Cell Biology Exam 1 Content

Vocabulary practice flashcards covering cell biology lectures on DNA structure, chromatin organization, chemical foundations, thermodynamics, metabolic pathways, activated carriers, and enzyme kinetics and regulation.

Mitosis

The process of cell division enabling a cell, genome, or DNA molecule to self-replicate and distribute complete chromosomal sets to daughter cells.

Chromatin

The complex of DNA and associated packaging proteins found within the nucleus of eukaryotic cells.

Complementary Base Pairing

The specific hydrogen bonding between nitrogenous bases in DNA, where adenine pairs with thymine via two hydrogen bonds and cytosine pairs with guanine via three hydrogen bonds.

Major and Minor Grooves

Alternating wider and narrower spiral grooves along the DNA double helix created by the coiling of the sugar-phosphate backbones.

Homologous Chromosomes

Pairs of matching chromosomes in a diploid cell, consisting of one chromosome inherited from the mother and one from the father.

Nucleolus

The prominent nuclear region in interphase cells where genes encoding ribosomal RNAs are clustered and transcribed.

Histone Octamer

An eight-protein complex comprising two molecules each of histones $\text{H2A}$, $\text{H2B}$, $\text{H3}$, and $\text{H4}$, forming the core spool of a nucleosome.

Nucleosome Core Particle Structure

The disc-shaped fundamental unit of chromatin packaging, consisting of a histone octamer wrapped by approximately $147\,\text{base pairs}$ of DNA with flexible histone tails projecting outward.

Linker DNA

The stretch of DNA connecting adjacent nucleosomes, ranging from $20\text{--}80\,\text{base pairs}$ with an average length of roughly $50\,\text{base pairs}$.

Histone H1

The linker histone that binds to the exterior of the nucleosome core particle to alter the exit path of DNA, favoring higher-order chromatin coiling.

Chromatin-Remodeling Complexes

Protein complexes that utilize energy from ATP hydrolysis to slide, remove, or restructure nucleosomes to regulate DNA accessibility.

Histone Acetyltransferases (HATs)

Enzymes that attach acetyl groups to positively charged lysine side chains on histone tails, loosening chromatin structure to increase DNA accessibility.

Histone Deacetylases (HDACs)

Enzymes that remove acetyl groups from histone tails, restoring positive charges on lysines to compact chromatin and decrease DNA accessibility.

Euchromatin

The relatively relaxed and open state of interphase chromatin that is active and accessible for gene expression.

Heterochromatin

Highly condensed and gene-silenced interphase chromatin accounting for approximately $10\%$ of the genome, concentrated at centromeres and telomeres.

Epigenetics

Heritable changes in gene expression and chromatin state that occur without changing the underlying DNA nucleotide sequence.

Covalent Bond

A strong chemical linkage formed when two atoms share one or more pairs of outer-shell valence electrons.

Electronegativity

The intrinsic affinity of an atom to attract shared electrons toward itself within a chemical bond.

Polar Covalent Bond

A covalent bond formed between atoms with differing electronegativities, leading to unequal electron sharing and partial positive and negative charges.

Ionic Bond

A noncovalent bond formed through the complete transfer of electrons from one atom to another, producing attracted cations and anions.

Hydrogen Bond

A weak noncovalent attraction between a partial positively charged hydrogen atom in a polar bond and an electronegative atom such as oxygen or nitrogen.

van der Waals Attraction

A weak noncovalent interaction generated by transient, induced fluctuations in electron clouds when two atoms come into close proximity.

Hydrophobic Forces

Forces that aggregate nonpolar, uncharged molecules together in aqueous solution to minimize interruption of hydrogen-bonded water networks.

Amphipathic Molecule

A chemical compound possessing both distinct hydrophilic (polar) and hydrophobic (nonpolar) regions.

Saturated Fatty Acid

A fatty acid hydrocarbon tail with no carbon-carbon double bonds, containing the maximum number of hydrogen atoms and forming straight chains.

Unsaturated Fatty Acid

A fatty acid hydrocarbon tail containing one or more carbon-carbon double bonds, creating rigid kinks in the chain.

