Molecular Genetics and Biotechnology Mid-Unit Review

Comprehensive vocabulary flashcards covering DNA structure, replication, protein synthesis, historical experiments, biotechnology techniques, and genetic mutations.

DNA Double Helix

A double-stranded helical nucleic acid molecule with an antiparallel sugar-phosphate backbone and complementary nitrogenous base pairs connected by hydrogen bonds, exhibiting a repeat distance of $3.4\,\text{nm}$ and a distance of $0.34\,\text{nm}$ between adjacent base pairs.

DNA vs. RNA

The structural distinction between deoxyribonucleic acid (double-stranded, contains deoxyribose sugar and thymine, stores genetic info in the nucleus) and ribonucleic acid (usually single-stranded, contains ribose with one extra oxygen, and uracil instead of thymine).

Purines

Nitrogenous bases containing a double-ring carbon and nitrogen structure; specifically adenine and guanine.

Pyrimidines

Nitrogenous bases containing a single-ring carbon and nitrogen structure; specifically thymine and cytosine in DNA, and uracil in RNA.

Antiparallel

The orientation of the two complementary strands in a DNA molecule running parallel to each other but in opposite chemical directions ($5' \rightarrow 3'$ and $3' \rightarrow 5'$).

Friedrich Miescher

The Swiss physician who first isolated a weakly acidic phosphorus-rich substance from the nuclei of white blood cells in pus, naming it nuclein (later recognized as DNA).

Bacterial Transformation

The transfer of genetic material from one bacterial strain to another, first demonstrated by Frederick Griffith when heat-killed pathogenic S cells transformed harmless living R cells into virulent living S cells in mice.

Rosalind Franklin

The chemist and X-ray crystallographer whose specialized diffraction image, Photo 51, revealed the helical structure and precise helical dimensions of DNA.

Gene

A specific sequence or segment of DNA located on a chromosome that codes for a specific protein or polypeptide chain and acts as the basic unit of heredity.

Genome

The complete set of genetic material, including all genes and chromosomes, that provides the entire biochemical blueprint for an organism's structure and function.

Semiconservative Replication

The mechanism of DNA replication in which each newly formed double helix consists of one original conserved parental strand and one newly synthesized strand.

DNA Replication Fork

The Y-shaped structure formed during DNA synthesis where double-stranded DNA unwinds, allowing enzymes such as helicase, primase, and DNA polymerase to coordinate leading and lagging strand replication.

DNA Helicase

An enzyme that unzips double-stranded DNA at the replication fork by breaking the weak hydrogen bonds between complementary base pairs.

Single-Stranded Binding Proteins (SSBPs)

Proteins that attach to exposed single strands of unzipped DNA to keep them separated and prevent them from annealing back together during replication.

DNA Primase

An enzyme that attaches short complementary RNA primers to the template DNA strand to supply a free $3'\text{-OH}$ group for DNA polymerase to begin synthesis.

DNA Polymerase III

The primary replication enzyme that synthesizes new DNA strands by adding complementary deoxynucleotides in the $5' \rightarrow 3'$ direction and proofreads for replication errors.

Leading Strand

The continuously synthesized complementary DNA strand that elongates in the $5' \rightarrow 3'$ direction moving toward the advancing replication fork.

Lagging Strand

The discontinuously synthesized DNA strand that elongates in the $5' \rightarrow 3'$ direction moving away from the replication fork, requiring repeated primer placement.

Okazaki Fragments

Short fragments of newly synthesized DNA separated by RNA primers formed on the lagging strand during DNA replication.

DNA Ligase

An enzyme that joins and glues DNA fragments, such as Okazaki fragments or recombined plasmids, by catalyzing the formation of covalent phosphodiester bonds.

Exonuclease

An enzyme (such as DNA Polymerase I) that recognizes, removes, and excises RNA primers from newly synthesized strands and fills the gaps with DNA nucleotides.

