to see spirochetes moving (in this case the spirochete that causes Lyme disease):


Axial filaments in Spirochetes-An axial filament is an "internal flagella" within the periplasmic space (between cell wall and cell membrane)
-also called periplasmic flagella
-Found in ALL spirochetes
-Looks like a snake or a wiggly worm when seen in motion (look at video below)























Fimbriae: (When we are referring to fimbriae we are NOT are not speaking of the Fimbriae found in the anatomical structure of the female body)

• Fine hairlike bristles from the cell surface
• Most fimbriae contain protein
  
• Function in adhesion to other cells and surfaces --- NOT locomotion
  • Pathogen colonies can colonize and infect host tissues due to the tight adhesion between the fimbriae and pilus.
    
    • Examples of specific pathogens are Gonococcus (gonorrhea) and E. Coli
      

**Note: some authors use the term somatic pile to refer to fimbriae, but we will use pilus only to refer to a "mating" appendage

Where might fimbriae be useful?

• Slippery surfaces such as a urethra or vaginal wall
• Rocks in a fast-moving stream
• Teeth
• Toilet bowls, air conditioners, pipes
• Practically anywhere!
• Fimbriae are a form of biofilms. Biofilms are handy!
• Note: glycocalyx also involved in biofilms

Pilus: (aka sex pilus/maturation)

• Elongate, rigid tubular structure made of a protein, Pilin.
• True Pili so far have only been found on gram-negative bacteria.
• Utilized in the mating process, Conjugation (Partial DNA transfer), providing a cytoplasmic connection.
• Conjugation of gram-positive bacteria doesn't occur but involves aggregation proteins rather than pili.
• Production of pili is controlled genetically.

Another side note on pili: Plasmids are extra genetic information that is not necessary for a bacteria to live.
Bacterial cells can exchange and share these plasmids through Pili/Pilus. (conjugation)

Here Kevin outsources the explanation of the pilus and its use in bacterial conjugation:




Glycocalyx: (Matrix of polysaccharides)

• Develops as a coating just on outside cell wall of a bacteria to protect it and in some cases help it to adhere to its environment.
• Can differ between bacteria in thickness, organization and chemical composition.
  
• Gelatinous glycocalyx is called a capsule.
  • Capsules are bound more tightly and has a thicker more gummy consistency then a slime layer.
  • Streptococcus pneumoniae and Haemophilius influenzae are examples of a bacteria that uses capsules.
  • Capsules also help the bacteria escape phagocytosis (property of a white blood cell).
  • Encapsulated bacteria that mutate to nonencapsulated forms lose their pathogenicity.
    
• Irregular, diffuse layer is called the slime layer.
  • Slime layers are able to protect against dehydration and loss of nutrients.
    
• Glycocalyces are also important in the formation of biofilms.

• Biofilm builds up when bacteria gets together and basically forms a complex community, making it more difficult to kill.
  
• Sometimes the biofilm can be 100 cells thick.
• Biofilm is found on teeth, catheters and artificial heart valves.
  • You can not get rid of biofilm by washing the catheter or by using antibiotics. You actually have to replace the catheter. There is a possible solution. Chitosan--is derived from Chitin, the main component of crustacean shells. As a possible coating for medical devices.

Cell Envelope:

HOME PAGE ~~ TOP of PAGE

• Bacteria have a chemically complex external covering called the Cell Envelope, which lies just outside of the cytoplasm.
• Composed of 2 layers, the cell wall and cell membrane.
• These layers are stacked and often tightly bound into a unit.
  
• Each layer can functionally differ from the other, however, they act as a single unit to maintain the cells integrity.
  • To distinguish between the 2 layers Hans Christian Joachim Gram developed a technique to differeniate between the two fundamentally different groups of bacteria, Gram-positive and Gram-negative.
  • Gram-positive cells have thick cell walls and are primarily composed of peptidoglycans and the cell membrane.
    