Triacylglycerol

A storage lipid formed by esterifying three fatty acid tails to a single glycerol molecule.

Phospholipid

An amphipathic membrane lipid containing a hydrophilic head group with phosphate and glycerol linked to two hydrophobic fatty acid tails.

Peptide Bond

A rigid planar amide linkage formed via a condensation reaction connecting the carboxyl group of one amino acid to the amino group of another.

Phosphodiester Bond

The covalent linkage connecting the $5'$ phosphate of one nucleotide to the $3'$ hydroxyl group of the next along a nucleic acid strand.

Metabolism

The sum total of all chemical reactions carried out by a cell to maintain life, growth, and reproduction.

Catabolism

Metabolic pathways that break down organic molecules from food to harvest free energy and molecular building blocks.

Anabolism

Metabolic pathways that consume energy and building blocks to synthesize complex macromolecules required by the cell.

Free Energy ($\Delta G$)

A thermodynamic parameter defined as $\Delta G = \Delta H - T \times \Delta S$, measuring the usable energy available to drive a reaction.

Activation Energy

The minimum energy input required to start a chemical reaction by forcing molecules into a reactive transition state.

Activation Energy Reaction Diagram

An energy pathway model demonstrating how an enzyme accelerates a reaction by reducing the required activation energy without altering the net free energy change.

Catalyst

A substance that accelerates a chemical reaction by lowering its activation energy barrier without being consumed or changing $\Delta G$.

Coupled Reaction

A process where an energetically unfavorable reaction ($\Delta G > 0$) is driven forward by linkage to an energetically favorable reaction ($\Delta G < 0$) through shared intermediates.

Activated Carrier

A small, easily diffusible molecule that temporarily stores free energy or high-energy chemical groups in transferable bonds or electrons.

Photosynthesis and Cellular Respiration Interconnection

The complementary biological cycle in which photosynthesis converts sunlight into chemical energy in sugars, and cellular respiration oxidizes those sugars to generate usable ATP.

NADPH

An activated electron carrier carrying high-energy electrons and a hydride ion, functioning predominantly in anabolic biosynthetic reactions.

NADH

An activated electron carrier generated during catabolic oxidation reactions that delivers high-energy electrons to fuel ATP production.

Ligand

Any molecule that selectively and reversibly binds to a specific binding site on a protein.

Binding Site

A localized region or pocket on a protein formed by folded amino acid side chains that interacts with a ligand via noncovalent bonds.

Antibody Molecule Conformation

A Y-shaped immunoglobulin protein consisting of two identical heavy chains and two identical light chains, featuring two identical antigen-binding sites.

Antigen

Any specific target molecule or pathogen surface structure recognized and bound by an antibody.

Active Site

The specific binding cavity of an enzyme where substrate molecules bind and undergo catalytic conversion into product.

Michaelis Constant ($\text{K}_m$)

The substrate concentration at which an enzyme-catalyzed reaction proceeds at half of its maximal velocity ($\frac{1}{2}\text{V}_{\text{max}}$), reflecting enzyme-substrate affinity.

Maximal Velocity ($\text{V}_{\text{max}}$)

The maximum achievable catalytic rate of an enzymatic reaction occurring when all active sites are completely saturated with substrate.

Lysozyme

An antibacterial enzyme present in tears and saliva that hydrolyzes glycosidic bonds in bacterial cell wall polysaccharides.

Coenzyme

A small organic molecule or inorganic metal ion that binds to an enzyme to assist its catalytic activity.

Feedback Inhibition

A regulatory mechanism where the end product of a metabolic pathway binds to an early enzyme to shut down its catalytic activity.

Allosteric Regulation

Control of protein activity mediated by regulatory ligand binding at a distinct site separate from the active site, inducing a conformational change.

Protein Kinase

An enzyme that transfers a terminal phosphate group from ATP onto specific amino acid side chains of target proteins.

Protein Phosphatase

An enzyme that hydrolytically removes phosphate groups from phosphorylated proteins.

Scaffold Protein

A protein containing binding sites for multiple partner proteins, organizing them into localized functional complexes.