Molecules of Life, Cell Structure, and Molecular Genetics

Comprehensive vocabulary flashcards reviewing chemistry of life, cell structure, nucleic acids, DNA replication, transcription, translation, and protein structure.

Proton

A positively charged subatomic particle located in the atomic nucleus that possesses mass.

Neutron

An uncharged subatomic particle located in the atomic nucleus that possesses mass.

Electron

A negatively charged subatomic particle that orbits the nucleus and has very little mass.

Atomic Number

The total number of protons contained in an atom's nucleus, which defines the element.

Atomic Mass

The combined total number of protons and neutrons in an atom's nucleus.

Isotope

Atoms of the same element that differ in their neutron number while maintaining the same number of protons and electrons.

Ion

An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Cation

A positively charged ion formed when an atom loses electrons.

Anion

A negatively charged ion formed when an atom gains electrons.

Valence Electrons

Electrons residing in the outermost shell of an atom that determine its chemical reactivity and bonding capability.

Electronegativity

The intrinsic ability of an atom to attract shared electrons within a chemical bond.

Covalent Bond

A chemical bond formed when two atoms share electrons to fill their valence shells.

Polar Covalent Bond

A covalent bond resulting from unequally shared electrons between atoms due to a difference in electronegativity.

Nonpolar Covalent Bond

A covalent bond resulting from equally shared electrons between atoms of similar electronegativity.

Ionic Bond

A chemical bond formed through the electrostatic attraction between oppositely charged ions.

Hydrogen Bond

A weak bond formed between a partially positive hydrogen atom in a polar covalent molecule and an electronegative atom in another molecule.

pH

A logarithmic measure of hydrogen ion concentration in a solution, defined by the formula $\text{pH} = -\text{log}([\text{H}^+])$.

Van der Waals Forces

Weak electrostatic attractions between nonpolar molecules or hydrocarbon chains caused by temporary charge distribution from constant electron movement.

Steroid

A type of lipid composed of carbon atoms arranged in four fused rings, functioning in membranes and as hormone precursors.

Glycosidic Bond

The covalent linkage formed between monosaccharides to create complex carbohydrates or polysaccharides.

Phosphodiester Bond

The covalent bond that links the $3'-\text{OH}$ group of one nucleotide to the phosphate group attached to the $5'$ carbon of the next nucleotide.

Peptide Bond

The covalent bond joining adjacent amino acids formed via a dehydration reaction that removes a water molecule.

Triacylglycerol

A lipid storage molecule formed by the addition of three fatty acid chains to a glycerol molecule.

Saturated Fatty Acid

A fatty acid chain that lacks double bonds between carbon atoms, producing a straight structure that favors tight packing.

Unsaturated Fatty Acid

A fatty acid chain containing one or more carbon-carbon double bonds that introduce kinks and reduce packing tightness.

Cell Theory

The fundamental unifying theory stating that all living organisms are made up of cells, the cell is the fundamental unit of life, and all cells come from pre-existing cells.

Prokaryotic Cell

A cell type characterized by the absence of a nucleus and internal membrane-bound compartmentalization.

Eukaryotic Cell

A cell type possessing a membrane-bound nucleus and internal membrane-bound organelles.

Amphipathic

Having both hydrophilic (water-loving) and hydrophobic (water-fearing) regions in a single molecule, such as a phospholipid.

Fluid Mosaic Model

The conceptual model of membrane structure describing a dynamic bilayer of lipids and proteins capable of lateral movement.

Selective Permeability

The property of a cell membrane that allows only specific molecules to pass through while restricting others.

Facilitated Diffusion

The passive transport of molecules across a membrane from high to low concentration through a specific protein channel or carrier.

Active Transport

The energy-dependent movement of molecules across a cell membrane against their concentration gradient.

Sodium-Potassium Pump

An active transport antiporter protein that uses ATP to transport three $\text{Na}^+$ ions out of the cell and two $\text{K}^+$ ions into the cell.

Secondary Active Transport

A transport mechanism in which an electrochemical gradient generated by primary active transport drives the movement of another molecule against its concentration gradient.

