Free BACE Genetics Questions and Answers 2 — Questions and Answers
Question 1: What is the central dogma of molecular biology?
- DNA to RNA to Protein describes the flow of genetic information from storage to functional form (Correct answer)
- Protein to RNA to DNA describes how proteins direct their own synthesis
- RNA to DNA to Protein describes retroviral replication
- Protein to DNA to RNA describes the reverse process in eukaryotes
Correct answer: DNA to RNA to Protein describes the flow of genetic information from storage to functional form
The central dogma states that genetic information flows from DNA (storage) to RNA (transcription) to protein (translation), with replication maintaining the DNA blueprint.
The three main processes: (1) Replication: DNA to DNA, (2) Transcription: DNA to RNA, (3) Translation: RNA to Protein. Exceptions exist: reverse transcriptase (RNA to DNA in retroviruses) and RNA replication in RNA viruses. The central dogma underpins all of molecular biotechnology, from PCR to gene expression studies to protein production.
Question 2: What is the difference between a gene and an allele?
- A gene is a segment of DNA; an allele is a segment of RNA
- A gene is a hereditary unit encoding a trait; an allele is one of the alternative forms of that gene at a specific chromosomal locus (Correct answer)
- A gene is found in somatic cells; an allele is found only in germ cells
- A gene exists only in diploid organisms; an allele exists in haploid organisms
Correct answer: A gene is a hereditary unit encoding a trait; an allele is one of the alternative forms of that gene at a specific chromosomal locus
A gene is a specific DNA sequence that encodes a functional product; alleles are the different sequence variants of that gene that can exist at the same chromosomal locus.
For example, the ABO blood group gene has three common alleles (A, B, O) encoding different glycosyltransferases. In a diploid organism, each individual carries two alleles — these can be identical (homozygous) or different (heterozygous). The combination of alleles (genotype) determines the observable characteristic (phenotype). In biotech, allelic variation in target genes can affect drug metabolism and therapeutic response.
Question 3: What is the result of a frameshift mutation in a protein-coding gene?
- A single amino acid change in the resulting protein at the site of the mutation
- Complete loss of gene function due to failure to transcribe the mutated DNA
- A shift in the reading frame that alters all downstream codons usually producing a truncated or non-functional protein (Correct answer)
- Increased protein production due to creation of an alternative start codon
Correct answer: A shift in the reading frame that alters all downstream codons usually producing a truncated or non-functional protein
A frameshift mutation (insertion or deletion of non-multiple-of-3 nucleotides) shifts the triplet codon reading frame, causing all downstream amino acids to change and often introducing premature stop codons.
The genetic code is read in non-overlapping triplets (codons). A frameshift occurs when the number of nucleotides inserted or deleted is not divisible by 3. This shifts the reading frame for all downstream codons, changing every amino acid from the mutation site onward and often creating premature stop codons. CRISPR-Cas9 gene editing often creates deliberate frameshift mutations (indels) to knock out gene expression.
Question 4: What is a promoter in the context of gene expression?
- A protein that promotes translation by binding ribosomes to mRNA
- A DNA sequence upstream of a gene where RNA polymerase binds to initiate transcription (Correct answer)
- An RNA sequence that promotes efficient ribosome binding for translation
- A protein that promotes DNA methylation to silence gene expression
Correct answer: A DNA sequence upstream of a gene where RNA polymerase binds to initiate transcription
A promoter is a regulatory DNA sequence upstream (5') of a gene that RNA polymerase recognizes and binds to, initiating transcription of the gene.
Promoters contain specific sequence elements that bind transcription factors and RNA polymerase. In prokaryotes, the -10 (TATAAT) and -35 (TTGACA) hexamers are recognized by sigma factor. In eukaryotes, the TATA box is recognized by TATA-binding protein (TBP). Promoter strength determines how often RNA polymerase initiates transcription. In expression vectors for recombinant protein production, strong, regulatable promoters (T7, CMV, EF1-alpha) are used to drive high-level protein expression.
Question 5: What is the purpose of gel electrophoresis in genetic analysis?
- To amplify specific DNA sequences from small amounts of starting material
- To separate DNA fragments by size in an electric field for visualization and analysis (Correct answer)
- To sequence DNA by determining the exact nucleotide order of fragments
- To cut DNA at specific recognition sequences using restriction enzymes
Correct answer: To separate DNA fragments by size in an electric field for visualization and analysis
Gel electrophoresis separates DNA fragments by size as they migrate through agarose under an electric field — smaller fragments move faster, allowing size-based analysis of DNA samples.
In agarose gel electrophoresis, DNA (negatively charged due to phosphate backbone) migrates toward the positive electrode. The gel matrix acts as a molecular sieve — smaller fragments move faster. Applications: (1) confirm PCR product size, (2) analyze restriction digestion patterns, (3) check quality of DNA purification. Gel percentage determines resolution range: 0.8% for large fragments; 2% for small fragments (100-1000 bp).
Question 6: What is epigenetics in the context of gene regulation?
- Mutations in the DNA sequence of genes that are inherited by daughter cells
- Heritable changes in gene expression that do not involve changes in the DNA nucleotide sequence (e.g., methylation, histone modification) (Correct answer)
- The process by which genes are transcribed faster in response to environmental signals
- The study of genetic differences between species in their promoter sequences
Correct answer: Heritable changes in gene expression that do not involve changes in the DNA nucleotide sequence (e.g., methylation, histone modification)
Epigenetics refers to heritable changes in gene expression or chromatin structure that do not alter the underlying DNA sequence — including DNA methylation and histone modifications.
Key epigenetic mechanisms: (1) DNA methylation of cytosine (CpG sites) — typically associated with gene silencing; (2) Histone modification: acetylation opens chromatin (activates transcription), methylation is context-dependent; (3) Chromatin remodeling; (4) Non-coding RNAs. Epigenetic marks are heritable through cell division and can be influenced by environment. In cell culture, passage number and conditions affect epigenetic marks — a concern in biotechnology.
Free BACE Genetics Questions and Answers 2
What is the central dogma of molecular biology?