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CHAPTER
12
DNA: STRUCTURE AND FUNCTIONS
I. The Genetic Material
A. Early researchers knew that the genetic material must be:
1. able to store information used to control both the development and the metabolic
activities of cells;
2. stable so it can be replicated accurately during cell division
B. Transformation of Bacteria
Bacteriologist Frederick Griffith (1931) experimented with Streptococcus pneumoniae (a
pneumococcus that causes pneumonia in mammals).
C. DNA: The Transforming Substance
Oswald Avery et al. (1944) reported that purified DNA is capable of bringing about the
transformation.
D. Reproduction of Viruses
Alfred Hershey and Martha Chase (1952) studied bacteriophage T2.
II. The Structure of DNA
A. Nucleotide Data
Erwin Chargaff (1940s) analyzed the base content of DNA.
B. Diffraction Data
Rosalind Franklin produced X-ray diffraction photographs.
C. The Watson and Crick Model
1. DNA as a double helix with sugar-phosphate groups on the outside, and paired bases
on the inside.
2. Their model was consistent with both Chargaff’s rules and Franklin’s X-ray diffraction
studies.
3. Complementary base pairing is the paired relationship between purines and
pyrimidines in DNA: A is hydrogen-bonded to T and G is hydrogen-bonded to C.
III. Replication of DNA:
A. Replication is Semiconservative
Matthew Meselson and Franklin Stahl (1958) confirmed
B. In test tube, DNA replication requires the following.
1. DNA template;
2. Primer
3. dNTPs (dATP, dCTP, dGTP, dTTP)
4. DNA polymerase
C.
Heat resistant DNApolymerase, such as Taq DNA polymerase is used in Polymerase
Chain Reaction (PCR) that is the base of forensic DNA analysis
D.
In vivo DNA synthesis:
1. Replication in eukaryotes starts at many points of origin and spreads with many
replication bubbles—places where the DNA strands are separating.
2. It needs many more factors, unlike the replication in vitro.
3. Eukaryotes replicate their DNA at a slower rate – 500 to 5,000 base pairs per minute so
that they take hours to complete DNA replication.
4. DNA polymerase is a Holo-enzyme, a complex of proteins, that has proof-reading
functions.
Review Qs:
1. If a DNA sample contains 13% adenine, what percentage of the sample contains cytosine?
2. Chargaff's rules states that __________________________________.
3. The DNA structure can be described as ___________________________________. The
building blocks (monomers) are _____________________. On the outside of the helix are
____________________. On the inside of the helix are ________________________. Its 5’ end
has _______________ and its 3’ end has _____________________.
4. If a DNA sequence 5’-ATTCCGATTCT-3’ is replicated, what is the sequence of the product?
5. In test tube, what is required for DNA synthesis?
6. Inside the cell, what are required for DNA synthesis in addition to what needed in test tube?
7. The fashion of DNA replication is _____________________.
8. What are required for DNA replication in vitro?
9. What are required for DNA replication in vivo?
10. What is the error rate in DNA replication?