General Biology I: Cell Structure, Membrane Transport, Metabolism, and Cellular Respiration

Comprehensive vocabulary flashcards covering the structural components of prokaryotic and eukaryotic cells, cell membrane transport and fluidity, thermodynamic laws and enzyme mechanics in metabolism, and the biochemical steps of cellular respiration and fermentation.

Nucleoid

The non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.

Nucleolus

A specialized structure in the nucleus where ribosomal RNA is synthesized from instructions in the DNA and ribosomal subunits are assembled.

Chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes; it exists in a dispersed fibrous form when the cell is not dividing.

Nuclear envelope

A double membrane perforated with pore complexes that encloses the nucleus, separating its contents from the cytoplasm and continuous with the endoplasmic reticulum.

Ribosomes

Complexes made of ribosomal RNA and protein that carry out protein synthesis; they can exist free in the cytosol or bound to the endoplasmic reticulum or nuclear envelope.

Endomembrane system

The collection of membranes inside and around a eukaryotic cell—including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, vacuoles, and plasma membrane—that coordinates protein traffic and metabolic functions.

Smooth ER

The portion of the endoplasmic reticulum that lacks ribosomes; functions include lipid synthesis, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions ($\text{Ca}^{2+}$).

Rough ER

The portion of the endoplasmic reticulum studded with ribosomes; aids in the synthesis of secretory and membrane proteins, adds carbohydrates to proteins to create glycoproteins, and produces new membrane.

Golgi apparatus

An organelle consisting of stacks of flat membranous sacs (cisternae) that has polarity ($cis$ face receiving cargo from the ER and $trans$ face shipping cargo out), modifying, sorting, and packaging products into vesicles.

Lysosome

A membranous sac of hydrolytic enzymes found in animal cells that functions at an acidic, low $\text{pH}$ to digest macromolecules, ingested substances, and damaged organelles.

Autophagy

The recycling process in which a cell consumes and degrades its own damaged organelles and intracellular components via lysosomal enzymes.

Central vacuole

A large membrane-bounded vesicle found in mature plant cells that plays roles in storage, waste disposal, water balance, cell growth, and holding inorganic ions such as potassium and chloride.

Mitochondria

Double-membrane enclosed organelles that perform cellular respiration, utilizing oxygen to extract energy from sugars, fats, and other fuels to generate $\text{ATP}$.

Chloroplasts

Photosynthetic organelles found in plants and algae that contain thylakoid sacs stacked into grana immersed in fluid stroma, converting solar energy into chemical energy.

Peroxisome

A specialized metabolic compartment bounded by a single membrane that contains enzymes transferring hydrogen atoms from substrates to oxygen, producing hydrogen peroxide ($\text{H}_2\text{O}_2$) which is then converted to $\text{H}_2\text{O}$.

Microtubules

Hollow rods measuring approximately $25\,\text{nm}$ in diameter constructed from globular tubulin dimers; they shape the cell, serve as tracks for motor proteins, and form cilia and flagella.

Microfilaments

Thin, solid rods about $7\,\text{nm}$ in diameter built from actin protein subunits; they function in cell motility, cell crawling, and interact with myosin to produce muscle contraction.

Intermediate filaments

Fibrous proteins coiled into thick cables measuring $8\text{--}12\,\text{nm}$ in diameter, such as keratins; they are more permanent fixtures found in some animal cells that maintain cell shape and anchor the nucleus.

Plasmodesmata

Open channels through plant cell walls that connect the cytoplasm of adjacent plant cells, allowing water and small solutes to pass freely between them.

Tight junctions

Intercellular junctions in animal cells where plasma membranes of neighboring cells are pressed together tightly to form a continuous seal preventing extracellular fluid leakage.

Desmosomes

Fastening junctions in animal cells that function like rivets, anchoring adjacent cells together and attaching to intermediate filaments.

Gap junctions

Animal cell junctions providing cytoplasmic channels between adjacent cells, consisting of membrane proteins surrounding a pore that allows ions, sugars, and small molecules to pass.

Fluid mosaic model

The model of cell membrane structure depicting the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.

Selective permeability

A property of biological membranes that allows them to regulate the passage of substances across them, permitting some to cross more easily than others.

Amphipathic

Having both a hydrophilic region and a hydrophobic region, a characteristic shared by phospholipids and membrane proteins.

Peripheral proteins

Membrane proteins that are not embedded in the lipid bilayer, but are loosely bound to the surface of the membrane.

Transmembrane proteins

Integral membrane proteins that completely span the hydrophobic interior of the phospholipid bilayer.

Osmosis

The diffusion of free water across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water, encompassing isotonic, hypertonic, and hypotonic states.

Plasmolysis

A phenomenon in walled cells where cytoplasm shrivels and the plasma membrane pulls away from the cell wall when placed in a hypertonic environment.

Facilitated diffusion

The passive passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins.

Active transport

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring energy investment (usually $\text{ATP}$).

Sodium-potassium pump

An active transport system in animal cell membranes that hydrolyzes $\text{ATP}$ to pump $\text{Na}^+$ out of the cell and $\text{K}^+$ into the cell against their concentration gradients.

Membrane potential

The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions, where the inside of the cell is negative relative to the outside.

