Cell Biology Lecture Notes

A comprehensive set of 200 vocabulary flashcards covering fundamental terms, structures, and concepts from the lecture on cell biology, cell theory, microscopy, organelles, and related processes.

Cell

The smallest structural and functional unit of life, capable of independent existence and reproduction.

Cell theory

Scientific theory stating that all living things are made of cells, cells are basic units of life, and all cells arise from pre-existing cells.

Unicellular organism

A living organism composed of a single cell, e.g., bacteria or protozoa.

Multicellular organism

An organism made of many specialized cells working together, such as plants and animals.

Organelle

A membrane-bound or specialized sub-structure within a cell that performs a specific function.

Cytoplasm

The cell’s interior between nucleus and plasma membrane, consisting of cytosol plus organelles.

Cytosol

The semi-fluid portion of cytoplasm in which organelles and molecules are suspended.

Cytoskeleton

A network of protein filaments that gives a cell shape, internal organization, and ability to move.

Microfilament

Thin actin filament (~7 nm) that supports cell shape and enables muscle-like contractions.

Intermediate filament

Rope-like filament (~10 nm) that provides tensile strength and structural stability to cells.

Microtubule

Hollow tubulin tube (~25 nm) that forms tracks for organelle movement and mitotic spindles.

Centriole

Cylindrical pair of microtubule triplets that organize the spindle during animal cell division.

Nucleus

Membrane-bound control center that houses DNA and directs cellular activities.

Nuclear envelope

Double membrane that surrounds the nucleus and separates it from cytoplasm.

Nuclear pore

Protein-lined opening in the nuclear envelope allowing selective trafficking of molecules.

Nucleoplasm

The jelly-like fluid inside the nucleus containing chromatin and nucleolus.

Chromatin

Complex of DNA and histone proteins that packages genetic material inside the nucleus.

DNA

Deoxyribonucleic acid; hereditary molecule carrying genetic instructions in all living cells.

mRNA

Messenger RNA; RNA copy of a gene that conveys coding information to ribosomes.

rRNA

Ribosomal RNA; structural RNA that combines with proteins to form ribosome subunits.

Nucleolus

Dense nuclear region where rRNA is transcribed and ribosome subunits are assembled.

Ribosome

Non-membranous organelle of rRNA and protein that synthesizes polypeptides from mRNA.

Polyribosome

Group of ribosomes simultaneously translating a single mRNA strand.

Svedberg unit

Sedimentation coefficient (S) used to express size of ribosomal subunits by ultracentrifugation.

Rough endoplasmic reticulum

ER studded with ribosomes; synthesizes and folds membrane and secretory proteins.

Smooth endoplasmic reticulum

ER lacking ribosomes; makes lipids, detoxifies chemicals, stores Ca2+.

Cisternae

Flattened membrane sacs that make up ER and Golgi apparatus.

Lumen

The internal space enclosed by an organelle’s membrane, e.g., ER lumen.

Golgi apparatus

Stack of membrane cisternae that modifies, sorts, and packages proteins and lipids.

Cis face

Receiving side of Golgi that faces the ER and accepts transport vesicles.

Trans face

Shipping side of Golgi that buds vesicles toward plasma membrane or lysosomes.

Vesicle

Small, membrane-bound sac that transports or stores substances within a cell.

Exocytosis

Process of fusing a vesicle with the plasma membrane to release contents outside the cell.

Endocytosis

Uptake of material by inward folding of the plasma membrane to form a vesicle.

Lysosome

Acidic, enzyme-filled vesicle that digests food particles, wastes, and pathogens.

Hydrolytic enzyme

Digestive enzyme found in lysosomes that breaks biomolecules by adding water.

Peroxisome

Organelle that breaks down fatty acids and toxins, producing and degrading hydrogen peroxide.

Mitochondrion

Double-membrane “powerhouse” that generates ATP through aerobic respiration.

Cristae

Inner-membrane folds of a mitochondrion that increase surface area for ATP synthesis.

Matrix

Innermost compartment of a mitochondrion containing enzymes, DNA, and ribosomes.

ATP

Adenosine triphosphate; primary energy currency of the cell.

Cellular respiration

Metabolic pathway that converts food molecules into ATP, mainly in mitochondria.

Chloroplast

Plant plastid containing chlorophyll; site of photosynthesis.

Stroma

Fluid inside chloroplast surrounding the thylakoid system.

Granum

Stack of flattened thylakoid discs within a chloroplast.

Thylakoid

Chloroplast membrane sac where the light reactions of photosynthesis occur.

