Prokaryotic and Eukaryotic Cells

A vocabulary-style review covering key terms and definitions from the lecture notes on prokaryotic and eukaryotic cells.

Prokaryotic cell

A cell lacking a membrane-bound nucleus and membrane-bound organelles; generally smaller and simpler; includes Archaea and Bacteria.

Eukaryotic cell

A cell with a membrane-bound nucleus and organelles; more complex and usually larger; includes plants, animals, fungi, and protists.

Nucleus

A membrane-bound organelle that houses the cell’s DNA and is the site of transcription; surrounded by the nuclear envelope.

Nucleoid

Region in a prokaryotic cell where the circular DNA chromosome resides; not bounded by a membrane.

Plasmid

Small, circular DNA molecules that carry nonessential but advantageous genes and can be transferred between cells.

Chromosome (bacterial)

Circular DNA molecule containing essential genetic information in prokaryotes.

Plasma membrane

Phospholipid bilayer that encloses the cell; regulates transport and contains proteins for movement and signaling.

Cytoplasm

Fluid interior of the cell that houses cytosol, organelles, and the cytoskeleton; site of many metabolic activities.

Ribosome (70S)

Ribosomes in prokaryotes composed of 50S and 30S subunits; site of protein synthesis.

Cell wall (bacteria)

Rigid layer outside the plasma membrane that provides shape and protection; in bacteria mainly composed of peptidoglycan.

Slime layer

An unorganized, loosely attached glycocalyx that helps with protection and attachment.

Capsule

A organized, tightly bound glycocalyx that is sticky and more protective, aiding defense against phagocytosis.

Glycocalyx

External coating of the cell composed of polysaccharides; includes slime layer and capsule; aids in protection and adhesion.

Fimbriae

Short, hairlike projections that enable attachment to surfaces and other cells.

Pili (pili/sex pili)

Longer appendages used for DNA transfer between bacteria (conjugation) and attachment in some species.

Flagellum

Whip-like appendage used for bacterial motility; made of flagellin; rotates to move the cell.

Teichoic acid

Anionic polymers in Gram-positive cell walls that help with maintenance and growth; embedded in peptidoglycan.

Lipoteichoic acid

Teichoic acids anchored in the cell membrane; contribute to cell wall properties in Gram-positives.

Outer membrane

Additional membrane in Gram-negative bacteria located outside the thin peptidoglycan layer; contains LPS and porins.

Lipopolysaccharide (LPS)

Endotoxin-containing component of the Gram-negative outer membrane; contributes to antigenicity and immune responses.

Porin

Protein channels in the outer membrane that regulate molecule entry and exit in Gram-negative bacteria.

Periplasmic space

Space between the inner cytoplasmic membrane and the outer membrane in Gram-negative bacteria; contains enzymes and transport proteins.

Gram-positive

Bacteria with a thick peptidoglycan layer and teichoic acids; no outer membrane; retains crystal violet stain.

Gram-negative

Bacteria with a thin peptidoglycan layer and an outer membrane containing LPS; stain counterstain (safranin) after decolorization.

Gram stain

Differential staining technique distinguishing Gram-positive and Gram-negative bacteria based on cell wall properties.

Crystal violet

Purple primary stain used in Gram staining; retained by Gram-positive cell walls.

Iodine (mordant)

Fixative in Gram staining that forms a complex with crystal violet to trap it in the cell wall.

Decolorization (alcohol)

Step in Gram staining that disrupts outer membranes and washes out dye from Gram-negative cells.

Safranin

Counterstain in Gram staining that stains Gram-negative cells pink/red after decolorization.

Acid-fast

Bacteria with waxy lipid-rich cell walls (mycolic acids) that retain stain; identified with acid-fast staining (e.g., Mycobacterium).

Mycolic acid

Waxy lipid in some bacterial cell walls (e.g., Mycobacterium) that impedes dye uptake and increases resistance.

Mycobacterium

Bacteria with waxy, mycolic acid-rich cell walls; includes TB and leprosy pathogens.

