Cell Biology Review: DNA, Proteins, Energy, and Cellular Components

Vocabulary flashcards covering key terms, historical milestones, molecular structures, metabolic concepts, and microscopy techniques across cell biology lecture materials.

Walther Flemming

German biologist who published drawings of mitosis in 1882, establishing that chromosomes are the physical carriers of hereditary information.

Phosphodiester Bond

Strong covalent bond that links the $5'$ phosphate group of one nucleotide to the $3'$ hydroxyl group of another, forming the sugar-phosphate backbone of nucleic acids in a $5' \rightarrow 3'$ direction.

Antiparallel

Arrangement of the two strands in a DNA double helix, running in opposite chemical directions ($5' \rightarrow 3'$ versus $3' \rightarrow 5'$).

Karyotype

An ordered display of the full set of chromosomes of a cell, lined up by length, centromere position, and chemical banding pattern during mitosis.

Chromatin

The complex of DNA and associated packaging, expression, and repair proteins that makes up eukaryotic chromosomes.

Nucleosome

The basic structural subunit of chromatin consisting of approximately $200$ nucleotide pairs of DNA wrapped around a core octamer of histone proteins.

Histone Octamer

Core protein complex composed of two molecules each of histones $H2A$, $H2B$, $H3$, and $H4$, around which $147$ nucleotide pairs of DNA wrap.

Histone H1

The linker histone protein that binds linker DNA and pulls adjacent nucleosomes together to condense chromatin into higher-order structures.

Chromatin Remodeling Complex

Protein complex that uses energy from ATP hydrolysis to alter chromatin structure by sliding DNA relative to the histone octamer.

Heterochromatin

Highly condensed form of interphase chromatin that is transcriptionally inactive and typically concentrated at centromeres and telomeres.

Euchromatin

Decondensed form of interphase chromatin that is accessible to transcription machinery and active in gene expression.

Nucleolus

Large nuclear structure formed around ribosomal RNA (rRNA) gene loops contributed by $10$ acrocentric chromosomes (chromosomes 13, 14, 15, 21, and 22), serving as the site of ribosome subunit assembly.

Peptide Bond

Covalent bond linking the carboxyl terminus of one amino acid to the amino terminus of another in a polypeptide chain.

Denaturation

Process by which a protein loses its folded 3D conformation and functional activity due to the disruption of noncovalent interactions.

Chaperone Protein

Helper protein that binds partially folded polypeptide chains or provides isolation chambers to ensure correct protein folding without harmful aggregation.

̑\alpha Helix

Common secondary structure motif in proteins, stabilized by hydrogen bonds between the backbone $N-H$ of one peptide bond and the $C=O$ of another located $4$ amino acids away.

Coiled-coil

Structural motif formed when $2$ or $3\, \alpha$ helices wrap around each other, burying hydrophobic side chains to minimize contact with aqueous surroundings.

$\beta$ Sheet

Secondary structure motif formed by hydrogen bonding between backbone peptide bonds in adjacent, parallel or antiparallel polypeptide strands.

Prion

An infectious, misfolded form of a protein that binds to normal copies of the protein and forces them to adopt the abnormal, aggregate-forming conformation.

Protein Domain

A modular segment of a polypeptide chain that folds independently into a stable structure with a specific function.

Disulfide Bond

Covalent $S-S$ cross-linkage formed by oxidation of two cysteine side chains, stabilizing a protein's favored conformation.

Lysozyme

Enzyme that catalyzes the hydrolytic cleavage of polysaccharide chains in bacterial cell walls.

Allosteric Control

Regulation of protein activity in which the binding of a regulatory molecule at a site distinct from the active site causes a conformational change that alters enzyme function.

Protein Kinase

Enzyme that catalyzes the addition of a phosphate group from ATP to specific amino acid side chains on target proteins.

Protein Phosphatase

Enzyme that catalyzes the hydrolytic removal of a phosphate group from a phosphorylated protein.

Catabolism

Metabolic pathways that break down complex food molecules into smaller ones, releasing energy that cells capture.

Anabolism

Biosynthetic metabolic pathways that use energy generated by catabolism to construct complex macromolecules from simpler building blocks.

Activated Carrier

Small molecule that temporarily stores energy or chemical groups in high-energy linkages (e.g., ATP, NADPH, Acetyl CoA) to drive energetically unfavorable reactions.

ATP (Adenosine Triphosphate)

The principal activated carrier in cells, containing two high-energy phosphoanhydride bonds whose hydrolysis to ADP releases $\Delta G^\circ = -30.5\,kJ/mole$ under standard conditions.

NADPH

Activated electron carrier specialized for anabolic and reductive chemical reactions, transferring two electrons and a hydride ion ($H^-$).

Amphipathic

Possessing both hydrophilic (polar) and hydrophobic (nonpolar) chemical properties within the same molecule, such as in phospholipids and fatty acids.

Saturated Fatty Acid

A fatty acid tail with no double bonds between carbon atoms, fully saturated with hydrogen atoms and capable of packing tightly into hard fats.

Unsaturated Fatty Acid

A fatty acid tail containing one or more double bonds ($C=C$), creating kinks that prevent tight packing and keeping the substance fluid at room temperature.

Glycosidic Bond

Covalent linkage formed by a condensation reaction that joins monosaccharide units together to form disaccharides and polysaccharides.

Light Microscopy

Microscopy technique using visible light to illuminate specimens, capable of magnifications up to $1000\times$ and resolving details down to $0.2\,\mu m$.

Transmission Electron Microscopy (TEM)

Electron microscopy method where an electron beam passes through thin tissue sections, providing detail of cell ultrastructure with resolution down to $1\,nm$.

Scanning Electron Microscopy (SEM)

Electron microscopy method where electrons bounce off a specimen's surface to construct a 3D image, resolving details between $3-20\,nm$.

Model Organism

An easily cultured species chosen for intensive laboratory study to uncover fundamental biological principles applicable to other organisms.

Arabidopsis thaliana

Model plant species valued in genetics and molecular biology because it can be grown indoors in large numbers and reproduces rapidly, producing offspring in $8-10$ weeks.

Caenorhabditis elegans

Model nematode worm with precisely $959$ body cells, widely used to study animal development and programmed cell death (apoptosis).