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Questions and Answers
What is the length range of a bacterial chromosome?
What is the length range of a bacterial chromosome?
Where does prokaryotic protein synthesis occur?
Where does prokaryotic protein synthesis occur?
Which of the following is a common carbon storage polymer in prokaryotic cells?
Which of the following is a common carbon storage polymer in prokaryotic cells?
What type of mRNA is found in bacteria?
What type of mRNA is found in bacteria?
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What are the main components of the large ribosomal subunit (50S) in prokaryotic cells?
What are the main components of the large ribosomal subunit (50S) in prokaryotic cells?
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What is the role of tRNA in protein synthesis?
What is the role of tRNA in protein synthesis?
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Which of the following structures is not involved in bacterial motility?
Which of the following structures is not involved in bacterial motility?
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What is a characteristic function of pili and fimbriae in bacteria?
What is a characteristic function of pili and fimbriae in bacteria?
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Which genetic structure can integrate into the bacterial chromosome and facilitate extensive genetic recombination?
Which genetic structure can integrate into the bacterial chromosome and facilitate extensive genetic recombination?
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What is the main advantage of conjugation for bacteria?
What is the main advantage of conjugation for bacteria?
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Which of the following is a storage product used by bacteria?
Which of the following is a storage product used by bacteria?
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What is the role of the Hfr strain in bacterial recombination?
What is the role of the Hfr strain in bacterial recombination?
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Which process allows donor cells to transfer part of their chromosome to recipient cells?
Which process allows donor cells to transfer part of their chromosome to recipient cells?
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What is the molecular weight of the protein composing fimbriae?
What is the molecular weight of the protein composing fimbriae?
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What is the general term for capsules and slime layers?
What is the general term for capsules and slime layers?
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Which component in a capsule is likely to be immunogenic?
Which component in a capsule is likely to be immunogenic?
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Which bacteria's capsule contains N-acetylneuraminic acid found on host cells?
Which bacteria's capsule contains N-acetylneuraminic acid found on host cells?
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Which of these statements is true about bacterial capsules?
Which of these statements is true about bacterial capsules?
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How do capsules benefit bacteria in host environments?
How do capsules benefit bacteria in host environments?
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What type of capsule attachment describes a slime layer?
What type of capsule attachment describes a slime layer?
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Study Notes
Pili and Fimbriae
- Fine hair-like filaments on the surface of many Gram-negative bacteria, not involved in motility
- Fimbriae composed of 20 kDa protein, while pili are generally longer
- Both involved in attachment of bacteria to host cells by binding to lectins on cell surfaces (e.g., sugar-binding proteins), giving tissue specificity
Sex Pili and Conjugation
- Used by conjugative plasmids to transfer copies of themselves to a new host (F+ and F- strains)
- Sometimes other genetic material is mobilized during conjugation
- After conjugation, the previously negative cell has a copy of the plasmid and can pass it on to another cell, efficiently transferring antimicrobial resistance
- The F plasmid of E. coli can also mobilize the chromosome to be transferred through cell-to-cell contact, leading to extensive genetic recombination (Hfr strain)
Cytoplasmic Components
- Glycogen is used as a storage product, a starch-like polymer of glucose subunits
- Smaller than PHB granules
- Genetic elements:
- Plasmids: circular and autonomously replicating
- Transposons: "jumping" genetic cassettes
Pili and Fimbriae
- Bacteria within a human host constantly lose and reform fimbriae, which are fragile structures
- Fimbriae aid in evasion of the immune system
- Bacteria (e.g., N. gonorrhoeae) can change the antigenic structure of their pili/fimbriae
Bacterial Conjugation and Recombination
- Donor cell attaches to a recipient cell with its pilus, drawing the cells together
- One strand of plasmid DNA transfers to the recipient, which synthesizes a complementary strand to become an F+ cell
- The donor synthesizes a complementary strand, restoring its complete plasmid
Hfr-specific Recombination
- Hfr cells contain genes that allow them to transfer some or all of their chromosome to another cell
- Conjugation tube connects Hfr cell to normal cell, and a copy of Hfr chromosome begins to move to the recipient cell
- Homologous sections of chromosome synapse, and cells separate
- Section of Hfr chromosome integrates into recipient chromosome by crossing over
Capsules and Slime Layers
- Consist of polysaccharide or sometimes protein, with a general term of glycocalyx
- Capsule: a thick, viscous gel outside and attached to the cell wall
- Slime: a capsule loosely attached to the cell wall and easily washed off
- Both are hydrophilic, appearing as halos around cells in a Gram stain
Composition of Capsules
- Mainly acidic polysaccharide, with acidic groups being glucuronic acid or phosphate
- Most are immunogenic, stimulating host antibody response
- Exceptions:
- Group B meningococci: capsule contains N-acetylneuraminic acid found on host cells
- Hyaluronic acid of S. pyogenes capsule can lead to host cell damage because it is found on host cells
Capsules and Slime Layers
- Variable thickness: up to 10µm thick in Klebsiella spp. and Streptococcus pneumoniae
- Microcapsule of E. coli and Salmonella spp. is too thin to be seen on a light microscope and is detected by antisera
- Capsule not always expressed under lab conditions
Advantage to Bacteria
- Protect cells from desiccation and toxic material
- Attachment to host cells
- Soluble material released into solution blocks opsonizing antibodies
- Resist complement alternative pathway
- Resist phagocytosis by neutrophils
Bacterial Chromosomes
- Single circular chromosome of double-stranded DNA, called a nucleoid
- 300 to 400 µm in length and supercoiled like a rubber band
- Genes arranged linearly along the chromosome
- Size range from 600 to 9500kb (9.5Mb)
- Composed of nucleotides: adenine, guanine, cytosine, and thymine (uracil in RNA)
Prokaryotic Protein Synthesis
- Protein translation via tRNA and mRNA
- 30S subunit initiation complex + 50S subunit
- Location of protein-encoding genes determined by looking for Open Reading Frames (ORF):
- Start codon
- Codon (triple sequences)
- Stop codon
Prokaryotic Protein Synthesis
- Takes place on ribosomes, 70S (30S+50S), in the cytoplasm
- 30S contains 16S RNA (small subunit)
- 50S contains 23S RNA (large subunit)
- Up to 10,000 ribosomes per cell
- Up to 35% of dry weight is RNA in growing cells
- Bacterial mRNA is polycistronic (multiple genes on one mRNA), which can be translated by several ribosomes simultaneously
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Description
Learn about the structure and function of pili and fimbriae in Gram negative bacteria, including their role in attachment and conjugation. Understand the difference between pili and fimbriae and their importance in bacterial interactions.
