DNA Structure And Replication Flashcards
What theory linked chromosomes to Mendel’s principles?
Chromosomal theory of inheritance
Developed in the early 1900s.
Who demonstrated sex-linked traits confirming the chromosomal theory?
Thomas Morgan Hunt
His work provided evidence for the chromosomal basis of inheritance.
What did Griffith’s experiments identify in bacteria?
The ‘transforming principle’
Conducted in the 1920s.
Which experiment confirmed DNA as the ‘transforming principle’?
Avery’s work
Conducted in the 1940s.
What was the purpose of the Hershey-Chase experiment?
To confirm DNA as the hereditary molecule
Used radio-labeled DNA and proteins in bacteriophages.
Who revealed DNA’s helical structure through X-ray diffraction?
Rosalind Franklin and Maurice Wilkins
Their work was crucial in understanding DNA structure.
What model of DNA did Watson and Crick propose?
The double helix model
Proposed in 1953 based on X-ray data.
What is DNA composed of?
A polymer of nucleotides
Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
What are the nitrogenous bases found in DNA?
- Adenine
- Thymine
- Guanine
- Cytosine
These bases pair to form the genetic code.
What is the structure of the DNA backbone?
Sugar-phosphate backbone with bases inside
Nucleotides form this backbone.
What structural feature of DNA involves strands running in opposite directions?
Antiparallel strands
This arrangement is critical for replication and function.
What base pairs complementarily in DNA?
- A-T (2 hydrogen bonds)
- G-C (3 hydrogen bonds)
These pairs are essential for the stability of the DNA molecule.
What does Chargaff’s rule state?
Equal amounts of purines and pyrimidines
It provides evidence for complementary base-pairing: A and G are purines, T and C are pyrimidines.
What is the primary model of DNA replication proposed by Watson and Crick?
Semiconservative replication: each new DNA molecule contains one parental strand and one newly synthesized strand.
This model was confirmed by Meselson and Stahl’s experiment using isotope-labeled DNA.
What are the three proposed replication mechanisms that could lead to different experimental results?
Conservative, semiconservative, and dispersive replication.
Each mechanism proposes a different way in which DNA strands could be replicated.
What initiates DNA replication at the origins of replication?
Formation of replication bubbles.
These bubbles allow for the simultaneous replication of DNA in both directions.
What is the leading strand in DNA replication?
The strand that is synthesized continuously.
It is synthesized in the same direction as the replication fork.
What is the lagging strand in DNA replication?
The strand that is synthesized in fragments (Okazaki fragments).
This occurs because DNA polymerase can only add nucleotides to the 3’ end.
What is the direction of DNA polymerase activity during replication?
5’ to 3’ direction.
DNA polymerase adds nucleotides only to the 3’ end of the growing strand.
What is the role of helicase in DNA replication?
Unwinds DNA.
This enzyme is crucial for separating the two strands of DNA.
What do single-stranded binding proteins (SSBs) do during DNA replication?
Stabilize unwound DNA.
They prevent the strands from re-annealing or forming secondary structures.
What is the function of topoisomerase in DNA replication?
Prevents supercoiling ahead of the fork.
It helps relieve the tension that builds up as DNA unwinds.
What does primase do in the context of DNA replication?
Synthesizes RNA primers.
These primers are necessary for DNA polymerases to initiate synthesis.
What is the role of DNA polymerase III in DNA replication?
Extends the DNA strand from primers.
It is the primary enzyme responsible for synthesizing new DNA.
What is the function of DNA polymerase I?
Replaces RNA primers with DNA.
This is critical for completing the DNA strand after primer synthesis.
What does ligase do during DNA replication?
Joins Okazaki fragments.
This enzyme is essential for linking the short pieces of DNA synthesized on the lagging strand.
What happens to the ends of linear DNA molecules during replication?
They shorten with replication.
This shortening occurs because DNA polymerase cannot fully replicate the ends of linear DNA.
What is the role of telomerase in DNA replication?
Extends telomeres in certain cells.
Telomerase helps maintain the length of telomeres, which protect the ends of chromosomes.
