Molecular Genetics, Gene Regulation, and Cellular Division

Vocabulary practice flashcards covering molecular genetics, protein synthesis, gene regulation, mutations, mitosis, and meiosis based on the comprehensive biology lecture notes.

Nucleotide

The basic building block of DNA, composed of three features: a nitrogenous base, a sugar (deoxyribose), and a phosphate group.

Complementary Base-Pairing

The specific hydrogen bonding pattern in DNA where Adenine ($A$) always pairs with Thymine ($T$) and Guanine ($G$) always pairs with Cytosine ($C$).

Chromatin

The combination of linear DNA molecules wrapped around proteins (histones) found inside the eukaryotic nucleus.

Gene

A specific sequence of DNA nucleotides, averaging approximately $3,000$ base pairs in length, that contains the instructions necessary for protein synthesis.

Dystrophin

The protein encoded by the longest gene in the human genome ($2.4\text{ million nucleotides}$) that assists in muscle contractions, with defects linked to muscular dystrophy.

Genome

The entire, complete set of DNA or chromosomes contained within the nucleus of an organism's cell.

Alleles

Alternative versions of a specific gene that code for the same trait, situated at the identical locus on homologous chromosomes.

Introns

Non-coding sequences of DNA located within genes, representing roughly $25\%$ of non-coding eukaryotic DNA, that are removed prior to protein synthesis.

Exons

The protein-coding regions of a gene that are retained and spliced together to produce mature messenger RNA.

Central Dogma of Biology

The core framework stating that genetic information flows from DNA to messenger RNA via transcription, and from mRNA to proteins via translation.

Transcription

The enzymatic process occurring in the nucleus in which the nucleotide sequence of a gene is copied into a complementary messenger RNA (mRNA) sequence.

RNA Polymerase

The enzyme that unwinds double-stranded DNA and synthesizes a complementary mRNA copy of a gene using RNA nucleotides.

Promoter

A specific non-transcribed DNA sequence located upstream of a gene that functions as the binding and landing site for RNA polymerase.

Terminator

A specific non-transcribed DNA sequence situated downstream of a gene that signals RNA polymerase to stop transcription.

Translation

The cytoplasmic process wherein a ribosome reads an mRNA nucleotide sequence three bases at a time to assemble amino acids into a polypeptide chain.

Codon

A three-nucleotide unit on an mRNA molecule that specifies a particular amino acid, start signal, or termination signal during translation.

Transfer RNA (tRNA)

A folded, cloverleaf-like RNA molecule possessing a unique anticodon at one end and a specific corresponding amino acid attached to the other end.

Anticodon

A triplet sequence of bases on a tRNA molecule that base-pairs complementarily with a specific codon on an mRNA strand.

Start Codon

The codon sequence AUG that specifies the amino acid Methionine (Met) and instructs the ribosome to initiate translation.

Stop Codons

The specific mRNA codons UGA, UAA, and UAG that signal the ribosome to cease polypeptide elongation and terminate translation.

Sickle-Cell Anemia

A hereditary condition caused by a single nucleotide substitution in the hemoglobin gene (CTC to CAC in DNA; GAG to GUG in mRNA), replacing Glutamic acid with Valine.

Gene Expression

The overall cellular process of turning on a gene to produce its functional encoded protein through transcription and translation.

Transcription Factors

Regulatory proteins that bind to specific DNA sequences near gene promoters to either recruit or block RNA polymerase activity.

Activators

Transcription factors that recruit RNA polymerase to a promoter, thereby turning on or enhancing gene transcription.

Repressors

Transcription factors that prevent RNA polymerase from accessing a promoter, thereby inhibiting or silencing gene transcription.

Epigenetics

Modifications that change chromatin packaging and alter gene expression accessibility without modifying the actual DNA nucleotide sequence.

Histones

Structural protein octamers that DNA wraps around to form nucleosomes, whose chemical modifications regulate whether chromatin is open or closed.

Alternative Splicing

A post-transcriptional mechanism wherein different combinations of exons from a pre-mRNA transcript are joined, allowing a single gene to encode multiple distinct proteins.

Point Mutation

A genetic alteration that involves a change in a single nucleotide base pair, including base substitutions, insertions, and deletions.

