chapter 7 Flashcards
(36 cards)
What was the experimental evidence that DNA is the genetic material before the discovery of the double helix?
Frederick Griffith’s transformation experiment showed that R strain bacteria could be transformed into S strain bacteria by cell debris from dead S strain cells.
This suggested that some substance from the S strain could convert the R strain cells.
What is the one-gene-one protein hypothesis?
It suggests that each gene corresponds to a specific protein.
Proposed by Beadle and Tatum.
Who demonstrated that DNA is the transforming agent in Griffith’s experiment?
Oswald Avery, Colin MacLeod, and Maclyn McCarty in 1944.
They used a reductionist approach to identify DNA as the transforming substance.
What method did Hershey and Chase use to confirm that DNA is the hereditary material?
They used radioactive labeling of DNA and proteins in T2 phage and tracked which substance entered bacterial cells.
They incorporated 32P into DNA and 35S into proteins.
What are the key properties necessary for hereditary material?
- Faithful replication
- Massive information content
- Ability to change (mutability)
These properties ensure that genetic information is accurately passed on and can evolve.
What are the three parts of a nucleotide?
- Phosphate group
- Sugar (deoxyribose)
- Nitrogenous base (A, T, C, G)
The structure of DNA is based on these nucleotides.
What do Chargaff’s rules state about nucleotide composition?
- Amount of T = A
- Amount of C = G
- Amount of pyrimidines (T + C) = amount of purines (A + G)
Chargaff’s rules helped in understanding DNA structure.
What did Rosalind Franklin contribute to the understanding of DNA structure?
Her X-ray diffraction data showed that DNA is long, skinny, and helical.
This data was crucial for Watson and Crick’s model.
How do hydrogen bonds contribute to the stability of DNA?
A-T base pairs form two hydrogen bonds, while G-C base pairs form three hydrogen bonds, making G-C stretches more stable.
This affects the overall stability and integrity of the DNA structure.
What is the significance of the antiparallel orientation of DNA strands?
It allows for complementary base pairing and proper replication.
One strand runs 5’ to 3’ and the other runs 3’ to 5’.
What is semiconservative replication?
Each new DNA strand consists of one parental strand and one newly synthesized strand.
This model was confirmed by the Meselson-Stahl experiment.
What is the role of DNA polymerase in DNA replication?
DNA polymerase synthesizes new DNA strands by adding deoxyribonucleotides to a growing chain using the parent strand as a template.
DNA polymerase I and III are key enzymes involved in this process.
What is the function of the replisome?
The replisome is a complex of proteins that coordinate the replication of DNA, including unwinding the double helix and synthesizing new strands.
It includes helicase, DNA polymerases, and accessory proteins.
What is the function of DNA ligase?
DNA ligase connects adjacent fragments of DNA on the lagging strand during replication.
It forms phosphodiester linkages between Okazaki fragments.
What is the estimated error rate during DNA replication?
About 1 error per 1 billion bases replicated.
This accuracy is enhanced by proofreading and repair mechanisms.
What is the role of telomeres and telomerase in DNA replication?
Telomeres protect chromosome ends, and telomerase replicates them to prevent loss of genetic information during cell division.
Defective telomere replication can lead to health issues.
True or False: DNA replication is a slow process in E. coli.
False. DNA replication in E. coli can occur at 2000 bp/second.
This rapid replication is crucial for bacterial growth.
What transforms DNA pol III into a processive enzyme?
DNA gyrase
DNA gyrase is a type of topoisomerase that removes extra twists in DNA.
What causes over winding at unwound regions during DNA replication?
Unwinding one region
This refers to the mechanical stress introduced by the unwinding of DNA strands.
What is the fixed point where prokaryotic replication begins called?
Origin
The origin is a specific location on the DNA where replication initiates.
What protein molecules bind to DnaA boxes during prokaryotic replication initiation?
DnaA
DnaA proteins recognize specific sequences to initiate strand separation.
What triggers strand separation at AT-rich sequences?
DnaA binding
AT-rich sequences are easier to unwind due to fewer hydrogen bonds compared to GC-rich sequences.
What is the function of helicase (DnaB) in DNA replication?
Unwind DNA in a 5’ to 3’ direction
Helicase is crucial for separating the two strands of DNA, allowing replication to occur.
Which enzyme and holoenzyme are recruited to the replication fork?
Primase and DNA pol III
These components are essential for synthesizing RNA primers and elongating the DNA strand.
