An Introduction to Cells — Key Terms (Vocabulary)

Vocabulary flashcards covering major terms and definitions from the lecture notes on cells, organelles, membrane transport, and the cell life cycle.

Cell theory

Cells are the building blocks of all organisms; all cells come from division of preexisting cells; cells are the smallest units that perform all vital physiological functions; each cell maintains homeostasis at the cellular level.

Cytology

Branch of cell biology—the study of cells; includes germ (sex) cells and somatic (body) cells.

Germ cells (sex cells)

Male sperm and female oocytes (cells that develop into ova).

Somatic cells

All body cells except sex cells.

Plasma membrane

Cell membrane that separates cytoplasm from the extracellular fluid; phospholipid bilayer with proteins and carbohydrates; provides isolation, exchange regulation, sensitivity, and structural support.

Glycocalyx

Glycoproteins and glycolipids forming a sticky sugar coat outside the plasma membrane; functions include lubrication, protection, anchoring, binding specificity, and immune recognition.

Phospholipid bilayer

Membrane with hydrophilic heads facing watery environments and hydrophobic tails inside; acts as a barrier to ions and water-soluble compounds.

Integral proteins

Proteins located within the membrane that function as channels, carriers, or receptors.

Peripheral proteins

Proteins bound to the inner or outer surface of the plasma membrane.

Anchoring proteins

Stabilizers that attach to inside or outside structures to help maintain cell shape.

Receptor proteins

Proteins that bind ligands and trigger cellular responses.

Carrier proteins

Transport specific solutes across the membrane (may be passive or active).

Channel proteins

Proteins that regulate water and solute passage; can be gated to control flow.

Ribosome

Organelle that synthesizes proteins; exists as free ribosomes in the cytosol or fixed ribosomes on the rough endoplasmic reticulum.

Free ribosomes

Ribosomes suspended in cytosol; synthesize proteins for intracellular use.

Fixed ribosomes

Ribosomes attached to rough endoplasmic reticulum; synthesize proteins for packaging/ secretion.

Cytoskeleton

Structural network of proteins (microfilaments, intermediate filaments, microtubules) that gives shape and strength and aids movement.

Microfilaments

Thin, actin-based filaments involved in mechanical strength and cytosol flow; interact with myosin in muscle contraction.

Intermediate filaments

Mid-sized cytoskeletal elements that provide durability and help maintain cell shape.

Microtubules

Large hollow tubes of tubulin that support the cell, position organelles, and form the spindle apparatus; thickenings during transport.

Microvilli

Extensions of the plasma membrane containing microfilaments; increase surface area for absorption.

Cilia (primary and motile)

Long extensions with microtubules; primary cilium is nonmotile and sensor-like; motile cilia move materials across surfaces.

Basal body

Structure at the base of a cilium that anchors it to the cell; similar to a centriole.

Centrioles

Paired, nine-triplet microtubule structures that organize the spindle apparatus during cell division.

Centrosome

Cytoplasmic region near the nucleus that surrounds centrioles and organizes microtubules.

Nucleus

Largest organelle; cell’s control center containing the nuclear envelope, nucleolus, and chromatin.

Nuclear envelope

Double membrane surrounding the nucleus; contains perinuclear space and nuclear pores.

Nucleolus

Site of rRNA synthesis and assembly of ribosomal subunits.

Nucleoplasm

Fluid inside the nucleus containing nucleotides, enzymes, nucleoproteins, and chromatin.

Chromatin

Nucleoprotein complex of DNA and proteins; condenses to form chromosomes during cell division.

Nucleosome

DNA wrapped around histone proteins.

Chromosome

Condensed DNA molecule visible during cell division; consists of two sister chromatids held at the centromere.

Nuclear pore

Protein complex that spans the nuclear envelope to regulate transport between nucleus and cytoplasm.

G1 phase

First growth phase of the cell cycle; cell grows, duplicates organelles, begins centriole replication.

S phase

DNA replication phase; chromosomes are duplicated.

G2 phase

Second growth phase; final protein synthesis and centriole replication complete.

Mitosis

Nuclear division producing two identical nuclei; includes prophase, metaphase, anaphase, and telophase.

Cytokinesis

Division of the cytoplasm, resulting in two separate daughter cells.

Apoptosis

Programmed, genetically controlled cell death.

Endoplasmic reticulum (ER)

Network of membranous channels; cisternae; transports and processes molecules within cytoplasm.

Rough endoplasmic reticulum (RER)

ER with ribosomes; synthesizes proteins and glycoproteins; proteins folded and packed into transport vesicles.

