Molecular Basis of Inheritance – Key Vocabulary

Vocabulary flashcards covering the core terms and definitions from the lecture on DNA structure, replication, repair, and chromatin organization.

Deoxyribonucleic Acid (DNA)

Hereditary molecule composed of nucleotides that stores and transmits genetic information.

Double Helix

The two-stranded, spiral structure of DNA discovered by Watson and Crick in 1953.

James Watson & Francis Crick

Scientists who proposed the correct double-helical model of DNA structure.

Transformation

Uptake of foreign DNA by a cell, causing a change in genotype and phenotype (first observed by Griffith).

Frederick Griffith

Researcher who discovered bacterial transformation in 1928 using pathogenic and harmless Streptococcus strains.

Bacteriophage (Phage)

Virus that infects bacteria; instrumental in showing DNA is genetic material.

Hershey–Chase Experiment

1952 study proving DNA, not protein, enters E. coli during phage infection and carries genetic information.

Erwin Chargaff

Scientist who showed DNA composition varies among species and that A=T and G=C (Chargaff’s rules).

Chargaff’s Rules

In any species, amounts of adenine equal thymine and guanine equals cytosine; base composition differs between species.

X-ray Crystallography

Technique used by Rosalind Franklin and Maurice Wilkins to photograph DNA and reveal its helical structure.

Rosalind Franklin

Scientist whose X-ray diffraction images provided key evidence for the DNA double helix.

Antiparallel

Orientation of DNA strands running in opposite 5′→3′ directions in the double helix.

Purine

Two-ring nitrogenous base (adenine or guanine).

Pyrimidine

Single-ring nitrogenous base (cytosine or thymine in DNA, uracil in RNA).

Complementary Base Pairing

Specific hydrogen-bonding of A with T and G with C in DNA.

Semiconservative Replication

Replication model in which each daughter DNA molecule contains one parental strand and one new strand.

Conservative Model

Disproved replication model proposing parental strands rejoin after serving as templates.

Dispersive Model

Disproved replication model proposing each strand is a mix of old and new DNA segments.

Meselson–Stahl Experiment

1958 study using heavy- and light-nitrogen isotopes to confirm semiconservative replication.

Origin of Replication

Specific DNA sequence where replication begins, forming a replication bubble.

Replication Fork

Y-shaped region at each end of a replication bubble where new strands are synthesized.

Helicase

Enzyme that unwinds the DNA double helix at replication forks.

Single-Strand Binding Protein

Protein that stabilizes separated DNA strands during replication.

Topoisomerase

Enzyme that relieves overwinding strain ahead of replication forks by cutting and rejoining DNA.

Primase

RNA polymerase that synthesizes short RNA primers needed to start DNA synthesis.

RNA Primer

Short stretch of RNA providing a free 3′-OH for DNA polymerase to begin DNA synthesis.

DNA Polymerase III (bacteria)

Main enzyme that adds nucleotides to a growing DNA strand during replication.

DNA Polymerase I (bacteria)

Enzyme that removes RNA primers and replaces them with DNA nucleotides.

Leading Strand

DNA strand synthesized continuously toward the replication fork in a 5′→3′ direction.

Lagging Strand

DNA strand synthesized discontinuously away from the fork as Okazaki fragments.

Okazaki Fragment

Short DNA segment produced on the lagging strand and later joined together.

DNA Ligase

Enzyme that seals nicks by forming phosphodiester bonds; joins Okazaki fragments.

Sliding Clamp

Protein ring that holds DNA polymerase to the DNA template for efficient replication.

dATP (deoxyadenosine triphosphate)

Nucleoside triphosphate that donates adenine during DNA synthesis, releasing pyrophosphate.

Pyrophosphate

Two linked phosphate groups released when a nucleotide is added to DNA, driving polymerization energetically.

Proofreading

Activity of DNA polymerase that removes and replaces mispaired nucleotides during replication.

Mismatch Repair

Post-replication process where enzymes fix incorrectly paired bases missed by proofreading.

Nucleotide Excision Repair

Repair mechanism where a nuclease cuts out damaged DNA, DNA polymerase fills in, and ligase seals.

Mutation

Permanent DNA sequence change; source of genetic variation and raw material for evolution.

Telomere

Repetitive nucleotide sequence at chromosome ends that protects genes from erosion during replication.

Telomerase

Enzyme that extends telomeres in germ cells, using an RNA template within the enzyme.

Chromatin

Complex of DNA and proteins (mainly histones) that packages eukaryotic chromosomes.

Histone

Basic protein around which DNA wraps, forming nucleosomes; subject to chemical modification.

Nucleosome

‘Bead-on-a-string’ unit of chromatin: DNA wrapped around an octamer of histone proteins.

Euchromatin

Loosely packed chromatin that is transcriptionally active during interphase.

Heterochromatin

Highly condensed chromatin (e.g., centromeres, telomeres) generally transcriptionally inactive.

Supercoiling

Compacting of bacterial circular DNA into a dense nucleoid structure through twisting.

Nucleoid

Region in a bacterial cell containing the supercoiled chromosome; not membrane-bound.

Replication Bubble

Open region of DNA where replication occurs, formed around an origin of replication.

DNA Replication Machine

Large multi-protein complex that coordinates enzymatic activities during DNA replication.

Mutation Source

Spontaneous errors or DNA damage from physical/chemical agents such as X-rays or cigarette smoke.