Comprehensive Biology Review: DNA, Gene Expression, Cell Cycle, Meiosis, and Inheritance

Vocabulary flashcards covering core topics in molecular biology, genetics, cell division, and inheritance patterns.

Johannes Miescher

A scientist who first described DNA in 1869, identifying it as a substance rich in nitrogen and phosphorus rather than a protein.

Transforming Principle

The phenomenon discovered by Frederick Griffith in which hereditary material is transferred from dead lethal S strain bacteria to live R strain bacteria.

Avery and McCarty

Scientists who proved in 1940 that the transforming principle was DNA, demonstrating that DNA-degrading enzymes prevented transformation while RNA-degrading enzymes did not.

Hershey and Chase

Researchers who established that bacteriophages inject DNA, not protein, into host bacteria to transmit hereditary information.

Chargaff's Rules

Two principles stating that 1) adenine equals thymine ($A = T$) and guanine equals cytosine ($G = C$), and 2) DNA proportions of adenine and guanine differ between species.

Nucleosome

A eukaryotic chromosome structural unit composed of a length of DNA wound twice around a histone spool.

Semiconservative Replication

The mechanism of DNA replication yielding two double helices, each containing one original parental strand and one newly synthesized strand.

Okazaki Fragments

Short segments of DNA synthesized discontinuously on the lagging strand that are subsequently joined together by DNA ligase.

Somatic Cell Nuclear Transfer (SCNT)

A reproductive cloning technique where the nucleus of an unfertilized egg is replaced with a nucleus from a donor somatic cell.

Transcription

The biological process of synthesizing an RNA strand using a gene's DNA sequence as a template.

Alternative Splicing

A post-transcriptional RNA modification in eukaryotes where exons are rearranged into different combinations to produce distinct mRNA transcripts.

Codon

A sequence of three nucleotides in mRNA that specifies a particular amino acid or a termination signal during translation.

AUG

The start codon in mRNA that initiates translation and specifies the amino acid methionine.

Frameshift Mutation

A mutation caused by nucleotide insertion or deletion that shifts the genetic reading frame and drastically alters the resulting protein.

Ribosome-Inactivating Proteins (RIPs)

Toxins, such as ricin, that completely halt cellular protein synthesis by removing adenine bases from rRNA.

Interphase

The main cell cycle interval consisting of $G_1$, $S$, and $G_2$ stages, during which the cell grows, replicates DNA, and prepares for division.

Mitosis

A nuclear division process in eukaryotic cells that preserves the chromosome number in descendant cells.

Contractile Ring

A ring of actin filaments that forms during animal cell cytokinesis to pull the plasma membrane inward and divide the cytoplasm.

Cell Plate

A disk-shaped structure formed by fusing vesicles at the division plane during plant cell cytokinesis, eventually developing into a new cell wall.

Telomeres

Noncoding, repetitive DNA sequences located at the ends of eukaryotic chromosomes that shield essential genetic information from degradation.

Telomerase

An enzyme found in stem cells and cancer cells that reverses telomere shortening to grant cellular immortality.

Oncogene

A mutated proto-oncogene that drives uncontrolled cell division and transforms a normal cell into a tumor cell.

HeLa Cells

An immortal human cell line derived in 1951 from cervical cancer patient Henrietta Lacks, extensively used in global medical research.

Meiosis

A nuclear division process in eukaryotes that reduces the chromosome number from diploid ($2n$) to haploid ($n$) to form gametes.

Red Queen Hypothesis

An evolutionary theory stating that species must continually adapt and evolve to survive against co-evolving competitors and changing environments.

Crossing Over

The exchange of genetic segments between nonsister chromatids of homologous chromosomes during prophase I of meiosis.

Chromosome Segregation

The random distribution of maternal and paternal homologous chromosomes during meiosis I, generating $2^{23}$ possible combinations in human gametes.

Bdelloid Rotifers

Microscopic asexual animals that have survived for 80 million years without sex by acquiring roughly 10% of their active genes from bacteria, fungi, and plants.

Law of Segregation

Mendel's principle that homologous chromosomes separate during meiosis so that each gamete carries only one allele for each gene.

Law of Independent Assortment

Mendel's principle that allele pairs for different genes on nonhomologous chromosomes distribute into gametes independently of one another.

Incomplete Dominance

An inheritance pattern in which the phenotype of a heterozygote is an intermediate blend of the two homozygous phenotypes.

Codominance

An inheritance pattern where both alleles in a heterozygote are fully and simultaneously expressed, as seen in human ABO blood types.

Epistasis

A genetic interaction where one gene masks or modifies the phenotypic expression of an entirely different gene.

Pleiotropy

A genetic pattern where a single gene impacts multiple, seemingly unrelated phenotypic characteristics.

Continuous Variation

A spectrum of minor phenotypic differences in a population for a trait influenced by multiple genes and environmental conditions.

$\text{F508}$ Mutation

A 3-base pair deletion in the CFTR gene that removes the 508th amino acid, causing thick mucus accumulation in individuals with cystic fibrosis.