Mader Biology: Cellular Respiration, The Cell Cycle, and Photosynthesis

Comprehensive vocabulary flashcards covering cellular respiration, cell cycle regulation, mitosis, and photosynthetic pathways based on Mader & Windelspecht Biology.

Cellular Respiration

An aerobic cellular process that breaks down nutrient molecules produced by photosynthesizers (usually glucose into $\text{CO}_2$ and $\text{H}_2\text{O}$) with the concomitant, stepwise production of $\text{ATP}$.

$\text{NAD}^+$ (Nicotinamide Adenine Dinucleotide)

A coenzyme of oxidation-reduction used repeatedly in cellular respiration; it is oxidized when it gives up electrons and reduced when it accepts two electrons and one hydrogen ion ($\text{H}^+$) to form $\text{NADH}$.

$\text{FAD}$ (Flavin Adenine Dinucleotide)

A coenzyme of oxidation-reduction sometimes used instead of $\text{NAD}^+$; it accepts two electrons and two hydrogen ions ($\text{H}^+$) to become $\text{FADH}_2$.

Glycolysis

An anaerobic phase of cellular respiration occurring in the cytoplasm that breaks down one glucose molecule into two molecules of pyruvate through a series of $10$ enzyme-catalyzed reactions, netting $2\,\text{ATP}$ and $2\,\text{NADH}$.

Substrate-Level ATP Synthesis

A mode of $\text{ATP}$ formation occurring during glycolysis and the citric acid cycle where an enzyme directly transfers a high-energy phosphate group from an organic substrate (such as $\text{BPG}$) to $\text{ADP}$.

Fermentation

An anaerobic process occurring in the cytoplasm when $\text{O}_2$ is unavailable, reducing pyruvate to either lactate (in animals and certain bacteria) or alcohol and $\text{CO}_2$ (in plants and yeast) to recycle $\text{NADH}$ back to $\text{NAD}^+$, yielding a net of $2\,\text{ATP}$ ($2.1\%$ efficiency).

Preparatory (Prep) Reaction

A phase occurring in the mitochondrial matrix that converts each of the two pyruvate molecules into a $2\text{-carbon}$ acetyl group attached to Coenzyme A ($\text{acetyl-CoA}$), releasing two carbons as $\text{CO}_2$ and producing $2\,\text{NADH}$ per glucose.

Citric Acid Cycle

A cyclical series of reactions in the mitochondrial matrix (also called the Krebs cycle) that begins by combining a $C_2$ acetyl group with a $C_4$ molecule (oxaloacetate) to form citrate ($C_6$); it turns twice per glucose, producing $4\,\text{CO}_2$, $2\,\text{ATP}$, $6\,\text{NADH}$, and $2\,\text{FADH}_2$.

Cytochrome

Iron-containing hemoprotein carrier molecules located in complex arrays along the mitochondrial cristae that successively transfer energy-rich electrons along the electron transport chain.

Chemiosmosis

The process of producing $\text{ATP}$ driven by an electrochemical gradient of hydrogen ions ($\text{H}^+$) flowing through the $\text{ATP}$ synthase complex across a membrane.

Catabolism

Degradative metabolic reactions that break down complex molecules into simpler ones; these reactions tend to be exergonic and release energy.

Anabolism

Synthetic metabolic reactions that build complex molecules from simpler precursors using intermediates from the metabolic pool; these reactions tend to be endergonic and consume energy.

Deamination

The removal of an amino group ($\text{NH}_2$) from an amino acid occurring in the liver, which generates poisonous ammonia ($\text{NH}_3$) that is rapidly converted to urea.

Cell Cycle

An orderly sequence of stages extending from the time a eukaryotic cell first divides until the resulting daughter cells divide, consisting of interphase ($G_1$, $S$, $G_2$) and the mitotic stage ($M$).

$G_0$ Stage

A resting state of the cell cycle where cells perform their normal daily functions but do not prepare for division or replicate DNA; typical of mature nerve and muscle cells.

Sister Chromatids

Two identical double-helical DNA strands formed during the $S$ phase of interphase, held together at a single region termed the centromere until separated during mitosis.

Cyclins

A family of internal signaling proteins whose concentrations rise and fall during the cell cycle, ensuring specific checkpoints ($G_1$, $G_2$, $M$) are satisfied before progressing to the next stage.

Apoptosis

Programmed cell death mediated by caspase enzymes, characterized by nuclear collapse, chromatin condensation, membrane blistering (blebbing), and engulfment of cell fragments by white blood cells.

p53 Protein

A critical signaling tumor suppressor protein that halts the cell cycle at the $G_1$ checkpoint when DNA damage occurs to attempt repair, or initiates apoptosis if repair fails; mutated or deleted in half of human cancers.

Nucleosome

A structural unit of eukaryotic chromatin consisting of a length of double-stranded DNA wrapped around a core octamer of eight histone proteins, appearing like beads on a string.

Euchromatin

The loosely coiled, genetically active form of chromatin organized into radial loops that is accessible to RNA polymerase and transcription factors for gene expression.

Heterochromatin

A highly compacted, tightly condensed form of chromatin containing inactive genes that are rarely transcribed.

Diploid ($2n$)

The condition of having two sets of each type of chromosome; in humans, the diploid number is $2n = 46$ ($23$ paternal and $23$ maternal).

Centrosome

The main microtubule-organizing center of the cell, which contains a pair of barrel-shaped centrioles oriented at right angles in animal cells and organizes the mitotic spindle.

