Bacteria Structure

Question 1

What types of cell are bacteria?

Answer 1

• prokaryotic cells

Question 2

What are prokaryotic cells?

Answer 2

• cells have simple structure and lack a nucleus an membrane- bound organelles i.e., specialized structures surrounded by a membrane

Question 3

What type of organism are bacteria and what is their size?

Answer 3

• unicellular organisms
• variable length (0.1-5 um)

Question 4

Bacterial morphology - what are the two main shapes?

Answer 4

• cocci (round-shaped)
• bacilli (rod-shaped)

Question 5

What causes the different bacteria shapes?

Answer 5

• the cell wall

Question 6

What components may up a bacterial cell?

Answer 6

• granules
• capsule
• cell wall
• cytoplasmic membrane
• flagella
• single coiled circular chromosome
• fimbriae
• cytoplasm
• ribosomes

Question 7

What is the cytoplasm?

Answer 7

• jelly-like aqueous solution (80% water)

Question 8

What does the cytoplasm contain?

Answer 8

• one nucleoid
• one or several plasmids
• many ribosomes
• granules
• various types of solutes

Question 9

What is a nucleoid?

Answer 9

• The bacterial chromosome is one large circular molecule that is largely composed of DNA (60%) with small amounts of RNA and proteins that regulate transcription (transcription factors) or carry out dynamic spatial organisation of the nucleic acid (nucleoid-associated proteins, NAPs)

Question 10

What is a plasmid?

Answer 10

• a large circular molecule of double stranded DNA that can replicate autonomously from the chromosome

Question 11

What are granules?

Answer 11

• concentrated deposits of various nutrients or wate such as starch or glycogen

Question 12

What are the various types of solutes found in the cytoplasm?

Answer 12

• macromolecules such as proteins (enzymes) and nucleic acids (DNA and RNA)
• small molecules that are energy sources, precursors of macromolecules, metabolites or vitamins
• inorganic ions required for enzymatic activity

Question 13

What is the structure if the nucleoid?

Answer 13

• 1000 times longer than a bacterial cell and extensively folded to form a dense body that can be visualised by electron microscopy

Question 14

Proteins encoded by plasmid genes are not essential under normal conditions but are important in what?

Answer 14

• important to cause disease (virulence factors) or to survive to antibiotics and heavy metals (resistance genes)

Question 15

What are ribosomes the site if?

Answer 15

• these organelles are the site of protein synthesis

Question 16

How is ribosome size measured?

Answer 16

• their size is measured by the Svendberg, which is a measure of sedimentation rate by centrifugation

Question 17

What is the difference in ribosome size in eukaryotic cell and bacteria?

Answer 17

• bacteria = 70S
• eukaryotic cells = 80S

Question 18

Ribosomes consist of two subunits what are they?

Answer 18

• A small subunit (30S) that reads the mRNA
• A large subunit (50S) that assembles amino acids into the peptide chain

Question 19

What is the cytoplasmic membrane?

Answer 19

• flexible structure composed of a phospholipid bilayer and proteins (e.g., membrane receptors, transport protein and enzymes)

Question 20

What are the three main functions of the cytoplasmic membrane?

Answer 20

• permeability barrier containing a variety of different transport systems that selectively mediate passage of substances into and out of the cell (selective permeability)
• it plays a key role in bacterial respiration since adenosine 5’ - triphosphate (ATP) is synthesized using electron transport systems located on the membrane
• anchor for external structures such as flagella and fimbriae

Question 21

Describe the phospholipid bilayer:

Answer 21

• Each phospholipid molecule has one head that ‘likes’ water (hydrophilic) and two tails that ‘hate’ water (hydrophobic)
• The inner double layer of tails forms a barrier to most hydrophilic molecules
• Only small molecules (H2O, O2 and CO2) and some lipid-soluble compounds can enter the bacterial cell by passive diffusion

Question 22

What is the cell wall or envelope?

Answer 22

• ridged structure that protects the cell from osmotic lysis and provided mechanical protection

Question 23

What is the main component of the cell wall or envelop?

Answer 23

• peptidoglycan, a polymer of alternating polysaccharide subunits (NAG and NAM) cross-linked by short chains of peptides

Question 24

What is the structure of gram positive cell wall?

Answer 24

• gram-positive bacteria have a thick peptidoglycan layer and tectonic acids

Question 25

What is the structure of a gram-neagtive cell wall?

