Cell Biology, Photosynthesis, Respiration, and Molecular Genetics

Comprehensive vocabulary flashcards covering the key terms, mechanisms, and structures of photosynthesis, cellular respiration, membrane transport, protein biology, and molecular genetics.

Light Capture Stage

The photosynthetic phase in which sunlight is captured by pigment molecules to excite electrons from water, transferring them through an electron transport chain to the final electron acceptor, $\text{NADP}^+$.

Carbon Fixation Stage

The phase of photosynthesis in which chemical energy stored in $\text{NADPH}$ and $\text{ATP}$ is used to reduce $\text{CO}_2$ to synthesize carbohydrates.

Lumen

The internal fluid-filled space located inside the thylakoid membrane within a chloroplast.

Stroma

The fluid-filled region outside the thylakoids in a chloroplast where the Calvin cycle reactions occur.

Photosystem II

A protein-pigment complex in the thylakoid membrane that oxidizes water to obtain electrons, though it cannot independently produce electrons with enough energy to form $\text{NADPH}$.

Photosystem I

A protein-pigment complex that energizes electrons to reduce $\text{NADP}^+$, but lacks sufficient oxidation strength to split water molecules on its own.

Cyclic Electron Transport

A process where electrons exiting photosystem I are redirected from ferredoxin back into the electron transport chain upstream of the Cytochrome $b_6f$ proton pump.

Rubisco

The enzyme that catalyzes the carboxylation reaction combining $\text{CO}_2$ with RuBP into an unstable 6-carbon molecule, and can also exhibit an oxygenase function during photorespiration.

Glycolysis

An anaerobic metabolic pathway consisting of preparatory, cleavage, and payoff phases that partially breaks down glucose into pyruvate while yielding a net production of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Lactic Acid Fermentation

An anaerobic pathway in which pyruvate generated by glycolysis is reduced to lactic acid to regenerate $\text{NAD}^+$, producing small amounts of $\text{ATP}$.

Ethanol Fermentation

An anaerobic pathway wherein pyruvate releases $\text{CO}_2$ to form acetaldehyde, which is subsequently reduced to ethanol in order to regenerate $\text{NAD}^+$.

Pyruvate Oxidation

The mitochondrial stage of cellular respiration in which pyruvate is oxidized into an acetyl group and linked to Coenzyme A, producing one $\text{CO}_2$, one $\text{NADH}$, and one acetyl-CoA per pyruvate.

Citric Acid Cycle

An eight-reaction cyclic pathway (also known as the Krebs cycle) that completely oxidizes acetyl-CoA into two $\text{CO}_2$ molecules, regenerating oxaloacetate and producing $\text{ATP}$, $\text{NADH}$, and $\text{FADH}_2$.

Oxidative Phosphorylation

The synthesis of $\text{ATP}$ powered by the facilitated diffusion of protons back across the inner mitochondrial membrane down an electrochemical gradient, utilizing 4 protons for every $1\,\text{ATP}$ generated.

Cell Theory

The foundational biological principle stating that all organisms are composed of cells, the cell is the fundamental unit of life, and all cells arise from preexisting cells.

Amphipathic

A chemical property of molecules possessing both hydrophobic (nonpolar) and hydrophilic (polar) regions, such as phospholipids.

Liposome

A spherical lipid bilayer structure surrounding a central aqueous compartment that forms spontaneously from phospholipids at $\text{pH } 7$.

Facilitated Diffusion

The passive movement of molecules from high concentration to low concentration through membrane-spanning channel or carrier proteins without requiring energy.

Primary Active Transport

Transport that directly utilizes energy released by $\text{ATP}$ hydrolysis to move substances against their concentration gradients, such as an antiporter pumping $3\,\text{Na}^+$ out and $2\,\text{K}^+$ into the cell.

Secondary Active Transport

Transport that uses the potential energy stored in an established electrochemical gradient to drive the movement of other molecules against their gradients.

Turgor Pressure

The hydrostatic force exerted by water inside a cell against an enclosing boundary or object.

Glycine

A small, nonpolar amino acid whose minimal side chain provides structural flexibility within a folded polypeptide.

Proline

An amino acid that constrains polypeptide backbone rotation, introducing sharp bends into protein structures.

Cysteine

An amino acid containing a reactive sulfhydryl group that can form covalent disulfide bridges within the same protein or between distinct polypeptide chains.

Peptide Bond

A covalent linkage formed between the carboxyl group of one amino acid and the amino group of another via a dehydration synthesis reaction, characterized by limited rotation.

Protein Chaperones

Specialized helper proteins that assist in proper folding and protect polypeptides against denaturation.

Aminoacyl tRNA Synthetase

The enzyme responsible for attaching the correct amino acid to its corresponding tRNA molecule, thereby charging the tRNA.

Wobble

The relaxed, more variable pairing between the third base position of an mRNA codon and the first base position of the tRNA anticodon, providing geometric flexibility.

Cohesion

The intermolecular attraction that holds molecules of the same substance together, notably through hydrogen bonding between water molecules.

Adhesion

The attraction or stickiness that occurs between molecules of two different substances.

Surface Tension

A measure of the force or pressure required to stretch or break the surface of a liquid.

Pyrimidines

A class of nitrogenous bases composed of a single aromatic ring, including cytosine, thymine, and uracil.

Purines

A class of nitrogenous bases characterized by a double-ring structure, including adenine and guanine.

Phosphodiester Bond

The covalent bond linking consecutive nucleotides in a nucleic acid, joining the phosphate group of one nucleotide to the $3'\text{-OH}$ group of the next.

Central Dogma

The core framework of molecular biology describing the sequential directional flow of genetic information: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

RNA Processing

The eukaryotic modifications applied to pre-mRNA transcripts prior to nuclear export and translation, comprising $5'$ capping, poly-A tail addition, and RNA splicing.