Chapters 7, 8, 9, 11, and 12 Exam Review: Cell Signaling, Metabolism, Cell Division, and Genetics

Comprehensive flashcard collection covering key concepts, vocabulary, enzymes, and regulators for cell signaling, energy metabolism, the cell cycle, and genetics.

Signal transduction pathway

The sequence of steps from a signal binding a receptor to the cell's response (signal, receptor, response).

Autocrine signaling

Signaling in which a cell releases a signal molecule that binds to receptors located on the cell itself.

Juxtacrine signaling

Signaling that requires direct physical contact between the signaling cell and the target cell.

Paracrine signaling

Signaling in which a chemical signal diffuses a short distance through extracellular fluid to affect nearby cells.

Hormones

Signaling molecules released into the bloodstream that travel to act on distant target cells (endocrine signaling).

Crosstalk

Interaction and communication occurring between different signal transduction pathways inside a cell.

Receptor

A protein that binds a specific ligand or detects a physical signal and initiates a cellular response.

Dissociation constant ($K_D$)

The ligand concentration at which 50% of the receptors are bound; a small $K_D$ indicates high binding affinity.

Agonist

A molecule that binds to a receptor and activates it to trigger a biological response.

Antagonist

A molecule that binds to a receptor and prevents or blocks it from being activated by its ligand.

G protein

A molecular switch protein that is active when bound to GTP and inactive when bound to GDP.

G protein-coupled receptors (GPCRs)

Transmembrane receptors that activate an associated G protein upon ligand binding.

Effector protein

A downstream protein (often an enzyme) activated by a G protein or receptor that executes the next step in signaling.

Protein kinases

Enzymes that transfer phosphate groups to proteins (phosphorylation), switching their activity on or off.

Second messengers

Small non-protein molecules or ions that diffuse rapidly to relay and amplify signals inside the cytoplasm.

Cyclic AMP (cAMP)

A second messenger synthesized from ATP by adenylyl cyclase that activates protein kinases.

Phosphatidylinositol bisphosphate ($\text{PIP}_2$)

A membrane phospholipid that is cleaved by phospholipase C to yield $\text{IP}_3$ and DAG.

Inositol trisphosphate ($\text{IP}_3$)

A hydrophilic second messenger that diffuses through the cytosol and opens calcium channels on the endoplasmic reticulum to release $\text{Ca}^{2+}$.

Diacylglycerol (DAG)

A hydrophobic second messenger that remains in the plasma membrane and helps activate protein kinase C.

Gap junctions

Direct protein channels composed of connexons connecting animal cells that permit small molecules and ions to pass directly.

Plasmodesmata

Membrane-lined channels running through plant cell walls that directly connect the cytoplasm of adjacent plant cells.

Phosphatase

An enzyme that removes phosphate groups from proteins, commonly shutting off cellular signaling pathways.

Ras

A G protein in the EGF pathway; when stuck in the active, GTP-bound state, it causes uncontrolled cell proliferation.

Anabolic reaction

A chemical reaction that builds larger, complex molecules from smaller ones, generally requiring an input of energy.

Catabolic reaction

A chemical reaction that breaks down complex molecules into simpler compounds, typically releasing energy.

First law of thermodynamics

Energy can be transformed from one form to another, but it cannot be created or destroyed.

Second law of thermodynamics

Every energy transfer increases the total disorder (entropy) of the universe.

Enthalpy ($H$)

The total energy of a thermodynamic system, encompassing its internal energy and heat content.

Entropy ($S$)

A quantitative measure of randomness, disorder, or unusable energy in a system.

Free energy ($G$)

The portion of a system's energy that is available to perform work under constant temperature and pressure.

Exergonic reaction

A chemical reaction that releases free energy ($\Delta G < 0$) and occurs spontaneously.

Endergonic reaction

A chemical reaction that requires an input of free energy ($\Delta G > 0$) and is non-spontaneous.

Activation energy ($E_a$)

The initial energy threshold that reactants must absorb to break existing bonds and initiate a reaction.

Induced fit

The subtle conformational change an enzyme undergoes upon substrate binding to optimize catalytic contact.

