Genetics and Molecular Biology: Key Concepts and Mutations

Gene

A segment of DNA that encodes a functional product (protein or RNA).

Heredity

The transmission of genetic information from parents to offspring.

DNA

Deoxyribonucleic acid; double-stranded molecule that stores genetic information.

RNA

Ribonucleic acid; single-stranded molecule involved in gene expression.

Protein

A molecule made of amino acids that performs structural or functional roles in cells.

Chromosome

A highly organized DNA molecule wrapped around histones.

Nucleotide

The building block of nucleic acids; contains a sugar, phosphate group, and nitrogenous base.

Nucleic Acid

A polymer of nucleotides (DNA or RNA).

Phosphodiester Bond

A covalent bond linking nucleotides in a DNA or RNA backbone.

Locus

A specific location of a gene on a chromosome.

Promoter

A DNA sequence where RNA polymerase binds to begin transcription.

Regulatory Promoter

A DNA region that helps regulate transcription levels.

Enhancer

A DNA sequence that increases transcription when bound by activators.

Transcription Factor

A protein that binds DNA to regulate gene expression.

Activator

A transcription factor that increases gene expression.

Repressor

A transcription factor that decreases gene expression.

Open Reading Frame (ORF)

A continuous stretch of codons beginning with a start codon and ending with a stop codon.

Codon

A three-nucleotide sequence on mRNA that codes for an amino acid.

Anticodon

A three-nucleotide sequence on tRNA complementary to an mRNA codon.

Ribosome

A cellular structure that synthesizes proteins.

rRNA

Ribosomal RNA; structural and catalytic component of ribosomes.

tRNA

Transfer RNA; delivers amino acids to the ribosome.

Amino Acid

The building block of proteins.

Peptide Bond

A covalent bond between amino acids in a protein.

Mutation

A permanent change in DNA sequence.

Somatic Mutation

A mutation in body cells; not inherited.

Germ-line Mutation

A mutation in gametes; can be inherited.

Base Substitution

The replacement of one nucleotide with another.

Transition

A substitution between purines (A↔G) or pyrimidines (C↔T).

Transversion

A substitution between a purine and a pyrimidine.

Insertion

The addition of one or more nucleotides into DNA.

Deletion

The loss of one or more nucleotides from DNA.

Repeat Expansion

An increase in the number of short repeated DNA sequences.

Forward Mutation

A mutation from wild-type to mutant form.

Reverse Mutation

A mutation that restores the original phenotype.

Missense Mutation

A mutation that changes one amino acid in a protein.

Nonsense Mutation

A mutation that creates a premature stop codon.

Silent Mutation

A mutation that does not change the amino acid.

Loss-of-Function Mutation

A mutation that reduces or eliminates protein function.

Gain-of-Function Mutation

A mutation that creates new or increased protein function.

Conditional Mutation

A mutation expressed only under certain environmental conditions.

Lethal Mutation

A mutation that results in death.

Suppressor Mutation

A second mutation that restores function lost by a prior mutation.

Intragenic Suppressor

A suppressor mutation within the same gene.

Intergenic Suppressor

A suppressor mutation in a different gene.

Tautomeric Shift

A temporary change in base structure that causes mispairing during replication.

Base Analog

A chemical that resembles a DNA base and causes mutations when incorporated.

Free Radicals / Reactive Ions

Highly reactive molecules that can damage DNA.

DNA Polymerase

An enzyme that synthesizes DNA during replication.

RNA Polymerase

An enzyme that synthesizes RNA during transcription.

DNA Helicase

An enzyme that unwinds the DNA double helix.

DNA Ligase

An enzyme that seals breaks in the DNA backbone.

Capping

The addition of a 5' cap to mRNA after transcription.

Splicing

The removal of introns from pre-mRNA.

Polyadenylation

The addition of a poly-A tail to the 3' end of mRNA.

Spliceosome

A complex that removes introns from pre-mRNA.

Provirus

Viral DNA integrated into a host genome.

Reverse Transcriptase

An enzyme that synthesizes DNA from an RNA template.

Chromatin

The DNA-protein complex that makes up chromosomes.

Histone

A protein around which DNA wraps to form nucleosomes.

Centromere

The region of a chromosome where sister chromatids attach.

Kinetochore

A protein complex that attaches spindle fibers to the centromere.

Telomere

A protective DNA sequence at the end of a chromosome.

Sister Chromatids

Identical copies of a replicated chromosome.

Ploidy

The number of sets of chromosomes in a cell.

Haploid (n)

A cell containing one set of chromosomes.

Diploid (2n)

A cell containing two sets of chromosomes.

Polyploid

A cell containing more than two sets of chromosomes.

Condensins

Proteins that help condense chromosomes during cell division.

Genetics

The study of genes, heredity, and variation.

Central Dogma

The flow of genetic information: DNA → RNA → Protein.

Antiparallel Strands

DNA strands that run in opposite 5' to 3' directions.

Complementary Base Pairing

Specific pairing of bases (A-T and G-C in DNA).

Colinearity

The order of codons in DNA corresponds to the order of amino acids in a protein.

Gregor Mendel

The scientist who discovered basic principles of inheritance using pea plants.

Rosalind Franklin

Scientist who used X-ray diffraction to reveal DNA's helical structure.

Watson & Crick

Scientists who proposed the double-helix model of DNA.

Human Genome Project

An international project that sequenced the entire human genome.

Beta-Globin Locus

A genomic region containing beta-like globin genes regulated by promoters and enhancers.

Exon

A coding sequence that remains in mature mRNA.

Intron

A noncoding sequence removed during RNA splicing.

TATA Box

A promoter DNA sequence where transcription machinery assembles.

DNA Looping

The bending of DNA that allows enhancers to interact with promoters.

Gene Activation

The increase in gene expression through activator binding and transcription machinery recruitment.

Gene Repression

The decrease in gene expression through repressor binding.

Nucleosome

A unit of DNA wrapped around histone proteins.

Higher-Order Chromatin Structure

Further folding and compaction of nucleosomes into chromatin.

Homologous Chromosomes

A pair of chromosomes with the same genes, one from each parent.

Allele

An alternative version of a gene.

Wobble

Mispairing incorrect base pairing during replication due to temporary base shifts.

Strand Slippage

DNA polymerase slipping during replication, causing insertions or deletions.

Unequal Crossing Over

Misaligned homologous chromosomes exchange unequal DNA segments.

Depurination

The loss of a purine base (A or G) from DNA.

Deamination

The removal of an amino group from a DNA base (e.g., C to U).

Ionizing Radiation

High-energy radiation that can cause double-strand DNA breaks.

UV Radiation

Radiation that causes thymine dimers in DNA.

Mutation Rate

The frequency at which mutations occur per gene per generation.

Cell Cycle Checkpoints

Control mechanisms (G1, G2, M) that ensure proper cell division.

G1 Checkpoint

Ensures the cell is ready for DNA replication.

G2 Checkpoint

Ensures DNA replication is complete and undamaged.