Molecular Basis of Inheritance

Practice flashcards covering the molecular basis of inheritance, DNA structure, replication, repair mechanisms, and genetic engineering techniques based on Chapter 13 lecture notes.

DNA Replication

The process by which hereditary information is reproduced in all cells of the body during cell division.

Transformation

A change in genotype and phenotype due to the assimilation of foreign DNA, first observed by Frederick Griffith in 1928.

Bacteriophages (phages)

Viruses that infect bacteria, consisting of DNA or RNA enclosed by a protective protein coat.

Chargaff’s rules

1. DNA base composition varies between species; 2. In any species, percentages of $A$ and $T$ bases are equal and percentages of $G$ and $C$ bases are equal.

Double Helix

The structural model of DNA introduced by James Watson and Francis Crick, characterized by two strands wound together.

Antiparallel

The arrangement of the sugar-phosphate backbones in a DNA molecule where the subunits run in opposite directions.

Nucleotides

The monomers of polynucleotides, each consisting of a nitrogenous base ($A$, $G$, $T$, or $C$), a $5$-C pentose sugar (deoxyribose), and a phosphate group.

Semiconservative model

Watson and Crick’s model of replication where each daughter molecule has one old strand derived from the parent and one newly made strand.

Origins of replication

Specific sites where the two DNA strands are separated, opening up a replication ‘bubble’ to begin replication.

Replication fork

A Y-shaped region at each end of a replication bubble where parental DNA strands are being unwound.

Helicases

Enzymes that untwist the double helix at the replication forks, separating the two parental strands.

Single-strand binding proteins

Proteins that bind to and stabilize unpaired DNA strands, preventing them from re-pairing during replication.

Topoisomerase

An enzyme that relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands.

Primase

An enzyme that starts an RNA chain from a single RNA nucleotide and adds RNA nucleotides one at a time using the parental DNA as a template.

RNA primer

A short initial nucleotide strand ($5–10$ nucleotides long) that serves as the starting point for DNA synthesis.

DNA polymerases

Enzymes that catalyze the elongation of new DNA at a replication fork by adding nucleotides to the $3'$ end of a preexisting chain.

Leading strand

The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory $5'$ to $3'$ direction.

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, synthesized in a direction away from the replication fork.

Okazaki fragments

Series of segments ($100–200$ nucleotides in eukaryotes, $1,000–2,000$ in E. coli) that make up the lagging strand.

DNA ligase

An enzyme that covalently joins Okazaki fragments in the lagging DNA strand or seals the free end of new DNA to old DNA during repair.

Mismatch repair

A process where specific enzymes remove and replace incorrectly paired nucleotides that have evaded proofreading by DNA polymerase.

Nucleotide excision repair

A DNA repair system in which a nuclease cuts out and replaces damaged stretches of DNA, such as those caused by X-rays or chemical agents.

Telomeres

Special repetitive nucleotide sequences at the ends of eukaryotic chromosomes that postpone the erosion of genes near the ends of DNA molecules.

Telomerase

An enzyme that catalyzes the lengthening of telomeres in germ cells, compensating for the shortening that occurs during DNA replication.

Nucleoid

The region in a bacterial cell where the circular, double-stranded DNA molecule is supercoiled and concentrated.

Chromatin

A complex of DNA and protein found in the nucleus of eukaryotic cells that undergoes multilevel packing.

Nucleosome

The basic unit of DNA packing, consisting of DNA wound twice around a protein core of 8 histones.

Heterochromatin

Highly condensed chromatin during interphase that is generally inaccessible to the machinery responsible for transcribing genetic information.

Euchromatin

The less compacted, more dispersed form of chromatin that is available for transcription.

Nucleic acid hybridization

The base pairing of one strand of a nucleic acid to a complementary sequence from another nucleic acid molecule.

DNA cloning

The process of preparing well-defined segments of DNA in multiple identical copies.

Plasmids

Small circular DNA molecules in bacteria that replicate separately from the bacterial chromosome.

Recombinant DNA

A DNA molecule produced by combining DNA from two different sources, such as inserting foreign DNA into a bacterial plasmid.

Cloning vector

A DNA molecule, such as a plasmid, that can carry foreign DNA into a host cell and replicate there.

Restriction enzymes

Endonucleases that recognize and cut DNA molecules at specific sequences called restriction sites.

Sticky ends

Single-stranded ends of DNA fragments resulting from staggered cuts by restriction enzymes, capable of bonding with complementary fragments.

Gel electrophoresis

A technique used to separate and visualize nucleic acid fragments based on their length as they move through an electrical field.

Polymerase Chain Reaction (PCR)

A technique used to amplify a specific target DNA segment into an exponentially growing population of identical molecules using Taq polymerase.

DNA sequencing

The process of determining the complete nucleotide sequence of a gene or DNA segment.

CRISPR-Cas9 system

A powerful gene-editing technique using a nuclease (Cas9) that cuts double-stranded DNA at sites directed by a guide RNA.

Gene drive

A process that uses an engineered allele to bias its own inheritance, rapidly spreading through a population.