Podcast Beta
Questions and Answers
What shape is associated with the term 'bacillus'?
Which of the following is a characteristic of spiral-shaped bacteria?
What is the typical length of most rod-shaped bacteria?
What factor does not typically influence bacterial morphology?
Signup and view all the answers
Which of the following is an example of a multicellular bacterial organization?
Signup and view all the answers
What is the primary energy source for the rotation of flagella in bacteria?
Signup and view all the answers
Which component is NOT part of a bacterial flagellum?
Signup and view all the answers
What type of motility involves the use of pili to extend and pull along a surface?
Signup and view all the answers
Which of the following accurately describes chemotaxis in bacteria?
Signup and view all the answers
What is a unique feature of spirochetes regarding their flagella?
Signup and view all the answers
What is the primary function of a sex pilus in bacteria?
Signup and view all the answers
Which structure helps bacteria resist desiccation and provides a defense against host immunity?
Signup and view all the answers
What role do surface arrays (S-layers) play in bacterial cells?
Signup and view all the answers
How do stalks benefit certain microbes like Caulobacter?
Signup and view all the answers
Which of the following statements about pili is true?
Signup and view all the answers
What role does the plasma membrane play in energy capture?
Signup and view all the answers
Which statement accurately describes the permeability of the plasma membrane?
Signup and view all the answers
What is the function of aquaporin proteins in the plasma membrane?
Signup and view all the answers
How do ABC transporters function in the plasma membrane?
Signup and view all the answers
What role does the cell wall play in relation to osmotic pressure?
Signup and view all the answers
What is peptidoglycan primarily composed of?
Signup and view all the answers
What distinguishes Gram-negative bacteria from Gram-positive bacteria?
Signup and view all the answers
What happens to a cell without a functional cell wall in terms of osmotic pressure?
Signup and view all the answers
What is a primary characteristic of hopanoids within the plasma membrane?
Signup and view all the answers
What mechanism is involved in co-transport across the plasma membrane?
Signup and view all the answers
What is the primary advantage of having a higher surface-to-volume ratio in small cells?
Signup and view all the answers
Which of the following is a mechanism that bacteria use to compress DNA within their nucleoid?
Signup and view all the answers
What is the minimum diameter that is unlikely for cellular structures to be smaller than?
Signup and view all the answers
Which of the following components is NOT typically associated with the cytoplasm of bacteria?
Signup and view all the answers
What function do gas vesicles serve in bacteria?
Signup and view all the answers
Which of the following statements is true regarding the bacterial cytoskeleton?
Signup and view all the answers
What term describes all layers surrounding the cytoplasm of a cell?
Signup and view all the answers
Which macromolecule is primarily responsible for the genetic material in bacteria?
Signup and view all the answers
What is the primary role of magnetosomes in bacteria?
Signup and view all the answers
How does Epulopiscium fishelsoni compare in size to Paramecium?
Signup and view all the answers
Study Notes
Bacterial Morphology
- Bacteria come in various shapes: spherical (cocci), rod-shaped (bacilli), comma-shaped (vibrios), spiral (spirilla), and pleiomorphic (variable shapes).
- Morphology is not always a reliable indicator of a bacterium's physiology, ecology, or phylogeny.
- Morphology can be influenced by selective forces, such as nutrient uptake efficiency (surface-to-volume ratio) and motility.
- Some bacteria form multicellular organizations like hyphae (branching filaments), mycelia (tufts of hyphae), and trichomes (smooth, unbranched chains).
Cell Sizes
- Prokaryotes typically range from 0.2 μm to over 700 μm in length/diameter.
- Most rod-shaped bacteria are between 0.5 μm and 4.0 μm wide and 1-15 μm long.
- Eukaryotic cells are larger, ranging from 10 μm to over 200 μm.
- Minimum size is limited by the minimum space needed for the genome, proteins, and ribosomes.
- There are exceptions to the general size of bacterial cells, such as Thiomargarita namibiensis (up to 700 μm in diameter) and Epulopiscium fishelsoni (200-700 μm long).
Advantages of Being Small
- A higher surface-to-volume ratio allows for faster nutrient/waste exchange per unit volume.
- This supports a higher metabolic rate and faster growth rate, leading to faster evolution.
Limits on Small Size
- Size reduction is limited by the minimum complement of cellular structures required for survival.
- Diameters below 0.15 μm are unlikely.
- "Very small" cells are common in open marine environments, typically ranging from 0.2 μm to 0.4 μm.
Bacterial Cytoplasm
- The largest area within the cytoplasm is the nucleoid region, which houses the chromosome(s) and DNA replication machinery.
- The nucleoid is not enclosed by a membrane and lacks histone proteins.
- DNA in the nucleoid is compressed by various mechanisms, including the use of cations to shield negative charges, binding of small, positively charged proteins, and DNA supercoiling.
- The remainder of the cytoplasm contains macromolecules like tRNA, rRNA, mRNA, proteins, and ribosomes.
- Inclusion bodies and microcompartments are also present, including:
- Sulfur globules (sulfur storage for energy)
- Polyhydroxybutyrate granules (carbon storage)
- Gas vesicles (buoyancy control)
- Carboxysomes (location of carbon fixation reactions)
- Magnetosomes (organelles for direction finding).