Mycoplasmas

Bacteria lacking a cell wall and having sterols in their membrane; highly variable shape and resistant to lysis.

Peptidoglycan

Macromolecule in bacterial cell walls made of glycan (sugar) chains crosslinked by peptides; provides rigidity.

Glycan

Sugar components of peptidoglycan; includes N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

N-acetylglucosamine (NAG)

Sugar component of peptidoglycan in the bacterial cell wall.

N-acetylmuramic acid (NAM)

Sugar component of peptidoglycan in the bacterial cell wall.

Gram stain procedure

Protocol: crystal violet, iodine, decolorization, safranin to differentiate Gram-positive and Gram-negative bacteria.

Acid-fast stain

Staining method used to identify acid-fast organisms with mycolic acid in their cell walls.

Endospore

Dormant, highly resistant cell form produced by some Gram-positive bacteria to survive harsh conditions.

Sporulation

Formation of an endospore in response to adverse conditions.

Endosymbiotic theory

Hypothesis that eukaryotic organelles originated from engulfed bacteria (mitochondria, chloroplasts).

Mitochondria

Organelle that generates ATP; contains its own DNA and 70S ribosomes; evidence for endosymbiosis.

Chloroplasts

Organelle responsible for photosynthesis in plants and algae; contains chlorophyll, circular DNA, 70S ribosomes; evidence for endosymbiosis.

Rough endoplasmic reticulum (RER)

ER studded with ribosomes; synthesizes and modifies proteins, adds carbohydrates/lipids to proteins.

Smooth endoplasmic reticulum (SER)

ER lacking ribosomes; synthesizes lipids, phospholipids, and steroids; metabolizes carbohydrates.

Golgi apparatus

Stack of cisternae that modifies, stores, and packages proteins for secretion or delivery.

Lysosome

Organelle containing digestive enzymes that break down waste, damaged organelles, and pathogens.

Peroxisome

Organelle that degrades fatty acids and detoxifies reactive oxygen species like hydrogen peroxide.

Cytoskeleton

Network of microfilaments, intermediate filaments, and microtubules that provide structure and enable movement.

Cilia

Short, numerous, whip-like structures used for movement or feeding in some eukaryotic cells; not found in prokaryotes.

Eukaryotic extracellular matrix

Complex network of carbohydrates and proteins outside the cell that supports adhesion, signaling, and protection.

Eukaryotic cell wall (fungi, algae, plants)

Rigid layer made of chitin (fungi), cellulose (plants/algae), or mannan (yeast) that provides structure.

Sterols in membranes

Sterol molecules in eukaryotic membranes that help regulate fluidity and stability.

Nuclear envelope

Double membrane surrounding the nucleus with pores for transport between nucleus and cytoplasm.

Nuclear pores

Protein-lined channels in the nuclear envelope that regulate exchange of materials between nucleus and cytoplasm.

Mitosis

Process of nuclear division in somatic cells leading to two identical diploid daughter cells.

Meiosis

Cell division that produces haploid gametes with genetic variation.

Rough endoplasmic reticulum ribosomes

Ribosomes attached to the rough ER that synthesize proteins destined for secretion or membranes.

Mitochondrial DNA

Circular DNA within mitochondria that encodes a subset of mitochondrial genes; evidence of endosymbiosis.

Chloroplast DNA

Circular DNA within chloroplasts that encodes a subset of chloroplast genes; evidence of endosymbiosis.

Cytosol

Fluid portion of the cytoplasm where many metabolic reactions occur.

Basal body

Structurally anchors a flagellum to the cell envelope and acts as a rotor in prokaryotic flagella.

Microtubule

Cytoskeletal element that supports cell shape and movement; part of cilia, flagella, and the spindle.

Microfilament

Thin cytoskeletal fiber of actin involved in cell movement and shape.

Intermediate filament

Cytoskeletal component providing mechanical support and stability.

Endomembrane system

Network of membranes including the ER, Golgi, and vesicles that work together in protein and lipid trafficking.

Protozoa, fungi, algae, plants, animals

Examples of organisms with eukaryotic cells.