HL of A 1.2 Flashcards
What are the three main processes that rely on complementary base pairing?
Replication, transcription, and translation.
In which direction do replication, transcription, and translation occur?
In the 5′ to 3′ direction.
What functional groups are found at the 5′ and 3′ ends of DNA?
The 5′ end has a phosphate group (-PO4), and the 3′ end has a hydroxyl group (-OH).
Why is the 5′ to 3′ direction important for DNA replication?
It ensures the conservation of the DNA sequence and proper enzyme function.
What enzyme is responsible for DNA replication, and where does it attach?
DNA polymerase, which can only attach to the 3′-OH group.
What is complementary base pairing?
The specific pairing of bases: Adenine (A) with Thymine (T) via two hydrogen bonds, and Cytosine (C) with Guanine (G) via three hydrogen bonds.
Why do purines always pair with pyrimidines?
To maintain a consistent DNA double-helix structure, ensuring a uniform diameter.
What happens if mismatched base pairing occurs during replication?
Structural instability may lead to cell division errors, cell death, or cancer.
What are nucleosomes?
DNA wrapped around histone proteins to help package and organize genetic material.
What is the length of DNA wrapped around a nucleosome?
About 150 base pairs.
What is the histone octamer?
A nucleosome core consisting of eight histone proteins (four types in pairs) with an H1 histone stabilizing the structure.
What role do nucleosomes play in gene expression?
They regulate DNA accessibility by allowing or restricting transcription machinery access to genes.
What happens to nucleosomes during transcription?
They temporarily loosen or shift to allow RNA polymerase to access DNA.
Why is prokaryotic DNA called ‘naked DNA’?
It lacks histone proteins and remains free in the cytoplasm.
Hershey and Chase and Chargaff’s data (HL)
Hershey and Chase and Chargaff’s data (HL)
What was the purpose of the Hershey–Chase experiment?
The experiment aimed to determine whether DNA or protein was the genetic material by using radioactive labeling in bacteriophages.
What did Hershey and Chase use to label DNA and protein in their experiment?
Radioactive phosphorus (³²P) to label DNA
Radioactive sulfur (³⁵S) to label protein
What were the key findings of the Hershey–Chase experiment?
Bacteriophages labeled with ³²P (DNA) infected bacteria, and the radioactivity was detected inside the bacterial cells and in the next generation of viruses.
Bacteriophages labeled with ³⁵S (protein) showed almost no radioactivity inside the bacterial cells.
Conclusion: DNA, not protein, is the genetic material.
Why was the Hershey–Chase experiment significant?
It provided strong evidence that DNA carries genetic information, resolving the debate over whether proteins or DNA were responsible for heredity.
What was the tetranucleotide model, and why was it incorrect?
The tetranucleotide model suggested that DNA was single-stranded and contained equal amounts of adenine, guanine, cytosine, and thymine in a repeating sequence.
It was later disproven by Chargaff’s data, which showed varying base compositions in different organisms.
What did Erwin Chargaff discover about DNA composition?
Chargaff’s analysis showed that:
The amount of adenine (A) = thymine (T) The amount of cytosine (C) = guanine (G) This supported the complementary base pairing concept and contributed to the discovery of the double helix structure of DNA.
How did Chargaff’s findings support the double-helix model of DNA?
Chargaff’s base-pairing rules (A=T, C=G) provided evidence for complementary base pairing, which Watson and Crick incorporated into their double-helix model of DNA.
