Cell Structure, Function, and Taxonomy – Lecture 2

Vocabulary flashcards covering fundamental terms, structures, and concepts from the lecture on cell structure, function, reproduction, and taxonomy.

Cell Theory

States that (1) all living organisms are composed of one or more cells, (2) the cell is the smallest functional unit of life, and (3) cells arise only from pre-existing cells.

Matthias Schleiden

German botanist (1838) who concluded that all plants are composed of cells.

Theodor Schwann

German zoologist (1839) who concluded that all animals are composed of cells.

Rudolph Virchow

German physician (1855) who proposed that cells arise from pre-existing cells.

Prokaryotic Cell

Cell type lacking a true nucleus and membrane-bound organelles; includes Bacteria and Archaea.

Eukaryotic Cell

Cell type possessing a nucleus and numerous membrane-bound organelles; includes plants, animals, fungi, and protists.

Cell Wall (Bacteria)

Rigid exterior composed mainly of peptidoglycan that determines bacterial shape.

Peptidoglycan

Unique bacterial polymer forming the main component of most bacterial cell walls.

Gram-Positive Bacteria

Bacteria with a thick peptidoglycan layer that retain crystal violet stain.

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer and an outer membrane; do not retain crystal violet.

Mycoplasma

Genus of bacteria lacking a cell wall, rendering them pleomorphic.

Cell Membrane

Phospholipid bilayer that encloses the cytoplasm and controls substance passage.

Prokaryotic Chromosome

Single, circular, supercoiled DNA molecule serving as the cell’s control center.

Plasmid

Small, circular, extra-chromosomal DNA molecule in prokaryotes.

Cytoplasm (Prokaryote)

Semi-liquid matrix of water, enzymes, nutrients, and wastes where metabolic reactions occur.

Ribosome

Organelle (70S in prokaryotes, 80S in eukaryotes) that synthesizes proteins.

Glycocalyx

External gelatinous layer in some bacteria; includes slime layers and capsules.

Slime Layer

Loosely attached glycocalyx enabling surface adherence (e.g., Pseudomonas spp.).

Capsule

Highly organized, firmly attached glycocalyx that inhibits phagocytosis (e.g., K. pneumoniae).

Flagellum

Whip-like appendage composed of flagellin that provides motility to bacteria.

Peritrichous

Having flagella distributed over the entire bacterial surface.

Lophotrichous

Having a tuft of flagella at one pole of the bacterium.

Amphitrichous

Having flagella at both poles of the bacterium.

Monotrichous

Having a single polar flagellum.

Pilus (Fimbria)

Thin, rigid protein projection used for attachment; sex pilus mediates conjugation.

Endospore

Dormant, highly resistant bacterial structure formed by Bacillus or Clostridium species.

Sporulation

Process of endospore formation as a survival mechanism, not reproduction.

Cytosol

Fluid portion of a eukaryotic cell’s cytoplasm containing organelles and solutes.

Nucleus

Prominent organelle surrounded by a double membrane; contains chromatin and nucleoli.

Nuclear Envelope

Double-layered membrane with pores separating nucleoplasm from cytoplasm.

Chromatin

DNA-protein complex in the nucleus that condenses into chromosomes during division.

Nucleolus

Nuclear region where ribosomal RNA is synthesized and ribosome assembly begins.

Plasma Membrane

Selective barrier made of lipids, proteins, and carbohydrates separating cell from environment.

Davson-Danielli Model

Obsolete ‘protein-lipid-protein’ sandwich model of membrane structure (1935).

Fluid Mosaic Model

Current model (Singer & Nicolson, 1972) describing membranes as fluid phospholipid bilayers with floating proteins.

Phospholipid Bilayer

Double layer of phospholipids forming the fundamental structure of biological membranes.

Transport Protein

Membrane protein that regulates movement of substances across the membrane.

Receptor Protein

Membrane protein that binds specific molecules to trigger cellular responses.

Recognition Protein

Membrane glycoprotein serving as cell-identity marker.

Glycoprotein

Protein with attached carbohydrate chain; functions in cell recognition.

Glycolipid

Membrane lipid with attached carbohydrate chain involved in cell recognition.

Endoplasmic Reticulum (ER)

Network of membranous tubules; rough ER makes proteins, smooth ER synthesizes lipids and detoxifies.

Rough ER

ER studded with ribosomes; site of protein synthesis.

Smooth ER

ER without ribosomes; site of lipid synthesis, detoxification, and Ca²⁺ storage.

Golgi Complex

Stack of membranous sacs that modify, sort, and package proteins and lipids.

Mitochondrion

Double-membraned organelle with cristae; site of aerobic respiration (‘powerhouse’).

Cristae

Infoldings of the inner mitochondrial membrane housing respiratory enzymes.

Lysosome

Membrane-bound vesicle containing digestive enzymes; ‘suicide bag’ of the cell.

Centrioles

Microtubule triplet cylinders at right angles; organize spindle fibers during cell division.

Cytoskeleton

Network of microtubules, intermediate filaments, and microfilaments providing cell shape and movement.

Microtubule

Hollow protein filament (tubulin) that forms part of the cytoskeleton and spindle apparatus.

Intermediate Filament

Cytoskeletal fiber providing mechanical strength.

Microfilament

Thin actin filament involved in cell movement and shape change.

Vacuole

Membrane-bound sac for storage, waste disposal, or water regulation.

Cilium

Short, numerous, 9+2 microtubule extension of plasma membrane for movement.

Flagellum (Eukaryote)

Long, usually single 9+2 microtubule extension for cell propulsion.

9+2 Arrangement

Microtubule structure of cilia/flagella: nine fused pairs surrounding two central microtubules.

Chloroplast

Green plastid in plants where photosynthesis occurs.

Plastid

Plant organelle such as chloroplast, chromoplast, or leucoplast.

Leucoplast

Colorless plastid specialized for storage (e.g., amyloplast, elaioplast).

Microvillus

Finger-like plasma-membrane projection increasing surface area for absorption.

Desmosome

Strong cell-to-cell junction ‘glued’ by proteins and carbohydrates, reinforced by intermediate filaments.

Tight Junction

Seal between adjacent cells preventing leakage between them.

Gap Junction

Protein channel connecting cytoplasm of adjacent animal cells for communication.

Taxonomy

Science of classifying, naming, and identifying organisms.

Classification

Arrangement of organisms into hierarchical taxa (Kingdom → Species).

Nomenclature

Assignment of names to organisms using binomial system.

Identification

Determination of an organism’s taxonomic placement.

Binomial System

Two-part scientific naming system: genus + specific epithet.

Genus

First part of scientific name; may be abbreviated to a single letter.

Specific Epithet

Second part of scientific name; together with genus forms species name.

Five-Kingdom System

Classification into Procaryotae, Protista, Fungi, Plantae, and Animalia.

Three-Domain System

Classification into Archaea, Bacteria, and Eucarya based on rRNA differences.

KDCOFGS Mnemonic

‘King David Came Over for Good Spaghetti’—Kingdom, Division, Class, Order, Family, Genus, Species.

rRNA Sequencing

Technique comparing 16S (prokaryote) or 18S (eukaryote) rRNA genes to assess relatedness.

16S rRNA Gene

Prokaryotic gene encoding small-subunit ribosomal RNA used in phylogenetic studies.

18S rRNA Gene

Eukaryotic counterpart of 16S, used for determining evolutionary relationships.