Bacterial and Archaeal Cell Structures

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Questions and Answers

What role do capsules serve in bacterial cells?

They function for attachment and prevent dehydration. (correct)

They are responsible for photosynthesis.

They help in the formation of flagella.

They provide energy storage.

Which type of cell envelope configuration is common in many Archaea?

Cell wall made of pseudomurein. (correct)

An outer capsule layer.

A double phospholipid bilayer with cholesterol.

Outer membrane composed of LPS.

What characterizes a slime layer compared to a capsule?

Composed of proteins rather than polysaccharides.

Loosely attached and not excluding small particles. (correct)

More resistant to heat and cold.

Tightly organized and easily visible.

Which of the following best describes fimbriae?

Short pili facilitating attachment. Signup and view all the answers

What is a unique feature of the heat-loving Archaea Ignococcus regarding its cell envelope?

It has an outer membrane of archaeal isoprenoid lipids. Signup and view all the answers

How do conjugative pili primarily function in bacterial cells?

To facilitate DNA transfer during conjugation. Signup and view all the answers

What structural adaptations do Mycoplasmas possess?

Sterols in their cytoplasmic membranes. Signup and view all the answers

What function do pili serve aside from attachment?

Conjugation and twitching motility. Signup and view all the answers

What is the primary function of the cell wall in Bacteria and Archaea?

To protect against osmotic lysis and maintain cell shape Signup and view all the answers

Which molecule is unique to bacterial cell walls?

Peptidoglycan Signup and view all the answers

How do the cells of gram-positive bacteria differ from those of gram-negative bacteria in terms of peptidoglycan layers?

Gram-positive cells can have 15 or more layers, while gram-negative cells have 2-3 layers Signup and view all the answers

What component is common between bacteria and archaea cell membranes?

Ester-linked lipids Signup and view all the answers

In terms of lipid structure, how do archaeal membranes differ from bacterial membranes?

Archaeal membranes have a lipid monolayer Signup and view all the answers

What are the components of the ATP-binding cassette?

Binding protein, transmembrane protein, and an ATP-hydrolyzing protein Signup and view all the answers

What type of cross-links are often present in the peptidoglycan of gram-positive bacteria?

Short peptide interbridges Signup and view all the answers

What is the significance of the branched fatty acids in archaeal membranes?

They enhance membrane stability at high temperatures Signup and view all the answers

What is the primary function of fimbriae, pili, and hami in Archaea?

To attach cells to surfaces and to each other Signup and view all the answers

Which carbon storage polymer is a polymer of glucose and produced when carbon is abundant?

Glycogen Signup and view all the answers

What role does polyphosphate serve when phosphate is limited?

It provides phosphate for nucleic acid biosynthesis Signup and view all the answers

Which of the following statements best describes gas vesicles?

They are structures that provide buoyancy to cells. Signup and view all the answers

What is the significance of biomineralization in microbial processes?

It forms minerals through microbiological action. Signup and view all the answers

What type of mineral do Gloeomargarita cyanobacteria form to potentially aid in their buoyancy?

Benstonite Signup and view all the answers

What is the main function of bacterial flagella?

To push or pull the cell through a liquid Signup and view all the answers

How do sulfur granules contribute to energy metabolism?

They oxidize reduced sulfur compounds. Signup and view all the answers

What type of flagellation occurs when flagella emerge from both poles of a cell?

Amphitrichous Signup and view all the answers

What is the range in carbon chain length for Poly-β-hydroxybutyric acid (PHB)?

C3 to C18 Signup and view all the answers

Which part of the flagellum connects the filament to the flagellum motor?

Hook Signup and view all the answers

In gram-negative bacteria, where is the L ring of the flagellum motor anchored?

In the outer membrane Signup and view all the answers

What is the primary protein composition of the flagellum filament?

Flagellin Signup and view all the answers

Which flagellation pattern involves flagella distributed around the cell surface?

Peritrichous Signup and view all the answers

Which rings are present in gram-positive bacteria's flagellum motor?

Only the inner pair of rings Signup and view all the answers

What motion do bacteria with flagella typically exhibit?

Move slowly in a straight line or change directions Signup and view all the answers

What is the role of the stator in the flagellum motor?

To anchor the flagellum in the cytoplasmic membrane Signup and view all the answers

Which structure is synthesized first during flagellar synthesis?

The MS ring Signup and view all the answers

How many protons are translocated by each rotation of the flagellum?

1200 protons Signup and view all the answers

What distinguishes archaella from flagella?

They are assembled from their bases Signup and view all the answers

What is the primary energy source that drives the movement of archaella?

ATP hydrolysis Signup and view all the answers

How do the swimming speeds of Archaea compare to those of Bacteria?

They swim much more slowly than Bacteria Signup and view all the answers

What type of secretion system is involved in synthesizing the flagellum?

Type III secretion system Signup and view all the answers

Which of the following statements about flagellin protein is true?

