DNA and RNA — Comprehensive Study Notes Flashcards

Front

Transformation

Back

The process Griffith observed where harmless bacteria became virulent after exposure to heat-killed virulent cells, implying a transferable "transforming factor." Transformation refers to the uptake and stable incorporation of genetic material from the environment into a recipient cell.

Front

Avery–MacLeod–McCarty

Back

A set of experiments that identified DNA as the transforming factor by fractionating bacterial components and using degradative enzymes. They showed transformation stopped only when DNA was destroyed, demonstrating DNA carries hereditary information.

Front

Hershey–Chase

Back

A classic experiment using bacteriophages labeled with radioactive sulfur (protein) and phosphorus (DNA) to track which molecule enters bacteria. They found only labeled DNA entered host cells and directed phage reproduction, providing decisive evidence that DNA is the genetic material.

Front

Double helix

Back

The canonical three-dimensional structure of DNA in which two antiparallel strands wind around each other in a right-handed spiral. This arrangement positions complementary bases inward and stabilizes the molecule while enabling faithful replication.

Front

Chargaff’s Rule

Back

The empirical observation that in double-stranded DNA the percent of adenine equals thymine and the percent of guanine equals cytosine (A = T, G = C). This symmetry supported the idea of specific complementary base pairing between strands.

Front

Base pairing

Back

Specific hydrogen-bonded pairing between nucleotide bases: adenine pairs with thymine and guanine pairs with cytosine in DNA. Complementary pairing explains how sequences are read and copied during replication and transcription.

Front

Hydrogen bonds

Back

Noncovalent interactions that stabilize base pairs in the DNA double helix; A–T pairs form two hydrogen bonds while G–C pairs form three. The differing bond counts influence helix stability and melting temperature.

Front

DNA backbone

Back

The repeating sugar-phosphate chain that forms the exterior framework of each DNA strand, with phosphate groups linking the 3' and 5' carbons of deoxyribose sugars. The backbone gives structural support while bases project inward to pair with the opposite strand.

Front

Antiparallel strands

Back

DNA strands run in opposite directions so one strand goes 5' → 3' while the complementary strand runs 3' → 5'. Antiparallel orientation is essential for the enzymes that replicate and transcribe DNA.

Front

Deoxyribose

Back

The five-carbon sugar in DNA (deoxyribose) that lacks a 2' hydroxyl group compared with ribose, making DNA more chemically stable. Deoxyribose forms part of the nucleotide monomer together with a phosphate and a nitrogenous base.

Front

Nitrogenous bases

Back

The four informational units in DNA—adenine, thymine, guanine, and cytosine—that pair complementarily to encode genetic information. The sequence of these bases along a strand constitutes the genetic code used to specify proteins and regulatory signals.

Front

RNA

Back

A typically single-stranded nucleic acid containing ribose sugar and uracil instead of thymine, making it more chemically reactive and transient than DNA. RNA serves as a messenger, an adapter, and a catalytic or structural molecule in cells.

Front

mRNA, tRNA, rRNA

Back

Major RNA types with distinct roles: mRNA carries coding information from DNA to ribosomes; tRNA brings specific amino acids during translation; rRNA is an integral structural and catalytic component of ribosomes. Together they enable decoding of genetic information into protein.

Front

Histones

Back

Positively charged proteins around which eukaryotic DNA wraps to form nucleosomes, the basic unit of chromatin. Histone interactions compact DNA and play key roles in regulating access to genetic information and gene expression.

Front

Nucleosome

Back

A structural unit of chromatin consisting of about 147 base pairs of DNA wrapped around an octamer of histone proteins. Nucleosomes compact DNA and help organize it for higher-order folding and regulatory control.

Front

Centromere

Back

A constricted chromosomal region where sister chromatids remain joined and where spindle fibers attach during cell division. The centromere is crucial for accurate segregation of chromosomes to daughter cells.

Front

Prokaryotic chromosome

Back

Typically a single circular DNA molecule located in the nucleoid region of bacteria and archaea, not enclosed by a membrane-bound nucleus. Prokaryotic genomes are usually gene-dense with relatively little noncoding DNA.

Front

Plasmid

Back

Small, circular, extrachromosomal DNA molecules commonly found in bacteria that carry accessory genes such as antibiotic resistance or metabolic traits. Plasmids can be transferred between cells and are widely used as cloning vectors in genetic engineering.

Front

Nucleoid

Back

The irregularly shaped region in prokaryotic cells where the chromosome is localized and compacted without a surrounding membrane. The nucleoid contains DNA and associated proteins that help organize and regulate the genome.

Front

Junk DNA

Back

A historical term for noncoding regions of the genome that do not encode proteins; the label is misleading because many such regions have regulatory, structural, or noncoding RNA functions. Promoters, enhancers, introns, and noncoding RNAs are examples of functional noncoding sequences.

Front

Semiconservative replication

Back

A mode of DNA replication where each daughter double helix contains one parental (old) strand and one newly synthesized strand. This mechanism, confirmed experimentally, ensures genetic continuity between generations of cells.

Front

Okazaki fragments

Back

Short DNA fragments synthesized discontinuously on the lagging strand during replication, later joined by DNA ligase to create a continuous strand. Their production reflects the unidirectional 5' → 3' activity of DNA polymerases on antiparallel templates.

Front

DNA polymerase proofreading

Back

Many DNA polymerases possess a 3'→5' exonuclease activity that removes incorrectly incorporated nucleotides, increasing replication fidelity. Proofreading, together with base-pairing specificity, greatly reduces the mutation rate during replication.

Front

Central Dogma

Back

A framework describing the flow of genetic information from DNA to RNA to protein. It emphasizes that DNA is transcribed into RNA, which is then translated into proteins that carry out cellular functions.

Front

Transcription

Back

The process by which RNA polymerase synthesizes an RNA copy of a DNA template, producing mRNA or other RNA types. Regulatory elements like promoters and transcription factors control which genes are transcribed and when.

Front

Translation

Back

The ribosome-mediated decoding of mRNA codons into a polypeptide chain using charged tRNAs and rRNA for structure and catalysis. Translation converts the nucleotide language of mRNA into the amino acid sequence of proteins.

Front

Genetic engineering

Back

The deliberate manipulation of an organism's genetic material to introduce new traits or produce desired products, often using plasmids and recombinant DNA methods. Applications range from producing therapeutic proteins (e.g., human insulin) to engineering crops with beneficial traits such as Bt-mediated insect resistance.

Front

Restriction enzymes

Back

Endonucleases that recognize specific DNA sequences and cleave the backbone at or near those sites, producing fragments useful for cloning and analysis. They are fundamental tools for creating recombinant DNA constructs.

Front

Polymerase chain reaction

Back

A technique (PCR) that amplifies specific DNA sequences exponentially using thermal cycling, a DNA polymerase, primers, and nucleotides. PCR enables rapid production of millions of copies of a target fragment for cloning, diagnostics, and research.

Front

Recombinant protein expression

Back

The production of a protein from an introduced gene using a host organism (e.g., bacteria, yeast, or mammalian cells) carrying a recombinant vector. This approach is widely used to manufacture therapeutics, enzymes, and research reagents.