Bacterial Cell Envelope Structures

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Questions and Answers

What is the main function of flagella in bacterial cells?

Attachment to surfaces

Horizontal gene transfer

Cell movement (correct)

Protection against antibiotics

What is the outermost region of a flagellum composed of?

Hook protein subunits

Flagellin protein subunits (correct)

Pili proteins

Basal body proteins

What is the function of the hook in a flagellum?

To connect the filament to the basal body (correct)

To sense the environment

To generate movement through rotation

To anchor the flagellum to the cell wall

What is the function of the basal body in a flagellum?

To generate movement through rotation Signup and view all the answers

What is the term for the movement of a bacterium towards or away from a particular stimulus?

Taxis Signup and view all the answers

What is the composition of the filament in a flagellum?

98% flagellin protein Signup and view all the answers

What is the function of flagella in gram-negative bacteria?

To move towards or away from stimuli Signup and view all the answers

What is the main function of pili in bacteria?

To facilitate bacterial conjugation Signup and view all the answers

What is the shape of a bacterium classified as a spirillum?

Spiral Signup and view all the answers

What is the speed of rotation of the basal body in a flagellum?

300 revolutions per second Signup and view all the answers

What is the arrangement of cocci after cell division?

Long chains Signup and view all the answers

What is the first step in the process of binary fission?

DNA molecule replication Signup and view all the answers

What is the result of the cell membrane pinching inward during binary fission?

The cell divides into two identical daughter cells Signup and view all the answers

What is the primary function of flagella in bacteria?

To respond to various stimuli Signup and view all the answers

What is the characteristic of bacterial cells that remain together in groups or clusters after cell division?

They have a particular arrangement of cells Signup and view all the answers

What type of taxis is a response to a chemical gradient of attractant or repellent molecules?

Chemotaxis Signup and view all the answers

Which of the following is a characteristic of pili?

Short, fine appendages surrounding the cell Signup and view all the answers

What is the term for the arrangement of flagella at each end of the bacterial cell?

Amphitrichous Signup and view all the answers

What is the function of axial filaments in spirochetes?

To facilitate motility Signup and view all the answers

What is the composition of the shaft of fimbriae and pili?

A protein called pilin Signup and view all the answers

What is the role of fimbriae and pili in bacteria?

To adhere to solid surfaces Signup and view all the answers

Which type of bacteria typically lacks fimbriae and pili?

Gram-positive bacteria Signup and view all the answers

Study Notes

External Structures of Bacterial Cells

Extend beyond the cell envelope in bacteria
Examples: Fimbriae, Flagella, Pili
Functions:
- Protection
- Attachment to surfaces
- Horizontal gene transfer
- Cell Movement

Flagella

Locomotory organelles (Move cell by propeller-like action)
Embedded in cell membrane, project as strands
Composed of flagellin (protein) subunits
Found in bacteria, fungi, algae, and animals
Functions:
- Movement
- Sensation
- Response to stimuli (chemotaxis, phototaxis, osmotaxis, aerotaxis, thermotaxis)

Ultrastructure of Flagella

3 parts:
1. Filament: long outermost region, constant in diameter, composed of flagellin arranged in helix around a hollow core
2. Hook: slightly wider, composed of different protein, connects filament to basal body
3. Basal body: anchors flagellum to cell wall and plasma membrane, composed of central rod inserted into rings (2 pairs in Gram-negative bacteria)

Patterns of Flagella Distribution

Monotrichous: single polar flagella
Lophotrichous: tuft of flagella at one end of cell
Amphitrichous: flagella at each end of cell
Peritrichous: flagella distributed over entire cell

Axial Filaments (Endoflagella)

Bundles of fibrils, arise at ends of cell, spiral around cell
Anchored at one end of spirochete, structure similar to flagella

Pili and Fimbriae

Thin, protein tubes originating from cytoplasmic membrane
Found in virtually all Gram-negative bacteria, but not in many Gram-positive bacteria
Fimbriae:
- Short, fine appendages surrounding cell
- Help bacteria adhere to solid surfaces
- Major virulence factor
Pili (sex pili or F pili):
- Similar in structure to fimbriae, but longer and fewer in number
- Involved in bacterial conjugation

Bacterial Morphology

Cocci: spherical bacterium
Rod or bacilli: cylindrical shape
Spirilla: rods that twist into spiral shapes
Cell arrangements:
- Long chains (e.g. Streptococcus)
- Three-dimensional cubes (Sarcina)
- Grapelike clusters (Staphylococcus)

Bacterial Growth

Binary fission:
- Begins with single DNA molecule replication and both copies attaching to cell membrane
- Cell membrane grows between two DNA molecules, then pinches inward
- Cell wall forms between two DNA molecules, dividing original cell into two identical daughter cells

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Description

Learn about the external structures of bacterial cells, including fimbriae, flagella, and pili, and their functions in protection, attachment, gene transfer, and cell movement.