Prokaryotic Cells and Their Internal/External Structures (Lecture Notes)

Flashcards covering key concepts on prokaryotes, cell walls, staining, and internal/external structures as per lecture notes.

What groups make up prokaryotes?

Bacteria and Archaea; they lack membrane-bound organelles and a true nucleus.

What is the glycocalyx and what are its two main forms?

A sticky layer outside the cell. Capsule: thick and tightly bound; slime layer: thin and loosely bound.

Name the external structures listed for prokaryotic cells.

Glycocalyx, Flagella, Axial filaments, Pili (fimbriae).

What is a capsule?

A thick, tightly bound glycocalyx that surrounds some bacteria and can aid protection and adherence.

What is the flagellum and its primary function?

A long, filamentous appendage used for motility; rotates to propel the cell.

What are the components of a bacterial flagellum?

Filament (made of flagellin), hook, and basal body anchoring in the cell envelope.

List the common flagellar arrangements in bacteria.

Atrichous (no flagella); Monotrichous (one at pole); Lophotrichous (multiple at one pole); Amphitrichous (tufts at both poles); Peritrichous (all over).

What are axial filaments and where are they found?

Internal flagella found in spiral bacteria; cause motility by rotating the cell body.

Describe axial filaments’ role in motility for spirally shaped bacteria.

Internal flagella anchored between the outer membrane and cell wall; contraction rotates the cell to produce movement.

What are fimbriae and pili and what are their functions?

Fimbriae: short, thin appendages for adhesion to surfaces and cells. Pili: longer; some mediate twitching motility and some (sex pili) mediate DNA transfer (conjugation).

What is the cell wall and its main functions?

External to the plasma membrane; maintains cellular shape and protects against physical damage and osmotic lysis.

What is peptidoglycan composed of?

A carbohydrate backbone of NAM and NAG with peptide cross-bridges linking the chains.

Gram-positive vs Gram-negative cell walls – main differences.

Gram-positive: thick peptidoglycan and teichoic acids. Gram-negative: thin peptidoglycan, outer membrane with LPS and porins.

Teichoic acids: what are they and what are their proposed roles?

Found in Gram-positive walls; may regulate cation movement, prevent excessive wall breakdown, and contribute antigenicity.

What features characterize the Gram-negative outer membrane?

Outer membrane with porins and LPS; protects from immune factors and chemicals; thin peptidoglycan layer beneath.

What are the LPS components and their functions?

O polysaccharides act as antigens; Lipid A is an endotoxin causing endotoxic shock; porins allow small molecules through.

What is Gram staining used for and who developed it?

Differentiates Gram-positive and Gram-negative bacteria; developed by Christian Gram in 1884.

Describe the steps of Gram staining.

Crystal violet (primary stain); Gram's iodine (mordant); decolorize with acetone-alcohol; counterstain with safranin.

What colors do Gram-positive and Gram-negative cells appear after Gram staining?

Gram-positive: purple; Gram-negative: pink.

Which bacteria lack a cell wall and how does this affect staining?

Mycoplasma lack cell walls; they lack many stains and are protected by sterols in their membranes.

Which bacteria have thick walls with mycolic acid and are stained with acid-fast stain?

Mycobacterium.

What additional components are found in Gram-positive cell walls besides peptidoglycan?

Teichoic acids.

What is the function of porins in the Gram-negative outer membrane?

Allow small molecules to pass across the outer membrane.

What is osmotic pressure?

The pressure required to stop the flow of water across a membrane; relates to isotonic, hypotonic, and hypertonic environments.

What is osmosis?

Movement of water across a membrane toward higher solute concentration.

What is the plasma membrane and its function?

Phospholipid bilayer enclosing the cytoplasm; selectively permeable; contains integral and peripheral proteins.

What is the cytoplasm?

Fluid interior of the cell; mostly water with inorganic/organic molecules, DNA, ribosomes, and inclusions.

What is the bacterial cytoskeleton?

Protein framework giving shape; supports cell division and movement of components; recently recognized in bacteria.

Where is the bacterial chromosome located and what is its shape?

Located in the nucleoid (not membrane-bound); circular chromosome attached to the plasma membrane.

What are plasmids and their significance?

Small circular DNA molecules; replicate independently; carry genes like antibiotic resistance; transferable between bacteria.

What is the 70S ribosome composed of?

50S and 30S subunits; 50S contains 23S and 5S rRNA; 30S contains 16S rRNA.

What are inclusions in bacteria?

Reserve deposits of macromolecules such as sugars, glycogen, starch, lipids, sulfur, etc.; reduce osmotic stress.

Name some common bacterial inclusions and what they store.

Metachromatic granules (volutin) store inorganic phosphate; polysaccharide granules (glycogen/starch); lipid inclusions; sulfur granules; carboxysomes; gas vacuoles; magnetosomes.

What are endospores and which genera commonly form them?

Resting, highly durable, non-reproductive structures formed under harsh conditions; Bacillus and Clostridium are common endospore-formers.

What is sporulation and germination in endospores?

Sporulation: endospore formation; germination: return to vegetative state.

What is a metachromatic granule and how is it detected?

Metachromatic granule (volutin) stores inorganic phosphate and stains red with methylene blue.

What is a gas vacuole and its role?

Gas-filled inclusion that provides buoyancy to aquatic prokaryotes to access light, oxygen, and nutrients.

What are magnetosomes?

Iron oxide-containing inclusions; act like magnets to anchor bacteria and protect against hydrogen peroxide.

What is taxis and which types exist?

Movement toward or away from a stimulus; includes chemotaxis (chemicals) and phototaxis (light).

How do capsules and slime layers differ in binding and protection?

Capsules are thick and tightly bound; slime layers are thin and loosely bound; both are glycocalyx with protective properties.

What is the role of teichoic acids in Gram-positive cells?

Contribute antigenicity, may regulate cation movement and help protect the wall.

What is the energy source for active transport and what is group translocation?

Active transport uses energy to move substances across the membrane; group translocation modifies the substance during transport (e.g., glucose to glucose-6-phosphate).

What is the nucleoid and how does it differ from a nucleus?

Nucleoid is the DNA-containing region in prokaryotes and is not membrane-bound; a nucleus is membrane-bound and found in eukaryotes.