It is synthesized in the cytoplasm and exported through the export apparatus Signup and view all the answers

Study Notes

ATP-binding cassette transport systems

Transport solutes and protons across membranes.
Three components: a binding protein, a transmembrane protein channel, and an ATP-hydrolyzing protein.
Two different mechanisms – solutes and protons can be transported in opposite directions or co-transported in the same direction.

Bacteria and Archaea membrane differences

Bacteria have lipid bilayers with ester-linked lipids and straight chain fatty acids.
Archaea have lipid monolayers with ether-linked lipids and branched fatty acids.

Bacterial Cell Wall

Contains a rigid polysaccharide called peptidoglycan, which confers structural strength.
Peptidoglycan is unique to Bacteria, not found in Archaea or Eukarya.
Peptidoglycan strands run parallel, forming layers around the cell.
Gram-positive bacteria have many layers of peptidoglycan (20-35 nm thick).
Gram-negative bacteria have 2-3 layers (2-7 nm thick).

Alternative Cell Envelope Configurations

Many Archaea have only an S-layer outside their cytoplasmic membrane.
Some Archaea have cell walls of pseudomurein, with or without an outer S-layer.
Heat-loving Ignicoccus have an outer membrane made of archaeal isoprenoid lipids but lack LPS.
Mycoplasmas lack cell walls and have sterols in their cytoplasmic membranes for strength.

Capsules and Slime Layers

Sticky coats of polysaccharide, formed outside the cell envelope.
Capsules are tightly organized and tightly attached, excluding small particles.
Slime layers are loosely attached, do not exclude particles, and are harder to see microscopically.
Functions:
- Attachment to surfaces
- Biofilm formation
- Infecting by bacterial pathogens
- Preventing dehydration

Fimbriae, Pili, and Hami

Thin filamentous structures made of proteins.
Short pili used for attachment are called fimbriae.
Other types:
- Conjugative pili – conjugation
- Electrically conductive pili (nanowires)
- Type IV pili – twitching motility
Hami are found in SM1 archaea and resemble grappling hooks.

Cell Inclusions

Store carbon, energy, and other cellular components.
Carbon storage polymers:
- Poly-β-hydroxybutyric acid (PHB) – stores carbon and energy.
- Glycogen – stores carbon and energy.
Polyphosphate:
- Inorganic phosphate (PO43-)
- Source of phosphate for biosynthesis when phosphate is limiting.
- Can be broken down to synthesize ATP.
Sulfur granules:
- Elemental sulfur (S0)
- Formed by oxidizing reduced sulfur compounds (like H2S).
- Generates electrons for energy metabolism or CO2 fixation.
Carbonate Minerals:
- Found in Gloeomargarita (a cyanobacterium).
- Benstonite granules (contain barium, strontium, and magnesium).
- Might function as ballast or sequester carbonate to support growth.

Gas Vesicles

Structures that confer buoyancy to cells, allowing them to position themselves in favorable environments.
Found in cyanobacteria, often forming blooms.
Impermeable to water and solutes, but permeable to gases.
Gas vacuoles are clusters of vesicles.

Flagella and Flagellation

Tiny rotating machines that propel cells through a liquid.
Long, thin appendages (15-20 nm wide), free at one end and anchored into the cell at the other.
Types:
- Polar: Flagella attached at one or both ends.
- Lophotrichous: A tuft of flagella at one end.
- Amphitrichous: Tuft of flagella at both ends.
- Peritrichous: Flagella inserted around the cell surface.
Some bacteria move slowly and in straight lines, while others move rapidly and can reverse direction.

Flagella Structure and Activity

Filament: Composed of flagellin protein.
Hook: Wider region at the base of the filament, connects filament to the motor.
Basal body: Flagellum motor anchored in the cell envelope.
Motor (rotor): Composed of rings:
- L ring: Anchored in outer membrane (gram-negative).
- P ring: Anchored in peptidoglycan (gram-negative).
- MS and C rings: Located within the cytoplasmic membrane and cytoplasm.
- Only the inner rings (MS & C) are present in gram-positive bacteria.
Stator: Surrounds inner rings and is anchored in the cytoplasmic membrane and peptidoglycan, composed of Mot proteins.
Export apparatus: Located on the cytoplasmic side of the MS ring, a Type III secretion system that facilitates flagellum synthesis.
Flagellum rotation is powered by the proton motive force.

Flagellar Synthesis

Steps:
- MS ring synthesis and insertion into the cytoplasmic membrane.
- Synthesis of anchoring proteins, hook, and cap.
- Flagellin molecule synthesis in the cytoplasm.
- Export of flagellin through the export apparatus.
- Assembly of flagellin molecules at the flagellum tip with help from cap proteins.

Archaella

Not related to bacterial flagella.
More closely related to type IV pili.
Smaller than flagella (10–13 nm wide), not hollow, and assembled from their bases.
Powered by ATP hydrolysis.
Archaea swim more slowly than bacteria.

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Description

This quiz explores the unique features of bacterial and archaeal cell structures, including the composition of their membranes and cell walls. It covers the components of ATP-binding cassette transport systems and the differences in lipid configurations between Bacteria and Archaea. Test your knowledge on these fundamental concepts in microbiology!