DNA and Role in Heredity

Who conducted the experiment proving a chemical substance from dead cells can transform living ones?

Frederick Griffith (implied by transformation of pneumococci)

What did the treatment of the S strain filtrate with DNase prove?

It proved that DNA is the transforming substance.

What radioactive isotope was used to label viral DNA in the Hershey-Chase experiment?

32P (Phosphorus)

What radioactive isotope was used to label the viral protein coat in the Hershey-Chase experiment?

35S (Sulfur)

What is a nucleoside?

A nucleotide missing the phosphate group (just base + sugar).

Which nitrogenous bases are Purines?

Adenine (A) and Guanine (G).

Which nitrogenous bases are Pyrimidines?

Cytosine (C), Thymine (T), and Uracil (U).

What is Chargaff's rule?

The amount of A equals T, and the amount of C equals G.

Are the two strands of a DNA double helix parallel or antiparallel?

Antiparallel (one is 5' to 3', the other is 3' to 5').

What was the conclusion of the Meselson-Stahl experiment?

DNA replication is semiconservative.

To which end of a growing DNA strand does DNA polymerase add new nucleotides?

The 3' end.

Where does the energy for binding a new nucleotide during replication come from?

Cleaving a pyrophosphate ion from the incoming nucleoside triphosphate.

What is the function of Helicase?

It uses ATP to unwind the DNA double helix.

What is the function of Single-strand binding proteins?

They keep the unwound DNA strands from coming back together.

What is the function of Primase?

It synthesizes a short RNA primer to initiate DNA synthesis.

What is an Okazaki fragment?

A short, discontinuous stretch of DNA synthesized on the lagging strand.

What is the function of DNA polymerase I?

It replaces the RNA primer nucleotides with DNA nucleotides.

What is the function of DNA ligase?

It joins the nicks left in the sugar-phosphate backbone.

What is the function of a Sliding DNA clamp?

It increases the efficiency of DNA polymerization.

Why do chromosomes shorten with each replication?

A single-stranded gap is left at the end of the lagging strand where an Okazaki fragment could not fit.

What is a telomere?

A repeating, non-functional sequence of bases at the end of a chromosome that protects genes from being lost.

What is the function of telomerase?

It uses an RNA template to add extra telomere sequences to the lagging strand.

Which two cell types heavily rely on telomerase?

Stem cells (e.g. bone marrow, gametes) and cancer cells.

What happens in mismatch repair?

Enzymes recognize the newly synthesized strand and replace mismatched bases shortly after replication.

Why is excision repair sometimes incorrect?

It happens long after copying when old and new strands are indistinguishable, so it replaces bases on a random strand.