Lecture 7: The Eukaryotic Cell

Vocabulary flashcards covering the structure and function of eukaryotic organelles, protein sorting mechanisms, cytoskeletal components, motor proteins, cilia/flagella, extracellular structures, and organelle evolution from Lecture 7.

Differential Centrifugation

A cell fractionation technique that separates cell components based on size and density, where larger and denser particles pellet at lower centrifugal forces.

Chromatin

A complex of DNA and associated histone proteins located within the nucleus.

Nuclear Envelope

A double-membrane structure enclosing the nucleoplasm whose outer membrane is continuous with the endoplasmic reticulum.

Nucleolus

A region within the nucleus that serves as the site for ribosome pre-assembly.

Nuclear Pores

Complex protein gates embedded in the nuclear envelope that regulate molecular traffic into and out of the nucleus.

Nuclear Lamina

A network of intermediate filaments attached to the inner nuclear membrane and chromatin that maintains nuclear shape.

Ribosome

A non-membrane-bound cell structure composed of rRNA and proteins that serves as the site for protein synthesis.

Prokaryotic Ribosome

A $70\text{S}$ ribosome consisting of a $50\text{S}$ large subunit ($5\text{S}$ rRNA, $23\text{S}$ rRNA, and $34$ polypeptides) and a $30\text{S}$ small subunit ($16\text{S}$ rRNA and $21$ polypeptides).

Eukaryotic Ribosome

An $80\text{S}$ ribosome consisting of a $60\text{S}$ large subunit ($5\text{S}$, $5.8\text{S}$, $28\text{S}$ rRNA, and $49$ polypeptides) and a $40\text{S}$ small subunit ($18\text{S}$ rRNA and $33$ polypeptides).

Chloramphenicol

An antibiotic that binds to the $50\text{S}$ prokaryotic ribosomal subunit and blocks peptide bond formation.

Tetracycline

An antibiotic that binds to the $30\text{S}$ prokaryotic ribosomal subunit and prevents incoming tRNA binding, interfering with protein synthesis.

Endomembrane System

A interconnected network of cellular membranes including the plasma membrane, nuclear envelope, endoplasmic reticulum, Golgi apparatus, and lysosomes connected via vesicular transport.

Rough Endoplasmic Reticulum (RER)

A membrane network of flattened sacs and cisternae associated with ribosomes that functions in protein folding, glycosylation, and tagging for cellular delivery.

Smooth Endoplasmic Reticulum (SER)

A tubular membrane network lacking ribosomes involved in lipid and steroid synthesis, toxin modification, glycogen degradation in animals, polysaccharide synthesis, and calcium storage.

Cis Face (Golgi Apparatus)

The receiving region of the Golgi apparatus situated close to the nucleus or RER that receives protein-containing vesicles.

Trans Face (Golgi Apparatus)

The shipping region of the Golgi apparatus located closer to the plasma membrane that dispatches sorted and packaged proteins in vesicles.

Lysosomes

Membrane-enclosed organelles containing hydrolytic enzymes at an acidic interior ($\text{pH} = 5$) that function in intracellular macromolecule digestion, autophagy, and phagocytosis.

Mitochondria

Double-membrane powerhouses of the cell where cellular respiration and ATP production occur, containing their own DNA, ribosomes, outer membrane, inner membrane, cristae, and matrix.

Cristae

Infoldings of the inner mitochondrial membrane that house key molecules required for generating ATP from fuel molecules.

Chloroplasts

Double-membrane plastids in plants and photosynthetic protists containing thylakoids, stroma, DNA, and ribosomes that convert light energy into chemical energy in sugars.

Thylakoid Membrane

The internal membrane system of chloroplasts composed of galactolipids, sulfolipids, and 10% phospholipids where chlorophyll harvests light energy to generate ATP and NADPH.

Chromoplasts

Plastids in plant cells specialized for pigment storage.

Leucoplasts

Non-pigmented plastids specialized for storing starch in plant tissues like potato tubers.

Peroxisomes

Organelles containing approximately 50 enzymes that function in breaking down toxic peroxides, oxidizing fatty acids, and synthesizing lipids.

Glyoxysomes

Specialized plant organelles where stored lipids are converted into carbohydrates.

Vacuoles

Large membrane-bound organelles in plants, fungi, and protists that function in turgor pressure maintenance, digestion, waste storage, and storing anthocyanin pigments.

Signal Peptide

A specific location-encoded amino acid sequence built into a polypeptide chain that directs a protein to its designated cellular location.

Nuclear Localization Signal (NLS)

A sequence-based signal peptide (e.g., -Pro-Pro-Lys-Lys-Arg-Lys-Val-) that directs nuclear proteins like DNA polymerase and histones into the nucleus via importins.

KDEL Sequence

A C-terminal sequence signal (Lys-Asp-Glu-Leu) that targets proteins for retention or retrieval back to the endoplasmic reticulum.

Signal Recognition Particle (SRP)

A complex that binds to a signal peptide on a nascent polypeptide, halting translation until binding to a receptor protein on the RER membrane.

Ubiquitin

A post-translational protein modification tag covalently attached to target proteins to mark them for degradation by the proteasome.

Microfilaments

Cytoskeletal strands ($7\,\text{nm}$ diameter) composed of actin monomers involved in cell shape, microvilli support, cytoplasmic streaming, muscle contraction, pseudopodia, and cytokinesis.

Intermediate Filaments

Ropelike cytoskeletal fibers ($8\text{--}12\,\text{nm}$ diameter) made of fibrous proteins that anchor cellular structures, form the nuclear lamina, and resist mechanical stretch in desmosomes.

Microtubules

Hollow cylindrical cytoskeletal structures ($25\,\text{nm}$ diameter) made of $\alpha$-tubulin and $\beta$-tubulin dimers that serve as motor protein tracks and form the mitotic spindle.

Kinesin

A motor protein that hydrolyzes ATP to walk cargo-loaded vesicles toward the plus ($+$) end of microtubule tracks.

Dynein

A motor protein that walks toward the minus ($-$) end of microtubules and powers the sliding of microtubule doublets in cilia and flagella.

9+2 Pattern

The structural arrangement of microtubules in cilia and eukaryotic flagella, consisting of nine outer fused doublets and two unfused central single microtubules.

Flagellin

The $53\,\text{kDa}$ protein subunit that assembles to form the rotatory, proton-driven flagella of prokaryotic cells.

Plasmodesmata

Membrane-lined channels traversing plant cell walls that connect the cytoplasm of adjacent cells.

Extracellular Matrix (ECM)

An extracellular network in animal cells made of collagen fibers, gel-like proteoglycans, and fibronectin linked to the cytoskeleton via integrins.

Endosymbiosis Theory

The evolutionary proposal stating that eukaryotic organelles such as mitochondria and chloroplasts originated when ancestral host cells ingested free-living prokaryotes.