PROKARYOTES

Prokaryote

Organism whose cells lack a membrane-bound nucleus and membrane-bound organelles.

Domains of Life

Three evolutionary domains: Bacteria, Archaea, and Eukarya.

Bacteria

Single-celled prokaryotes with peptidoglycan cell walls and diverse metabolic strategies.

Cell Size (Prokaryotes)

Typically 0.5–5 µm; small size allows efficient diffusion.

Cell Shape (Morphology)

Common bacterial shapes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

Nucleoid

DNA-rich region containing a single circular chromosome; not membrane-bound.

Plasmid

Small circular DNA molecule that replicates independently and carries accessory genes.

Plasma Membrane (Prokaryotes)

Phospholipid bilayer that regulates transport and houses metabolic and energy-generating proteins.

Cell Wall (Bacteria)

Rigid outer layer composed of peptidoglycan; maintains shape and prevents osmotic lysis.

Gram-Positive Bacteria

Thick peptidoglycan cell wall; retain crystal violet stain (purple).

Gram-Negative Bacteria

Thin peptidoglycan layer plus outer membrane; stain pink and often antibiotic-resistant.

Capsule

External polysaccharide or protein layer that aids adhesion, immune evasion, and protection.

Ribosomes (Prokaryotic)

70S ribosomes responsible for protein synthesis.

Flagellum (Bacterial)

Rigid, rotating helical appendage used for motility.

Proton Motive Force

H⁺ gradient across the membrane that powers flagellar rotation and other processes.

Fimbriae

Short hair-like structures used for attachment.

Pili

Long hollow appendages used for horizontal gene transfer.

Cytoskeleton (Prokaryotic)

Simple protein filament system maintaining shape and assisting division.

MreB

Actin-like protein that maintains rod-shaped cell structure.

FtsZ

Tubular-like protein forming a division ring during cell division.

Binary Fission

Asexual reproduction producing two genetically identical daughter cells.

Archaea

Prokaryotes evolutionarily closer to eukaryotes than bacteria; lack peptidoglycan.

Archaeal Cell Wall

Composed of polysaccharides and proteins, not peptidoglycan.

Extremophile

Organism adapted to extreme environments (high heat, salinity, acidity).

Metabolic Diversity (Prokaryotes)

Ability to use varied energy and carbon sources.

Photoautotroph

Uses light for energy and CO₂ for carbon.

Chemoautotroph

Uses inorganic chemicals for energy and CO₂ for carbon.

Photoheterotroph

Uses light for energy but organic molecules for carbon.

Chemoheterotroph

Uses organic molecules for both energy and carbon.

Human Microbiota

Microbial communities living in and on the human body.

What defines a prokaryotic cell?

Lack of membrane-bound nucleus and organelles.

Why are bacteria small?

High surface area-to-volume ratio improves exchange efficiency.

Why does penicillin mainly affect gram-positive bacteria?

They rely heavily on peptidoglycan cell walls.

Why are gram-negative bacteria more resistant to antibiotics?

Their outer membrane blocks many drugs.

What powers bacterial flagellar movement?

Proton motive force (H⁺ gradient).

Difference between fimbriae and pili?

Fimbriae attach; pili transfer DNA.

Why are plasmids evolutionarily important?

They allow rapid gene acquisition.

Role of FtsZ in reproduction?

Forms a ring guiding septum formation.

Why are Archaea not bacteria?

They differ in membrane chemistry, gene expression, and cell wall structure.

Are any archaeal pathogens known?

No.

Why is the gut microbiota important?

Digestion, immunity, metabolism.

Archaea (Superficial Similarity)

Appear similar to bacteria in size and shape but differ significantly in molecular biology and cell wall composition.