Bacterial Cytoskeleton
- Bacterial cytoskeleton is composed of a series of internal proteins that help maintain cellular structure.
- Some cytoskeletal proteins are involved in cell wall synthesis during cell division, such as MreB (homolog of actin) and FtsZ (homolog of tubulin).
- Other cytoskeletal proteins are involved in moving internal components, like plasmids.
Cell Envelope
- Encompasses all layers surrounding the bacterial cytoplasm: cell membrane, cell wall, and outer membrane (if present).
Cytoplasmic Membrane
-
All cells have a plasma membrane that separates the cell's interior from the environment.
-
It plays crucial roles in:
- Capturing energy (electron transport chains, proton motive force)
- Holding sensory systems (detecting environmental changes)
- Acting as a permeability barrier (but not structural)
-
The plasma membrane is typically a phospholipid bilayer with embedded proteins.
-
It has a hydrophobic core and hydrophilic surfaces interacting with the external environment or the cytoplasm.
-
Variation in fatty acid groups attached to a glycerol backbone creates chemical differences, connected by ester linkages.
-
It may contain sterol-like molecules called hopanoids, which contribute to stability across temperature ranges.
Transport Across the Plasma Membrane
- Small molecules like O2 and CO2 can readily diffuse across the membrane.
- Water is helped across by aquaporin protein channels (osmosis).
- Facilitated diffusion and co-transport: protein channels move particles down a concentration gradient, requiring no ATP energy.
- Co-transport is a form of active transport, leveraging energy from a concentration gradient.
- Active transport example (ABC transporters): ATP-Binding Cassette protein transporters move particles against a concentration gradient, requiring ATP energy.
Protein Secretion
- Protein secretion involves shipping proteins outside the cell using ATP energy.
- Examples of secreted proteins include toxins, siderophores, and enzymes for breaking down substrates.
Cell Wall
- Provides shape and protection from osmotic lysis and mechanical forces.
- Composed of a matrix of crosslinked strands of peptidoglycan subunits (NAM, NAG, and a small peptide chain).
Peptidoglycan Structure
- Peptidoglycan is composed of N-acetylmuramic acid (NAM), N-acetylglucosamine (NAG), and a small peptide chain.
- The structure of the peptides and crosslinks varies between species, leading to the distinction between Gram-negative and Gram-positive bacteria.
- Some amino acids found in the peptidoglycan are D-forms, which are stereoisomers (mirror images) of the L-forms usually found in biological proteins.
- Cell wall formation involves transglycosylation and transpeptidation.
Cell Wall Degradation
- Lysozyme and lysostaphin are enzymes that can degrade the cell wall.
- Without a cell wall, bacteria cannot resist osmotic pressure changes.
The Bacterial Cell Surface
- The cell surface includes flagella, pili, capsules, surface arrays, and stalks.
Flagella
- Spiral, hollow, rigid filaments extending from the cell surface, with variations in location and number across species.
- Composed of three main parts:
- Filament (multiple flagellin proteins, 5-10 μm long)
- Hook protein portion (connects the filament to the basal body)
- Basal body (disk-like structure that rotates the filament like a propeller).
- Energy for spinning flagella is derived from the proton motive force (PMF).
- Flagella generate runs and tumbles through spinning, a process that is energetically expensive (requiring ~1000 H+ translocated per rotation).
Chemotaxis
- involves chemoreceptor proteins sensing changes in concentrations of attractants or repellents, leading to directed movement.
Internal Flagella
- Some spirochetes have flagella in the periplasm that rotate the entire cell body like a corkscrew.
Nonflagellar Motility
- Gliding motility: smooth sliding over a surface, not fully understood (e.g., Myxobacteria, Cyanobacteria).
- Twitching motility: slow, jerky process using pili to extend, attach, and pull along a surface (e.g., Pseudomonas aeruginosa).
- Act-dependent motility: polymerization of actin in host cells propels bacteria into adjacent cells (e.g., Shigella dysenteriae, Listeria monocytogenes).
Adherence Molecules
- Allow cells to stick to surfaces.
- Pili (fibers of pilin protein), with additional proteins on their tips for sticking.
- Sex pili are different structures involved in conjugation (transferring plasmids between cells).
- Adhesive pili (fimbriae) also contribute to adherence.
Stalk
- An extension of the cell envelope tipped by a "holdfast" of polysaccharides.
- Provides extra surface area for nutrient absorption (e.g., Caulobacter, Hyphomonas).
Capsules
- Thick layer of polysaccharides surrounding some cells (both G+ and G-), providing adhesion, defense against host immunity, and protection from desiccation.
- Can help form biofilms, enhancing survivability in harsh environments.
Surface Arrays (S-layers)
- Crystalline array of interlocking proteins that can provide protection against predation or bacteriophage infection.
- Found in both Gram-positive and Gram-negative cells, and even in Archaea.
Bacterial Taxonomy
- Most microbial species remain uncultured.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the fascinating world of bacterial morphology and cell sizes in this quiz. You'll learn about the various shapes bacteria can take, their sizes, and how these characteristics relate to their functions and environments. Test your knowledge on how characteristics like motility and nutrient uptake influence these organisms.