Electrochemical gradient

The combined diffusion gradient of an ion, determined by both its concentration difference across a membrane (chemical gradient) and its tendency to move relative to membrane potential (electrical gradient).

Cotransport

The coupling of the downhill diffusion of one substance down its gradient to the uphill transport of another substance against its own concentration gradient.

Endocytosis

Cellular uptake of biological molecules and particulate matter via inward budding of the plasma membrane, forming new vesicles.

Pinocytosis

A type of endocytosis where the cell continuously gulps droplets of extracellular fluid into tiny vesicles, acquiring unspecific dissolved solutes.

Exocytosis

The cellular secretion of biological molecules by the fusion of vesicles with the plasma membrane.

Catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules into simpler compounds, such as cellular respiration.

Anabolic pathway

A metabolic pathway that consumes energy to build complex molecules from simpler ones, such as the synthesis of amino acids or carbohydrates.

First law of thermodynamics

The principle of conservation of energy stating that energy can be transferred and transformed, but cannot be created or destroyed.

Second law of thermodynamics

The principle stating that every energy transfer or transformation increases the entropy (disorder) of the universe.

Free energy ($G$)

The portion of a biological system's energy that can perform work when temperature and pressure are uniform, governed by the formula $\Delta G = \Delta H - T\Delta S$.

Exergonic reaction

A spontaneous chemical reaction in which there is a net release of free energy, characterized by a negative change in free energy ($\Delta G < 0$).

Endergonic reaction

A nonspontaneous chemical reaction that absorbs free energy from its surroundings, characterized by a positive change in free energy ($\Delta G > 0$).

Energy coupling

The use of an exergonic process to drive an endergonic one, primarily mediated by $\text{ATP}$ in cellular metabolism.

Adenosine triphosphate (ATP)

An adenine-containing nucleoside triphosphate consisting of ribose sugar and three phosphate groups that releases free energy when hydrolyzed to $\text{ADP}$ and inorganic phosphate.

Phosphorylated intermediate

A molecule that has received a phosphate group from $\text{ATP}$, making it more reactive, less stable, and possessing more free energy than the unphosphorylated molecule.

Activation energy ($E_A$)

The amount of energy that reactants must absorb before a chemical reaction will start; representing the energy barrier lowered by enzymes.

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, brought about by chemical interactions upon initial contact.

Competitive inhibitor

A substance that reduces the activity of an enzyme by mimicking the structure of the substrate and binding directly to the active site to block substrate entry.

Noncompetitive inhibitor

A substance that impedes enzymatic reactions by binding to an alternative regulatory site rather than the active site, altering the enzyme's shape so the active site functions less effectively.

Feedback inhibition

A method of metabolic control in which the end product of a metabolic pathway allosterically inhibits the enzyme that catalyzes an early step in that pathway.

Cooperativity

A kind of allosteric regulation whereby a shape change in one subunit of a multi-subunit protein, caused by substrate binding, is transmitted to all other subunits, stabilizing the active conformation.

Oxidation

The complete or partial loss of electrons from a substance involved in a redox reaction.

Reduction

The complete or partial addition of electrons to a substance involved in a redox reaction.

Nicotinamide adenine dinucleotide ($\text{NAD}^+$)

A coenzyme and electron carrier that cycles between its oxidized state ($\text{NAD}^+$) and reduced state ($\text{NADH}$) during cellular respiration.

Glycolysis

A ten-step metabolic pathway in the cytosol that splits one molecule of glucose into two molecules of pyruvate, generating a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Pyruvate oxidation

The step in the mitochondrion where pyruvate is converted to acetyl $\text{CoA}$, releasing $\text{CO}_2$ and producing $1\,\text{NADH}$ per pyruvate ($2\,\text{NADH}$ per glucose).

Citric acid cycle

An eight-step metabolic pathway in the mitochondrial matrix that oxidizes acetyl $\text{CoA}$, yielding $6\,\text{NADH}$, $2\,\text{FADH}_2$, $2\,\text{ATP}$, and $4\,\text{CO}_2$ per glucose molecule.

Electron transport chain

A sequence of four multiprotein electron-carrier complexes embedded in the inner mitochondrial membrane that shuttles electrons down an energy gradient to oxygen, pumping $H^+$ into the intermembrane space.

ATP synthase

A complex of membrane proteins that functions like a reverse ion pump, utilizing the energy of a hydrogen ion ($\text{H}^+$) gradient across the inner mitochondrial membrane to phosphorylate $\text{ADP}$ into $\text{ATP}$.

Chemiosmosis

An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, specifically the synthesis of $\text{ATP}$.

Alcohol fermentation

An anaerobic catabolic pathway in which glycolysis is followed by the conversion of pyruvate to acetaldehyde and then ethanol, regenerating $\text{NAD}^+$ and releasing $\text{CO}_2$.

Lactic acid fermentation

An anaerobic catabolic pathway in which pyruvate is directly reduced by $\text{NADH}$ to form lactate, regenerating $\text{NAD}^+$ without producing carbon dioxide.

Obligate anaerobes

Organisms that carry out only fermentation or anaerobic respiration and cannot survive in the presence of oxygen.

Facultative anaerobes

Organisms capable of making enough $\text{ATP}$ to survive using either fermentation or aerobic respiration depending on the availability of oxygen.