DNA history
What discovery by Watson and Crick in 1953 explained how DNA could replicate and store genetic information?
the double-helix model of DNA
Define transformation. And briefly outline what the study discovered about this recombination method.
This process allows bacteria to take up naked DNA from their environment, leading to genetic changes. It was first demonstrated by Frederick Griffith’s experiment using mice and Streptococcus pneumoniae, which led him to propose the existence of a “transforming principle.”
Why, structurally, do bacterial chromosomes only have one origin or replication compared to eukaryotes?
Bacteria have circular chromosomes while eukaryotes have linear genomes.
If a diploid human has monosomy, how many total
chromosomes will their somatic cells contain?
(2n = 46)
46 - 1 = 45
According to Chargaff’s rules; If a double-stranded DNA molecule has 40% adenine (A), what are the percentages of the other three bases?
T = 40%
C = 10%
G = 10%
Define Transduction
A type of viral gene transfer that occurs when a bacteriophage mistakenly packages bacterial DNA and transfers it to another cell.
This DNA replication model was confirmed by the Meselson–Stahl experiment, which showed that each new DNA molecule contains one original strand and one newly synthesized strand.
What is the semi-conservative model of DNA replication?
Define Aneuploidy
When a cell has too few or too many individual chromosomes, instead of the normal pair (for example, 45 or 47 instead of 46 in humans).
What were the two key VERY early-stage researchers' works that we need to understand DNA? (Give their name and discovery)
Miescher:
Discovered nucleic acids (high in nitrogen and phosphorus) in white blood cells; he called the substance nuclein.
Chargaff:
[A] = [T] the amount of adenine always equals the amount of thymine.
[C] = [G] the amount of cytosine always equals the amount of guanine
What's the role of a topoisomerase?
Relieves supercoiling (Introduces negative supercoiling)
What's a nucleosome?
The basic structural unit of chromatin that helps compact DNA around histone proteins
Define Polyploidy
When a cell has extra complete sets of chromosomes, not just one or two extra: like 3n (triploid) or 4n (tetraploid) instead of the normal 2n.
What is the Avery–MacLeod–McCarty experiment?
This 1944 experiment by Avery, MacLeod, and McCarty demonstrated that DNA, not protein or RNA, is the molecule responsible for transformation in bacteria.
Define conjugation and the experiment that explained its main physical requirement.
Conjugation is the direct transfer of DNA between two bacterial cells through cell-to-cell contact. The Bernard Davis U-tube experiment showed that this physical contact is required for genetic recombination to occur.
In E. coli DNA replication, why does the lagging strand require multiple primers while the leading strand only needs one?
DNA polymerase can only synthesize in the 5′→3′ direction. The lagging strand is made discontinuously in short Okazaki fragments, each requiring a new RNA primer.
At which stage of meiosis 1 do the consequences of an inversion become visible?
Prophase 1
What was the key difference between Griffith’s and Avery–MacLeod–McCarty’s experiments, and how did this difference lead to identifying DNA as the transforming material?
Griffith showed transformation occurred but didn’t identify the molecule; Avery–MacLeod–McCarty purified cellular components and proved only DNA, not protein or RNA, caused transformation.
Outline the Lederberg & Tatum experiment (Think conjugation if the name is unfamiliar)
Experiment: Mixed two E. coli auxotrophic strains and recovered prototrophic recombinants.
What is the goal of DNase sensitivity assays?
Determine which regions of DNA are transcriptionally active. (Expressed)
Which stage(s) of Meiosis would an error explain an aneuploid condition like trisomy 21 or XO?
Anaphase 1 and 2