Chapter 4-1: DNA Study Questions
1.
What is the “central dogma” of molecular biology?
Protein synthesis:
DNA
mRNA
Protein
2. Define “transformation” as described by Griffith.
Some “factor” was transferred between bacteria (harmless vs. disease causing). We now
know that plasmids are the genetic material that can be exchanged between bacteria.
3. Describe Griffith’s early DNA experiment.
S vs R strain of bacteria; something in heat-killed dangerous bacteria transformed living not
dangerous bacteria into killer bacteria. Implied not a protein because heat would have
denatured the protein.
4. Describe Avery, McCarty, and MacLeod’s experiment. What were their results?
Tested one component of Griffith’s experiment at a time; only DNA transformed the nondangerous bacteria into killer bacteria
5.
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
6. 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
7.
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
8. Describe the semiconservative model of DNA replication proposed by Watson and Crick.
Original DNA molecule splits and the resulting 2 molecules each have 1 of the original strands
and 1 new strand
9. What is meant by “antiparallel”?
The 2 DNA strands run in opposite directions
10. Draw the nucleotide below. Circle and label the 5’ end and the 3’ end of the molecule.
5’
3’
11. What is the source of energy that drives the polymerization of DNA? Name all four of
these molecules and add the abbreviations. 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
12. 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
13. 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
14. Make an enzyme table:
1) Helicase: untwist and separate DNA strands
2) *Single-strand binding protein (protein but not an enzyme): keep DNA strands apart
3) 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)
5) DNA polymerase III: adds nucleotides onto elongating DNA strand
6) DNA Polymerase I: remoives RNA nucleotides of primer & replaces with correct DNA
nucleotide
7) DNA ligase: “seals” DNA fragments together (phosphodiester bond fragments together)
15. Draw and label a simple diagram (3 parts) showing nucleotide structure.
16. Draw 2 nucleotides bonded together. Use an arrow to point out the COVALENT bond and
specify the specific name of that bond.
17. Draw and study the following diagram showing the synthesis of DNA and then answer the
questions that follow.
3’
5’
5’
Parental DNA
3’
Overall direction of DNA Replication
5’
3’
Parental DNA
3’
DNA helicase
5’
a) On the model above, draw with a continuous arrow where and in which direction the continuous
strand of DNA would be synthesized. What is the name of this strand? Leading strand
b) Label the 5’ and 3’ ends on the arrow you drew in part a.
c) On the model above, draw with discontinuous arrows where and in which direction the
discontinuous sections of DNA would be synthesized. What is the name of this discontinuous
strand? Lagging Strand What are the names of these sections? Okazaki fragments
d) Label the 5’ and 3’ ends on each of the arrows you drew in part c. see diagram above
18. Summarize the evidence Watson and Crick used to deduce the double helix structure of
DNA. (remember their calculations)
model building (wire & sticks)
-used Rosalind Franklin’s X-Ray diffraction picture which showed the width of the helix
(2nm), distance between base pairs (0.34nm), & the length of a full twist (3.4nm)
19. What is the difference between a replication bubble and a replication fork?
Replication bubble: formed as DNA replicates along the replication forks. The bubble gets
larger as DNA replication proceeds.
Replication fork: 2 forks that go in opposite directions from the original replication site as
DNA replication proceeds.
20. What does dNTP stand for? Name the four dNTP’s involved in DNA replication.
dNTP = Deoxyribonucleotide Triphosphates
dATP = Deoxyadenosine triphosphate
dGTP= Deoxyguanosine triphosphate
dTTP= Deoxythymidine triphosphate
dCTP = Deoxycytidine triphosphate
21. What are the 3 parts of a dNTP’s?
5-carbon sugar: deoxyribose
*nitrogenous base: A, G, C, or T
*3 phosphate groups
22. DNA Replication Puzzle! This is optional! If you need a little more help, cut out these
pieces and put them in order. If you want to check the key, put the numbers in the correct
order and check with me during class. (Answers: 1,4,8,2,7,11,9,5,10,3,6,12)
SEE THE TABLE BELOW!!!!!
1
As the excited Biology
student was running to
class, eager to take
notes, he/she fell and
skinned their knee. In
order to make new
cells to replace those
lost to the concrete,
DNA must be
replicated in the Sphase of Interphase.
5
DNA
Polymerase I must
remove the RNA
nucleotides and
replace them with
DNA nucleotides.
Hydrogen bonds are
made between the
bases.
9
The lagging strand
forms in segments
called Okazaki
fragments. DNA
Polymerase III will
continue to build the
fragments until it
reaches another
primer…it then falls
off.
2
3
4
The enzyme helicase
attaches to specific
regions of DNA
called Origins of
Replication and
unwinds the DNA by
breaking the
hydrogen bonds
between DNA basepairs.
The enzyme Primase
makes/attaches RNA
nucleotide primers which
will allow the addition of
DNA nucleotides to the
exposed DNA strands.
Nuclease cuts out any
mistakes or mismatches
allowing DNA polymerase
III to put on the
correct base and ligase
seals the repair
6
We now have two identical
DNA strands. Each one has
one original DNA strand and
one newly synthesized DNA
strand (this is called
semiconservative
replication)!
7
DNA elongation can now
begin; leading DNA
strands will elongate
toward the replication
fork and lagging DNA
strands will elongate
away from the
replication fork.
8
Single-stranded
binding proteins hold
the two DNA strands
straight and apart.
10
11
12
DNA polymerase III
adds a DNA nucleotide
to the 3’ end of the RNA
primers following
complementary base
pairing rules.
With the S-phase of
Interphase complete,
G2 of the Cell Cycle
will commence
followed by Mitosis;
the excited Biology
student will now gain
new skin cells!!
The enzyme DNA ligase
bonds seals all gaps
(phosphodiester bonds)
**What does nuclease do?
The leading strand is
elongated continuously
while….