7️⃣ The Genome Flashcards
(26 cards)
How many base pairs are in the human genome and what percentage codes for proteins?
~3.2 billion base pairs; ~1.5% codes for proteins.
How many protein-coding genes and transcripts exist in humans?
~21,500 protein-coding genes; ~390,000 transcripts due to alternative splicing.
How is human DNA organized in chromosomes?
Into 23 pairs: 22 autosomes plus 1 pair of sex chromosomes; chromatids joined at centromeres; telomeres protect ends.
What are nucleosomes and chromatin types?
Nucleosomes = DNA wrapped around histone octamers; chromatin exists as euchromatin (active, loose) and heterochromatin (inactive, dense).
List major RNA types and key features vs DNA.
RNA is single-stranded, uses uracil (U) instead of thymine (T); includes mRNA, rRNA, tRNA, miRNA, lncRNA.
State the central dogma.
DNA → RNA (in nucleus) → protein (in cytoplasm).
What is RNA splicing and alternative splicing?
Splicing removes introns; alternative splicing creates multiple protein isoforms from one gene.
How does epigenetics regulate transcription?
Via histone and DNA modifications (e.g., methylation, acetylation) that alter chromatin structure and accessibility.
Name and define the five main coding-region mutation types.
Synonymous (no AA change), missense (AA substitution), nonsense (premature stop), frameshift (1–2 bp indel altering frame), in-frame deletion (3 bp deletion preserving frame).
What are trinucleotide repeat expansions?
Expansion of a 3-nt sequence (e.g., CAG in Huntington’s; CGG in Fragile X) that increases over generations.
List non-coding-region mutation targets and effects.
Mutations in promoters, enhancers, UTRs, splice sites; can alter transcription regulation, RNA processing, mRNA stability, or translation efficiency.
Define pseudogenes, SNPs, and CNVs.
Pseudogenes: nonfunctional gene copies (e.g., via retrotransposition); SNPs: single nucleotide polymorphisms (may be neutral or functional); CNVs: copy number variations (large DNA segments, often affecting coding regions).
How can coding mutations affect proteins?
Alter folding, stability, or function; cause loss of function or toxic gain (e.g., Huntington’s).
How can non-coding mutations affect gene expression?
Change expression level/timing; disrupt splicing → truncated proteins; alter mRNA stability/translation.
What are epigenetic mutations?
Abnormal DNA/histone modifications (e.g., methylation) that silence or activate genes inappropriately.
What cellular functions can protein dysfunction impair?
Enzymes, receptors, transporters, structural proteins, growth regulation, DNA replication/repair.
Describe autosomal dominant inheritance.
One mutated allele causes disease; equal in males/females; 50% transmission; example: Huntington’s (CAG expansion).
Describe autosomal recessive inheritance.
Both alleles mutated; carriers asymptomatic; example: Cystic fibrosis, Tay-Sachs.
Describe X-linked recessive inheritance.
Mutation on X; males affected; carrier females transmit to ~50% of sons; example: Duchenne muscular dystrophy.
What are numerical chromosomal aberrations?
Aneuploidy = gain/loss of individual chromosomes; examples: Trisomy 21 (Down), 18 (Edwards), 13 (Patau).
What are structural chromosomal aberrations?
Deletions, duplications, translocations (balanced/unbalanced), detectable cytogenetically; affect multiple genes.
How does Huntington’s disease arise?
CAG repeat expansion in HTT exon 1 → toxic protein aggregates → neurodegeneration.
How does Cystic fibrosis arise?
CFTR gene mutation (e.g., ΔF508) → defective chloride channel → thick mucus buildup.
How does Tay-Sachs disease arise?
HEXA gene mutation → GM2 ganglioside accumulation → neuronal lysosomal toxicity.
