Genetics: DNA Structure, Replication, and Clinical Disorders

A set of vocabulary-style flashcards covering DNA structure, replication, repair mechanisms, cell biology, and high-yield genetic disorders based on lecture notes.

Nucleosides

A molecule consisting of a sugar combined with a base.

Nucleotides

A molecule consisting of a sugar, a base, and a phosphate group; these are the building blocks incorporated into DNA and RNA.

Purines

A class of nitrogenous bases that include Adenine and Guanine.

Pyrimidines

A class of nitrogenous bases that include Cytosine, Thymine, and Uracil (where Uracil replaces Thymine in RNA).

G-C bonds

Strong nitrogenous base pairings held together by $3$ hydrogen bonds.

A-T bonds

Nitrogenous base pairings held together by $2$ hydrogen bonds.

Lesch-Nyhan Syndrome

An X-linked recessive HGPRT deficiency characterized by hyperuricemia, Gout, aggression ("Pissed off"), random muscle contractions, and intellectual disability.

SCID (Severe Combined Immunodeficiency)

A life-threatening condition caused by adenosine deaminase deficiency, resulting in recurrent infections.

Azathioprine

A pharmacology agent used for immunosuppression that is metabolized into $6$-Mercaptopurine ($6MP$) in the body and activated by HGPRT.

Topoisomerase I

An enzyme that creates single-stranded breaks in DNA to remove supercoiling without requiring $ATP$. Inhibited by Irinotecan and Topotecan.

Topoisomerase II

An enzyme that creates double-stranded breaks in DNA to remove supercoiling in an $ATP$-dependent manner. Inhibited by Etoposide and Teniposide.

DNA Polymerase III

An enzyme that adds nucleotides to the growing DNA chain in the $5' \rightarrow 3'$ direction and possesses $3' \rightarrow 5'$ exonuclease activity for proofreading.

DNA Polymerase I

An enzyme that removes RNA primers via $5' \rightarrow 3'$ exonuclease activity and performs proofreading via $3' \rightarrow 5'$ exonuclease activity.

DNA Telomerase

A reverse transcriptase that adds $TTAGGG$ sequences to the ends of DNA to protect chromosomes from degradation; it is highly active in stem cells and some cancer cells.

Promoter

An upstream DNA sequence ($10-35$ bp) where transcription factors and RNA polymerase II bind; often contains TATAAT and CAAT boxes.

Exons

DNA sequences that are expressed and remain in the mature mRNA.

Introns

Non-coding DNA sequences that are spliced out of the primary transcript in the nucleus.

Wobble

The phenomenon where the third position of a codon allows for redundancy, meaning multiple codons can code for the same amino acid.

Shine-Dalgarno sequence

A ribosomal binding site in prokaryotic mRNA, located approximately $7$ bases before the start codon.

Kozak sequence

A sequence in eukaryotic mRNA that contains the start codon and facilitates the initiation of translation.

Lac Z

A gene in the Lac Operon that encodes the enzyme $\beta$-galactosidase.

Lac Y

A gene in the Lac Operon that encodes lactose permease.

Nonsense mutation

A point mutation that results in an early stop codon ($UGA$, $UAA$, or $UAG$).

Frameshift mutation

An insertion or deletion of a number of nucleotides not divisible by $3$, resulting in the misreading of all downstream codons.

Xeroderma Pigmentosum

An autosomal recessive defect in Nucleotide Excision Repair ($NER$) resulting in an inability to repair thymine dimers, leading to sunlight intolerance and skin cancer.

Lynch Syndrome

An autosomal dominant mutation in $MLH1$ or $MSH2$ leading to defective mismatch repair ($MMR$) and hereditary non-polyposis colorectal cancer ($HNPCC$).

Ataxia Telangiectasia

An autosomal recessive condition caused by an $ATM$ mutation resulting in defective Nonhomologous End Joining ($NHEJ$); characterized by ataxia, telangiectasias, and $IgA$ deficiency.

Colchicine

A gout therapy drug that inhibits tubulin polymerization, thereby preventing mitotic spindle formation and neutrophil chemotaxis.

Nondisjunction

The failure of two chromosomes to separate during meiosis, resulting in aneuploidy such as Trisomies ($21, 18, 13$).

p53

The "guardian of the genome" that activates $p21$ to inhibit $CDKs$ and prevents the cell cycle from progressing in the presence of DNA damage.

Southern Blot

A laboratory technique used to detect specific DNA sequences using radiolabeled DNA probes.

Northern Blot

A laboratory technique used to detect RNA levels and gene expression.

Western Blot

A laboratory technique used to detect specific protein expression using labeled antibodies.

Variable Expressivity

The phenomenon where individuals with the same genotype exhibit different phenotypes or varying degrees of disease severity.

Pleiotropy

A single genotype producing multiple, seemingly unrelated phenotypic effects.

Prader-Willi Syndrome

A disorder caused by paternal deletion or maternal uniparental disomy of chromosome $15$, presenting with hyperphagia, obesity, and intellectual disability.

Angelman Syndrome

A disorder caused by maternal deletion ($UBE3A$ gene) or paternal uniparental disomy of chromosome $15$, presenting with inappropriate laughter, seizures, and ataxia.

Cystic Fibrosis

An autosomal recessive defect in the $CFTR$ gene (most commonly $Phe508$ deletion) on chromosome $7$ causing thickened mucus and pancreatic insufficiency.

Fragile X Syndrome

An X-linked dominant disorder caused by $CGG$ trinucleotide repeat expansion in the $FMR1$ gene, presenting with macroorchidism and a long face.

Huntington Disease

An autosomal dominant disorder caused by $CAG$ trinucleotide repeat expansion in the $HTT$ gene on chromosome $4$, leading to caudate atrophy.

Patau Syndrome

Trisomy $13$ characterized by rocker bottom feet, holoprosencephaly, cleft lip/palate, and polydactyly.

Edwards Syndrome

Trisomy $18$ characterized by clenched fists with overlapping fingers, low-set ears, and rocker bottom feet.

Down Syndrome

Trisomy $21$ characterized by intellectual disability, flat facies, single palmar crease, and duodenal atresia.

Cri-du-chat

A microdeletion of chromosome $5$ characterized by microcephaly and a distinctive high-pitched "cat cry."

Williams Syndrome

A microdeletion of chromosome $7$ (elastin gene) characterized by "elfin" facies, hypercalcemia, and an over-friendly personality.