Coenzyme

A small organic non-protein molecule (such as $\text{NAD}^+$) required by an enzyme to assist in catalysis.

Ribozyme

An RNA molecule that possesses biological catalytic properties.

Allosteric regulation

Modulation of enzyme activity caused by the binding of an effector molecule to a non-active site, altering protein shape.

Competitive inhibitor

An inhibitor that binds directly to an enzyme's active site, competing with the substrate, which can be overcome by higher substrate concentrations.

Noncompetitive inhibitor

An inhibitor that binds to an allosteric site rather than the active site, changing enzyme function regardless of substrate levels.

Feedback inhibition

A regulatory mechanism in which the final product of a metabolic pathway allosterically inhibits an early enzyme in that pathway.

$$V_{\max}$$

The maximum rate of an enzymatic reaction achieved when all active sites on the enzyme molecules are fully saturated with substrate.

$$K_m$$

The substrate concentration at half of $V_{\max}$; an indicator of affinity where a low $K_m$ reflects high affinity.

Glycolysis

The cytosolic breakdown of glucose into 2 molecules of pyruvate, generating a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Citric acid cycle

A metabolic cycle located in the mitochondrial matrix that finishes glucose oxidation to $\text{CO}_2$ and yields reduced electron carriers.

Chemiosmosis

The generation of ATP using energy stored in an electrochemical $\text{H}^+$ gradient across a membrane through ATP synthase.

ATP synthase

A membrane-bound protein complex that synthesizes ATP from ADP and inorganic phosphate as protons flow down their gradient.

Phosphofructokinase (PFK)

The primary committed regulatory enzyme of glycolysis that is allosterically inhibited by high levels of ATP.

Binary fission

The asexual reproduction mechanism in prokaryotes where DNA replication and cell division proceed concurrently.

Cyclins

Proteins whose cellular concentrations oscillate through the cell cycle, binding to and activating specific CDKs.

Cyclin-dependent kinases (CDKs)

Protein kinases that drive transitions through the cell cycle checkpoints, requiring association with cyclins to become active.

Centromere

The constricted DNA region of a replicated chromosome where sister chromatids join and kinetochores assemble.

Kinetochores

Specialized multi-protein structures assembled at the centromere to which spindle microtubules attach during division.

Apoptosis

Genetically programmed, highly organized cell suicide mediated by caspases.

Necrosis

Uncontrolled cell death resulting from acute physical or toxic injury, characterized by swelling and membrane rupture.

Oncogenes

Mutated forms of proto-oncogenes that stimulate excessive cell division when abnormally overexpressed or hyperactive.

Tumor suppressors

Proteins that normally restrain cell cycle progression or promote apoptosis; loss of their function contributes to cancer.

Rb protein

A tumor suppressor protein that sequesters and inhibits the transcription factor E2F, blocking entry from G1 into S phase.

Law of segregation

Mendel's principle stating that the two alleles for a gene separate during gamete formation so each gamete carries only one allele.

Law of independent assortment

Mendel's principle stating that alleles of distinct genes assort into gametes independently during meiosis.

Codominance

An inheritance pattern in which the phenotypes produced by both alleles are simultaneously and fully expressed in a heterozygote.

Incomplete dominance

A condition in which the heterozygous phenotype is an intermediate blend between both homozygous phenotypes.

Pleiotropic

A phenomenon where a single gene impacts multiple distinct, seemingly unrelated phenotypic traits.

Epistasis

A genetic interaction where the phenotypic expression of one gene alters or masks the expression of a second gene.

Penetrance

The proportion of individuals carrying a specific genotype who visibly demonstrate the expected phenotype.

Expressivity

The degree or severity to which a specific genotype is phenotypically manifested among individuals showing the trait.

Hemizygous

Possessing only one copy of a gene or chromosome segment in an otherwise diploid cell, such as X-linked genes in human males.

Plasmid

A small, extrachromosomal circular DNA molecule that replicates independently and often carries accessory genes like antibiotic resistance.

Bacterial conjugation

The horizontal transfer of genetic material between two bacterial cells via direct cytoplasmic contact using a sex pilus.