Genomics and the Human Genome

Vocabulary flashcards covering genomic structure, nuclear DNA organization, genetic variation, epigenetics, noncoding RNAs, and CRISPR-Cas9 gene editing based on lecture material.

Telomeres

Repetitive nucleotide sequences that cap the termini of chromatids, permitting repeated chromosomal replication without deterioration of genes near the ends.

p arm

The short arm of a chromatid, designated 'p' for petite.

q arm

The long arm of a chromatid, designated 'q' as the letter following 'p' in the alphabet.

Promoters

Noncoding regions of DNA located on the same strand and upstream of their associated gene that initiate gene transcription.

Enhancers

Noncoding DNA elements that modulate gene expression over distances of $100\,\text{kb}$ or more by looping back onto promoters to recruit expression-driving transcription factors.

Heterochromatin

Densely packed, cytochemically dense chromatin that is transcriptionally inactive.

Euchromatin

Dispersed, cytochemically loose chromatin that is transcriptionally active.

Nucleosome

A basic unit of DNA packaging consisting of $147\,\text{bp}$ of DNA wrapped around an octameric core of highly conserved, positively charged histone proteins (H2A, H2B, H3, H4).

Single Nucleotide Polymorphisms (SNPs)

Biallelic DNA variants occurring at single nucleotide positions throughout coding and noncoding genomic regions.

Copy Number Variations (CNVs)

A form of genetic variation consisting of different numbers of large contiguous stretches of DNA ranging from $1000\,\text{base pairs}$ to millions of base pairs.

Epigenetics

Heritable changes in gene expression that are not caused by alterations in the underlying DNA sequence.

Chromatin Writers

Enzymatic complexes that carry out over $70$ different histone modifications (marks) via covalent alterations such as methylation, acetylation, or phosphorylation.

Chromatin Erasers

Enzymes responsible for removing covalent histone modifications, allowing epigenetic marks to be reversible.

Chromatin Readers

Proteins that bind histones bearing specific covalent marks to regulate downstream gene expression.

microRNAs (miRNAs)

Small noncoding RNA molecules averaging $22$ nucleotides in length that modulate translation and post-transcriptionally silence target messenger RNAs.

Dicer

A cytoplasmic enzyme that trims precursor miRNA (pre-miRNA) hairpin structures to generate mature double-stranded miRNAs of $21\text{ to }30\,\text{nucleotides}$.

RNA-induced Silencing Complex (RISC)

A multiprotein aggregate that incorporates a single-stranded miRNA to direct complementary target mRNA cleavage or translational repression.

Small interfering RNAs (siRNAs)

Synthetic, short RNA sequences introduced experimentally into cells that serve as substrates for Dicer and RISC to silence specific target mRNA species.

Long Noncoding RNAs (lncRNAs)

Noncoding RNA molecules greater than $200\,\text{nucleotides}$ in length that regulate gene expression by interacting with chromatin, transcription factors, or histone-modifying enzymes.

XIST

A long noncoding RNA transcribed from the X chromosome that plays an essential role in physiological X chromosome inactivation in females.

CRISPRs

Clustered Regularly Interspaced Short Palindromic Repeats; genomic DNA segments in prokaryotes derived from foreign DNA that provide adaptive immunity against phages and plasmids.

Cas9

A nuclease protein guided by artificial or natural gRNA sequences to induce targeted double-stranded breaks in genomic DNA.

Nonhomologous End Joining (NHEJ)

A DNA repair pathway following double-stranded breaks that rejoins DNA ends, frequently generating random insertions or deletions.

Homology-Directed Repair (HDR)

A precise DNA repair mechanism that uses donor DNA to introduce specific, targeted genetic mutations into a cleavage site.