DNA & CENTRAL DOGMA
A mutation changes the DNA sequence from:
Predict how this could affect the final protein.
One amino acid may change, potentially altering protein structure or function.
A student opens a Petri dish near a fan while streak plating bacteria. Explain why this is a problem.
Airborne contaminants could enter the plate and contaminate the culture.
A scientist inserts human insulin genes into bacteria. Why are bacteria useful for this process? Give TWO reasons.
Rapid reproduction; easy genetic manipulation.
Why must DNA be purified before PCR or gel electrophoresis?
Contaminants can interfere with enzymes and accurate results.
A scientist changes data that does not support their hypothesis. Why is this unethical?
It compromises scientific accuracy and integrity.
A scientist discovers two cells with identical DNA but completely different functions. Explain how this is possible.
Different genes are expressed in different cell types.
A scientist isolates bacteria from soil but notices multiple colony types growing. What likely happened?
The culture was not isolated properly or contamination occurred.
A plasmid enters a bacterium, but the inserted gene is never expressed. Name ONE plasmid component that may be missing.
Promoter
A DNA sample has a very low A260 reading. What does this suggest about the sample?
Low DNA concentration.
A new experiment disproves a previous scientific theory. Why is this consistent with the nature of science?
Scientific knowledge is tentative and changes with evidence.
During replication, one strand is copied continuously while the other is copied in fragments. Explain why.
DNA polymerase can only build in one direction (5’ → 3’), causing the lagging strand to form Okazaki fragments.
Why is a pure bacterial culture important before performing experiments?
Ensures results come from only one species and improves reliability.
A selectable marker fails during transformation. What problem would this create for researchers?
They could not identify which bacteria successfully received the plasmid.
A PCR reaction produces no amplified DNA bands. Predict TWO possible causes.
Contaminated DNA, missing primers, incorrect temperature, or degraded DNA.
A scientist is testing whether temperature affects bacterial growth. They accidentally use different amounts of nutrient broth in each test tube. Explain why this weakens the experiment.
The amount of nutrient broth becomes an uncontrolled variable that could also affect bacterial growth, making it difficult to determine whether temperature caused the results.
A mutation prevents complementary base pairing from occurring correctly. Predict what would happen during replication.
Incorrect nucleotides could be added, leading to mutations.
A virus cannot reproduce on its own. Explain why.
Viruses require host cell machinery to replicate.
A genetically engineered bacterium produces no protein even though the plasmid is present. Predict one possible cause.
Promoter failure, mutation, or gene transfer didn't work
A scientist accidentally skips the cell lysis step during DNA extraction. Predict the outcome.
DNA would remain trapped inside cells.
A researcher repeats an experiment multiple times before publishing. Which characteristic of science does this demonstrate?
Empirical
A toxin destroys ribosomes inside a cell. Predict TWO effects this would have on the organism.
Protein synthesis would stop; cell functions and growth would fail.
A bacterium survives antibiotic treatment and reproduces rapidly. Explain how this can lead to antibiotic resistance in a population.
Resistant bacteria survive and pass resistance genes to offspring.
Explain one ethical concern related to human gene editing and why it matters.
Possible unintended mutations, inequality, or misuse of technology.
During gel electrophoresis, DNA fragments move in the wrong direction. What mistake most likely occurred?
Electrodes were reversed.
A scientist performs an experiment one time and concludes their hypothesis is proven correct. Explain why this is poor scientific reasoning.
Scientific conclusions require repeated trials, sufficient evidence, and reproducible results before claims can be strongly supported.