Smooth endoplasmic reticulum (SER)

ER without ribosomes; synthesizes lipids and carbohydrates; stores glycogen; detoxifies drugs.

Golgi apparatus

Stacked membranes that modify, package, and sort proteins and lipids for secretion or delivery to other organelles.

Lysosome

Digestive vesicles containing enzymes; primary lysosomes become secondary lysosomes when fusing with damaged organelles; autolysis can occur.

Autolysis

Self-destruction of damaged cells via lysosomal enzymes.

Proteasome

Enzyme-containing organelles that disassemble damaged proteins for recycling.

Peroxisome

Small vesicles containing enzymes; break down fatty acids and neutralize toxins; produce H2O2 which is broken down by catalase.

Mitochondrion

Double-membrane organelle with cristae; produces ATP via aerobic metabolism (glycolysis in cytosol, Krebs cycle and ETC in mitochondria).

Cristae

Folded inner membrane surfaces of mitochondria where the electron transport chain occurs.

Matrix

Fluid inside the mitochondrion where the Krebs cycle occurs and where enzymes reside.

ATP

Adenosine triphosphate; primary energy currency of the cell.

Diffusion

Net movement of solutes from an area of higher concentration to lower concentration along a concentration gradient.

Osmosis

Diffusion of water across a selectively permeable membrane toward higher solute concentration.

Osmolarity

Total solute concentration of a solution; relates to tonicity (isotonic, hypotonic, hypertonic) regarding cellular effects.

Isotonic solution

Solute concentration equal to that inside a cell; no net osmosis; cell size remains stable.

Hypotonic solution

Lower solute concentration than the cell; water enters the cell; may cause swelling or rupture.

Hypertonic solution

Higher solute concentration than the cell; water leaves the cell; cell shrinks.

Facilitated diffusion

Carrier-mediated diffusion down a concentration gradient; requires a carrier protein (e.g., glucose transport).

Active transport

Transport that moves substrates against their concentration gradient; requires energy (ATP) and carrier proteins.

Primary active transport

Direct use of ATP to pump substances across the membrane (e.g., Na+/K+ pump: 3 Na+ out, 2 K+ in per ATP).

Secondary active transport

Uses a gradient established by primary active transport to drive transport of another solute (e.g., Na+ gradient drives glucose uptake).

Endocytosis

Bulk transport into the cell via vesicles; includes receptor-mediated endocytosis, pinocytosis, and phagocytosis.

Exocytosis

Bulk transport out of the cell; vesicles fuse with the plasma membrane to release contents.

Receptor-mediated endocytosis

Ligand binding to receptors triggers vesicle formation at clathrin-coated pits or caveolae.

Pinocytosis

Cell drinking; endosomes engulf extracellular fluid and small solutes.

Phagocytosis

Cell eating; engulfment of large particles by pseudopodia forming phagosomes.

DNA replication

Process by which DNA duplicates before cell division; helicases unwind; DNA polymerase adds complementary nucleotides; ligases join fragments.

Helicase

Enzyme that unwinds double-stranded DNA to expose bases for replication.

DNA polymerase

Enzyme that bonds complementary nucleotides to form new DNA strands; operates on leading and lagging strands.

Leading strand

Continuous DNA synthesis toward the replication fork.

Lagging strand

DNA synthesis away from the replication fork; formed in segments later joined by ligase.

Ligase

Enzyme that joins Okazaki fragments on the lagging strand to create a continuous strand.

Transcription

Synthesis of RNA from a DNA template; RNA polymerase binds promoter and builds mRNA; introns may be removed and exons spliced later.

RNA polymerase

Enzyme that catalyzes RNA synthesis from a DNA template.

mRNA

Messenger RNA; carries the genetic code from DNA to ribosomes for protein synthesis.

tRNA

Transfer RNA; delivers specific amino acids to the growing polypeptide at the ribosome; contains anticodon that pairs with mRNA codon.

rRNA

Ribosomal RNA; component of ribosomes aiding in protein synthesis.

Codon

Three-base sequence on mRNA that specifies a particular amino acid.

Anticodon

Three-base sequence on tRNA that pairs with a complementary mRNA codon.

Genetic code

Table mapping codons (mRNA triplets) to amino acids.

Start codon

Most often AUG; signals the beginning of translation and the start of methionine incorporation.

Stop codon

Codons (e.g., UAA, UAG, UGA) that signal termination of translation.

Sodium–potassium pump

Na+/K+ ATPase; uses one ATP to exchange 3 Na+ out and 2 K+ in, maintaining electrochemical gradients.

Interphase

Nondividing phase of the cell cycle comprising G1, S, and G2 (and G0 for some cells) when the cell conducts normal functions and prepares for division.