Cell Division, Genetics, and Molecular Biology Review

Comprehensive vocabulary flashcards covering the cell cycle, mitosis, meiosis, Mendelian and non-Mendelian genetics, DNA replication, and gene expression.

Binary fission

The process by which bacterial cells divide, which is also the method used by eukaryotic organelles such as mitochondria and chloroplasts to divide.

Somatic cells

Body cells that are typically diploid ($2n$).

Gametes

Reproductive cells (sperm and egg cells) that are haploid ($n$).

Diploid ($2n$)

Having two complete sets of chromosomes.

Haploid ($n$)

Having one set of chromosomes.

Homologous chromosomes

Matching chromosomes—one inherited from each parent—carrying the same genes, though possibly different alleles.

Sister chromatids

Identical copies of a single replicated chromosome that are joined together initially.

Centromere

The specific region of a chromosome where sister chromatids are joined together.

Interphase

The stage of the cell cycle during which the cell grows and replicates its DNA; composed of the $G_1$, S, and $G_2$ phases.

S phase

The synthesis phase of interphase during which DNA is replicated so each daughter cell receives a complete set of genetic material.

Cell-cycle checkpoints

Surveillance mechanisms that monitor whether the cell is ready to advance and halt the cycle if errors or unfavorable conditions are detected.

$G_1$ checkpoint

A regulatory checkpoint that evaluates cell size, environmental conditions, and DNA damage before committing to cell division.

$G_2$ checkpoint

A regulatory checkpoint that assesses whether DNA replication has completed fully and without damage before entering mitosis.

M/spindle checkpoint

A checkpoint that verifies whether all chromosomes are correctly attached to spindle fibers before sister chromatid separation occurs.

Proto-oncogene

A normal gene involved in regulating cell growth and division that can promote uncontrolled division when mutated into an oncogene.

Oncogene

An overactive or mutated form of a proto-oncogene that can drive uncontrolled cell division.

Tumor suppressor gene (e.g., p53)

A gene that prevents uncontrolled cell division; for example, p53 can halt the cell cycle for DNA repair or induce apoptosis if damage cannot be fixed.

Benign tumor

A noncancerous mass of cells that does not invade adjacent tissues.

Malignant tumor

A cancerous mass of cells capable of invading surrounding tissues and spreading throughout the body.

Metastasis

The dissemination of cancer cells from their primary site of origin to distant areas of the body.

Mitosis

Nuclear division that partitions duplicated chromosomes into two genetically identical nuclei for growth, tissue repair, and asexual replacement.

Prophase (mitosis)

The first phase of mitosis in which chromosomes condense, the mitotic spindle forms, and the nuclear envelope disintegrates during late prophase.

Metaphase (mitosis)

The mitotic phase where individual chromosomes align along the equator or middle of the cell.

Anaphase (mitosis)

The mitotic phase during which sister chromatids pull apart and travel toward opposite poles of the cell.

Telophase (mitosis)

The final mitotic phase where new nuclear membranes assemble, chromosomes decondense, and the mitotic spindle disassembles.

Cytokinesis

The division of the cytoplasm resulting in two distinct daughter cells, distinct from nuclear division (mitosis).

Cleavage furrow

An indentation that constricts and pinches an animal cell into two separate daughter cells during cytokinesis.

Cell plate

A structure formed along the midline of a dividing plant cell that develops into a new cell wall separating the two daughter cells.

Spindle fibers

Microtubule structures responsible for organizing and segregating chromosomes during cell division.

Kinetochore

A specialized protein complex assembled at the centromere that serves as the attachment point for spindle fibers.

Meiosis

A two-round nuclear division process that produces four genetically diverse haploid daughter cells from a diploid cell for sexual reproduction.

Meiosis I

The reduction division of meiosis in which homologous chromosomes separate, decreasing the ploidy from diploid ($2n$) to haploid ($n$).

Meiosis II

The second division of meiosis in which sister chromatids separate into distinct haploid cells.

Crossing over (Recombination)

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

Independent assortment

The random orientation and segregation of maternal and paternal homologous chromosome pairs along the metaphase plate during metaphase I.

Nondisjunction

The improper segregation of homologous chromosomes or sister chromatids during cell division, yielding gametes with abnormal chromosome numbers.

Trisomy 21

A chromosomal condition resulting from three copies of chromosome 21, causing Down syndrome.

Gene

A defined sequence of DNA that encodes instructions for synthesizing a functional RNA or protein product.

Allele

A specific variant or alternate form of a given gene.

Locus

The specific physical location of a gene on a chromosome.

Genotype

The underlying genetic or allelic composition of an organism (such as Pp).

Phenotype

The observable physical or physiological traits of an organism (such as purple flowers).

Homozygous dominant

A genotype consisting of two identical dominant alleles (e.g., PP).

Heterozygous

A genotype consisting of two distinct alleles for a given gene (e.g., Pp).

Homozygous recessive

A genotype consisting of two identical recessive alleles (e.g., pp).

