MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1c Mutations Inborn Errors

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This deck focuses on 1c Mutations Inborn Errors, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Flashcard 1: Which mutation preserves the reading frame: deletion of $1$ nucleotide or deletion of $3$ nucleotides?

Answer: Deletion of $3$ nucleotides. Deletion of 3 nucleotides removes one codon entirely, preserving the downstream reading frame unlike single nucleotide deletions.

Flashcard 2: What is the definition of a point mutation?

Answer: A single-nucleotide change at a specific DNA position. Point mutations involve a substitution, insertion, or deletion of a single nucleotide, altering the DNA sequence at one specific position.

Flashcard 3: What is the definition of a silent (synonymous) mutation?

Answer: A nucleotide change that does not alter the amino acid. Silent mutations occur due to the degeneracy of the genetic code, where multiple codons specify the same amino acid.

Flashcard 4: What is the definition of a missense mutation?

Answer: A nucleotide change that substitutes one amino acid for another. Missense mutations change the codon to one that codes for a different amino acid, potentially altering protein function.

Flashcard 5: What is the definition of a nonsense mutation?

Answer: A mutation that converts a codon into a premature stop codon. Nonsense mutations introduce a stop codon prematurely, leading to truncated proteins.

Flashcard 6: What is the definition of a frameshift mutation?

Answer: Insertion or deletion not in multiples of $3$ that shifts reading frame. Frameshift mutations disrupt the triplet reading frame of codons, resulting in altered amino acid sequences downstream.

Flashcard 7: What is the definition of an in-frame insertion or deletion?

Answer: Insertion or deletion in multiples of $3$ that preserves reading frame. In-frame mutations add or remove whole codons, maintaining the original reading frame and downstream sequence integrity.

Flashcard 8: What is the typical protein-level effect of a frameshift early in a coding region?

Answer: Truncated, nonfunctional protein due to altered downstream sequence. Early frameshifts often introduce premature stop codons, producing shortened proteins that lack functionality.

Flashcard 9: What is the definition of a splice-site mutation?

Answer: A mutation that disrupts intron removal or exon joining in pre-mRNA. Splice-site mutations affect consensus sequences at intron-exon boundaries, impairing proper mRNA splicing.

Flashcard 10: What is the definition of a promoter (regulatory) mutation?

Answer: A DNA change that alters transcription factor binding and gene expression. Promoter mutations modify regulatory regions, influencing the rate of transcription initiation and overall gene expression levels.

Flashcard 11: What is the definition of a loss-of-function mutation?

Answer: A mutation that reduces or abolishes normal gene product activity. Loss-of-function mutations impair gene product efficacy, often leading to recessive phenotypes in diploid organisms.

Flashcard 12: What is the definition of a gain-of-function mutation?

Answer: A mutation that increases activity or creates a new function. Gain-of-function mutations enhance or confer novel activities, frequently resulting in dominant phenotypes.

Flashcard 13: Which inheritance pattern is most common for inborn errors of metabolism?

Answer: Autosomal recessive. Most inborn errors of metabolism follow autosomal recessive inheritance due to loss-of-function mutations in enzyme-coding genes.

Flashcard 14: What is the typical biochemical mechanism of many inborn errors of metabolism?

Answer: Enzyme deficiency causing substrate buildup and product deficiency. Inborn errors often stem from mutations causing enzyme deficiencies, disrupting metabolic pathways with substrate accumulation and product shortage.

Flashcard 15: What is the definition of haploinsufficiency?

Answer: One functional allele is insufficient for normal phenotype. Haploinsufficiency occurs when a single copy of the gene fails to produce enough product for normal function, leading to dominant inheritance.

Flashcard 16: What is the definition of a dominant-negative mutation?

Answer: Mutant protein interferes with the function of the normal protein. Dominant-negative mutations produce defective proteins that inhibit wild-type counterparts, often in multimeric complexes.

Flashcard 17: What is the definition of penetrance in human genetics?

Answer: The fraction of individuals with a genotype who express the phenotype. Penetrance measures the proportion of genotype carriers showing the expected phenotype, influenced by genetic and environmental factors.

Flashcard 18: What is the definition of variable expressivity?

Answer: Differences in severity or features among individuals with same genotype. Variable expressivity reflects how modifiers and environment cause phenotypic variation in individuals sharing the same mutation.

Flashcard 19: What is the key inheritance feature of mitochondrial DNA mutations?

Answer: Maternal inheritance. Mitochondrial DNA is inherited solely from the mother, as sperm contribute negligible mitochondria to the zygote.

Flashcard 20: What is heteroplasmy in mitochondrial genetics?

Answer: A mixture of normal and mutant mtDNA within a cell or individual. Heteroplasmy arises from random segregation of mutant and wild-type mtDNA during cell division, affecting disease manifestation.

Flashcard 21: Identify the expected phenotype of a heterozygous carrier for an autosomal recessive IEM.

Answer: Typically asymptomatic (one functional allele is usually sufficient). In autosomal recessive IEMs, heterozygotes usually have sufficient enzyme activity from one allele to remain unaffected.

Flashcard 22: Which mutation type is most likely to produce a premature stop codon: missense or nonsense?

Answer: Nonsense. Nonsense mutations directly change a sense codon to a stop codon, unlike missense which alters amino acids without stopping translation.

Flashcard 23: If a coding sequence loses $2$ nucleotides, what mutation class best describes the effect on translation?

Answer: Frameshift mutation. Loss of 2 nucleotides shifts the reading frame, as it is not a multiple of 3, altering all subsequent codons.

Flashcard 24: What is the probability that two carrier parents have an affected child for an autosomal recessive disorder?

Answer: $$ $\frac{1}{4}$. For autosomal recessive disorders, each child has a 25% chance of inheriting two mutant alleles from carrier parents.

Flashcard 25: What is the probability that a child is a carrier if both parents are carriers for an autosomal recessive disorder?

Answer: $\frac{1}{2}$. With both parents as carriers, children have a 50% chance of being heterozygous carriers per Mendelian inheritance.