Kinetochore

A specialized protein complex that develops on each side of a centromere during prometaphase, connecting sister chromatids to kinetochore spindle fibers stretching to opposite poles.

Metaphase Plate

The equatorial plane across the center of the fully formed mitotic spindle along which centromeres of duplicated chromosomes align during metaphase.

Cleavage Furrow

An indentation that appears between daughter nuclei during animal cell cytokinesis, produced by a contractile ring of actin filaments constricting like a drawstring to pinch the cell in two.

Cell Plate

The precursor of a new plant cell wall that forms during cytokinesis from the fusion of Golgi-derived membrane-bounded vesicles across the dividing mother cell.

Metastasis

The process by which malignant cancer cells detach from the primary tumor, invade blood or lymphatic vessels, and establish new secondary tumors at distant sites in the body.

Angiogenesis

The formation of new blood vessels stimulated by cancer cells to supply a growing tumor with nutrients and oxygen.

Proto-oncogene

A normal gene coding for a growth factor, receptor protein, or signaling protein in a stimulatory pathway that promotes cell cycle progression; when mutated, it can become an oncogene causing cancer.

Tumor Suppressor Gene

A gene that codes for proteins inhibiting the cell cycle or promoting apoptosis (such as $RB$ and $p53$); its inactivation or loss of function leads to uncontrolled cell division.

Telomeres

Specialized repeating nucleotide sequences located at the ends of eukaryotic chromosomes that shorten with each cell division, eventually limiting the division potential of normal cells.

Binary Fission

An asexual reproductive process in prokaryotes (bacteria and archaea) where a single circular chromosome replicates, attaches to the plasma membrane, and separates as the cell elongates and splits into two identical daughter cells.

Autotrophs

Organisms (including plants, algae, and cyanobacteria) that capture solar energy and synthesize their own organic food molecules (carbohydrates) via photosynthesis.

Stomata

Microscopic openings on the leaf epidermis through which carbon dioxide ($\text{CO}_2$) enters and oxygen ($\text{O}_2$) and water vapor exit.

Chloroplast

The double-membraned organelle in photosynthetic eukaryotes containing chlorophyll, thylakoid membranes, and a fluid stroma, where photosynthesis takes place.

Thylakoid

A flattened, saclike membrane structure inside chloroplasts organized into stacks called grana, containing chlorophyll pigments and electron transport chains for the light reactions.

Stroma

The fluid-filled internal space of a chloroplast surrounding the thylakoid membranes where the Calvin cycle reactions take place to reduce $\text{CO}_2$ into carbohydrates.

Absorption Spectrum

A graph plotting the relative absorption of various wavelengths of visible light ($380\text{ nm}$ to $750\text{ nm}$) by a photosynthetic pigment such as chlorophyll $a$, chlorophyll $b$, or carotenoids.

Carotenoids

Accessory photosynthetic pigments that absorb light in the violet-blue-green wavelengths and reflect yellow and orange light.

Photosystem

A light-capturing unit located in the thylakoid membrane consisting of a pigment complex antenna and electron acceptors, designated as photosystem I ($\text{PS I}$) or photosystem II ($\text{PS II}$).

Noncyclic Pathway

A photosynthetic light reaction pathway beginning in $\text{PS II}$ that extracts electrons from water, pumps protons to generate $\text{ATP}$, and transfers the electrons permanently via $\text{PS I}$ to $\text{NADP}^+$, producing $\text{NADPH}$.

Cyclic Pathway

An alternate photosynthetic pathway using only photosystem I ($\text{PS I}$) and an electron transport chain to produce $\text{ATP}$ without generating $\text{NADPH}$ or oxygen.

Calvin Cycle

The cyclical light-independent series of reactions in the chloroplast stroma ($C_3$ photosynthesis) that uses $\text{ATP}$ and $\text{NADPH}$ to reduce atmospheric $\text{CO}_2$ into carbohydrates via fixation, reduction, and regeneration.

RuBP Carboxylase (Rubisco)

The enzyme that speeds up carbon dioxide fixation in the Calvin cycle by attaching $\text{CO}_2$ to a $5\text{-carbon}$ ribulose-1,5-bisphosphate ($\text{RuBP}$) molecule, forming an unstable $6\text{-carbon}$ intermediate that splits into two $3\text{-carbon}$ molecules ($\text{3PG}$).

Glyceraldehyde-3-Phosphate (G3P)

The $3\text{-carbon}$ carbohydrate product of the Calvin cycle that serves as the versatile building block for glucose phosphate, sucrose, starch, cellulose, fatty acids, and amino acids.

Photorespiration

A wasteful process in $C_3$ plants occurring in hot, dry conditions when stomata close and oxygen combines with $\text{RuBP}$ instead of $\text{CO}_2$, producing $\text{CO}_2$ and reducing photosynthetic efficiency.

$C_4$ Plants

Plants that avoid photorespiration by spatially partitioning carbon fixation, fixing $\text{CO}_2$ to $\text{PEP}$ in mesophyll cells to form oxaloacetate ($C_4$), which releases $\text{CO}_2$ to the Calvin cycle inside bundle sheath cells.

CAM (Crassulacean-Acid Metabolism)

A photosynthetic adaptation to extreme aridity found in pineapples and other plants that temporarily partitions carbon fixation by fixing $\text{CO}_2$ into $C_4$ molecules at night and releasing it to the Calvin cycle during the day while stomata remain closed.