Internal Structures:

HOME PAGE ~~ TOP of PAGE

Ribosomes - are complexes of RNA and protein that are found in all cells. The ribosome functions in the expression of the genetic code from nucleic acid into protein, in a process called translation.

Inclusions (Cytoplasmic) are chemical substances that may or may not be present in a cell, depending on the cell type. Inclusions are stored nutrients, secretory products, and pigment granules.

Cytoplasm - a dense, gelatinous solution and is a prominent site for many of the cell's biochemical and synthetic activities. Its major component is water (70 - 80%), which serves as a solvent for a complex mixture of nutrients including sugars, amino acids, and other organic molecules and salts.

Plasmids - These are tiny strands that exist as seperate double-stranded circles of DNA. During bacterial reproduction they are duplicated and passed on to the offspring.

Nucleoid - This is where the DNA is aggregated in a central area of the cell. It is an extremely long molecule of DNA that is tightly coiled to fit inside the cell compartment. Arranged along its length are genetic units that carry information required for bacterial maintenance and growth.

Facts and News:

HOME PAGE ~~ TOP of PAGE

WHO IS HANS CHRISTIAN JOACHIM GRAM?

• Hans Gram invented a staining technique in 1884 that made specimens more visible but also differentiated between two fundamentally different groups of bacteria.
• This is the most useful lab technique in microbiology!
• You can learn a lot about an infection in only 15 minutes.
• You must be careful and follow the steps precisely or you will get the wrong result.

For other uses of "Gram", see Gram (disambiguation).Hans Christian Joachim Gram (September 13, 1853 - November 14, 1938) was a Danish bacteriologist. He was the son of Frederik Terkel Julius Gram, a professor of jurisprudence, and Louise Christiane Roulund. Gram studied botany at the University of Copenhagen and was an assistant in botany to the zoologist Japetus Steenstrup. His plants introduced him to the basis of pharmacology and the use of the microscope. He entered medical school in 1878 and graduated in 1883. He travelled throughout Europe between 1878 and 1885. In Berlin, in 1884, he developed a method for distinguishing between two major classes of bacteria. This technique, the Gram Stain, continues to be a standard procedure in medical microbiology.
In 1891, Gram became a lecturer in pharmacology, and later that year was appointed professor at the University of Copenhagen. In 1900 he resigned his Chair in Pharmacology to become Professor of Medicine. His initial work concerned the study of Red blood cells in man. He was among the first to recognise that macrocytes were characteristic of pernicious anaemia.
After his appointment as professor of Medicine in 1900 he published four volumes of clinical lectures which became widely used in Denmark. He retired in 1923.

The Gram Stain
The work that gained him international reputation was his development of a method of staining bacteria. The stain later played a major role in classifying bacteria. Gram was a modest man, and in his initial publication he remarked "I have therefore published the method, although I am aware that as yet it is very defective and imperfect; but it is hoped that also in the hands of other investigators it will turn out to be useful."




1. Which of the following is not found in all bacterial cells?
a. cell membrane
b. a nucleotide
c. ribosomes
d. capsule

2. The major locomotor structures in bacteria are_____________.
a. flagella
b. pili
c. fimbriae
d. cilia

3. Thanks to this structure of a procaryote cell (most of the time E.coli) it is very easy to get bladder infections
a. pili
b. cell wall
c. flagella
d. fimbriae
e. none of the above

4. What is the quickest easiest way to see if a cell has a flagella?
a. an electron microscope
b. use a hanging drop slide
c. acid-fast stain
d. gram stain
e. all the above work just as fast

5. Bacterial endospores functions in
a. reproduction
b. survival
c. protein synthesis
d. storage

6. The movement of a cell in the direction of a favorable chemical stimulus is called
a. positive attraction
b. positive magnetism
c. positive chemotaxis
d. positive gravitation

