Name
Date
Per.
Study Questions for Chapter 16: The Molecular Basis of Inheritance
1) Summarize the experiments performed by Alfred Hershey and Martha Chase which proved that DNA is
the genetic material in the bacteriophage known as T2.
Radioactive label on P & S (separately) in viruses; see what part (protein with radioactive S or DNA with
radioactive P) ends up inside all of the bacteria; radioactively labeled P ended up inside the bacteria
2) What information did Erwin Chargaff’s research show about the nitrogenous bases of DNA?
T pairs w/ A *always found in equal amounts
C pairs w/ G *always found in equal amounts
*% of bases is different from species to species
3) Distinguish between purines and pyrimidines. How do they pair with one another in DNA? Why?
1 Purine pairs w/ 1 pyrimidine; purines have 2 rings (A, G) and pyrimidines have 1 ring (C and T); pair with each
other 2 keep consistent distance between Sugar-Phosphate backbones
4) Describe the semiconservative model of DNA replication.
Original DNA molecule splits and the resulting 2 molecules each have 1 of the original strands and 1 new strand
5) What is the source of energy that drives the polymerization of DNA?
Nucleoside triphosphate → last 2 phosphates are hydrolyzed by DNA Polymerase and this provides the E needed
to form Phosphodiester bonds between the Phosphate group of 1 nucleotide & the 3’ end of another nucleotide
6) What is meant by “antiparallel”?
The 2 DNA strands run in opposite directions
7) In what “direction” does DNA synthesis occur? Why?
5’ → 3’ (5’ to 3’); nucleotides can only be added to the 3’ end of another nucleotide
8a) Distinguish between the leading and lagging strands in DNA replication.
Leading strand: continuous synthesis; going into replication fork
Lagging strand: discontinuous synthesis; synthesis in fragments; going away from replication fork
8b) List and explain the function of the enzymes involved in replication at each location.
Helicase: untwist and separate DNA strands
*Single-strand binding protein (protein but not an enzyme): keep DNA strands apart
Primase: makes a primer (RNA nucleotides) so that DNA Polymerase II has a nucleotide to add the 1st DNA
nucleotide onto (on the 3’ end of RNA nucleotide at end of primer)
DNA polymerase III: adds nucleotides onto elongating DNA strand
DNA Polymerase I: remoives RNA nucleotides of primer & replaces with correct DNA nucleotide
DNA ligase: “seals” DNA fragments together (phosphodiester bond fragments together)
9) List at least 4 factors or agents which can cause damage to DNA.
1) UV Rays 2) radioactive emissions 3) X-Rays 4) reactive chemicals 5) pollution 6) cig. smoke
10) Describe the DNA repair mechanism known as excision repair, including the enzymes involved.
Nuclease cuts out damaged DNA segment; DNA Polymerase III adds in the correct DNA nucleotides; DNA ligase
seals the DNA together (phosphodiester bond)
11) What are telomeres? What is the advantage of having telomeres?
Multiple repetitions of a nucleotide sequence (100 → 1000 repetitions);
function: protect an organism’s genes from being eroded through successive rounds of DNA Replication
12) Nerve cells do not replicate their DNA after reaching maturity. A cell biologist observed that there was
x amount of DNA in a human nerve cell. In four other types of human cells, labeled A-D, she measured the
following amounts of DNA:
cell A, 2x; cell B, 1.6x;
cell C, 0.5x; cell D, x
Match the four cell types with the following choices: (1) sperm cell; (2) bone cell just beginning interphase;
(3) skin cell in the S phase; (4) intestinal cell beginning mitosis. (Hint: review the phases of the cell cycle and
mitosis in chapter 12 if needed!).
Cell A, 4;
Cell B, 3;
Cell C, 1;
Cell D, 2
13a) Draw and label a simple diagram (3 parts) showing nucleotide structure.
13b) Draw 2 nucleotides bonded together. Use an arrow to point out the covalent bond and specify the name
of that bond.
Deoxyribose sugar
Deoxyribose sugar
14) Outline the structure of a nucleosome.