Chlorophyll

Green pigment in thylakoids that absorbs light energy for photosynthesis.

Photosynthesis

Process by which plants convert light energy, CO₂, and water into glucose and O₂.

Intergrana thylakoid

Membranous channel (stroma lamella) linking separate grana stacks.

Vacuole

Membrane sac for storage or transport; prominent in plant and protozoan cells.

Central vacuole

Large plant vacuole that stores sap and maintains turgor pressure.

Tonoplast

The membrane that surrounds a plant cell’s central vacuole.

Turgor pressure

Pressure exerted by fluid inside the vacuole against the plant cell wall.

Cell membrane

Flexible phospholipid bilayer that encloses the cell and controls substance movement.

Plasma membrane

Alternate term for cell membrane.

Phospholipid bilayer

Double layer of phospholipids forming the fundamental structure of membranes.

Semipermeable membrane

Barrier that allows some molecules to pass while restricting others.

Glycoprotein

Molecule composed of a protein covalently bonded to carbohydrate chains.

Integral membrane protein

Protein embedded within the lipid bilayer, often spanning the membrane.

Peripheral membrane protein

Protein loosely attached to the membrane’s surface.

Receptor protein

Membrane protein that binds specific ligands and triggers cellular responses.

Cholesterol

Steroid lipid inserted in animal membranes that modulates fluidity and stability.

Phospholipid

Amphipathic lipid with a phosphate head and two fatty acid tails; basic membrane unit.

Cell wall

Rigid extracellular layer that supports and protects plant, fungal, bacterial, or algal cells.

Cellulose

Structural polysaccharide forming the primary component of plant cell walls.

Primary cell wall

Thin, flexible first wall produced by a growing plant cell.

Secondary cell wall

Thick, rigid wall deposited inside the primary wall after growth stops.

Lignin

Complex polymer that adds rigidity and waterproofing to secondary cell walls and wood.

Plasmodesmata

Microscopic channels through plant cell walls that connect adjacent cytoplasms.

Peptidoglycan

Mesh of sugar chains cross-linked by peptides forming most bacterial cell walls.

Chitin

Nitrogenous polysaccharide forming fungal cell walls and insect exoskeletons.

Root hair

Thin extension of a root epidermal cell that increases surface area for absorption.

Flagellum

Long whip-like appendage enabling cell motility through fluid.

Cilium

Short hair-like projection that moves fluid over a cell or propels unicellular organisms.

Axoneme

9 + 2 microtubule core of cilia and flagella responsible for their bending motion.

Basal body

Organelle anchoring cilia or flagella, structurally similar to a centriole.

Prokaryote

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

Eukaryote

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

Nucleoid

Irregular region in a prokaryotic cell where the circular chromosome is located.

Capsule

Sticky polysaccharide or protein layer outside some bacteria that aids protection and adhesion.

Pili

Hair-like protein appendages on bacteria used for attachment or DNA transfer.

Fimbriae

Short, numerous pili specialized for surface adhesion.

Plasmid

Small circular DNA molecule in bacteria that replicates independently of the chromosome.

Inclusion body

Cytoplasmic reserve deposit of nutrients such as glycogen, sulfur, or polyphosphate.

Endospore

Dormant, tough bacterial structure that permits survival in extreme conditions.

Binary fission

Asexual process by which a prokaryote replicates its DNA and divides into two cells.

Gram-positive bacteria

Bacteria with thick peptidoglycan walls that retain crystal violet stain.

Gram-negative bacteria

Bacteria with thin peptidoglycan and outer membrane; appear pink after Gram stain.

Mitosis

Nuclear division producing two genetically identical diploid nuclei.

Meiosis

Two-successive cell divisions producing four genetically diverse haploid gametes.

Prophase

First stage of mitosis when chromosomes condense and spindle begins to form.

Metaphase

Mitotic stage where duplicated chromosomes align at the cell’s equatorial plane.

Anaphase

Stage in which sister chromatids separate and move to opposite poles.

Telophase

Final mitotic stage where nuclear envelopes reform around separated chromosomes.

Sister chromatid

One of two identical DNA copies attached at a centromere after replication.

Chromosome

Threadlike structure of DNA and proteins carrying genetic information.

Tetrad

Pair of homologous chromosomes (four chromatids) aligned during meiosis I.

Crossing-over

Exchange of DNA segments between homologous chromatids during prophase I.

Diploid

Cell containing two sets of chromosomes (2n), one from each parent.

Haploid

Cell with one complete set of chromosomes (n), typical of gametes.