Frameshift Mutation

A mutation caused by the insertion or deletion of nucleotides that shifts the three-base reading frame, changing every downstream codon.

Chromosomal Aberrations

Large-scale mutations involving whole sections of a chromosome, including gene deletions, gene relocations, and gene duplications.

Telomeres

Protective non-coding, repetitive nucleotide sequences at the tips of eukaryotic chromosomes that progressively shorten with each cell division.

Binary Fission

The asexual division process in prokaryotes where a single circular chromosome replicates and the cell divides into two genetically identical daughter cells.

Interphase

The extensive preparatory stage of the eukaryotic cell cycle consisting of Gap 1 ($G_1$), DNA synthesis (S phase), and Gap 2 ($G_2$).

$$G_0\text{ Phase}$$

A quiescent, non-dividing resting state outside the eukaryotic cell cycle that cells can enter from Gap 1 ($G_1$) for varying durations.

Antiparallel Strands

The structural property of double-stranded DNA where two complementary strands run in opposing orientations, one running $5'\rightarrow 3'$ and the other $3'\rightarrow 5'$.

DNA Helicase

The enzyme responsible for breaking hydrogen bonds to unwind and separate the two parental strands of the DNA double helix during replication.

Replication Fork

The dynamic Y-shaped junction where parental DNA strands are unzipped and separated by DNA helicase for replication.

DNA Polymerase

The enzyme that synthesizes new DNA strands exclusively in the $5'\rightarrow 3'$ direction by adding nucleotides to a free $3'\text{-OH}$ group, while providing proofreading ability.

Semiconservative Replication

The mechanism of DNA replication in which each newly formed double helix retains one conserved template strand from the parent molecule and one newly synthesized strand.

Sister Chromatids

Two identical copies of a linear chromosome produced during S-phase replication, joined together at the centromere.

Centromere

The specialized, constricted chromosomal region that tethers two sister chromatids together until they are separated during anaphase.

Prophase

The initial phase of mitosis characterized by chromosome condensation, breakdown of the nuclear envelope, and formation of the mitotic spindle.

Metaphase

The mitotic stage during which replicated chromosomes (sister chromatid pairs) are aligned across the center or equatorial plate of the cell.

Anaphase

The mitotic stage in which spindle fibers shorten and pull sister chromatid pairs apart toward opposite poles of the dividing cell.

Telophase

The final stage of mitosis during which two nuclear membranes reassemble around the separated identical sets of chromosomes, and chromosomes begin to uncoil.

Cytokinesis

The division of the cytoplasm and physical splitting of the parental cell into two independent daughter cells following nuclear division.

Cell Cycle Checkpoints

Critical surveillance points ($G_1/S$, $G_2/M$, and Spindle Assembly) where cycle progression is halted until conditions ensure accurate DNA replication and division.

Diploid

A eukaryotic cell containing two complete homologous copies of each chromosome ($2n$; $46\text{ chromosomes}$ in human somatic cells).

Haploid

A cell that possesses only one copy of each chromosome ($n$; $23\text{ chromosomes}$ in human gametes), generated by meiosis.

Homologous Chromosomes

Pairs of matching maternal and paternal chromosomes in a diploid cell that possess the same genes at the same loci, though potentially having different alleles.

Germline Stem Cells (GSCs)

Specialized reproductive stem cells located in the ovaries and testes that undergo meiosis to form gametes (eggs and sperm).

Meiosis

A two-round cell division process in germline cells that reduces chromosome content from diploid ($46$) to haploid ($23$), generating four genetically distinct gametes.

Synapsis

The intimate pairing and alignment of replicated homologous chromosomes that occurs exclusively during prophase I of meiosis.

Crossing Over

The reciprocal exchange of corresponding DNA fragments between non-sister chromatids of homologous chromosomes during prophase I of meiosis.

Fertilization

The fusion of a haploid sperm cell with a haploid egg cell, restoring the diploid state to initiate organismal development.

Zygote

The single diploid cell formed immediately following the fertilization of an ovum by a spermatozoon.

Nondisjunction

The error during meiosis where homologous chromosomes (in meiosis I) or sister chromatids (in meiosis II) fail to separate correctly into daughter cells.

Trisomy 21

A condition characterized by an extra third copy of chromosome 21, typically resulting from meiotic nondisjunction, which causes Down syndrome.