Chapter 8: DNA Structure and Function

Vocabulary flashcards covering the key terms, historical experiments, molecular structures, enzymes, replication mechanisms, chromosomal organization, and cloning technologies from Chapter 8 (DNA Structure and Function).

Johann Miescher

The scientist who first isolated DNA (deoxyribonucleic acid) from cell nuclei in 1869, although its hereditary function was unknown at the time.

Griffith's Experiment

An early 1900s experiment showing the transfer of hereditary material; mice injected with live R cells or heat-killed S cells survived, while those injected with live S cells or a combination of heat-killed S cells and live R cells died of pneumonia, with live S cells recovered from their blood.

Transforming Principle

The substance identified as DNA in 1940 by Avery and McCarty, who proved that destroying lipids, proteins, and RNA did not stop heat-killed S cell extracts from transforming harmless live R cells into lethal S cells.

Bacteriophage

A type of virus that infects bacterial cells, consisting of a DNA core enclosed within a protein coat.

Hershey–Chase Experiment

A 1940s study showing that bacteriophages labeled with $^{32}\text{P}$ injected radioactive DNA into bacteria, whereas $^{35}\text{S}$-labeled viral coat proteins remained outside, proving DNA is the hereditary material.

Nucleotide

A nucleic acid monomer composed of a five-carbon sugar (deoxyribose), three phosphate groups, and one of four nitrogen-containing bases.

Pyrimidines

Single-ring nitrogenous bases found in DNA, comprising thymine (T) and cytosine (C).

Purines

Double-ring nitrogenous bases found in DNA, comprising adenine (A) and guanine (G).

Chargaff's First Rule

The principle stating that in DNA, the amount of thymine equals the amount of adenine ($A = T$), and the amount of cytosine equals the amount of guanine ($G = C$).

Chargaff's Second Rule

The principle stating that the relative proportions of adenine and guanine differ among different species of organisms.

Rosalind Franklin

The scientist whose X-ray crystallography research revealed the dimensions, shape, and helical structure of the DNA molecule.

Double Helix

The structural model of DNA formulated by Watson and Crick, characterized by two antiparallel nucleotide strands linked by internal base pairs with a $2\,\text{nm}$ diameter, a $3.4\,\text{nm}$ full twist length, and $0.34\,\text{nm}$ between each base pair.

Chromosome

A structure consisting of a DNA molecule and associated proteins that carries part or all of a cell's genetic information.

Sister Chromatids

Two identical DNA molecules that make up a duplicated eukaryotic chromosome, joined together at a centromere.

Centromere

The constricted attachment site that holds two sister chromatids together in a duplicated chromosome.

Histones

Structural proteins that act as spools around which eukaryotic DNA winds at regular intervals.

Nucleosome

The smallest unit of chromosomal organization in eukaryotes, composed of a segment of DNA wrapped around a core of histone proteins.

Chromosome Number

The total number of chromosomes in a cell, which is characteristic of a given species (such as 46 in human body cells).

Diploid ($2n$)

Having two sets of each type of chromosome in a cell, with one inherited from the mother and one from the father.

Karyotype

An image displaying the complete set of chromosomes in an individual cell, used to determine chromosome count and identify major structural abnormalities.

Autosomes

Chromosomes with the same length, shape, and centromere location in homologous pairs, encompassing all chromosomes except sex chromosomes.

Sex Chromosomes

Chromosomes that differ between biological sexes; human females have two X chromosomes ($\text{XX}$) and human males have one X and one Y chromosome ($\text{XY}$).

DNA Replication

The energy-intensive cellular process by which a cell makes an exact duplicate copy of its DNA prior to cell division.

DNA Helicase

An enzyme that breaks the hydrogen bonds holding complementary base pairs together to unwind and separate double-stranded DNA during replication.

Topoisomerase

An enzyme that untwists the DNA double helix ahead of the replication fork to relieve structural tension.

DNA Polymerase

An enzyme that synthesizes new DNA strands by joining free nucleotides in the $5'$ to $3'$ direction and proofreads sequences for mismatched bases.

Primer

A short, single strand of DNA or RNA complementary to a targeted sequence that provides an attachment point for DNA polymerase to begin synthesis.

DNA Ligase

An enzyme that seals breaks and gaps in the sugar-phosphate backbone by covalently linking adjacent DNA fragments.

Hybridization

The spontaneous pairing of complementary bases between two separate DNA or RNA strands, driven entirely by hydrogen bonding.

Semiconservative Replication

The copying mechanism in which each new double-stranded DNA molecule consists of one conserved parental template strand and one newly assembled complementary strand.

Okazaki Fragments

Short, discontinuous segments of synthesized DNA formed on the lagging strand that are subsequently joined together by DNA ligase.

Mutation

A permanent change in the nucleotide sequence of a cell's DNA that arises when proofreading and repair mechanisms fail to correct replication errors or lesions.

Free Radicals

Highly reactive chemical molecules that cause oxidative damage to DNA bases, serving as a source of mutations.

Pyrimidine Dimers

Distortions in the DNA backbone caused by ultraviolet (UV) radiation that create abnormal bonds between adjacent pyrimidine bases (such as thymines).

Ionizing Radiation

High-energy radiation that knocks electrons out of atoms and can physically break the DNA backbone into fragments.

Cell Differentiation

The developmental process by which cells become specialized in structural form and functional role, typically operating as a one-way path in animal cells.

Somatic Cell Nuclear Transfer (SCNT)

A reproductive cloning technique in which the nucleus of an adult body cell is inserted into an enucleated donor egg, where cytoplasmic factors reprogram the DNA to direct embryo development.

Trakr

A 9/11 Ground Zero search dog handled by James Symington that found the final living survivor and whose genetic material was later used to generate identical cloned puppies via nuclear transfer into donor eggs.