Answer 25

- Gram-negative bacteria have a thin layer of peptidoglycan surrounded by an outer membrane, which is similar to the cytoplasmic membrane but the outer surface contains lipopolysaccharides (LPS) and open channels (porins) that allow diffusion of small hydrophilic molecules into the periplasmic space

Question 26

The LPS structure has 3 regions what are these?

Answer 26

- An external polysaccharide chain (somatic O antigen used for serotyping) - A core oligosaccharide that contains unusual sugar residues (e.g., heptose) - An internal lipid region (lipid A) responsible for the toxicity if Gram-negative bacteria (endotoxin)

Question 27

What are two types of atypical bacteria?

Answer 27

1. mycoplasma 2. mycobacteria

Question 28

Mycoplasma do not have a cell wall which means what?

Answer 28

- they cant be visualised by Gram stain and are resistant to antimicrobials targeting the cell wall such as penicillin

Question 29

What are mycobacteria?

Answer 29

- Gram-positive bacteria with a wax-like outer membrane composed of mycolic acids that prevent uptake of the dyes used in the Gram stain. Their detection by microscopy requires another method (Ziehl-Neelsen staining) based on the use of carbol fuchsin, a dye that binds to lipids.

Question 30

What is a capsule or glycocalyx?

Answer 30

- a polysaccharide layer outside of the cell wall, which confers mucoid appearance to bacterial colonies

Question 31

What do capsules mediate?

Answer 31

- mediate attachment to particular surfaces that protect bacteria from phagocytosis by protozoa or white blood cells (phagocytes) and from antimicrobial agents

Question 32

Why are surface components important in bacterial ecology?

Answer 32

- they mediate contact of the bacterial cell with the surrounding environment

Question 33

What are the three main types of surface components?

Answer 33

- flagella - fimbriae - endospores

Question 34

What are flagella?

Answer 34

- (3-20 um long, 0.01 um diameter) are filamentous protein structures that allow the bacterial cell to move/swim and have antigenic properties (H antigen of Salmonella)

Question 35

What are fimbriae?

Answer 35

- (0.5 um long, 10 nm diameter) are shorter and stiffer than flagella and are usually involved in adherence to surfaces (virulence factors)

Question 36

Bacteria can have one or multiple flagella that can be arranged in 4 different ways - what are these?

Answer 36

-Monotrichous - Lophotrichous - Amphitrichous - Peritrichous

Question 37

What is monotrichous?

Answer 37

- bacteria have a single flagellum

Question 38

What is Lophotrichous?

Answer 38

- bacteria have multiple flagella located at the same end on the bacterial surface

Question 39

What is Amphitrichous?

Answer 39

- bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time).

Question 40

What are peritrichous?

Answer 40

- bacteria have flagella projecting in all directions

Question 41

Name 4 example of flagella in veterinary pathogens:

Answer 41

1. Vibrio Cholera 2. Pseudomonas 3. salmonella 4. campylobacter

Question 42

Some bacteria produce endospores - what are they?

Answer 42

- dormant highly resistant bodies that ensure survival during adverse environmental conditions (heat, dessication and toxic chemicals)

Question 43

Spore structure - what does the core contain?

Answer 43

* The core contains genomic DNA and is surrounded by the inner membrane and a ‘normal’ peptidoglycan layer (germ cell wall) followed by: - A thick but ‘looser’ peptidoglycan layer that confers resistance to heat and desiccation (cortex) surrounded by the outer membrane - A keratin-like protein coat that serves as a permeability barrier (coat) - The outermost layer (exosporium) has variable composition and is not present in all spore-forming bacteria

Question 44

What can be used for classification of endospore-forming species?

Answer 44

- Shape, size and position within the mother cell

Question 45

What are the non-bulging classes of endospores?

Answer 45

- oval central - spherical central - oval sub terminal

Question 46

What are the bulging classes of endospore?

Answer 46

- oval sub terminal - oval terminal - spherical terminal - free spore (not bulging)

Question 47

What are the spore-forming bacteria of veterinary interest?

Answer 47

- Bacillus - Clostridium

Question 48

What are examples of bacillus?

Answer 48

- B anthracis - B larvae

Question 49

What are examples of clostridium?

Answer 49

- C. perfringens and C. difficile - C. tetani -C. botulinum

Question 50

What is sporulation and germination?

Answer 50

- The process leading to spore formation is called sporulation - the reverse process leading to the vegetative cycle is called germination

Question 51

How is sporulation triggered?

Answer 51

- triggered by unfavourable conditions

Question 52

Germination occurs in response to what?

Answer 52

- Germination occurs in response to specific factors such as heat, abrasion of the spore coat or environmental acidity