7. Which of the following is true:
a. A capsule is highly organized
b. Glococalyces are the same in thickness among bacteria
c. A slime layer in not soluble and highly organized
d. Glycocalyx is connected to the cell membrane

8. A plasmid is which of the following
a. a component of blood
b. is a double-stranded DNA
c. part of a the cell wall
d. is a lipid structure of cell wall

9. Which type of bacteria have a lipopolysaccharide outer-membrane, periplasmic spaces, petidoglycan and a cell membrane?
*a. gram negative
b. gram positive

10. What are some characteristics of plasmids?
*a. They are transferred by conjugation
b. They are essential to bacterial growth
*c. They pass on traits such as drug resistance.
d. They are hard to manipulate in the laboratory.

11. Why are gram negative harder to kill?
a. The outer barrier makes them more impervious to antimicrobial chemicals like disinfectants.
b. The cell wall can interact with human tissues & contribute to disease.
c. The lipids in the outer membrane are endotoxins and can stimulate fever and shock reactions.
*d. all of the above.

12. Pili are only found on what type of organisms?
a. Spirochetes
b. Fungi
c. Encapsulated organisms
d. Gram negatives
e. Gram positives




Comprehension Questions for Chapter Four

1. What macromolecule used to build the cell wall is only found in prokaryotes?
2. Where is lipid A found?
3. What stain is used to diagnose tuberculosis and leprosy?
4. What is the cell membrane made of?
5. What is it called when the membrane folds into the cytoplasm? Are Gram-negative or Gram-positive organisms more likely to experience this?
6. Where does ATP synthesis occur in the cell?
7. What part of the cell regulates transport and assists in secretion?
8. What cell structure is important in genetic engineering due to the ease of manipulation?
9. In cells, where does protein synthesis occur?
10. What do bacterial cells draw from when outside nutrients are depleted?
11. What two genuses of bacteria produce endospores?
12. How are the bacteria arranged if they're sarcinae?
13. How are the bacteria arranged if it's streptobacilli?
14. How many chromosomes does a bacterial cell have?
15. Which cell is resistant to penicillin, a gram-positive or gram-negative?
16. Pili hae been only found on ________ bacteria: gram-positive or gram-negative?
17. What cell structure protect bacteria from phagocytes?
18. What extra structure/part is found in all spirochetes?
19. Which kind of bacteria has a thicker periplasmic space, gram-negative or gram-positive?
20. What special protein are pili made of?
21. What is the glycocalyx made of?
22. What type of bacteria contains techoic acids in the chemical composition of its cell wall?
23. What cell structure causes gram-positive bacteria to trap the primary stain more than gram-negative bacteria?
24. What is the chemical composition of gram-positive cell walls?
25. What is the chemical composition of gram-negative cell walls?
26. What do all bacterial cells have?


Comprehension Answers

1. peptidoglycan
2. in gram-negative cell walls
3. acid-fast stain
4. a phospholipids bilayer with embedded proteins
5. mesosome; gram-positive
6. cell membrane
7. cell membrane
8. plasmids
9. ribosomes
10. inclusions/granules
11. Clostridium and Bacillus
12. in groups of 8, 16, or 32
13. in chains
14. only one
15. gram-negative
16. Gram-negative. Conjugation in gram-positive bacteria involves aggregation proteins rather than sex pili.
17. the capsule
18. axial filaments
19. Gram-negative has a thick perplasmic space; gram-positive have a narrow periplasmic space.
20. pilin
21. sugars and/or proteins
22. gram-positive
23. Gram-positive bacteria have a thicker cell wall, which entraps the dye more than the thinner wall of gram-negative.
24. peptidoglycan, techoic acids, lipotechoic acid, mycolic acids, and polysaccharides
25. lipolysaccharide, lipoprotein, peptidoglycan, and porin proteins
26. Cell membrane surrounding the cytoplasm which contain ribosomes and a chromosome

Home Page~~Top of Page