Central Dogma

The foundational biological principle describing the flow of genetic information: DNA is transcribed into mRNA in the nucleus, and mRNA is translated into protein in the cytoplasm.

Transcription

The enzymatic process occurring in the nucleus where RNA polymerase copies the nucleotide sequence of a DNA sense template strand into a single-stranded messenger RNA ($\text{mRNA}$).

Poly-A Tailing

A post-transcriptional modification consisting of a sequence of adenine nucleotides added to the $3'$ end of eukaryotic mRNA to protect it from enzymatic degradation.

GTP Cap

A modified guanine nucleotide structure added to the $5'$ end of eukaryotic mRNA that protects the transcript and signals ribosomes to initiate translation.

RNA Splicing

The post-transcriptional modification process that cuts out non-coding sequences (introns) from pre-mRNA and splices together coding sequences (exons).

Translation

The multi-stage process occurring at cytoplasmic ribosomes where transfer RNA ($\text{tRNA}$) anticodons read mRNA codons to assemble a specific sequence of amino acids into a polypeptide.

Gel Electrophoresis

A laboratory method that separates charged nucleic acid or protein fragments based on size and molecular charge by migrating negatively charged DNA through an agarose matrix toward the positive anode.

Hershey-Chase Experiment

A blender experiment utilizing bacteriophages with radioactive sulfur ($^{35}\text{S}$ in protein) and radioactive phosphorus ($^{32}\text{P}$ in DNA) that proved DNA, not protein, enters bacterial host cells as the hereditary material.

Chargaff's Rules

The discovery by Erwin Chargaff that within double-stranded DNA, the ratio of adenine equals thymine ($\%A = \%T$) and the ratio of guanine equals cytosine ($\%G = \%C$).

Recombinant DNA

Artificial DNA molecules constructed in a laboratory by combining genetic fragments from two or more different biological sources or species.

Restriction Endonuclease

A bacterial enzyme that cuts double-stranded DNA at a specific symmetrical, palindromic recognition sequence, such as $\text{EcoRI}$ cutting at $5'\text{-GAATTC-}3'$.

Sticky Ends

Staggered, single-stranded nucleotide overhangs produced when a restriction enzyme cuts DNA, which can anneal via complementary base pairing to other fragments cleaved by the same enzyme.

Polymerase Chain Reaction (PCR)

An in vitro biotechnological technique used to rapidly amplify and generate millions of copies of a target DNA sequence through repetitive cycles of thermal denaturation, primer annealing, and enzymatic extension.

Taq Polymerase

A heat-stable DNA polymerase enzyme isolated from thermophilic bacteria that synthesizes complementary DNA strands without denaturing during high-temperature PCR cycles.

DNA Fingerprinting

A forensic identification method that compares restriction-digested, gel-separated DNA fragment patterns transferred to nylon membranes and visualized on X-ray film.

Transgenics

The genetic engineering procedure of inserting a functional foreign gene (such as the human insulin gene) into a bacterial plasmid to mass-produce human proteins in cultured host cells.

Silent Mutation

A point mutation (base substitution) in a coding sequence that alters a codon to a synonymous codon that specifies the exact same amino acid, leaving the protein unchanged.

Missense Mutation

A point mutation in which a single base substitution alters an mRNA codon so that it codes for a different amino acid, resulting in an altered protein structure.

Nonsense Mutation

A point mutation in which a base substitution prematurely transforms an amino-acid-coding codon into a termination/stop codon, yielding a truncated, nonfunctional polypeptide.

Frameshift Mutation

A mutation resulting from the insertion or deletion of a number of nucleotides not divisible by three, which shifts the reading frame and changes all downstream amino acids.

Cystic Fibrosis

A genetic disease caused by a frameshift/deletion mutation in the CFTR gene, resulting in defective chloride ion transport and the accumulation of thick, airway-blocking lung secretions.

Viral Vector

A modified, harmless virus stripped of pathogenic traits that acts as a delivery vehicle to introduce therapeutic genes directly into host cells during gene therapy.