Turgor Pressure

The osmotic pressure exerted by water pressing against the cell wall in plant and fungal cells.

Endomembrane System

A system of interconnected eukaryotic membranes including the nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, and cell membrane.

Rough Endoplasmic Reticulum

A membrane network studded with ribosomes that is actively involved in protein synthesis and processing.

Smooth Endoplasmic Reticulum

A membrane network lacking ribosomes that acts as the primary site of lipid and steroid synthesis.

Golgi Apparatus

An organelle composed of flattened cisternae that modifies, sorts, and packages proteins and lipids for transport.

Lysosome

A specialized organelle containing digestive enzymes maintained at $\text{pH} = 5$ to degrade damaged or unneeded macromolecules.

Endosymbiont Theory

The evolutionary theory stating that eukaryotic organelles such as mitochondria and chloroplasts originated from engulfed free-living prokaryotes.

Purine

A class of double-ring nitrogenous bases found in nucleic acids, comprising Adenine (A) and Guanine (G).

Pyrimidine

A class of single-ring nitrogenous bases found in nucleic acids, comprising Cytosine (C), Thymine (T), and Uracil (U).

Nucleoside

A molecule consisting of a nitrogenous base covalently bound to a pentose sugar (ribose or deoxyribose) without phosphate groups.

Nucleotide

The monomer building block of nucleic acids consisting of a pentose sugar, a nitrogenous base, and one or more phosphate groups.

Base Stacking

Stabilizing nonpolar interactions between adjacent stacked nitrogenous bases in a nucleic acid double helix.

Central Dogma

The basic framework of genetic information flow stating that DNA is transcribed into RNA, which is then translated into protein.

Promoter

A conserved region of DNA located upstream of a gene that binds transcription factors and RNA polymerase to initiate transcription.

RNA Polymerase

The enzyme responsible for transcribing DNA into a complementary RNA strand in the $5' \rightarrow 3'$ direction.

Sigma Factor

A bacterial protein factor that associates with RNA polymerase to recognize promoter sequences on DNA.

5' Cap

A modified 7-methylguanosine base linked via a $5'-\text{to}-5'$ phosphate bridge to the $5'$ end of eukaryotic pre-mRNA for protection and ribosome recognition.

Polyadenylation

The addition of a poly(A) tail to the $3'$ end of eukaryotic primary mRNA transcripts for protection and cytoplasmic transport.

Spliceosome

A molecular machine that carries out RNA splicing by removing non-coding introns and joining coding exons together.

Amino Acid

The monomer subunit of proteins, consisting of a central alpha carbon bound to an amino group, a carboxyl group, a hydrogen, and a variable R group.

Primary Structure

The specific linear sequence of amino acids in a polypeptide chain linked together by peptide bonds.

Alpha Helix

A coiled protein secondary structure stabilized by hydrogen bonds between carbonyl and amide backbone groups four amino acids apart.

Beta Sheet

A pleated protein secondary structure formed by hydrogen bonding between adjacent parallel or antiparallel polypeptide strands.

Tertiary Structure

The overall three-dimensional folded conformation of a single polypeptide chain governed by noncovalent side-chain interactions.

Quaternary Structure

The functional multi-subunit protein complex resulting from interactions between two or more individual polypeptide chains.

Codon

A triplet sequence of nucleotides in mRNA that codes for a specific amino acid or translation stop signal.

Anticodon

A three-nucleotide sequence on the anticodon loop of a tRNA molecule that base-pairs with a complementary mRNA codon.

Aminoacyl tRNA Synthetase

An enzyme that attaches the correct amino acid to its corresponding tRNA molecule to form a charged tRNA.

Shine-Dalgarno Sequence

A ribosomal binding site sequence ($5'-\text{AGGAGGU}-3'$) in prokaryotic mRNA that positions the ribosome at the start codon.

Signal-Recognition Particle

A protein-RNA complex that binds the signal sequence of a nascent polypeptide, halting translation and targeting the complex to the ER membrane.