Unit 1: What's Your Code? - Genetics, Cell Division, and the Origin of Life

Vocabulary practice flashcards covering cellular evolution theories, nucleic acid structure, karyotyping, cell cycle, mitosis, meiosis, molecular biology's central dogma, and mutations.

Endosymbiotic Theory

The theory that eukaryotic cell organelles, such as mitochondria and chloroplasts, originated from prokaryotes (bacteria) that were engulfed by a primitive host cell, survived, and developed a mutually beneficial symbiotic relationship over evolutionary time.

Autogenous Hypothesis

A hypothesis proposed by Dobson and Taylor suggesting that complex eukaryotic internal structures, such as the nucleus and endoplasmic reticulum, evolved through inward foldings (infoldings) of the ancestral prokaryotic plasma membrane.

Spontaneous Generation

An ancient theory proposed by Aristotle (~4th century BCE) stating that living organisms could arise spontaneously from non-living matter through a 'vital force' (e.g., maggots from rotting meat, frogs from mud).

Biogenesis

The biological principle proven by Louis Pasteur in the 19th century using swan-neck flask experiments, demonstrating that living organisms only arise from pre-existing living organisms.

Panspermia

The hypothesis proposed by Arrhenius in the early 20th century suggesting that life originated in outer space and was carried to Earth by meteors or cosmic dust.

Primordial Soup Theory

The theory proposed by Oparin and Haldane in the 1920s positing that early Earth's oceans were a chemical mixture from which organic molecules like amino acids formed under energy from lightning and UV radiation; later supported by the Miller–Urey experiment in 1953.

Nucleotide

The fundamental monomer of nucleic acids, consisting of three components: a phosphate group, a pentose sugar (ribose or deoxyribose), and a nitrogenous base.

Complementary Base Pairing

The specific pairing of nitrogenous bases in nucleic acids held together by hydrogen bonds, where Adenine (A) pairs with Thymine (T) (or Uracil (U) in RNA) and Guanine (G) pairs with Cytosine (C).

Antiparallel Arrangement

The structural orientation of the two complementary strands of DNA running in opposite directions, essential for double helix stability, complementary pairing, and accurate replication.

Chromosome

A condensed, tightly packed molecule of DNA and associated proteins located in the nucleus that carries hereditary information.

Homologous Chromosomes

A pair of matching chromosomes—one inherited from each parent—that have the same length, centromere location, and the same genes arranged in the same positions (loci).

Gene

A specific fragment or sequence of DNA located on a chromosome that encodes instructions for synthesizing a protein or determining a particular trait.

Allele

One of the alternative forms of a specific gene, differing slightly in its nucleotide sequence and resulting in variations of a trait (e.g., light vs. dark eye color).

Karyotyping

A laboratory procedure in which dividing cells are harvested (often prenatally), chemically arrested during mitosis when chromosomes are condensed, and arranged by size to detect chromosomal abnormalities.

Karyotype

The complete set, total number, and visual types of chromosomes present within the cells of an individual eukaryotic organism.

Karyogram

A visual photographic profile or chart of stained, condensed chromosomes arranged systematically in homologous pairs by decreasing size.

Sex Chromosomes

The 23rd chromosome pair in humans that determines biological sex: females have two $X$ chromosomes ($\text{XX}$) and males have one $X$ and one $Y$ chromosome ($\text{XY}$).

Trisomy

A chromosomal mutation characterized by the presence of three copies of a specific chromosome instead of the normal homologous pair.

Edwards Syndrome

A clinical genetic disorder caused by trisomy 18 (an extra chromosome in pair $18$).

Down Syndrome

A genetic condition caused by trisomy 21, resulting from an extra copy of chromosome $21$.

Klinefelter Syndrome

A chromosomal condition in males resulting from the presence of an extra $X$ chromosome, producing an $\text{XXY}$ sex chromosome genotype.

Cell Cycle

The ordered series of cellular events in which a cell grows, replicates its genetic material, and divides to form two identical daughter cells; comprised of interphase and cell division.

Interphase

The longest period of the cell cycle during which the cell obtains nutrients, grows, synthesizes proteins, and replicates its DNA in preparation for mitosis.

DNA Replication

The semi-conservative process by which a single double-stranded DNA molecule is copied into two identical DNA molecules, each containing one conserved parental strand and one new strand.

Helicase

The enzyme responsible for unwinding the double helix during DNA replication by cleaving the hydrogen bonds between complementary base pairs.

DNA Polymerase

An enzyme that synthesizes new DNA strands by joining free complementary nucleotides to the exposed template strands according to base-pairing rules.

Sister Chromatids

Two identical copies of a single replicated chromosome joined together at a centromere.

Centromere

The constricted, central region of a chromosome that links sister chromatids together and serves as the attachment site for spindle microtubules.

Mitosis

The division of the cell nucleus that produces two genetically identical diploid ($2n$) daughter nuclei, occurring in somatic cells.

Cytokinesis

The physical division of the cytoplasm and cell membrane that separates the cell into two distinct daughter cells after nuclear division ends.

Prophase (Mitosis)

The first phase of mitosis, characterized by chromatin condensing into visible chromosomes, centrioles migrating to opposite poles, and the breakdown of the nuclear envelope.

Metaphase (Mitosis)

The mitotic stage where condensed chromosomes align along the equator (center) of the cell, connected to centrioles via spindle microtubules.

Anaphase (Mitosis)

The stage of mitosis where spindle microtubules contract, dividing the centromeres and pulling sister chromatids apart toward opposite poles.

Telophase (Mitosis)

The final stage of mitosis during which nuclear membranes reform around separated single-chromatid sets of chromosomes, and the genetic material uncoils.

Meiosis

A two-division reductional cell division process in germ cells that yields four genetically distinct haploid ($n$) gametes.

Haploid

A cell that possesses a single set of unpaired chromosomes ($n$), characteristic of gametes (sperm and egg cells, with $23$ chromosomes in humans).

Diploid

A cell containing two complete sets of chromosomes ($2n$), one from each parent, characteristic of somatic body cells ($46$ chromosomes in humans).

Crossing Over (Recombination)

The random exchange of genetic material between non-sister chromatids of paired homologous chromosomes during Prophase I of meiosis, creating genetic variation.

Central Dogma of Molecular Biology

The fundamental biological framework describing the unidirectional transfer of sequential genetic information: $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

Messenger RNA (mRNA)

A single-stranded RNA transcript synthesized during transcription that carries genetic instructions from nuclear DNA out to the ribosome in the cytoplasm.

Transfer RNA (tRNA)

An adaptor RNA molecule that carries specific amino acids to the ribosome and matches them to corresponding codons on mRNA during translation.

Ribosomal RNA (rRNA)

The structural and functional RNA component that makes up ribosomes, the molecular machines catalyzing protein synthesis.

Transcription

The enzymatic synthesis of an RNA molecule from a DNA template gene catalyzed by RNA polymerase inside the nucleus.

Translation

The ribosomal process occurring in the cytoplasm where an mRNA codon sequence is decoded to assemble amino acids into a polypeptide chain.

Codon

A sequence of three consecutive nucleotides in mRNA that specifies a single amino acid or signals a stop termination during translation.

Mutation

Any spontaneous or induced alteration in the nucleotide sequence of an organism's DNA, including substitutions, insertions, or deletions.

Mutagen

Any physical, chemical, or biological agent—such as UV radiation, tobacco tar, asbestos, or viruses—that induces genetic mutations.

Silent Mutation

A base substitution mutation that does not alter the encoded amino acid due to redundancy (degeneracy) in the genetic code, resulting in an unaffected functional protein.