molecular basis Flashcards
(51 cards)
Who first discovered the phenomenon of bacterial transformation?
Frederick Griffith in 1928.
How is transformation now defined in molecular biology?
A change in genotype and phenotype due to assimilation of foreign DNA.
What did Griffith observe when he mixed heat-killed pathogenic bacteria with living harmless bacteria?
Some living harmless bacteria became pathogenic — a process he called transformation.
Who demonstrated that DNA is the genetic material in viruses?
Alfred Hershey and Martha Chase in 1952.
What key structural insights did Franklin’s images provide?
DNA is a helical molecule with a width of 2 nm and a base pair spacing of 0.34 nm; one full turn every 3.4 nm (10 base pairs).
What are Chargaff’s rules?
DNA composition varies between species; 2) In any species, A = T and G = C.
What did Hershey and Chase’s experiment with T2 phage show?
Only DNA, not protein, entered E. coli during infection and provided genetic information
What technique did Rosalind Franklin use to study DNA?
X-ray crystallography.
What was Watson and Crick’s main structural contribution?
DNA is a double helix with antiparallel sugar-phosphate backbones and complementary base pairing.
Why must a purine pair with a pyrimidine in DNA?
: To maintain a uniform width of the double helix.
What did the Watson-Crick model explain about Chargaff’s rules?
The specific base pairing accounts for equal A=T and G=C ratios
Which bases pair together in DNA?
Adenine with Thymine (A-T), Guanine with Cytosine (G-C).
Who is Linus Pauling and what were his contributions?
Nobel laureate; proposed protein secondary structures like the alpha helix, and studied molecular disease like sickle cell anemia.
How does replication proceed in DNA?
Bidirectionally from each origin until the molecule is fully copied.
What were the competing models of DNA replication?
Conservative model and dispersive model.
What does the semiconservative model of DNA replication state?
Each daughter DNA molecule has one old (parent) strand and one newly synthesized strand.
Where does DNA replication begin?
At origins of replication, forming replication “bubbles”.
What is the role of helicase in DNA replication?
It untwists the DNA double helix at replication forks.
What do single-strand binding proteins do?
Stabilize unwound DNA strands during replication
What does topoisomerase do during replication?
: Relieves strain ahead of the replication fork by cutting and rejoining DNA.
What is the role of DNA polymerase?
: It adds nucleotides to a primer to synthesize a new DNA strand.
Compare prokaryotic and eukaryotic DNA replication.
- Prokaryotic: One origin, fewer polymerases, faster, no telomeres.
- Eukaryotic: Many origins, more polymerases, slower, telomere handling
Why does eukaryotic DNA replicate faster than expected?
Multiple origins of replication allow simultaneous copying
What does primase do?
Synthesizes RNA primers by adding RNA nucleotides using parental DNA as a template
