Protein Structure, Enzymes, Nucleic Acids, and Cell Biology

Comprehensive vocabulary flashcards covering the structural hierarchy of proteins, enzyme kinetics, nucleic acids (DNA/RNA/ATP), cellular organelles, and plasma membrane dynamics from the lecture.

Dehydration synthesis

A chemical reaction that combines two amino acids together to form a peptide bond while releasing a molecule of water.

Dipeptide

A molecule formed by two amino acids connected together by a peptide bond.

Polypeptide

A polymer chain consisting of over $50$ amino acids linked by peptide bonds.

Hydrolysis reaction

A reaction that breaks a peptide bond by adding back a hydrogen atom from water to one amino acid and an oxygen and hydrogen atom to the other amino acid.

Primary structure

The linear sequence or unfolded chain of amino acids linked together by peptide bonds.

Secondary structure

The structural level formed by folding or winding an amino acid chain into corkscrew-shaped alpha helices or antiparallel beta pleated sheets, stabilized by hydrogen bonds.

Tertiary structure

The third-order three-dimensional folding of a polypeptide into a functional globular protein.

Quaternary structure

A fourth-order structural level that forms when two or more individual proteins or subunits combine, such as hemoglobin or transthyretin.

Transthyretin

A functional transport protein made of four identical subunits that moves thyroid hormone (thyroxine) through blood and cerebrospinal fluid.

Fibrous proteins

Stable, strand-like, water-insoluble structural proteins that provide mechanical support and tensile strength, such as collagen, keratin, and elastin.

Globular proteins

Compact, spherical, water-soluble functional proteins possessing active sites that are sensitive to environmental shifts in temperature and pH.

Denaturation

The process where a globular protein unfolds and loses its functional three-dimensional shape and active sites due to decreased pH or increased temperature.

Enzyme

A globular protein that acts as a biological catalyst to increase reaction speed by lowering the required activation energy without being consumed.

Apoenzyme

The large protein portion of a functional holoenzyme.

Cofactor

A small helper component needed by an enzyme to function, which can be a metal ion like iron or an organic coenzyme such as a vitamin.

Substrate

The specific chemical target that interacts temporarily with an enzyme's active site to undergo a reaction.

Induced fit model

The model of enzyme action where the enzyme and substrate cause each other to bend upon binding to force a chemical reaction to occur.

Nucleotide

The monomer building block of nucleic acids, consisting of a nitrogenous base, a five-carbon pentose sugar, and a phosphate group ($\text{PO}_4^{-2}$).

Purines

The larger class of nitrogenous bases composed of two linked rings of atoms, specifically adenine and guanine.

Pyrimidines

The smaller class of nitrogenous bases composed of a single ring of atoms, including cytosine, thymine (in DNA), and uracil (in RNA).

Complementary base pairing

The specific bonding rule in nucleic acids where adenine pairs with thymine via hydrogen bonds, and guanine pairs with cytosine.

Adenosine triphosphate (ATP)

An adenine-containing RNA nucleotide bonded to three phosphate groups that provides usable energy when its high-energy terminal phosphate bond is broken.

Phosphorylation

The process of transferring a phosphate group, typically from ATP, onto another chemical compound or protein to add energy or change its activity.

Fluid mosaic model

A model of the plasma membrane describing it as a dynamic, semi-solid lipid bilayer containing floating proteins whose fluidity is regulated by cholesterol.

Glycocalyx

A carbohydrate-rich sugar coating on the outer surface of the plasma membrane, made of glycolipids and glycoproteins, that serves as a biological marker for cell recognition.

Integral proteins

Membrane proteins firmly inserted into the lipid bilayer, typically spanning both layers as transmembrane proteins with hydrophobic and hydrophilic regions.

Peripheral proteins

Proteins that are not embedded in the lipid bilayer but are attached to the inner or outer surfaces, often hanging off integral proteins.

Tight junctions

Impermeable cell junctions formed by fused integral proteins of adjacent cell membranes that prevent fluids and molecules from leaking between cells.

Desmosomes

Anchoring junctions consisting of plaques, cadherin linker proteins, and keratin filaments that act like molecular Velcro to distribute tension and prevent tissues from tearing.

Gap junctions

Communicating junctions formed by transmembrane protein tunnels called connexons that allow ions and small molecules to pass directly from cell to cell for electrical coordination.

Rough endoplasmic reticulum (RER)

A network of intracellular chambers attached to the nucleus and studded with ribosomes that serves as a site for protein manufacturing.

Golgi apparatus

A cellular organelle of membranous chambers that processes and packages proteins and other molecules into vesicles for transport or exocytosis.

Mitochondria

Double-membraned organelles with folded inner membranes that utilize glucose and oxygen to synthesize ATP.

Peroxisomes

Membranous cellular sacs containing chemicals that neutralize dangerous metabolic byproducts known as free radicals.

Lysosomes

Membranous bubbles containing digestive chemicals that fuse with and destroy cellular debris or materials inside the cell.