Dominant allele

An allele whose associated phenotypic trait is expressed when at least one copy is present.

Recessive allele

An allele whose phenotypic expression is concealed in heterozygotes and only manifested when two copies are present in complete dominance.

True breeding

Organisms that consistently yield offspring displaying the same trait upon self-fertilization due to being homozygous.

Law of segregation

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

Incomplete dominance

A pattern of inheritance where the heterozygous phenotype is an intermediate blend between both homozygous phenotypes (such as pink snapdragons).

Codominance

A condition in which both alleles in a heterozygote are fully and distinctly expressed, such as the A and B antigens in AB blood type.

Epistasis

An interaction where the expression of one gene masks or modifies the phenotypic expression of a different gene.

Polygenic inheritance

An inheritance pattern where multiple separate genes collectively influence a single phenotypic trait (e.g., human height and skin pigmentation).

Pleiotropy

A genetic scenario where a single gene impacts multiple distinct, seemingly unrelated phenotypic traits (e.g., CFTR mutations causing both pulmonary and digestive defects).

Central dogma of molecular biology

The foundational principle stating that genetic information flows from DNA to RNA and subsequently from RNA to protein.

Nucleotide

The basic building block of nucleic acids, consisting of a five-carbon sugar, a phosphate group, and a nitrogenous base.

Phosphodiester bond

A strong covalent linkage that connects adjacent nucleotides along the sugar-phosphate backbone of a nucleic acid strand.

Hydrogen bond (in DNA)

Noncovalent interactions holding complementary nitrogenous bases together across opposite strands of the double helix.

Semiconservative replication

The mechanism of DNA replication in which each newly formed double helix comprises one intact parent strand and one newly synthesized daughter strand.

Helicase

An enzyme that unzips double-stranded DNA by breaking the hydrogen bonds holding base pairs together.

Primase

An enzyme that synthesizes short complementary RNA primers to supply a free 3′ hydroxyl end for DNA polymerase.

DNA polymerase

An enzyme that assembles new DNA strands by adding complementary nucleotides to the 3′ end of a primer or growing chain and performs proofreading.

DNA ligase

An enzyme that facilitates the joining of DNA fragments by sealing nicks in the phosphodiester sugar-phosphate backbone.

Topoisomerase

An enzyme that alleviates excessive supercoiling and torsional strain ahead of the advancing replication fork.

RNA primer

A brief sequence of RNA synthesized by primase that furnishes a free 3′ end required for DNA polymerase initiation.

Leading strand

The DNA strand that is synthesized continuously toward the progressing replication fork in the $5' \rightarrow 3'$ direction.

Lagging strand

The DNA strand synthesized discontinuously away from the replication fork as a series of short segments called Okazaki fragments.

Okazaki fragments

Short stretches of newly synthesized DNA formed on the lagging strand that are later covalently united by DNA ligase.

Mutation

A permanent change in the nucleotide sequence of an organism's DNA, which can be deleterious, neutral, or advantageous.

Gene expression

The cellular process of utilizing instructions within a gene to direct the synthesis of functional RNA molecules and proteins.

Transcription

The synthesis of a complementary RNA molecule from a DNA template directed by RNA polymerase.

Translation

The synthesis of a polypeptide by ribosomes decoding the nucleotide sequence of an mRNA molecule.

Promoter

A specific regulatory region of DNA upstream of a gene where transcription machinery binds to initiate RNA synthesis.

RNA polymerase

The principal enzyme of transcription that reads a DNA template strand and polymerizes RNA in the $5' \rightarrow 3'$ direction.

Enhancer

A DNA control sequence that binds transcriptional activator proteins to upregulate gene transcription rates.

5′ capping

A post-transcriptional modification involving the addition of a modified guanine nucleotide to the 5′ end of pre-mRNA to prevent degradation and facilitate ribosome binding.

Poly-A tail

A series of adenine residues attached to the 3′ terminus of eukaryotic pre-mRNA that enhances transcript stability and assists in nuclear export.

RNA splicing

The post-transcriptional editing process wherein non-coding introns are excised from pre-mRNA and coding exons are joined.

Introns

Intervening, non-protein-coding sequences within pre-mRNA that are excised during mRNA processing.

Exons

Expressed regions of pre-mRNA that are spliced together and preserved in mature mRNA to encode polypeptide sequences.

Alternative splicing

A regulatory mechanism where pre-mRNA exons are assembled in diverse combinations, allowing a single gene to encode multiple distinct protein isoforms.

Codon

A triplet sequence of three consecutive nucleotides in mRNA specifying a single amino acid or a termination signal.

Messenger RNA (mRNA)

The transcript that carries genetic information from nuclear DNA out to cytoplasmic ribosomes to direct protein synthesis.

Transfer RNA (tRNA)

An adaptor RNA molecule carrying a specific amino acid that pairs with complementary mRNA codons via its anticodon during translation.

Ribosomal RNA (rRNA)

Structural and catalytic RNA components of ribosomes that help catalyze the formation of peptide bonds between amino acids.