4 - The Molecular Basis of Inheritance Flashcards
who was friedrich miescher
the discoverer of nucleic acid
Frederick Griffith (1928)
discovered transformation in bacteria
Oswald Avery (1944)
identified the “transforming substance” of Griffith’s experiment — DNA
Hershey-Chase Experiment
confirmed that DNA is the genetic material because only radiolabeled DNA could be found in bacteriophage-infected bacteria
Chargaff’s Rule
A=T and C=G
what are the 3 components of a nucleotide?
sugar, phosphate, nitrogenous base
What is a purine base?
It has 2 rings- Adenine and Guanine
what is a pyrimidine base?
It has 1 ring- Thymine and Cytosine
which nitrogenous bases are found in DNA?
adenine, guanine, cytosine, thymine
adenine, guanine, cytosine, thymine
- composed of polynucleotides
- Has a doubled helix that is formed by hydrogen bonds between polynucleotides
- Densely compacted into chromosomes to fit into nucleus
Explain semi-conservative replication
One strand acts as a template
Each new DNA molecule contains one original strand and one new strand
which enzymes are involved in DNA replication?
DNA helicase and DNA polymerase
what is the role of DNA helicase in replication?
unwinds the DNA molecule for replication
What is the leading strand?
The strand where replication moves towards the replication fork (follows helicase)
Synthesis of leading strand
- Priming: primase
- Elongation: DNA polymerase
- Replacement of RNA primer by DNA: DNA polymerase
What is the lagging strand?
The strand where DNA replication moves away from the replication fork
synthesis of lagging strand
- primer added
- first fragment synthesized
- second fragment synthesized
- primer replaced
- gap closed
Mehelson Stahl Experiment
experimental proof for semi conservative replication
- Bacteria cultured in medium with 15N (heavy isotope)
- Bacteria transferred to medium with 14N (lighter isotope)
- DNA sample centrifuged after 1st replication
- All DNA of intermediate density = 1 light strand and 1 heavy strand
what is the role of single-strand binding proteins
hold the helix open
what is the role of primase?
synthesises the RNA primers needed for initiation of DNA synthesis
what is the role of DNA polymerase III?
extends the DNA( or RNA) strand from the 3’ end, copying the template
what is the role of DNA polymerase I?
removes the RNA primer and fills in gaps between Okazaki fragments
removes the RNA primer and fills in gaps between Okazaki fragments
seals the gaps between Okazaki fragments
DNA polymerase
• Requires:
– Single-stranded template DNA
– All four nucleoside triphosphates (dNTPs)
– Free 3’ hydroxyl (primer)
• Synthesises DNA in 5’ to 3’ direction
• Inserts complementary nucleotides
• Uses energy from breaking phosphate bonds
•“Proof-reading” ability – can remove incorrectly inserted nucleotides
